Solar Water Heating
When most people think of solar power they imagine large, dark blue panels supplying electricity to a home or business. And that's certainly one very popular application. But there are other ways to harness the energy of the sun. Solar heating is one, and its roots actually go much further back than the use of photovoltaic arrays.
Using directed sunlight to warm water goes back thousands of years. Crude mirrors and lenses were used by the ancient Greeks to warm water. In the 1920s some municipalities had functional solar systems that heated water supplied to homes.
Today, those applications have taken on the shine of high technology.
One common form is the use of collector panels, often mounted on a rooftop. Unlike photovoltaic modules, these arrays don't use layered silicon wafers to generate electricity. Instead, they are more like large, thin, double-paned windows that contain water often mixed with types of salt. The sunlight heats the water by means of the greenhouse effect and the water moves through a series of channels, tubes and pipes into the home or business.
The greenhouse effect, as most people know by now from discussions of global warming, occurs when light enters a transparent medium, but not all the energy is allowed to escape out again. It happens to a high degree with glass because the material allows certain wavelengths of the light spectrum, such as infrared, to enter more efficiently than it lets the energy back out again. So, there's a net gain in energy on the inside.
Heated water has direct uses, obviously. Whether it's showering, washing dishes or other purposes, nothing more has to be done to the water other than simply make it available. That's typically done by storing the heated water in essentially the same way as with ordinary water heaters.
In the ordinary hot water system the water heater storage unit also heats the water. With a solar-powered water heating system there's no need to, since the water that enters the tank is usually between 95F-150F (35C-66C). The storage tank acts like a big thermos bottle. It's double-lined and/or made of well-insulated material so the heat doesn't dissipate much out the walls of the tank.
The temperature range of such systems is fully adequate for bathing, cleaning clothes and other ordinary applications. The only difficulties are ensuring enough sunlight to generate enough heat, and minimal loss of heat through the panels and pipes.
Costs can run to $50,000 or more, though. And local climate conditions may limit the usefulness of the system. But given the local cost of electricity or gas, a home or business solar water heating system may well pay for itself over 10 years.