Tomorrow’s energy storage

There has been some progress: earlier this summer the first contracts in National Grid’s enhanced frequency response were awarded, but doubts have been voiced about the financial viability of the contracts.

While regulatory barriers remain in place, attention has turned to the future, with forecasts being made about the potential dominance of domestic storage beyond 2020, bolstered by a second-life electric vehicle battery market that is set to explode as first generation EVs reach the end of their lives.

And scientists are not resting on their laurels. Lithium-ion is expected to rule supreme for at least the next decade, but work is under way to improve various technologies, such as flow batteries and flywheels, that could take over grid service applications where lithium-ion cannot be used effectively because of degradation – which has recently been studied to beautiful effect at New York University (see image caption)

Here Network brings insight into some key next generation energy storage developments:

Flywheels

Flywheels store energy through movement. Electric energy input accelerates a spinning mass to speed via an integrated motor-generator, where it is stored as kinetic energy.

The rotor continues to spin in a vacuum on magnetically levitated bearings until the energy is needed again, at which point the same motor-generator discharges the energy back into the grid. Flywheels are low maintenance, have a long life cycle and negligible environmental impact.

 Early deployment

Flywheels are being used as one half of a new hybrid energy storage system in Rhode, County Offaly in Ireland. Irish company Schwungrad Energie has developed the system in collaboration with the Department of Physics and Energy at the University of Limerick. The project has been funded by a €2.55 million grant from the European Commission Horizon 2020 fund.

The system includes two 160kW generators by US manufacturer Beacon and a Hitachi 160kW/576kWh deep-cycle lead-acid battery. These batteries work in tandem with

the flywheels to provide a complete solution for grid stability, including both rapid frequency response and longer-term storage discharge, which allows for higher levels of renewable energy on the grid.

Superfast next generation?

A Lancaster engineering undergraduate has created a superfast design for a flywheel energy store as part of her degree. Rather than being electromagnetically levitated, the rotor is permanently levitated, without requiring additional control mechanisms.

Abigail Carson initially aimed to achieve a rotation speed of 100,000rpm, but simulations and calculations reveal the design can easily rotate at 144,000rpm without any adjustment, far quicker than aver- age existing designs which spin at around 60,000rpm.

The design is ideally suited to domestic uses, being the size of a football, but it can be scaled up for industrial applications using a stacking approach. Multiple individual units also means if one unit suffered a fault the entire system would not be required to shut down.

Carson currently has a patent pending for the design and is seeking investment opportunities to implement the FES.

Lithium-Air

Lithium-air batteries are touted as a highly promising technology for powering electric vehicles (EVs) because of their potential for delivering a high energy output in proportion to their weight, but they have serious drawbacks. They degrade quickly, waste up to 30% of electrical energy as heat in charging, and require expensive extra components to pump oxygen in and out.

But scientists at MIT in the US have created a new fully sealed battery that overcomes

these problems. In the nanolithia cathode battery the same kind of electrochemical reactions take place between the lithium and oxygen, but without the oxygen being allowed to revert back to a gas.

This is achieved through the creation of miniscule (billionths of a metre) scale particles, which contain both lithium and oxygen in the form of a glass, embedded within a cobalt oxide matrix to maintain stability.

The process reduces the voltage loss by a factor of five, so only 8% of electrical energy is lost to heat. This increased efficiency means faster charging for cars, but also slower degradation of the battery and therefore a longer life span.

These new batteries are also inherently protected from overcharging because the chemical reaction is self-limiting, whereas irreversible structural damage can be caused to normal lithium-air batteries when overcharged. They can even explode.

The scientists behind the battery at MIT tested its resilience by overcharging it for 15 days at a hundred times its capacity without it suffering any damage. Cycling tests also revealed that on a 120 charging-discharging cycle less than a 2% capacity loss was observed.

In the future the lightweight design means EV batteries could have twice the amount of capacity for the same weight, and with refinement this could be increased still further.

These scalable, cheap and safer batteries could also be used for grid-scale applications. The team at MIT expects to have a practical prototype of the nanolithia within a year. 

Redox flow

Redox flow batteries are considered a viable next generation technology for highly efficient energy storage. They use electrolytes – chemical components in solution – to store energy.

A vanadium redox flow battery, for example, uses vanadium ions dissolved in sulphuric acid. Being separated by a membrane, two energy-storing electrolytes circulate in the system.

The storage capacity depends on the quantity of electrolytes and can be increased or decreased depending on the application. To charge or discharge the battery, the vanadium ions are chemically oxidized or reduced while protons pass the separating membrane.

 

Where are they now?

In the UK, vanadium flow batteries are just reaching commercialisation. RedT a UK energy storage technology company, announced last month that the first largescale containerised  systems have passed the pre-testing phase at the Power Networks Demonstration Centre in Scotland.

The systems have now completed installation and commissioning on the Isle of Gigha and are being used to manage grid constraints.

The future

RedT has also embarked upon a three-year knowledge transfer partnership with Newcastle University to develop the first hybrid storage system using the technology. The flow battery, ideal for long duration energy intensive industrial applications, will be combined with a lead acid, lithium battery or super capacitor for short duration power intensive applications.

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