When most people think “solar,” they think in terms of solar power – electricity! Solar electric systems, or photovoltaics (PV for short) allow you to power your home with the sun as fuel.
But if you’re shopping for your first solar system, it pays to do your homework. PV isn’t the only type of solar energy out there – and it may not be the most sensible place to start. If you are an average to heavy user of hot water – or would like to be – a solar thermal system may be your best bet.
Solar Water Heating
Solar thermal, or solar hot water, uses energy from the sun to heat your domestic hot water supply. Put simply, it works like this: an antifreeze solution flows through collectors mounted on your roof, the side of your house or on the ground. The solution is pumped to a heat exchanger, where the heat is transferred to your domestic hot water supply. The heated water is then kept in an insulated storage tank until you’re ready to use it.
Solar thermal can also be used for space heating purposes.
Solar Hot Water vs. Solar Electric: A Cost Comparison
The cost to put in a solar water heater is not much different than installing PV. Solar thermal panels cost about the same as PV panels per unit, and the balance of the system plus labor is usually comparable in price.
The difference is in efficiency. Thermal panels average about 40 sq. ft., vs. 15 for the PV collector. That means you’ll get almost 2 ½ tomes the solar energy coming in. Plus, the thermal panel converts over 50% of that energy into heat, while a good PV panel won’t get much more than 15%.
Add it all up and the solar water heater will give you about 10 times the energy output per dollar invested.
What’s Your Best Choice?
Is solar thermal always the best choice? Not necessarily. If you use very little hot water you may not be able to take full advantage of it – but most people benefit from putting in solar water heating first. Fulfilling your domestic hot water needs with a properly sized system will give you a lot more bang for your buck.
Once you’ve done that, it makes sense to add solar electric. The advantage of PV is that you can sell your excess solar power to the grid. So once you’re set up with all the hot water you need, feel free to go PV!
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Andy, I got such a kick out of the description on your “about” page. I totally agree with you! My father was a dairy farmer, and I definitely know country ways, even though I’m a certified city slicker now!
Keep up the good work with renewable energy!
Thanks for the kind words, Lynn. I added you to the blogroll.
HI
AM AN ARCHITECT IN FL.
LIKE YOUR OPINION OF SOLAR THERMAL VS PV .
CRITERIA:
200MW
DESERT APP.
WE HAVE TO MANAGE FOR 20 YRS
LIKE DOLLAR COMPARISONS COST AND MAINTENANCE
LAND IS NOT AN ISSUE
THANKS
Hi there, Andy. I’ve been trying to find an equivalence between solar water and solar
electric, which is to say: How many squares of photovoltaic panel would equal one
square of solar water panel in energy capture given the same solar exposure?
I know this is apples and oranges here (Btu’s and watts) but I would be pleased if you could shed some light, so to speak, on this.
Bob
Wow, that’s a good question – and one that is beyond my expertise. A lot of people make decisions based on estimating stuff like that, but I’m not aware of a formula.
The problem here is that PV depends on subsidies. Without the subsidies, it would not pay for home owners to have PV power. Thus, when a neighbor installs a PV system, I am paying for part of his subsidy, which I consider unfair.
Power companies lose out with home PV systems. Most of the cost of generating electricity is not in the fuel, but rather, in investment and labor costs. Thus, even if home PV systems slightly reduced the cost of fuel for power companies, the amount saved could not justify the power company’s paying PV owners for the power. Moreover, because the power from PV systems is somewhat unpredictable, it makes it difficult for power companies to adjust their generating output as the power from PV systems change.
The PV systems described here do not provide power at night, yet homeowners use power 24 hours a day.
If PV systems were not connected to the grid, were not subsidized in any way, and included storage so that adequate power would be provided 24 hours a day without fail, then the cost would be well beyond what most homeowners would be willing or able to pay. However, that may not be a permanent problem. It may be that at some future date, the costs will decline so that even with adequate storage, PV systems could be justified on an economic basis. However, that time may never come.
Regarding Mr. Mikulewicz’s question, the energy collection in thermal applications is typically around 2.5 times greater than in conventional PV applications per area of exposure. However, thermal energy is only good for a few applications (hot water, space heating), while PV is much higher grade energy in that you can use it for appliances, electronics, air conditioning, etc. So displacing electrical demand for heating applications (especially water) by the use of thermal is a no-brainer, but after you’ve done that, you are better off to use PVs for your other needs. Of course it is a bit more complicated, since you can store thermal energy more easily in a highly insulated water tank than you can store electricity, which gives it some advantages (solar hot water at night). On the other hand, for space heating applications, solar thermal has the problem that a system designed to provide winter heating will vastly overproduce in the summer and the waste heat will have to be dumped. A new application of the Sterling engine by Cool Energy of Colorado is working on making a cost-effective residential scale system to convert that waste heat to electrical energy.
a parabolic solar furnace going to a steam engine and generator is more efficient than both of these. it uses less materials and has a smaller footprint.
Actually, solar thermal may be useful for air conditioning.
Absorption air conditioning systems have been around for well over half a century. The large ones use a lithium bromide solution for the absorber and water vapor for the refrigerant. Typically these systems are very large, although they would not need to be large. They generally use waste heat for energy, such as waste heat from engines or an industrial process. However, they could be powered from heat from solar collectors.
So far as I know, currently there are no absorption air conditioning systems available for household use that are solar powered, but they could be made; it’s just a matter of economics. Probably more work should be done on absorption air conditioning systems which operate on solar generated heat since air condition is a major portion of the load for power companies in the summer time.