Solar Electric System Installation Basics

How does a solar electric (photovoltaic) system work?

Simply put, photovoltaics (PV) work by converting light energy into electrical energy. The PV cells consist of a positive and a negative slice of silicon placed under a thin slice of glass. As the protons of the sunlight beat down onto the photovoltaic cell they knock the neutrons off the silicon. The negatively-charged free neutrons are attracted to the silicon but are trapped by the magnetic field that is formed from the opposing fields. Small wires on the silicon catch these neutrons and when connected in a circuit an electric current is formed.

For greater detail:

· PG&E description of a grid-tied system http://pge.com/about_us/environment/solar/about_solar_energy.html

What does installation entail?

The installation process is fairly straightforward. The equipment used varies by roof type and installation company but the universal components are the panels, a support structure for the panels, an inverter, electrical pipe called conduit, and AC/DC disconnect switches. As with anything in the construction industry, each installation is unique, but we have provided a generic example.

On the roof:

1) Posts called stand-offs are lag-bolted into your roof’s supports beams (flashings and sealants are used to protect any roof penetrations).

2) Racking is attached to the standoffs in rows.

3) The solar panels are positioned and bolted to the racking.

4) Panels are wired together and connected to wiring that runs down to the inverter in conduit pipe (depending on your situation, the conduit may go through the attic or on the outside of your home).

Ground floor:

5) An inverter that converts the DC power from the panels into AC power for your residential use is mounted (typically in your garage or on an outside wall in a relatively shady position).

a. If required by your city, a disconnect switch is mounted near the inverter.

6) Wires from the roof go into the inverter, then to your main electrical panel or subpanel.

7) System is turned on and net-metering begins.

How long will installation take and do I have to be home?

A typical residential installation should take 2-5 days and you do not necessarily need to be home as long as the installation crew has the necessary access.

How big of a system will I need?

This depends on many things and can be as complicated as you would like it to be. Typically homeowners choose to cover 50-85% of their total electrical bill. There are two very simple ways to estimate a system for your needs.

1) Give a reputable solar company your electric bills. They will use their analysis tools to provide you with a proposed system and corresponding financial analysis.

Additionally, you’ll want to consider any expected decreases/increases in your electrical usage (i.e. a child moving away from home, spa installation, etc.).

How long will my system last?

This can vary and you should definitely talk to your installer about it, but nearly all solar panels are guaranteed to produce for 25 years and most inverters have a 10 year warranty. While inverters will most likely last past 10 years, you should expect to replace the inverter during the life of the system (price range: $1,500 – $4,000).

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