How do you size a PM-LV rack battery bank for a given daily home load?

Direct answer: Start from the daily energy of the loads you want backed up, divide by the usable share and inverter efficiency, then check that the modules’ combined current covers your peak power. Example: 9 kWh per day needs about 12 kWh of nominal battery under the stated assumptions, so two 5.12 kWh modules fall short and three give margin.

Gather three numbers: daily energy (kWh) of the loads you want backed up, peak power (kW) when several run together, and days of autonomy if the grid or solar fails. Take the figures from bills or a plug-in meter, and list essentials only, such as refrigeration, lighting, internet and a heating pump.

Know the modules. The PM-LV51100-3U is listed at 51.2V, 100Ah, 5.12 kWh, 42 kg and 420 × 440 × 136 mm. The PM-LV51200-5U is 10.24 kWh, about 77 kg and 570 × 440 × 222 mm. The PowerAll page lists 5.37 kWh per battery unit and up to six units (32.25 kWh). The rack pages give different maximum parallel counts (64 for the 3U page, 16–32 for the 5U pages), so check the number against your inverter.

The arithmetic: nominal kWh needed = daily kWh ÷ (usable share × inverter efficiency). Example, using assumptions rather than Redway data: 9 ÷ (0.80 × 0.92) is about 12.2 kWh. Two PM-LV51100-3U modules give 10.24 kWh, which is short. Three give 15.36 kWh, which leaves margin for ageing and a cloudy day. The pages quote cycle life at 80% DOD, but the usable window depends on the BMS and inverter settings, so confirm it with Redway.

Then check power. Each module lists 100A maximum continuous charge and discharge, about 5.1 kW at 51.2V nominal. Modules in parallel add capacity and current capability, but the real limit is the inverter and the wiring. Add up starting surges too: pumps and compressors can draw several times their running power for a moment. Verify the inverter’s surge rating against your list.

Finally, plan for growth and verification. Leave space to add modules, and read our post on paralleling PM-LV rack batteries of mixed age before mixing old and new units. After commissioning, run a capacity test and record it as your baseline. Solar recharge capacity is a separate calculation and is not covered here.