A little planning.
A lot more confidence.

Use actual running hours for cycling equipment. Add individual appliance results to build a daily load budget.

Nameplate storage estimate. Add inverter idle use and other losses to your loads; also check battery power and surge limits.

Steady-load estimate without solar charging. Available capacity means energy you can discharge now, after your reserve. Include inverter idle use in the load estimate.

Example assumptions, not a site forecast. Enter seasonal peak sun hours; check PVWatts for a more detailed production model.

Energy-balance estimate. It excludes extra recovery capacity after cloudy weather and does not check inverter or controller limits.

Use the roof’s horizontal footprint, not its sloped surface. Result covers the rainfall period you enter and is before tank overflow. Allow for first flush and collection losses.

For a straight-sided vertical cylindrical tank. Enter water depth for current volume or usable fill depth for capacity. Freeboard and dead storage reduce usable water.

No-rain reserve estimate at a constant daily usage. Exclude water below the pump intake from usable volume.

Use flow at your operating head, not unrestricted flow. This estimates running energy, not motor-start surge or required inverter size.

Nominal stored energy before usable-capacity limits and losses. Use the battery’s stated nominal voltage.

For an open tank pumping uphill to an outlet. Include the lowest expected water level. Enter friction losses from a pipe-loss calculation at your design flow; horizontal distance is not vertical lift. Pressurized source systems need a separate calculation.

Planning estimate using combined pump and motor efficiency. Confirm the manufacturer’s curve and rated electrical input at your operating point. Motor startup, inverter surge and suction limits are not calculated.

Rainfall depth required before household consumption during the storm. Collection efficiency includes roof and first-flush losses. This is not a rainfall forecast.

Collection minus consumption for the entered month, before tank overflow. A positive balance does not prove adequate storage: dry spells and storm timing still matter.