How Solar Photovoltaics Work

1. The photovoltaic effect.
Photovoltaic cells convert the sun's radiant energy into electrical energy.  Sunlight excites electrons on the surface of the solar cell that shake loose and start a flow of electrons, or direct current (DC) electricity.  The amount of power (current) and the strength of that power (voltage) will vary depending on the number and configuration of the solar cells, the orientation of the cells, the temperature, and intensity of the sunlight.

The photovoltaic effect is completely solid-state and self-contained, meaning there are no moving parts and no materials are consumed or emitted. (See Photovoltaic Energy Conversion tab on the left.)

2. An inverter transforms the DC power produced to AC power that we all use.
Once the power has been converted to AC, the building uses it as needed, with excess power generated put back onto the grid for use by your neighbors.

3. You can either use your power yourself or sell it all to your utility company.
In some locations the utility company pays a premium for solar power, as is the case with Green Mountain Power. In this scenario, you will have two meters, one for the power you buy, and one for the solar power you sell.

A Couple Things to Note:
> When you are not producing power, your energy will still be supplied by the utility.  There is nothing to switch over, your building does not know the difference between solar power and regular power.

> If the power goes out on your street, your solar energy system will turn off too.  This is to protect line workers who are trying to restore power to your neighborhood and is a requirement to operate your system. An option for a battery back up can provide power to selected loads during a utility power outage.

Assess your Site’s Solar Potential

The first step is to determining if a solar project will work on your site.  Here’s a little information to give you an idea if solar will work on your site.  Please remember, if you are unsure, feel free to give us a call.

Orientation:  Find a location that has a clear southern exposure.  If you’re not sure which direction is south, to locate due south either use a compass, go out at noon and see where the sun is or look up your home on an aerial view of Google Maps or comparable software.  Panels would ideally face within 15% of south, although larger variation is acceptable, just not ideal.

Shading: Take note of Shading.  Shading can severely degrade the output of your system and may be difficult to overcome.  Impact of slight to moderate shading can be reduced with the proper design.  However, if more than 30% of your “solar window from 9AM to 3 PM” is shaded, you may want to consider a different site.  A good rule of thumb is that the solar panels should be set away from a shade obstruction at least 2-3 times the height of the obstruction. 

Not sure?  Let us perform a more formal assessment of your site for free.

Tilt: Ideal tilt for our area is approximately 40 degrees (about a 10-12 pitch), but this is less critical than other considerations.  For most flat roof applications, 15-20 degrees is selected for  more efficient roof area utilization, and lower wind load characteristics.  For tilted roofs, matching the existing roof pitch will make the most sense and give the best aesthetics.

Area: Estimate the size of your roof that can accommodate solar.  No need to climb on the roof.  Simple dimensions of your home or building are sufficient for starters.  On average, each kW of installed capacity will require 100-150 sq.ft.

Solar Links of Interest

The Database of State Incentives for Renewables & Efficiency. DSIRE is a comprehensive source of information on state, local, utility and federal incentives and policies that promote renewable energy and energy efficiency. Established in 1995 and funded by the U.S. Department of Energy, DSIRE is an ongoing project of the N.C. Solar Center and the Interstate Renewable Energy Council.