# Selection of a Photovoltaic Panel Cooling Technique Using Multi-Criteria Decision Analysis
## 2 Methods and Criteria
### Economic Performance  
The investment cost and operating cost of the cooling system involved differs according to the type of method used. Since PV panels operate with a very low margin of cost-effectiveness, cost reduction in the cooling mechanism is important [35]. The actual cost analysis of a cooling mechanism is determined from the initial fixed cost, annual maintenance cost and net savings achieved due to the cooling mechanism. Net present cost (NPC) is given by the following relation (refer to Equation (5) below):  
\[\text{NPC}=\sum_{\text{t=0}}^{\text{n}}\frac{\text{MC}-\text{AS}}{\left(1+ \text{i}\right)^{\text{n}}}-\text{FC} \tag{5}\]  
In above Equation (5), MC is the maintenance and operation cost; AS is the annual savings in energy; i is the rate of interest; and n is the number of years and FC is fixed cost.  
Fins are used to liberate heat from solar panels by air convective movement by natural convection or wind movement. Normally, two types of arrangements are used, namely, lapping fins and longitudinal fins [36]. PV panels using fins made of different materials incur the additional cost of the fin. The average fixed cost of fins is USD 58 per square meter panel area and the maintenance cost is USD 4/year [37]. Heat pipes come at a cost of USD 168 for a 1 m\({}^{2}\) area [37]. PCM cooling of PV involves PCM casing with heat transfer arrangements in the form of fins to enhance the phase change. The PCM is the component with the maximum cost in this method with an average cost of USD 20-30/kW-hr. PCM material such as paraffin costs about USD 25 per kilogram, and a 1 square meter panel has a thickness of up to 5 cm per layer of PCM [14]. This will be equal to 45 kg of PCM per square meter PV area. Thermosiphon cooling mechanisms have round or rectangular piping embedded at the back of PV panels with either a storage tank or heat dissipation arrangement. The total cost of the piping and heat dissipation mechanism is roughly USD 25 USD for a 1 square meter area of the panel. Thermosiphon mechanisms using clay pot cooling have evaporative cooling of coolant water in the pot. The cost of this method is the same as that of the normal thermosiphon describe above. Force convection fan cooling uses the fin mechanism for heat dissipation and fans for maintaining air movement. The fans used for air circulation have power requirements proportional to the panel area. Usually, a 0.84 W fan is sufficient to cool a 1 square meter panel area [38]. Water spray cooling and evaporative cooling use pressure pumps to force water through nozzles and have a power rating of 50-100 W [39]. Table 3 gives the cost particulars for the different methods.  
\begin{table}
\begin{tabular}{l l c c} \hline \hline \multirow{2}{*}{**Sr. No.**} & \multirow{2}{*}{**Cooling Method**} & \multicolumn{2}{c}{**Total Cost**} \\  & & **USD/m\({}^{2}\)** & \\ \hline
1 & Aluminum fins & 58 & [37] \\ \hline
2 & Heat pipe cooling & 168 & [37] \\ \hline
3 & Phase change material & 1125 & [14] \\ \hline
4 & Thermosiphon cooling & 25 & [40] \\ \hline
5 & Thermosiphon with clay pot cooling & 25 & [40] \\ \hline
6 & Forced convection fan cooling & 68 & [38] \\ \hline
7 & Water spraying & 75 & [39] \\ \hline
8 & Evaporative cooling & 75 & [39] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Cost of different cooling methods per square meter of the panel area.