Class: Principles of Engineering Practice (3.004)
Term: Spring 2017
Presented at "UTokyo-MIT International Seminar on Materials"
To meet the base power load of a city with solely renewable energy, our team proposed a system that combines solar energy and thermal electricity from heat storage.
The solar cells will be 2-layered parallel junction PV. Parallel junctions solar cells use multiple materials with varying band gaps to capture a wider range of rays. Parallel junctions, as opposed to stacked multi-junction cells, also generate less heat, which increases efficiency. There will be two materials used in the cells, GaAs (band gap: 500-700 nm) and Ge (band gap: 900-1200 nm), which have already demonstrated success in multi-junction solar cells.
The thermal component of our system will harness the wavelengths of light in the ultraviolet spectrum from 100-500 nm. Transparent piping will run over the cells. The piping is filled with thermal heating fluid, which absorbs ultraviolet light that is below the band gap of the materials in the solar cell. The system is elevated above ground level on a platform that can tilt and pivot depending upon the sun’s position. The piping and the heating fluid will allow for the absorbance of light in the ultraviolet spectrum, but the light within the range of band gaps of the solar cells will be transmitted. Proposed heating fluids include organics or refrigerants, such as ammonia, which do not absorb visible light. The piping will be curved; this concavity will focus the light on the cell, similar to a magnifying glass. The material of the piping must be strong enough to carry the heating fluid and heat resistant above the maximum temperature the heating fluid will reach. Cross-linked polymers have the potential to provide both of these properties. The energy generated from the thermal component of our system can be used during times when solar is not optimal, like at night.