Solar Water Heaters
The initial costs of solar water heaters are high, but they can be big money savers over the long run.
Solar heaters are used to preheat water going into conventional water heaters, which then use much less power than they ordinarily would to bring the water up to the temperature you require.
Solar water heaters used to be more common in the 70s and early 80s when the government supported them with tax credits. There are fewer units available today, but they are cheaper and more reliable.
You need a qualified installer to design and size the back-up water heater system.