Gravity Storage May Solve Growing Battery Demand

In a market where battery storage solutions continue to push complicated and expensive technologies to compete with lithium ion batteries (Li-ion), maybe the answer does not involve complex chemistry. Several emerging gravity storage startups promise industry leading performance and cost numbers by using basic physics. Pumped hydro is a simple technology that leads the long-duration energy storage market. The technology, however, is severely limited by geographic restrictions, environmental concerns, high upfront costs, and long construction times. Gravity storage takes the attractive cost of pumped hydro and makes it accessible for practically any location.

Levelized Cost, Efficiency, and Lifespan

A recent report from London College Consultants highlights the price disparity between gravity storage and its closest competitors, pumped hydro and compressed air energy storage. Comparing capital, operating, and replacement costs, and residual value, the third-party report found that gravity storage can range from a levelized cost of $88.00-$114.00 per megawatt-hour depending on the discount rate, and many gravity storage startups claim they can beat these numbers at larger scale. For comparison, pumped hydro, the next cheapest form of long-term storage, costs between $113.00-$153.00 per megawatt-hour. Aside from an industry leading levelized cost, these energy storage technologies also claim relatively high round-trip efficiencies (80%-90%), quick construction times, long lifespan duration (up to 50-60 years for most systems), and the ability to cheaply scale up. While these numbers are appealing, many startups are still in the pilot phase of development meaning they have not hit the megawatts required to take advantage of economies of scale. Given the risk averse nature of storage financing, emerging companies face an uphill battle to secure the capital needed to demonstrate the viability of their technology and prove their reported figures.

Leading Vendors

There is a large range of applications for gravity storage among leading vendors. From heavy weights controlled by winches underground to rail cars traveling up and down slopes, gravity storage pushes the boundaries of innovative engineering. One of the fastest emerging gravity storage companies, Energy Vault, uses a six-arm crane to lift and stack recycled 35 ton concrete blocks up and down a 500-foot building. The company is planning a 35 MWh plant for Tata Power in India, with more projects in the pipeline. EarthPumpStore is another advanced startup that seeks to raise and lower containers of compacted earthen materials in abandoned mines and quarries. Finally, Heindl Energy is building a pilot project to demonstrate its hydraulic lifting concept on a large rock mass, with third-party testing to confirm its sealing technology and projected lifespan. Other emerging companies include ARES North America, Gravitricity Ltd., Energy SRS, and Sink Float Solutions.

Looking to the Future

In an industry where the price of Li-ion continues to drop at rates that mirror solar PV, why would an investor commit to a long-term project when price trends can change dramatically in only 5 years? First, Li-ion and other promising redox flow, zinc-air, and molten-salt batteries degrade over time. They also come with safety concerns and high maintenance costs, and excel primarily in short-duration applications. Gravity storage can scale up to meet customer’s needs, meaning it can provide peak shaving and ancillary services at high capacity or long-term bulk storage.

The current grid has been able to support a surge of renewables with cheap and quick electric batteries. However, a future grid with much higher percentages of solar and wind will require longer storage durations to ensure stability all day. The flexibility of gravity storage will offer services that these other batteries cannot, no matter how quickly their prices fall. Finally, the technology does not require expensive materials, which may face shortages as demand continues to rise. As pilot programs transition to grid-scale projects, the economics may become too compelling to ignore—gravity storage may be on the rise.