TEXEL Energy Storage (A simple cheap thermochemical battery uses limestone for renewable energy storage)

TEXEL Energy Storage, a Swedish energy storage startup founded in 2018, develops a simple, cheap thermochemical battery that can store electricity from renewable sources like solar cells and wind turbines. The battery is charged with renewable electricity by heating limestone (CaCO₃), which breaks down into CO₂ gas and calcium oxide (CaO). CO₂ can be stored with minimal energy loss. During discharge, CO₂ combines with CaO to regenerate CaCO₃. Heat released from the reaction is used to produce electricity. The design of the battery system improves its efficiency to 90%.

Challenges: Using lithium batteries to store renewable energy costs too much

More and more solar cells and wind turbines are being installed to produce clean electricity and cut down carbon emissions. The ability to store these intermittent renewable electrical energy would significantly increase the efficiency and reliability of solar and wind energy.

In order to preserve the high quality of electricity generated by renewable electric energy sources, it should be stored in rechargeable batteries, such as lithium-ion batteries. According to a BloombergNEF report, the average cost of lithium-ion batteries in 2021 was $132 per kWh. The cost of energy storage must range between $30 and $70 per kWh in order to provide baseload electricity at $0.10 per kWh with the optimal wind-solar mix. The high cost of lithium-ion batteries prevents their widespread applications as grid-scale energy storage solutions.

The storage of electricity as low-grade heat is a cost-effective solution. Nonetheless, this downgrade is not considered to be commercially viable. Instead, concentrated solar power has been used to focus the solar radiation either directly to a Stirling engine to produce electricity or to a heat storage to generate heat.

As solar cells and wind power plants become less expensive and more efficient, thermal storage of renewable electricity would become a solution that is simple and inexpensive.

TEXEL Energy Storage Technology

TEXEL Energy Storage (TEXEL) has developed a simple and cost-effective thermochemical battery for storing electrical energy from renewable sources. During charging, the thermochemical battery uses renewable electricity to heat calcium carbonate (CaCO₃, limestone), which decomposes at a high temperature into CO₂ gas and calcium oxide (CaO). CO₂ is stored in a tank. During discharge, CO₂ is released to react with CaO, and the resulting heat is used by a Stirling engine to produce electricity. Heat generated during the charging and discharging is supplied to buildings or used to preheat CO₂ gas, thereby improving the total efficiency of the system.

TEXEL energy storage

The diagram below depicts the TEXEL energy storage system.

TEXEL Energy Storage thermochemical battery for renewable energy storage (ref. US20230272981A1)
TEXEL Energy Storage thermochemical battery for renewable energy storage (ref. US20230272981A1).

The system includes a reaction chamber, a CO₂ storage tank, a compressor, a pressure relief valve, a thermocline filter, a Stirling engine, a heat exchanger, as well as sensors and controllers (not shown).

  • Reaction chamber

The reaction chamber includes resistive heaters and powders of thermochemical material. The resistive heaters can heat the reaction chamber to around 900 ºC by receiving power from renewable energy sources, such as solar cells and wind turbines.

The thermochemical material is CaO when the battery is fully charged. When the battery is fully discharged, the thermochemical material is transformed into calcium CaCO₃ via the reaction between CaO and CO₂ gas.

  • CO₂ storage tank

CO₂ from the decomposition of CaCO₃ is stored as liquid in a tank at 20 ºC and 65 bars. The storage of liquid CO₂ reduces the storage tank’s volume. CO₂ can be stored with minimal energy loss for long time periods. When the battery is discharging, CO₂ is released into the reaction chamber where it reacts with CaO to produce heat. A Stirling engine uses this heat to generate electricity.

  • Compressor

When the battery is being charged, the compressor moves the CO₂ gas from the reaction chamber to the storage tank and compresses it to a high pressure.

  • Pressure relief valve

The pressure relief valve is completely closed when CO₂ is stored in the tank. When the battery is discharging, the pressure relief valve is open and controls the CO₂ release pressure into the reaction chamber.

  • Thermocline filter

The thermocline filter contains sand. During the charging process, the hot CO₂ gas from the reaction chamber passes through the sand to cool before being stored in the tank. Sand stores the absorbed heat from CO₂ gas. When the battery is discharging, the hot sand can preheat the CO₂ gas before reinjecting it into the reaction chamber. Therefore, the thermocline filter increases the efficiency of the energy storage system.

  • Stirling engine

When the battery is discharging, the reaction of CaO and CO₂ gas in the reaction chamber generates heat. This reaction heat is transferred to the heater head of the Stirling engine. The Stirling engine starts to rotate and drives the generator to produce electricity. The Stirling engine operates between 750 and 900 ºC, providing a high efficiency and high power output.

Depending on the requirements of the system, the Stirling engine has a nominal power output of between 1 and 100 kW. Several thermochemical batteries can be arranged in parallel for higher power outputs.

  • Heat exchanger

When the battery is being charged, the Stirling engine is not in operation. The heat exchanger’s coolant is at a low temperature. The heat exchanger can be used to cool the CO₂ gas for storage.

When the battery is discharging, the heat exchanger collects and dissipates heat from the Stirling engine. This increases the efficiency of the Stirling engine. The heat exchanger now supplies heat for buildings or preheats CO₂ gas. The heat exchanger increases the energy storage system’s efficiency.

How TEXEL energy storage works

The TEXEL thermochemical battery outputs about 90% of total input renewable energy: 40% electric energy and 50% heat. The battery’s charging and discharging processes are described below.

  • Charging
Charging process of TEXEL thermochemical battery.
Charging process of TEXEL thermochemical battery.

During charging, renewable energy sources supply electricity to the resistive heaters that heat the reaction chamber to about 900 ºC. CaCO₃ decomposes via the following reaction into CO₂ and CaO:

CaCO₃ → CaO + CO₂↑

This reaction is endothermic. The hot CO₂ gas passes through the sand in the thermocline filter. The sand absorbs heat from CO₂ gas and stores it for use during the battery’s discharge. A heat exchanger can cool CO₂ gas further. The cool CO₂ gas is compressed and stored in the tank as a liquid with minimal energy loss for long time periods.

When the battery is fully charged, 70-90% of CaCO₃ is decomposed.

  • Discharging
Discharging process of TEXEL thermochemical battery.
Discharging process of TEXEL thermochemical battery.

During discharge, the pressure relief valve is open. Liquid CO₂ becomes gas, which then passes through the thermocline filter and enters the reaction chamber. The sand in the thermocline filter and the heat exchanger preheat CO₂ gas. This improves the thermochemical battery’s efficiency.

In the reaction chamber, preheated CO₂ gas reacts with CaO via the reaction:

CaO + CO₂ → CaCO₃

This reaction is exothermic. The reaction heat raises the temperature of the reaction chamber to about 900 ºC. The heat is transferred to the Stirling engine that drives a generator that produces electricity.

The heat exchanger cools the Stirling engine. The transferred heat preheats CO₂ gas and/or is supplied to buildings.

When fully discharged, most CaO reacts with CO₂.

TEXEL Energy Storage Patent

  • US20230272981A1 Thermochemical energy storage device

TEXEL Energy Storage Applications

  • Renewable energy storage

TEXEL’s thermochemical batteries are applied to the renewable energy sector. The following companies use TEXEL’s products:

Svevind: Svevind, a Swedish wind energy company, has collaborated with TEXEL to develop energy storage systems for renewable energy.

AltaSea: AltaSea and TEXEL Energy Storage signed an agreement in 2022 to demonstrate large-scale energy storage/battery technology in California.

TEXEL Energy Storage Products

TEXEL produces thermochemical batteries for renewable energy storage.

TEXEL Energy Storage Founder

Lars Jacobsson is Founder.

TEXEL Energy Storage CEO

Lars Jacobsson is CEO.

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