Energy balance and battery
The balance matches, hour by hour, the AC production with consumption and decides what is self-consumed, stored, exported and imported.
Algorithm (each hour)
- Direct self-consumption: min(production, consumption).
- What is left over is surplus; what is missing is deficit.
- Battery (if any): the strategy decides how much to charge with the surplus and how much to discharge to cover the deficit.
- The remaining surplus is exported, curtailed or lost, depending on the installation type.
- The remaining deficit is imported from the grid (off-grid it remains as uncovered deficit).
The balance works in AC (after the inverter). The economic compensation is not applied here, but in the economic analysis.
By installation type
| Type | Surplus | Deficit |
|---|---|---|
| With export | Exported (up to the export limit; the rest is curtailed) | Imported |
| Without export | Curtailed | Imported |
| Off-grid | Curtailed | Not covered (recorded) |
Battery strategies
Self-consumption
- Charges only with solar surplus.
- Discharges only when there is a consumption deficit.
- Does not charge from the grid.
It is the most common strategy in residential systems and maximises self-consumption.
Backup
Same as self-consumption, but the battery always keeps a reserve (backup hours × critical load power) for a grid outage. The reserve is refilled with solar surplus and is never used day to day.
Price-driven strategies
A strategy that charges from the grid during cheap hours (TOU) is planned but not yet available.
Physical limits
- Maximum charge and discharge power = nominal voltage × maximum current.
- Efficiency: charging and discharging with √(round-trip efficiency) each.
- Usable capacity (already includes the depth of discharge) and backup reserve.
- A bank of n identical batteries in parallel is equivalent to one battery with capacity and currents ×n.
State of charge
The simulation starts with the chosen initial state of charge (50 % by default) and repeats the year until the final state matches the initial one (steady state, up to 4 passes), so that the result does not depend on the start.
Balance results
| Quantity | Definition |
|---|---|
| Generation | AC production of the array |
| Consumption | Client's curve (plus special loads) |
| Self-consumption | Generated energy consumed by the client, directly or via the battery |
| Export | Energy fed into the grid |
| Curtailment | Energy not used (surplus that cannot be exported or stored) |
| Import | Energy bought from the grid |
| Self-consumption ratio | Self-consumption / generation |
| Self-sufficiency ratio | Self-consumption / consumption |
See Summary and balance.