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NETWORK / 26 / MAY 2017 A s people icked the kettle on or sat down to watch their fa- vourite Friday night TV show last month, few would have realised that, for the rst time since 1882, the UK had spent 24 hours without coal-generated energy. The increasing use of renewable genera- tion was one of the factors that contributed to that historic moment. However, as the number of wind and solar farms multiplies across the UK, managing the intermittent nature of renewables has become a signi - cant challenge for system operators (SOs). Flexibility is key in meeting that chal- lenge, and SOs and distribution network operators are turning to storage to give them the ability to call on key balancing services to meet changes in demand and supply. In recent months, energy storage has hit the headlines – National Grid's EFR tender, the closing of UKPN's Leighton Buzzard project and 500MW con rmed in the main four-year-ahead (T-4) capacity market auc- tion. This is unusual considering battery energy storage had won no contracts at all in the previous capacity market rounds, and historically only pumped hydro storage had ever had a look-in. Storage o™ ers an alternative to curtail- ment as the proportion of renewable gen- eration increases. Harnessing this energy in a storage device that can charge and discharge when called upon will o™ er not only cost bene ts to the customer, but also smooth the peaks and troughs in demand. No one technology is a panacea for net- work storage needs. Where one option o™ ers short-term response services, another will give DNOs storage in the triple-digit mega- watt range. The choice o› en depends on the services required, and the location. Network has compared ve di™ erent, but equally important, storage technologies. ENERGY STORAGE Lithium-ion Before National Grid's EFR tender and Tesla's social media-savvy chief executive Elon Musk made headlines extolling battery energy storage, there was UKPN's Smarter Network Storage (SNS) project. The pioneering project in Leighton Buz- zard proved lithium-ion battery storage was able to meet a network operator's needs, speci cally sub-second demand-response times, which made it ideal for providing fast frequency response, the most valued service for the network according to UKPN's low-carbon technology and customer en- gagement manager Adriana Laguna. Funded through Ofgem's Low Carbon Network Fund, the project demonstrated the UK's rst multi-purpose application of a 6MW/10MWh energy storage device at a primary substation. The facility supported National Grid for more than 7,500 hours and fed the local elec- tricity network on more than 180 occasions. The project explored ways to access mul- tiple "stacked" bene ts, maximising value from alternative revenue streams for storage, and deferring network reinforcement costs. It showed that cost is still the most signi cant factor in business case viability, and determines the size of a project. How- Redox fl ow battery RedT's CEO Scott McGregor is quick to point out that redox technology is a "storage machine". In part, this is to avoid the "bat- tery" label, but also to invoke the sense that the technology is mechanical and will not gradually lose capacity like a battery. In fact a redox ow battery (RFB) has a shelf life of more than 40 years because the electrolyte at the heart of the machine doesn't degrade. The technology works by transferring, or "pumping", ions between two tanks of electrolyte through a mem- brane. The system can be scaled up by simply making the tanks bigger. The other thing with RFB is it's easily moveable. This has allowed RedT to move batteries from its project in Gigha in Scot- land to a working farm in Cornwall. Housed in six, 20-foot containers, the footprint is not small, and suited to projects where space is not at a premium. "Batteries are very good for short-term services such as frequency response for 30 minutes or an hour every day," says McGregor. "Deep-discharge from solar, which is what a DNO wants, that's when a ow machine helps." RFB can o™ er STOR, sub-second fre- quency response, demand-side turn-up and a number of other balancing services that allow the technology to meet various requirement throughout the day. Deployment is quick. McGregor says RedT's RFB system can be installed within a The Glyn Rhonwy pumped storage scheme is set to bring two disused quarries near Llanberis in Wales back to life with the rst new pumped hydro storage facility in more than three decades. In March 2017, Snowdonia Pumped Hydro (SPH) was given permis- sion to double the output of its pumped hydro plant to 99.9MW (700MWh) – three years a› er the company was§ rst granted permission to build a 600MWh facility at Glyn Rhonwy. The location is important because geolog- ical suitability and planning risks – as well as market risk, environmental performance and market need – had to be considered before SPH decided to build the project. Pumped hydro is a mature, large scale technology, making it good value for mon- ey, says David Holmes, managing director of Quarry Battery Company, the parent com- pany of SPH. Electricity pumps water from a reservoir to a higher reservoir then allows it to run through a turbine generator to turn the potential energy in the water back into electricity. The new facility will export that power, via underground cables, from NETWORK / 26 The Glyn Rhonwy pumped storage scheme is set to bring two disused quarries near Llanberis in Wales back to life with the rst new pumped hydro storage facility in more than three decades. In March 2017, Snowdonia Pumped Hydro (SPH) pumped hydro plant to 99.9MW (700MWh) – three years a› er the company was§ rst granted permission to build a 600MWh facility at Glyn Rhonwy. Pumped hydro