TALKING Mailbox
POINT
20
July 2020 / www.theengineer.co.uk
SINKING
FEELING
With big weights and cables.
this amounts to quite heavy
engineering , so therefore
downtime for replacing the
cables, attachments and also the
motor/generators too, could be
considerable and quite costly.
However compared to
maintenance of offshore turbines
I’d estimate considerably less. I
think the quite heavy duty cycles,
especially kicking out high energy
bursts may also be challenging.
But much within the scope of
current technology. All that said I
very much like the concept and
wish the company much success
rolling this out to industry. I’m
sure it can work well if engineered
properly.
John Wood
My students have been
developing grain-silo sized
flywheel energy storage systems
(FESS), but I have to admit I like
this concept even better. I think
‘the penny is beginning to drop’
about the serious disadvantages,
toxicity and sustainability
problems of bulk battery storage
systems and (like FESS) this
simple system could be used for
decades without any loss of
storage capacity or its very high
efficiency. I’m sure the costbenefit
analysis of drilling several
shafts in on place will also turn
out most favourably – we should
not forget suitable slope-drop
sites too.
Richard Masters
With an ever-increasing
amount of electricity produced by
renewables, we need large
amounts of high-volume storage. I
struggle to see that this technique
would ever have enough capacity
to provide much overall capacity,
even with multiple sites. So, I
The news that Scottish firm Gravitricity is to
build a gravity-based energy storage system
provoked some lively debate amongst readers.
pumped storage, requires a
lot less infrastructure
(abandoned mine shafts
already exist, damming up
valleys tends to be a large
unpopular change to the
countryside) and has faster
response times.
ekij
Nice idea….. but not new by
any means.
The concept has been around
for a long time and even ‘back
garden’ engineers etc. have
dabbled with building such
devices. There are some similar
small scale portable lighting
systems working on very similar
gravity-based designs.
The main issue is that there are
other companies developing
similar approaches to utilising
weight-based designs such as
rolling rail-based stock that
essentially run on track running
down steep or very long sloped
mountain/hillsides. Some contain
the batteries on board to act as
ballast and extra energy as they
roll down or are used to drive the
equipment back up the track.
The main, and probably only,
advantage of either this, or any
of the other systems, is that they
should be viewed as a means
to “decentralise” power supply;
particularly to remote/rural areas.
Ian Leppert
This like uranium flywheels
provides the necessary
momentum to maintain
frequency long enough for more
lasting sources of power to ramp
up when the battery banks can’t
cope. At the moment of crisis, this
can be a strong support to the
system. However, the amount of
energy stored is trivial. There
would have to be a PPA that
reflected it’s value as a standby
resource that would almost never
be used. A use for depleted
uranium. I looked at oil wells for
this. The casings are usually still
in good nick unlike older
mineshafts and the depths can be
substantial. The limitation
becomes the thickness and
number of cables required to
support very heavy weights.
Philip Owen
Vergani Fotografia/stock.adobe.com
would have thought that it would
be very good for cheap, fast
response storage but never good
for high volume storage.
Phil Harbord
To Mr Harbord’s question,
lifted and lowered weights has
better end-to-end efficiency than
Another great contribution
to Grid level fast response
storage. Has the use of rail
guided weights on steep sided
surfaces such as disused
quarries etc. been considered?
Whilst vertical displacement is
generally less, the system is
highly scalable (e.g. using the
whole side of a cliff face). Such
a system should have
significantly lower capital build
and through-life maintenance
costs.
Simon
I am curious as to the speed at
which the weight (s) will drop. If the
weight is a close fit into the mine
shaft, will there not be a buffer of
air below the weight? How will that
be dissipated? Any possibility the
dissipated air stream could be
further used to provide additional
generation? Interesting venture.
Good luck.
Morkullen
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