ABB solution connects large rooftop solar power system to MV network

ABB solution connects large rooftop solar power system to MV network

South Hesse is home to one of the largest rooftop photovoltaic (PV) systems in Germany. A solar power system on top of a logistics warehouse in Dieburg is the first rooftop system to receive the highly sought-after funding of the Federal Network Agency. ABB plays a relevant role by connecting the solar system to the medium-voltage network.

The blue sparkle can be seen from afar: The roof of the freight forwarding company Fiege in Dieburg, Hesse, shimmers like a gigantic sapphire. This PV roof system has been in operation since the beginning of 2019 and has an output of no less than 6.4 MWp. The engineering service provider MaxSolar installed 20,365 Q.Peak Duo-G5 modules, each with a capacity of 315 watts. It is the largest of its kind in Hesse, a German federal state with a population of 6 million, and one of the five largest in the whole of Germany. The system feeds most of the energy generated into the grid through ABB technology, helping prevent 3,193 tons of CO2 emissions every year.

Connection to the medium-voltage network

Three transformer stations, each with an output of 2,000 kVA, connect the solar system to the medium-voltage network. UniPack-G is a compact secondary substation (CSS) made of glass fiber reinforced polyester (GRP). The modular design offers the perfect layout for all equipment and application requirements. The particularly robust and weatherproof solution, ideal for harsh environments, has been designed for a lifetime of more than 30 years. ABB’s SafePlus medium-voltage switchgear, REF 615 protection relays and the Emax-2 low-voltage circuit breakers complete the all-round solution.

Ground-mounted systems advantage

Since January 1, 2017, all solar systems in Germany with an output of more than 750 kWp, not used for self-supply, must participate in the tenders of the Federal Network Agency (BNetzA). The aim is that only the most economical projects are supported with funds from the Renewable Energy Sources Act (EEG). Due to their design, roof systems have significant disadvantages compared to ground-mounted systems since they have additional requirements – for example, fire and lightning protection or static requirements. For this reason, ground-mounted systems have always been given preferential funding treatment.

Competitive concept

MaxSolar has shown that roofs can also accommodate competitive solar power systems – but only if the conditions are right. MaxSolar Managing Director, Christoph Strasser, emphasizes this: "At present, a coherent framework must be in place in the large-scale plant segment for such power systems to be implemented on a tailor-made basis. Standardization is only possible for an area of 30,000 square meters – but is definitely worthwhile."

Self-supply thanks to a clever trick

The electricity produced by BNetzA-funded systems must be fed into the grid. In order to be able to supply the logistic warehouse building with renewable energy itself, MaxSolar initially planned part of the system as an independent 750 kWp system. This arrangement of two systems at one site, entered separately in the BNetzA register, has now been accepted by the network operator. The only requirement is for the 750 kwp system to be commissioned before the tender system.

New concept developed for low-voltage main distribution

Lukas Didden, Product Marketing Manager Compact Secondary Substation at ABB, says: "The very short delivery time, the attractive price and the flexibility to meet the requirements were decisive factors for the customer."

Before this project, ABB had never built a low-voltage main distribution board with a busbar current above 2,500 A. "With 100 percent load on the transformer, we are talking about a low-voltage busbar current of almost 2,900A. This means that a completely new layout for low-voltage distribution had to be developed and engineered," explains Didden.

Success: The developed concept even works with currents of up to 3,200A. Since three infeed strips are measured separately, ABB also had to revise the busbar system so that current transformers could be mounted on the main busbars.

New material in transformer stations – light but robust for harsh environments

It's not just the technology that is interesting here, but also the design of the compact transformer stations themselves. ABB used the UniPack-G model for the first time in Germany; the "G" stands for glass fiber reinforced polyester (GRP). Even though the material is lighter, the GRP design has mechanical properties that are comparable with concrete and surpass those of steel stations. The concept is not susceptible to corrosion or cracking. The double wall design even exceeds the thermal properties of conventional housings.

"We are still in very close contact with the key people at MaxSolar," says Lukas Didden. "Since the Dieburg project, we have sold several additional stations to MaxSolar, seven of which have already been delivered and put into operation."

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