There has been a great deal of focus on energy storage
for solar and wind power storage domestically since US
firm Tesla launched its 75 kWh Powerwall battery storage
system which should be available in many countries by
early next year.
If we can store our own renewable energy with a view to using it to power our electric cars and home appliances, why aren’t we looking more closely at grid-scale energy storage as the route to solving the irregularity/seasonality of wind and solar power generation?
The problem is not one of technology availability but simply of failure of Government policy to properly recognise and incentivise investment in building industrial-scale power storage facilities.
One article included in Utility Week last month and written by leading experts in the field Professor Phil Taylor of the University of Newcastle Upon Tyne and Dave Holmes, Managing Director of Quarry Battery Company, make the case for building energy storage with a view to storing and managing consistent supply of renewable power to the Grid.
There are some startling findings in the piece. Firstly, on current projections, by 2020 we are likely to be generating 28-30GW of wind energy alone. Imperial College estimated that if this happens, and no new investment in energy storage facilities is made alongside it, some 27% of that power output will have to be effectively thrown away? Bear in mind that each additional 10GW generated by wind after that will cost us £2.7bn in lost power alone and £6.3bn in total annually.
But just a 10GW/50GWh fleet of new storage facilities would unlock full potential of wind power - cutting curtailment (shutting down of turbines) from 27% to just 7% of the usable time, effectively mopping up 31.4GW of wind power. Over the 25-year lifespan of a windfarm this could save £91.3bn.
Based on these numbers, surely the Department of Energy and Climate Change needs to be looking at energy storage investment - starting with allowing storage infrastructure investment to be included in contracts for difference (CfD) and establishing a system for rewarding storage for the way it offers a more reliable and lower carbon alternative to calling on thermal reserves?
By including storage investments in CfDs, the cost of borrowing to build new storage capacity would fall. It would also stimulate innovation in the space. We simultaneously need to lift restrictions on connection to distribution from 100MW+-sized storage facilities.
Pumped hydro electric storage (PHES)
One ready energy storage solution is pumped hydo electric storage (PHES) which provides extremely high capacities of storage relatively low cost. PHES facilities typically have operational lives in excess of 125 years and require simply an environmentally-benign maintenance for continued operation.
Although this is the only storage technology ready to do the heavy-lifting required today, there are many other technologies being developed elsewhere. Let’s looks at just two other technology areas that are being developed around the world:
Chemical Energy Storage
At the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany, Dr Gunter Ebert’s team are researching the use of electrolysis to turn excess output from wind and solar generators into hydrogen and methane.
Ebert’s plan is to use caverns to store hydrogen, which can then be used for vehicles or in fuel cells. Alternatively, it can be converted into methane for use in the gas grid, or it can be used for direct heat and power generation.
His team is conducting various practical tests which will be concluded by end of next year. The unit under investigation has a power capacity of 315 kilowatts and can produce 60 cubic meters of hydrogen per hour.
Ebert says there are still many possibilities about how such a scheme could be put together, but he contends that some form of long-term storage will be needed after 2020, when the share of renewables grows beyond 40% and more thermal generation is side-lined in Germany.
Compressed Air Energy Storage
The second big technology that is being looked at is compressed air energy storage (CAES). The Boston-based firm General Compression recently opened a 2-megawatt/500-megawatt-hour pilot plant in Texas. Development officer Peter Rood says CAES would work best at the utility scale with 10 megawatts to 100 megawatts. It requires below-ground storage, either natural or man-made, and could work with storing the output of wind energy, or even as a “storage bank” for thousands of rooftop and other distributed solar systems.
Rood said that CAES will help wind energy act like a flexible gas-fired power station, providing baseload and peaking generation when needed, and storing energy produced on some windy days for use later in the week -- or even the month.
That means it would not only be able to mimic the services delivered by gas turbines, but it would also be able to compete with even combined-cycle gas turbines as gas prices head above $10/MMBTU.
“I think there will be a pretty compelling case to build wind plus storage,” he added, noting that a lot of thermal generation is aging, and a renewables-focused energy system will need storage and other ancillary services, such as frequency, that such a system could provide.
General Compression is working on a model that will provide around 20 megawatt-hours to 40 megawatt-hours of storage for each megawatt of peak power production. For a 100-megawatt wind project, the ideal would be to have a facility that could deliver between 200 megawatt-hours and 400 megawatt-hours of storage. CAES would be able to deliver this at a quarter of the price of battery technologies, according to Rood.
General Compression also has a proposal for a “solar bank,” which would allow solar households to store excess energy, and either draw down that energy when needed or sell it other users.
General Compression has received some funding from interesting sources, including oil giant ConocoPhillips and the largest utility in the U.S., Duke Energy.
But what power storage capacity do we need to build to help transition to renewables dominance?
Fraunhofer Institute undertook a study to assess the feasibility of a 100% renewable electricity mix by 2050. The results showed such a mix would be possible with a large amount of storage: 56 GWh of battery, mostly in residential systems; 60 GWh of PHES; and 69 GWel /68 TWh of Power to Gas.
In France, another study was financed by the French Agency for the environment and energy management (ADEME) and the ATEE, an association of companies involved in the electricity market and storage (e.g. EDF, DGF, Total).
This study estimates a need for 50 GWh more of weekly storage by 2030. Although the study identifies PHES as the only suitable technology, other large storage technologies are not excluded provided a significant drop in investment cost occurs.
In summary, the UK has clear decisions to make to back energy storage technology (or technologies) and create the right environment for investment in this area and it needs to do so fairly fast if it wants to see the UK hit its carbon-reduction targets while securing the nation’s baseload.
Subsidises are not necessarily required to stimulate the building of new PHES capacity but changes to UK energy policy are. The UK needs to recognise, incentivise and reward power storage capacity building and storage innovation rather than paying relatively scant attention to it and, in turn, disincentivising further investment in renewables.
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