Balancing with batteries

Solar cells generate power when the sun shines, and wind turbines when the wind blows, but not necessarily when the need for energy is greatest. Can batteries store renewable energy "in a can" – for later use?

When solar or wind do not meet the market's energy needs, we must look to other sources. Today, supply and demand in the energy market are largely balanced by traditional energy sources such as gas, coal, hydropower or nuclear power. If the share of renewable energy is to reach 70 per cent in 2040, as Statkraft expects, we must find solutions that provide the necessary flexibility without using fossil energy sources. It is tempting to look at batteries, but is this a realistic option?

Battery revolution

Electrification is one of the megatrends of our times. Electric cars are becoming increasingly common, and the first electric aircraft have already taken off. Buses, transport lorries and other utility vehicles will also eventually become electric.

An important driving force for this development is battery storage. Lithium-ion batteries are currently the most popular option, and they are becoming cheaper and more efficient. Would using such batteries to also store surplus energy from sun and wind be a good idea?

"Lithium-ion batteries are first and foremost a good solution for short-term balancing in the grid, from a few seconds to an hour," says Matthias Holzenkamp, head of commercial asset management in Statkraft Germany.

"The batteries are able to deliver large amounts of power in a short period of time, and are therefore very effective in dealing with short-term fluctuations in the power supply. Batteries may also be relevant for balancing in the course of a day, but then they often compete with other, cheaper technologies.

Power flexibility solutions

Not for long-term storage

When it comes to storing power for weeks or months, Holzenkamp believes today's battery technology is not suitable.

"For example, if you store power to compensate for a week without sun, you need a huge battery, and it wouldn't be profitable because the battery is rarely used," he says. "Batteries are very expensive and therefore need many operating hours to pay off."

Holzenkamp has recent experience from Statkraft's full-scale battery storage project at the run-of-river power plant in Dörverden, Lower Saxony, Germany. In 2016, three large lithium-ion batteries were installed with a total capacity of three megawatts, equivalent to 600 000 smartphone batteries.

"The purpose wasn't to store energy from the adjacent hydropower plant, but to deliver frequency support to grid operators. The batteries are located here because we have space, expertise and grid access," says Holzenkamp.

"The batteries work very well, have very high capacity, and there is almost no decomposition. Technically, the system works better than expected."

Solar panels in rural IndiaIn countries with ample and predictable access to the sun – such as here in India – battery technology can be useful for storing power for those hours of the day when the sun is not shining on the solar panels. (Photo: Shutterstock)

Important flexibility

Nevertheless, Holzenkamp does not believe there will be a need for additional battery capacity in Europe in the near future. The German energy network is well developed and already provides a high level of flexibility. This means that customers will always receive power from elsewhere, in the event of inadequate sun or wind power locally.

"In countries with a lot of sun, like India, batteries can be a good solution. There they need the flexibility in the short and medium term to store power for use in the evening and night. The European market primarily needs long-term flexibility over days and weeks, and for this the batteries have limited value," says Holzenkamp.

"Not everyone is as lucky as Norway, with its big green batteries in the form of highly flexible hydropower. In large parts of Europe, we'll be dependent on natural gas for a long time to provide sufficient flexibility. Combining this with the production of hydrogen and methane from solar and wind power – referred to as a power-to-gas solution – will provide power generation that is almost CO2-free.

Water reservoir in NorwayThe advantage of regulated hydropower – of which there is a great deal in Norway – is that it is renewable, and at the same time the power can be stored in the form of water in reservoirs, and produced as needed. (Photo: Hans Fredrik Asbjørnsen)

Future local solutions

Although battery technology may not be suitable for long-term storage of surplus energy from solar and wind power, improved battery technology is likely to be of major importance for local small-scale solutions.

"In Germany, and in more and more countries in Europe, we see people installing solar cells on the roof at home and adding battery packs to their own power supply system. Then they can save energy for maybe up to a day's consumption, which means they don't have to sell excess power cheaply back to the power grid. This also gives private households protection against short-term power outages. Many customers also like the idea of being independent of the big energy companies," says Holzenkamp.

He also believes that some companies can take advantage of batteries to reduce energy costs. They can buy electricity at lower prices – at night – and store it for later use. They can also reduce consumption peaks and grid fees.

"This provides both security and predictability for customers, and can therefore be a sensible solution," says Holzenkamp.

Has learned a great deal

Holzenkamp believes that the experience gained from the Dörverden battery project is important to Statkraft, even though it is perhaps not yet commercially interesting.

"We have learned a great deal about battery technology, limitations and possibilities, and the pros and cons. It's also taught us that the use of such batteries is limited and that much depends on the local market," says Holzenkamp.

"Nevertheless, a great deal of research and development is being done on battery technology that will improve energy density, storage, lifespan and efficiency. The future will give us improvements and surprises, so we must be prepared!"

Text: Morten Ryen
Infographics: Lucas Veil

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