Batteries: Making Electricity from Rotting Soil

For those curious, "200Wh/year" translates to ~0.02W average (per square meter). Low power indeed.

(For comparison, a dozen of alkaline D-cells provide about 200 Wh as well and can last several years. Or if you can install solar panels, they'll provide 140,000Wh/year to 280,000Wh/year per square meter -- but you'll need some evegy storage for the night)