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All About Solar: Passive Solar, Solar Thermal, and Photovoltaic

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Thanks to advancements in solar energy, we’re now able to efficiently heat air and hot water through passive solar design and active solar thermal systems.

Although this energy is not available all the time, and the earth’s protective atmosphere allows only some of it to reach the earth, it is still an integral renewable resource for our clean energy portfolio.

Passive Solar Design

Buildings can be designed to collect, store, and distribute solar energy as heat. Referred to as passive solar buildings, they maximize absorption of sunlight through south-facing windows and use dark-colored, dense materials in the building to act as thermal mass – they store the sunlight as solar heat (light colors are less effective for heat storage). In order to take the best advantage of solar gain, a passive-designed building will have an east-west axis, so that the front of the building is facing south. Find additional information on how to design a passive solar home at DOE’s “Energy Savers” website.

Even if you have a conventional home with south-facing windows but no thermal mass, you probably still have passive solar heating potential. To maximize passive solar heating, keep windows clean and install window treatments that enhance this type of heating, reduce nighttime heat loss, and prevent summer overheating.

Solar Thermal

Active solar thermal systems collect solar radiation to heat air and/or water for domestic, commercial, or industrial use. The collector for a solar hot water system is typically a 4 ft. x 8 ft. box structure that has a glass top with a black absorber underneath it to circulate water. As the water is pumped through the collector, it is warmed and then circulated through a large, insulated tank inside a building. The warmed water can then be used to provide heat or hot water to the building. A solar hot water system can comprise one or more solar collectors, which are mounted on either a pitched, south-facing roof or on the ground. A solar water heater can offer a cost-effective way to produce hot water. The DOE’s “Energy Savers” website outlines the types of solar water heaters available and can help you assess the best system for your home or business.

A solar air heating system uses the sun’s energy to heat air. The indoor air is drawn through the collector, which heats the air up to an additional 30 degrees. A small fan pushes the warmed air back into the building. The DOE’s “Energy Savers” website provides a complete overview on the types, benefits, and maintenance of active solar heating systems.

Solar Voltaic

A solar photovoltaic module is an array of cells containing semiconductor materials that convert solar radiation into direct current electricity. If a solar PV system is connected to the power grid, any excess electricity it produces is fed into the grid and credited on the customer’s electricity account. When the sun isn’t shining, a PV system cannot produce electricity; however, the grid will supply additional electricity that is needed to the connected system, as necessary.

PV systems are quiet and non-polluting, and they help to reduce electricity bills. Although they are relatively expensive when compared to conventional power sources, PV systems can be the lowest-cost electricity source for locations that are not served by the electric grid. As the PV market matures, the price of PV decreases. Over the last 10 years the installed cost for solar PV has dropped 30% [1]. Even small purchases can play an important role in expanding the PV market. DOE’s “Solar Explained” web feature provides more details on Photovoltaics and Electricity.

(Image: “Solar panels on house roof” by Gray Watson User:E090 Licensed under CC BY-SA 3.0 via Wikimedia Commons.)