I recently noted that Hawaii has enacted a law that requires all new homes to install solar water heaters. Eventually, Hawaii may have as many water heaters as Israel, where 90% of homes have solar water heaters installed. When viewed from above, the Jerusalem often glitters with the shine of the thousands of solar heaters that adorn rooftops.
These heaters were first installed when the country experienced a fuel supply crisis in the early 1950s. The government responded by severely restricting the times when water could be heated. Israelis in turn responded by purchasing huge quantities of solar water heaters. By 1983, 60% of the population heated their water with the sun. A law was eventually passed requiring the installation of solar water heaters.
In 2005, Spain became the second country (after Israel) to require solar water heaters. It also became the first country to require the installation of solar cells for electricity generation in new buildings.
In many climates, a solar heating system can provide a very high percentage (50% to 75%) of domestic hot water energy.
In many northern European countries, solar power is used not only to heat water, but also to provide 15 to 25% of home heating energy.
For more info about different solar water heating systems for the home, see the Solar Water Heating by Bob Ramlow.