Three novel ways to store wind energy went on show at the European Wind Energy Association (EWEA) 2014 annual meeting held in Barcelona, Spain, last week.
Two, aimed at short-term and longer-term storage respectively, were discussed during a hardware technology session that also looked at grid integration. The third, involving hydraulic storage, was among the poster presentations featured in the exhibition.
In the hardware technology session, Rajni Burra of GE Power & Water in the US shared the early operational experience of GE’s Brilliant turbine, believed to be the only fully integrated turbine-and-storage combination from a single vendor.
Burra pointed out that GE’s strategy of connecting battery storage to the turbine’s DC link could help the system deliver improved inertial response, frequency regulation and ramp control. These areas are a problem for traditional turbines.
Improving inertial response
When a turbine loses power, either because of a shutdown or a drop in wind, it usually has enough momentum to maintain inertial response for a few seconds.
Over longer time spans, of more than an hour, forecasting is usually good enough to predict when auxiliary power systems will be needed. Brilliant aims to bridge the power dip that happens in between, ensuring a smoother supply to the grid.
Burra said the Brilliant concept would likely be of value in markets such as the US, where grids are moving from 15-minute to five-minute despatch windows and the ability of plants to respond more quickly could increase performance-based revenue.
Another application Burra highlighted was the ability to maintain power to the turbine even when it is cut off from the grid, for example as a result of storm damage. This would let the turbine feather its blades and thus minimise potential damage from severe gusts.
Integration reduces balance of plant
Compared to non-integrated systems, said Burra: “With GE Brilliant there is no balance of plant cost. Balance of plant can be 30% to 60% and with this the balance of plant is largely integrated. This way it is largely economical.”
He confirmed three Brilliant turbines have been deployed since launch. It is understood these have been installed by Invenergy in Texas, but “we are talking to others,” Burra told Energy Storage Report.
At the other end of the delivery spectrum, Graeme Hawker of the University of Strathclyde considered how wind power and energy storage are helping to power Shetland, a UK island group with no gas supply or mainland grid connection.
Currently, power for the islands is delivered from an ageing 67MW diesel generator plus a 3.7MW wind farm with a 50% capacity factor.
Use of storage heaters
SSE, the local utility, is planning to build a new gas plant and recruited Hawker and his team to if energy storage could be used to help minimise the size of the facility.
Hawker’s suggestion, being tested in 234 Shetland homes, is to install an active network management system and advanced water and storage heaters in every household.
The idea is that the heaters, which will add up to about 2.5MW of storage across the whole of Shetland, will store excess power coming off the wind farm and be able to feed it back into the electricity system in times of need, while providing on-demand heating.
These distributed storage systems will help the Shetland power system deal with frequency response constraints. Swapping out storage heaters is a simple measure that would add up to 6GW of capacity if extended across the whole of the UK, Hawker said.
Deferring system upgrades
“I believe there are many more networks than this where this could become a way of deferring system upgrades,” he commented.
The initiative, part of a project called Northern Isles New Energy Solutions (NINES), will also involve a 1MW/3MWhr lead-acid battery store for daily peak shaving, along with district heating.
While innovative, even NINES looked relatively mainstream compared to Impressive Engineering’s hydraulic storage proposal, exhibited in the poster section of the conference.
Aberdeen, UK-based Impressive is touting a system that dispenses with a nacelle gearbox and instead uses wind power to compress water in a “gigantic hydraulic cylinder made of a borehole excavated underground” directly underneath the turbine.
Hydraulic storage for wind
“The hydraulic storage is mechanically connected to a wind turbine by means of a pump to the rotor and a Pelton turbine to the generator,” says the company. “The rotor drives the pump to inject water into a gigantic hydraulic cylinder.
“The high-pressure water lifts a heavy solid mass while it is getting accumulated in the underground borehole.”
This solid mass will feature a nozzle that releases the water to drive the Pelton turbine. The company claims six hours’ worth of storage a day could increase capacity factors from 35% to 75%.
The company is apparently on the lookout for investors to build a prototype, but did not respond to a request for further information from Energy Storage Report.
Written by Jason Deign
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