How Do You Run a Computer on Solar Power?

A solar powered computer runs from a battery that a solar panel recharges during the day. The panel feeds a charge controller, the controller charges the battery safely, and the computer draws from the battery around the clock. Nothing about the computer itself is special, but it has to be efficient, because every watt it draws has to be generated, stored and carried through the night and through days of poor weather.

Off-grid computers are common at remote sites: weather and environmental stations, pipeline and pump monitoring, traffic and roadside cameras, telecoms cabinets and agricultural sensors. They usually sit in a sealed enclosure on a pole or in a cabinet, with a cellular modem for reporting.

Designing one is a sizing exercise in three steps: work out how much energy the site uses each day, size the battery and panel to supply it in the worst month, then choose a charge controller and a computer that waste as little of it as possible. The steps below follow that order, and the figures are typical starting points rather than a substitute for a proper site survey.

Start with energy, not power. Daily energy in watt-hours is the computer’s average power multiplied by 24 hours, plus everything else on the battery: modem, cameras, sensors and heaters. Use measured average power where you can, because the processor’s rated power is a ceiling, not a typical figure.

This is where processor choice pays off. A low-power embedded processor drawing around 6 W needs a fraction of the panel and battery that a 30 W system needs, which is why efficient embedded CPUs dominate off-grid builds. Our processor base power guide compares CPUs for efficiency.

The battery has to cover the load for the number of days without useful sun you want to ride through, known as days of autonomy. Divide by the usable depth of discharge: around 80 to 90 per cent for lithium iron phosphate, and around 50 per cent for lead-acid if you want it to last.

The panel has to replace a day’s energy in the sun hours available in the worst month. Peak sun hours fall to around one or less in a UK December, so winter sizing drives the design. Allow for losses in the controller, wiring and panel temperature by derating to around 75 per cent.

The table assumes two peak sun hours, a typical spring or autumn figure in northern Europe; halve the sun hours and the panel doubles. It shows why cutting the load is the cheapest way to shrink the system.

Use an MPPT charge controller for anything beyond the smallest system: it extracts noticeably more energy than a PWM controller, especially in cold weather and low light. Set its low-voltage disconnect to protect the battery, and check that the battery chemistry suits the site temperature.

An off-grid computer has to recover without a visit. Set the BIOS to power on when power returns, so the system restarts after the controller reconnects a flat battery. Enable the hardware watchdog to reboot a hung system, and schedule non-urgent work, such as uploads, for the middle of the day when the panel is producing.

Our fanless PCs include many low-power systems with wide DC inputs, and industrial IoT gateways suit sites that mainly collect sensor data. The outdoor weather station case study shows a typical solar site.

We supply low-power fanless computers for off-grid sites with power-on recovery, watchdog and wide DC input set up as standard, and test each system before it ships. Send us your loads and location, and we will specify the computer to match.