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Joanne Schwartz, of Tustin, CA, writes:
It seems that subsidies for installing solar energy systems on residential rooftops is a great deal less efficient than installing large systems, as on giant industrial rooftops or on already degraded tracts of land. Outside of educating consumers on broad energy topics, why is there such an emphasis—in the form of funding, legislation and media—on tiny residential solar projects?
Jon Fisher, data management specialist at The Nature Conservancy, replies:
It is true that residential solar systems (especially photovoltaic, or “PV” systems) are substantially less efficient than their commercial counterparts. One estimate (admittedly controversial) from UC Berkeley professor Severin Borenstein says that residential PV systems cost roughly twice as much as their commercial counterparts (40 cents/kWh vs 20 cents/kWh)1.
Commercial systems have many advantages over residential: they are typically developed in locations with lots of sun, they can take advantage of innovative technologies that don’t work at small scales, they can utilize larger storage cells, and many other reasons.
Which brings us back to the question of why so many people love the idea of putting solar panels on their roofs. In talking to friends and co-workers who have solar panels, there seem to be two common reasons: the appeal of being energy independent and an “every little bit counts” desire to do their part to help. Installing solar panels on your own home is a more readily achievable goal than successfully lobbying to change the way we subsidize different kinds of power plants.
The good news is that there’s an often overlooked form of residential solar power that is almost always far more efficient than photovoltaics. Solar Water Heating Systems (SWHS) are typically much cheaper than PV systems, and focus on using heat from the sun to produce hot water (which is much simpler than converting sunlight to electricity).
While PV systems may take decades to pay for themselves (although this varies considerably state-by-state due to considerable variation in both subsidies and how much sun is available), solar water heaters can pay for themselves much more quickly. There is an article on payback times in Home Power magazine (note that it doesn’t include subsidies, which vary substantially by state and city). When subsidies are included, I found out that for my condo in Arlington, VA, a SWHS would pay for itself in 2-4 years as opposed to about 30 years for a PV system.
Since SWHS are much more efficient than PV systems (in electrical energy equivalent per area), you could even install a solar water heater and still have room for some PV panels if you want them and the local conditions are favorable. While I am excited about the evolving technology behind commercial solar power plants, using the sun to heat water in your home is a no-brainer if you can afford to pay for the initial cost while gas savings pay you back. As the cost of natural gas rises (and drilling puts more pressure on natural areas) this will likely become even more appealing.
Those still interested in residential PV systems may be interested in a cost calculator, and if you really want to understand the technology the Department of Energy has a very detailed handbook available which covers both PV and SWHS. Installing a PV system in your home is still a great idea if you’ve already taken care of easier green improvements (including a SWHS) and still want to do more, especially in states with lots of sun and good subsidies. If you’re on the fence, an energy audit is an excellent way to find out what the easiest and most effective changes you can make around your home to ensure that you can put your conservation dollars to the most good.
1. Note that Dr. Borenstein’s estimates are controversial; read one of his major analyses of solar’s costs and benefits, two critiques of his work (by Bill Powers and Tom Beach/Patrick McGuire), and his response to those critiques.