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Viewpoint: Wind should learn from solar PV on storage

WORLDWIDE: Battery-storage technology has very high public visibility at present for several reasons.

There are major investments, such as Tesla's Gigafactory and equivalents, rapid cost reduction, and a realisation by everyone except the oil industry that electric vehicles are not just here to stay, they are here to take over.

In the UK, two separate developments in electricity markets - for frequency response and capacity - have created the conditions for a pipeline of battery projects totalling hundreds of megawatts, which is sure to grow.

Amid all this positivity, it is easy to lose sight of several important facts. Currently, adding a battery system to a wind farm, megawatt for megawatt, will increase project capital cost by about half, and increase energy losses significantly.

Energy storage can provide solutions to many different problems, but so far none of those applications provides sufficient revenue by themselves.

Developing the business case is complex, project-specific and, as a consequence, expensive and risky. There are lower-profile competing alternatives, such as flexible generation, electricity-system reinforcement; and many forms of demand management.

Batteries are often seen as the "silver bullet" to allow deep decarbonisation of electricity supply by the variable renewables, wind and solar. So it is important to look at these issues as they are playing out in the wind industry for large-scale electricity systems.

To the outsider, the value of storage to a wind project seems obvious: it reduces the variability of wind. In practice, that is almost worthless at present. There simply isn't a variability problem with identifiable value to be gained. However, predictability is a different matter.

Where wind operators are exposed to the full market costs of production forecast errors, energy storage can provide significant benefits.

The next obvious benefit is time-shifting energy production to high-price periods. At present, this does not appear to provide sufficient value, but as wind penetration increases, and as markets adapt to provide true marginal pricing, it will grow in importance.

We can already see this in markets with high penetration of solar PV, where there is significant value in being able to defer production from midday to the evening.

Constraint management is similar to time-shifting, and a picture is emerging that shows storage is valuable in this regard, but reinforcement of the distribution or transmission system is notably cheaper in most cases. However, battery storage is much faster to build than reinforcement.

Several battery projects of 20MW upwards have just been completed in California on timescales of a few months in response to problems created by the failure of the Aliso Canyon gas storage facility.

Also, battery storage is portable: it can be installed to allow a wind project to run with minimal constraints, then, once the electricity system has caught up, it can be moved to the next problem area.

Globally, there are currently very few battery-storage installations that can claim they are making money in an open electricity market without some form of support or protection. Any wind-project operator considering battery storage for other reasons should ensure they fully understand these sources of value.

Seasonal storage

Seasonal storage is the showstopper for very high penetration levels of wind. Studies of 100% renewables scenarios indicate the problems posed by extended periods of low wind, especially in winter. Battery storage looks highly unattractive in this situation.

There are many better options, including storage of (decarbonised) heat. Where there is little seasonal variation in renewables production, very high penetration is easier to achieve and battery storage looks more credible.

However, many areas of the globe without much seasonal variation are more suited for solar PV than wind.

For many of these issues, the storage device does not need to be located at the wind project. Battery storage costs per unit are not strongly related to project size. There is not a huge cost advantage in building one 50MW installation over ten 5MW systems.

So, many different ownership models are being progressed, from project-level to a "cloud" of distributed installations, providing aggregated flexibility services to wind project and electricity system operators.

What happens next for battery storage in the wind industry depends on how regulators respond to the new opportunities, on local factors such as generation mix, and available alternatives such as pumped hydro and demand response.

However, it is worth noting that most of the benefits storage can provide for wind apply more strongly to solar. The wind industry would do well to pay close attention to how things play out for the solar industry, especially in markets with proactive electricity regulators.

Paul Gardner is global segment leader for energy storage at DNV GL-Energy

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