Off-Grid Survival Books for Beginners

Daily consumption is the sum of the appliance estimates you tick. Each estimate is shown beside the appliance (kWh per day) and is a typical figure, for example a 750 W pump for 1 hour is 0.75 kWh. Your own appliances will differ, so check their power labels.

Peak sun hours are the equivalent number of hours per day of full midday sunshine (1 kW per square metre). They vary by place and season; the slider runs from 2 to 6 hours. For your location, use the European Commission’s free PVGIS tool.

Panels = daily kWh ÷ (0.4 kW panel × peak sun hours × 0.8), rounded up. The 0.8 is a planning allowance for 20% overall losses (wiring, controller, inverter, heat, dirt). Real losses vary. 400 W is a common rating for a modern panel.

Usable energy, 2 days = daily kWh × 2. This is the energy you would draw from the battery over two days without any sun. It is not the size of battery to buy.

Nominal battery capacity = usable energy ÷ the usable share you choose. Batteries should not be fully discharged, and the usable share depends on the chemistry and manufacturer, so check your battery’s datasheet. The 50%, 80% and 90% options are common reference points, not recommendations.

With nothing ticked the calculator shows zero and asks you to tick an appliance. At 2 peak sun hours the panel count roughly doubles compared with 4 hours.