Frequent grid outages have made reliable backup power essential for many factories in Ukraine. Diesel generators can keep production running, but prolonged operation brings high fuel costs, inefficient low-load performance, frequent maintenance, and continuous noise.
To reduce the costs and improve the efficiency of the existing backup power system, the customers chose to add energy storage. SCU supplied several Ukrainian factories with BRES-1200-625 energy storage containers, each featuring 1.2 MWh battery capacity and 625 kW PCS power. By integrating BRES with existing solar PV and diesel generators, the factories built an AC-coupled solar energy storage diesel generator hybrid power system designed to reduce diesel use while maintaining uninterrupted power.
The role of energy storage is critical: instead of allowing the diesel generator to run whenever solar power is insufficient, BRES supplies low-load demand and allows the generator to operate only when necessary.
The Value of Adding Energy Storage
The economic impact can be significant. A diesel generator operating at low load typically consumes more fuel per unit of electricity than when operating closer to its optimal load range.
For example, if BRES replaces around 750 hours of low-load diesel operation per year, and the generator would otherwise consume approximately 40–45 liters of diesel per hour, annual fuel savings could reach 30,000–34,000 liters.
At an illustrative diesel price of €1.50/L, this is equivalent to approximately €45,000–€51,000 in annual fuel savings, excluding additional maintenance savings.
Reducing diesel consumption by this amount can also avoid approximately 81–91 tonnes of CO₂ emissions per year, based on about 2.69 kg of CO₂ per liter of diesel burned.
Lower generator runtime also means less wear. If energy storage reduces annual operating hours by around 30%, the time required to accumulate the same engine operating hours can increase substantially. In practical terms, a generator that would otherwise reach a major operating-hour milestone in about 10 years could take roughly 14 years under a reduced-runtime profile.
Noise is reduced as well. Large industrial diesel generators can typically produce around 79–90 dB(A) at 7 meters, depending on the enclosure and generator model. When BRES supplies the load and the generator is shut down, engine and exhaust noise are eliminated during those periods.
（These figures are representative engineering estimates rather than measured results from the individual SCU projects. Actual savings depend on load profile, generator efficiency, fuel price, PV generation, SOC settings, and annual operating hours.）
How the Hybrid System Works
The system uses a parallel, AC-coupled architecture, connecting solar PV, BRES, the diesel generator, and factory loads on the AC side.
Solar power is always prioritized. When PV generation exceeds the factory load, the surplus electricity charges BRES. When solar generation falls or the grid is unavailable, BRES supplies the load.
Battery SOC controls diesel generator operation. When SOC reaches the preset threshold A, the diesel generator starts. When SOC reaches the preset threshold B, the generator stops, and BRES continues supplying power together with available solar generation.
This control strategy prevents the diesel generator from running continuously at inefficient low loads. BRES handles fluctuations and low-load periods, while the generator operates only when additional power is required. At the same time, the PCS enables zero-millisecond, seamless switching between battery power and diesel generator power, helping prevent outages and voltage or power fluctuations during source transitions and ensuring a smooth, reliable power supply for factory loads.
Why Energy Storage Makes the Difference
Solar PV reduces fuel consumption during daylight hours, but its output is variable. Diesel generators provide reliable backup, but they are costly when used continuously or at low load. BRES connects the two more efficiently by storing excess solar energy, supporting the load when solar power is insufficient, and controlling when the diesel generator should start and stop.
This increases solar utilization while reducing diesel runtime, fuel consumption, maintenance, emissions, and noise. Instead of three independent power sources, the factory gains one coordinated hybrid energy system.
For Ukrainian factories facing frequent outages and high diesel costs, adding energy storage is not simply about increasing backup capacity. It is the key to making the entire solar diesel system operate more efficiently, economically, and reliably.