Turn essential loads and backup hours into a practical battery-energy target, then verify discharge power, inverter compatibility and expansion.
For each essential appliance, multiply running power in kilowatts by operating time in hours. Add the results to estimate required load energy in kilowatt-hours. Use realistic duty cycles for equipment that switches on and off.
A 1 kW essential load operating for 5 hours requires about 5 kWh of load energy before system losses and reserve margin.
kW is instantaneous power; kWh is energy used over time.
A practical starting formula is: nominal battery energy = required load energy ÷ usable depth of discharge ÷ overall discharge efficiency. Add reserve for temperature, ageing, unexpected loads and future expansion.
Use the value permitted by the selected battery and warranty conditions rather than assuming the full nameplate energy is available.
Allow for inverter conversion, cabling and battery losses.
A design margin reduces nuisance shutdowns and leaves room for normal variation.
The battery and BMS must also deliver the inverter's required current and the site's short-duration surge. Confirm continuous and peak discharge limits, parallel connection rules, cable sizing and protective devices.
Higher power at 48 or 51.2 V can require substantial DC current, so connections and protection are critical.
Commercial architectures use series battery modules and matched high-voltage controls; system compatibility must be verified.
Check nominal and operating voltage, charge and discharge current, CAN or RS485 communication, supported inverter protocols, maximum parallel quantity, installation environment and expansion method.
Compatible BMS communication supports coordinated charge limits, state of charge reporting and protection.
Confirm whether batteries may be added later and what age, state-of-charge or commissioning rules apply.
Runtime depends on the essential load and usable battery energy. A lower continuous load runs longer; inverter losses, battery limits and reserve capacity reduce the energy available to appliances.
Multiply the essential load energy over those 10 hours, then divide by the permitted usable depth of discharge and system efficiency. The answer cannot be determined from backup time alone.
Many low-voltage models support parallel expansion, but the maximum quantity, cable arrangement, protection, firmware and commissioning procedure must follow the manufacturer's instructions.
They are related but not equal. The PV array must cover daytime loads and provide enough surplus energy to recharge the battery under the expected solar conditions.
We will match the inverter, LiFePO4 battery and solar array for technical confirmation.
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