Science //

Can gravity batteries decarbonise our energy?

Is the solution to the renewable energy storage dilemma hiding in our high school textbooks?

Art by Khanh Tran.

There are a few excuses favoured by the anti-renewables brigade whenever the topic of clean energy is raised:

What about the jobs in fossil fuels?

What about the impact it will have on the economy and the Australian consumer?

What happens when the sun goes out and it isn’t windy?

All could be properly dissected in an article of their own, but the latter question is of particular interest to me as, despite being phrased like a question you’d hear in a Year 4 science class, it’s not entirely unfounded. 

Maximum renewable energy production typically occurs between 11am and 4pm, diminishing just as demand begins to peak between 4pm and 8pm. This incongruence can be offset through storing energy; the question is how? Enhancing storage capacity is particularly sensible given that energy companies already curtail renewables to avoid excess production. As utility-scale solar power is the cheapest energy available in Australia in terms of dollars per megawatt-hour, it is essential that storage capabilities for renewable energy are efficient so that this uniquely generative energy source is properly harnessed.

Those adverse to renewables — ironically concerned about the environment now the supremacy of coal is threatened — proceed to question:

Battery technology isn’t where it needs to be for the large-scale adoption of renewables — what materials are you using to make these batteries?

Again, a valid question. Commonly used lithium-ion batteries struggle to last beyond 15 years, necessitating replacement, hopefully with proper disposal and recycling practices. The mining, procurement, and subsequent transport of raw materials to repeatedly create these batteries cyclically damages the environment.

The most effective alternative storage method to lithium-ion batteries is ‘pumped-storage hydropower’ according to the Environmental and Energy Study Institute, who claim that PSH facilities provide 10 hours of energy, compared to the six offered by lithium-ion. While a cursory glimpse would indicate that hydro is a clean form of energy, when the specific geographical conditions required for its success are accounted for, it looks less appealing. The volume of water required, the impact it has on surrounding ecosystems, and its suitability for widespread usage in drought-prone Australia reveal the inextricable problem of hydro: water is a precious and challenging medium to utilise. 

As such, new solutions are required. Initially, it is the glaring simplicity of gravity batteries that appeals to me. Operating under the same principles as hydro, these batteries are able to store gravitational potential energy to be converted into electrical energy, resolving the discrepancy between peak production of renewable energy and peak demand.

To provide a dramatic oversimplification of the technology, an unfathomably heavy object is winched up using surplus energy generated during the day, before being lowered at night when the sun goes out. The slow descent creates kinetic energy to power a generator which then provides electricity to the grid — from the battery, to substations, to homes. 

Gravitational power storage start-ups are already being established. London-based company Gravitricity is perhaps the most renowned example, boasting “zero to full power in less than one second” with a levelised storage cost of AU$147 per megawatt-hour, compared to the lethargy of lithium-ion batteries at AU$530. Most crucially, Gravitricity anticipates that their “20MWp system could power 63,000 homes for every hour that it discharges,” with the battery technology possessing “a 50-year design life.” 

Closer to home, Green Gravity, a similar start-up operating out of Wollongong, emphasises the renewable circularity of their approach to gravity batteries, reusing abandoned mineshafts to house their systems. In an interview with RenewEconomy, founder Mark Swinnerton stated that Green Gravity has “already identified” 3GWh of capacity in largely “concrete-lined, premium shafts that are no longer required for mining operations.” Swiss-based Energy Vault also partakes in this circular economy, utilising “local industrial and energy waste (such as remunerated coal ash and recycled wind blades) converted to recyclable materials” to construct the weight for their battery.

Gravity batteries present a unique set of favourable conditions: they take up very little horizontal space, can be housed underground, can be implemented at a small or large scale and are less resource-intensive than the prolonged construction of lithium-ion batteries. The technology can also be divided into many easily-replaceable components, ensuring a considerable lifespan. 

Despite this, the promising new tech isn’t without its drawbacks. There is a finite number of suitable mineshafts, and their presence above-ground could be considered unsightly. The technology is only in its infancy, providing both hope and uncertainty. This article doesn’t advocate to immediately jettison all other forms of energy storage in favour of gravity batteries. Instead, with proper investment in their development, gravity batteries can be a single component of a broad collection of carbon-zero energy-storage methods. 

And most of all, hopefully it’s this kind of innovation that will shut all the renewable-truthers up.