# Selection of a Photovoltaic Panel Cooling Technique Using Multi-Criteria Decision Analysis
## 2 Methods and Criteria
### Technology Reliability  
The reliability of the cooling mechanism depends on the complexity of the technique used as well as prevailing weather conditions in the location. Solar PV installations are subjected to changing atmospheric conditions in different temperature, humidity, wind and dust levels. The different possible possibilities of failure in cooling equipment are listed and a negative ranking for each possibility is given along with its corresponding weight depending on the type of cooling method [33]. The different possible factors are listed below:  
* Corrosion, coating formation and scaling of heat transfer surfaces;
* Physical degradation of heat transfer fluids;
* Leakage of fluid conduits;
* Electric equipment failure.  
The following Table 2 gives the corresponding weights of the failure possibility under each type of cooling method. The weights are \(-1\), \(-2\) or \(-3\) depending on the degree of possibility in the individual cooling method, with \(-1\) representing minimum adverse impact or maximum reliability and \(-3\) representing maximum adverse impact or minimum reliability. Data obtained from existing literature regarding the performance of different cooling systems were used to make Table 2.  
Aluminum fins are located at the bottom of the panels and are subjected to air contact and dust particles that form layers which can cause resistance to heat flow from the fin and thereby cause panel temperature elevation over years of operation. Since this factor is minimal due to air cooling, the weight given is \(-1\). Other causes of failure are negligible in this case and hence given 0. Heat pipe cooling involves low-boiling point organic or inorganic fluids such as water, acetone and other low-boiling liquids. These fluids cause coatings on surfaces as well as undergo degradation due to continuous heating and cooling [34]. Thermosiphon cooling uses water as a heat transfer fluid, and the cooling fluid moves through the bottom side of the panel through ducts or pipes in contact with the panel. The possibility of coatings on the heat transfer fluid as well as the possibility of leakage are dominant in this method. Thermosiphon cooling with a clay pot is another method where evaporative cooling taking place in the clay pot is used to produce cold fluid. The possibility of leakage loss of the fluid is very high over a longer period of time in  
\begin{table}
\begin{tabular}{c l c c c c c} \hline \hline \multirow{2}{*}{**Sr. No.**} & \multirow{2}{*}{**Cooling Method**} & \multicolumn{3}{c}{**Weights of the Reliability Factors**} & \multicolumn{2}{c}{**Total Rank**} \\ \cline{3-7}  & & **A** & **B** & **C** & **D** & \\ \hline
1 & Aluminum fins & \(-1\) & 0 & 0 & 0 & \(-1\) \\ \hline
2 & Heat pipe cooling & 0 & \(-2\) & \(-2\) & 0 & \(-4\) \\ \hline
3 & Phase change material & 0 & \(-1\) & \(-1\) & 0 & \(-2\) \\ \hline
4 & Thermosiphon cooling & \(-1\) & \(-1\) & \(-2\) & 0 & \(-4\) \\ \hline
5 & Thermosiphon with clay pot cooling & \(-1\) & \(-1\) & \(-3\) & 0 & \(-5\) \\ \hline
6 & Forced convection fan cooling & \(-1\) & 0 & 0 & \(-2\) & \(-3\) \\ \hline
7 & Water spraying & \(-1\) & \(-1\) & \(-1\) & \(-2\) & \(-5\) \\ \hline
8 & Evaporative cooling & \(-2\) & \(-1\) & \(-1\) & \(-2\) & \(-5\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Weights of different cooling methods in terms of reliability.  
this method. Forced convection fan cooling also results in coating formation over the heat transfer surface thus reducing heat transport. Since electrical components are involved, failure of these components is also possible over several years of operation. This is also the case for water spray cooling as well as evaporative cooling in which the wastage of water and equipment degradation due to water impacts over a period of time reduces reliability.