Solar energy production encompasses several power sources, both passive and active. It’s important to differentiate among the different types of solar energy production systems since it’s not uncommon for the average homeowner to confuse them. We’ll start with a diagram of solar energy hitting the earth surface.
Then we’ll present diagrams and discuss photovoltaic solar, solar hot water, and concentrated solar power. The easiest way to think about these is: am I using solar energy to heat water (solar hot water and CSP) or am I converting sunlight directly into electricity (photovoltaic cells)?
Much of the sun’s energy is reflected (by clouds or reflective surfaces like snow) or absorbed before it hits the earth’s surface. To get an idea of how much energy makes it through our protective atmosphere: it’s more energy than is currently stored on the planet in all fossil fuels (see Solar Energy Fact #1).
Solar power (electricity) is produced in two ways: by direct transformation of solar energy into current through photovoltaic panels (solar PV), or by the concentration of solar energy to create steam and drive a turbine (concentrated solar power).
Solar photovoltaics, which can be installed on your roof or in large ‘solar farms’, are relatively easy to understand. Solar energy in the form of light hits the solar panel, which excites electrons in the panel and creates an electric current. The current created by the solar panel is direct or DC current, and it flows to an inverter box which converts it into alternating or AC current (this is what’s used by all of your appliances and the electric grid in the United States).
Most homeowners don’t know that residential solar panel systems are grid-tied, meaning that there is no backup battery system involved. Current supplied by the solar panels either flows into the home or into the grid through the home’s electric meter. In some areas the homeowner can be compensated for this surplus power.
Passive solar refers to any structural design element that converts sunlight into usable heat. This crude but effective diagram illustrates how simple design can have substantial impacts on home heating. The slope of the roof prevents high summer sun from shining into the home, while the lower winter sun has direct access. In the summer this type of home will stay cool, while winters will provide plenty of heat–all without any additional energy input.
Solar hot water is quite different from solar photovoltaics. A solar collector concentrates the sun’s rays to heat water, which makes a closed loop through the heating tank. The hot water is passes into a tank that contains a heat exchanger (usually used in conjunction with the hot water heater already installed in the home). As heat is exchanged in the tank, the water is pumped back up to the solar collector (determined by a controller unit). Cold water that passes through the tank heats up and makes its way to your tap.
Concentrated solar power, or CSP, works by using an array of lenses or mirrors to focus a large area of sunlight (solar thermal energy) onto a small area. Most CSP systems work by heating up water which, in the form of steam, drives a steam turbine and produces electrical power. It’s easy to confuse CSP with solar photovoltaics, but photovoltaics transfer solar energy directly into electrical current, while concentrated solar power transfers solar energy into a carrier (water) in the form of heat. See a video of concentrated solar power.
CSV is one of the newest forms of solar technology. These systems focus a large amount of sunlight onto a small photvoltaic area–sort of like a mini solar panel. However, compared to standard solar panels, CSV systems are typically much cheaper to produce since the use of expensive parts (solar cells) are minimized.
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