## 2 Materials and Methods
### Parametric Investigation  
In the parametric investigation, eight characteristic solar days were simulated. The climatic data for each examined day are given in Table 7. The climatic data were taken from the Hellenic National Meteorological Service for a simulated greenhouse which is located in Central Greece (city of Agchialos). The greenhouse is situated in Velestino with \(\varphi=39^{\circ}\,23.4^{\prime}\) and \(\lambda=22^{\circ}\,45^{\prime}\). For the days with average external temperature less than 22 \({}^{\circ}\)C, the winter geometry was used (with the small openings), while for the other days, the summer geometry was used.  
For each day, four simulations were performed for the three examined combinations of OPV/cover, corresponding to normal transmittance in the PAR spectrum equal to 30%, 45%, and 60% and for the case of the bare PE cover with PAR normal transmittance (89%). The examined OPV/cover combinations are presented in Table 8. In the last column, the corresponding installed PV power per meter of greenhouse is given considering the whole width of the arched roof (8.93 m).  
Simulation results are presented in terms of available PAR and photosynthesis rate. The photosynthesis rate, P (in \(\upmu\)mol (CO\({}_{2}\)) m\({}^{-2}\) s\({}^{-1}\)) was calculated according to the following relationship:  
\[\mathrm{P=}\frac{\alpha\mathrm{I}+\mathrm{P}_{\mathrm{max}}-\sqrt{(\alpha \mathrm{I}+\mathrm{P}_{\mathrm{max}})^{2}-4\theta\alpha\mathrm{I}\mathrm{P}_{ \mathrm{max}}}}{2\theta} \tag{4}\]  
where \(\alpha\), light-limited quantum efficiency (\(\sim\)0.5 \(\upmu\)mol (CO\({}_{2}\)) \(\upmu\)mol\({}^{-1}\) (photons)); I, the incident PAR radiation in \(\upmu\)mol (photons) m\({}^{-2}\) s\({}^{-1}\) (in the PAR spectrum 1 W m\({}^{-2}\)\(\sim\) 2 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\)); P\({}_{\mathrm{max}}\), the maximum photosynthesis rate (here considered equal to 30 \(\upmu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)); and \(\theta\), the convexity (here considered equal to 0.7, dimensionless).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Day**} & **Monthly** & **Monthly** & **Monthly** & **Monthly** & **Monthly Average** & **Monthly Average** & **Monthly** \\  & **Average Day** & **Average Air** & **Minimum** & **Average** & **Total Solar** & **Average** \\  & **Temperature** & **Velocity** & **Minimum** & **Maximum** & **Radiation in** & **Diffusive** \\  & **[\({}^{\circ}\)C]** & **[m s\({}^{-1}\)]** & **Temperature** & **Temperature** & **Horizontal Plane** & **Radiation** \\  & **[\({}^{\circ}\)C]** & **[\({}^{\circ}\)C]** & **[\({}^{\circ}\)C]** & **[\({}^{\circ}\)C]** & **[kWh m\({}^{-2}\)]** & **[kWh m\({}^{-2}\)]** \\ \hline
6 February & 9.1 & 2.9 & 3.5 & 12.3 & 74.3 & 30.9 \\
21 March & 11.3 & 2.7 & 4.9 & 14.4 & 112.5 & 49.1 \\
6 May & 20.9 & 2.4 & 12.2 & 24 & 189.7 & 82.1 \\
21 June & 25.9 & 2.8 & 16.4 & 29 & 212.7 & 86.1 \\
6 August & _27.7_ & 2.8 & 18.7 & 30.8 & 195.1 & 73.5 \\
21 September & 23.7 & 2.6 & 15.7 & 27.1 & 146.8 & 54.7 \\
6 November & 13.5 & 2.3 & 8.2 & 16.8 & 63.1 & 24.8 \\
21 December & 9.4 & 2.7 & 4.5 & 12.5 & 51.5 & 20.5 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Climatic data parametric investigation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Normal PAR**} & **OPV/PE Cover** & **Structure I/PE** & **Structure II/PE** & **Bare PE Cover** & **Installed PV** \\  & **[\%]** & **Cover [\%]** & **Cover [\%]** & **[\%]** & **Power [W/m]** \\ \hline \(\tau_{\mathrm{n,PAR}}=30\%\) & 96 & 75 & 21 & 4 & 278 \\ \(\tau_{\mathrm{n,PAR}}=45\%\) & 72 & 56 & 16 & 28 & 209 \\ \(\tau_{\mathrm{n,PAR}}=60\%\) & 47 & 37 & 10 & 53 & 136 \\ \(\tau_{\mathrm{n,PAR}}=89\%\) & 0 & 0 & 0 & 100 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Examined OPV/cover combinations.