Wood Composite Thermal Battery Provides Sustainable Heating and Cooling Solution

While thermal batteries are typically used for high-power applications such as military equipment and spacecraft, it is possible to use the principles of thermal energy storage to heat or cool homes.

 

A wood composite thermal battery combines renewable sources, including coconuts, lemons, and modified wood. Image used courtesy of Pixabay

 

Researchers at Stockholm’s KTH Royal Institute of Technology have developed a wood composite thermal battery that utilizes a combination of renewable sources–coconuts, lemons, and modified wood–to provide sufficient heating and cooling for homes. This innovative building material incorporates the three components to create an efficient and sustainable solution for thermal energy storage.
 

Thermal Battery

The use of transparent thermal energy storage solutions that utilize latent heat has the potential to reduce energy requirements in buildings significantly. Transparent wood (TW) biocomposites, which offer controlled nanostructure, present numerous possibilities to exploit optical transmittance in various engineering applications, including smart windows. 

TW can be utilized for energy-saving building applications if the thermal insulation properties of polymers are taken advantage of. Incorporating organic phase-change materials (PCMs) into polymer composites is a suitable method for utilizing PCMs as latent heat storage media, which can effectively shift or reduce thermal load peaks in buildings. As they undergo phase transitions, PCMs can absorb and release latent heat through melting and crystallization.

 

Transparent wood biocomposites can be used to shift or reduce building thermal load. Image used courtesy of Pixabay

 

In a thermal battery system for a home, the PCM would be contained in a vessel and heated or cooled when energy is abundant and cheap, such as during the day when solar energy is available or during off-peak hours when electricity rates are lower. The stored energy could then be used when energy is more expensive, such as at night or during peak hours.

For example, during the day, excess solar energy could heat the PCM, releasing heat into the home as it solidifies overnight. Similarly, during off-peak hours, the PCM could be cooled using electricity from the grid and then release cool air during peak hours when air conditioning is needed.

As reported in Small, the latest breakthrough by researchers at KTH shows that they have developed a material that can store both heat and cold. The material has the potential to save approximately 2.5 kWh per day in heating or cooling, per 100 kilos of the material used in housing construction, with an ambient temperature of 24°C (77°F).

Any heat source can charge the thermal battery besides sunlight if the temperature fluctuates around the transition temperature of 24°C. This temperature can be adjusted based on specific application requirements and location.

 

Battery Development

The first step of the process involves removing lignin from the wood, creating open pores in the cell walls, and removing color. Next, a citrus-based molecule called limonene acrylate and a coconut-based molecule are infused into the wood structure. When heated, the limonene acrylate transforms into a bio-based polymer, restoring the wood's strength and allowing light to pass through. At this point, the coconut molecules are trapped within the material, enabling energy storage and release.

The coconut molecules can transition from a solid-to-liquid state, which absorbs energy, or from a liquid-to-solid state, which releases energy, much like water freezes and melts. In the case of transparent wood, this transition occurs at a more comfortable 24°C.

This transition allows for surroundings to be either heated or cooled, depending on the situation.

The versatile material has the potential to be used for both interior and exterior building applications, offering transparency and energy savings. Initially, the material would be used for regulating temperatures around the 24°C mark to cool and heat interior spaces. Further research is necessary to develop the material for exterior use.
 

Transparent wood is versatile and could be used in horticulture and agricultural applications. Image used courtesy of Pixabay

 

The material's potential applications are not limited to homes or buildings, however. It could also be used as a future material in greenhouses. As the sun shines, the wood becomes transparent, allowing for the storage of more energy, which is then released at night when the wood becomes cloudy. This process would help reduce energy consumption for heating and improve plant growth.