How much webserver load can be served from 1m² of sunlight?

Timothy Downs uses a one meter square solar panel to find how much load can be sustained by a webserver powered by the solar energy.

Let’s set up a webserver and power it only from sunlight, plus a battery for night-time. We’ll see how much load we can handle. Our testing setup is:

  • 200-watt solar panel (1.48m by 0.67m,~1 square meter)
  • 12v MPPT to convert solar panel variable voltage to battery fixed voltage
  • 12v 100ah Lithium Iron Phosphate Battery — 92% efficient
  • 12v to 240v inverter — 92% efficient
  • An AMD Ryzen 9 4900HS CPU (in a laptop with the screen turned off)
  • An electricity meter to measure how many watts of power the computer is drawing
  • A 4.6b year old yellow dwarf as a light source

Based on recent data, spring on the east coast of Australia gives sunshine for 3 full hours of panel capacity daily (after night-time and weather), or 600 watt-hours of energy per day. Divide 600Wh (daily energy available) by 24 (hours in a day), is around 25W of constant power available without depleting the battery. Removing the efficiency losses from battery and inverter, this brings it down to a constant supply of 21W. Our energy budget: 21W

We’re spending 14 watts of our energy budget just to power the idle CPU & RAM. The additional 7 watts we have for our constant energy budget of 21W is already exceeded from one client repeating their request as it drains 26W — so to reduce to utilisation to 21W we need to make a request (300ms of processing), then 500ms pause before making the next request. This gives us 1.2 RPS and averages our consumption at 21 watts.

Doubling the energy budget from 21W to 42W, a load test with 4 simultaneous users achieves a total energy consumption of 42w — and gives 12.48 RPS. By doubling the power consumption, processing goes from ~1 RPS to ~12 RPS. By increasing the utilization rate, it has increased power efficiency by a factor of 6.

Read details on Medium here.

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