A new material can generate solar energy and store this energy for several months at room temperature. Among other things, the material can help harness surplus solar energy generated in the summer into the winter months. It is a crystalline material, which once energy is needed can release it in the form of heat.
The material was developed by researchers John Griffin, Kieran Griffiths and Nathan Halcovitch from the UK's University of Lancaster. Globally, and certainly in Europe, we are moving away from fossil fuels and making the switch to renewable energy sources. However, this also brings challenges. For instance, the sun is an interesting source of renewable energy, but does not always provide the same amount of energy. Due to the sun's intensity, for example, the yield in the summer months can be significantly higher than in the winter months.
Imbalance
This creates an imbalance in energy production and demand, which needs to be addressed. The University of Lancaster's development could potentially help with this. The university reports having developed a material that can not only generate solar energy, but also store this energy for longer periods of time. This theoretically allows solar energy generated in the summer to be stored in the material and released in the winter months.
However, the researchers also foresee other applications. For example, they envisage a thin coating of the material, which could be applied to the outside of office buildings and homes to store energy. Another example the researchers describe are car windows. By applying a coating of the material on these, the energy needed to defrost the windows during winter could be stored directly in the windows.
Metal-organic framework
The material is based on a so-called metal-organic framework (MOF). A MOF consists of a network of metal ions connected via carbon-based molecules to form 3D structures. A key feature of MOFs is that they are porous, meaning they can become composites by incorporating other small molecules into their structures.
University of Lancaster researchers have investigated an existing MOF composite: DMOF1. This was previously developed by Japan's Kyoto University for a different purpose. The UK researchers have investigated whether DMOF1 is also suitable for energy storage, something not previously investigated.
Azobenzene molecules
During their experiment, the researchers filled the pores of MOF with azobenzene molecules, a material that strongly absorbs light. These molecules can act as photoelectric switches. These are a kind of molecular machines that change shape if stimulated by external factors such as light or heat.
The material is then exposed to UV light, which causes the azobenzene molecules to change shape and come under tension. This stores energy, similar to the way a spring stores energy. Because the molecules are stored in the small pores of the MOF, it can be kept at room temperature for an extended period of time.
Suitable for at least four months of storage
The stored energy can be released by applying external heat, which can be used to change the state of the switch. The experiments at the University of Lancaster also show that the energy can be released very quickly. During the experiments, the material was found to be capable of storing energy for a period of at least four months. In comparison, for most comparable materials, this is only a few hours or days.
Another key difference between the DMOF1 and other concepts for energy storage in photoelectric switches is that in previous experiments, these switches had to be in a liquid. This is not the case with DMOF1. Because a solid material is used, it is more chemically stable and easier to store, the researchers report. Among other things, this makes it easier to incorporate the material into coatings and stand-alone devices.
"The material functions a bit like phase transition materials, which are used in hand-heaters. However, hand warmers need to be heated to charge them. The beauty of this material is that it obtains 'free' energy directly from the sun. There are no moving or electronic parts and there is no loss in storing and releasing solar energy. We also hope to develop other materials that can store even more energy," explained Dr John Griffin, Professor of Materials Chemistry at Lancaster University and involved in the research.
More information is available here.
Author: Wouter Hoeffnagel
Image: Karolina Grabowska via Pixabay
