One Year of Solar Power

Mid 2009. Depression. Ground flat interest rates. Oppressing unemployment. What better time than now to invest on tangible assets? That was the mindset that led me to consider investing in Solar Photo-Voltaics (PV). I started studying the subject in order to become a micro-producer, taking advantage of newly passed legislation. Coincidence or not, a family member had recently returned from a working commission in Angola to set up a company that sells and installs solar micro-generation systems. I embarked on a interesting adventure that has had relevant developments.

Parts of this post were written in 2009 when I first attempted to apply for a special feed-in tariff. This experience has been logged at the European Tribune (part I, part II) where the original text contains several mistakes that have been corrected.

Weekly data for the first year of production. Click for full version.

The Prospects

Portugal is a lovely place at the westernmost tip of Europe, with a long Atlantic coast, rich orography, and clement weather. There is more sunshine only in the desert. Still, this nation imports 85% of all the energy it consumes, with 100% for fossil fuels. A 10% of GDP foreign deficit is due in most part to the energy bill.

After successive failures (due to different reasons) to base the nation's electric generation on Nuclear, then Coal, and more recently on Natural Gas, governments started shifting focus to internal renewable energies by the late 1990s. Several programmes have been taken up, providing feed-in tariffs to projects licensed to large investors (mostly Wind and small-Hidro, with a few stakes on large scale Photo-Voltaics).

In 2008, the national electric grid was opened to small investors, that up to that point had to rely solely on their own means to balance or store the energy they produced. Now legislation exists that sets a few rules for micro-generators to connect to the grid, including:

  • to connect a photo-voltaic system to the grid a thermal water heating system must also be in place;

  • each micro-production system can only feed to the grid up to 3.68 kW at any given time;

  • grid connection permits are issued in packages of 1000 units, totalling 3.68 MW of new installed capacity; the issuing time frame is open ad hoc and closes as soon as the 1000 licenses are attributed;

  • the feed-in tariff attributed to the first lot of 1000 permits is 0.65 €/kWh, decreasing with each new lot, down to a minimum of 0.31 €/kWh;

  • this feed-in tariff is valid during the first 6 years of operation, comes down to 0.30 €/kWh from the seventh to the twelfth year and from then at standard grid prices;

The photo-voltaic panels we considered for installation are made in Portugal by a local manufacturer. When we started working on this project in 2009, this factory seemed to be setting the state of the art for industrial photo-voltaic cells, by then furnishing high end panel makers in Germany and Japan.

The system was projected to be set at my mother's place, a house that has two stories and a roof shared with a single neighbour. Beyond that, this house is already paid for, with no financial liabilities against it. The roof is divided in two sides, one facing sunrise and another sunset, which is not the best of settings. But being the highest in a radius of several hundred meters and at this particular latitude, it gets plenty of sunlight. The sunset side receives full radiation from 11 o'clock onwards in the summer, this being the side where we planned to set the panels. The electricity consumption at this household varies from 110 kWh in the summer to 150 kWh in the winter. At the time we were expecting the system to generate from six times those figures during Summer to two times in winter.

A Rigged Process?

With the project consolidated on paper, we went into the licensing process. It comprises the following steps:

  • pre-registering on-line the household and the technical data;

  • applying on-line for the license during the licensing period;

  • installing the infra-structure in the 120 days following the licensing period;

  • submitting the system to a technical inspection by a certified third party;

The on-line licensing took place at a website with the ironic name (Portuguese for “renewables on the hour”). Sometime in October of 2009, a new licensing period was announced to start on the 2nd of November at 10 a.m.. The pre-registration was made and all we had left to do was wait. The vendor warned me that there were 5000 pre-registrations and that we could experience difficulties applying, but at the time I wasn't expecting major problems.

On the morning of the 2nd of November I tried to log on to the website around half past nine. Nothing. The other end was dead. I tried pinging the server and tracing the connection, but silence was all I got; the website was simply down. After one hour of continuously trying, I quit.

I attempted to connect several other times during the day, also without success. On the morning of the 3rd of November I finally managed to log on. To my complete startlement the following announcement had been posted:

The licensing period opened on the 2nd of November at 10:00 am closed at 11:04 am, after the maximum number licenses had been attributed.

Something looked terribly wrong in this picture. The information I had pointed to the server being down during that time, or at least in a state of denial of service. So how could 1000 candidates have successfully applied for a license? A few days later, after some inquiries, we were unofficially informed that at least half of the licenses were attributed to two of the largest banks in the country and hundreds others ended up in the hands of large institutional investors. There were horror stories floating around of entire call-centers mobilised to generate traffic to block the server from the common man. This was all very disheartening and I started to think I wouldn't become a Solar producer.

A new internet auction-like round of applications took place during the first days of December 2009. Like before, at 9 a.m. it was impossible to access the registration server, clogged with the huge numbers of applicants trying to access it. But this time something went differently - the server was so overwhelmed that it went down. Those responsible were only able to bring it back online close to mid-day when everyone thought it already hopeless to keep trying to apply. Every one except my vendor, who was able to register my system plus a few others of his clients.


Roof mounting started less than two months later; by March we were able to call in the certification process and finally on the 9th of April of 2010 I became an happy electricity producer, right in time for the best period of the year. The system is composed by the following elements:

  • 18 x 215 W solar panel
  • 1 x electric current inverter, limiting at 3850 W
  • 1 x 2 m2 water heating panel
  • 1 x 200 litres water tank
  • 1 x electric boiler
The panels are mounted on the rooftop with an inclination of 30º and oriented to sunset (bearing: South 78º West). Not the best of settings (optimal would be to the South) but re-orienting the rooftop wasn't an option. The critical thing about this sub-optimal orientation is the push back of break-even beyond the period of maximum feed-in tariff, the first six years. The data provided by the vendor at the time left me comfortable, even though it was considerably higher than that provided by the JRC Solar Calculator (a map of horizontal irradiation in Europe can be found here).

The installation included structural reinforcement to the roof; the cabling linking to the electric grid and new power meters, one for consumption, another for production; linkage of the water tank to the house water circuit and an electric water boiler that overrides the traditional natural gas boiler. Sunlight is able to heat water for all home needs from mid-March to mid-November; in the remainder of the year the electric boiler is timed to heat the water in the tank for about one hour, right before wake-up time.

One year of electricity

From April of 2010 to April of 2011 I thoroughly monitored the system output, collecting weekly data whenever possible. As the winter came to an end it became obvious the energy generated during the first year of operation would exceed 5 MWh. Here's that data:

Weekly data for the first year of production. Click for full version.

The first interesting thing is to compare this data to the projections by the JRC Solar Calculator:

Monthly data compared to the JRC Solar Calculator projection. Click for full version.

There are two things that immediately stand out from this graph: the wider variation of the real data and the better performance of the system in place. The latter may be due to the Calculator not including recent advancements in PV efficiency, but also to a less than perfect usage of this handy tool; I fully endorse it to assess site adequacy. The actual data for yearly production is 5140 kWh, in contrast to the 4420 kWh projected by the Calculator, a difference of more than 16%.

The wide seasonal variation, about 5 times from Winter Solstice to Summer Solstice, is very relevant for the planning of a national Energy Mix. Even in a place like Portugal, solar energy can't provide the majority of the electricity needs, especially in winter, when light hours are at the minimum and cloudiness peaks. The good thing is that other renewable energies promoted in the country are highly complementary to solar: wind peaks during the stormy seasons around the equinoxes, and rainfall peaks around the Winter Solstice, providing Hydro-power with its fuel.

Marginal price

Another important piece of information that can be calculated from this data is the marginal electricity price required by this system; it will take several steps. First of all is the computation of the total of energy produced by the system during its lifetime. The solar panel maker provides a warranty of 40 years during which time a linear decline of efficiency down to 78% of the original nameplate capacity should take place (materials worn out with time). An expression can be produced to calculate expected production as a percentage of the original at the nth year of operation:

E(n) = -0.54n + 100

Production at the nth year of operation can be calculated simply using the figure for the first year of production:

P(n) = P(1) x E(n)

The total energy produced by the system during its 40 year lifetime is the integral of this production curve, which can also be calculated as a simple sum. In the case of this system it is just over 180 MWh. The upfront cost, excluding the water heating components, was in the order of 18 000 €. The marginal price is hence 0.01 €/kWh, well above traditional energy sources. This value doesn't count maintenance or debt servicing costs, which shall be dealt with later.

Optimal System

But in the meantime prices have fallen down and panel efficiency has continued to rise. Right now a system like mine, but with 245 W panels, can be bought for 13,500 €. Considering that my system isn't optimally oriented, the actual marginal price is in reality quite low. To have an idea of what this may be, the Solar Calculator can produce optimal orientations and inclinations that help identifying an optimal site. In Portugal this would be at the Algarve, where by sheer coincidence a lot of folk from the northern states are presently spending their vacations. At 37º 14' North, 7º 56' West the Solar Calculator recommends an inclination of 32º for a bearing at South 3º East, which for a 4.4 kW system should produce 6.25 MWh in a year. But since my own experience showed that the Solar Calculator, as is, is underestimating production by some 16%, the actual value may be closer to 7.27 MWh in a year. With these figures new values for the marginal price can be computed:

Site Upfront Cost (€) First year of production (kWh) Total Energy Produced (MWh) Marginal Electricity Price (€/kWh)
Setúbal Peninsula 18700 5140 183 0.102
Algarve (JRC) 13500 6250 223 0.061
Algarve (adjusted) 13500 7268 259 0.052

These figures are compelling and not only show huge improvements in Solar power efficiency, they also point to an important approximation to other energy sources. The 5 cents per kWh is actually lower than what can be calculated from the data on Jérôme's latest offshore Wind project. So far these feed-in tariff programs for Solar micro-generation have been a success, creating an industry and most importantly reducing renewable electricity costs.

Other costs

The issue with the previous figures is that they do not take into account costs such as maintenance or debt servicing. In the 15 months my system has been in operation, there has been a single maintenance issue, but with an escape valve on the water tank. It is hard to foresee what sort of maintenance issues may come up with the PV system, but of note is the warranty of the inverter being shorter than for the panels. Hence adding a parcel for a substitution of this equipment seems a sensible choice. Insurance costs are not included for this sort of micro-generation systems are usually covered by standard home insurance policies; though for industrial applications this is an issue.

Debt is the real problem because interests have soared since last year. Even renewable energy dedicated lines of credit are imposing interest over 6%/a. A 60 month loan for the upfront costs discussed above easily add over 4 500 € to the total project cost. The following table summarizes these new costs with debt on 100% of the up front investment, thus providing a top to marginal electricity prices:

Site Upfront Cost (€) Maintenance (€) Debt Servicing (€) Total Energy Production (Mwh) Marginal Electricity Price (€/kWh)
Setúbal Peninsula 18700 2000 5650 183 0.144
Algarve (JRC) 13500 2000 4700 223 0.091
Algarve (adjusted) 13500 2000 4700 259 0.078

Suddenly things got a bit bleak. Banks are charging spreads of some 5% over the Euribor interbank lending rate and with it, killing many investments. Naturally this is about micro-generation systems that amount to relatively low investments, assuming financing is required for 100% of the upfront cost is a worst case scenario. Wrapping up these calculations, it can be said that the marginal electricity price for a solar PV system optimally sited at the Algarve ranges somewhere between 5 and 8 cents per kWh. While not spectacular, these figures point to Solar PV entering a maturity stage now comparable to Wind power. In Portugal the consumer is presently paying close to 13 cents per kWh, with that figure projected to go over 15 cents per kWh by 2013.

Feed-in tariffs

Of all the numbers referenced before, one that may be have passed discretely so far is actually the most problematic: the 40-year system lifetime. It is like investing in oak wood, with the difference that electricity generated from solar panels is indistinguishable from that generated by other sources (actually natural gas and hydro can differentiate their product, but that's an issue for another time). Investors may choose oak wood because it is a finer product than pine, for instance, but with electricity this doesn't happen. Electricity can be seen as a perfect concurrency market where profit only exists in the presence of scarcity; on a abstractly normal market the investor would get financial break-even only at the very end of project lifetime. In other words, solar PV is a very unattractive investment from the perspective of the individual investor.

The main consequence of this is the indispensableness of feed-in tariffs. They are not a tool to increase the competitiveness of supposedly expensive renewable energies, their main function is to anticipate financial returns in time, and with it break-even. There will be no private investment on Solar energy without feed-in tariffs.

In closing, an important question can be answered with the data collected here: what feed-in tariff would be needed to anticipate financial break-even to the nth year of operation? This can be computed using the efficiency decline function, and the quotient between total energy produced at the nth year of production and cost:

B(n) = Sum1n[P(n) x E(n)] / C

Where C is the cost. For the several scenarios analysed above the resulting curves look like this:

Feed-in tariff as a function of break-even time. Click for full version.

Financial break-even before the 6th year of operation requires huge feed-in tariffs, but even at 10 years of operation all systems require 20 cents per kWh or more. As a comparison, wind energy is today an healthy business, usually reaching break-even at the 10th year of operation with a feed-in tariff around 7.5 cents per kWh. This is the sheer weight of such a long lifetime, and possibly the biggest challenge to the success of Solar power.


So far I'm pretty happy to have become a solar electricity micro-producer. Financial break-even is still some 6 years away, which is not fantastic but perfectly manageable; even with a less than optimal setting, the system should after that generate a small but regular profit for decades to come. I also had the opportunity to participate in a very interesting moment for the solar industry, where the efforts of several governments producing generous feed-in tariffs for micro-producers resulted in visible cost reductions and efficiency increases with economies of scale.

Optimally set systems (regarding inclination and bearing) at sunny places like southern Portugal, Spain or northern Africa are operational with marginal electricity prices between 5 and 8 cents per kWh, mostly depending on debt servicing costs. While not cheap, these figures are not expensive either and point to an important level of maturity of Solar PV technology.

But for solar PV to make any relevant penetration on the energy mix, high feed-in tariffs will continue to be required, a product of the long lifetime of this technology. Governments face a huge challenge to continue the promotion of solar PV with this scheme, reliant on private investors and private lenders. Especially at a time where austerity and budget cuts are the main policy, it will be very hard to keep pushing feed-in tariffs that are multiples of present electricity prices.

It would interesting to explore what sort of projected lifetime a solar energy system could be engineered to have. The electricity cost from a large (multi MW) system is ultimately dependant upon the interest charged on the financing loan, the size of the loan and the lifetime over which the payment is spread (usually assumed to be 20 years).

However, if solar power plants can be engineered to last 60 years or more, then the investmnet is much more attractive to a nation, even if capital costs are high, rather like hydropower. I have read that panels accumulate radiation damage. This is presumably because of UV exposure? If they are protected from UV, could we get 50 years out of them?

Magyar is the man to answer this, but it is my understanding that, even though most PVs are rated to last 20-25 years, those actually in service have gone far beyond this. I imagine that it could be hard to convince investors that a product has a 50+ year lifetime when none of them have been around for that long, especially those made with newer types of production.

It is my understanding that there are various schemes around already to help finance PV systems to spread out the cost, as you suggest. You might look around to see what is available in your area.

If you do the present value of production stuff, because of the high discount rate, production between 25 and 50 years is of very little value (to the bean counter). A big problem with making solar competive is high interest and discount rates. If you use an interest rate (and discount rate) comparable to what you can get from very low risk bonds, the calculation will look much better. From that I conclude, for an investor, with cash looking for a safe return, PV may be a good investment. For the person who needs to take out a bank loan no-so much.

So, if I read it right: They require you to convert your water heater to electric to qualify for the FIT? I assume this was supposed to disqualify banks and financial players and favor homeowners. However it is a step backwards efficiency wise (if I understood the intent). Nevertheless it sounds like some large investors figured out they could make some nice low risk gains by doing this, since they seem to have flooded the application process. This is a risk with any too generous FIT.

Magyar is the man to answer this,

Thanks for the vote of confidence, dohboi!

There are quite a few TOD commenters other than myself who are more that qualified to address this question, case in point, Solarevolution beat me to the punch.

I certainly agree with what he said.


Any opinion on the longevity of thin films?

AFAIK, The new record holder for size of solar PV installation is going to consist of First Solar's cadmium-telluride thin film panels.

I have read that panels accumulate radiation damage. This is presumably because of UV exposure? If they are protected from UV, could we get 50 years out of them?

The degradation of crystalline PV is negligible year-over-year. At one time the encapsulants (which keep moisture out) were made of a plastic which degraded under UV but these have improved dramatically in recent years. Standing alone, the cells (silicon), glass and aluminum frames are not affected by UV and could last indefinitely.

Electronic components (inverters mostly) need servicing every 10 years or so (often designed with hot-swap components).

PV product warranties are 20-25 years, so as long as wiring terminals are not in a corrosive environment, it is easy to imagine panels functioning well at 50 years and I would not be surprised if good quality panels will perform well even at 100 years. (I'm not going to stick around to find out, however.) There will be some decline in performance, no doubt, but probably not enough to justify swapping them out and starting over sooner than 50-100 years.

This level of durability by the way has not typically been factored into EROI (EROEI) analyses. That will be rectified as we gain more experience.

I have some 30 year old panels which still perform well.

Roofing is a potential point of failure. When doing large commercial solar systems, we specify SPF (Spray Polyurethane Foam) roofing which lasts the life of the building if properly maintained (recoating every 20 years). Our team has been called upon to provide enduring SPF roofing to replace conventional roofing which failed in less than 5 years under large solar systems.

The actual data for yearly production is 5140 MWh, in contrast to the 4420 MWh projected by the Calculator, a difference of more than 16%.

Great article, Luis; thank you. I take it you meant to say 5,140 kWh as opposed to MWh?


Thanks for pointing this, not it's ok.

Luis, aren't there tax breaks for interest paid for solar installations in Portugal? We have them in Germany, if memory serves, two from n percent interest rate deductible from your tax debt.

And thanks for all this detailed information.

The whole investment can be deducted from the income tax in the year of installment. As for the interest I'm not certain, but it probably is deductible too. Banks themselves charge spreads considerably lower than those charged on other sorts of credit.

A very thoughtful, thorough analysis, Luis.

We have a 5KW ground-mount system in upstate NY. The first year produced 5700 kwh, the second year, 5400 kwh. This region gets fairly heavy cloud cover from the Great Lakes -- less than 50% of daylight hours have sunshine on an annual basis.

The break-even for our system is 12+ years at current rates, after the NYSERDA rebate and the state and federal tax credits. It is not an economic decision to do PV here, only a moral one.

We do not have a feed in tariff, only net metering, which is netted out on an annual basis. Very few areas in the US have feed-in tariffs.

Retail rates are approximately 16 cents per kwh (supply and delivery cost), but any excess produced is paid back annually at base load generation cost (approximately 4.5 cents). It should be noted that such high retail rates came about from mandatory divestiture of generation plants in the late 1990s, some for 10 cents on the dollar and the implementation of marginal pricing and the establishment of the NY Independent System Operator (a "trading" casino established for the likes of Enron and Goldman Sachs). The stranded investment cost was dumped into the retail rates.

Our system went on line in August 2009. In August 2010, a 1400 kwh surplus was credited back to our account. During the winter months, with the surplus gone, we were again paying retail rates. We have been able to change the anniversary date on our system to March, which should zero-out our electricity costs for the year.

Feed-in tariffs would radically change the economics of PV in New York state. Our peak monthly production roughly coincides with peak demand periods in the state's grid. Marginal costs in the grid during summer are very expensive, yet we are compensated at 1/20 of that peak rate.

Further, we are delivering our excess on the end of a long semi-rural distribution feeder. There are essentially no delivery charges incurred
because the surplus is immediately consumed by by my neighbors.

It is obvious that the US has no serious interest in renewables -- only lip service is paid. Once the budget cuts take place, we'll be back to the PV economics of the 1970s.

One way to get around the assymetry between residential rates and what they pay for excess, is to only install a sysmtem that produces well under your annual needs. In my area PG&E, overproduction pays a bit over $.08, but it is an annual thing, and I don't expect to ever run into it.

I made my own calculator for production (from clear skies). I assumed the atmosphere scatters 20% divided by the cosine of the sun angle, and 40% of scattered is diffuse light. Mine greatly overestimated production, at least for the warm part of the year. The problem I think is panel temperatures. The nameplate output for a panel is for 25C panel temp. Panels in full sunlight run tens of degrees warmer than ambient air temps. So a clear winter day produced similar to my model, but summer was quite a bit lower. Summer max air temps of 35C or more are very common here. Thinfilm has a much lower thermal coeficient, it might be a better choice for hot climates. There is a slight reduction in AC as well, as some of your roof is shaed by the panels. Many modern panels seem to have skirts that go down to the rooftop. This must be for fashion, as losing the airflow under the panels will increase panel temperature, which is not what you want to do.

"after the NYSERDA rebate and the state and federal tax credits. It is not an economic decision to do PV here, only a moral one."

An immoral one. You draw obscene amounts of resources and you make others pay through tax subsidies and production shifting.

An immoral one. You draw obscene amounts of resources and you make others pay through tax subsidies and production shifting.

Uh Huh! Though I gather you don't consider driving an automobile immoral, do you? What's a little tax payer subsidized war for oil or the consequences of climate change to someone so much holier than the rest of us? After all there is not a single penny of tax subsidy anywhere in the entire supply chain for the manufacture and fueling of ICE powered personal transport! Oh, aren't you also the guy who thinks riding bikes and taking trains is part of an evil communist plot?
Yes, I know all those people who ride trains are being subsidized by your tax dollars, the immorality of it all is nothing less than shocking!

And why beholdest thou the mote that is in thy brother's eye, but considerest not the beam that is in thine own eye?
Matthew 7:3

Disclaimer: I'm an atheist but I did go to bible school!

I feel the war wasn't for oil, and that un-internalized GHG emissions is less of a direct subsidy than getting tax subsidies for PV. I've not read very much about US tax subsidies to big oil/big car, but disregarding the latest bailout, I've read that common spectacular tax subsidy calculations are too inclusive. For instance that big oil/car, just like everybody else, are allowed to give their employees tax free medical insurance is not a subsidy of big oil/car, but of big insurance and health care industries.

No, I don't recognize what you write on communist plots, so that isn't me. However, I don't like train subsidies either, but I do advocate equal subsidies. If roads are tax financed, I'm fine with rail getting equivalent financing (based on capacity and such).

“I am saddened that it is politically inconvenient to acknowledge what everyone knows: the Iraq war is largely about oil”

Alan Greenspan, in his 2007 memoir.

I would agree. You grind the face of the poor to get your solar panels. You make utilities pay you to feed their grid even they do not want or need your power. This requires them to raise rates on everybody including windows and poor folks.

as for solar panels lasting 100 years... get real. The sand blasting from the wind and dirt hitting them that long will degrade them long before that time.

Can you provide further clarification on what you mean by solar consumes obscene amounts of resources? I would love to see your evidence that producing solar power consumes more resources than blowing the top off a mountain to generate coal-fired power.

Regarding your claim that solar is fleecing consumers, you should look at the facts first. Solar is actually cheaper than virtually every other form of peaking power.

Since solar power is a very diffuse, a lot of material is required to collect it. That is reflected in the price as well as in LCAs.

I would say that you link says that solar is more expensive than natural gas, even. And I would like to remind you that not all solar PV production can be expected to replace NG - quite a lot should be produced during weekends and/or in non-AC-intensive periods.

Diffuse, yes, but it does not require a substantial load-bearing structure as does an 8-story tall boiler on a coal plant, for example. Remember, with solar we are dealing with a panel a few inches thick at most and some minor support structure - not trains, excavators, trucks, load-bearing conveyor belts, boilers and other heavy industry. I believe that Rambrandt is working on a study that should allow us to more fully understand the lifecycle material costs involved with various forms of energy.

I think you missed the point of the link if your take-away was that solar is more expensive than gas. Costs for any energy source can vary widely based on location, local fuel supply conditions, etc. In regions such as the Southwest, solar is already cheaper when all costs are considered. While it is still moderately more expensive in less insolated regions, it is substantially less than non-gas competitors such as oil and far below peak power prices. You are correct to point out that solar will not always be produced during periods of ultra-high demand and ultra-high prices - however the value of the costs avoided during peak summer days more than outweighs the additional costs incurred vs. winter peak demand.

Big boiler, yes, but a coal plant may generate 1e9 watts on average. PV averages what, 250 W/m^2, so you need 4 square kilometers of "minor support structures", cabling and a few inches thick panels to match the coal plant. That's A LOT.

If solar PV is cheaper than gas, then we'll see it make rapid and big inroads in big utility scale installations. I don't see it, currently. With all due respect to enthusiast calculations, real life investments is the authoritative guide to current economic realities.

We are seeing big inroads in utility-scale solar installations. Take for example the BLM Priority Projects with over 3GW of solar capacity in the queue. This does not represent the entire BLM queue by the way - only projects requiring BLM approval (itself a subset of solar projects) that have been identified as "priority." Most major utilities now have a substantial solar (and other renewable) pipeline, e.g. NRG, AES. Gas is still being built as well, but coal is virtually absent.

Enthusiast calculations certainly have their place, but there aren't any in this discussion, at least not from my side. The LCOEs referenced are calculated using actual numbers from actual project financings proposed within the past year.

Mostly CSP, and they collect big subsidies. Not very impressive.

Are we looking at the same data? Only 38% of the projects listed in the link are CSP, which I don't think qualifies as mostly. A majority, 62% are PV. And this is only the BLM pipeline, which I thought would be enough to prove that there are significant utility-scale solar developments currently being built. There are also many non-BLM utility-scale projects such as NRG's 290 MW Agua Caliente project, also PV.

We in Sweden have now got feed in tariffs for homemade electricity here in Sweden, N 59 E 18. One supplier, Fortum will pay for the net 3,5-6,1 öre/kWh and the Nord Pool spot-price for one hour minus 4 öre/kWh. During the summer when we have sunshine the spot-price is in the range 30 to 35 öre/kWh. It is not that much when the price is high in the winter there are no sunshine!

100 öre = 1 SEK
1 SEK = 0,1 € = 0,15 $ = 0,09 £

I think this is an excellent point. Most people do not properly acknowledge that solar is a form of peaking power and as such should be compared to other forms of peaking power such as natural gas CTs and STs, and oil-fired generation. I recently conducted an in-depth analysis of the unsubsidized cost of solar vs. other peaking power technologies, and not only can solar help save us from $2,500/MWh power price spikes like those recently seen in Texas, it is also very economically competitive with even the cheapest conventional form of peaking power, natural gas.

Handicapping solar production by only paying a pittance compared to market power rates, and failing to attribute value to the transmission savings you mention as well, is causing us to underinvest in an economical technology that can save us money today with no subsidies.

This story, and others like it, lead me to think that off-grid is the only way to go.

Which leads to some cognitive dissonance if you are in an area with available grid power...

But what will the grid power picture look like in five or ten years? It may be not so much a matter of saving money on electric rates, as it will be having electricity at all.

I'm expanding an off-grid system even though I also have grid power. It lends itself more to doing it yourself - there are a lot of hurdles to jump over here to get a grid-tie system, the biggest being that you have to use an "approved" installation company, and they charge caviar prices. The actual PV is pretty cheap these days. So I've started with a 1.2kw system to run pond pumps, ventilation fans, a freezer and various electronics which would otherwise have to be run using grid power. I have a bank of 16 golf cart batteries to save a bit of it too... if there's ever a time when the grid goes down, the local houses with the very-expensive grid-tied systems will be dark at night while we have power.. at a tiny fraction of what they paid for their much-larger pro-installed systems.

As I sit here, I've got a fan blowing on me which is all it takes to make the summer comfortable. I like knowing that the blades are being turned by fusion energy rather than oil being burned on the other side of the island. I'm migrating more and more appliances to the solar power and using grid as standby. (I've also removed the blade cages which allows the fans to throw more air on "low" than they used to throw on "high", though that's one of those "kids don't try this at home" strategies which you wouldn't want to use if you have free-flying parakeets, children, house guests, litigious visiting nudists, etc).

Having solar electricity also helps make one conscious of energy usage in general. I have always kept close track, but with the solar aspect, my wife is getting into it as well, and thinking about using energy. Since the panels take in a lot more during the day than can be stored, we also shift power usage to the daytime and use it sparingly at night; I'm setting the freezer up with a timer and some bottles full of water so thermal inertia will coast it through the night without running; which will mean the batteries don't get deeply discharged and should last longer.

I think the regulations and permitting to do grid-tie make the whole thing a bit of a headache. Some people are buying gold coins with their savings, but I think solar panels might be a great way to go if you have room to store 'em. I have more than I'm now using.

Very-small PV standalone systems are also a good deal less complex, and I have a couple scattered around the house. I haven't done any sort of financial analysis, because part of the benefit is aesthetic, and part is individual resilience. As hobbies go it isn't that expensive.

And here's something I seldom see mentioned: it's fun.

With your bottles in the freezer, are you planning to salt the water so you can hold them at colder temps than 32? Is that the way another poster mentioned recently?

I'm trying to remember if it's correct that water plateaus at 32 for a while before it gets colder..

Salt wont help you to store cold. You get heat capacity of liquid water and the enthalpy of fusion basically to store the cold. When you make ice cream salt is useful, the salt causes the ice to melt which makes it draw heat from the cream/sugar mixture. Ice melting is a very good heat sink

Yair...hello folks. I just thought I'd mention this again.

When we lived on the Gulf Coast back in the 'Seventies we were on Gen. sets...I had a 4kva Lister for the main and an 8kva for back up and to run the welder.

Daytime temperatures were commonly over forty but our generator was shut off about seven every morning when we went to work. the fridges and freezers were commonly off for ten hours or so per day.

I never got too scientific about measuring temperatures but in five or six years of doing this we never lost a thing. We kept the freezers full of tucker or ice (water in garbage bags conforms to the internal shape of the cabinet)and the main thing of course is that they were not opened while the power was off.

There seems to be far to much concern about having no power overnight.


Add 150g salt to each litre of water and you have a mix that freezes/thaws around -9C. Makes a good backstop if the power goes out. Saved me the other day and I've added a few more since.


But when you try to freeze it, does it make a mixture of ice, and even more concentrated brine? I wouldn't think it would all freeze at thesame temp. But maybe that isn't needed, since what you are looking for is high heat capacity btween say (-10C and -5C).

This should help you (PDF warning)

If the brine concentrates it will dissolve some of the ice so it stays pretty constant. You can see the temperature plateau on a thermometer. I use one of those cheap indoor/outdoor ones and put the outdoor end in the freezer, it has max/min so I can see what has gone on. When I lost power overnight the commercial ice packs I keep in there plus the salt water bottles stopped things from thawing out. The 150g/l gives a point about -9C so that's in your range. If you add more salt you can drop that but I feel that is a good point for backing up as it shouldn't thaw/freeze in normal operation. You could take it to -12 or -14 if you are sure your freezer temperature stays below -16 but to protect in emergencies -9 is good. You can also move 1 or 2 bottles to the fridge part to keep stuff cool there.


PS Tip for ice cream making, mix some water and salt to the eutectic and put that in the freezer for a day before. It stays liquid and when you pour it over ice you get a really cold freezing mix fast.

"I'm trying to remember if it's correct that water plateaus at 32 for a while before it gets colder.."

Yes it does. Study latent heat vs. sensible heat.

Well there's a range of answers.. thanks all (Too late to research your links tho)

I just remember the advice for winter campers keeping water/milk from freezing by making a snow cave to insulate it in, as the snow sits at 32, and won't let liquids get below that for a good long stretch..

With your bottles in the freezer, are you planning to salt the water so you can hold them at colder temps than 32?

You got good answers from others, but since you ask, I just figured I'd mess around with it. Salting the water makes sense if I don't want the other stuff in there to freeze-thaw every night as well; but I do want to take advantage of the "heat of fusion" transition so want to make sure the freezer will freeze it solid. I like the idea of an appliance which can even out the day-nite cycle of PV generation. I only spent $50 on the freezer, and I may try adding insulation as well. All good fun, and it should enable me to make icy tropical drinks out of what grows in my yard and the rain that falls on my roof, even if things get weird otherwise.

The "intermittency" of PV can be planned around, seemingly, particularly in locations like this one. My fan isn't on now and the sun is down... but I don't need it now since it's cooler. PV isn't a panacea, but it makes more sense than cars do.


Adding insulation helps alot. Make sure to use closed cell foam board and seal the edges with tape or you'll get condensation. I'm in the process of adding 1 1/2" blue board to our refrigerator.

I used 'No More Nails' to stick my foam on and that also seals it. Watch out for condensation for any parts of the metal that are sticking out from under the foam eg around the door. If you have 2C inside and 32c outside then an uncovered fridge will have the metal at marginally below 32C. If the fridge has 2" of insulation inside and 2" outside then the metal will be at a chilly 17C and collects a lot of moisture when the dew point is 25C (temperatures represent current conditions here). I have though about tapering the foam near these edges to try and alleviate this. It may be an idea to give any exposed metal a good coat of paint before applying the foam.


"The actual PV is pretty cheap these days...I think the regulations and permitting to do grid-tie make the whole thing a bit of a headache. Some people are buying gold coins with their savings, but I think solar panels might be a great way to go if you have room to store 'em. I have more than I'm now using."

I couldn't agree more. My system is off-grid for that exact reason. Also, I just picked up a bunch of these, even though I have no need for the extra capacity at this time. I've always been a diy'er and have repaired PV panels before. A bit of work and a junction box is attached and nice cheap PV! And with a 20year warranty to boot!

SUN Laminate 180 Watts 24.30 Vmp $133.20 $0.74/watt

I'm trying to scrounge enough cash to get some of these (min. order 10). I originally thought they were amorphous (which I don't quite trust yet), but these are crystaline on tempered glass. As for junction boxes, I wonder if mc connectors would work. Any ideas for framing? I have a bunch of screen door aluminum stock for patio doors-may work. Properly flashed, you could shingle a roof with these things ;-)

Add one of these and I'd be a happy camper.

They also sell junction boxes with MC4 connectors for $20. I got a discount to $15 since I've bought a bunch from them before.

Aug, those laminates are one hell of deal! Looks like the ideal sort of thing for a DIY'er doing the roof of a carport or shed, or the like.

Would also make a *great* project for a high school class - buy 10kW worth, and the class has to make the frames, do the connections etc etc. Back to the old school way of learning how to make things, rather than like most school projects where they buy them and pay a contractor to do the whole thing and the kids just watch.

The school could even hire their local Fred Magyar to co-ordinate the whole project, and teach the kids about being ion the solar business.

If the 10kW worth could be mounted for less than $20k in out of pocket costs, the school would have a real winner on their hands, and certainly a great learning experience.

All probably totally illegal in the US...

The school could even hire their local Fred Magyar to co-ordinate the whole project, and teach the kids about being ion the solar business.

With the right group I might even do it for free!

BTW I know a few of the folks from the Sun Electronics Miami office.
Their instruction videos for building panels from laminates are pretty good.

"And here's something I seldom see mentioned: it's fun."

Yeah, 'nish, it's a lot of fun. There's been alot of talk about solar cookers these days. I took an old slow cooker, bypassed the thermostat/electronics, and hooked an old 80 watt panel directly to it. Worked great! I tested it out in the yard, just in case :-/ I plan to add a small mechanical t-stat because it got kind of hot at one point. Not as simple as some cardboard and aluminum foil, but at least as much fun.

I enjoy direct solar cooking, which is dead-easy here on Oahu for those patient enough. But I have to say that one very useful way - for now - is to simply add a storage battery and cheap inverter, then use a microwave oven. Microwave ovens are pretty energy-cheap when it comes to putting the heat where you want it, and of course they're fast and flexible for our current short attention spans. That combination of stuff is an interesting way to bridge the gap between a long period of distributed energy falling on the earth versus a short period of high energy use for making food.

I'll even mention a link for a deal in keeping with that great link for .74/watt solar laminates - go to amazon and do a search on "roadpro inverter" and you'll see that currently you can get that brand with free shipping fairly dirt-cheap for some reason. Not pure sine wave but you don't need it for a lot of stuff. Under $70 even shipped to Hawaii for one that'll run a microwave... or $105 for one that'll run a bigger microwave. All the "roadpro" brand inverters are freakishly cheap at Amazon now if you order through them. Put it together with a couple of golf cart batteries and some cheap PV, and nuking food at whim becomes easy.

The coming decades may be an interesting mix of high and low tech. I may be having microwaved breadfruit, along with icy coconut-mango smoothies, just with what falls on my property plus some cheap hardware. It ain't sustainable, but it's at least as sustainable as my body is.

Being able to make ice in August is my benchmark. The world can fall apart and I'll be OK as long as I've got some chill to my swill ;-)

Roadpro RPPI-2500W 2000/5000 Watt DC to AC Power Inverter for $105.12 at Amazon.

Why is it so cheap? What is the catch?

Who knows? Maybe it will fall apart. I have used that brand in the past in smaller size and it worked well. Just thought I'd point out this "price anomaly" to the TOD readers. It may not continue. Seems to be roughly half-price, for some reason.

I got one of each of the sizes, and that 2000/5000 one is quite hefty; uses double cables on each terminal. Haven't hooked it up yet, but it certainly feels substantial. And they ship to Hawaii for free, which makes it extra-ridiculous in my case. Most places would charge $70+ just to ship one here.

ymmv. Just sharing what may be a deal. Amazon is actually shipping them, I can confirm.

It looks to me like it is a close-out sale at Amazon. Roadpro's site lists different models with the prefix RPPD. The maximum operating ambient temperature is a rather low 40 C (104 F). It might not work well in the summer here, but for $105, it might be worth a try.

Owners Manual for RoadPro RPPI-2500 Inverter (PDF warning, 443 kB)

This story, and others like it, lead me to think that off-grid is the only way to go.

That can't be exactly what you meant. The story offers no positive comparison of off-grid solar as compared to grid-tied.

Now, on your own, you came up with...

what will the grid power picture look like in five or ten years? It may be not so much a matter of saving money on electric rates, as it will be having electricity at all.

I don't know if I buy that the grid will be in a lot of trouble in 5 or 10 years, although no doubt it will depend a lot on the particular location. But regardless, it will be much easier and cheaper to convert a grid-tied system to a battery-backup system than to start from scratch or drop the grid entirely.

Nice writeup, Luis. Some thoughts:

Being confronted with two or more sub-optimal locations to mount an array can be frustrating. For instance, in your case, if the eastern orientation was only determined to get 10% less insolation than the west, it's possible that it could still be more productive because the lower temperatures in the morning result in greater efficiency, especially with poly-crystaline panels. This, of course, doesn't apply to solar thermal.

While many folks only have the option to roof mount their systems, considering productivity, the roof isn't the best place for PV, mainly because it's hot up there. Roof mounting also precludes the option of tracking, something that improves our production 30% - 40%, especially in winter. Then again, having a roof mounted array may offset production losses by reducing heat gain to the structure in summer.

Before choosing between two less than optimal locations, I suggest doing a thorough survey over time. While simple observation can go a long way, devices are available to quantify/log actual insolation over time, and I suggest logging temperature as well. One example of a site survey tool may be seen at:

I also recommend ongoing data logging of production. When manual tracking of production gets tedious over time, having a log can indicate if there is a problem with the system, and makes tweaking the system less 'intuitive'.

The production curve at my location is much flatter due to temperature and weather. While the days are longer in summer, the heat and atmospheric haze tend to restrict output, while the days of late winter, early spring and fall tend to be some of our most productive due to cooler temps and typically very clear weather. Several of our production records have been set in February and March, despite the shorter days. Our arrays frequently exceed their rated output during periods of cold, clear weather. Latitude also plays a big part. (FYI: we are at 34 degrees north latitude.)

As the discrepancy between your actual production and that predicted by the JRC Calculator shows, specific site productivity can be quite subjective.

For instance, in your case, if the eastern orientation was only determined to get 10% less insolation than the west, it's possible that it could still be more productive because the lower temperatures in the morning result in greater efficiency, especially with poly-crystaline panels.

On a temperate climate sunrise will always be worse than sunset. Most especially on polar highs are right on the site mornings tend to be misty (fog and frost) and the afternoons dry. This is very well reflected by the Solar Calculator.

Several of our production records have been set in February and March, despite the shorter days. Our arrays frequently exceed their rated output during periods of cold, clear weather. Latitude also plays a big part. (FYI: we are at 34 degrees north latitude.)

Ok, I see you are out of the main climate circulation pathways. What's the yearly output of 1 MW installed capacity optimally oriented?

The closest city on the Insolation Chart is Charlotte, NC. Their average KwH/day is 4.2 (1533/year) per square meter. Not sure how that converts to /MW of installed capacity. We, however, are a bit west of there in what is considered a temperate rain forest. Our rated installed capacity is 3524 watts and our annual average production last two years is 3834 KwH (using tilt and roll trackers).

Advantages/disadvantages of being at higher elevation. More of the direct sunlight gets through at higher elevations (assuming the smokey mountains haze doesn't reverse that). Temperatures are lower. Wind speeds should be greater, which aids panel cooling. But, then usually mountains have more clouds, especially during the convective (thunderstorm) cloud season. Conditions can vary dramatically over short distances in the mountains, so the city may be a poor proxy for local conditions.

"Solar Insolation Levels In North America", when will they learn that North America is not limited to the USA? Oh, and while I've got the grumpy hat on, what other types of Insolation are there other than Solar?


what other types of Insolation are there other than Solar?

Unfortunately the SOL in inSOLation refers to our favorite star. So other sources of illumination need not apply.

Morning versus afternoon isn't so clear to me. Mornings you can have low clouds and fog. But convective cloud buildups are concentrated in the afternoons. I suspect it is site specific which is the greater factor. Of course the value of the power is greater in the afternoon -at least for regions with significant cooling requirements. But your FIT just pays by the KWhr, not weighting by the time varying marginal cost of power.

How much of your cost was accounted for by needing to strengthen the roof? I thought your estimation of unsubsidized return on investment seemed a bit pessimistic. A lot depends on the cost per watt of the system. Large scale PV utility is now a bit over $3/watt. Supposedly Germany can build residential PV for not much more than that. Perhaps your local suppliers are inefficient? Thats a possible outcome of large subsidies. Why be inefficient if subsidies guarantee a profit without even trying to optimize operations?

In the Southern California high desert I live in, we get our peak records in May and June, although we have a major issue with obscuration with dust during these months. It's a problem most of the year, but it's especially an issue in spring, because that's when we get morning dew condensing on already dusty surfaces, and/or winds that deposit more dust on the dew.

I took a picture of some panels in a large installation in spring: They're worse now, and yes, that's bird poop. Google did a study of their Googleplex installation and found that their installation had 50% degradation due to dirty panels. It's a southwestern US thing, I suppose, because our rainy season is in the winter.

Obviously this isn't that much of an issue on a home installation, because it'll take minimal water and time to spray time off, but it's definitely an issue with utility scale installations in some areas.

One company in my town has one project consisting of over 150 of the following canopies:

Imagine having to clean all of those. They're quite dirty now, but I'm afraid to image them. With my luck, I'll get up there to take a picture, and get harassed by some authorities.

Even in town, in Northern Cal, I like to wash them off about once every month to six weeks. Bird poop depends on which cell it lands on. I mentioned elsewhere on the comment thread, that the weakest panel in the series determines your output current. So if the poop lands on the weakest link, it just got weaker. Parodoxically, if it lands on your best cell, it may not matter. I think those installations just need to plan on occasional cleanings. It should cost less per square meter cleaned of an industrial scaled system than for a home system. Especially since getting within hose range is a hastle. I go up a stepladder, and spray from there, maybe five minutes every six weeks during the dry season. My best days are usually during May, butcertainly before the summer solistice. Temperature really does matter.

"I think those installations just need to plan on occasional cleanings."

I read a report of a 100 MW PV installation being installed in my town, and their plan is to only clean it twice per year. I'm thinking they'll change their mind on that once they find out just how much of an issue it is out here. I'm 4 miles from esolar's 5 MW modular power tower demonstration plant. They clean their 24,000 mirrors at least every two weeks. SEGS, the largest installation of solar in the world, supposedly cleans their over 200 miles of troughs once or twice every two weeks. Google's study of their Googleplex installation:

I have a 3kWh Grid-tie system and have been involved with alternative energies (wind and various solar applications) for 40 years. Having said that, they are at best transition technologies. I once thought and was invested heart, energy and financially in alternatives. Now I see a bigger picture and consider these attempts as simply “business as usual” new verse.

Solar and Wind are not renewable. The energy from solar and from wind is of course renewable but the devices used to capture the energy of the sun and wind is not renewable. Nor are they green or sustainable.

An oak tree is renewable. A horse is renewable. They reproduce themselves. The human-made equipment used to capture solar energy or wind energy is not renewable. There is considerable fossil fuel energy embedded in this equipment. The many components used in devices to capture solar energy, wind energy, tidal energy and biomass energy – aluminum, glass, copper, rare metals, petroleum in many forms to name a few – are fossil fuel dependent.

Wind used by sailing ships and old style “dutch” wind machines is renewable and sustainable.
From: Energy in the Real World with pictures of proof.

Gosh, sunweb, I'm not sure what your point is. Viewing the issue in absolutes doesn't seem useful.

Well sure as you say nothing is renewable that is touched by human hands, well sort of. After the system has reached the end of its useful life, the glass and aluminum could be recycled or better yet the aluminum structure could be re-used for the next mount. Same for the copper wiring. All is not lost.

So you are arguing about the thin sheets of PV material in the panels. Well, lets compare that to the embedded energy in the iron and steel needed to shoe a horse or the equipment required to run a farm. Or even a shovel or hoe and any simple garden tool

That should end this debate. Nothing is renewable. Yes, so ride your horse bareback and do not put a fence around your farm and claw the soil with your bare hands. That is the extreme I am reading here.

Life is complicated. Why not move in the direction of this type of renewable?

It gets even worse on his blog posting, where he goes on to talk about how EROEI is "everything", with the oft misused used example of when it takes more energy to get oil out of the ground, than the energy of the oil, then it's over. This is certainly not true, as long as you can use a much cheaper form of energy than oil.

Taken to his extremes, it would seem there is little point in doing anything beyond stone age technology.

I can;t see many people opting for that.

Interesting article, but it is proof solar is not yet economic. It is at best a labor of love.

Government should not be giving you feed in tariffs. Why should your neighbors pay for their own electricity and be forced to pay part of yours too? It's more socialist folly.

For those living off grid... why? You pay for the energy infrastructure. You'd like to pay again and have sporadic service? Wait for energy prices to rise and solar (+ storage) costs to decline. In 20 or more years, maybe you won't be such a sucker.

Here's a hint. When the utilities prefer solar PV farms instead of traditional plants, it probably means it's safe to invest.

They are paying to reduce the impact of global warming on their future lives and the lives of their children, and also getting an insurance policy reducing the risk of reduced availability of fossil fuels in the future. You could easily ask, why should I pay for my neighbours' feckless use of fossil fuels which will incur greater future costs to me?

Clearly you view short term profit as more important though, have you considered a career in banking?

Oh, and in Europe, even conservative governments are socialists by US standards, it is the normal form of government and a compliment, not an insult.

He's also using other sorts of tunnel vision. The marginal change in fossil fuel demand caused by a kilowatt of PV, means that the market clearing price of fossil fuels is marginally lower. But, that benefit is distributed across a wide area, possibly as widely as the entire planet. The reduced peak demand might mean expensive new capital investment in a new power plant can be deferred or cancelled. Again this benefit is distributed widely, and isn't captured by simple accounting.

Actually his assumption that the neighbours pay more for electricity may not even be correct. Since electricity is priced on the marginal unit, it is entirely possible that reducing peak demand will result in average lower prices for everyone. There may be less profit for the utilities however.

In case you've missed it, there are a few posters here with Off-grid experience, either thorough or partial, and I've heard very few of them express disappointment at the experience.

You want to call them suckers, and then suggest that you're happy to wait and take your go signals from the Utilities? Ok..

In 20 or more years, it might not be 'whether' you're getting sporadic service as much as how much one sporadic supply costs from month to month as opposed to another, and the length and quality of the outages. If you can hold your breath for a couple days, it might be more reasonable to expect the sun to come out after a storm, than for a Line-repair team to show up, or for a bankrupt utility or powerplant to be replaced by a new one by the time you REALLY need a few watts for this or that.

"For those living off grid... why?"

It's just one of those things, mkkby. If you haven't been there, done that, it's easy to find fault, though, judging from a selection of your other posts, this seems to be your forte`. After 15 years of living quite nicely off-grid, I still have folks explaining to me why it doesn't work. Perhaps they're trying to reinforce their own choices to be utterly reliant upon failing systems.

Know this: After double layoffs 3 years ago, a severe downturn in our local economy, and an equally constrained financial situation, our off-grid systems have been one of the few things we've been able to count on and take for granted. Choosing to do these things, to pay them forward during good times, has been one of the best choices and most reliably consistant investments of my life, very low on my list of uncertainties. What's it worth, peace of mind? My per-kilowatt costs are constantly declining. What are your's doing?

BTW: We used no incentives, credits or tax breaks, nor is our energy taxed. Your energy is likely taxed several times by the time you pay for it. Enjoy!

Edit: Not meaning to pile on ;-/

I think the argument is that if you go offgrid the cost of storage is high. But, then the incentives to be efficient are much greater. So, if that will help family memebers feel motivated to conserve, I can see that being a factor. In my grid tied house, the only incentive is me grumbling. [Tons of cause to grumble today, they're going on a cleaning binge, and laundry, and all the lights are on...., and well since the morning thats 20KWhours, easily overwhelming my panels production]. You can bet they'd think twice after running out of battery charge with an offgrid system.......

The batteries don't run out of charge. The inverters are programed to shut down one at a time when voltage drops, least critical sytems first. Of course, I decide which systems are critical.

Always protect your batteries. Mine never drop below 60% without my permission. The family knows the drill :-/

Oh golly, "the socialist are coming. The socialists are coming." Do you know what the Tennessee Valley Authority is? Have you heard of the Hoover Dam? How much money is paid to the average Alaskan for oil extraction in that State? Do you know what socialism is? Who built the power grid? Who underwrites the insurance for Nuclear Reactors? Why do the drivers using gasoline not pay 100% of the taxes for the roads and bridges?

Most energy products and the infrastructure using the energy in the US are "socialist." Seriously. You know this and yet you post the socialist folly thingy. LOL.

Well maybe you want to sell off the other Federal assets, make nuclear rate payers pay for nuclear insurance, charge the right gasoline tax to pay for the roads and bridges. You may be a pure capitalist after all. Sounds great. But without a level playing field people cannot compete with the entrenched fossils can they? ;-)

Oh golly, "the socialist are coming. The socialists are coming."

You mean the 'solarists', right? Those are the people you really have to be afraid of... >;^)

Yes, Fred, my house is getting appraised for panels. I will need to talk with you. I will not do anything until I get quotes from at least three outfits, but the first quote is due this Saturday.

Interesting article, but it is proof solar is not yet economic...

Exactly! Economics is above all else an instrument of policy. Saying something is not economic is equivalent to saying "not politic." I couldn't agree more. What we need therefore is a change in the politics of energy, such that we charge people for polluting the air the same way we charge people for carrying out their garbage. We don't allow people to throw garbage in the street but there is still no charge for polluting (except carbon trading in Europe).

Government should not be giving you feed in tariffs. Why should your neighbors pay for their own electricity and be forced to pay part of yours too?...

Anyone who is willing and able to capitalize energy for their children and their neighbors' children instead of burning up their children's future access to plastics, metallurgical coal, etc., is to be commended. "Socialism" or other such labels are irrelevant. We're talking here about Peak Oil.

Government should not be giving you feed in tariffs.

My electricity bill used to tell me the cost of production for my electricity, though they do not do that any more. Why should I not be paid that for electricity I produce and supply to the company?


Disclaimer: I am not grid tied in this house but am planning it for my future house.

Feed in tariffs are higher than the retail cost of production. You should absolutely be paid for the electricity you export to the grid, but should you be paid more than it would cost you to buy it?

A feed in tariff like the one described by Luis has a couple virtues compared to some other schemes, namely:
-it's limited in amount
-its planned to step down to more normal rates, which means less investment uncertainty

I'm supportive of limited subsides that are designed to jump start the industry and then wean it off support, with the intention that the industry gets going faster but then stands on its own economically. Step-downs should be planned ahead of time, not requiring later legislative attention. (Of course there are some who will always object to taking any penny of 'their' money to benefit anyone else, anywhere, even if it leads to a more prosperous community down the road.)

Payment for the electricity you supply should be based on the purchase price but we have a subsidised purchase price for low usage so the guideline 'cost of production' makes more sense. We actually get charged the CoP if we use over a certain amount so that seems fair. If most of the electric usage was offset by solar then we might only mach the lowest, heavily subsidised purchase rate which would not be good.

Any FiT over and above would form part of a policy to encourage installation. How much and how long would depend on how badly the suppliers/government want to boost solar. It does seem correct that an installation encouragement should taper off reasonably quickly.


When the utilities prefer solar PV farms instead of traditional plants, it probably means it's safe to invest.

Well, it must be that time then... Do a google news search for 'utility scale solar' and you'll get plenty of hits for projects under construction or development.

the feed-in tariff attributed to the first lot of 1000 permits is 0.65 €/kWh, decreasing with each new lot, down to a minimum of 0.31 €/kWh;

Good lord. That's 2-4 times the retail price of electricity. Is it any wonder why there was a gold rush for applications? And no wonder the applications were limited to a few thousand: if everyone in Portugal did this, you'd bankrupt the government.

Also, when feed-in tariffs are far larger than the retail cost of electricity, everyone has a huge incentive to commit fraud by borrowing from Pedro to pay Paulo. This can be as simple as an extension cord running to your neighbor's house, or it can be industrial scale, as happened in Spain a few years back. I'm not saying this is happening in Portugal, but it's a serious risk.

It seems to me that the lesson we should take from your story is that the megawatts are there, but a much smaller feed-in tariff, available to a larger number of people, would be a better way to promote solar power.

if everyone in Portugal did this, you'd bankrupt the government.

If everyone in Portugal _doesn't_ do this, peak oil will bankrupt the government, as is now happening for example in Egypt. See Jon Callahan's Oil Export Browser if you have any doubts about who's solvent -- exporters -- and who's not -- importers like Portugal -- and the riotous Egypt, UK and others.

If everyone in Portugal _doesn't_ do this, peak oil will bankrupt the government, as is now happening for example in Egypt.

The fact, that so few people who rail against solar, wind and other alternatives, as being uneconomic, ever really grasp this point, continues to leave me utterly flabbergasted!

If everyone in Portugal _doesn't_ do this, peak oil will bankrupt the government,

That's my point! The Portuguese government has set up a tariff *far* higher than what's needed to encourage solar panel construction, so high that they can't afford to let everyone participate. If the tariff were smaller, they could afford to let more people into the program, and make much more progress.

Government subsidies are all about getting the maximum social change for the minimum cost. Too low, and nobody bothers to participate. Too high, and you waste resources and encourage fraud. Looks like Portugal didn't quite get the balance right here.

I like your theory about subsidies. Well stated. And it allows the size of the subsidies to change as market conditions change. Something that fixed FIT schedules are poor at.

I'd like to see a sealed reverse auction for feed-in tariff contracts. Each year, the government would budget $X for renewable energy promotion. Everyone would submit a single bid for the smallest feed-in tariff they're willing to accept. The contracts go to the lowest bidders: the cut-off for who gets a contract and who doesn't is set so that the total cost of the program is $X.

Everyone who doesn't get a tariff contract can still sell power to the grid, but at a market rate rather than the government-subsidized one.

Competition sets the tariff price to a level where it's just barely worth your while to go green. As renewable tech improves, people will be able to make lower bids, and more people will compete to get on the gravy train.

Never underestimate the power of capitalist socialism!

but a much smaller feed-in tariff, available to a larger number of people, would be a better way to promote solar power.

I'm in full agreement about that. The fact that some big players were gaming the system shows a poorly designed program. And that can backfire against renewables, as people without them figure they are paying too much to those who got in when the getting was so good. At this point, with decent net metering, and maybe net metering weighted by varying time-of-use power rates, which attempt to approximate the cost to the system of providing power is all solar needs.

a much smaller feed-in tariff, available to a larger number of people, would be a better way to promote solar power.

The California Solar Initiative was designed to transition quickly from 'a lot for a few' to 'a little for many.' I think it was designed well, because at the beginning a program like this needs to help the industry more to get off the ground. Once the industry begins to establish itself the subsidy (per watt or kWh) should become less and less and eventually not be required to keep the industry alive.

I often look at our solar installations in terms of BOE (barrels of oil equivalent). Here's a little "stripper well" equivalent -- about a barrel a day -- that we built four years ago. Monthly data for the last 2 years in BOE:

This and our other solar installations combined produce about 10 barrels equivalent a day, quickly making up for a lifetime of "sins" (wild guess, I've consumed on the order of a thousand barrels).

Keep that solar coming, Luis!

What is the kW (DC) of that system?

FWIT I installed a 5kW DC rated grid connected system in Florida at about 30degrees N and facing due south, just over a year ago. It uses separate inverters for each panel, providing flexilility in case of failure, and higher efficiency than single inverters. The system is connected to the Enphase "Enlighten" ( data collection which gives me near real time performance data. In the first year it produced 7.9 MWh, 108% of the model expectation, with just under 6 tons of carbon offset. The then available Florida rebate, plus the federal tax credit made the system quite affordable. The rebate program was so beneficial to the local utility, FPL, that they have now offered their own rebate program, that was oversubscribed in one hour, without cheating by investors.

I wish I could post the enlighten display, but have found no way to do that.

Go here for a link to Enlighten

At some other time, perhaps you can let us know how your experience with micro-inverters has been. Would you recommend them? Are they worth the extra price per nameplate watt? What about reliability issues?

Microinverters certainly deliver greater AC to DC rations, as with typical inverters connected to strings of panels, the weakest panel determines the current. So if your panels are mismatched, you won't get as much AC as you would with a single larger inverter. But a single inverter is less expensive, so you could probably afford an extra panel or two.

Luis, thank you for the interesting article.

I cannot comment on experience of using these microinverters. However, I am in the process of putting in a sub-4kw ground system and my installer is now saying that they are having difficulties with the microinverters on other installations. Reported difficulties are affects on the grid as reported by the grid operator and incompatibilities with various panels despite an apparent certification. Sorry not to be more precise.

My rational for originally going for the microinverters was to remove a single point of failure and the likelihood of having to replace the traditional type of inverter after about 10-15 years, and to maximise the output of the array. However, it seems leading edge technology is once again more like 'bleeding edge'.

BTW, here in the UK most domestic electricity supply is single phase and a 4kw system appears to be the maximum being connected via single phase with larger systems requiring three phase supply, an additional cost. Single phase supply may be a factor in the difficulties with grid connected systems. Anyone knowledgeable on this? My point is that it is essential to compare the whole installation including any local factors when trying to make comparisons.

Other factors I am considering are whether to mount the inverter outside by the array or in the loft, and whether to go for the higher yield panels such a Sanyo or the lower cost panels. Temperature-wise, we don't live in the extremes, so it doesn't get that hot in summer but any excessive heat could well shorten the lifetime of the inverter. As for the choice of panels, this will depend on the expected additional output and hence the rate of return. It could be better to go for the cheaper panels now and replace them after a few years, assuming the cost-performance of panels continues to improve. I guess with the stock market so volatile and the interest rate so low, I am likely to get a pretty good return whatever the decision.


My inverter is in the garage, which can reach 100plus. I have an 8watt persoal fan mounting so it can blow on the heat sink. I like to run the fan when the inverter output is a KW or more, it keeps the heatsink temps(measured) down by about 30 degrees or more.

Unless you are space rather than capital limited, I'd go for the panels that minimize overall system cost (including mounting and wiring costs, which are higher for low efficiency, since you need more of um). That isn't necessarily the cheapest panels, but it probably isn't the most efficient ones either.

See Aug's link from above. $0.74/watt, and they're 14% efficient crystaline panels. No frames or J-boxes, but that shouldn't stop an off-grid guerrilla like you ;-)

I have had my system since mid-July 2009, with an increment at the end of August 2010. The collected data is here There have been no issues, even though, in retrospect, I was probably something of a guinea pig. The company had clearly been working hard over the course of the 1 year between installations. The newer inverters were about 10% smaller, did not require a bulky heat finned aluminum case, and peak out at 50C running temperature instead of 55C. The data stream has been invaluable for learning things about production. From it I can clearly see:

- production peaks out on the winter side of the solstices (predicted from my roof slant of about 29 degrees)
- production is slightly higher in the spring than the fall, likely due to lower overall temperature
- my neighbors palm tree's morning shadow falls straight across the first set of panels in the summer.
- my banana plants' morning shadows sweep across both sets of panels in the winter

I'm not sure about your point concerning mismatched panels and a single inverter. It seems like you have the argument backwards. The microinverters have been invaluable in my situation. As each panel becomes unshaded, it goes to full production, while it is my understanding that the other panels would have been held back with a single inverter. There has also been no issue with my first set of panels being different from my second set.

The shading effect can be observed by selecting "Today's Energy" or "Past 7 Days" and moving the slider.

Maybe I stated it confusingly. Shading issues hurt single inverter systems, but only affect the shaeded panel with microinverters (which is what you state). And jsut like shading of one panel hurts the entire serially wired string, a weak panel on s string will likewise bring down the production from the other panels. And panels like any manufactured product will have some variance. A really good conscientious installer would measure them ahead of time, and try to match them up as well as possible to max output. So microinverters minimize these loses, although macroinverters probably have higher conversion efficiency, but probably more than give that back due to mismatching issues.

And jsut like shading of one panel hurts the entire serially wired string,

That's not really true of modern panels equipped with internal bypass diodes. For example My KD135's are equipped with 2 bypass diodes. If shading occurs to a side of a single panel in my string, while for example it's putting out 7 amps, the 7 amps from the other panels will flow through the bypass diode and the loss will only be about 6 volts(42 watts) to the entire string.

Bypass diodes mitigate against very small amounts of shading, buy they don't eliminate the problem of shade reducing power in series strings. If all three sections of one of your panels are shaded, then the entire output of the string will still be massively reduced even if no other panels are shaded at all. Microinverters mitigate against this situation. If one entire panel is shaded all others can still output at full power if they are not shaded.

Some other DC technologies are beginning to hit the market that provide the same shading mitigation as micro-inverters.

This calls for a real world test. I just hooked in the "DocWattson", I'll be back with the results just after solar noon in about 5 hours.

Results are in. 2 135W panels in series, MPPT SGPV microinverter.

28W with a magazine covering a small portion of one panel.

You are right, a small amount of shading drastically reduces output of the whole string. I'm going to have to do some further research to find out why the bypass diodes are of no help.

I believe that the major purpose of the bypass diodes is actually not to mitigate shading, but to protect the conducting pathways between the cells (i.e. the solder) from overheating. (Shading prevents current from flowing through the shaded cells, and when other cells are trying to push current through the shaded cells this causes heat buildup, I believe. But I'm fuzzy on the physics and maybe I'm not describing it well.)

That is correct, if a cell is shaded the other cells will drive it into a reverse voltage situation causing localized heating which will damage the cell or connections.

I did another test with a purely resistive load. The results were closer to what I expected.

92 Watts 2.7A normal.
54 Watts 2.06A with the magazine covering a small area.

In fact even with the whole panel covered, and the other putting out 1.3 amps, I could only drive it reverse 1.5V, and most of that was probably in my 24' #14 wire.

It is like the MPPT inverter is doing it's own thing protecting the panels from localized heating, and not taking advantage of the potential gains offered by the blocking diodes.

Inverters should have an option switch- "Panels equipped with bypass diodes: Y-N". No if unsure.

I got 3 quotes, and the least expensive one on a total $ per installed watt basis was with the microinverters. I had no good place to instal a large inverter, and the microinverters go under the panels. Also it was the only system that gave me real near time monitoring. They were the best choice for me in every respect. Only one year of operation, so no idea wrt reliability.

I got 3 quotes, and the least expensive one on a total $ per installed watt basis was with the microinverters.

That's somewhat surprising. Were the quotes from different companies?

Also it was the only system that gave me real near time monitoring.

Real time monitoring can be added to string systems, but for an extra cost of course, and with less 'granularity'.

I live in the UK to the east of London and I have a 1.88 Kw grid-tied system.

In the UK the feed-in tariff (FIT) for domestic users installing grid-tied PV less than 4Kw onto existing buildings is £0.435 per Kwh produced, plus half of production is assumed to be exported to the grid, and for this you get another £0.03 ... also any PV power that you use results in a saving of ~£0.12 per Kwh.

There are different FITs for different ways of producing electricity from non fossil fuel sources ...

The income tax free FIT is paid by your electricty supplier (not the government!), is index linked to inflation annually, and runs for 25 years! To claim the FIT the system must be installed by an approved installer.

I was told to expect 7-10% return on the money invested ... so far after 9 months usage my system has returned 8% tax free and I fully expect to make the 10% (ignoring the savings I make on using some of the electricty my panels produce!) My annual electricity bill is now around half of my FIT so my supplier now pays me! ... a major result. If you add in the PV not exported then the return becomes ~ 15%, payback time looks like it will be less than 7 years ... sooner if we have annual inflation!

The reason for the FIT is that in Europe cheap forms of electricty from fossil fuels are soon going to be gone ... FOR EVER! Fossil fuel is the low cost 'low hanging fruit' ... from here on electricity will be much more expensive ... IMO stop complaining about it 'cos it won't do any good and try and make the best of a serious predicament ... predicaments don't have full solutions.

If the payout is really anywhere near 15%, it is way too high! Congratulations on finding a fantastic deal/investment. Sure beats putting the money in the stockmarket -or on Greek Bonds! But, don't expect the offer to remain so generous for long, once enough people get wind of it far too many will apply.

The FIT is as high as it is because some clueless twonk in the UK Government signed us up to a binding European agreement to meet a certain reduction in CO2 by 2020 ... as things stand in the UK we are nowhere near meeting the target! ... hence the panic measures.

You can tell it is a good deal because electricity suppliers will fit PV for you at no expense and you can use as much of the generated power for free thus they avoid paying out the too high FIT. Other companies that aren't electricty suppliers will do the same deal but claim the FIT for themselves ... because the high FIT makes it profitable some of these companies are buying up land in sunny parts of the country to put in large PV arrays.

BTW: Luis, a belated welcome to the club!

We took the plunge and installed a 3kW grid-tie system on our roof here in Nelson NZ in January of this year.We already had an existing solar water heating system (which is very effective) and as we get a ton of sun here (2500 sunshine hours a year) and our house is north facing thought it a wise investment. Because there is no feed in tariff in NZ and because the best deal you can get is from Meridian energy (a 1:1 rate of exchange) we purposely went for a system that would generate about what my wife and I use (4500kWh/year) as there is no point in building up credits. NZ is fortunate in that close to 80% of our power already comes from renewables (Meridian solely generates its power from renewables, maily hydro). Although part of our rationale was green motivation the main inducement was that we had the cash available and since inflation is just eating its value away we thought it sensible to invest in something which would actually act as an inflation hedge. Thusfar the system is performing some 5-10% ahead of spec. This year electricity companies in NZ raised electricity prices by 7% (which is the average rise for the past 10 years). At that rate of rise the system will have paid the initial capital back in 12 years - and that is with zero inducements from govt etc. We are as happy as Larry with the decision to buy the system.

I notice quite a few antipathetic comments on this page. Household solar is either part of a socialist plot, a waste of money, or an affront to the idea of pure renewability. Ha! And you thought TOD attracted the finest minds, eh? Back to reality, I highly recommend the books by Cam Mather on this topic. He is a PO-aware guy who lives in the Canadian backwoods and runs on his own PV solar.
Interview with Cam Mather (mp3 podcast, 1 hour)
Thriving During Challenging Times: The Energy, Food and Financial Independence Handbook (Amazon link)
Off the Grid and Thriving! (Mother Earth News article by Cam)

A very interesting article. I have been looking for real generation data for ages now, so thank you for posting this article.

One other important consideration, and a lot of people seem to be ignoring it, is the maintenance lifetime of the average house roof, which is dependent on local climate. If your roof gets damaged - in the UK often due to wind damage, to a lesser extent frame rot, then you would often need to disassemble the whole solar array (depending on configuration - many have a backing plate for PVCs), repair the damage, then reassemble the array. A significant cost, as well as loss of generation (lucky in the UK most roof damage occurs during autumn/winter when generation is lower anyway).

A very interesting article.

Thats actually a big deal breaker for many. If your roof is only a few years away from needing a redo, it isn't worth it. In our area we have very long lifetime fake tile roofs, so it isn't a problem. But for a lot of people with older generation roofing it is an issue. Much roof degradation is due to high heat, and the panels help in this regards. But, you aren't likely to cover 100% of your roof, so if the uncovered portion ages faster than the covered portion you could have an awkward partial redo.

We installed solar PV about 3 years ago. As stated, you don't want to have to re-roof after the panels are installed, so I re-roofed the house prior to installing the panels. We have fairly high winds in our area (up to 90 mph), so I bought Dow Corning lifetime warranty fiberglass-based shingles with an extra row of adhesive which glues down the bottom edge much better, making them far more wind resistant. They should outlast me, if not the panels. Btw, roofing was a MUCH more difficult job than installing the panels (26 215W). It took me almost 2 weeks to re-roof, and about 4 days to install and connect the panels using Unirac. I was required by the local utility and county to have a licensed electrical contractor do the final hook up to the service panel (even though I have an MSEE). We saved about $6k doing the roof ourselves, and about $14k doing the panels ourselves - not bad pay for 4 days work.

The nominal 5.6kW panels have put out a max of a bit over 6kW AC power on a clear, cool, windy day. Power output is only about 4.8kW on a hot summer day, due to higher panel temperature. Total output over 2 years 9 1/2 months is 26733kWh, or 26.7MWh. About 9.58MWh/yr, 798Wh/month. La Nina resulted in much more cloudy weather here this past winter, so cut down the output a bit. Our house uses about 420Wh/month, and our electric car uses about 130Wh/month, so we have about 248Wh/mo excess.

We plan to purchase another electric car if the manufacturer's ever get their act together (I converted the one we have: I'll likely install a solar hot water system when we buy another ev, which should reduce our house electric by around 15-20% (only two of us, so we don't use a lot). That should give us enough electric for the second car. If not we have the other 1/3 of the south facing roof for more PV.

We saved about $6k doing the roof ourselves, and about $14k doing the panels ourselves - not bad pay for 4 days work.

That's one thing that's keeping prices too high. It is not the cost of the solar it is the amount companies are taking to do the job, especially if they have shareholders and the shareholders want the big cut. The hope has to be that , as solar becomes more popular, more companies get in on the act and competition ensues.


It is surprising, to me at least, that more small electrical contractors aren't getting in on the act.

Look for the residential part of the solar industry to evolve to a point where the 'solar company' does little more than design the system and warehouse and deliver the panels and other equipment. (Actually they may even contract a warehousing and logistics company for the latter parts. It's the biggest piece of overhead and thus the biggest opportunity for savings.) They then contract with a local electrical contractor and/or roofer to actually install the system.

Concerning longevity, I believe the actual cells can last 100 years in UV. However, I have no clue if the resin like clear encapsulant (EVA?) between and around the cells will not yellow and crack after 30 years.
I know that the cheaper amorphous panels do not have tempered glass and take up twice the space. They also decay faster than silicon.
If only ambitions could be directed at creating the machines needed to quickly mass produce batteries and solar dishes... for cheap. The stuff that NASA uses, GaAs, is twice as efficient and is obviously UV resistant. Even to the concentration of a 1,000 suns!
A world powered by such would require about 1% of the land to be covered, to provide a western standard of living to 10 billion people, assuming major efficiency gains like led lighting, more insulation and the switch to electric cars... On the other hand, if the world was powered by flat panels, 2% of the land space getting that hot may actually cause problems, whereas the dish would not get so hot and reflect unused light back into space.

I searched "solar storm" and nuclear, hoping to find out if most nuclear plants around the world really do depend on the grid indefinitely (to prevent meltdown). Can someone point me to the right thread if there is one. I believe that a major solar storm could cause some nasty problems... but don't want to be over hyped.

Most nuclear plants have diesel generators to prevent meltdown. New designs rely on natural convection and gravity to circulate enough coolant, and so don't need electricity, but may need to have coolant water added every week or so.

I fully endorse it to assess site adequacy. The actual data for yearly production is 5140 kWh, in contrast to the 4420 kWh projected by the Calculator, a difference of more than 16%.

and you later 'correct' for what you believe is a large 16% error.

This is actually a small error, and may be a seasonal variation from an average - so you cannot presume your numbers, are 'better' than the calculator.

Cloud makes a significant impact on solar, and the area under that curve is going to be annually variable.

Also, for lifetime costs, it is better to budget an annual fee for maintenance, and to expect to replace some small percentage of components from failures.

Here, good system monitoring can make a huge difference, and the cost & quality of good monitoring is falling faster than panel costs.

A system that can be split into subsets, that can be compared will mean fade-outs in ratings are simply obvious.