Eccentric Energy: Unlocked cells to set decarbonisation free
9th May 2019
The electricity industry – as well as governments, academics and climate-change activists – see power storage using batteries (or cells) as a key to decarbonisation. Reducing carbon dioxide (CO2) emissions implies a reliance upon renewables such as wind and solar. However, the intermittent nature of these natural resources means that, to take full advantage, we need to be able to store the power they generate – at scale – for later use.
So, this month’s Eccentric Energy looks at three energy storage developments that respectively involve salt crystals, cathodes, and ammonia.
Read more below:
Salty hot air makes sense
Two Swedish companies, energy firm Vattenfall and technologists SaltX, are running a project in Berlin with a battery that contains nano-coated salt crystals heated by renewable electricity.
The insulated unit takes 10 hours to fully charge and retains the heat until it’s released, either as hot air or steam. The companies envisage the discharge taking place in periods of peak demand, such as the morning and evening.
The unit’s two reactors charge and discharge the salt, while its two storage tanks (one for charged and one for uncharged salt) don’t need to be pressurised. The discharging process releases air at temperatures suitable for heating a district of Berlin, or steam that could be used in a range of industrial processes.
New cathode packs a power punch
Researchers at Massachusetts Institute of Technology (MIT) and in China have developed a new “hybrid” cathode that combines the best aspects of two different approaches to lithium battery development.
One approach increases the energy output per pound (gravimetric energy density) and the other causes energy per litre (volumetric energy density) to rise. The new hybrid system has both a relatively high electrical conductivity and lower overall volume. The former reduces the carbon content to about 10% (compared to the 20-30% needed for sulfur cathodes) and the latter reduces weight and extends usability.
Today’s commercial lithium-ion batteries can have energy densities of about 250 watt-hours per kilogram (Wh/kg) and 700 watt-hours per litre (Wh/l). On the other hand, lithium-sulfur batteries can reach around 400 Wh/kg yet only achieve the same number of Wh/l.
In contrast, the new hybrid cathode can achieve more than 360 Wh/kg and 581 Wh/l, meaning its combination of energy densities outstrips both lithium-ion and lithium-sulfur batteries.
Ammonia proving to be both clean and "green"
The Energy Research Unit (ERU) of the Science & Technology Facilities Council (STFC), two universities and Siemens have shown it’s possible to use surplus renewable electricity to create “green ammonia”.
Linking with universities at both Oxford and Cardiff, the demo used ERU’s 12kW wind turbine to generate renewable electricity. This powered the electrolysis needed to get hydrogen from water, and extract nitrogen through air separation. The two gases are fundamental to the accepted industrial procedure – the Haber-Bosch process – for producing ammonia. In the demo, the ammonia produced was carbon-free and has the potential for use as a bulk energy source.
Adopting the solution at scale would reduce the likelihood (quite common at present) of National Grid being unable to accept all the wind power being generated across the UK. In such circumstances, the system operator sometimes has to ask generators to turn off their turbines and the power of the wind is lost.
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