# New Light on Phtyoremediation: The Use of Luminescent Solar Concentrators
## 2 Materials and Methods
### LSC Panel Design  
A typical greenhouse hard cover is made of double-wall PolyCarbonate (PC) panels with sizes that range from 1.2 \(\times\) 0.6 m to 3 \(\times\) 2 m. In contrast with this, large LSC modules rarely exceed a short-side length of 50-60 cm. In fact, the performances of larger devices are limited by self-absorption of the fluorescent dye (multiple absorption-emission events  
Figure 3: Absorption (red curve) and photoluminescent emission (blue curve) spectra of Lumogen F305.  
that reduce the light transport efficiency, due to the overlap between the absorption and emission spectra, Figure 3).  
A reasonable trade-off is a module with a fixed short side of 50-60 cm and a variable length of 0.5 to 2 m; this size permits to have modules with a large area but where the optical path inside the slab is not so long to limit the performance due to self-absorption [42].  
In addition, proper structural characteristics as rigidity and thermal insulation are required in practical use as roofing. Hence, a suitable LSC device for greenhouses requires a dedicated design with the integration of additional materials to fulfill these specifications.  
In the present work, LSC panels with dimensions of 50 \(\times\) 50 \(\times\) 0.6 cm and 100 \(\times\) 100 \(\times\) 0.6 cm were used, fabricated by Altuglas (Arkema Group) using an industrial method of \"cell-casting polymerization\" [43]. In particular, PMMA ShieldUp(r) (impact resistant) was used as transparent material. LSCs with ShieldUp(r) are a patented technology [44] resulting from the collaboration between Arkema Group and Eni S.p.A, specially developed to provide a polymer composition that is highly resistant to shocks, remains transparent regardless of temperature, and possesses greater flexibility, all while it absorbs and re-emits light. These characteristics make it suitable for greenhouse roofing.  
Measures of electrical efficiency of a complete LSC device were also performed. Eight silicon cells IXYS SLMD142H01 LE (dimensions 24.7 \(\times\) 0.6 cm each and an active surface of 14.8 cm\({}^{2}\)) were glued on the four edges of the slab, wired in series, and connected to a Keithley 2602A (3A DC, 10A Pulse) digital multimeter to record the power response. A 50 \(\times\) 50 \(\times\) 0.6 cm device was exposed directly to the sun and the current-voltage (I-V) curves were collected.  
The corresponding power conversion efficiency (PCE) was estimated though the following formula:  
\[\frac{V_{\text{OC}}\cdot J_{SC}\cdot FF}{P_{in}} \tag{2}\]  
where in \(V_{oc}\) is the open-circuit voltage, \(J_{sc}\) is the short-circuit current density, \(P_{in}\) is the intensity of the light incident on the device (Global Normal Irradiance GNI = 1000 W/m\({}^{2}\)), and \(FF\) (Fill Factor) is defined by the following ratio:  
\[FF=\frac{V_{MPP}\cdot J_{MPP}}{V_{\text{OC}}\cdot J_{SC}} \tag{3}\]  
with \(V_{MPP}\) and \(J_{MPP}\) defined as the voltage and current density, respectively, corresponding to the maximum power point.  
Considering Equations (2) and (3), it results \(PCE=P_{max}/P_{in}=V_{MPP}*J_{MPP}/P_{in}\).  
The power production from the panel estimated in this way represents the peak value, obtained with a naked LSC slab. However, the effective power conversion efficiency is influenced by the final configuration of the device, so measures on the building-integrated panel are deemed necessary.