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How well do solar panels work in cloudy conditions?
A cloudy day provides sufficient diffuse light by which the panel will produce electricity. Optimum electrical production occurs with bright and sunny weather conditions. Under a light overcast, the modules might produce about 1/2 to 2/3 as much energy as under full sun. On really dark days, that can drop to as low as 10%. In off-grid applications, a PV system is connected to a battery storage system as a backup power source. In grid-connected applications, the PV system works in parallel with the utility power grid. So, if electrical needs exceed the solar power output, the local utility makes up for the shortfall. Conversely, when the PV system generates more energy than the building requires, the excess power is exported to the utility grid, reversing the electrical meter.