A new form of energy storage – which uses massive weights in disused mine shafts – could store green energy more cheaply than batteries, an industry reports says.

Edinburgh start-up Gravitricity has patented their multi-weight system, which uses up to 24 weights totalling 12,000 tonnes stacked in a mine shaft, to capture power and then release it with sub-second response time.

See a short (30 second) explainer animation here.

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The energy innovators have already received a £640,000 grant from Innovate UK, the UK Government’s innovation agency, and have teamed up with Dutch winch specialists Huisman to build a 250kW scale prototype of their idea [pictured].

Now a report by independent analysts at Imperial College London, working independently via Imperial Consultants, predicts that Gravitricity’s multi-weight system offers a better long-term cost of energy storage than batteries or other alternatives.

This leaves the firm ideally placed to tap into the growing energy storage market, which Bloomberg New Energy Finance estimates will be worth $620 billion globally up to 2040.

“The climate emergency means we need to find new ways to capture and store green energy so we can use it when we need it,” says Gravitricity Managing Director Charlie Blair [pictured].

“Our idea is very simple. We use excess energy to lift a massive weight or weights to the top of a shaft. These can then be stacked and released when required, delivering energy rapidly back to the grid. The beauty of this is that this can be done multiple times a day for many years, without any loss of performance. This makes it very competitive against other forms of energy storage – including lithium ion batteries,” Blair says.

Gravitricity has already received support from a number of angel investors and is now about to launch a crowdfunding campaign with CrowdCube to support their development plans.

Initially the firm will target former mine shafts, then in the longer-term they plan to sink purpose-built shafts wherever required. They are currently in discussion with mine owners in the UK, South Africa, Finland, Poland and the Czech Republic.

The report says the Gravitricty system performs particularly well in the ‘peak shaving’ market, a service which ensures the balancing of electricity demand and supply during peak demand periods to reduce the strain on power system infrastructure.

This typically requires a storage system to discharge for two to six hours, twice a day. The analysis was based on a 10MW maximum capacity delivering 24 MW hours (MWh) – this translates to around 2.5 hours discharge duration at maximum power output.

The system is also well suited to the fast frequency response market where the requirement for multiple short cycles and high power availability play to Gravitricity’s strengths.

“‘The report validates our belief that energy storage with a long-life can be built into the infrastructure of the grid, potentially saving billions in grid upgrades,” Blair says.

“Mechanical systems such as ours are very cost effective, as we can cycle several times per day with no performance degradation, enabling us to deliver a range of different services to grid operators. This means we can also stack up different revenue streams to improve our business case.”

The report was authored by Oliver Schmidt, a specialist in modelling energy storage cost reductions at Imperial College London, who was working independently via Imperial Consultants.

Schmidt says:

“The study has been rigorous in comparing all technologies on a level playing field. We have investigated a number of sensitivities, including discount rate, project duration and expected cost reductions using industry-specific learning rates.

“Gravitricity’s new system has a relatively low upfront capex and a design life of over 25 years. This explains why it is so competitive against other storage options. It is sensitive to the discount rate and the modelled project lifespan.  If we model a shorter response duration, a lower discount rate or a longer project life, then Gravitricity looks even more competitive.  I don’t expect Gravitricity to displace all lithium batteries on grids, but it certainly looks like a compelling proposition.”

For a copy of the report please contact neil@neildavidson.org.

To invest on CrowdCube please go here.

Key findings:

• Low capex per unit of energy and high cyclability represent the key advantage of Gravitricity.
• The relatively high specific power cost for the multi-weight system is offset by very long lifespan (over 25 years), high power availability, 100 per cent depth of discharge and zero percent degradation.
• Ideal for peak shaving and frequency response market and any application with multiple daily cycles.
• Well suited to ‘benefit-stacking’ (also known as ‘revenue-stacking’).

Key facts

• Shaft depth – typically 800 metres in Europe rising to over 2000 metres in South Africa.
• Size of weights – up to 24 weights of 500 tonnes. So a total 12,000 tonnes per system.  Equivalent to 84 blue whales.
• 24MWh system could power 63,000 homes for one hour.
• Gravitricity has submitted four patents; two have been accepted for grant and two are in examination.

www.gravitricity.com