If an outage stops production, spoils stock or breaks a series of measurements, you need backup power. The traditional answer is a diesel generator: proven, and able to run for days on fuel. But it takes time to start, needs fuel and test runs, and stands idle almost all year. Battery storage changes that trade-off.
Guide · Backup power
Battery storage or diesel generator: choosing backup power
Generators have been the default for decades. For many sites, a battery now does the job better and keeps earning between outages.
How fast the backup takes over
A standby generator typically needs several seconds to start and take the load. Without a separate UPS to bridge the gap, your equipment sees an interruption.
A battery system with fast switchover takes over in milliseconds. The SolisStorage EverCore system at the research station of the National Forest Centre in Gabčíkovo switches to backup in under 10 milliseconds, according to the manufacturer’s specifications, so the instruments keep running through a grid failure.
How long it lasts
A generator runs as long as there is fuel. A battery runs as long as its stored energy lasts: divide the usable capacity by the load. A 1,305 kWh system can carry a 50 kW load for around 20 hours or more, before conversion losses.
For outages measured in days, combine the battery with solar, which recharges it during the day, or keep a generator for the rare long outage.
What it costs to keep it ready
A generator needs fuel management, regular test runs under load and engine servicing, and stored diesel ages. A battery needs no fuel and no test runs. It does need monitoring, firmware updates and periodic inspection, but far less hands-on work.
A generator also burns fuel next to your building, with noise and exhaust. A battery is silent and has no local emissions. Both need the right location and a proper fire safety design.
Side by side
Diesel generator
- Several seconds to start and take the load
- Runs as long as there is fuel
- Fuel deliveries, test runs and engine servicing
- Noise and exhaust on site
- Idle between outages
Battery storage
- Switchover in milliseconds
- Runs as long as the stored energy lasts
- No fuel, no test runs
- Silent, no local emissions
- Works every day: solar storage, peak shaving, cheap-hour charging
The real difference: the other 364 days
A generator earns its keep only during an outage. A battery can work every day: storing solar surplus, cutting demand peaks, or charging when electricity is cheap and discharging when it is expensive.
You decide how much capacity to hold in reserve for outages, and the rest works for savings. That daily value is often what makes the investment pay back.
When to keep the generator
If outages can last for days, or the backup load is very large compared with the energy you can store, a combination makes sense. The battery takes over instantly and covers most outages, and the generator starts only for the long ones. It runs less, uses less fuel and lasts longer.
To size battery backup, start from the loads that must stay on and the runtime you need. Our guide on how to size battery storage lists the data to prepare.
Questions we hear
For many loads, yes: a system that switches over in milliseconds covers what a UPS does, at site level. Sensitive IT equipment may still keep its own UPS. We check the switchover time against what your equipment tolerates.
The system shuts down in a controlled way when it reaches its minimum charge. With solar on site it can recharge during the day, and with a generator in the system, the generator takes over.
Only by the share you reserve. The reserve is a setting, not a separate battery: the rest of the capacity keeps working for savings every day.
It depends on the size, the location and local rules. We check what applies to your site and handle the paperwork.
Free backup assessment
Protect the equipment you cannot switch off
Tell us what has to stay powered and for how long. We size a backup system for your site and send you a configuration and a price.
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