Solar limits

Something unexpected with my solar power setup: the cable loss is limiting the power produced by the panel, but it’s due to the voltage drop and not the power loss.

The cable is ~20 m of 1 mm2 flex for a total of 0.71 Ω. The peak power point of the panel is 34.3 V and the Victron charge controller needs 30.1 V to charge an 8S LiFePO4 battery.

This means the maximum current is I = (34.3 - 30.1) / 0.71 = 5.9 A, which is 34.3 * 5.9 = 202 W generated, 24 W of loss, and 178 W delivered.

Power delivered versus generated

Changing to 2.5 mm2 flex will cut the resistance to 0.28 Ω, ups the current to 9.2 A, and deliver 291 W.

Michael Hope
Software Engineer