The pumped-storage power plant in Erzhausen is situated in a forest setting between Hannover and Göttingen in Germany. After Statkraft took over operation in 2009, the plant generated steady earnings from supplying primary control reserve – until the grid operator changed this practice almost overnight. After 2014, it was no longer possible for Erzhausen to deliver only positive control reserve.
"This was a huge shock," says Maik Thalmann, then manager of the German hydropower plant group and today responsible for operating and maintaining Statkraft's power plants in Germany. He was put under pressure to find new business opportunities for Erzhausen.
"The change not only impacted a business model – after all, 30 people work in the power plant," he says.
Despite the sudden change in the grid operator's practices, Statkraft was already in the process of expanding its range of services at the pumped-storage power plant. The plant was prequalified to provide positive secondary control reserve, and the operating range was increased from the original 87 MW to 109 MW, which had a positive impact on earnings.
In addition to the delivery of secondary control reserve, the plant has also been prequalified for tertiary control reserve.
"The changes required a lot of the employees at the plant and their colleagues at the trading office in Düsseldorf. In connection with the prequalification, extensive reprogramming of the machinery was required to meet the terms the grid operator had set," says Thalmann.
"The trust and cooperation between Düsseldorf and Erzhausen has been essential for the excellent results we achieved," he emphasises.
The pumped-storage power plant in Erzhausen also has an important role to play as a backup in Statkraft's new investment in the large-scale lithium ion battery storage system in Dörverden. If this multi-megawatt battery is unable to deliver primary control reserve for technical reasons, Erzhausen can step in and carry out the control reserve services the company has committed to.
Importantly, the plant also interacts with Statkraft's virtual power plant in Germany, with over 8 700 MW of wind and solar power. Erzhausen's rapid pumping and production output can offset deviations in this electricity production and enable Statkraft to deliver the quantities of power it has sold, or to absorb overproduction. This will limit balancing costs.
The trust and cooperation between Düsseldorf and Erzhausen has been essential for the excellent results we achieved.
Flexibility and speed are the pumped-storage power plant's biggest advantages.
In just 90 seconds, the plant can switch from producing hydropower to pumping water back into the reservoir. While two machines at any time provide secondary control reserve, the other two provide tertiary control reserve to offset deviations in the virtual power plant and for daily sales in the spot market – unless they have to complement the first two machines.
This flexibility was one of the reasons why the expansion of the power plant's water storage capacity was approved.
Another reason was that the expansion gave savings in the plant's grid tariffs of EUR 1.6 million annually over the next 10 years.
Operating volume was increased by installing breakwaters on the dam in the upper reservoir, giving it about 10 per cent higher capacity. In the lower reservoir the overflow threshold was raised to accommodate the increased volume of water.
"We have invested EUR 4 million in the expansions," says Thalmann. "Through the annual savings in grid tariffs alone, we can recoup that investment within a few years. Not to mention the plant's increased flexibility! Now we have even more legs to stand on."
Text: Judith Tranninger
Photo: Dag Spant
The article has also been published in Statkraft's magazine People & Power no. 3/2016.
> POWER: 220MW
> NUMBER OF EMPLOYEES: 30
> COMMISSIONED: 1964
> STATKRAFT TOOK OVER OPERATION: 2009
> MORE LEGS TO STAND ON:
1. Prequalified for delivering secondary control reserve.
2. Prequalified for delivering tertiary control reserve.
3. Backup for primary control reserve of multi-megawatt battery.
4. Balancing of the virtual power plant.
In addition, Erzhausen can provide so-called black starts. A black start is the process of restoring an electric power station or a part of a power grid to operation without relying on the external transmission network
The term control reserve refers to power capacity that is instantly available to even out power production and consumption, and counteract unwanted voltage or frequency fluctuations in the power grid. Deliveries of control reserve are often defined by how fast and long the control reserve can be provided, namely primary, secondary and tertiary control reserve respectively.
06. Jan. 2017