Hybrid plant energy balance
The key idea
At every time step, power entering a common bus must have a destination. Storage moves energy between steps; it does not remove the need to balance each step.
Read one hour before the whole year
Solar can serve demand directly. Surplus can charge a battery if the converter and battery state allow it. When solar is insufficient, storage or a backup generator can supply the difference. If the available sources cannot meet demand, the result is unmet demand.
Unused available generation is different: curtailment means that some potential output was not used. A design can have midday curtailment and an evening shortage on the same day.
Follow the power
The explorer has a morning and daytime load, a larger evening demand, solar, storage and a 12 kW backup generator. Change PV and battery sizes. Use the hour control to inspect the individual flows at noon and during the evening peak.
- Demand
- 186 kWh
- Unmet energy
- 2.6 kWh
- Curtailed solar
- 32.3 kWh
- Demand
- Available solar
- Backup generator
Read the exact values
| Time / step | Demand | Available solar | Backup generator |
|---|---|---|---|
| 00:00 | 4.00 | 0.00 | 0.20 |
| 01:00 | 4.00 | 0.00 | 4.00 |
| 02:00 | 4.00 | 0.00 | 4.00 |
| 03:00 | 4.00 | 0.00 | 4.00 |
| 04:00 | 4.00 | 0.00 | 4.00 |
| 05:00 | 4.00 | 0.00 | 4.00 |
| 06:00 | 4.00 | 0.00 | 4.00 |
| 07:00 | 8.00 | 5.04 | 2.96 |
| 08:00 | 8.00 | 9.75 | 0.00 |
| 09:00 | 8.00 | 13.78 | 0.00 |
| 10:00 | 8.00 | 16.88 | 0.00 |
| 11:00 | 8.00 | 18.83 | 0.00 |
| 12:00 | 8.00 | 19.49 | 0.00 |
| 13:00 | 8.00 | 18.83 | 0.00 |
| 14:00 | 8.00 | 16.88 | 0.00 |
| 15:00 | 8.00 | 13.78 | 0.00 |
| 16:00 | 8.00 | 9.75 | 0.00 |
| 17:00 | 14.00 | 5.04 | 0.00 |
| 18:00 | 14.00 | 0.00 | 4.00 |
| 19:00 | 14.00 | 0.00 | 4.00 |
| 20:00 | 14.00 | 0.00 | 12.00 |
| 21:00 | 14.00 | 0.00 | 12.00 |
| 22:00 | 4.00 | 0.00 | 4.00 |
| 23:00 | 4.00 | 0.00 | 4.00 |
At 18:00 · common AC bus
- solar
- 0.00 kW
- generator
- 4.00 kW
- battery discharge
- 10.00 kW
equals
- served load
- 14.00 kW
- battery charge
- 0.00 kW
- curtailed
- 0.00 kW
Unmet demand: 0.00 kWStored at hour end: 16.05 kWh
Model note · Constructed 24-hour AC-bus example with 12 kW backup, 10 kW battery converter and 95% one-way storage efficiency. Battery begins at 20% SoC; end SoC may differ. This is not a cyclic or annual performance result.
More solar cannot directly serve a load after sunset. More battery energy can help only when charging energy is available and the power limit is sufficient. A larger plant component may therefore shift the limiting condition to another component.
Account for the battery's beginning and end
The example starts at 20% SoC. Energy already in the battery is an initial condition. If the battery ends the day with less stored energy, some delivered power came from that initial store. If it ends with more, the plant has retained energy for later use.
This is why a single-day fuel result is incomplete without its starting and ending SoC. A full study must make its initial condition and simulation horizon explicit.
The math, if you want itOptional — the page reads completely without it
At the AC bus, every hour, what flows in must flow out. With no grid connection:
power balance at the common bus
Psolar + Pgen + Pdischarge = Pserved + Pcharge + Pcurtailed
demand splits into served and unmet
Pdemand = Pserved + Punmet
Psolar is the available solar, including the part later curtailed. If you use dispatched solar instead, drop the curtailment term. State which quantity a chart shows.
the battery keeps its own ledger
ΔEstored = Echarged − Edischarged − Elosses
Battery losses belong in the state equation. Counting them again at the bus would break conservation; the model checks both identities every hour. It omits network losses, voltage limits, reactive power and transients, so an energy-balanced plant still needs its electrical checks.
See it in Phasor
Simulate a saved design version and inspect demand, component outputs, storage state and unmet energy together. Use the dispatch view to examine the hours that explain the annual result.
Continue the design path
Learn how dispatch strategy changes generator operation. When you connect the plant to a feeder, use power-flow basics to check quantities that this energy model does not solve.