1. Numerical Analysis of Micro Channel Heat Sink Cooling
System for Solar Concentrating Photovoltaic Module
by
K. S. Reddy1*, S. Lokeswaran1, Pulkit Agarwal1,Tapas K. Mallick2
Department of Mechanical Engineering
Indian Institute of Technology Madras, Chennai - 600 036, India.
Environment and Sustainability Institute, University of Exeter, Cornwall, UK
*Corresponding Author-E-mail: ksreddy@iitm.ac.in, Tel: (044)
22574702, Fax: (044) 22574652
International Conference on Advances in Energy Research
IIT Bombay, Powai, 10th-12th December 2013

2. Organization of Talk
•
Introduction to CPV
•
Types of CPV system
•
Need for an Effective Cooling system
•
Dense Array CPV system
•
Numerical Simulation of Micro-channel heat sink
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Serpentine Flow Channel
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Parallel Flow Channel
Combined Flow Channel
Summary

3. Introduction to CPV
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Cost of electricity by conventional photovoltaic system is high
CPV objective is to reduce system cost by
Replace expensive semiconductors with inexpensive lenses/mirrors
Incorporate small-area, high-efficiency solar cells
•
The generation cost per unit energy is given by
Reduce use of semiconductor material
Higher efficiency can reduce
area costs
•
Reduced area allows to afford the high cost for cells.
R. King, “MultijunctionCells: Record Breakers,” Nature Photonics, Vol2, 284-286 (2008).

4. Types of CPV System
 Based on Concentrator
SPIE 2009 David Miller, et al
 Based on geometry
• Single cells
cell has an area roughly equal to that of the
concentrator available for heat sinking
• Linear geometry
parabolic troughs or linear Fresnel lenses
Heat dissipated from two of the sides
and the back of the cell.
• Densely packed modules
dishes or heliostat fields
Only way to dissipate heat is from cells’s rear
side
Images courtesy of Amonix
Images courtesy of Airlightr Energy
courtesy of Solar Systems, Australia

5. Dense Array CPV System
Components of CPV System
Parabolic Concentrator
Secondary Concentrator
Optical Homogenizer
CPV Module
Active Cooling System
Images courtesy of IBM
CPV Cells
Substrate
Images courtesy of Airlightr Energy

6. Need for an effective cooling system
•
Increased light intensity will
–Increases photocurrent (additional photons)
–Reduces open-circuit voltage (increased heat)
I sc
Voc
•
•
•
•
CI sc0
Voc0
nVt h ln(C )
n - diode factor and
Vth -thermal dependency of the cell efficiency
Irradiance on cell should be homogeneous both in quantity and quality
Conversion efficiency increase with concentration factor but fill factor is degraded by
increasing resistance losses
The solar cell performance will decrease drastically by 50% when the cell’s surface
temperature increased from 46 C to 84 C [1].
Excessive thermal energy may degrade the CPV resulting in permanent damage.

7. Parallel Serpentine and Straight Flow Module
Parallel Serpentine Module
Parallel straight flow Module
 A combinatory model
High heat removal effectiveness of
Serpentine micro-channels
Low
pressure
drops
in
straight
micro channels

8. Combined Micro-channel for CPV Module
Flow arrangements patterns
3 inlets
Complete micro-channel module
6 inlets -single flow
6 inlets - alternate flow

9. Numerical Simulation of Micro-channel heat sink
•
•
The analysis was carried out Using CFD software ANSYS 13
Steady, incompressible, laminar flow conditions Parameters used for micro channel heat sink simulations.
Parameters
Values
Properties of plate (Copper)
Parameter
values
Properties of coolant (water) at 40°C
Density
8978 kg/m3
Density
998.2 kg/m3
Specific heat Cp,S
381 J/kg K
Specific heat Cp,S
4182 J/kg K
Thermal conductivity
Kp
387.6 W/m
K
Thermal conductivity
Kw
Viscosity µS
0.6 W/m K
0.000653 Pa s
 The optimal design is determined by minimizing and comparing the following four parameters:
Pressure drop the micro channel ΔP,
Average temperature of the heat sink bottom
Temperature uniformity index UT
Surface temperature difference ΔT = Tmax - Tmin
Boundary conditions used in micro channel heat sink simulations.

10. Results for Straight Flow channel
Effect of Reynolds number on pressure drop
Effect of width of micro channel on T ,Tavg and UT(K)
Effect of aspect ratio on T ,Tavg and UT.
Effect of Reynolds number on T , Tavg and UT.

11. Results for Serpentine Flow channel
•
•
•
PV cell width constrain is 12 mm
Decreasing pitch results in higher volume flow rate leading to higher pressure drops across
the micro channel array
Micro channel
Width 0.5 mm
Pitch = 0.5 mm
Aspect ratio = 0.125

12. Analysis of profile region
Figure : Velocity contours of micro-channel and profile region in transition flow conditions
Figure : Pressure contours of micro-channel and profile region in transition flow conditions

13. Results for Combined Flow Channel
Cumulative pressure drop along flow direction
Variation of Vout2-Vin2and pressure drop for different profile regions
Complete velocity profile in single channel
Variation of flow velocity pressure drop for different microchannel
arrays

14. Results for Combined Flow Channel
Temperature profile of surface of water along fin height with the flow direction
Temperature contour of bottom surface of heat sink along the flow direction

15. Summary
•
•
•
Investigation of micro-channel cooling technology with different flow arrangement has been
carried out.
The optimized geometry of micro channel for the CPV receiver was found to be
W=0.5 mm
Aspect ratio = 0.125
Pitch = 0.5mm
The final results
Temperature of CPV module of dimensions 24x24 cm = 10 K rise
Pressure drop of 8.8 kPa along a single channel with six such channels
Flow rate of 6.35 L/min.

16. References
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Leonardo Micheli, NabinSarmah, XichunLuo, K.S.Reddy, Tapas K Mallick, (2013)
Opportunities and challenges in micro-and nano-technologies for concentrating photovoltaic
cooling: A review, Renewable and Sustainable Energy Reviews, 20: pp. 595–610.
Royne, C.J. Dey and D.R. Mills, (2005) Cooling of photovoltaic cells under concentrated
illumination: a critical review. Solar Energy Materials and Solar Cells, 86(4): pp. 451-483.
Lasich, J.B. (2002) Cooling circuit for receiver of solar radiation.Patent no. WO02080286.
Vincenzi, D., Bizzi, F., Stefancich, M., Malagu, C., Morini, G.L., Antonini, A. and
Martinelli, G. (2002) Micromachined silicon heat exchanger for water cooling of concentrator
solar cells. PV in Europe Conference and Exhibition - From PV technology to Energy
Solutions, Rome
Min, J.Y., Jang, S.P. and Kim, S.J. (2004) Effect of tip clearance on the cooling performance
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Lee, D.-Y.andVafai, K. (1999) Comparative analysis of jet impingement and microchannel
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Ryu, J.H., Choi, D.H. and Kim, S.J. (2003) Three-dimensional numerical optimization of a
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Bejan, A.(1993) Heat Transfer, John Wiley & sons, Inc.,Singapore.