A 5 kW solar system describes the maximum rated output of the PV array under standard conditions. It does not determine battery size by itself. Battery capacity should be based on surplus solar energy, evening consumption, backup loads and the inverter.
Use electricity consumption as the starting point
Review several recent days of consumption. Separate daytime use from the energy used after sunset. If the aim is solar self-consumption, the battery should store the surplus that would otherwise be exported and supply the evening load.
For example, if a home exports about 8 kWh on a typical sunny day and uses 7 kWh after sunset, a 10 kWh nominal battery may be a reasonable starting point after allowing for reserve and conversion losses.
Estimate backup energy
List the appliances that must remain on during an outage. Add their average running power and multiply by the required hours.
Backup energy at the loads = average load in kW × hours.
| Average essential load | Required time | AC energy required |
|---|---|---|
| 0.8 kW | 6 h | 4.8 kWh |
| 1.5 kW | 6 h | 9 kWh |
| 2 kW | 8 h | 16 kWh |
The nominal battery must be larger than the AC energy requirement because of reserve, inverter losses, temperature and battery condition.
Compare common battery sizes
- 5.12 kWh: short essential-load backup or modest evening use.
- 10.24 kWh: more evening solar use and longer backup for selected circuits.
- 15–16 kWh: higher overnight consumption or longer backup.
- 20.48 kWh: larger homes, longer autonomy or selected off-grid systems.
See the Graspmart home battery comparison.
Check charging power and winter solar
A 5 kW array will rarely produce 5 kW continuously. Weather, orientation, shading, season and system losses affect daily generation. Use the lowest relevant solar season for off-grid or resilience planning. Also check whether the inverter can recharge the battery within the available solar window.
Check power separately
Battery kWh determines runtime; inverter kW and battery current determine the supported load. Refrigerators, pumps and air conditioners may draw high starting current. Provide running and starting power when asking for a system recommendation.
Information to send Graspmart
- Country and typical daily solar generation
- Daily and overnight electricity consumption
- Essential loads and required backup time
- Exact inverter brand and model
- Battery quantity and installation location
