Earle Wilson, PhD; PE Di Director, Energy Unit t E U it School - - PowerPoint PPT Presentation

Theoretical and Operational Thermal Performance Theoretical and Operational Thermal Performance

• f a 'Wet' Crystalline Silicon PV Module under

Jamaican Conditions

Earle Wilson, PhD; PE Di t E U it Director, Energy Unit

School of Engineering University of Technology, Jamaica

Overview of Presentation Overview of Presentation

• Problem Statement

Problem Statement

• Attempted Solutions to Problem

h S l i

• My Approach to Solution
• Conclusions from my approach
• Questions???

Problem Statements Problem Statements

• The conversion of light energy to electrical

The conversion of light energy to electrical energy (conversion efficiency) of photovoltaic (PV) cells is reduced as the working (PV) cells is reduced as the working temperature of the cells is elevated.

• The Power Output (conversion efficiency) of
• The Power Output (conversion efficiency) of

the cells is further reduced when the cells

• perate in low latitude conditions such as
• perate in low latitude conditions such as

those in Jamaica, West Indies

What affects Power Output (Conversion Effi i ) f h C ll i ll h f Si? Efficiency) of the Cells, especially those of c‐Si?

• Voc ≈ UTln(Isc/Io)
• c

T ( sc/ o)

Where, Voc, = open circuit voltage I0 = saturation current But

I0 proportional to T4

Where T is working temperature of cell Therefore, cool cells = higher efficiency

Attempted Solutions to Problem (A li d C li T h i ) (Applied Cooling Techniques)

• Cells laminated on copper fin absorber
• Cells laminated on copper fin absorber

with water tube welded on the back is d b B d K i used by Brogren and Karisson

• Heat spreader made of aluminum plate

attached to cells is proposed by Araki et attached to cells is proposed by Araki et al.

Cooling Techniques cont’d Cooling Techniques cont d

• Farahat employs evaporative cooling based

Farahat employs evaporative cooling based

• n heat pipes theory
• Increasing thermal mass of modules by

attaching them to small water filled tanks is attaching them to small water filled tanks is used by Ronnelid et al.; and Krauter

• Sweelem et al. blows air across the back of

the cell through an adjustable air‐gap. the cell through an adjustable air gap.

Most Efficient Cooling Solution Most Efficient Cooling Solution

• Circulating water over the back surface of the

Circulating water over the back surface of the cell proves to be the most effective (Brogren and Karisson) and Karisson). Drawback: This system needs a circulating pump which requires power to run; so the pump which requires power to run; so the pump becomes a power drain on the PV system system.

Other Solutions Other Solutions

• Furushima and Nawata employed siphonage

Furushima and Nawata employed siphonage with controller for valve‐openings, utilizing city water to supply tank on top of the

• building. No need for circulating pump

Drawbacks: Complex; Hard to keep siphonage; Some level of maintenance is needed.

• My Solution

My Solution My Solution

• Gravity‐Fed Technique

y q

Water being diverted from upstream a source such as a river, channeled across the back of a PV module (‘wet’ module), cools the module and returns to the river module), cools the module and returns to the river downstream. The power required to drive the water through the system comes from the hydraulic head of the flow stream under comes from the hydraulic head of the flow stream under gravity, due to the difference in elevation.

Drawback: Limits the system to regions that have water Drawback: Limits the system to regions that have water

• supply. Hence use in remote or semi‐remote PV

power generation

Schematics of a Gravity‐Fed Cooling (GFC) System

Theoretical Consideration Theoretical Consideration

(Performance Modeling)

• How does the temperature (U) across a cell varies with

position (x) and time (t)

]} [ ] {[ ] [

2 2 2 ) , (

4 ) 1 2 ( 2 ) 1 2 ( ) ( L t n Exp L x n Cos F x L k q U U

n L t x

π α π − − × − + − + =

∑

∞

]} [ ] {[ ] [

2 1 ) , (

4 2 L L k

n

∑

=

Operational Performance

(experimental setup)

water tank t i water in

Picture of Photo‐voltaic (PV) Module

water to drain pv module

Si l t d GFC S t Simulated GFC System

Results from Mathematical Modeling

55 60 Temp profile after 0.05 sec of switching on cooling water

Front face Back face

45 50 Temp (deg C)

face

35 40 Temp profile after 0.1 sec of switching on cooling water 0.5 1 1.5 2 2.5 3 25 30 Cell thickness (mm) Temp profile after 1.0 sec of switching on cooling water

Time-Steps of Temperature profiles for a modelled 3mm thick ‘wet’ PV cell with irradiance of 1000 W/m2 incident on front face and back face held at water with irradiance of 1000 W/m incident on front face and back face held at water temperature of 28 oC

Results from Experiments

4.3 4.4

Open Circuit Voltage(Voc ) vs Module Temperature

4.1 4.2

t voltage (V)

3 9 4 4.1

• pen circuit

3.8 3.9 30 35 40 45 50 55 60

PV ModuleTemperature(deg C) PV ModuleTemperature(deg C)

Impact of elevated temperature on open circuit voltage of a PV module

Results from Experiments Continues

70 4 5 Voc Temp

Results from Experiments Continues

40 50 60 4.1 4.3 4.5 emperature (C) e Voltage (V) 10 20 30 3.7 3.9 PV Module Te PV Module 3.5 5 10 15 20 25 30 35 40 45 50 Time (min)

Voltage and Temperature profiles of a ‘wet’ PV module with cooling water switched on at 25.5 minutes.

Conclusions Conclusions

The following are the conclusions drawn from the investigation g g

• f the impacts of a Gravity Fed Cooling (GFC) system on a PV

cell/module

• The GFC system increases the conversion

efficiency (power output) of a PV cell/module by 12.8%

Conclusions Continues Conclusions Continues

• The system demonstrates that cooling a PV

The system demonstrates that cooling a PV array can be achieved without the use of a circulating pump circulating pump. Th GFC k h i

• The GFC system keeps the operating

temperature of the module from rising above 5 0C f h d i d 5 0C of the designed temperature.

Conclusions Continues Conclusions Continues

• The increase in power obtained by the ‘wet’

The increase in power, obtained by the wet PV module, is a ‘true’ increase as none is utilized to circulate water utilized to circulate water.

• The mathematical model results show very

close agreement with those from the close agreement with those from the experiments and therefore the model can be used as a “predictive” tool to determine used as a predictive tool to determine temperature profiles across PV modules.

QUESTIONS QUESTIONS