Maximizing Power from the Sun
By mounting solar photovoltaic (PV) converter panels to a metal surface and forming a wall, Professor Van Carey at UC Berkeley has created an evaporator passage through which a Rankine-cycle coolant flows. A reflective structure concentrates solar energy on the photovoltaic element, increasing its electrical power output roughly proportional to the increase in incident radiation. This is advantageous because a reflective surface is generally cheaper than photovoltaic cells, per unit area. The trick is to keep it cool.
This design is of interest because the evaporator channel can remove heat from the back of the PV panel at high flux levels, provided that an optimal two-phase flow regime is maintained in the evaporating coolant flowing through the channel. The proposed research would explore the use of model-based digital control to conduct the flow conditions and collector angle that would maximize the conversion efficiency of the hybrid system while keeping the PV temperature within acceptable bounds. This hybrid design has the potential to be much higher efficiency than power generation using PV only.
For this type of system, the two-phase flow in the evaporator may exhibit pressure and temperature oscillations. The processor must therefore have the capability to monitor sensors in order to detect variations in frequency and alter the system valve and/or pump setting to keep the two-phase flow in the proper regime.
Next Steps: The next steps for this project include (1) designing and building a prototype hybrid solar system of the type described, and (2) developing the sensors and control system to optimize system performance.