Belles_Modern Energy Review 24/02/2010 10:52 Page 32
Stockpiling Electrons
a report by
Industry Outlook
Manel Romeu Bellés
Group Communications, Vestas Wind Systems A/S
Electricity is slippery: invisible and almost impossible to store in and then replaced during the expansion phase, compressed-air
quantity except by converting it to some other form of energy. energy storage typically has an efficiency below 50%, but the
However, many experts believe that the widespread adoption of technology is proven.
wind and other renewable energy sources will depend on our being
able to store electricity effectively. Research and development ideas in large-scale storage include
underground pumped storage hydro based on mines and aquifers,
Time-scales for energy storage in electric power systems range from huge plastic bags of compressed air tethered to the seabed and heat
seconds to days. “Wind power shows random variations over almost storage to make compressed-air systems more efficient.
any time-scale,” points out Claus Nygaard Rasmussen, who researches
energy storage at the Institute of Energy Technology at Aalborg Batteries Find the Right Chemistry
University. For power companies this means that the ability to smooth For shorter run times, batteries provide flexible electricity storage that
out power dips of just a few seconds or minutes can be just as useful does not rely on geology. Starting from the traditional lead–acid
as for variations lasting hours or days. rechargeable battery, this fast-moving research area now includes a
dozen or more battery types, including lithium ion, zinc–air and
The one-hour horizon is important because it is the shortest time-scale sodium–sulphur (NAS) batteries.
over which electricity is traded, and because it is achievable with
existing battery technology. “Our research shows that a storage Lead–acid batteries are competing with more modern battery types for
capacity of 30% of actual generation has a big effect,” Rasmussen now, but have poor power density and short working lives. Lithium ion
says. Such guarantees are worth a lot to power companies because batteries, as used in mobile phones and other small electronic
they make it possible to shut down fossil-fuel-generating units. gadgets, offer a larger number of charge–discharge cycles and the
highest energy density of any commercially available battery type. A
Over even shorter time-scales, storage allows wind power plants to different type known as lithium iron magnesium phosphate
increase their output briefly to cover ‘spikes’ in power demand. (FeMgPO
4
) has lower energy density than lithium cobalt oxide, but
“Conventional power plants have a reserve that allows this longer life, especially in stationary applications.
‘upregulation’, whereas standard wind and solar plants do not,” says
Henrik Vikelgaard, an energy storage expert at Vestas. “Using storage NAS batteries operating at around 300°C have three times the energy
to help maintain frequency stability on the grid will make wind power density of lead–acid batteries and a predicted lifetime of 2,500 cycles,
more acceptable to the generating companies” (see Figure 1). says developer NGK Insulators of Japan. The company recently
supplied a 1MW NaS system to a bus depot in New York and has a
Even for short-term storage, cost is an obstacle. “Either the cost of 34MW demonstration plant running alongside a wind farm in Japan.
batteries will have to fall to half or one-third of its current level, or the A 1MW NaS unit with a capacity of 7MWh is as large as three 20ft
value of reliable wind power will have to double,” says Rasmussen. shipping containers, says Vestas’ Henrik Vikelgaard.
The next step up in storage, with capacity for six to eight hours
to cover demand variations between day and night, would cost Expanding the Battery Vision
significantly more. Whatever their chemistry, conventional batteries are self-contained
units in which power is quite closely linked to capacity. Flow batteries,
Large-scale Storage from the Earth also known as redox batteries or reversible fuel cells, decouple
For immediate electricity storage, the answer lies in geology. Above power from capacity, potentially making very high capacities
ground, mountainous areas can use pumped storage hydro, which more affordable. They achieve this by storing charge in a liquid
relies on off-peak or surplus electricity to move water up to a high electrolyte that can be stored in large tanks and pumped through the
reservoir. Pumped storage can achieve a ‘round-trip’ efficiency of battery as needed.
70–85%, and hydro’s ability to start generating within a few seconds
makes it a good fit with other renewables. The US has around 20GW “At the moment, flow batteries are comparatively low-powered and
of pumped storage and the EU around 32GW. expensive,” says Claus Nygaard Rasmussen. The case of VRB, a
pioneer in flow batteries, shows how challenging the new energy
Below ground, surplus electricity can be used to pump air into storage market can be. Despite its strong position in Japan, where
caverns or rock fissures such as those in which natural gas is stored. several demonstration-scale flow batteries have been installed, the
To reclaim the energy, the compressed air drives turbines attached company laid off most of its staff last year and was recently acquired
to generators. As compression creates heat that must be removed by Prudent Energy of Beijing.
© TOUCH BRIEFINGS 2010
32
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108