Off The Grid

Back in the 1970s, when solar energy made its public debut, solar systems were usually installed “off-the-grid.” That is, the energy produced by the system was completely independent of the public utility grid. Usually, these systems were installed on remote cabins that were far from a utility source or in an area where electricity was too expensive, or simply because the homeowner chose to “go solar.” Whatever the reason, the key component in the system was a bank of batteries that stored any surplus power for later use. On sunny days, the home’s energy came directly from the solar modules; on cloudy days, the power came from the batteries. If your batteries ran out and it was still cloudy, you either used a back up gas generator, or lit a fire in your woodstove.

On The Grid

These days, solar energy systems have invaded suburbia, where public utility systems are close-at-hand. Independent systems have given way to on-the-grid systems – systems that are connected to the public utility grid in the following way:

• The PV modules on your roof are connected to an inverter which converts the system’s DC electricity to AC (compatible with the utility grid and your home).
• The inverter then connects to a bi-directional public utility meter which tracks the difference between the amount of energy your PV system produces and the amount of energy your household consumes.
• The public utility grid serves as a storage system. When you produce more energy than you need, the electricity goes to the grid. On cloudy days (when PV systems operate at a lower level), or when the sun goes down, you get it back. When you need more power than your system has created, you automatically revert to the public utility system. (See below for Net Metering.)
• Some homeowners install either a bank of batteries, or a gas generator for backup during public power outages

What You Need

The most cost effective way to go solar is to build an energy efficient house from the ground up, with passive solar ideas in mind: thicker walls, thermal windows, well-placed windows and awnings, tankless water heater, and energy efficient major appliances. PV modules can be installed as part of your roof, rather than over an existing roof, which will save you money. But if you’re retrofitting an existing house, you must think about the following crucial features:

• Sunshine - You need unobstructed sunshine for most or all of the day, all year long.
• Size - You need about 80 to 100 square feet of solar panels for every kilowatt hour you want to produce annually
• Roof Location - The best roof location is south-facing. Slight variations may be acceptable, depending on where you live. Flat roofs also work well. Ground mountings, car ports, and window awnings are other options.
• Roof Surface - Shingles are easiest to work with; slate is the hardest. If your roof is very old, consider replacing it before or during your PV system installation, to take advantage of panel styles that become part of the roof itself.