Grid-Connected Systems

Grid-connected system are relatively simple and straight forward to size. The historic energy use can usually be obtained from the utility bills, either printed records, obtained online, or from the utility company. The utility grid functions as an infinite battery bank so that the array only has to be sized to match the yearly energy use and not the worst-case month. This is assuming that the utility company will allow the meter to be run backwards, called net metering. Net metering is available almost everywhere but not universally. Consult with the utility company before getting started.

The only major difficulty is providing a place to put the array. The roof is usually chosen, but it may not be oriented or tilted optimally, and may have shading due to trees or other obstructions.

Financial incentives, such as rebates and tax breaks, can shorten the payback time to a few years, typically 5 to 8. Since the system will last 25 years or more, grid-connected systems can be more economical than paying the utility company. Since they reduce pollution, reduce utility bills, and help the utility company with their distribution cost, everyone wins.

The inverter is sized to deliver the array power to the grid. Large systems sometimes use two or more inverters. Conductors, breakers, disconnects, ground fault protection devices, and grid connection all have to conform to the National Electric Code. In addition, the utility company and building department are going to want to approve the equipment and installation.

The utility company requires that approved equipment and licensed contractors be used. Even if you are a licensed contractor and fully qualified, the rebate may be reduced if you install the system yourself. There are strict rules to follow. Consult with the utility company and building department before getting started. If you are a homeowner, the easiest path may be to use a licensed installer in your area.

Remember to do the energy audit first. Rebates may be available to help with any energy efficiency improvements. A dollar spent in reducing energy use may save four dollars in the cost of the solar system. If you are considering using an installer, do the energy audit first.