## 2 Materials and Methods  
### Experimental Design  
The study was conducted in a 2.415 m\({}^{2}\) (57.5 m length and 42.0 m width) Venlo greenhouse structure located in South-East Spain, in the experimental center of Tecnova located in Paraje Cerro Gordo s/n Viator, Almeria, Spain (36 deg53'44.23'' N, 2 deg22'31.35'' W, 185 m above sea level).  
The greenhouse structure was formed by galvanized steel tubes. The greenhouse roof structure was a two-span metal frame with 6 modules of 7 m of width (Figure 1). The ridge height in the roof was 6.63 m and gutter height was 5 m. The cover material of the greenhouse was plastic in lateral and frontal walls, while several materials (plastic, photovoltaic panels, opaque sheets of polyethylene and transparent sheets of corrugated polycarbonate) were located in the rooftop, as Figure 1 shows.  
Opaque sheets of polyethylene were installed on the greenhouse rooftop to simulate the effect of shading that would produce opaque photovoltaic panels. Figure 2 shows the location of opaque sheets of polyethylene on a greenhouse rooftop, in 50% of the shade treatment. The plastic cover of the greenhouse was thermic polyethylene (LDPE) three-layers, coextruded manufactured. These three layers give different properties to the plastic cover, depending on their composition: the external layer of the plastic is very resistant, with non-stick properties and protection additives against UV-radiation. The intermediate layer is high in copolymers of ethylene and vinyl acetate (EVA) content, giving thermicity to the plastic. Finally, the internal layer (inside the greenhouse side) increases light diffusion and is stable against chemical agents like phytosanitaries. The plastic cover had a 200 \(\upmu\)m thickness, a transparent white color, 3 years of shell life and a visible light transmission rate of 84%.  
Figure 1: The photovoltaic panels and opaque polyethylene sheets location in the greenhouse rooftop.  
The greenhouse has passive ventilation, through lateral openings of 2.5 m height located around the perimeter of the structure and 5 zenithal openings of 50 m of length and 1 m width. The opening and closing of these openings are automatically controlled depending on climate conditions inside the greenhouse (temperature and relative humidity). The total ventilation area in the greenhouse was 20.7% of total floor area. Each opening was protected by insect-proof nets of 20 \(\times\) 10 threads cm\({}^{-2}\) (50 mesh).  
Thirty six photovoltaic panels, with a 1.65 m length and 1.00 m width of area by panel, were installed in the roof-top of the greenhouse. Modules were installed in 2-units groups. Besides, to simulate the shading effect that would produce roof-top photovoltaic panels in different treatments of shading, opaque polyethylene sheets were used. The size and radiation transmission of these polyethylene sheets were identical to the effect of real photovoltaic panels. Figure 1 shows the location of both materials on the roof-top greenhouse.  
In order to evaluate the effect of different shading levels that would produce the installation of photovoltaic panels in the rooftop greenhouse, an experimental design was planned with 3 shadow treatments of 15%, 30%, and 50%. The three treatments were compared with a control treatment with 0% shading. Shaded treatments were 630 m\({}^{2}\) of the surface and the control treatment, 0% shade, of 525 m\({}^{2}\) (Figure 3). Each treatment was evaluated and climatic control, yield and quality parameters registered.  
Figure 2: (**Left**) Roof-top installation of opaque polyethylene sheets in the greenhouse outside face in the 50% shade treatment. (**Right**) The inside view of the 30% shade treatment in the greenhouse.