Diesel dispatch strategies
The key idea
Dispatch is the rule that decides which source supplies power and when storage charges. The same equipment can produce different fuel use and battery behaviour under different rules.
Two ways to use the generator
Under load following, the generator supplies the demand left after other available sources. It does not deliberately produce extra energy just to charge the battery in this teaching example.
Under cycle charging, a running generator can produce more than the immediate residual demand. The surplus charges storage for later use, subject to the charge-power and SoC limits.
Neither rule always uses less fuel. The result depends on the generator's fuel curve, demand pattern, solar resource, storage losses and control settings.
Compare the same plant
Switch strategy without changing the plant sizes. Inspect generator output, charging and stored energy. Then change battery capacity and compare again.
- Generator fuel
- 30.4 L
- Running hours
- 14 h
- End stored energy
- 4.0 kWh
- Demand
- Generator output
- Battery charge
Read the exact values
| Time / step | Demand | Generator output | Battery charge |
|---|---|---|---|
| 00:00 | 4.00 | 0.20 | 0.00 |
| 01:00 | 4.00 | 4.00 | 0.00 |
| 02:00 | 4.00 | 4.00 | 0.00 |
| 03:00 | 4.00 | 4.00 | 0.00 |
| 04:00 | 4.00 | 4.00 | 0.00 |
| 05:00 | 4.00 | 4.00 | 0.00 |
| 06:00 | 4.00 | 4.00 | 0.00 |
| 07:00 | 8.00 | 3.80 | 0.00 |
| 08:00 | 8.00 | 0.00 | 0.12 |
| 09:00 | 8.00 | 0.00 | 3.49 |
| 10:00 | 8.00 | 0.00 | 6.07 |
| 11:00 | 8.00 | 0.00 | 7.69 |
| 12:00 | 8.00 | 0.00 | 8.24 |
| 13:00 | 8.00 | 0.00 | 7.69 |
| 14:00 | 8.00 | 0.00 | 0.39 |
| 15:00 | 8.00 | 0.00 | 0.00 |
| 16:00 | 8.00 | 0.00 | 0.00 |
| 17:00 | 14.00 | 0.00 | 0.00 |
| 18:00 | 14.00 | 4.00 | 0.00 |
| 19:00 | 14.00 | 4.00 | 0.00 |
| 20:00 | 14.00 | 12.00 | 0.00 |
| 21:00 | 14.00 | 12.00 | 0.00 |
| 22:00 | 4.00 | 4.00 | 0.00 |
| 23:00 | 4.00 | 4.00 | 0.00 |
- Stored energy at hour end
Read the exact values
| Time / step | Stored energy at hour end |
|---|---|
| 00:00 | 4.00 |
| 01:00 | 4.00 |
| 02:00 | 4.00 |
| 03:00 | 4.00 |
| 04:00 | 4.00 |
| 05:00 | 4.00 |
| 06:00 | 4.00 |
| 07:00 | 4.00 |
| 08:00 | 4.12 |
| 09:00 | 7.43 |
| 10:00 | 13.19 |
| 11:00 | 20.50 |
| 12:00 | 28.33 |
| 13:00 | 35.63 |
| 14:00 | 36.00 |
| 15:00 | 36.00 |
| 16:00 | 36.00 |
| 17:00 | 25.69 |
| 18:00 | 15.16 |
| 19:00 | 4.64 |
| 20:00 | 4.00 |
| 21:00 | 4.00 |
| 22:00 | 4.00 |
| 23:00 | 4.00 |
Compare fuel together with end-of-day stored energy. A strategy that finishes with more charge has also supplied energy for later use.
Model note · Teaching dispatch, not an engine run: 20 kW DC solar, 12 kW generator, 10 kW battery converter. Generator starts when storage cannot cover residual demand. Cycle charging targets at least 80% generator loading. Assumed fuel = 0.08 × rated kW + 0.25 × generated kW litres/hour while running. No enforced generator minimum-load constraint, minimum run time or start fuel.
A fuel curve can include consumption associated with keeping the engine running as well as consumption related to output. Under such a curve, low generator loading has a higher fuel consumption per generated kWh. Charging storage at higher loading can reduce that penalty, but the stored energy incurs conversion losses and may not be needed later.
Read fuel with the final state
Do not compare only the fuel total. A run that finishes with more battery energy has performed additional work that may benefit the next day. This example shows end-of-day stored energy for that reason.
The charging rule below is deliberately simple. It does not include every start condition, charging setpoint, generator minimum-load constraint, minimum run time, maintenance effect or reserve policy used by a real controller or the production Phasor engine.
The math, if you want itOptional — the page reads completely without it
The assumed fuel curve has a term for keeping the engine turning and a term for the energy it produces, in litres per hour while it runs:
the teaching fuel curve
F = 0.08 · Prated + 0.25 · Pgen
The coefficients carry units of L/(rated kW·h) and L/kWh. They are illustrative, not manufacturer values. For the 12 kW generator:
specific consumption at 4 kW
FPgen = 0.96 + 1.004 = 0.49 L/kWh at 4 kW
and at 9.6 kW
0.96 + 2.409.6 = 0.35 L/kWh at 9.6 kW
Low loading costs more fuel per kilowatt-hour, which is the case for cycle charging. Storage losses and whether the stored energy is needed later decide whether it pays.
The toy controller starts the generator when solar and available battery output cannot meet demand. In cycle-charging mode it then targets at least 80% loading, bounded by the rating. The full simulator has its own strategy definitions; these thresholds are not product defaults.
See it in Phasor
Run saved versions with the intended dispatch settings. Compare fuel, generator operation, storage state and unmet energy. Keep the same demand and resource inputs when testing the strategy itself.
Continue the design path
Turn operating quantities into a cost comparison in plant cost and LCOE. Revisit the energy balance to check where generator charging appears.