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?

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).

Battery operation: 14 nighttime hours

The other 14 hours during which the solar cells deliver no power must be serviced by energy stored in the battery. This means a discharge of 855 Wh (14 hours x 61 Watts = 854 Wh, rounded to 855).

Because we must also factor a 20% energy loss from battery use into this equation, we require that the battery must store 1030 Wh (855 Wh + 20% = 1026 Wh).

Adding the daytime energy consumption to the nighttime consumption we come up with a total daily energy budget of 1636 Wh (610 Wh by day + 1030 Wh by night = 1636 Wh total).

The battery at work in our test installation

Together our two solar panels must deliver an average of 163 Watts during the day so that the PC is able to operate 24 hours a day. If we fail to attain this value, the PC will shut down in the middle of the night when it runs out of power.

Each solar cell produces 130 Watt under optimal conditions. Thus, our solar power rig must produce at least 62.9% of that value for at least 10 hours a day, to keep it running around the clock.