Check your batteries' spec sheet for the depth of discharge the manufacturer allows, and have a qualified installer design the wiring and fuses.
How the bank is sized
- Energy to store: watt-hours you use per day × days of autonomy, the days the bank must cover without sun.
- Bank capacity: that energy ÷ (system voltage × usable depth of discharge × inverter efficiency).
- Batteries in series: system voltage ÷ the voltage of each battery. Series raises the voltage.
- Strings in parallel: bank capacity ÷ the amp-hours of each battery, rounded up. Parallel raises the amp-hours.
Depth of discharge
The usable depth of discharge is the share of the battery's capacity you plan to use. Lithium batteries usually allow a deeper discharge than lead-acid batteries, which last longer when they are not drained deeply. Use the figure from your batteries' spec sheet.
Why a higher voltage
For the same power, a 48 V system carries a quarter of the current of a 12 V system, so it can use thinner wire and loses less energy in it.
To find how many watt-hours you use, add each device's watts × hours per day. For a home battery that backs up the grid, use the home battery backup calculator.