The benefits of solar water heating are numerous and considerable. First, you're going to save money on your electric bill.
Most likely, your water-heating electricity use will be cut by at least half [source: PE]. How much you actually save depends on the climate where you live. If you're in the U.S. Northwest, where the sun doesn't shine much during a good portion of the year, your savings will be lower than if you live in an extremely sunny place like Arizona, because there's less fuel available for your system. But if you live in Arizona, you could decrease your water-heating bill by up to 90 percent [source: EWH].
And then there's the corresponding reduction in pollution. A 50 percent reduction in traditional (emitting) energy use means a 50 percent reduction in CO2 emissions. So installing a solar water heater would reduce your hot-water carbon footprint by half. At the same time, you're conserving nonrenewable fuels for applications for which there are currently no easily available renewable energy sources.
Because of the benefits of solar water heating, adding a unit to your home will also increase its value. So you could end up getting back whatever money you put into a solar heating system when you sell your house.
Which brings us to the primary negative: the money you put in. While sunlight is free, the system required to convert it into hot water for your home can cost a pretty penny if you go the professional route.