Solar Energy

Solar power is another “clean” and renewable source that is emission-free and will never exhaust the sun. Not only do photovoltaic panels not drain the sun of energy, they do not diminish the capacity of other panels, so long as one panel is not placed on top of another.

There are two ways to use solar energy, active and passive use. Photovoltaic electricity (PV), solar heating and cooling, and concentrated solar are active systems. Passive solar building use design features capture and utilize solar radiation.

PV cells turn sunlight into electricity. This technology was accidentally discovered in 1954 when a scientist noticed that silicon created an electrical charge when exposed to sunlight. The solar powered calculator was born and eventually evolved into today’s solar panels. The early panels were made of silicon, but second generation panels use thin film and semiconductors. Thin film panels can be used as shingles, tiles, or façades and incorporate electrical generation into the design of a building. PV units can be found powering individual homes or on roadsides, collecting energy for lighting for highway signs.

How solar energy works (Sunpower)

Solar heating and cooling uses the sun’s radiant energy to heat or cool a building with the use of PV panels. A transpired collector is a black metal panel on the south-facing wall of a building that absorbs heat from sunlight. Holes in the panel allow heated air to pass through to the other side, where it is sucked into the ventilation system and throughout the building.

Solar process heating uses a solar collector (usually an evacuated tube or parabolic trough), a pump, a heat exchanger, and water tanks to heat a building. The evacuated tube is a series of glass tubes and reflectors that heat water inside. A parabolic trough is a U-shaped mirror focusing sunlight in a central tube. The focused sunlight heats water in the tube. The heated water is pumped throughout the building to warm it up. Solar cooling uses the same collection system, along with the magic of chemistry to cool the air.

Concentrated solar power is a generating system that reflects and focuses sunlight to create heat and steam that turns a turbine to create electricity. Because the system converts sunlight into thermal energy, it can be stored and generate electricity even on cloudy days or at night. Concentrated solar power can accompany a traditional fossil fuel plant as a carbon offset or as a stand-alone plant.

Solar array collection system (Colorado Springs Business Journal)

Passive solar uses site, climate, and material to use the sun’s radiant energy to heat and cool a building without the use of active mechanical systems like those mentioned above. Energy efficiency measures to reduce the required amount of heating and cooling is the first step. The second step is an unobstructed south face to maximize sun exposure. Sunlight entering the south facing windows is absorbed by thermal mass- material such as concrete, stone, or brick. The thermal mass absorbs heat from the sunlight during the winter and from warm air during the summer. Conduction, convection, and radiance are natural phenomena that circulate the heat throughout the building.

Like all other energy sources examined so far, solar energy is not completely “green”; it too has negative environmental impacts. Habitat loss for large solar arrays and concentrated solar plants can be mitigated by siting these in repurposed areas such as brownfields and reclaimed mine sites. Small scale units that power a single building typically have minimal impact, especially when roof-mounted.

Water use is a concern with concentrated solar plants. The sunniest areas in the US are often the driest, and water is scarce so a massive withdrawal of 600 to 650 gallons per megawatt hour of electricity can have a negative impact on desert denizens.

An additional concern is the hazardous materials used in the manufacture of PV cells. Many are used to polish the semiconductor surface and include hydrochloric acid and acetone. Petroleum is used in the manufacture of PV cells also, so even solar energy is somewhat dependent on fossil fuels. However, new technology that uses cotton and castor beans is being developed.

Next week we'll look at geothermal energy. This week's information comes from Solar Energy Industries Association, National Renewable Energy Laboratory, Renewable Energy World, US Department of Energy, Union of Concerned Scientists, and Scientific American.