Batteries
Data used by the engine
| Data | Use |
|---|---|
| Nominal and usable capacity (kWh) | The usable capacity already includes the depth of discharge: it is not deducted again |
| Maximum DoD | Informative |
| Technology | Report |
| Nominal voltage | Maximum charge and discharge power |
| Maximum charge and discharge currents | Maximum power = voltage × current |
| Round-trip efficiency | Charge and discharge losses |
| Cycle life | Report and replacement |
| Price, warranty | Economics and report |
Efficiency
The round-trip efficiency is split equally: charging efficiency = discharging efficiency = √(round-trip efficiency). For example, with 94 % round trip, each direction is 97 %.
Battery bank
You can use several identical units in parallel: they behave like a single battery with capacity and currents multiplied by the number of units (same voltage and efficiency). In automatic sizing the engine tries from 1 up to a configurable maximum number of batteries (4 by default).
Backup during grid outages
Reserves a minimum amount of energy that the battery does not use day to day, to supply the critical loads for a few hours during a power cut:
- Backup hours × critical load power (kW), without exceeding the usable capacity.
- The reserve is refilled with solar surplus, never from the grid.
- With 0 hours there is no reserve.
State of charge
The simulation starts from an initial state of charge (by default, 50 % of the usable capacity). With a battery, the balance repeats the year until the final state of charge equals the initial one (steady state), so the result does not depend on the starting hour.
Management strategies
There are two today: self-consumption (charges only with solar surplus, discharges only with a deficit, never charges from the grid) and backup (self-consumption with a reserve). See Balance and battery.
Replacement
The economic analysis includes the battery replacement (year 12 and 60 % of the cost by default). See Financial assumptions.