# Floating Photovoltaic Plant Monitoring: A Review of Requirements and Feasible Technologies
## 4 Sensors for Water Quality Monitoring
These three probes have similar weights (about 2 kg) and dimensions, as indicated by data sheets (see Table 2). In contrast, probes with two or three sensors (UltraPen PT1, CTD Diver, and MiniDOT Logger) are much lighter (80 g-340 g) and smaller. All the probes have a maximal operating depth ranging from 100 m (AP2000) to 250 (EXO3). Six additional papers from 2021 to 2023 on WQM in applications other than FPV were included in the list, in decreasing order of publication year listing six more commercial multiparameter probes. AP-7000 (Aquared, UK) and EXO2 (YSI, USA) provide all necessary sensors except Light Intensity, while MANTA +35 (Eureka, USA) and RBR Concerto (RBR, Canada) cannot measure Chlorophyll-a, but are the only probes that measure Light Intensity. Almost all identified probes have a maximum operating depth of 100 m (AP-7000, Manta+35, EXO2, Ocean Seven 316) while Aqua TROLL 600 can operate at 200 m depth, and RBR Concerto up to 750 m. The higher the operating depth, the more advanced the technology required to withstand water pressure, which generally increases the probe's cost. The probes' weight ranges from 1.4 kg (AP-7000) to 3.6 kg (EXO2). The probes' diameters  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline  & & & & & & & & & & & & & & & & \\ \multirow{2}{*}{**Ref. **} & \multirow{2}{*}{**FFV**} & \multirow{2}{*}{**Probe**} & \multirow{2}{*}{**Pr/ Name**} & \multirow{2}{*}{**Mfr. **} & \multirow{2}{*}{**Depth**} & \multirow{2}{*}{**T**} & \multirow{2}{*}{\(\sigma\)} & \multirow{2}{*}{**NTU**} & \multirow{2}{*}{**DO**} & \multirow{2}{*}{**pH**} & \multirow{2}{*}{**I**} & \multirow{2}{*}{**Chl-a**} & \multirow{2}{*}{**Max**} & \multirow{2}{*}{**Depth**} \\  & & & & & & & & & & & & & & & **(m)** & **(kg)** & **(cm)** \\ \hline \multirow{2}{*}{ \begin{tabular}{} \end{tabular}  } & \multirow{2}{*}{*} & EXO3 & \multirow{2}{*}{YSI} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{250} & \multirow{2}{*}{2} & \multirow{2}{*}{7.6} & \multirow{2}{*}{58.7} \\  & & & [74] & & & & & & & & & & & & & \\ \multirow{2}{*}{ \begin{tabular}{} \end{tabular}  } & * & n.s. & YSI & * & * & * & * & * & * & & & & & \\ \multirow{2}{*}{ \begin{tabular}{} \end{tabular}  } & * & n.s. & & YSI & * & * & * & * & * & * & & & & & \\ \multirow{2}{*}{\ \begin{tabular}{} \end{tabular}  } & * & 6920 & \multirow{2}{*}{YSI} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{200} & \multirow{2}{*}{1.8} & \multirow{2}{*}{7.2} & \multirow{2}{*}{45.7} \\  & & & [75] & & & & & & & & & & & & & \\ \multirow{2}{*}{ \begin{tabular}{} \end{tabular}  } & * & QAM30-DE & \multirow{2}{*}{Quadlink} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{*}{*} & \multirow{2}{span from 4.7 cm (Aqua-TROLL 600) to 10 cm (Ocean Seven 316, Idronaut), while lengths range from 44 cm (AP-7000) to 70.5 cm (EXO2). Quantitative monitoring is of course of paramount importance for assessing primary drivers of environmental effects. Measuring environmental end ecosystem impacts may, however, be more complex and subtle, with the need for targeting particular analyte/parameter mixture patterns as well as specific metabolites signaling peculiar ecosystem conditions which may be relevant for the FPV application. A typical example is bacterial or algae activity monitoring [94]. In this case, electronic tongues may emerge as a viable concept to avoid lengthy and complex sampling and sample processing activities. Electronic tongues are nothing more than multiparametric sensing nodes which are usually coupled with computational intelligence software components to implement detection, identification, and quantification tasks in liquid matrices including water.