Solar systems tied to the grid have the advantage that no batteries are required since the grid acts as a backup for nighttime and cloudy-day power. Many utilities will allow you to reduce your power costs by feeding extra power back into the grid, but all will have some conditions which the solar power installation will have to meet before it is allowed to connect to the grid. Key requirements are power quality, system safety and metering of the power generated. Once these requirements are addressed, grid connection of solar power systems can substantially reduce power costs.
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Things you need
- Solar panels
- Grid-connect inverter
- Automatic disconnect switch
Wire up the solar panels and the grid-connect inverter. Attach a lead with a quick-connect plug to the positive terminal of the inverter and plug into the quick-connect plug coming from the positive side of one of the solar panels. Attach a quick-connect plug to the negative terminal of the inverter and plug into the quick-connect plug coming from the negative side of the solar panel. Connect all additional solar panels the same way. They will all be connected in parallel and the inverter will have several leads coming off each terminal and going to the individual solar panels.
Connect the inverter and the automatic disconnect switch. Connect the two 220V AC output terminals from the inverter to the two input terminals of the disconnect switch. This switch is an essential safety feature which disconnects the solar power when there is a power failure in the grid. Test the switch -- it should not close when there is power on the solar panel side but not on the other side.
Look up the rated output current on the inverter nameplate and select the AC cable running from the automatic disconnect switch to the electric panel. Connect to the appropriately sized breaker. For most solar systems, the current at 220V will be less than 15A, so a 15A breaker connected to a AWG No. 14 wire will be enough. For 20A, 30A and 40A, the breakers of the corresponding sizes should be connected to AWG No. 12, No. 10 and No. 8 wires.
Check the utility requirements for metering and install additional metering as required. Many utilities will allow you to run the existing power meter backward, which means the meter will slow down as some of your power needs are covered by the solar panels. If the solar system is generating more power than is needed, the extra power will flow into the grid through the existing connection and make the existing power meter run in reverse. No additional metering or additional hookup is required for this arrangement and the utility is crediting you for power you generate at the same amount as it charges you for power used. Some utilities will pay for power generated at a different rate than the rate they charge for power used. In this case, a separate power meter has to be installed to measure only the power generated by the solar panels and sent into the grid. Install this power meter between the automatic disconnect switch and the breaker. Wire the two 220V AC terminals from the disconnect switch to the two input terminals of the power meter. Wire the power meter output terminals to the circuit breaker.While this is an extra expense, the rate paid for solar power is often higher than the amount you pay for grid power so there may be a long-term advantage.
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