Solar energy is most efficient if used directly as thermal energy for heating water, air, or thermal appliance. Many systems are available for using the sun's heat, and by designing an appropriate system for your needs, a solar thermal system can assume a central role in your energy supply.

Heating water is the most common use of solar energy. Most backyard system costs of a flat panel, storage tank, and delivery pipes. Advanced systems included evacuated tubes, pumps, complex electronic controls, storage tanks, and innovative delivery systems. The system needs to be able to collect the heat in an efficient manner, deliver it to the water that needs to be heated, and deliver the heated water to the use, like the kitchen sink. For areas that experience freezes, it is advantageous to have a different working fluid other than water. Oils, antifreeze, and special thermal fluids are available to bring the heat from your collector to a tank where it then delivers its heat to the water in a insulated container, safe from outside freezing temperatures.

Solar energy can also be used to heat your home in a variety of ways. One of the most efficient, is an active solar system that heats a thermal fluid and delivers it to pipes under or in your floor. This is a ground-up type system and is best installed when the house is built. Passive systems involve double-glazed windows and heat collectors that can heat a thermal mass like brick, rock or concrete and slowly release it throughout the day and night. These systems are design to reduce their heat gain in summer, where heating is not needed. If designed from the ground up, a solar space heater can provide 60-100% of your heating needs in winter.

Some designers insist on concentrating the incoming solar energy to generate higher temperatures and efficiencies. These systems are more complex, however, and require tracking mechanisms, heat tolerant materials, and advanced safety mechanisms. It is our opinion that simple systems outlast complex ones. They are also generally cheaper. So, unless you are providing power for many households, concentrating the sun's energy will probably not be worth the extra effort and design requirements.