Cache Energy ($5M to develop low-cost thermochemical battery for renewable energy storage and industrial or residential heating)

Cache Energy, an American energy storage startup founded in 2022, develops a low-cost thermochemical battery for renewable energy storage. The thermochemical battery converts renewable electricity to heat, stores heat, and releases heat or electricity as needed. This is achieved through the reversible chemical reactions of Ca(OH)₂ dehydration and CaO hydration. Both thermal storage materials are cheap, earth-abundant, non-toxic, non-flammable, and non-explosive. Cache Energy’s battery is capable of providing cost-effective, long-duration renewable energy storage.

Challenges: renewable energy storage at a low cost

By 2022, the world had about 1,185 GW of installed solar capacity and about 906 GW of installed wind capacity. Solar power has grown at a 24% annual rate over the last decade. The US solar industry installed 6.1 GW of capacity in the first quarter of 2023, 47% more than in the first quarter of 2022. On the other hand, the average power of new wind turbines installed in the US in 2022 was 3.2 MW, 7% higher than in 2021.

As more and more solar cells and wind turbines are installed, electricity storage systems with long durations would significantly increase the efficiency and reliability of these intermittent renewable energy sources. Although current technologies such as lithium-ion batteries are suitable for a number of applications on the grid, they are not suitable for longer-duration energy storage.

Heat battery

Heat batteries are a promising technology for renewable energy storage due to their efficiency, environmental friendliness, and cost-effectiveness. They are particularly useful for storing energy from intermittent renewable sources like wind and solar, and can play a significant role in the transition towards a more sustainable and renewable energy system. The heat battery technology converts renewable electricity into heat, stores heat, and releases heat or electricity when the sun is not shining or wind is weak.

The heat battery based on reversible thermochemical reactions of slaked lime (Ca(OH)₂) dehydration and quicklime (CaO) hydration has attracted much attention.

During heat storage, Ca(OH)₂ absorbs heat and decomposes to solid CaO and steam, storing the heat as chemical energy. Under atmospheric pressure, the Ca(OH)₂ heat storage temperature ranges from 400 to 600 ºC.

In the exothermic process, CaO reacts with steam to form Ca(OH)₂, releasing stored chemical energy as heat. The released heat temperature ranges from room temperature to 500 ºC. These temperatures allow for the integration of this heat battery with the steam Rankine cycle to generate electricity.

The energy process of this heat battery is depicted by the diagram below.

The energy process of Ca(OH)₂ dehydration and CaO hydration.
The energy process of Ca(OH)₂ dehydration and CaO hydration.

Ca(OH)₂/CaO thermal storage materials are cheap, earth-abundant, non-toxic, non-flammable, and non-explosive, however, their low thermal conductivity (~ 0.1 W/mK) results in a high heat transfer resistance. This causes large temperature gradients within the material bed. Consequently, some parts of the bed materials can reach much higher temperatures than favored for thermodynamics. This exposure to higher temperatures over repeated cycling causes sintering, which reduces thermal storage material’s reactivity and the heat battery’s energy capacity.

Cache Energy Technology

Cache Energy develops a Ca(OH)₂/CaO thermochemical battery based on a well-designed honeycomb fixed bed reactor. Its fixed bed reactor is able to maintain temperature uniformity within the Ca(OH)₂/CaO bed, provide stable power output over a sustained period, and alleviate sintering problems. Since the cost of the fixed bed reactor accounts for about 70% of the total reactor cost, Cache Energy uses cost-effective aluminum or steel material for the reactor to reduce the cost of the heat battery, realizing a cost-effective renewable energy storage solution.

Cache Energy battery

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