A new startup, Energy Vault, is attempting to be one of the pioneers of a new system for storing renewable energy with the help of cranes and concrete blocks. It’s a low-tech energy storage solution so promising that the company recently raised $100 million in a Series C funding round.
Understanding Gravity Based Storage
Before we get to concrete, we can understand how this works by looking at dams and hydro electric power. Essentially, all water above sea level is pulled down to the lowest possible point by gravity. This is what drives the motion of water through rivers. When we dam those rivers, we “store” that moving water. If we put turbines at engineered “escape points” in the dam, gravity pulls the water through the turbines, spinning them, and generating electricity. We control the amount of water we let escape dynamically based on the energy demand at the time. In this way, gravity-based energy storage systems are not new, but traditionally these systems are usually built to utilise hydropower.
A Problem and Solution When it Comes to Storing Excess Power
To prevent brownouts, energy producers always produce more power than is required, but that excess power is usually wasted. This is both inefficient, and bad for the environment. Battery technology still hasn’t quite caught up to the massive requirements of our electricity grids.
A novel solution to this storage problem in use today by hydro electric generators is to use that surplus power to recapture the water and re-store it behind the dam. Essentially, surplus energy is used to pump water to a reservoir at a higher elevation. Then, as before, gravity pulls this water back down through a turbine to generate electricity a second time. It’s an efficient system but one that can only be built in topographically accommodating locations. We need a solution that could store surplus energy in any location.
A Bigger Problem with Renewables
Solar and wind power have big limitations when it comes to regulating their output. The weather can be highly unpredictable, so power generation can drop on a cloudy day or spike during a windy one. If power generation is low during peak hours, the energy grid must rely more heavily on power derived from fossil fuels.
Likewise, if power generation spikes on a hot, windy day to the point where it exceeds demand, storing that surplus and distributing it later is not really possible. Renewables, more than other types of power, need a reliable storage solution to help them match supply with demand.
Concrete blocks: the low-tech, cleantech, battery alternative
Often the most simple solution is the best one. Energy Vault’s twist on gravity-based energy storage involves cranes that extend from the top of a 35-story tower. The six cranes use surplus energy generated from wind or solar farms to haul 35-ton blocks up to the top of the tower. Then, the cranes slowly release them allowing them to be pulled back down by gravity, which, you guessed it, spins turbines that generate electricity.
It’s an innovative system with massive potential. Each tower has a storage capacity of 80 megawatt-hours and can discharge this energy at a level of 4 to 8 megawatts for 8 to 16 hours. For context, the average US household uses about 12 MWH per year.
By cooperating with wind and solar farms, Energy Vault’s towers can help store excess energy generated by optimal weather conditions and disperse it to the grid later when usage peaks.
There are other advantages besides grid efficiency as well. For example, the blocks are much more environmentally friendly than batteries. Batteries are made from polluting chemicals and are difficult to recycle and manufacture. In contrast, the blocks used in Energy Vault’s towers can be made directly on-site using dirt and waste material mixed with concrete. Even better, the towers are half as expensive as batteries to operate, and can last up to 35 years.
Gravity-based energy storage may not be new, but Energy Vault’s environmentally sound approach may be one solution to a significant obstacle preventing further renewable energy adoption.