SpaceTEG feasibility study May 1, 2005 B. Tuinstra

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 2 Contents  Introduction  Components and initial trade-off  Preliminary design  Performance study  Weight, Volume, Cost comparison

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 3 Introduction Why SpaceTEG?  Current solar cell arrays have disadvantages Relatively low efficiency High cost Relatively high weight & volume Large area  With developments in TPV and TEG technology a combined TPV and/or PV/TEG system might have advantages over existing state-of-the-art solar panels

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 4 Requirements  General requirements for satellite power  Performance of state-of-the-art rigid panels  Preliminary design based on 0.2 m 2 ( W) modules

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 5 Radiator Sunlight Concentrator PV TEG System Light Heat Electricity Cooling

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 6 Components: concentrator  Light-weight, low volume, low cost  High concentration factor ( )  Combined with radiator Al Black Reflective 50  m Heat conducting rods

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 7 Components: power generator  Different power generator concepts are assessed: TEG (Thermo-electric generator) Thermo-photovoltaic (TPV) cell with absorber/emitter Multi-junction PV cell TPV in combination with TEG MJPV in combination with TEG

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 8 Components: TEG  Convert heat to electricity according to the Seebeck effect  Used in RTGs (radioisotope thermoelectric generators) for satellites, e.g. Cassini  Current technology: Bismuth Telluride based. Efficiency up to 4-5 %.  Emerging technology: nano- scale, quantum well systems (JPL). Efficiencies up to 20% and beyond claimed possible.

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 9 Components: TPV  Absorber/Emitter  GaSb photovoltaic cells ( nm)  Efficiency 25-30% within spectral window  Spectral specific emitters and/or filters emitterfilterTPV cooling electric power sunlight or flame

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 10 Components: TPV  Active development: Self-powered residential heating (flame) Power (co-)generation Solar power  Paul Scherrer Institut, Switzerland  Jx-Crystals, USA  Frauenhofer Institut, Germany  EDTEK, USA

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 11 Components: Multi-junction PV  State-of-the art 3-junction PV cell (data from RWE solar)  Available for TEG: Out-of window Not absorbed Recombination?

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 12 Power generator concepts absorber TEG hot TEG cold Cooling block TEG only reflecting chamber TEG hot TEG cold cooling block MJC reflecting layer MJC + TEG TEG hot TEG cold TPV reflecting layer cooling block filter reflecting cone Absorber TPV (+ TEG)

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 13 Preliminary power generator trade-off  TEG only Very simple, reliable Will become interesting with TEG efficiencies of 20-30% Current and near future TEG efficiencies too low  MJPV + TEG TEG power is limited with current technology Interesting mass, cost ratio?  TPV (+ TEG) TEG not useful when low-frequency radiation is recovered Interesting mass, cost ratio?

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 14 Components: cooling  High heat flux (order 100 W/cm 2 )  Cooling medium: ammonia  Heat pipe technology Similar loads as microprocessor cooling Light-weight grooved aluminium tube Also functions as structural support for concentrator  Transfers heat to concentrator foil

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 15 Components: deployment mechanism  Allow unfolding of umbrella  Transfer heat from power generator to radiator foil keep heat pipe function in tact Elastic deformation pig tail or torsion spring Plastic deformation flat heat pipe, single spring system

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 16 SpaceTEG preliminary design  Primary reflector diameter 0.5 m  Mirror surface 0.2 m 2  Power generator surface 2 cm 2  Secondary reflector diameter 0.05 m

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 17 Modelling: TPV/TEG concept Sun & mirrors -K- TPV rel. area I in P elec P cool I refl TPV -K- TEG rel. area I in I reflect P elec P cool TEG filter I refl. in Solar in T I out Radiative loss Emitter Spectrum Power TPV cooling TPV electrical TEG cooling Emitter temperature loss

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 18 Modelling results: Emitter balance

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 19 Modelling results: TPV balance

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 20 Modelling: MJPV/TEG concept solar spectrum nsun I in I reflect P elec P cool TEG I in P loss I refl Reflection I in loss I refl Reflection I in I refl P elec P cool MJC mirror efficiency MJC cooling MJC power TEG cooling TEG power Radiation loss

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 21 Modelling results: MJC balance

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 22 Modelling results: MJC/TEG performance

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 23 Modelling results: performance  Even for 30% TEG efficiency, a TEG parallel to the TPV does not increase efficiency because low-frequency radiation is effectively recycled  Addition of a TEG does increase MJPV cell system efficiency, marginally for current TEG efficiencies

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 24 Results: Mass estimate  Mass without support structure  BOL

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 25 Results: stowed volume  SpaceTEG can be stowed in a cylinder of 300 x 150 mm  Volume without support structure 300 mm 150 mm

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 26 Results: Cost  Cost for a 0.2 m 2 module, based on rigid solar panel system cost  Costs for panel surface only, without support structure  System cost are dominant; little difference between concepts Item Cost EUR/cm 2 Required [cm 2 ]Total [EUR] TPV/MJC TEG Foil12000 Emitter1000 System Total43600

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 27 Conclusions  Promising technology for solar power generation in space  Including a TEG currently does not or marginally increase efficiency  Mass-specific power up to 450 W/kg  about 6 times lighter than a rigid panel solar array  Volume-specific powers of about 12 kW/m3 are predicted  about as good as a rigid panel  Estimated specific cost as low as 630 Euro/W  3-4 times less expensive than a rigid panel solar array

Stork Product Engineering SpaceTEG feasibility study CONFIDENTIAL 28 Recommendations  Critical points that should be investigated further, in the following areas: Reflecting foil Heat pipes Radiation housekeeping: filters, mirrors Degradation of PV cells Support structure, deployment and pointing devices  Component-level investigations and tests are proposed before designing an integrated breadboard