This is a common question and an unfortunate reminder of how little attention Solar Thermal collectors get. Solar thermal technology for domestic water heating is remarkably simple, reliable and inexpensive – but it just can’t share the limelight with its sexier rooftop sibling, Solar PV. This situation will probably change as energy efficiency and building integrated renewable energy move more and more into mainstream culture. In the meantime, here is some very basic and generalized math to outline the differences for the two technologies. In order to make the comparison, Thermal’s btu’s need to be converted to Photovoltaic’s kWhrs (1 BTU equals 0.0003 kilowatt-hours).
The average solar thermal collector of 100 square feet captures about 10 kW Hours of energy per day. The approximate cost of 100 square feet of solar thermal panels is $900.
The similar sized PV array will capture 6 kW hours in the same day at a cost of about $3000.
So the answer is “yes”, you can heat water with Photovoltaic Energy, but it’s much less expensive to do it with Solar Thermal.
[image credit: toonpool]
Comments
What are the installation cost ranges for solar thermal vs. PV? It sounds like the capital costs are higher in PV but is that true for the installation cost too? Do you know a rough estimate to use as a cost for installing solar thermal? Thanks- MG
MG, Thanks for the question.
Just to put a number out there, the cost for adding a solar thermal "circuit" to your domestic hot water for a household of 3 or 4 people is about $5000. This is roughly equivalent to the $20,000 all in cost for a 2.5 - 3kW PV system. Both Solar Thermal and PV have incentives that vary depending on location. The interesting thing about solar thermal is that it's extremely simple and reliable, and if set up correctly will directly effect the amount of time your water heater turns on. Payback for Solar Thermal can be dramatically shorter than for PV - rarely more than 5 years - mainly due to that lower capital cost.
So, for both the above systems, actual labor involved is about the same. You can use 24 man hours (2 guys working 12 hours) as a baseline time to install either system under IDEAL conditions. PV has lots of modules to mount, but the electrical hookup is fast. Domestic solar thermal may only have one or two panels, but the plumbing down to the water-heater and tie-in is time consuming. Just translate the man-hour number into your local labor rate.
More detail - brought to you by the folks at NREL
Solar water heaters are a great source of getting warm water at a low price.