The factor we publish ourselves
0.82 € against 0.20 € per kilowatt hour — a factor of 4.2. That figure sits in the calculator on our homepage, and anyone can retrace it. It is just not a law of nature; it is the result of six assumptions. Change one and the factor changes.
The six assumptions, disclosed
- Load: 70 % of rated output
- Operating time: 6 hours per day
- Diesel price: 2.26 €/l — ADAC, October 2026 monthly average (2.261 €/l)
- Consumption: 0.30 l per kWh
- Maintenance: around 0.24 € per operating hour
- Electricity price: 0.172 €/kWh
The arithmetic closes: 0.30 l/kWh × 2.26 €/l = 0.68 €/kWh for fuel. At 70 % load over six hours, 0.24 €/h maintenance spreads over 10.5 kWh — roughly 0.14 €/kWh. Together 0.82 €/kWh. From the grid: 0.172 € divided by a 0.86 charging efficiency, so around 0.20 €/kWh.
Per day that is 10.5 kWh and a 6.51 € difference. Over 21 working days a month, 137 €; over a year, 1,640 €.
Where the factor breaks
Part load makes diesel more expensive, not cheaper. Small generators need more litres per kilowatt hour at low load — the factor then climbs above 4.2.
Two costs are deliberately missing: CO₂ costs under the German BEHG are not included in the diesel price, and charging effort plus transport are not counted. The first shifts in favour of the battery, the second in favour of the generator. Naming both is the only way to keep the number usable.
The case that matters
A rental fleet runs the generator two hours a week instead of six hours a day. What was 126 operating hours a month becomes 8.7. The saving shrinks in the same proportion: instead of 1,640 € a year, around 113 € remain.
At that usage profile the battery does not pay for itself through running costs. It pays through what the diesel costs on top: fuel logistics, cold starts in frost, exhaust indoors, noise restrictions. Anyone who does not put a number on those items compares only half the picture.
How to run it for your own case
Daily energy first, then the comparison. Load times runtime, plus headroom for inrush currents. Peak power alone says nothing about cost.
Payback is a division: the price difference between the two purchases divided by the saving per day. At 6.51 € per day and a 3,000 € difference, that is around 460 working days.
Every assumption can be overwritten in the calculator — Diesel or battery: cost per kWh. Anyone computing with their own figures gets a number they can defend.
HITAMA is the industrial mobile energy storage brand of Shenzhen Yusong Technology.