Solar Water Desalination
Two conventional methods to harvest solar energy are Solar PV and Concentrated Solar Power (CSP). PV could not utilize the full solar spectrum limited by the bandgap of the absorbing material. CSP, on the other hand, does absorb full solar spectrum. However, the conversion efficiency is lower than PV.
Therefore, a hybrid concept to fully utilize the solar spectrum efficiently was then proposed and supported by ARPA-e’s FOCUS program. In this approach solar spectrum was divided into two bands – PV band and CSP band. A modified CSP trough along with specially designed double junction PV cells was used for the project.
The project team led by Sharp Labs of America and the University of Arizona built this demo system.
A spectrum splitting mirror was inserted into the concentrated light pass to divert a desired solar spectrum band to PV modules. Based on the PV module in use, the split light band is turned by changing the optical coatings. In a perfect scenario, the overall system conversion efficiency can reach 36% annually, surpassing CSP and PV combined for the same footprint.
To test the system with a real application we worked closely with the University of Arizona to develop it further to drive their water desalination units, in which the heat is used to drive the membrane distillation and the electricity is used for the unit operation.
To bring the system cost down, the Si PV module is then employed and the dichroic coating is adjusted accordingly.
Since the heat generated by the hybrid CSP-PV collector is used to drive the distillation process, there is no need to have one more step of energy conversion, such as in the case of using Si PV for water desalination, in which Si PV is used to generate electricity and then the electricity is converted to heat for distillation.
Therefore, the hybrid CSP-PV collector provides an efficient energy solution for water desalination plants. Not only it has a higher solar conversion efficiency but also, for the same footprint of the Si PV area, it produces more electricity.
This technology, continued being developed, shall have a market potential for Solar-Water-Desalination applications.
