Solar collectors are a relatively simple concept. The point of them is to redirect the suns rays (or 'collect' them) on one focal point. This can be to increase the heat or amount of light at a focal point. But how do you redirect them? By reflective surfaces, polished metal, mirrors, aluminum, refractive lenses (like magnifying glasses). A lot of homemade collectors use foil as it is cheap, readily available and easy to manipulate. One of the best factors about solar collectors is they are very affordable and very low tech, so everyone can use them.
Homemade solar collector
Here is an easy collector starting project to show it in action.
Some common uses of solar heat collectors-
Many reflectors onto collecting onto a box or pot to increase the temperature to one which you can cook with. These are extremely cheap and easy to do at home and very low-tech.
To Heat water:
To increate the efficiencies of solar panels:
There are some big examples currently being built in the US which use solar collectors to power sterling engines.