By Tom Tate
If a person had a Rip Van Winkle moment and fell asleep under a tree a decade ago, they would be amazed at how far solar photovoltaic (PV) systems have come. And they’d be right to feel that way as the technology continues to evolve at a rapid pace. Once the most expensive form of electricity generation, economies of scale in manufacturing and advances in technology are steadily driving prices down.
The typical PV system has two main components, the panels and the inverter. Disconnect switches are also necessary so the system can be safely isolated for maintenance and other reasons.
Let’s take a look at the solar panels first. Each panel is composed of many smaller cells that are all connected and together produce a certain amount of direct current (DC) electricity. When the system is being designed, the number of panels used is determined by the amount of electricity required and the amount of space available to mount them. The collection of panels is called an array.
Since solar cells generate DC power, but our homes and businesses use alternating current (AC) power––the next major system component is the inverter. This piece of equipment converts the DC electricity into AC power, which flows into your home. Like the panels, the inverters are evolving and becoming more capable with many now bearing the “smart” label indicating they can play an active role in the smart grid.
Many people are surprised to learn that heat has no part in the production of the electricity. In fact, solar panels increase in efficiency as temperatures drop. This often strikes people as odd since many solar arrays are shown in deserts and other hot, arid locations. A solar array will produce at its best on a cold, clear winter day all things being equal.
Scientists are constantly working with the solar cell components to develop more efficient and powerful combinations. Today, the best commercially available panels have an average efficiency around 17 percent with some high efficiency panels exceeding 21 percent.
PV systems are installed in what is called a grid-tied configuration. This means that the system will only operate when electricity is present on your cooperative’s power lines. When a power outage occurs, the inverter automatically shuts down the flow of electricity from the solar array. Without this protective feature, the PV system could potentially back feed electricity into the co-op’s lines, becoming a life-threatening danger to line crews and anyone in the area. When the inverter shuts down, the solar power stops flowing, so members should not install a system with the expectation that it will power their home or business during an outage.
While systems are sized to come close to the expected electrical needs of the member, there is no way to continuously match the output of the array to the current need for electricity. At times, the amount of solar power will be more than needed. At other times, it will be less. Here is where net metering comes into play.
The co-op’s meter measures both the amount of electricity they supply when the solar production is less than required and the amount of electricity sent into the co-op’s lines when solar output exceeds what is needed. On a regular basis, these flows are compared and credits or debits applied to the member’s account. How this all works is determined by your co-op’s net metering rate. Find out more about net metering and how it effects all members by visiting the Fairness Down the Lines website.
Solar PV has come a long way since first used on satellites in 1958. With this short overview, you now have a basic understanding of how these systems work.