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Energy storage: A different view from Germany

Germany leads the world in solar photovoltaic generation, so it would seem to follow that the country’s interest in energy storage would also be soaring. But when Ben Kaun, an expert storage specialist with the Electric Power Research Institute (EPRI), traveled to an international energy storage conference in Dusseldorf earlier this year, he found that storage is viewed somewhat differently there than in the U.S.

As Germans look to the future, Kaun notes that they have a broader definition of energy storage than in the United States. The U.S. definition of energy storage typically focuses on electric power in, electric power out – that is, electricity storage. In Germany’s definition is broader, characterized by three main categories: power to heat, power to gas (specifically hydrogen) and power to power, which can utilize a range of storage technologies, including electrochemical (batteries), mechanical or thermal.

In the first category, electric power is stored and converted to heat for direct use as heat in buildings, district heating or industrial processes. For power to gas, electricity is converted to hydrogen through an electrolysis process and then stored (with some challenges), combusted and used in fuel cell generators. It can also be further converted into natural gas or liquid transportation fuels. Power to power — or direct electricity storage — may be lagging, in part due to a historical lack of enthusiasm for electric cars in Germany when compared to the growing electric vehicle battery market in the U.S.

“German car manufacturers have emphasized hydrogen over batteries in the past,” Kaun said. “Several Germans even referred to a birthright to fill up instantly and drive as far as they want as fast as they want on the Autobahn. However, they all know about Tesla Motors, and the simple reference to Tesla’s activities seems to be an accepted rebuttal to assertions that electric cars will not happen.”

A second difference between the U.S. and Germany: when the Germans discuss “long-term storage,” they are talking about storing hydrogen for weeks, months, or longer. In the United States, we typically think of compressed air or pumped hydro storing energy for a few to tens of hours.

The German approach may be indicative of a longer-term vision for the role of storage in the energy sector, and the expectation of an electric sector that will be dominated by renewable energies in 2050 and beyond. In contrast, the emphasis of storage research in the U.S. is decidedly shorter.

Third, the Germans don’t emphasize the instantaneous grid-balancing advantages of storage as we do with utility-scale storage. The bulk power system of western Europe is well-connected, so flexible hydropower and generators historically have been readily available to provide those services.

Instead, the Germans envision using storage to capture excess generation from wind and solar production, as they encounter an increasing number of hours with negative energy prices and renewable curtailment. They are willing to sacrifice conversion efficiency to increase the overall return on their huge renewable investment.

"As Germany looks out to 2050, the expectation is that the penetration of renewables could be as large as 80 to 90 percent," Kaun said.

Coping with variability and the times when renewable production exceeds grid demand raises the perceived value of storing solar and wind in the form of hydrogen, a dispatchable resource.

"There is significant loss in conversion from solar to hydrogen," he said. "But it's viewed as being better than zero” if faced with curtailment.

Germany doesn’t have the large ramps in late afternoon and early evening demand that are an ongong concern for U.S. utilities, largely because Germans have very little air conditioning, he said.

"The concept of dealing with peaks is a foreign one in Germany," he said.

Still another point of difference, he said, is that Germany has only a nascent ancillary services market, whereas in some market-based operating regions in the U.S. (independent system operators such as PJM and ERCOT), a high value has been placed on some ancillary services where storage has an inherent competitive advantage of speed and accuracy compared with conventional generators.

A market for frequency regulation services was launched in the U.S. with the issuance of the Federal Energy Regulatory Commission's Order 755 in 2011.

Kaun noted that the Germans are focusing on the development of a pan-European “supergrid” to achieve greater flexibility through resource and geographical diversity. Germany does not have access to cheap natural gas, so it won’t be adding large number of combustion turbines to compensate for the variability inherent with solar and wind power.

Instead, it is anticipating that a supergrid will allow it to tap, for example, Scandinavian hydro resources for flexible balancing of the grid. The supergrid also would allow the Germans to distribute their renewable energy all over Europe.

"Even with a pan-European super grid, there will still be seasonal differences," Kaun said. "Hydrogen electrolysis and storage are viewed as a link for avoiding loss of the solar and wind produced domestically."

Pumped hydro storage, compressed air energy storage and other emerging storage technologies may provide the long-duration storage that Germany is seeking to support its desired end state, he said.

In the United States, the challenges of integrating increasing amounts of renewable energy into the grid — intermittency, variability and ramping up and down of thermal generation — are driving utilities and regulators to utility-scale energy storage and short-term storage integrated into the operation of the distribution system.

In Germany, rising retail electric rates and lower feed-in tariffs are driving a strong interest in onsite consumption and battery storage at the customer location. Retail electricity prices higher than the price customers receive from selling their onsite generation creates a strong incentive to use that energy on site and store any excess for later use.

Check out the Solar Electric Power Association's recent report, "Electric Utilities, Energy Storage and Solar: Trends in Technologies, Applications and Costs" at the SEPA website, www.solarelectricpower.org.



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