Help CenterPV Calculations
Energy balance - is the PV surplus enough for the night?
Once the PV array and batteries are sized, SolarDim Pro automatically checks whether the daytime PV surplus is sufficient to fully recharge the batteries before night. This check is separate from capacity sizing (Ah): it verifies the daily energy flow, not storage.
E_pv = kWp × PSH × η_system × 1000Energy produced by panels per day (Wh)
E_surplus = E_pv - E_daytime_loadEnergy available for battery recharge after feeding daytime loads
E_required_recharge = E_night_load ÷ η_round_tripEnergy to inject into batteries. Dividing by η_round_trip accounts for round-trip losses: to recover 100 Wh at night with LiFePO4 (η=0.92), you must inject 100÷0.92 = 108.7 Wh during the day.
Condition: E_surplus >= E_required_rechargeIf this condition holds, batteries fully recharge every day and the system can operate indefinitely.
| Technology | η round-trip | Inject to recover 1 kWh |
|---|---|---|
| LiFePO4 | 0.92 (92%) | 1 ÷ 0.92 = 1.087 kWh |
| AGM | 0.80 (80%) | 1 ÷ 0.80 = 1.250 kWh |
| Gel | 0.81 (81%) | 1 ÷ 0.81 = 1.235 kWh |
| Open lead | 0.75 (75%) | 1 ÷ 0.75 = 1.333 kWh |
The most dangerous case is a partial deficit: surplus is positive, but below E_required_recharge. The first day everything works, then batteries gradually discharge until the system stops.
Green banner
PV surplus exceeds the energy required for recharge. The margin shows how comfortable the system remains.
Orange banner
Surplus is positive but insufficient for a full recharge. SolarDim Pro shows how many kWp to add.
Red banner
PV production does not even cover daytime consumption. The PV array must be revised.
To improve the balance without adding panels: shift energy-intensive loads to solar hours. Each Wh consumed during the day reduces what must be stored.
Common mistakes
- Sizing batteries and PV separately without checking daily PV recharge is sufficient
- Forgetting round-trip efficiency and counting only DoD
- Ignoring an orange banner (partial deficit) because "it works on day one"