PROTOTYPE DEVELOPMENT AND TESTING OF INFLATABLE CONCENTRATING SOLAR POWER SYSTEMS

Drs. Mithra & Usha Sankrithi RIC Enterprises

drsankrithi@gmail.com 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

High efficiency silicon solar cells are the largest cost element for PV

http://solarpanelsguides.com/wp-content/uploads/2009/05/solar-panels.jpg

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 WORKEffective linear focus of 8+ suns concentrated sunlight reflected by the reflective membrane

SURYA IN THE MORNINGDew 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 & net-

metering Private Homeowners, off-grid Commercial buildings, roof mount, grid-

connected & 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 low-cost 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.