This large-scale battery storage system, the first to be installed at a large PV farm, is set to put the solar park’s operator on a equal footing with conventional power plants. The lead-acid batteries installed at the part are designed to provide primary operating reserve to the high-voltage transmission network.
Bernhard Beck is one step closer to his goal. "Were now on an equal footing with conventional power plant operators," says Belectric’s founder and general director at the official ribbon-cutting ceremony for the so-called Energy Buffer Unit at the Alt Daber solar power plant.
The battery storage system makes it possible for the plant to feed primary operating reserve power into the 110 kV high-voltage distribution network to which the solar power plant is connected. That is an exception, as most solar power plants are connected to either medium-voltage or low-voltage networks.
"You’re always hearing the claim that solar power plants can’t do this. Now we’re proving that opposite is true," said Beck. Vattenfall, which was also present at the ribbon cutting, markets the operating reserve power.
Beck sees this as PV’s contribution to the energy economy and also as justification for the rapid expansion of solar power. The project fits nicely into Beck’s portfolio; in the past he has equipped solar power plants with systems that were capable of providing reactive power to the network: not only during the day but at night as well. Within a matter of seconds, primary operating reserve energy compensates for rapid fluctuations in electricity supply and demand, ensuring stable voltage and frequency within the network.
The primary operating reserve power is billed separately from power traded on the electricity exchange and is paid for out of network operation fees (see the energy market glossary from Energy Brainpool, pv magazine September 2014).
In other words, the new storage system is not intended to provide solar power generated during the day, at night.
Premium reserve power from batteries
Beck emphasizes that the battery storage system can not only provide operating reserve power but, with its reaction time of less than a second, it can do so faster than conventional power plants, which until now have been solely responsible for supplying the reserve.
This, said Beck, saves additional costs. "If you can react quickly to changes in frequency, you don’t have to hold as much operating power in reserve as you do with units that react more slowly," Beck explains, which is why he’s convinced that these battery storage systems already make good sense for the energy economy. This is particularly true as increasing numbers of renewable power plants are added to the grid, which will create more rapid fluctuations.
Although it makes sense in principle, under the current regulatory scheme the new storage system can only be operated profitably because it was partially subsidized. "For this system to be financially viable under these conditions, costs have to come down by about a third."
That may soon be the case, however. After all, Alt Daber was a pilot project in which Belectric "learned a great deal." Under the right conditions an inexpensive grid connection, for instance it may very well be possible to fund subsequent installations with market revenue alone. Alt Daber also takes advantage of the synergy effect that the storage system can tap into the high-voltage network.
Storage systems are currently at a regulatory disadvantage, though, as operators of pumped-storage power plants are often quick to point out. The operators of such plants are treated as consumers and thus have to pay fees and surcharges for the electrical energy they store. Then they have to pay the same costs again when the storage system is discharged.
Currently, an active discussion is going on among experts about how much primary operating reserve energy is needed and how it can be provided. Agora Energiewende studied a number of scenarios in an energy storage study aimed at analyzing when and how much storage capacity is necessary. The primary load-balancing energy market in the transmission network ignored them, however, because "it is such a small amount of energy (some 5 to 600 MW in Germany and 3 GW in Europe)."
With its Alt Daber project, Vattenfall is on board as the marketer of the operating reserve power. That should be seen as a strong indicator that transmission system operators see a market for operating reserve energy from battery storage systems.
Belectric is taking a different technical route than Wemag and Younicos, for instance, which opened a large lithium-ion battery storage system not directly connected to a solar or wind power plant for marketing primary operating reserve power.
Lead-acid battery with a high operational voltage
Unlike Wemag and Younicos, Belectric has opted for lead-acid batteries due to their lower overall cost. According to Beck, the project optimized other costs as well and selected a high operational voltage of 1500 V for the batteries, which to his knowledge are "the first-ever" with this voltage.
The high operational voltage requires less cabling and thus saves copper while reducing the number of inverters. Doubling the operational voltage reduces storage costs by around half, he said. The battery storage system has a feed-in capacity of 800 kW and a capacity of 948 kWh. The Alt Daber power plant has a capacity of 68 MW and was connected to the grid in 2011.
Belectric also sells the Energy Buffer Unit separately. It is supplied in a container weighing some 36 t and is being marketed both domestically and abroad.