What Happens to Solar Energy During the Night?

Thermal Mass

• One method of storing thermal heat in solar homes is the incorporation of a large, highly conductive mass of material into the structural design. This most often means a masonry wall or floor is placed so it is bombarded with the sun's rays during the daylight hours. Peak temperature in the thermal mass usually occurs during the late afternoon. As darkness falls, stored heat radiate backs into the house. As the night progresses and the outside air cools, the ability of the thermal mass to heat the building diminishes. When the sun rises on the next day, this cycle begins again. This means of thermal heating from the sun is known as passive solar energy.

Seasonal Storage

• Since passive solar heat is of greater benefit in the winter season than in summer, builders and solar architects have designed systems that use winter sunshine while keeping the hotter summer radiation out of the building because the heat exchange produces too much heat. One simple method uses metal reflectors over windows during the summer season to block out the sunshine. More sophisticated systems allow the low-angle solar rays to enter the house and strike the thermal mass, while higher-in-the-sky summer radiation is blocked by roof angles and overhanging verandas. Designers also prize the thermal mass's ability to absorb solar heat throughout winter, thus raising the overall interior temperature during this time of the year.

Direct Current Storage

• Photovoltaic solar panels directly generate electricity in the form of direct current. This type of electricity is the result of the interaction of energy from the sun's rays striking the solar panel cells of a solar collector. Because of a complex chemical configuration, each solar cell located within the panel is able to generate a small electrical charge when the sun shines. Collectively, the electrical power can be useful, but since it is created in the form of direct current, the energy is transferred to a deep-cell battery, similar to a car battery. When needed, this energy can be withdrawn from the battery and, after being transformed to alternating current, can power house lights and appliances during all hours of the night.

Solar-Heated Water

• Another method of providing home solar heat involves direct heating of water by energy from the sun. As the water gets hot it is circulated to an internal and insulated heat reservoir. During the evening hours, a closed heating system mechanically circulates the heated water through the house. This is known as active solar heating.