Developing viable energy
storage technologies is one of the big engineering challenges when it comes to
cutting carbon emissions, and yet the issue has received relatively little
mainstream attention or support.
We desperately need energy
storage to make renewable generation more practical and cost-effective, to
remove the sight of wind turbines shut down during windy but off-peak times and
reduce the need for backup fossil-fuel power when renewable energy runs short.
So the announcement that
12 projects have been put through to the first stage of the government’s energy
storage competition is very welcome, even if the amount of money allocated at
this feasibility stage (£500,000) is relatively small.
Those groups that reach
the second, demonstration phase of the competition will be competing for a
share of £17m – a more substantial sum but one that still requires plenty of
private investment if these technologies are to be brought to a commercial level.
What’s perhaps most
interesting about the winners list (and about the field of energy storage
research in general) is the breadth of technologies identified as possible
solutions. It’s both an opportunity and an obstacle: the UK is bursting with
ideas of different ways to capture energy for different scenarios, but that
means we need more funding to develop them.
In particular there are a
huge number of battery technologies put forward as having potential for
grid-scale storage, from lead acid to lithium ion to more unusual concepts.
They’re costly but offer very high efficiencies, sometimes up to 95 per cent or
more.
The one chosen to go
forward in the DECC competition is for a vanadium redox flow battery. A group
led by Wokingham firm REDT hopes to built a 1.2MWh system on the Isle of Gigha
off the west coast of Scotland to store surplus energy from a wind turbine for
use in the local network. The company claims the technology offers 75 to 80 per
cent efficiency depending on duty cycle at a cost of £1.7m to £1.9m per MW, and
says this is a lower cost over the 10 to 15-year life of the system than any
other battery storage.
But several other groups
in the competition are hoping to bring the cost of battery storage down by
using existing batteries. The Aston University-led group plan to combine new
lithium titanate batteries with old electric vehicle units to provide
grid-balancing services: the second-hand batteries will provide most of the
capacity while the new ones will cater the rare occasions when National Grid
needs up to 30 minutes of extra power.
Yuasa Battery Europe,
meanwhile plans to convert existing uninterruptible power supply (UPS)
equipment used for backup in industry by replacing lead acid batteries with
lithium ion ones, possibly pre-used from electric vehicles. The electricity
doesn’t go back to the grid but it would help with balancing and would cost an
estimated £600,000 per MW of capacity.
Other competition entries
make use of batteries as part of an energy and money-saving domestic service,
such as the Maslow system that Moixa Technology hopes to install in 750 homes.
It stores energy from the grid overnight or from solar panels on the roof for
use in a DC lighting and electronics system, but can also help with grid-level
storage and balancing.
Alongside the batteries
there are numerous other storage mediums being proposed. Liquid air storage
might sound like it should be an experimental technology but could actually
reach a commercial scale if it goes through to the next stage of the
competition. Its efficiencies are below those of batteries but can be increased
if waste heat (and cold energy) streams from power plants or other industrial
sources are harnessed, and it uses a free medium (air) and well established
liquefaction and evaporation technology. The firm developing it, Highview Power
Storage, have even created a cryogenic system it says is the equivalent of a
diesel generator powered by air.
Another alternative in the
competition is storing energy by producing methane, which can then be burnt to
produce electricity or used in industrial processes. Hydrogenics Europe wants
to build the first power-to-gas plant in the UK, and the first power-to-methane
plant based on biological methanation in the world at a waste water treatment
plant. It says the efficiency is 58 per cent, rising to 78 per cent if heat
from the process is recovered. The costs are currently £1.4m/MW but the company
claims this could fall to £800,000/MW.
Using gas (air, methane or
hydrogen) means you can effectively move the energy from where it is captured
to where it is needed, and the technology is easily scalable and less
location-dependant than pumped hydro storage or compressed air systems that
pump into caves. But we’ve yet to see whether the efficiencies or costs can
make the technology viable as a widespread commercial solution.
There’s also another more
unusual concept amongst the competition winners: using gravel as a storage
medium by carrying it to the top of a hill in buckets attached to what looks like
a ski lift. It’s a messy idea (literally and perhaps metaphorically) but its US
inventors Energy Cache claim it beats pumped hydro and compressed air for cost
and performance and is also more easily sited. The company has yet to respond
to The Engineer’s requests for more details but we’ll bring you a more in-depth
report when we can.
Looking at the huge range
of ideas for energy storage suggests two things: that not all of them will be
successful but also that there probably won’t be a single winning technology.
Just as with renewable energy generation, we’re likely to need multiple ways to
store energy. Let’s hope the UK can provide the necessary support to turn our
wealth of ideas into viable solutions and businesses.
This article first appeared on The Engineer.
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