# Assessment of the RACPC Performance under Diffuse Radiation for Use in BIPV System
## 4 Experimental Performance Analysis
### Fabrication of the RACPC-PV Cell  
A flat lead wire of 1 mm width and 0.1 mm thickness was used to tab the solar cell on the edge to maximise the active area; the soldering iron rod with a power of 81 W is heated to 350 \({}^{\circ}\)C and must be controlled since the high temperature can damage the solar cell. However, before the soldering process, the components should be clean and free from grease. Once they have been cleaned a liquid flux is applied to both ends of the connector to remove oxidation that prevents solder from bonding to metals and thus, having more effective use of the soldering material. Then, one of the ends of the connector piece is connected to the back of the solar cell (positive side) and soldered. It is important to clarify that the amount of soldering material used can increase the resistance of the circuit thus affecting the efficiency.  
A standard superglue was used to glue the PV circuit on a glass plate of 70 mm \(\times\) 70 mm \(\times\) 40 mm used in controlled amounts in order to avoid flood or overflowing the solar cell and thus generating damage on it. Then, the RACPC can be attached to the PV cell using an encapsulation material which functions simultaneously as an adhesive and as an index matching gel [34]. It is important to mention that the selection of the encapsulation material is a main factor in order to ensure the correct operation of the optical concentrator, as the refraction may be affected by the obstruction of the sunlight flow from the optical concentrator to the solar cell. Sylgard(r) 184 Silicone Elastomer (Dow Chemical Company Ltd., Dewsbury, UK) provides a good transmission and has an index of refraction of 1.4225. Knowing that the refraction index of the silicon is 3.8821 and for the concentrator it is 1.49, the refractive index of the encapsulation material is not ideal because the value is not the same or close to one of the components of the system, hence, optical losses are expected due to reflection at the borders [34].  
Figure 4: Simulation setup for diffuse analysis; side view (**left**), and isometric view (**right**).  
One of the important steps of mounting the RACPC on the solar cell is the preparation of the index matching gel as it may affect the performance of the system. However, with the aim of ensuring a better adhesion between the silicon and the cell, Dow Corning Primer 92-023 (Dow Chemical Company Ltd., Dewsbury, UK) was applied to the solar cell leaving it to dry for 10 min. Once the cleaning was completed, a small beaker was used to prepare the Sylgard-184(r) by mixing in a 10:1 weight ratio and stirred for 10 min. The bubbles in the solution can generate dispersion inside the RACPC reducing the number of photons traveling through the PV material. Therefore, in order to reduce losses, a Heraeus Vacuthertm vacuum chamber (Heraeus Holding GmbH, Hanau, Germany) was used to eliminate any air bubbles present in the solution working with a pressure of 400 bars at 23.9 \({}^{\circ}\)C (as shown in Figure 5) for 15 min. Then, using a painting brush, the index matching gel was spread over the surface and the RACPC was finally placed on the PV cell with precaution. It is important to be precise in order to prevent misalignment between the solar cell and the RACPC leading to significant optical losses. The sample was cured for 48 h at room temperature.