About Solar Energy

There are three methods by which solar energy can be employed to lower utility bills and reduce the consumption of fossil fuels: passive solar, solar thermal, and solar electric. Since solar energy is relatively expensive, it is imperative to first reduce all loads through energy efficiency measures.

Passive

Passive solar, also called sun smart design, refers collectively to a set of design principles that optimize a building’s interaction with the sun in order to achieve a thermally comfortable, energy efficient structure that provides most of its own heating and cooling throughout the year. Orientation of the building, depth of overhangs, size of windows, amount of thermal mass and insulation together have enormous potential to improve the thermal performance of the final product. These building elements are designed with reference to the location of the sun in the sky throughout the daily and seasonal cycles. For example, south facing windows allow the low winter sun to shine into the building, heating the surfaces and warming the air. Overhangs over these windows serve to block the high summer sun, keeping the building cooler in the summer.

Thermal

Solar thermal systems produce useful heat from sunshine. There are many different technologies and these can be used to heat homes, pools, and water for domestic tasks (DHW) as well as for industrial processes, commercial and institutional facilities. Solar thermal energy can even be used to make electricity. Most commonly, a solar thermal system is comprised of collectors, storage tanks, piping, pumps, and controls. The collectors (or panels) are mounted on the roof, ground, or attached to a wall. The most commonly used collectors in Colorado are “flat plates”. Evacuated tube collectors are more expensive but advantageous in cloudy climates and when a higher temperature is desired. Parabolic trough collectors deliver an even higher temperature and are useful for large applications and for air conditioning and generating electricity with a turbine.

Electric (Photovoltaics)

Photovoltaics produce electric current directly from sunshine. They come as panels that are mounted on the roof or ground and can also be incorporated into building elements such as walls, roof, or awnings. The electricity produced is DC and must be converted to AC with an inverter for use by most appliances. The inverter may be connected to the electric grid and, if your utility offers net metering, feed any excess solar electricity into the grid during the day and draw electricity from the grid at night. Alternatively, batteries are used to store enough electricity during the day for use at night and during cloudy periods.

Fast Facts

• If you want it any time other than when the sun is shining, you will need to store it (electricity is stored in batteries or the grid, hot water is stored in a tank).
• A 10 kW (peak DC rating, stc) photovoltaic system mounted facing South at 40 degrees in Colorado will provide approximately 15,000 kWh of electricity per year. The panel area would be roughly 800 square feet.
• To produce the same amount of energy (15,000 kWh) from solar water heating panels, you would need 250 square feet of panels.
• Each kWh of electricity generated by the PV system saves one pound of carbon dioxide emissions from local coal power plants.