In conjunction with Combustion Analysis Laboratory and the Laboratory for Manufacturing and Sustainability in Mechanical Engineering, our research aims to develop a Rankine cycle heat engine system which will convert sunlight to heat at 60-80% solar-thermal efficiency and electricity at 8-10% solar-electric efficiency using concentrating solar collectors. In contrast to photovoltaic systems which cost ~$7/Watt [Solarbuzz, 2007] of generator rated peak electrical output, in mass production the proposed collector and generator system sized at 1-10kW would cost ~$4/Watt electricity or $0.80/Watt heat, allowing adjustment of heat and electrical output on demand. Considering that 112 MW of grid-connected PV was installed in the U.S. in 2006, there is a large proven market for solar energy. With widespread market penetration, this system would reduce greenhouse gas and criteria pollutant emissions from electricity generation and heating for a significant portion of the developed and developing world.
There are currently two prevalent technologies for solar-electric energy conversion: photovoltaics harness the photo-electric effect for direct conversion of light to electricity, and solar thermal collects light as heat, driving mechanical-electrical generators; typically using a Rankine Cycle. While photovoltaics exist in both centralized and distributed power applications, solar-thermal power is exclusively used in centralized plants. This is due to the fact that the expanders required in a Rankine cycle do not operate efficiently at low power levels (1 - 10 kW). If this technical barrier can be overcome, distributed solar-thermal could have several advantages over distributed photovoltaics: photovoltaic technologies cannot currently store excess energy economically; while energy in the form of heat can be cost effectively stored using available thermal storage technologies. Additionally, semiconductor processing requires large amounts of energy, water, and harmful chemicals; whereas solar-thermal technology uses more easily processed engineering materials, such as steel, glass, and rubber. Solar thermal may thereby provide cheaper, more reliable and environmentally benign distributed generation in a variety of economies worldwide. As outlined in the 2005 Dept. of Energy publication “Basic Research Needs for Solar Energy Utilization,” moderate temperature distributed solar thermal is an area where there is potential for significant breakthroughs to reduce the cost of solar energy.
Current research focuses on the following: (1) Determine likely candidates for the power generation device in moderate temperature heat engine applications. (2) Characterize the environmental impact (embodied energy, toxicity, and global warming pollution) of each potential design, and provide an example of how to consider these impacts during the design stage. (3) Optimize the system design using integrated multi-objective design-optimization over the following parameters: solar conversion efficiency, weight, cost, and environmental impacts. (4) Produce a moderate temperature expander design and prototype and a viable business model.