PROTOTYPE DEVELOPMENT AND TESTING OF INFLATABLE CONCENTRATING SOLAR POWER SYSTEMS Drs. Mithra & Usha Sankrithi RIC Enterprises [email protected] ricenterprises.org SOLAR POTENTIAL 2010 world power consumption ~ 17,000 GW Solar radiation at Earth’s surface ~ 90,000,000 GW Recoverable solar power ~ 1,000,000 GW far exceeds humankinds needs CENTRAL RECEIVER SOLAR THERMAL POWERPLANTS ARE AN ATTRACTIVE SOLUTION FOR UTILITY SCALE SOLAR POWER Current Central Receiver Powerplants use Expensive Mirrors (Heliostats) CENTRAL RECEIVER SOLAR THERMAL POWERPLANTS ARE AN ATTRACTIVE SOLUTION FOR UTILITY SCALE SOLAR POWER Heliostats are the largest cost element for Central Receiver Powerplants HOW COULD COST OF HELIOSTATS BE SUBSTANTIALLY REDUCED? Insights & Hypothesis: Most current heliostats use heavy steel and glass mirrors for wind and storm resistance and precise pointing control A very light and inexpensive membrane mirror can reflect sunlight as well as a heavy and expensive steel and glass mirror Could such a light inexpensive membrane mirror be protected for wind and storm resistance using “sandwiching” light inexpensive inflated chambers? INFLATABLE HELIOSTAT RESEARCH OBJECTIVES Conduct trade studies and component / subassembly tests to evolve a preferred subscale prototype design for a lightweight, low-cost inflatable-structure heliostat Refine the design then construct a prototype Test the prototype for: ability of the heliostat pointing system to accurately aim the heliostat ability to form beam shape and concentration on a simulated target ability to function / survive in winds and gusts and precipitation Develop a preliminary design for a production heliostat Develop and document conclusions and recommendations INFLATABLE HELIOSTAT V1.0 REFINED INFLATABLE HELIOSTAT DESIGN GOALS Provide a simple drive system using only two motors, and having low torque requirements Design for inertia and aerodynamic loads to act directly through the support system (no overhanging moments) Design for low aerodynamic loads from winds and gusts using a near-spherical shape Use differential pressure to focus / defocus the membrane mirror Use “sandwiching” inflated domes to protect mirror from exposure to weather Combine the use of direct load paths and the inherent efficiency of inflated structures to yield a lightweight, low-cost design INFLATABLE HELIOSTAT V2.0 Patent 5,404,868 Additional Patents Pending INFLATABLE HELIOSTAT FEATURES INFLATABLE HELIOSTAT TESTING PHOTOVOLTAICS AND CONCENTRATING PHOTOVOLTAICS (CPV) ARE ATTRACTIVE SOLUTIONS FOR SMALLER SCALE APPLICATIONS http://solarpanelsguides.com/wp-content/uploads/2009/05/solar-panels.jpg High efficiency silicon solar cells are the largest cost element for PV INFLATABLE CPV MODULE RESEARCH OBJECTIVES Evolve a preferred design for an inflatable CPV module that leverages the inflatable heliostat design Enable much reduced per-watt cost for high efficiency silicon solar cells through the use of modest (5 – 15 sun) concentration Design and test a full-scale proof-of-concept prototype for: ability of a 1-axis heliostat pointing system to accurately aim the heliostat ability to form a linear focus beam shape on a linear CPV receiver ability to adequately cool the linear CPV receiver ability of inflatable chambers to protect the reflective membrane in winds and gusts and precipitation Develop and document conclusions and recommendations “SURYA” CONCENTRATING PV MODULE FEATURES Patents Pending BUILDING THE SURYA PROTOTYPE BUILDING THE SURYA PROTOTYPE BUILDING THE SURYA PROTOTYPE SURYA SET UP SURYA SET UP SURYA INSTALLED SURYA INSTALLED SURYA INFLATABLE CONCENTRATING PV MODULE SURYA AT WORK Effective linear focus of 8+ suns concentrated sunlight reflected by the reflective membrane SURYA IN THE MORNING Dew covering the ETFE transparent membrane SURYA AT WORK VIDEO: SUN SENSOR TRACKING SURYA AT WORK VIDEO: INVERTED STOW SURYA POTENTIAL APPLICATIONS Private Homeowners, ground mount Private Homeowners, roof mount Private Homeowners, grid-connected & netmetering Private Homeowners, off-grid Commercial buildings, roof mount, gridconnected & net-metering Rural and agricultural area integrated applications Variants suitable for floating applications on ponds, reservoirs, lakes etc. CONCLUSIONS Prototype efforts have validated that: Lightweight, low-cost reflective membranes can be effectively utilized for concentrating solar power Sandwiching inflatable chambers can effectively protect a reflective membrane under adverse conditions Inflatable heliostats with 2-axis tracking for central receiver solar thermal powerplants are technically feasible Inflatable linear concentrating photovoltaic modules with 1-axis tracking are technically feasible RECOMMENDATIONS Additional design and manufacturing refinements will be needed for production lowcost inflatable solar energy harvesting devices, building on lessons learned from the prototype efforts The next step for inflatable heliostat R&D is design, manufacture and test of full-scale prototype or pre-production units The next step for Surya inflatable CPV modules is manufacture and in-service evaluation of pre-production units, leading to certification and commercial production ACKNOWLEDGEMENTS The authors acknowledge with gratitude the dedicated and skilled work of Gary Reysa and Lloyd Hagan in fabricating the prototypes of the inflatable heliostat and inflatable CPV module, respectively. Funding from the US Department of Energy for the inflatable heliostat research is also gratefully acknowledged.