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On rainy days when the solar panels produce only a small amount of power, and at night, when they produce no power at all, our solar-powered PC still needs juice to operate. We use a storage battery to provide this power, and use the charge controller to charge it up during the day. In our installation, this is a lead-acid battery that weighs in at nearly 75 lbs (32 kg).
Solar battery from the Sonnenschein (sunshine) company, made by Exide Technologies
Under optimal conditions, our solar array deliver up to 260 Watts of power. In idle mode, the solar-powered PC consumes 61 Watts, which leaves nearly 200 Watts available to charge the battery.
Our gel-filled lead-acid battery offers a capacity of 130 Ah. At 12 volts this produces 1560 Wh. With a full charge, our battery can run the PC for about 23 hours, without any input from the solar panels. But this is possible only during optimal conditions, which occur only seldom, if at all.
Terminal connectors for the lead-acid battery
Energy Distribution
To support a clear understanding of where and how much power is consumed in our solar powered installation, here's a block diagram of all the components with supporting details.
Power Expended For 24-hour Use
How much energy must the solar array collect during the day, to keep the computer running 24 hours a day?
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The lead-acid battery operates at about 80% efficiency, which means that 20% of the stored energy is lost.
Power Collection: 10 Hours Per Day
We calculated an average of 10 hours of sunshine per day. During this time, the PC does not access the battery for energy, so we can forgo the 20% loss that battery use otherwise entails. This explains how we produce energy consumption of 610 Wh in the preceding figure (10 hours x 61 Watts = 610 Wh).
