The web has probably thousands of pages with instructions on how to build solar devices for heating air, water, and probably things I've never even thought of.
Wikipedia describes different types of thermal solar collectors, but really has a commercial focus.
However, when it comes to choosing an affordable design that might be useful for a DIY project at home (or for a small business), it's unclear exactly where to start looking and how to compare designs.
Are there any websites that act like a hub for this information and index or categorise the different techniques and devices?
For this question I'd like to focus, if possible, on finding a site that compares and rates different designs, as well as possibly providing instructions on building them.