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:


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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:

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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

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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.