Rondo Energy ($82M to develop low-cost heat battery for renewable energy storage and industrial decarbonization)

Rondo Energy, an American clean tech startup founded in 2020, has developed a low-cost thermal storage system to store intermittent wind and solar energy at grid scale and outputs heat, steam, and/or electricity for various industrial applications. Such a thermal storage system is known as a heat battery. The Rondo heat battery has a capacity to store 300 MW and continuously delivers a hot gas stream at a constant temperature between 800 and 900 ºC, as well as superheated steam when coupled with a steam generator. The hot gas flow and steam provided by the Rondo heat battery help energy-intensive industries, such as cement production and steel manufacturing, reduce carbon emissions.

Challenges: renewable energy storage

Renewable energy storage

Renewable energy sources like wind and solar power are becoming more important as the world moves toward sustainability. These renewable energy sources are unpredictable. They might make more energy than is needed during the day, but not enough energy to meet needs during the night. Therefore, this transition requires grid-deployable large-scale energy storage solutions to deliver a stable and reliable energy supply for homes and industrial applications.

Wind turbines produce clean electricity in Austria.
Wind turbines produce clean electricity in Austria.

Renewable energy storage solutions include pumped hydroelectric storage, compressed air energy storage, flywheel energy storage, stacked blocks, liquid air, underground compressed air, and flow batteries. Lithium-ion battery technology for grid-scale energy storage has limitations of material sourcing, high cost, and performance, which make them less than ideal for large-scale energy storage. Most of these storage solutions only deliver electricity on demand, which might not be suitable for industrial applications that need heat or steam.

Heat battery

The thermal storage system is a promising way to store energy on a grid scale. It involves putting heat converted from extra renewable energy into a storage medium and then using that heat to make heat, steam, or electricity when it is needed. The thermal storage system is called a “heat battery”. So, the heat battery can be used in residential and industrial locations that need heat, steam, and/or electricity.

Many heat batteries have problems with uneven heat distribution, brick wear from heating and cooling cycles, and safety and maintenance issues.

They have issues of “thermal runaway” or “heat runaway” which happens when there are even small imbalances between how local heating is done with resistive heating elements and how local cooling is done with heat transfer fluid flow. Changes in how fast things heat up and cool down can cause temperatures to get out of control, which can cause heaters to break and refractory materials to wear out. Any such failure  would require the powering down of heaters, disassembly, and replacement of cracked bricks, which would be time-consuming and expensive.

They also have severe limitations in terms of the temperatures that are practically achievable, as well as material usage and storage capacity.

Rondo Energy Technology

Rondo Energy (Rondo) has developed a low-cost heat battery that efficiently stores thermal energy generated from intermittently solar and wind energy and delivers continuous flows of hot air (or hot CO₂) and steam at a controllable temperature for many industrial processes, such as making cement, steel, hydrogen, and ethanol. By integrating the Rondo heat battery with these industrial processes, we can use less fossil fuels and reduce carbon emissions.

The Rondo heat battery’s key innovation is that it prevents “thermal runaway” or “heat runaway” by cooling thermal storage bricks well below their operating temperature in alternate discharge cycles. In addition, the Rondo heat battery can be heated by electrical energy while delivering convectively heated air and steam. That is, the heat battery can simultaneously charge and discharge.

Rondo heat battery

The diagram below depicts the Rondo heat battery system.

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