When it comes to solar water heaters, be realistic. They're typically only 30% more efficient than any other form of water heater. Second, don't think that just because you shower in the dark means you'll have to deal with cold water. Water heated by solar power should stay warm for 24 hours.
Solar water heaters have been around for hundreds of years. For over 50 years people have been using them to heat everything inside and outside the home. Over the years, these solar water heating systems have become much more efficient. If you are located in sunny areas of the country, you should look into buying a solar water system.
There is no need to tear apart your roof to use solar energy. You can make small switches like putting in solar powered outside lights. They charge their batteries during the day, switching on and providing illumination all night.
If you have a pool, don't even think of heating it any other way than solar! This is easily the most efficient use of solar power there is and it will save you a bundle. Solar heating systems cost about the same or less than conventional systems and basically operate themselves so stop wasting your money doing it the old-fashioned way!