Up on the Roof, Another Green Weapon

Reading the Letters about green power in the June 2004 issue of Physics Today (page 11), I was reminded of an observation I made some years ago in the Bay Area of San Francisco and in Los Angeles; there appear to be almost no solar water heaters on the roofs of buildings there. Many parts of California enjoy essentially the same sunny weather as southern European countries such as Greece, where individual solar water heaters can be seen on the roofs of almost all buildings. Consisting essentially of a small black water-storage tank, such solar collectors are efficient water heaters that offer a low-cost supplement (not replacement) to more conventional technologies. Why are they not used in the sunnier parts of the US? If they were, the financial savings to each household would be great, and the combined energy savings across the US would be enormous.

Local energy-saving solutions have enormous potential to reduce our dependency on fossil fuels. A full account of the economics of solar water heating is contained in the publication A Consumer's Guide: Heat Your Water with the Sun, available from the US Department of Energy (http://www.nrel.gov/docs/fy04osti/34279.pdf). According to that document, for homes with electric water heaters, up to 25% of domestic energy costs go to heating water. The adoption of local energy-saving solutions should be considered wherever practical and built into new homes. The nature of the solutions depends on the location; excellent insulation and good use of sunlight should be high on everybody's list.