Energy Storage Solution Uses Gravity and AI-Controlled Cranes

April 08, 2019 by Scott McMahan

Most energy storage solutions for renewables thus far have focused on some form of rechargeable batteries on a large scale. Battery-based energy storage has the issue of how many charge cycles the batteries can last. Inherent in battery technologies is a gradual decrease in its capacity to hold a charge. One company, Energy Vault, a startup based in Switzerland and California,  has devised a unique solution to the energy storage problem that avoids some of the issues in terms of storage capacity reduction over time, and it also significantly reduces the overall costs.

Energy Vault employs a cylindrical stack of bricks. An AI-controlled crane system lifts bricks to gain potential energy in the form of gravity. Then, when an intermittent renewable energy source is temporarily not producing electricity, the crane system allows gravity to take over. This gradual lowering of the bricks (kinetic energy), in turn, generates electrical power while the renewable energy source is not adding power.

System Inspired by Pumped Hydro Plants

Energy Vault says that their solution was inspired by pumped hydro plants that rely on gravity and the movement of water to generate power. In a similar fashion, the Energy Vault, solution employs the same fundamentals of physics and kinetic energy as pumped hydro. However, it replaces the water with the company's custom made cylindrical blocks that use low-cost materials.

These low-cost blocks, combined with the company's patented system design and some very clever control software, lets their system deliver all the benefits of a pumped hydro system but at a much lower price, and starting size.

Also, unlike such a hydro system, the Energy Vault system does not need to find the right topography.

Energy Vault points out that its system can be safe and simply constructed of waste debris/concrete materials. Furthermore, the system offers safe, long-term operation, according to the company.

Their energy storage stack boasts a cost/kWh that is said to be 50% of current competitor solutions with minimal operating expenses.

It is in the long-term where the system is expected to outperform other energy storage technologies. Energy Vault claims that its system of stacked bricks offers a 30+ year life with essentially "zero" loss/degradation.

The strategy has about a 90% round trip efficiency; Unlike other storage solutions, it enables rapid, on-demand power and discharge. The modular, cylindrical stack can provide a capacity of between 10MWh and 35MWh and more with 2MW to 5MW power output, the company notes.

Energy Vault says that the system is suitable to most industrial and non-suburban locations. While the system is well suited for longer duration storage, it also allows for a rapid response time to deliver short and medium term ancillary services.

Simple and Safe Construction

The firm says that the system is both simple and safe to construct. Construction would begin with an easy-to-install foundation pad and a self-constructing crane. Then, block material is delivered and constructed on-site. Afterward, each completed block is lifted and placed by the crane. Then, once all blocks are in place, the system is operation ready.

While the claims that their energy storage system is much less expensive than other energy storage solutions, the cost is dependent on three primary factors, the capacity of the plant, the cost of the foundation pad, and the cost of the waste materials.