Q&A with Howie Michaelson, Catamount Solar
Can I use a Solar Electric system to run my Electric Hot Water heater?
Haven’t you already advised against this?
Recently, this question has resurfaced, particularly since the cost of Solar Thermal has been steadily rising while Solar Electric costs have fallen precipitously. So we ran the cost comparison exercise again fully expecting the answer to be “Using electricity generated by solar energy might make sense if fuel costs double or triple.” We were amazed to realize that in many circumstances Solar Electric is actually the better choice. Not only has Solar Electric has become cost competitive with Solar Thermal but it may even have significant logistical advantages!
A direct comparison of the cost of a Solar Thermal system for heating domestic hot water (DHW) against a Solar Electric system to do the same thing shows they are very competitive with each other. And, for smaller to medium sized systems (typical 2-5 person households), Solar Electric systems hold a noticeable advantage over Solar Thermal. This is true for installation costs, as well as long term production and maintenance costs.
A Solar Electric system has an advantage too in that it can be sized to provide any amount of the heat load (up to 100%) without any special design considerations. Solar Thermal systems, though, heat load (up to 100%) without any special design considerations. Solar Thermal systems, though, are sized to produce 50-75% of the annual load. The reason is this: if they are sized to cover all the hot water load during the winter months, there will be summertime over-production. This excess heat production creates system stresses requiring greater complexity (i.e. expense).
The economics of heating water with Solar Electric work as well as they do because we are able to “store” or “bank” heat energy (in the form of excess electricity) on the grid during the sun-rich summer for later use in the sun-deprived winter. Having a simpler, less maintenance-prone system is another major advantage of Solar Electric. It’s important to remember this analysis is only specific to Grid-Tied systems. Off-grid systems have a very different design and cost calculation.
Remember, though, the devil is in the details. Designs must take into account all the household circumstances, with issues including: good solar access (solar electric needs more), size of DHW load (people in household), type of existing DHW system, size of your existing utility service and any plans to install a solar electric anyway. Be sure your installer looks at your situation thoroughly and explains the pros and cons of either choice. In any case, it is a surprising and exciting finding that Solar Electric can be a cost effective approach for DHW.
Howie Michaelson (who has lived in a solar, off-grid home for 14 years) answers solar questions in a simple, clear fashion. Submit your questions to G.E.T. or to: firstname.lastname@example.org
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