The Alternative Site at www.draaisma.net describes in this video a method for cheap DIY installation of solar water heating. As you can't make your home self-sufficient on solar energy anyway (unless you live in a small camping trailer), you must keep your installation costs low to make it worthwhile. Plain water is a perfect infra-red radiation absorber. Infra-red contains most of the heat energy in solar radiation (although ~50% of its spectrum). A black metal surface absorbes the whole spectrum, but its heat transfer to water is dependent on temperature differences, which limits, or even disables its function in cold weather. Water fully absorbes the infra-red radiation directly, independent of any temperatures and is therefore in the end more efective than a metal plate absorber, the more, the colder the climate zone in which it is applied. You pay for energy, not for temperature and thus the temperature at which solar energy is absorbed, has no meaning whatsoever - a "hot" solar water panel is not necessarily a "good" one. The final usage temperature must be adjusted with a regular boiler anyway, regardless what kind of solar water panel is used.
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