Friday, November 22, 2019
Weights show the way to cheap stored power
New ways to generate renewable
electricity will offer cheap stored power and a solution to balancing supply
and demand.
November 22nd, 2019, by Paul
Brown
Finding effective ways to
store energy until it’s needed is a major obstacle for the renewable
electricity revolution, but two new mechanical systems mean cheap stored power
could soon be widely available.
Cheaper than batteries, both
have the virtue of being able to produce full power within a second of being
switched on. And the energy they generate can also be stored for months without
any loss of power.
Although developed by
different teams completely independently and with different markets in mind, the
two systems have great similarities. They use surplus electricity from
renewables (wind or solar power) to winch a weight up a mineshaft or a
mountain. When there’s a need to generate more electricity, the weight is
released to fall to the bottom again, turning turbines attached to it by cables
and so providing instant power to the grid.
One system envisages helping
populations on isolated islands or in dry places where conventional
hydro-electricity is not available, but where surplus sun and wind power can
haul loads of sand or water up thousands of feet of mountainside.
The system, combining a
technique known as Mountain
Gravity Energy Storage (MGES) with hydropower, has been proposed by
IIASA, the Austria-based International Institute for Applied System Analysis,
and is described in the journal Energy. It allows the
energy to be stored for months.
If a water source is available
halfway or further up a mountain the empty containers can be filled nearer the
top, making the system even more financially attractive.
Julian
Hunt, a researcher at IIASA, said that cranes built on a mountaintop would
haul sand or gravel to the summit rather like a ski lift. He said: “One of the
benefits of this system is that sand is cheap and, unlike water, it does not
evaporate – so you never lose potential energy and it can be re-used
innumerable times. This makes it particularly interesting for dry regions.”
Unlike hydro-power systems
that were limited to a height differential of 1,200 metres, MGES plants could
cope with differences of more than 5,000m.
“Regions with high mountains,
for example the Himalayas, Alps, and Rocky Mountains, could therefore become
important long-term energy storage hubs. Other interesting locations for MGES
are islands such as Hawaii, Cape Verde, Madeira, and the Pacific Islands with
steep mountainous terrain,” Dr Hunt said.
50-year life
The mine shaft system, being
developed by Gravitricity and
based in the Scottish capital, Edinburgh, is designed to use weights from 500
to 5,000 tons. The company reckons its system will last at least 50 years
without wearing out and will work with 80 to 90% efficiency, offering “some of
the best characteristics of lithium batteries” at costs well below them.
It uses the same principle as
MGES, but relies on old mines from the coal industry, where it uses surplus
power to raise weights from the bottom of the shaft to the top. Many shafts,
sometimes thousands of feet deep, remain in heavily industrialised areas of
Europe.
Depending on the need,
Gravitricity’s installation can be geared to produce between one and 20
megawatts of peak power within seconds, and depending on the output required
can run for between 15 minutes and eight hours.
Gravitricity says it has
already had a rush of interest from industrial partners and is working on a
demonstration project.
There is already a different
type of generation and storage system at work in the UK, known as pumped storage,
which relies on transferring water from one underground reservoir to another.
It is in use at Dinorwig in
North Wales, where it is known as Electric Mountain.
− Climate News Network
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