An Introduction to PV Systems
Essential Components
Solar Photovoltaic (PV) Panels
Sheets of silicon wafers which when excited by photons from the sun, release electrons. In simple terms, the "pressure" of the sun light "pushes" electrons from the silicon semi-conductor to the aluminum conductor pathways which when combined across all the panels, form a substantial amount of current at a specified voltage. By combining the panels in parallel or in series, one can design a system of a particular power offering depending upon what the Charger Controller and Inverter prefer to receive.
Solar Charge Controller
This is required only if you have batteries. This device takes the Direct Current (DC) from the PV panels and regulates it to maintain a constant voltage (as the amperage fluctuates) in order to a) charge the batteries, and b) delivery power to the Inverter (see Inverter, below). A good Charge Controller will track the daily power generation, giving you a feeling for how well your system is performing. Coupled with a home or laptop computer, this data can graphed to showcase performance (not required, by quite interesting to see if you are a geek at heart).
Batteries
Batteries are an option, as is the Solar Charge Controller (above). The cost can can range from $100 to $1000 each (average of $250 to $350), depending upon the type, power capacity, and quality. A typical combination system would use 6V (volt) AGM (Applied Glass Matt), 300AH (amp hour) batteries, either 4, 8, or 16 combined in series for 24V, 48V, or 96V. AGM batteries are safe to be used indoors with basic room ventilation because they are completely sealed. Traditional lead acid and gel-cell batteries usually cost less, and can handle great temperature extremes, but also require greater maintenance and should be used in a well ventilated room.
Inverter
This unit converts Direct Current (DC) to Alternating Current (AC). Direct Current is what we use with battery powered devices such a flashlight or battery powered toy. Alternating Current is what comes into our homes from the power utilities. If a home PV system's purpose is to offset power consumption, then it is likely an Inverter will be used. The exception to this are those individuals who are using a PV system with DC appliances, such as refrigerators or TVs found in RVs.
The Inverter is tied to the home breaker box to power the home appliances and/or push back to the utility through the house breaker box. This can be as simple as adding a single breaker (most common) in order to push power back to the grid through this connection; or to support one or more house-hold circuits (less common) which are deliberately diverted to run through the Inverter and battery system. If the power coming into my home from the power utility, most of my house continues to run from battery with an almost unnoticeable transition (momentary flicker of the lights).
There are a other components, such as a master Control Panel for the Solar Charge Controller and Inverter, as is available with the Xantrex product line, but this is not necessarily a part of all systems nor required. And of course, breakers, conduit, wire, mounting brackets, and in some cases, new breaker boxes.