Passive Solar or solar thermal collects heat as the sun shines and retains it in materials that store heat, known as thermal mass. This method is commonly used for heating water for homes or for swimming pools. The picture to the left shows a solar water heater that uses this method. Notice, it is mounted on the roof and is designed to collect the sun’s energy. There are many different solar water heater designs on the market today with varying configurations and materials used, but they all have basically the same goal — to capture and retain heat from the sun so that water can be heated.
Passive solar can also be used for heating homes. This article from the Department of Energy goes into quite a bit of detail on the subject, and provides some design guidelines for passive solar homes.