How PV works:
Photovoltaic cells are made of very pure semiconductor grade silicon similar to that used in computer chips. Silicon is the most common element in the Earth's crust. Electricity is produced as photons of sunlight penetrate the element, bumping electrons into a flow. PV cells are connected together to make a module. Modules are the building blocks connected together to make an array. The photovoltaic effect produces DC (Direct Current) electricity. This DC power is converted to AC (Alternating Current) electricity to match the American standards of AC frequency and voltage. The conversion is made by an important system component called the inverter. The array and inverter are engineered for efficiency and compatibility.
Utility Interactive PV:
A Utility Interactive, or grid-tied, PV system has the photovoltaic system connected and acting in parallel with the electric grid. As power is produced it is used primarily for loads within your building. If more power is produced than needed in-house, the remainder is automatically exported through your billing or revenue meter to the electric grid. In effect, the grid acts as your storage medium and your revenue meter tallies the 'net metering' exchange. The inverter constantly monitors grid power quality to provide a seamless generation match. If there is a power outage the PV system will automatically shut down. This prevents a small PV system from trying to power the neighborhood, but more importantly it ensures the safety of utility personnel working on downed lines. Upon stable restoration of grid power, the PV system will automatically re-connect.
A Utility Interactive PV System:
Stand Alone and Bi Modal PV:
These are two similar types of systems which store power from the sun for night and inclement weather use and both require batteries. A stand alone system is cost effective when the expense of extending the utility grid is high. For some of our residential stand alone customers this has meant cost effectiveness for sites more than 1/4 mile from the grid. A bi-modal system will act in parallel with the electric grid like a utility interactive system and use solar power to maintain a fully charged set of batteries. In the event of a grid outage it automatically isolates from the grid and provides standby power. Both systems need to maintain batteries which makes them less efficient users of photovoltaic power. Both involve more controls and safety features and requires significant storage space and expense. Often because of this, our customers select bi modal systems to power only critical loads. Batteries need replacement every 5 years if heavily used and every 10-12 years at maximum and these systems need periodic maintenance. Better storage technology, for example hydrogen and a reliable fuel cell or flywheels to match with PV will make these types of system commonplace.