In short. Battery storage can cut generator run hours by carrying short outages and light loads, and by letting the generator run only at efficient loading. This reduces emissions and fuel use, but needs careful control, sizing and protection design.
How it reduces emissions
- Short outages ride on the battery; the generator never starts.
- Light loads run on the battery instead of a lightly loaded diesel.
- When the generator runs, it runs near an efficient load and charges the battery.
- Peak demand is shaved, so smaller or fewer sets are needed.
Architecture
Utility + generator + BESS with converter and supervisory controller → critical loads. See utility, DG, UPS and BESS.
| Design item | Question |
|---|---|
| Energy size | How long should the battery carry load? |
| Power size | Can it handle the largest step? |
| Control | When does the generator start and stop? |
| Protection | Converter fault contribution and coordination. See coordination |
| Safety | Battery siting and fire protection |
Sizing logic
Battery energy (kWh) ≈ load (kW) × bridging time (h) ÷ usable depth and efficiency
Include ageing and temperature. See system studies.
Limits
Batteries cover minutes to hours, not multi-day outages. Charging from a generator adds load; limit it. Rules on emissions treatment should be checked.
Illustrative example
A building with frequent 10-minute outages adds storage sized for 15 minutes. The generator starts only for longer events, so its annual run hours fall sharply.
Sizing the battery for run-hour reduction
Start with a load profile. For each hour of the day, note the load. Identify two things: how often outages occur and how long they last, and how much of the generator’s running time is at light load.
- For ride-through: energy = critical load (kW) × outage duration (h) ÷ usable efficiency.
- For light-load support: size so that the battery carries the base load for the periods in question.
- For power: the converter must handle the largest step of load it will see.
Include allowances for ageing, temperature and reserve. Take quotations only on the basis of measured profiles.
Control logic example
| Condition | Action |
|---|---|
| Utility fails, battery above reserve | Battery carries load; generator on standby |
| Battery falls to a start threshold | Generator starts and takes over |
| Generator running above efficient load | Surplus charges the battery within limits |
| Utility returns and stable | Return to utility; recharge |
Where emission reduction comes from
- Fewer start-ups, which are high-emission events for cold engines.
- Elimination of light-load running, which is inefficient and fouls engines.
- Shorter total run hours.
Quantify using your own logs. Report hours and fuel before and after.
Protection and safety
Converters limit fault current, so protection coordination must be checked. Battery rooms need ventilation, detection and fire protection suited to the chemistry. See coordination.
Financial view
Savings come from fuel, reduced engine wear and possibly tariff benefits. Costs include the battery, converter, controls and installation. Compare with the cost of the alternative, such as a new generator. Treat battery replacement as a future cost.
Limits to remember
Storage does not replace a generator for long outages. Plan for both.
The master engineering question
Which outages and light loads can the battery take over so the generator runs less and better?
What to send us
Send outage history and load profile. Send your application details.
Questions engineers ask
Does BESS replace the generator?
For long outages, no.
Is it cost-effective?
Depends on outage pattern and tariffs.
What about fire safety?
Design siting and protection per codes.
Can it help with restrictions?
Yes, for short events.
General guidance only. Values illustrative.