Theoretical and Operational Thermal Performance Theoretical and Operational Thermal Performance of a 'Wet' Crystalline Silicon PV Module under Jamaican Conditions Earle Wilson, PhD; PE Di Director, Energy Unit t E U it School of Engineering University of Technology, Jamaica
Overview of Presentation Overview of Presentation • Problem Statement Problem Statement • Attempted Solutions to Problem • My Approach to Solution h S l i • 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 operate in low latitude conditions such as operate in low latitude conditions such as those in Jamaica, West Indies
What affects Power Output (Conversion Efficiency) of the Cells, especially those of c ‐ Si? Effi i ) f h C ll i ll h f Si? • V oc ≈ U T ln(I sc /I o ) T ( sc / o ) oc Where, V oc , = open circuit voltage I 0 = saturation current 0 But I 0 proportional to T 4 Where T is working temperature of cell Therefore, cool cells = higher efficiency
Attempted Solutions to Problem (A (Applied Cooling Techniques) li d C li T h i ) • Cells laminated on copper fin absorber • Cells laminated on copper fin absorber with water tube welded on the back is used by Brogren and Karisson d b B d K i • 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 on 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) − π − α − π ∞ 2 2 q ( 2 n 1 ) x ( 2 n 1 ) t ∑ ∑ [ [ ] ] {[ {[ ] ] [ [ ]} ]} = + − + × 0 U U ( L x ) F Cos Exp ( ( x , , t ) ) L n 2 2 k k 2 2 L L 4 4 L L = 1 n
Operational Performance (experimental setup) water tank water in t i Picture of Photo ‐ voltaic (PV) Module pv module water to drain Si Simulated GFC System l t d GFC S t
Results from Mathematical Modeling 60 Front face 55 Temp profile after 0.05 sec of switching on cooling water Back face face 50 (deg C) Temp 45 40 Temp profile after 0.1 sec of switching on cooling water 35 30 Temp profile after 1.0 sec of switching on cooling water 25 0 0.5 1 1.5 2 2.5 3 Cell thickness (mm) Time-Steps of Temperature profiles for a modelled 3mm thick ‘wet’ PV cell with irradiance of 1000 W/m 2 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 o C
Results from Experiments Open Circuit Voltage(Voc ) vs Module Temperature 4.4 4.3 t voltage (V) 4.2 4.1 4.1 open circuit 4 3.9 3 9 3.8 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 Results from Experiments Continues Voc Temp 70 4 5 4.5 60 emperature (C) e Voltage (V) 4.3 50 40 4.1 PV Module Te PV Module 30 3.9 20 3.7 10 3.5 0 0 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 of 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 . • The GFC system keeps the operating Th GFC k h i temperature of the module from rising above 5 0 C f h d 5 0 C of the designed temperature. i d
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
Recommend
More recommend
