solar water heat is almost embarrassingly easy to do, at least out here on the Sunny West Coast anyway.
Florida, too. For a very long while most people in South Florida had solar hot water heaters on their roofs. It is so sunny, even systems with just a tank and no panels worked.
If anybody is interested "1000 dollar solar water heater" in a web search gets you to a great site with many DIY projects that have all been working for their builders.