Wind and Heat Pumps: A Winning Combination

The following is a guest post by Tom Konrad, PhD. Tom is an investment blogger who brings readers ideas for investments that may benefit from Peak Oil and Climate Change at, where this article is cross published.

Last month, I posted some nice maps showing when and where good wind resources are found in the US. Now I've found something better: a visual comparison of electrical load with wind farm production[pdf file], published by the Western Area Power Administration in 2006. The study compared electricity production from five wind farms in Northern Colorado, Southwestern Nebraska, and Central Wyoming in 2004, 2005, and the start of 2006, compared with electricity consumption in the same area over the same time period.

Comparison of Wind Production to Electricity Demand

I've copied four of the most representative graphs below.

The first and third heat graphs below show electricity production at the five wind farms studied in 2004 and 2005, respectively. The second and fourth show electricity demand in the surrounding territory. Red(blue) denotes areas of high(low) production or demand.

For wind advocates, these are probably rather scary graphs. The first thing you probably noticed was the big blue patches of wind production during summer peak demand, roughly 10am to 10pm in June, July, and August. This is why wind is referred to as an "energy resource" not a "capacity resource." Right when demand is often highest, the wind is least likely to be blowing, namely hot summer afternoons.

On Second Thought - How Much Backup Do You Need?

That is just the first impression, and while it is a true impression, it's also an oversimplification. If you look at the scale, you will notice that the blues on the wind production graphs actually represent wind generating at 10% to 15% of nameplate capacity. If you factor in the fact that a normal capacity factor for wind is about 25-40%, that means that even on these hot summer afternoons, the farms are generating at one-third to one-half of their "normal" output. This means that, contrary to popular misconception, wind does not require a "100% back-up with natural gas." It is true that wind is less reliable than baseload power plants such as coal and nuclear, which typically run about 90% of the time, but in an apples-to-apples comparison, a 100 MW coal or nuclear plant will produce as much energy over the course of a year as a 270 MW wind farm. During the peak summer months, the coal plant will need some backup power in case of an unscheduled shut down due to lack available coal (this happened in Colorado in 2005 due to problems with dust in rail tracks) or lack of available cooling water during a heatwave, and when a coal or nuclear plant goes down, it goes all the way down, so the 100 MW baseload plant has a small chance of needing 90 MW of backup to produce at its "normal" rate of power production. On the other hand, the wind farm will be operating at (a conservative) third of its "normal" capacity, producing about 30MW. To bring that up to its normal capacity for the year, it will need 60MW of back-up power.

In other words, because some part of a large distributed group of wind farms is always producing some power, it will never go completely down. A large baseload power plant, on the other hand, is completely down about 10% of the time (although less during peak summer months, because utilities schedule maintenance in off seasons.)

Pick Farms to Match Your Load

Another point worth noting, is that the wind has different annual patterns in different locations. The smallest (8.4 MW out of 139MW) of the five farms in the study was "Wind Farm B" in central Wyoming. If you look at the following two heat maps below for 2004 and 2005, which show the production of just this wind farm, you will note that during the peak summer demand, this farm was producing at over 50% of "normal" capacity for much of the summer peak.

Since we know what electricity demand looks like, if we plan new wind farms (and adequate transmission), we can choose to build wind farms that produce more power when we most need it. If all the farms in the example in the last section had more favorable production patterns like Farm B, even less back-up generation would be needed to bring them up to "normal" capacity.

For instance, in the Texas Competitive Renewable Energy Zones study [.pdf 7.64MB] wind in the coastal area (along Texas's southern gulf coast) was found to be a much better match for the ERCOT load shape than wind in other areas, although the average capacity factor was considerably lower than panhandle wind. See chart below:

Hence, careful selection of wind farms can lead to wind production with higher capacity during peak loads, and correspondingly less need for dispactchable power. Although Texas is currently focusing on developing wind farms in West Texas and the Panhandle because of their high capacity factors and correspondingly high annual energy output, the power from coastal wind farms is likely to become increasingly valuable as wind reaches higher penetration.

It's Not All About Summer Peak

Statements about wind's need for large dispatchable backup generation because of low capacity factors during peak times contain an implicit assumption that electricity demand is fixed. This assumption is both false and pernicious, because shifting demand can be done cheaply, and often produces multiple benefits. While it is true that most large scale electricity storage technologies, such as pumped hydropower, compressed air energy storage, and utility scale batteries are expensive or limited to a few available sites (pumped hydro,) technologies which shift the demand curve are not.

If you look back at the first set of four heat maps, you will note that wind actually does a quite good job serving the winter peak. In 2004 (a year with a moderate summer) winter peak demand actually exceeded summer peak.

Capacity during winter peak has some advantages over summer peak. First of all, natural gas prices are higher during the winter, because natural gas is used extensively for home heating as well as power generation. In February 2006, Xcel Energy had a series of major power outages in Northern Colorado which they blamed on insufficient natural gas in storage due to unusually cold temperatures. Yet as this heat map

shows, wind farms in the region were operating at 40-60% capacity factors (i.e. well above "normal" production) for January and February. Note that the blue at the end of the year was due to lack of data, not lack of production. Had there been more wind farms installed, this would have had a large impact on the amount of natural gas needed for electrical generation, and the outages would not have happened. I don't have data to back it up, but my personal experience leads me to believe that cold winters in the great plains are also particularly windy winters, meaning that winter wind capacity is ideally suited to displace natural gas needed for heating.

How Heat Pumps Fit In

Which brings me to the title of this article: why heat pumps are an excellent fit with wind generation. In my article on how to invest in the Pickens Plan, I mentioned that ground-source heat pumps (GHP) can displace gas used for heating with a smaller amount of electricity from wind. Since a GHP is both an efficient air conditioner as well as an efficient heat source, it not only reduces natural gas used for heating, but also reduces electricity used for cooling in hot summer months, which in turn reduces summer peak loads.

Deployment of GHPs does three things to make energy supplies fit energy demand:

1. Winter electricity usage is increased just when wind capacities are highest.
2. Summer electricity consumption is decreased when wind capacities are lowest.
3. Use of natural gas for heating is reduced during times of peak gas demand.

GHPs, because of their extreme efficiency, also have the benefit of saving users a lot of money.

The Dual Fuel Option

Unfortunately, GHPs have not been widely adopted, due to the difficulties of installing the buried heat exchange loops, especially in urban areas (although some utility programs have been very successful.) When I bought a house, it was in a New Urbanist development with very small lots which was close to my work. While this saves me countless gallons of gasoline, it meant that I was unable to use a heat pump. I opted instead for the most efficient natural gas furnace available from my homebuilder, in combination with the most efficient air-source heat pump. Unlike GHPs, air-source heat pumps lack a ground loop, meaning that they only work efficiently when temperatures are above about 40F. In my dual-fuel system, the heat pump heats my house during milder weather (which is frequent in Denver winters), and the natural gas furnace takes over when it is cold. Since the heat pump is only slightly more expensive than the air conditioner I would have bought anyway, the dual fuel system will pay for itself rapidly, especially when natural gas prices are high.

From the perspective of the electric grid, my electric usage is higher and my natural gas usage is lower during the heating season, when gas demand is high and wind farms are at their most productive. So while a dual fuel house is much less of a strain on the energy infrastructure than one with a furnace and an air conditioner, it also saves the homeowner money for a much smaller investment. In addition, while the need for a ground loop makes a GHP nearly impossible to retrofit to an existing home, an air source heat pump is an option for anyone considering replacing or installing an air conditioner, and has the added advantage of having a back-up heat source during a natural gas outage.

Another retrofit option I hope to see available soon is a hybrid ground/air source heat pump [pdf]. These systems combine a short ground loop with an air heat exchanger. By using the air exchanger during milder weather, only a smaller ground source loop is needed for use during more extreme conditions, reducing the up-front costs compared to a GHP, but without the performance loss of an air source heat pump. A startup called Co-Energies has developed a way to retrofit existing air conditioners into hybrid heat pumps; see slides 33 and later of this PowerPoint.

Electricity Demand Can Shift

Heat pumps are just one option for changing the shape of the electricity demand curve. Many such efficiency measures can do so. Other examples are improved home sealing and insulation, which typically pay for themselves in a couple years or less, and, because air conditioners work less hard in the summer, reduce summer peak loads. Wind is undoubtedly a tricky sort of electricity to use in the existing grid, but the fallacy that demand is fixed makes the problem seem much harder than it needs to be.

I had a very deep overburden (200 feet of sand, clay and marl) above bed rock at my last home. There was no problem in drilling 6 loops in a teepee shape from a platform about 6 ft by 10 ft in the back yard. The driller said he could have done a much shallower job if necessary. I suspect retrofit is quite possible in many cases. I also had a 2 stage compressor that could run a/c at 1, 2, or 3 tons as needed to add to the efficiency.
I agree completely with your wind analysis. Given a wind farm that has excess capacity when the wind is strong, the excess capacity could be used to generate hydrogen to run a gas turbine when the wind is weak and further level the supply. A lot of hydrogen could be stired under pressure in the rurbine tower. Murray

I was under the impression that the hydrogen storage (via fuel cell, or compressed air) concept wasn't very efficient? My understanding is based on that thread "The Hydrogen Economy" on this site.

Like the author here suggests, shifting demand or pairing supply/demand locations based on their production/demand data seems like the most efficient way of reducing problems with peaks. Though obviously it can't be entirely relied on.

I really don't know how the electrical grid works, but it seems obvious that dulling the blades edge on production spikes means more diversity. So distribution and various sources ie. solar, wind, geothermal, etc.

My question is, is it more or less efficient to have large solar/wind/etc installations at prime locations and then transmitting that electricity as required, or would small-medium sized installations distributed and providing power locally (for the most part) be more efficient? You must take into account the "backup" situation described above, because one large centralized installation would have a much greater fluctuation in production than a distributed network of smaller installations.

(Horray for my first post!)

I was under the impression that the hydrogen storage (via fuel cell, or compressed air) concept wasn't very efficient?

Correct - but it's a storage method. I wish that I could find it again - but there was a prof in the UK who had a nice setup - wind and PV generation as well as hydro-electric. Now when he had spare energy he charged the batteries (hours of energy storage) and when they were full he pumped water up into the pond (a day or two of storage) and if that was full then hydrogen was created and stored (a week or so of energy).

Now hydrogen does tend to leak out of containers, and it is inefficient creating, storing and then converting it back into energy - but if you've got energy to waste then it's a viable option.

What's nice about being grid intertied is that someone out there will be able to use the energy.

It would be nice if a good energy storage scheme (ultra-capacitors, flywheels, batteries, whatever) came online to smooth out energy from turbines and PV.

But then I hold strongly that we need to pitch the toys and dump the crap. Freezers don't need energy 24x7 and fridges can mostly survive without it. We could also do without fridges. Hot water heaters can easily get by with electricity during only part of the day (but then do we really NEED hot water?) - but energy for cooking is the rub. It's an issue with our food storage. We store a fair bit of food - but we have far more food than fuel to cook it with. We've tried solar cookers and white gas stoves are thirsty beasts and a lot more expensive than an electric range.

You make a few very strong points, but this point needs to be made: cooks use gas-fired ranges because of the very fine and fast temperature control these ranges offer - it is hard to cook a simple omelette on an electric range: you need a very hot plate to go down to a simmer very fast -
This may seem a frivolous argument, but I don't think it is. I think the single most important thing we humans do is to prepare food for each other and eat it together. Cooking is the only art that produces more artists than music.
It is obvious that we need to become independent of fossil fuels, but we do need usable temperature controls in order to do even the most simple of cooking. Bread is best baked in a very slowly cooling oven, for example: a refractory brick hemisphere heated by a charcoal fire, the cinders of which are removed before placing the loaves in the oven. Steak takes two minutes a side on a hot fire. Potatoes need 20 minutes in (slowly) cooking water, 25 minutes steamed.
Making a meal starts with the ingredients, but you need rather precise control of the energy applied to your ingredients, if you want to put something edible on the table.
There are quite efficient and well designed ranges for gas, wood and coal. Coal is a nightmare, gas burns clean but is finite, wood could be renewable if we had lower population. Prospects look dire.
But then, how long will tv-dinners last in post peak times?

it is hard to cook a simple omelette on an electric range: you need a very hot plate to go down to a simmer very fast -

"Simmer"??? what are you doing to those eggs? Plain omelette should take 30 to 45 seconds on high heat if cooking on an electric burner from butter in to eggs out, no change in temp. req'd, then onto a heated plate and serve. If you Simmer you are on the road to chewiness, a bad place to go in this case :-(

Never more than 3 eggs, if you need more than that make another omelette.

What CAN'T you learn on TOD?

your description is much better than mine, but essentially it is the same process.
I heat the pan with oil or butter on a big flame, throw in the lightly beaten eggs, turn the heat very low, sculpt the omelette, season and serve within a minute of the eggs having hit the pan. Yum!

Just my 2 cents, energy used for cooking is nothing compared to everything else. I drive a propane powered car and I can burn up full tank in 3.5 hours. That same tank could last me 6 months for cooking.

More for emergencies, but one of these puppies allows you to use small pieces of wood and twigs to produce a very effective cooking appliance.

I have one, and the claimed outputs (3Kw) are correct !


I agree on hydrogen storage; it has a quite low round-trip efficiency. Demandshifting and long distance transmission are the low hanging fruit. When it comes to storage, there are many other technologies for storing electricity which outperform hydrogen. Most efficienct are flywheels (Beacon Power has just commissioned a plant to provide frequency regulation to the NY grid using this technolofy), and then utility scale batteries... NaS batteries have been used for years in Japan and are now being installed experimentally in the US, while Vanadium Redox batteries are also making inroads and scale up very well.

I've written more extensively about how to integrate renewables into the grid here

As to Large scale wind farms vs distributed, larege scale is currently favored by the production tax credit. The economies of scale are also an advantage, but this may be trumped in the near future by lack of adequate transmission... small scale is more expensive, but it we can do a lot more distributed generation as we build out the transmission we need.

Small scale installations have the advantage of being cheaper and higher volume. These two properties make a product more likely to be caught by the river of mass production, mass marketing, and mass competition.

I don't know why windmills costs so much damn money, when I've seen dozens of designs that were built from scrap, old hard drives, etc, that were dirt cheap. If someone comes up with a way to mass produce a 1KW wind turbine and energy storage system that pays for itself in under 3 years, it will sell like hotcakes.

It's pretty difficult to build a residential wind turbine which works at any reasonable efficiency.

One big point is do NOT attach one to your house, unless you have a proper survey done.
The vibrations from them can do serious to the structure, and can also cause a lot of disturbance.

Far better is a stand alone turbine, for two reasons: they obviously avoid the structural problems mentioned above and the further they are from the house the less disturbance, but they can also be built higher.
Wind has a surface effect, so the higher the better, as you get a lot more power.
They don't build those 80 meter high towers for the fun of it - they are far more efficient.

Some of those roof-top jobs get as little as 4% or so of rated power on average.

Home-built wind can work out in rural areas, where you can put a dedicated wind turbine at a good height and distance from your house, and particularly where grid electricity is not available.
Backup will still cost you a lot of money though.

So first ask yourself an obvious question, which surprisingly many do not seem to ask:'Is it consistently windy where I live?'

Hydrogen production/storage/use may be economically competative using the usual electricity generating tech at ~20-30% efficiency provided the wind power is cheap enough (class 5 resources?) since it could be offered as competition to peaker plants that are at ~15-30+c/kWh based on what I've read. Granted, for the time being programs to encourage efficiency increases in order to not use that electricity in the first place are far cheaper, so that's probably where we'll start, but it's interesting IMO looking at the huge difference between peaker and baseload rates.

Given a wind farm that has excess capacity when the wind is strong, the excess capacity could be used to generate hydrogen to run a gas turbine when the wind is weak and further level the supply.

That's a really clever idea.

patricks - It wouldn't matter much how efficient it was (it's more important to ask what the capital expense is compared to an otherwise similar wind farm). After all... if the energy would otherwise be wasted, even a small % recovery is gravy.

If that were the case, then it's better to use a thermal storage to electricity scheme. Store subcritical hot water and run it through a saturated steam cycle to release it. MUCH cheaper and simpler than a hydrogen storage scheme, and about the same efficiency.

But that efficiency is still crap, a much better way would be to try to sell the energy produced in the grid at lower sales price. At half the wholesale price, odds are you'd be able to find a buyer, especially in a smart grid which we need to build anyways. One example that comes to mind are plugin hybrids and electric vehicles, these are schedulable demands, plugged in most of the day and only driving a few hours and most can be charged in 1-6 hours depending on grid limitations and battery technology. A lot of offpeak wind production that would otherwise strand can find it's use here.

The difficulty of GHPs on retrofit I was referring to is in urban areas with small lots. It's just a matter of getting the drilling rig in (and paying for it, because even if you can get one in, it's going to be much more expensive than in rural areas.

Please read "stored" and "turbine". sorry

Good post, and one that I read with more than passing interest, as we installed a ground-source heat pump (vertical closed-loop system) in our place about two years ago.

One potential obstacle I can see to greater use of GHPs, especially in urban / suburban areas, is that many municipalities and county governments have siting restrictions for the ground loops. In Montgomery County, Maryland (Washington, DC area), where we live, the ground loop must be installed at least thirty feet from the house, ten feet from any buried utility line and ten feet from the property line. Although we have a decent-sized lot, these restrictions meant that the driller had only a narrow band in which to put the ground loop. I foresee that local governments may have to ease up on siting requirements, or expedite waivers, if GHPs are to be more widely used, as well as speed up the permitting process for drilling. In Maryland, one needs both county and state drilling permits.

I have a few questions about this:

1. How does adding heat pumps at the time of year when electric demand is highest (or at least sometimes highest) help the electric situation? At this point the alternative, natural gas, is in good supply.

2. Doesn't all of this depend on subsidies of various types--extension of the renewable energy tax credits and subsidy for the additional electric infrastructure that is required. If ground source heat pumps were used, they would require subsidies as well, it seems like.

3. Do you have figures on the real energy savings that can be achieved with your approach? If a homeowner in Colorado installs an air source heat pump, how many years of operation would it take to pay back the difference in cost between that and an a regular air conditioner, assuming no subsidies?

First, I like practical posts with reasonable thinking behind it. I have some interest in this area, as I have been soliciting quotes for HVAC replacement (including GSHP) for a couple of my houses.

In my opinion, wind works nicely for winter peak but solar works much better for cooling peak. A combination of both would go a long way toward covering the "peaking problems" faced today.

1) GSHP works better than existing AC during the summer. Average AC SEER is 13-15, very good is 19. GSHP is rated a little differently but comes out in the high 20's. These are day-to-day, month-to-month savings you can bank. For heating it does add some loading, and it's a regional case whether Nat Gas or GSHP is actually cheaper, but for an all-elect house GSHP will work without requiring resistance-heat fallback, and is far preferable. Of course solar thermal heating and other sources of heat could be considered as well.

2) It would benefit from subsidies, but it's not terrible without. Kinda like windpower in that regard. It is expensive. For my house, a cheap HVAC would be $13K, a good one is $16.5, and a full GSHP would add $15K more. It really makes sense to spend on insulations and weatherproofing first, and they get a smaller system. Much of this cost is the vertical bores, which are expensive (and more-so for already-built suburban lots). Still, it is possible to have pay-back within a decent number of years (<10) in many circumstances. The ground loops are rated 30-50 years, so you can expect to go through several mechanical systems with the same underground system (all high-eff HVAC units will last about 10-15 years, at most).

3) I have heard of numbers like $100 or less per month for a 4100 sq ft house in the Sun Belt, and some less than that. I never worked numbers for an air-source heat pump specifically, but I think that gives a SEER of about 19. Payback depends a lot on current efficiency of an existing unit and how much the power costs. It would be an interesting table to build (payback curves for ASHP and GSHP versus existing eff ratings for given current power consumption). I assume CO is a heating-dominant state, and an ASHP won't save you as much for one lesser season versus GSHP for both seasons, though it would cost a lot less.

I got a SEER 19 air conditioner but I live in Tucson. It is guaranteed for 10 years. Federal law requires ACs to be at least SEER 13. If a GSHP has a SEER in the twenties and costs an extra $15K, can you ever justify that? I can buy a lot of solar panels for $15K.

Robert a Tucson


I think it depends on where you live, and what you're switching from. A GSHP system works best when the heating and cooling seasons are roughly equal. In Arizona, where there is less need for heating, a GSHP system probably wouldn't make much sense. In the mid-Atlantic region, where we are, it is hot and muggy in the summer and cold in the winter, a GSHP system would save energy in both cases. Additionally, the desuperheating (hot-water generation) contributes a lot to the energy savings. If one has a reasonably high-efficiency air-source heat pump that is less than 15 years old, it wouldn't make much sense to switch to a GSHP. But in our case, we had a 32-year-old oil furnace that was about to eat us out of house and home with heating bills. We didn't spend a lot of time crunching the numbers -- I wouldn't call our switch to a GSHP a no-brainer, but it was pretty clear we would save a lot of money on heating.

The SEER for an efficient GSHP installed in Michigan is likely to be in the low 30s (or even higher since the ground is likely to be lower than average temperature due to the winter heating demand). Also a conventional air conditioner's efficiency decreases at higher temperatures, while a GSHPs is fixed depending on the ground temperature. What is the SEER for your unit when the air temperature is above 100F?

The heat extracted from the house in the summer can then used for pre-heating (or heating, depending on the system) hot water.

GSHPs require a lot of capital dollars though. Ours cost $23,000, plus another $1000 for new ducts and electrical switchgear, for a 4 ton system with a hot water superheater.


Hi Retsel,

EER is normally used to describe GSHP cooling performance whereas SEER is generally considered a more appropriate metric for air-source units; unfortunately, the two units of measure are not directly interchangeable, at least to my knowledge. In any event, according to Natural Resources Canada "[e]arth-energy systems intended for ground-water or open-system applications have heating COP ratings ranging from 3.0 to 4.0, and cooling EER ratings between 11.0 and 17.0. Those intended for closed-loop applications have heating COP ratings between 2.5 and 4.0, while EER ratings range from 10.5 to 20.0."


The Fujitsu 12RLQ mini-split has a SEER rating of 21 and an EER of 12.5, which appears to make it as efficient as some GSHPs (the larger 2-ton 24RLXQ I will be installing in my home is rated at 17.0 SEER/11.1 EER). Even a humble window air conditioner can provide fairly decent performance; for example, the Friedrich QuietMaster KS12L10 has a EER of 11.0.

At $0.15 per kWh, say, the cost per million BTUs of coolth -- the amount of cooling as would be provided by a 10,000 BTU/hr air conditioner operated for 100 hours -- for the 12RLQ is $12.00 and for a GSHP with an EER of 20.0, it's $7.50. For a GSHP with an EER of 30, the cost per MM BTUs falls to $5.00.

According to the U.S. DOE, Michigan has 594 cooling degree days (CDD) and 6,152 heating degree days (HDD), so it appears heating demands outrank cooling requirements by more than ten to one.


On that basis, for a larger, older home with an annual space heating demand of 120 MM BTUs, we might reasonably assume the a/c requirements run in the range of 12 MM BTUs. At $0.15 per kWh, the cooling costs of the Fujitsu would be about $145.00, whereas for a GSHP it might be somewhere between $60.00 and $90.00, assuming the EER is within the 20 to 30 range and not 10.5 or 11.0 which NRC defines as the bottom end of the scale. The difference, in this case, is about $70.00/year and for a more energy efficient home, it's likely to be one-third to one-half that.

There's no right or wrong choice but, for me, I would rather spend $3,000.00 to $5,000.00 on a good quality, high-efficiency air source heat pump and take the $20,000.00 or so left over to improve the thermal efficiency of my home. Alternatively, I could invest that $20,000.00 in a fixed, guaranteed investment and perhaps earn $800.00 or $1,000.00 a year, which would preserve my capital and presumably more than offset any difference in operating cost.


My house was 3200 sq ft and designed to be efficient. Rule of thumb for a house that size called for 5 tons of a/c. Mine ran at 3 tons for only about 90 days a year, the extra cost for the GSHP was $7,000. I think I estimated the payback at about 8 years. Murray

$1,800 per ton for GSHP delta matches what I was quoted. But my leaks-like-a-sieve builder/model home has 8 tons of inefficient AC that barely keeps up.

Which is why a new house is on my two-year planning horizon, if my job will just hold out long enough.

1. How does adding heat pumps at the time of year when electric demand is highest (or at least sometimes highest) help the electric situation? At this point the alternative, natural gas, is in good supply.

This idea removes a barrier to the implementation of wind turbines by shifting the demand of energy to the time when the wind is blowing. It is not the heat pump that matters, it is that more wind turbines will get installed. The heat pumps will get their electricity from wind. This will help the grid.

The post summarized the idea as follow:

Deployment of GHPs does three things to make energy supplies fit energy demand:

1. Winter electricity usage is increased just when wind capacities are highest.
2. Summer electricity consumption is decreased when wind capacities are lowest.
3. Use of natural gas for heating is reduced during times of peak gas demand.

The other idea is a wind turbine/heat pump combo is a technology that can be used for local production. A municipality, a business with large enough land or a farmland can implement it and remove some load out of the grid.

1) GHPs substitute for air conditioners, but they use less electricity to do the same amount out cooling, reducing electricty demand at peak.

2) While subsidies would be nice, like many energy efficiency measures, ground source heat pumps (and even air heat pumps) pay for themseleves in less than 10 years. What's more necessary is breaking down market barriears, like zoning laws, and encouraging ground loops in new construction (for instance, by requireing that buiders offer them as an *option*)

3) I have not lived in my house for a full winter. My A/C installer thought it would payback in 5 years, but I don't know how accurate that was, but much of it depends on the relationship between natural gas and electricity prices. I have to admit that the main reason I did it was because that way I could heat with renewable energy.

From the two months of heating season data I have, I was saving about $30 a month; I'd guess that's about $100-$200 for the entire heating season. The extra cost for the heat pump was $1000, so assuming energy prices do not rise, that's an okay 5-10 year payback; good enough that if you wrapped it into your mortgage, you'd come out ahead after interest.

Before I comment, I want to qualify that I support the Pickens plan (really like it in fact). And there is also a lot of good information in this post. Great contribution in fact.

However, I must strongly express my displeasure with data presented such as this:

One way or another, this isn't what it seems and I think the explanation of what this is showing is terribly lacking. Let me specify what I mean by what this is showing.

Simply, this has to be showing some sort of averages. If you really posted this graph with data sampled from a wind farm every hour (average -i.e. net- power over that hour) it would be nearly pure static, complete chaos. I have seen example over and over again of when a wind farm produces huge quantities of power one day and then very little the next day. A simple qualitative argument goes a long way to reinforce what I'm saying: why is the highest power 40%??? How does someone make a power plant with a certain capacity expecting that it will never, at any time, produce near that capacity? That just doesn't happen.

By this graph, October 1st, 2nd, 3rd, ... and September 1st, 2nd, 3rd, ... are producing in a very narrow range around 20% at 2am. This is simply not the case. It CAN NOT be the case. Aside from not even making rational sense, there is not data that says this.

Nonetheless, the commentary about daily demand and heat pumps in this post are perfectly valid. Wind power does, indeed, stand a much stronger chance of making a productive contribution in areas with large winter electricity demand peaks.

But while you may have an average of 40% factor for 7pm in December, that still means that any given day can be from 5% to 95%, and you must build capacity to manage that. One's anecdotal experience with the weather draws a correct conclusion: it changes every day.

And it seems like that was somehow ignored and subtly smoothed over in this post.

You make a good point. I looked at the underlying report. It took the wind output at one particular time of day for each of five wind locations, and added them together. The results for any one location, at the one time of day, were all over the map. If they had been sampled more than once a day, they would have been much more "spikey".

Adding the five locations (scattered over four states) together smoothed out the results from the one point a day chosen, but I am sure there still would have been a lot of variability in the result.

My reaction to the paragraph about not needing as much backup power was to sort of scratch my head. I didn't find anything to that effect in the original report. A person could kind of get that idea from this once a day sampling and averaging, but I find it hard to believe in practice.

My reaction to the paragraph about not needing as much backup power was to sort of scratch my head. I didn't find anything to that effect in the original report. A person could kind of get that idea from this once a day sampling and averaging, but I find it hard to believe in practice.

The DOE 20% wind study talked about this: when you add various independent, (so, not right next to each other,) wind sources, the amount of variablity doesn't increase arithmetically, and so the standby requirements don't increase arithmetically. Of course, that isn't to say that it isn't possible that all the wind turbines in the US couldn't be calmed on the same day, just according to the statistical models, as long as the turbines were spread out in various wind regimes, it shouldn't happen more often than say, all the coal fired power plants breaking on the same day. (Okay, I don't know the exact odds of that, but the point is it is a very low probability.)

And the 20% wind study said that 20% wind would require about 1.4 times more standby capacity than we already have "standing by" right now to meet normal conditions. And that the plants for the rest are already built, but are running right now, (and burning natural gas,) instead of standing by...

I still don't buy that this is appropriate reporting for 5 wind farms combined. I would not discredit the report much if that were the case, transportation from state to state isn't a ginormous deal. Now I'm looking more closely at the report:

And red flags go off in my mind all over the place. It gives lots of charts of generation at peak demand by month.

Fine, except for THAT DOESN'T MAKE SENSE! What on Earth does it mean?? Does it mean the moment of peak demand for the entire month? Does it mean the average of all daily peaks throughout the month (the most likely situation)?

Simply, these graphs do not show the fidelity to be displaying what they are claiming to. Errr! This drives me nuts. What is the real data?! When will wind advocates realize they won't get anywhere by hiding the facts?!

The Pickens plan is good, but it is no silver bullet but IMO makes a good frame work for a larger plan,

Using nukes to push coal off base-load.
Realtime pricing and smart meter along with demand response and thermal energy storage for end users to improve load factors and allow more variable capacity into the system.
Use of PV and large scale CSP to shave peaks from load profiles in warm areas.
Switch as many VMT as possible to electric, natural gas, diesel, bicycle, rail and any other non gasoline fuel.
Investigate technology of running diesel engines on a mixture of diesel / natgas using the diesel as a liquid spark plug to detonate the gas.
Radical overhaul of building energy efficiency particularly heating/cooling & lighting.
Shift towards high EROEI, sustainable non food biofuel production such as digestion of wastes & fast growing woody crops for gasification and returning the carbon to the soil.

You seem to be under the impression that traditional means of electricity production have extremely high capacity factors. Something also implied in the post above incidentally.

Capacity factors of coal fired and gas fired stations are in practise much lower, more like 50-60% due to down time for maintenance and market trading conditions. Coal fired power stations do not run at full tilt all day every day. Nuclear may approach something like 90% as it is so cheap to produce once the capital investment is made.

I believe if people were more aware of this they might be more forgiving of wind's low capacity factors.

A lot of thee typical low capacity factors for these plants is because they are good at following load - they are simply turned off when not needed for peak.
Neither nuclear nor renewables are good at following demand.
Many renewable developments in fact build in a substantial element of coal, or more usually natural gas, into the mix, as they need the back-up.
In fact, some of the so-called solar thermal plants in Algeria are more properly natural gas burning plants, with the gas stretched a bit by the use of solar thermal when available.

Gotta love the TOD spirit of trying to solve very complex problems that face humanity. I posted some weeks back, a biogas stove that anyone can make for free and power using alcohol that anyone can make with ease...also for free.

Since an oft repeated phrase on TOD by many posters is
"My 2 cents worth", I thought it would be aprapro to
introduce a micro alcohol stove that cost exactly 2 penny. The women should be warned that the music that accompanies this video has induced swooning and caution should be exercised. (The men should take note
of the music and desired effects it produces in the female gender)!

For those that missed the prior link to a more practical alcohol stove that you can make for free...

Here's one that's creative and the music is GREAT also

This summer, I saw a number of ground heat pumps being installed in rural Quebec. The normal heating for this area is hydro-electric with wood stoves as backup.

Also, much of the newer construction comes with triple-glazed windows and extra insulation.

It seems that a lot of homeowners have decided that it makes economic sense to invest in higher energy efficiency.

I have some questions may be stupid but oh well. :p How far can wind power ( any power really)be transported. For example would it be feasible to send wind farm energy from Idaho to Ny and any point in between or would to much power lost on the transmission lines?

Right now, NYC is supplied by a LOT of power from West Virginia. State-to-state but within a geographic region is extremely commonplace in our world. Moving it from wind alley to the coasts is rather unprecedented, however. Not in that it's not really done, but the scale and distance are of a magnitude never really seen before.

It's entirely feasible and within known technology, we're just not equipped for it right now and it will require huge investments. Our current grid is old, that's all.

There are multiple issues. One is that you really have to factor in the time (10 years plus) and cost if you want to think about sending wind power long distances.

The other issue is how many folks are really going to want these lines. If, as a byproduct, they go past areas where coal fired electricity is generated more cheaply than natural gas, these lines are also going to be used to transport the cheaper coal-fired electricity to people who are currently using higher-priced gas fired electricity.

I am sure those who are getting the cheaper coal-fired electricity will think this is great, but the people who had the foresight to build the cheap plants will not necessarily agree. They will then be stuck buying higher priced electricity elsewhere.

If you could build all new lines, and devote them exclusively to wind (very expensive!), maybe you could make long-distance transport work, but that will never happen. I don't think shared lines will work either. The cost will be high, and too many power users say between Idaho and NY will find themselves worse off as a result.

these lines are also going to be used to transport the cheaper coal-fired electricity

I can vouch for that. My neighbourhood was 0% coal powered in 2006 and in 2008 it is up to 50% coal powered at times as a result of new transmission line. Think of new cables like a trail of cake crumbs for ants at a picnic. Absent tough carbon caps cheap coal power will find its way into everything.

Why heat pumps?

A better alternative is electric thermal storage(ETS) heaters in the winter(good for 8 hours of heat without heating electricity) and ice storage in the summers. These units would reduce electric utility spikes/troughs considerably.

But FIRST one must radically eliminate heat loss with Passivhaus design methods.

I can't see putting heat banks at several thousand degress in individual homes. People will do stupid things, resulting in fires, etc.

I also have issue with Passivhaus designs (or any ultra-insulated one). I despise the air quality in super-sealed homes, office buildings, etc. I suspect the O2 content is low or something, but it just makes me feel unhealthy.

There's other ways to explore the concept. Freezers and refrigerators could store cold in a phase change material when there's cheap electricity and take it back when electricity is expensive.

Here's a plug on DOE's site for an air conditioning retrofit,

While demand management and (small scale) energy storage are great, those "technologies" can (and should) be put into place is right now, with the current 4-5 pm summer time peak grid, no need to wait for wind/solar/wave/whatever. And yet they aren't...

A lot of people blame the utilities for that, but I know that Portland General Electric has had a Time of Use option for at least 10 years, and yet they have very few people on it, (something like 1% of their residential customers,) and I imagine that other utilities have similar numbers... Initially all I did was install a water heater timer, and try to do my laundry late at night or on Sundays, not exactly earthshaking, and I was saving about 10%/month over what I would have paid on the regular billing. (I've since installed solar panels, and so the on-peak and mid-peak sections of my bill are generating credits right now.)

But when I tell people about it, they are like, "what if I want to cook dinner at 5pm", or whatever, and I tell them they still can, that I do, just run the dryer after 10pm, and install a water heater timer, (I've even offered to install the water heater timer for them.) And then they think it sounds complicated, and so I've convinced exactly zero people to sign up.

And I think this points to an interesting issue with human nature, (something about them not liking change or something,) but I suspect that ETS and phase changing salt water walls in their freezers may not come easily, and as such, we might need to plan to integrate wind power into the demand curves that we currently have, and not the ones that we could have...

Our firm recently installed an electronic timer control (Aube TI040) on one of four electric water heaters at a local elementary school -- in this case a 3-phase, 9.0 kW 450-litre cylinder equipped with a circulator pump that ran 24 hours a day, 365 days a year.


By locking out the tank's operation during normal school hours and by reducing the runtime of the circulator pump by some 90 per cent, I estimate we will save the school board more than $2,500.00/year in electricity costs for this one tank alone. The savings break down as follows:

1) $892.08 in reduced demand charges (9.0 kW x $8.26/kW x 12 mths/yr)
2) $557.28 related to the school's improved load factor (21,600 kWhs/year charged at the lower-cost second tier)
3) $128.98 in reduced pump operation (0.265 kW x 7,850 hrs/yr x $0.062/kWh)
4) $973.40 in reduced line related losses (2.0 kW x 7,850 hrs/yr x $0.062/kWh)

The timer kicks the water heater and circ pump on at 04h00 each morning, Monday through Friday, and shuts it back down at 07h30 when the school doors open; the water heater remains off over the weekend. There are two additional 5-minute cycles at 11h45 and 15h45 to basically push more hot water through the lines (five minutes should be sufficient to purge any cooled water sitting in the lines without bumping up the meter's demand needle).

So that's one down and three more to go!

BTW, the school uses an average of 1,000 litres of fuel oil per day for space heating purposes. I keep looking at these little puppies that also run 24-365 thinking they should be next on our hit list:


I've been hoping the Eco-Cute will come to the US.

Efficient in cold climates, the auxiliary heater doesn't kick in until -20 celcius. For my area its COP is high enough at typical winter temperatures a ground loop wouldn't be worth the extra effort.

The information in the article uses older heat pumps as the comparison, and so over-estimates the costs as ground source heat pumps are far more expensive.

As well as the mentioned Eco-cutes, which the Japanese are now turning out in great quantities, the American company Hallowell produces low temperature air source pumps:

In addition, it is perhaps worth pointing out that although it would be nice to run the heat pumps with wind power it is not necessary to go to an ideal solution straight away, vast amounts of energy would be saved and CO2 emissions kept within bounds even if they were coal-powered - CO2 emissions would then be around the same as if the scarcer natural gas had been used.

Here is a British study looking at the back-up needed for a wind-powered system:

It should however be noted that wind power matches use in the UK far better than in the States, as demand in the summer is much lower.

I get a bit frustrated by approaches which look at individual resources such as wind and solar and try to work out how to run everything on them - although they are useful exercises to assess the potential of them, in reality a mixed approach always works much better, as you can use different resources far more efficiently when they are used where most suitable, and a lot of the back-up is then inherent in the system.

This is a great idea, although I don't think it obviates the need for energy storage for attaining very large penetrations of wind power. Your comment that energy storage is only available in limited sites, is certainly true for pumped hydro, but not for compressed air energy storage:

Further, the extent to which storage is expensive will be relative. It would be interesting to see what the total capital cost is of GSH units required to change the total demand profile substantively. Its not clear to me that the economic impact is negligible.

The hydrogen storage concept for wind was explored here:

DeCarolis, J. F. and D. W. Keith (2006). "The economics of large-scale wind power in a carbon constrained world." Energy Policy 34(4): 395-410.

and it was found that the cost of these systems means you need a huge price on carbon to make them worthwhile.

Again - I applaud this analysis and thank you for taking the time to put it up. The more ways we have of addressing these issues the more likely we will find a combination of strategies that get us to where we need to be

This means that, contrary to popular misconception, wind does not require a "100% back-up with natural gas."

Your claim that wind only needs to be backed up to the lowest average production does not hold up. During those times of production at 30% of nameplate, there is still great variation minute to minute. If a front moves through (pick your meteorological quirk), there can be an instantaneous drop to near zero. If the power going into the grid does not keep up with the demand, even minute to minute, the grid needs to drop demand (brownout). And it is not enough to use the deus ex machina of saying you will buy it from somewhere else. If we look at the system as a whole, there is no somewhere else.

Wind is undoubtedly a tricky sort of electricity to use in the existing grid, but the fallacy that demand is fixed makes the problem seem much harder than it needs to be.

You could manage demand but then you do not have a power on demand system. That is not how the current system works and it is not what people expect. If you expect people to live at the whim of the wind, you need to tell them and plan how you are going to deny service or incent them away from using it. If this were the only option, that would be one thing, but since we could continue the current power on demand characteristic with nuclear, you are going to have to explain to them why it is better that they have to do without it.

Another point worth noting, is that the wind has different annual patterns in different locations.

Yes but the world is going to have to come up with at least 10 TW of electricity in 40 years or so. To do it all with wind, at a max of 10 MW nameplate per square mile according to the US DOE, you are going to need millions of square miles of wind farms. You are not going to be able to cherry pick the few locations that have good wind and good time/season distribution.

Sterling: On your first comment, you ignored the effects of geogrphic diversification.

On the second comment, I do expect SOME natural gas backup in the short term, and dispatchable CSP as well as other storage options in the long term.

On the third comment, I don't expect wind to ever produce more than 30-40% of our electricity. 100% renewable will requre that most come from solar (CSP and PV, probably, plus storage.) The problem I'm trying to solve is how we can get as much cheap wind onto the grid as quickly as possible.

I don't expect wind to ever produce more than 30-40% of our electricity. ... The problem I'm trying to solve is how we can get as much cheap wind onto the grid as quickly as possible.

I am with you 100% on trying to get as much wind as soon as possible. However, do not think 40% wind is remotely possible. 100% renewables is neither achievable or desirable if you exclude nuclear.

In many ways, nuclear is nearly as bad as wind in terms of meeting fluctuating demand. Be careful what you wish for.

Geographical diversity is an important mitigation factor for wind's intermittency. However, more important when it comes to the backup argument is that you don't have to install 100% new backup capacity because backup is already used to couple baseload plants in the existing grid. These can, of course be shared; baseload and wind would share the same backup plants. The backup capacity is already there in any grids with baseload (and pretty much all of them are based on that system).

And because a lot of wind energy will coincide with natural gas peakers, the system effect is also a large savings in total natural gas usage. Which is amplified by the use of demand side managment such as thermal storage (hot water or ice as mentioned) and heat pumps (which help with seasonal correlations).

In other words, because some part of a large distributed group of wind farms is always producing some power, it will never go completely down. A large baseload power plant, on the other hand, is completely down about 10% of the time

Let's consider the base load reliability of interconnected wind farms based on the Stanford study available here. The Stanford study uses wind speed data from nineteen locations in Texas, Oklahoma, Kansas, and New Mexico, combined with a performance model for a GE 1.5 MW wind turbine with 77-m blade diameter at 80-m hub height. The average power output over all 19 sites was 670kW corresponding to an average capacity factor of 44.7%. This average capacity factor is substantially higher than the 25% to 30% wind farm capacity factors that are commonly quoted. I do not know whether the common wisdom is just wrong or whether there is some aspect of the Stanford model that is overly optimistic about the wind harvesting capability of the GE turbine. They calculated a firm base load number for the 19 site array by using 87.5% as the average availability of a typical coal plant and determining the power output per turbine of the total array which was equaled or exceeded 87.5% of the time. They determined this power output to be to 222kW/turbine which is almost exactly 33% of the average power level of 670kW.

This comparison of 19 wind farms to one coal fired power plant is incorrect. A system of 19 interconnected coal fired power plants would fail to provide 33% of their total rated power only if 13 or more plants were unavailable at the same time. If the probability that any one plant will be unavailable is 0.125 the probability that 13 will be unavailable at the same time is .125 raise to 13'th power which equals=1.8E-12. Obviously this level of reliability is absurdly high. The transmission system would limit the reliability to a far lower level. Coal plants are sufficiently reliable that you would not need massive transmission interconnections between 19 plants over a four state area in order guarantee acceptable reliability.

My intention in these comments is not to imply that wind is useless for supplying base load power or to claim that the Stanford study is useless. I am trying to make two points:

1. The metric of comparing interconnected wind farms to a single coal plant is not correct. Utilities undoubtedly use some statistical criterion for load reliability and if you want to quantitatively analyze the base load capability of wind farm you should use a similar criterion. As far as I know utilities do not designate a single plant to provide base load, and when that particular plant goes down the load goes down.

2. More importantly, getting base load out of wind without storage requires a larger and stronger (power variability over a given line is larger) transmission system than is required for fossil fuel generation systems. The costs of building and maintaining these transmission systems has to be accounted for in determining the economics of wind power. Also the potential costs of system disturbances could go up. Imagine that the Ohio ice storm of several years ago (I was visiting my parents at the time, and spent four days in a motel.) had effected electricity supplies in four states.

Roger: good points on both 1 and 2. I was pushing the comparison between interconnected wind and a single coal plant. However, since wind farms are smaller than coal plants, you will have more farms than plants. The 5 farms in the study quoted didn't even add up to a single SMALL sized coal plant- they were 139 MW nameplate total, producing about the same energy as 47 MW of coal.

I agree about transmission. It's necessary, but the cost is only a fraction of the cost of the wind farms it interconnects... usually less than 1 cent per kwh, vs 5-8 cents total.

I agree about transmission. It's necessary, but the cost is only a fraction of the cost of the wind farms it interconnects... usually less than 1 cent per kwh, vs 5-8 cents total.

Do you have source for the 1 cent number? If you are connecting wind farms over a four state area with the intention that any given farm can supply electricity to any part of the whole service area that seems like a lot of transmission.

The Pickens wind project had a long and expensive transmission connexion, but it's still only about 500 USD/kW and transmission could, if cleverly designed and sited, be partially shared between various wind farms or even other sources (storage, other renewables, or fossil backup perhaps) so could get higher capacity factor than an individual wind turbine. They also last a long time which helps with lowering the levelized cost further. 1 cent per kWh seems about right to me. Here's a document that agrees with 1 cent levelized cost, but line losses add extra costs.

They calculated a firm base load number for the 19 site array by using 87.5% as the average availability of a typical coal plant and determining the power output per turbine of the total array which was equaled or exceeded 87.5% of the time.

Just to point out another reason this is an invalid metric: a system which randomly went offline three times a day for an hour each time but otherwise gave full power would fulfill their requirement for base load reliability. Obviously, though, a system like that would not be "reliable" by any stretch of the imagination.

Baseload reliability requires temporal coherence - long stretches of similar production - and I was very disappointed to see that their study completely ignored that by reordering the hours of the year based on production level. Their study might not be useless, but it's surprisingly close.

GHP and conventional geothermal are stable but old versions of the technology. Borehole Thermal Energy Storage (BTES) takes geothermal to a new level. Instead of using a GHP with the earth's constant temp of 53 F or 12 Cel, store seasonal thermal energy (summer heat for winter heating or winter cold for summer AC) under ground in vertical boreholes.

I built four joined townhouses in a very urban part of Halifax, Nova Scotia 2 years ago with four vertical boreholes. The townhouses had big windows facing west (not other way to window them because of city lot grid) which caused a big over heat in the Summer. We used a special air exchanger to cool the houses and capture the solar induced over-heat and PUMPed back into the boreholes. In essence we took the negative summer over heat and made it a positive energy gain. The houses themselves became giant solar thermal collectors. We raised the temp of the boreholes (2 500 ft, 2 600 ft deep), at their bottom, to about 90 Far (instead of the earth's constant 53 Far). This extra heat in the boreholes created what are called heat plumes or large tear drop shaped bodies of thermal heat deep in the earth. We calculated the above ground heat load of the buildings to ensure that we created large enough heat plumes underground. The boreholes are relatively close and so form a big monolithic plume (each supporting the other). So, we get a kind of shared district heat system. Each year the heat plumes get bigger and more efficient as we have excess summer heat moving into the holes. In a few years we may have excess heat to sell to neighbors. The result here is a combination of vertical boreholes containing temps of 90 Far with GHPs -- you get extreme savings and efficiencies far greater than conventional geothermal and GHP combos.

There is a small engineering firm in Halifax, Nova Scotia, Canada that I worked with to do this. They are currently pushing the envelope of this stuff by taking cold thermal energy and lowering the borehole earth's temp to about 2-4 cel or 35-40 or so Far. They're storing enough high quality cold thermal energy (at 2-4 Cel) in enough quantities to cool several city buildings in Halifax, Nova Scotia. This is dramatic as it often takes more energy to cool through AC buildings than it does to heat them. This cooling BTES system is the first of its kind in the world. The Swedes first pioneered BTES and these guys are pushing again by storing cold thermal. Check this website out for a bit more:

and this for more on the cooling project:

Maybe you could do a similar thing on a larger scale using the compressed CO2 from a coal power station acting as a giant heat pump for a large residential area.

Greetings fellow Haligonian,

I installed a small mini-split heat pump in my home three and a half years ago and it supplies roughly 80 per cent of my home's total space heating needs, at a little less than $0.045 per kWh(e) or one-third that of my oil-fired boiler. Within the next couple of weeks I will be replacing it with a new, high efficiency Fujitsu 24RLXQ. The 24RLXQ has a nominal heating capacity of 27,600 BTUs/hr (twice that of my Friedrich) and operates all the way down to -18C.

I calculate my home's heat loss at 0.18 kW/C at temperatures below 13C (above 13C, it's assumed internal heat gains such as lighting and appliances and passive solar are sufficient to maintain normal room temperatures). This works out to be an annual heat requirement of some 11,500 kWh or just over 1,300 litres of fuel oil demand at 82% AFUE. I expect this new heat pump to supply virtually all of my needs at a cost of about $460.00/year.

See: (PDF format)

The following PDF shows the hourly temperatures for Halifax for the winter of 2007. I've also graphed the heat output of the 24RLXQ based on this data and overlaid the estimated heat loss of my home. The gap between the blue line (heat demand) and red shaded area (heat supply) represents the portion of demand that cannot be met by this particular unit. Note that most minor/transient shortfalls are undetectable because the home's thermal mass acts much like a giant capacitor and the loss can be recovered in the hour(s) that follow; in practice, the deficiency may not be as significant as these graphs would have you believe.


I closely monitor the weather forecast and if cold weather is expected, I run the heat pump a little more the day before to "bank" extra heat that I can use ride through these colder periods. When conditions permit, I also run it more during daytime hours when outdoor temperatures are typically higher, thereby minimizing usage overnight when outside temperatures are generally several degrees colder. This approach works well during spring and fall when the spread between daytime and night time temperatures is greatest and heating demand is moderate; I figure this sort of active, hands-on management allows me to extract up to 25 per cent more heat per dollar than what would be possible otherwise.

My installed cost for the 24RLXQ is about $3,200.00. The operating cost at an estimated seasonal COP of 2.94 is $0.036 per kWh(e); that's the equivalent of paying less than 32 cents per litre for fuel oil/$1.20 per U.S. gallon. A GSHP might lower my costs by another $50.00 or $100.00 a year, but I could never recover the added cost of capital.

Best regards,

An interesting variation on the theme of storing summertime solar energy in the earth to use for winter space heating is a design called annualized geo solar (AGS) heating which you can read about here. In this design a thermal and moisture insulating skirt goes down into the earth around the edges of the house. In the summertime heat from the roof is directed down into the earth beneath the house through pipes that penetrate through the central part of the floor. The earth beneath the house is warmed up over the summer and in the fall and winter radiates heat into the house through the floor. The system is completely passive. With super insulation the method can provide 100% of space heating needs even in climates with lots of cloud cover during the winter. The problem with this method is that it requires building from the ground up, so it would take quite a long time for this method of building to have significant impact on our energy needs. However, I like thinking about the long term future since the short to intermediate term seems pretty grim.

The problem of thermal comfort with less energy is one that will worsen with current trends. More severe cold snaps, increasing humidity that weakens evaporative cooling and baby boomers becoming seniors will each make the problem harder. The suggestion that population should relocate from rainfall drying zones to subtropical areas should be with the proviso of no increase in air conditioning. If I recall a recent post said that active solar air conditioning is too bulky and expensive for private homes even though it may solve the low wind problem.

Since most of the housing stock is already built I think that limits new ground loops and passive methods. It may be easier to ration thermal comfort in existing homes by a separate wiring loop which is smart metered. The allocation could be say half a kilowatt for 45 minutes straight, then turned off for 15 minutes. For conditions of extreme discomfort houses could be fitted with a 'survival room' or partitioned with curtains. That would be the only part of the house heated or cooled. When that fails we might have something like astronaut suits for emergencies. This is yet another way PO and GW interact to make each problem harder to solve.

I find the concept of building power plants to back up wind rather odd. I have never heard of one being built for that reason at least here in North Iowa. It is putting the cart before the horse IMO.

Wind is supplemental to the existing power plants around here and is a relatively small part of total electricity production. And Iowa ranks among the top 4 or 5 wind electricity states.

Since wind is supplemental and relatively small it should take an only minor adjustment to conventional power plants to accommodate it.
So long as wind is given priority the necessity for backup escapes me. The back up already exits. The storage for wind is in the saved fossil fuel, nuclear fuel or water not let though the dam.

It seems to me that the back up for wind would only be problematical if the percentage of electricity produced were much higher than now contemplated. It will take years, decades even, to get to such a point. The local Crystal Lake wind farm is now only nearing completion going on two years since I first found out about it.

Wind capacity is supplemental not primary for now. Storage of wind energy is in the form of the saved fuel at conventional plants if wind production is given priority though regulation or pricing.

This will be the last comment I post here... there's no way I can keep up with the volume of comments on TOD, and I've noticed that there often seem to be other commenters who answer questions as well as I can. If you have a specific question for me, please leave a comment on this post at

Thanks for an interesting article. You have raised some issues of wind power and how heat pumps can complement this form of energy by better matching production with load.
The Archer and Jacobson study of 19 wind farms is still covering a relatively small part of US( 4 states) considering that long distance HVDC connections cover a much wider area and go into northern Canada. Interconnections of wind power on east and west coasts should give a more robust power output because of accessing different weather systems. Also accessing colder states and Canada balances summer and winter demand a bit.
Another Jacobson study showed that wind resources have been underestimated because of measurements at 10m rather than >80m appropriate for large wind turbines. The higher wind speed at greater heights means a lot more consistent(firm) power. Design changes can also mean more power at lower wind speeds by compromising maximum output.
Solar energy is a better match to US peak summer demand, while some regions such as the SE of USA don't have very good wind resources or solar resources so these would be better locations for nuclear and or long distance grid connections.
The length of a possible disruption is also important, 1h to 1 day is very different to a 2 month disruption that can occur if the oil or gas infrastructure is damaged or if coal mines become flooded. Many industries can tolerate short term power shedding.

You claim "because some part of a large distributed group of wind farms is always producing some power, it will never go completely down". If one peruses the website of IESO, the Ontario, Canada grid operator, it is easy to see that for example on Mar. 8, 2008, the connected 475 MW of wind generation, located in 5 well-distributed locations around this huge province, from 3:00PM to 4:00PM produced a total of 19 mwh, for a capacity factor of 4%. That date was just randomly chosen for analysis for other reasons, but there are many worse days in the record, often dropping below 1% on-peak during summer business days. Most of the energy produced by wind generation here is generated at night in midwinter, when all it is doing is forcing large run-of-river hydro (Niagra) and nuclear to shut down, a foolish act.

The ratinal for wind generation clearly needs to be re-evaluated in light of current experience. It looks to me that promotion of wind generation is mainly a benefit for natural gas producers.

On the US side the of the Niagara hydro plant is a huge pumped storage facility. Does that plant need extra pumps/turbines or something? I don't see why that area of the grid shouldn't be able to integrate a lot more wind than it has right now.

While Ontario is a large Provence, the combined area of Canada and USA is ten times larger. In winter blocking highs can cover areas larger than Ontario, but not cover all of N America. At least in Manitoba and Quebec, any hydro displacement by wind power, saves water for generating power for peak demand anywhere in the N American grid. As more wind capacity is installed hydro peaking can be increased without building any more dams, but by installing additional generators and transmission lines. These costs pay for themselves because additional power can then be sold at prices received by NG peaking plants.

While Ontario is a large Provence, the combined area of Canada and USA is ten times larger. In winter blocking highs can cover areas larger than Ontario, but not cover all of N America. At least in Manitoba and Quebec, any hydro displacement by wind power, saves water for generating power for peak demand anywhere in the N American grid. As more wind capacity is installed hydro peaking can be increased without building any more dams, but by installing additional generators and transmission lines. These costs pay for themselves because additional power can then be sold at prices received by NG peaking plants.

If those gaps are never more than diurnal (which I suspect) they can be almost completely accomodated by demand side thermal storage (in this case, hot water or other thermal media for space heating and domestic hot water).

Interconnecting windfarms does markedly improve the seasonal generation pattern.

What we need to know is how to increase the effective load carrying capacity of wind and how to do that most cost effectively. Demand side thermal storage (for reducing diurnal intermittency) and geographical interconnection of distant wind farms (for reducing diurnal and seasonal intermittency) look like winners.

Thermal comfort and fairness.

It's great that the well-to-do can afford ground source heat pumps and that pensioners get home energy rebates, but for how long? As the weather gets weirder and energy costs climb perhaps swathes of people need to tough it out or pay more. I'd ask are healthy people aged 10-65 'entitled' to air conditioning? We could all pay maybe $1 entry fee to cover HVAC costs when we visit a shopping mall. It might force the management to find energy savings to keep the customers coming back. How about meaner thermostat settings in legislatures? T-shirts in summer, parkas in winter, not so many black suits.

Increasingly those who can live their lives in the thermal comfort zone will be the privileged or the 'kept' members of society. Others and most of the middle class will do it tough.

The information given on air source heat pumps was somewhat dated. Modern air pumps can run efficiently at very low temperatures, and so the cost is much lower.
They increase the efficiency of electric heating by around 2.5 times for existing buildings, and 4 times for new.
Space heating/cooling is a massive component of energy use, and this could be greatly reduced at reasonable cost.

The latest ones revealed in Japan are COP >5 for moderate climates.