Hybrid generator + battery systems

What changes when you add a battery

A site generator is chosen for the largest demand it will ever see. Most of the time the demand is far lower, and a diesel engine at low load is at its least efficient: it burns fuel to keep itself turning, and long light running is hard on the engine.

Put a battery between the generator and the site and the roles change:

• The battery supplies the site continuously. It meets peaks from stored energy and carries low-load periods on its own.
• The generator runs in blocks. When the battery needs charging, or when demand is heavy, the generator starts, runs at a useful load, and stops again.

The site sees an uninterrupted supply. The engine sees fewer hours and a steadier load.

How charging works

While the generator runs, its output is shared between the site’s loads and charging the battery. The unit’s maximum charging input, 205 kW for the Ampd 200 and 410 kW for the Ampd 400, is the most it can accept. What it actually receives depends on the generator’s spare capacity at that moment.

So charging time is not a fixed figure. It depends on the generator size, the site load while charging, and how far the battery was discharged. The guide to charging a construction site battery works through the factors.

Controls: who starts the generator

For a hybrid system to work unattended, the battery system has to be able to start and stop the generator. The Ampd brochures describe an integrated microgrid controller and list compatibility with ComAp or DeepSea generator controllers.

Three points follow from the manufacturer’s data:

• The listed supported configuration is one battery unit with one generator. Other arrangements are not established by the brochure and need engineering review.
• The recommended maximum generator capacity is 350 kVA for the Ampd 200 and 650 kVA for the Ampd 400. These are upper limits, not required sizes and not a default recommendation.
• No minimum generator size is stated. The right generator is the one that covers the site’s energy across the day with sensible running hours.

Send the generator’s make, model and controller. Compatibility and the control arrangement are confirmed in the technical review.

What decides generator runtime

How many hours the engine runs in a day comes down to four things.

Factor	Effect on generator runtime
Average site load	Higher average means more energy to replace, so more running
Generator size	A larger generator charges faster, up to the unit’s input limit
Battery capacity in use	More usable energy means longer gaps between runs
Required quiet periods	The battery must be full enough before each one starts

The energy has to balance. If the site uses a given number of kWh in a day, the generator must produce at least that much, plus losses, while it runs. A battery changes when and how efficiently the engine produces that energy. It does not reduce the energy the site needs.

Savings: fuel is one line, not the answer

Fewer running hours at a better load normally means less fuel. Whether it means lower cost is a wider calculation:

• battery hire or ownership cost;
• any change in generator hire, if a smaller set is used;
• fuel, at the generator’s real consumption for its real load;
• delivery, lifting, installation and commissioning;
• maintenance and servicing visits.

On a long project with a badly under-loaded generator, the saving can be clear. On a short hire, one-off costs can outweigh it. The cost comparison lets you test this with your own figures, and shows the result when it is unfavourable.

When a hybrid system is a good fit

• The generator spends most of its hours well below its rating.
• The load has short peaks, such as cranes, hoists or large motors.
• There are hours when the engine must not run.
• The project is long enough to recover delivery and set-up costs.

It is a weaker fit when the load is high and steady, so the generator is already well loaded, or when the hire is only a few weeks.

What to send

• Generator make, model, rating and controller.
• Fuel use, if it is recorded, and the period it covers.
• The main loads and working hours.
• Any quiet periods.
• Project duration.

Start a site power assessment with what you have. A generator rating alone is a workable starting point.

Product figures on this page: Ampd 200 Brochure IEC Rev 1.3, dated 29 April 2026; Ampd 400 Brochure IEC Rev 1.3, dated 29 April 2026. Manufacturer-published, not independently tested.