A common drawback of any battery technology – whether traditional, or modern – is their use of natural materials. Storing clean energy in something which has a negative environmental impact, and needs to be replaced regularly, is counterproductive.
So, what are some alternative storage techniques, and are any of them likely to be more sustainable than a battery?
Hydrogen
Long seen as the potential low-carbon solution to a number of problems; as an alternative to petrol, diesel fuel and natural gas, and – by being produced through electrolysis – a way to utilise surplus renewable electricity.
However, there are unavoidable issues regarding the economics and efficiency of using Hydrogen. Electrolysers and batteries often share common materials, however the electrolysis process is only 40% efficient, so as a “storage” method, there is very little return compared to batteries. Once created, there is then the issue of transport.
Hydrogen has the lowest density of all gases, and is highly flammable. If transported in its natural gaseous form, it requires either
- High pressure tankers, which present safety issues (and associated costs) or
- Specialist pipelines – due to hydrogen molecules being smaller than a typical methane molecule, there is likely to be a far greater level of leakage if standard gas network infrastructure is used.
Liquefying hydrogen – in order to theoretically aid transportation – would take even more energy, and require constant cooling, reducing the already low level of energy efficiency.
A useful way to avoid issues with transportation would be to transport excess power across the grid, to be electrolysed closer to where the Hydrogen may be used. Though in this case:
- It assumes a network capable of transmitting large amounts of power across the country (one of the very challenges the National Grid is currently facing amidst growing electricity demand and surplus renewables).
- Where – and for what purpose – will there be the substantial demand for Hydrogen? As a storage method, there are many other more efficient and more established means.
Unless the efficiency of electrolysis can be improved – or alternative production methods are improved – and demand rises to the point where redeveloping infrastructure to incorporate Hydrogen is justified, it will remain on the fringes in terms of a clean fuel and/or storage option.
Mechanical Storage
Compressed Air Energy Storage (CAES)
In CAES, energy is stored by using electricity to compress air, which can then be released to help generate electricity at time when demand requires. This method allows energy to be stored for longer periods than traditional batteries, and requires less maintenance.
However, during the compression process, heat is created. Managing the loss of heat – especially when dealing with storage on a large scale – is crucial to the efficiency of CAES.
Most existing systems have an efficiency on a par with Hydrogen (50% or less) and whilst methods such as isothermal or near-isothermal – which can capture the heat generated during compression – have a much greater efficiency, they have been unable to be implemented at a commercial level.
Gravity Storage
Gravity storage uses the same principles employed by dams to produce hydroelectricity. Potential energy is stored in an object or body, and when required, that energy is released to generate electricity.
With gravity storage, excess power generation (such as that produced by renewables) is used to move a large mass – such as water or rock – upward, where it is then suspended. When released, it converts the potential energy into kinetic energy, which can then be applied to a generator to create electricity.
There are a number of different methods to achieving gravity storage, though most require suitable geological conditions. Underground Gravity Storage and Pumped-Storage both require lots of space and specific materials (Pumped-Storage requires the added complication of natural elevation) but each have a healthy efficiency of 70%-75%. There are minimal emissions associated, though they can be seen to have a negative environmental impact by disrupting habitats and ecosystems.
An alternative form is storage towers – purpose-built facilities using artificial objects to store gravitational energy. There are fewer natural restrictions on where these can be constructed (so they can be set up close to generation assets), and the objects/weights can be made from recycled materials, minimising their environmental impact.
The greatest obstacle for any gravity storage project – whether it requires navigating substantial geological and environmental challenges, or constructing entire facilities from scratch – is cost, and being able to operate at a frequency and efficiency which makes any investment viable.
This is absolutely key, because unlike many of the other storage methods we have covered, gravity storage technology is ill-suited for smaller-scale applications, such as EV or domestic storage.
Ultimately, the flexibility of lithium-ion batteries is going to keep them front and centre as an energy storage option.
It is unlikely that any alternative will allow the UK to avoid reliance on overseas supply chains (whether manufacturing or raw materials) and this should not be an obstacle in adopting energy storage technology.
Technology will improve over time, but the onus is – much in the same way that we approach a fuel mix – to consider all solutions, and pursue those which hit the other key elements of Sustainability and Scalability.
In addition to their energy efficiency, we must consider both the production impact and the life span/recyclability of any storage options. And in terms of scalable solutions, long-term viability is essential – with the UK network poised to undergo its most significant overhaul since the 1970s, any large-scale storage technology will need to form a lasting part of the national electricity system, and the generation assets they support.
