Sum the system wattage — total watts = light + pump + fan. Pumps and fans often run 24 h/day, so their daily share rivals the lights.

Compute the daily energy: total watts × run hours ÷ 1000 = daily kWh. That single number is the whole load story.

Scale to the month (× 30) and bill it (× rate) for the monthly cost, then fold in the annual CO2 at 0.4 kg/kWh.

Size the battery from the daily draw against your depth of discharge: bank kWh = daily ÷ (DoD/100), then convert to amp-hours at the bus voltage.

Size the solar array so it recharges the daily draw inside peak sun hours after system losses: panels = daily kWh ÷ (sun hours × panel watts × (1 − loss/100)).

Size the inverter at 1.25x the continuous load so the draw sits at 80% of rating, and read the safety and cost bands from the load and the bill.