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The Rodney Dangerfield of Cleantech

By David Gold, Entrepreneur
October 25, 2010   |   8 Comments

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8 Reader Comments
Comment
1 of 8
October 27, 2010
Your first factor is THE factor. The inconsistent payback shown in your bar graph is evidence. Too often, either by poor site selection or poor system design, geothermal fails to meet projections. There needs to be more system consistency and better performance prediction tools if the geothermal sector is going to thrive as it should.

Your points regarding "out of sight" or "low tech" are diversions from the two real factors you mention.
Comment
2 of 8
October 27, 2010
I really wanted a geothermal heat pump when our house was built in 2005, but we have very rocky soil and I was quoted over $50k. Our annual heating and cooling bill is a little over $1000 so I was looking at 50 year simple payback and an infinite payback considering time cost of money. I still strongly support the technology for appropriate locales, though.
Comment
3 of 8
October 27, 2010
Next to installation costs, the biggest obstacle to geothermal/geoexchange/ground-coupled heat pumps is the high output temperatures required by most heating systems in North America.

Pre-existing radiators and air ducts are designed and sized for high temperatures. High temps are the bane of heat pumps. The higher the output temp, the harder must work the compressor, and the greater the amount of electricity required. Heat pump efficiency drops lower for every degree higher of output. Perhaps not such a problem in Oregon where electricity costs $.06/kWh, but a big problem in the Northeast, where electricity costs are around $.20/kWh.

Also not mentioned is that, as the heating season progresses, the ground cools from around where heat is extracted. To below freezing, which is why antifreeze must be added to the loop. As the ground temperature falls, less thermal energy is available for the heat pump to capture, so the efficiency of the heat pump drops. Again, the compressor must work harder to make up the difference.

Biomass solutions, such as wood pellet central heating have lower installed costs, have low fuel costs relative to oil and propane, and run at higher output temperatures, so they are most often a better choice in retrofit situations.

New construction is the best place for geothermal heat pumps. In the case of new construction, homes are typically better insulated so anticipated heat losses are less and heat pump installation costs can be reduced. Also, radiant floors can be used which reduces the output temps, so the heat pumps can run efficiently.
Comment
4 of 8
October 27, 2010
The Solar PV payback graph that you provide doesn't seem to take into account state and local incentives. In Washington state, which I'm most familiar with, the state production credit ranges anywhere from $0.15 to $1.08 per kWhr of Solar Electricity produced. This makes simple paybacks of less then 10 years achievable on commercial systems even with our relatively poor sun availability.

I agree ground source heat pumps (GSHP) will often have a much greater impact on energy usage then solar and can be a better investment. Another factor you didn't mention, but that I often see as an issue for GSHP systems, is the energy savings are much harder to accurately quantify then Solar PV.

Solar PV doesn't care about your specific electricity usage patterns. It produces electricity when the sun shines and stops when the sun goes down. It is easy to accurately predict for any location what the average annual PV energy production will be with commonly available tools for shading measurement and historical weather data.

For GSHP the energy savings are totally dependent on the home owners life style. The same exact house with two different families can have twice the energy usage. Even with full fuel bill history it's incredibly hard to pull out the energy usage for heating and cooling vs lighting or electronics. A full heat loss with energy modeling really isn't very accurate either.

So the uncertainty of GSHP savings is much higher then with Solar PV which is another detriment. It's the same problem Solar Hot Water has compared to Solar PV. Frankly, Solar PV is also much easier and less disruptive to install on an existing building. Destroying the flower garden vs. a stick of conduit on the side of a house makes a lot of decisions in a lot of households.
Comment
5 of 8
October 27, 2010
The author focuses on comparisons to PV solar, which is not the most efficient use of solar energy. As an engineer he must be aware of the higher efficiencies of distributed solar thermal over PV. The use of coaxial vacuum tube solar heaters would lower the load on any ground source system greatly and avoid excess chilling of the ground. It is even easily possible to use distributed solar thermal to heat directly from a stored thermal bank without a heat pump for heating at all. This avoids the large electrical load the heat pump requires, which is the main reason that many heat pump systems never achieve a reasonable payback. They are not renewable energy, but energy efficiency technology, a step above burning stuff, but not entirely separate from large electrical loads. Distributed solar thermal can be driven with a small, 40 watt solar PV panel to run the circulation pump and in that way use no grid power at all. In northern states a heast pump for heating cannot begin to compare to distributed solar thermal for cost efficiency if one is planning to heat their living spaces for at least ten years.
Comment
6 of 8
October 27, 2010
Geothermal can be pretty complicated. I know of an installation in Oregon where the architect warned that thermostat placement is important or you can get fast-cycling, which requires quite more power than may have been anticipated.

It also matters where you are. One consultant said it pays back better in a climate with more extremes than western Oregon.

I know of a household, that of Ole Ersson here in Oregon, who heated water with compost for many years, in a single-family dwelling with 5 persons. This effort is probably still searchable, though he has now downsized to a 32-unit, low-income, rental ecovillage called Kailash.

I like the idea of geothermal, but it is a science project still, at least so far as I have been able to do research on it. There is an Episcopal church in Boston that needed the room its furnace was taking up, so they installed under-the-church geothermal. I have not yet seen readily-available recent research on how that worked out, though I am much interested.
Comment
7 of 8
October 27, 2010
I like that you've given the real numbers here on geothermal heat pumps. Too often we hear fantastic claims of 3-4 year payback periods. Your numbers are more believable.

Solar is PV and solar thermal, neither of which have attractive economics, but the solar energy that existed before the rebates was solar swimming pool heating with unglazed plastics. Millions of these systems heat swimming pools across the country and do so with an incredible 2-4 year payback in many cases. Not only that but often in residential situations they replace the gas heater so the payback period is measured in months not years based on incremental costs.

Furthermore I would like to take this opportunity to add that well proven solar pool heating technology can easily be transferred to assisting ground source heat pumps. Stepping back a little further I think its important to note that when you're talking econiomics, unglazed panels for pool heating are far more cost effective for solar thermal applications in general especially water preheating where half the load is cold water. Why are we using boxed and glazed collectors abd vacuum tubes to heat cold water? Unglazed collectors at 10 times less cost are actually more efficient when air temperature and water temperature are the same. The reason is that technology has not been allowed ro develop naturally over time. Instead we have subsidies and rebates promoting one type of technology over another. In a fair world where there were no subsidies for fossil fuel exploitation or for solar or wind or heat pumps, I think we'd see more intelligent and appropriate technologies advance quicker but instead we have a big push for pv, dare I mention, one of the least economically viable cleantech options out there. www.h2otsun.com demonstrates the technology that is unglazed solar energy.
Comment
8 of 8
October 27, 2010
Ground source heat pumps are much more diverse than indicated above. I retrofitted one 5 years ago off an existing water well ( open loop ). My installer did his own system off a pond in his yard. I estimate a 6 year payback on my system (1 to go ). The ground cooling mentioned above is possible on a closed loop system but indicates inadequate design. On new construction, the foundation trench can be enlarged for horizontal slinky loops. Here in the northeast we are beginning to see new houses that are super insulated with PV driving GSHPs for net zero energy per year
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David Gold

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About: David Gold serves as the lead Partner for Clean Technology investments. He earned a Bachelor of Science degree in Mechanical Engineering with Special Honors fro... more »

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