Engineering skills for a smarter world

Coal mines powered the first industrial revolution, turning our nation into a world leader in engineering, but now a British engineering start-up is looking to put some of the estimated 59,000 disused mineshafts in the UK to use to help us prosper from the renewable energy revolution.

Edinburgh-based Gravitricity1 is developing a novel technology, to help store electricity generated by intermittent sources such as wind and solar. In doing so, they’re tackling the biggest barrier to the unstoppable growth of clean energy – what happens when the sun goes down and there is no wind?

If we fail to install enough storage when switching from dispatchable, baseload generation to renewables, it could lead to frequent power shortages during periods of high demand. This could be exacerbated by the adoption of other clean technologies such as electric vehicles leading to greater peak surges on the grid. The cancellation of nuclear projects, which could have supplied 15% of the UK’s demand, and the potential impact of Brexit on energy imports, which met 36% of our needs in 2017, make solving the intermittency problem of renewables a priority in the UK.

The UK is not alone in facing this challenge – there’s a growing global need for technologies to capture and store renewable energy during periods of low demand and release it rapidly when required. The International Energy Agency estimates that, in order to limit global warming to below 2°C, the capacity of storage connected to the grid worldwide should increase from 140gW in 2014 to 450gW by 2050, while Bloomberg New Energy Finance has forecast over $620 billion of global spend on energy storage to 2040.

We need to store excess energy when the wind blows or the sun shines, so it can be released when demand outstrips supply.

Charlie Blair,
Managing Director of Gravitricity

Gravitricity’s patented technology is based on a simple principle: harnessing the power of gravity to store and release energy.

During times of high renewable energy generation and low demand, excess electricity turns motors to lift a large weight in a vertical shaft, which can then be released, turning the winches into generators. The shaft can be up to 1,500m deep – over four times the height of the Eiffel Tower – and the weight can be anything from 500 up to 5,000 tonnes, which is equivalent to
37 adult blue whales. The heavier the weight, the more energy is stored.

The weight is guided by a system of tensioned guide wires to prevent it from swinging and damaging the shaft. The winch system can be accurately controlled through the electrical drives to keep the weight stable in the hole.

The grid connection technology uses modern power electronics to allow rapid switching between generation and absorption of power, and the system can deliver active as well as reactive power to help with grid stability.

“The basic concept is the same as that inside an 18th-century grandfather clock,” explains Miles Franklin, Lead Engineer at Gravitricity. “You’re winding up a weight to store some energy in the position of that weight. Then that weight descends, powering the system for a period.”

A chartered mechanical engineer with seven years’ experience in new technology innovation across a number of fields, including borehole drilling machines in West Africa and new product development at Dyson, Miles was recently nominated for Scottish Renewables’ Young Professionals Award. He leads the engineering team in Edinburgh, which also works with partner engineers Huisman Equipment BV. The Dutch winch manufacturer has cranes capable of lifting 10,000 tonnes, which is significantly more than the weights involved in the Gravitricity system.

The key requirement for this innovative storage technology is a deep hole in the ground, either a disused mineshaft brought back into use or a purpose-sunk shaft. Shaft depths can be from 150m for new shafts down to 1,500m for existing mines.

Charlie Blair, Managing Director of Gravitricity, is the former Head of Marine Energy in the Carbon Trust’s Innovation Team as well as being a fellow of the Energy Institute and a member of the Institution of Engineering and Technology. “There’s a huge global opportunity in existing mineshafts here in the UK, as well as in Europe, South Africa and Australia,” comments Charlie.

“In the Czech Republic, there are hundreds of coal shafts that may be in good condition. In Poland and Germany, there are also lots more shafts that have closed recently or will be closing soon, and, in South Africa, there are many shafts over 3,000m.”

Currently, the best-known large-scale electricity storage technologies are lithium-ion batteries – such as Tesla’s 100mW ‘mega battery’ in South Australia – and pumped hydroelectric.

While batteries offer good short-term rapid response, which is useful to electricity networks that need to stabilise the grid at 50Hz, they aren’t great at discharging over more than an hour and they degrade over time.

Pumped hydroelectric, which is estimated to account for97% of the world’s connected energy storage, is difficult and expensive to install, and reliant on geographical features often found a long way from urban centres, industry and renewable energy generation.

Gravitricity’s technology has the fast response times of lithium- ion batteries, with the winches and control systems lowering the weight very fast to deliver shorter bursts of very high power. Unlike batteries, it can be charged and discharged, again and again, many times a day, for up to 50 years, with zero degradation. Each unit operates in the 1mWh to 20mWh peak power range, with output duration ranging from 15 minutes to an impressive 8 hours.
Once the technology is proven in mineshafts, Gravitricity plans to sink purpose-built shafts wherever superfast, long-life energy storage is required – for example, near to towns, factories and renewable energy installations. So, do Charlie and his team of engineers have the potential solution to versatile, durable energy storage?

Several people can see the potential. Gravitricity has been selected from 300 entrants, as one of seven finalists in the New Energy Challenge, shortlisted for the UK’s Renewable Energy Association Innovation Award and awarded £650,000 in funding from Innovate UK’s Infrastructure Systems Innovation competition. Charlie has also been recognised as one of the UK’s leading business innovators by Clean + Cool, the UK’s leading programme for clean and sustainable technology entrepreneurs.

Gravitricity is currently designing and building a 250kW (10m) concept demonstrator in Scotland, with the aim of deploying its first full-scale 4mW prototype in 2021 or 2022 at a disused mine in Northern England. A crowdfunding campaign to help fund its concept demonstrator will launch shortly on Crowdcube.

Given the opportunity, one engineer can change their world and ours.