Spectrally selective solar heat absorbers
A new efficient, low cost solution based process to composite films, coatings and high surface area structures consisting of metal nano-particles in a ceramic matrix has been developed. The process allows for great control of particle sizes and metal loadings up to ca 85% can be achieved without coalescence of the metal particles. A very wide range of metals and ceramic matrixes of different complexities have been studied. So far, most attention has been paid to the Ni-Al2O3 system, which has many possible cutting edge applications, e.g. as hard light-weight ceramics, catalysis, magnetic sensors and spectrally selective solar heat absorbers.
Spectrally selective solar heat absorbers absorb energy of the solar light over a wide range from UV to IR and convert it to heat which is used for heating and cooling homes, offices and factories world-wide. Solar heat absorbers are already highly efficient and give 50-75% efficiency compared to 12-20% for solar cells. Presently new techniques allow also for conversion of solar heating to electricity. A high efficiency solar absorber consists of a reflective metal such as aluminum or copper and a thin UV to IR absorbing coating that is transparent in the MIR range, not to get heated and re-radiate heat.
We have optimized a graded three layer structure consisting of two layers of Ni-Al2O3 composites and a top layer of SiO2 together with SSP at UU. The structure yields glossy black films with word record good absorption (97%; 100°C) and emission (5%; 100°C) properties, and is highly durable, which together with the possibility of low cost and high through-put deposition makes it highly competitive. The process has been scaled to roll-to-roll production of 50x0.3 m bands at S-Solar in Finspång. Much larger production for the world market is now considered.
Present research is directed to increase the temperature stability for solar-to-electricity conversion and preparation of different appealing coatings in based on desires from architects. The durability and large absorber elements made possible with our route opens new possibilities in the integration into buildings. Some collaborators are; Dr. K. Jansson at SU, Prof. E. Wäckelgård at Solid State Physics UU and LBNL Berkeley, USA
Examples of publications
- ”Composite materials” G. Westin, A. Pohl, and Å. Ekstrand. Swedish application submitted January 7 2005: 0500031-0, International application submitted January 3 2006; PCT/SE 2006/000004, United States Patent 8034152
- T. Boström, G. Westin and E. Wäckelgård, Durability tests of solution-chemically derived spectrally selective absorbers, Solar Energy Materials and Solar Cells, 89, 197-207, 2005.
- T. Boström, G. Westin and E. Wäckelgård, Optimization of a solution-chemically derived solar absorbing spectrally selective surface, Solar Energy Materials and Solar Cells, 91, 38-43, 2007.