Howwould you like to have free hot water for the next 40 years? That should soundpretty good — about 15 percent to 20 percent of a typical household’s energyoutlay goes to make sure the “H” tap means what it says. If energy pricesincrease by 6 percent annually, the average family would save thousands ofdollars over the coming decades by installing a solar water-heating system thatsupplies just 65 percent of their hot water.