How It Works - Commercial

Solar Energy - It’s Clean, It’s Green and Best of All It's Free

A photovoltaic (PV) system consists of one or more photovoltaic (PV) modules, the basic building block of PV-systems. One PV-module consists of about 36-72 photovoltaic solar cells. The cells convert the light into electricity. The PV modules are connected either in several series called an array. Because PV Arrays are built with PV modules of 150 to 300 watts each, photovoltaic systems are exceptionally modular, which provides for easy transportation and rapid installation, and enables easy expansion if power requirements increase.

To be able to use the generated electricity, more components need to be added to the system. PV systems for grid-connected or “grid-tied” applications need an inverter or power conditioner to convert the direct current (DC), generated by the PV-modules, into alternating current (AC) for use by your building. Excess power generated and not used immediately is “sold” back to the utility for a credit to be used when sunlight is not available. This is called Net-Metering.

For more information please read these Frequently Asked Questions.

How PV (Photovoltaic) Cells Work

The photovoltaic cell is the component responsible for converting light to electricity. When sunlight strikes a photovoltaic cell, part of the light particles (photons), which contain energy, is absorbed by the cell. By the absorption of a photon a (negative) electron is knocked loose from a silicon atom, and a positive "hole" remains. The freed electron and the positive hole together are neutral. Therefore, in order to be able to generate electricity, the electron and the hole need to be separated from each other. A photovoltaic cell has an artificial junction layer, also called the p/n-layer. Now, the freed electronics cannot return to the positive charged holes. When the electric contacts on the front and rear are being connected through an external circuit, the freed electrons can only return to the positively charged holes by flowing through this external circuit, thus generating current. The electrical power that can be extracted from a photovoltaic cell is proportional to its area and to the intensity of the sunlight that hits the area, and is measured in watt (W).

The PV cells currently on the market convert an average of 12% to 15% of the sunlight that strikes them into electricity.

Orientation

Due south (180-200 Degrees) is the optimal orientation, but facing the array to the East or West of due south is acceptable. Also remember that utility rate schedules also affect the orientation. For example, Pacific Gas and Electric Co offers a Time of Use rate schedule that pays four times more in credits during 12n to 6pm. If this rate is used orienting the solar array to be more efficient during 12n - 6pm makes better financial sense.

These modifiers are used for the central California area and may be different for other areas of the country or different climatic circumstances.

The number one rule is to never design or install a solar electric system that faces in any portion of the 180 degree arc of the compass that faces north. When you need it the most it won't work. Needless to say, installing solar panels in the shade of a tree or building will also not be functional.

Inverters

Inverters are the "brains" of the solar electric system. The inverter converts DC electricity to the AC electricity that your building uses. The inverter monitors the utility grid and controls your solar energy systems production, as well as shutting your system down during a utility black-out.

Most modern Utility-Tied (also grid-tied) inverters do not utilize batteries, and are much more efficient than the older battery type systems that were design for off-grid homes.

All modern grid-tied inverters are UL Listed for grid connection (UL1741). Without the listing individual inverters are not able to be legally connected to your house's eletrical system, and do not qualify for state rebates.

How Net Metering Works

Grid-connected solar energy systems produce electricity in parallel with the electrical utility, and can feed power back into the utility grid if all of the electricity isn’t used on site.

California's net metering law allows residential and business users to sell their extra electricity back to the grid (PG&E) at retail prices during the day and draw from the grid during the night. During the day, the electric meter spins backwards as it registers excess energy. At night, or during off-peak producing times, the electric meter spins forward as it returns electricity from the grid into the customer’s home or business.

PG&E's standard net energy metering program offers customers the opportunity to get credit for the electricity they have produced in excess of the amount that they have used within a given month. The credit appears on the customer’s monthly utility statement, and is applied to electricity-related charges within each 12-month reconciliation period.