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!