Yesterday I reported on the installation of solar panels on our garage roof.
Today they completed the electrical part of the installation.
There are two rows of eleven panels on the roof. Each row is wired in series to deliver about 400 volts direct current (DC, like a battery). The two rows are wired in parallel to deliver more current (amperage).
The wires from the roof go down to the basement to a box of electronics that converts it to match the approximately 240 volts alternating current (AC) coming from National Grid.
The step-by-step photos are not as appealing as yesterday's unless you are an electrician so I'll just show the end result:
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| Click to enlarge |
The largest box, in the upper right is the inverter - that converts the direct current from the solar panels to match the alternating current being provided by National Grid. This system is not designed to work off-grid or when electricity from National Grid is down. That is a much more expensive proposition and we have a propane-powered generator for times like tropical storm Irene. (As proven during the aftermath of Irene, we are far enough away from the main road that we're just about the last house in Charlestown to get power restored.)
The small box right below the inverter is the switch that can turn off the DC electricity feeding from the panels on the roof, in case the inverter needs repair or replacement.
The other two boxes are a cut-off switch for the AC electricity out of the inverter and an electric meter to provide a long-term record of the amount of electricity produced. That electric meter is not really necessary and seems, to me, to almost be a waste of money. That cut-off switch is only needed because the inverter in our installation is more than 50 feet away from the main breaker box.
From that electric meter the wires run over to the main breaker panel and feed into a circuit breaker. Any power from the solar panels reduces the amount that comes from National Grid. If the solar panels produce more than the house uses the National Grid meter will run backwards and one of our neighbors will use it (paying National Grid, of course).
We still have two steps to complete before this is "live" and the savings start piling up. First, our building inspector has to come out and give his ok to the electrical work. Then we have to wait until National Grid comes out to install the new meter that can run backwards. Those two things will probably take a couple weeks.
We're anxious to get it turned on, even if we have short days and dim winter sun right now. I'll give another report when the system starts running.