How To Size A Home Battery Without Guessing

Battery sizing goes wrong when it starts from the wrong number. The array size tells you how much energy arrives; the inverter rating tells you how fast it can move. Neither tells you how much energy the household needs after dark, which is the only number the battery actually serves.

Start With Evening Consumption

Take a day of interval data and add up everything consumed between sunset and sunrise. That figure, not the daily total, is the minimum useful battery size. A household using 18 kWh a day might only need 8 of them after dark, in which case a 10 kWh pack covers the evening with margin.

Then Decide What The Battery Is For

1. Self-consumption: store the afternoon surplus and use it in the evening. Size to the evening load.
2. Tariff arbitrage: charge in the cheap window, discharge in the expensive one. Size to the expensive window's consumption.
3. Backup: carry critical loads through an outage. Size to critical load times the hours you want to survive.
4. Off-grid: carry the whole house overnight with a margin for bad weather. Size to daily consumption times the autonomy in days.

Match That To A Product

Leave The Expansion Path

Every one of these is 51.2V, so a bank grows by paralleling modules rather than replacing the system. The work to do at the first install is unglamorous: cable and breaker capacity sized for the final bank, and physical space left next to the first unit. Do that and phase two is an afternoon.

If interval data is not available, we will size from appliance ratings and run hours and tell you plainly that it is an estimate. An estimate with its assumptions written down is auditable; a confident number is not.

Do Not Forget The Inverter

The battery stores energy; the inverter decides how fast it can be delivered and whether it works during an outage. Send us the inverter brand and model with your enquiry so protocol compatibility is confirmed before the order rather than at commissioning.