2.3.2. Other Loss Factors

This study focuses on the FPV system; therefore, the other factors considered are only related to the panels. In the case of a complete system design, losses from other equipment such as the inverter or transformer need to be considered. Other factors that could impact the efficiency of the floating solar PV modules are the same as conventional land-based PV systems. These factors are solar irradiance losses, shading losses, soiling, mismatch losses, and DC cabling losses [60,88,89].

The foam-based support as well as the PV are mounted flat on the water surface (e.g., tilt angle = 0 degrees); therefore, they are not exposed to the optimum amount of solar irradiation for any location other than those on the equator. A study conducted by Jacobson et al. has provided an estimate of the optimal tilt for fixed tilt solar PV systems for different locations throughout the world [90]. The loss due to the tilt angle has been taken into account in this study and only the global horizontal irradiation for the energy yield calculation is used.

The impact of shading losses on FPV is low because water surfaces are flat and there are no nearby obstacles that could cause a direct shade to the modules. In the case of foam-based FPV, there is no mutual shade between the modules either because the mounting systems are flat on the water surface. Lake Mead is located in a mountainous region; therefore, far horizon shading may occur during certain times of the day or the year but is expected to be minimal. A detailed shading losses analysis has not been conducted during this study and an estimated value of zero percent has been used.

Soiling can be significant on FPV panels. Soiling in the case of FPV systems is mostly due to bird dropping or algae growth [54]. According to a report on FPV systems by the World Bank Group, nesting birds have been found to prefer the use of FPV modules as a nesting place [60]. In the report of the World Bank Group, however, the floating systems used were inclined; thus, allowing the presence of sheltered places where the birds were nesting. In the case of foam-based FPV, it has been assumed that the effect of birds will be lower because the modules are mounted directly on the water surface and the mounting system offers no sheltered space for nesting. A detailed study of the impact of birds nesting on foam-based FPV panels would be interesting for future studies. In addition, by ensuring the FPV are above the water surface, the growth of algae on the front surface of the FPV can be minimized.

Mismatch losses and DC cable losses can be higher in FPV systems due to the relative movement of the modules on the water surface, but an optimum design can minimize these losses [60].

#### 2.3.3. Parameters Used for Energy Yield Simulation

The energy production model simulates a floating solar PV system on the surface of Lake Mead. The area covered by the solar PV installation is described in Section 2.4. The values used for the energy production simulation as well as the sources of the values are given in Table 1.


**Table 1.** Energy modeling simulation parameters.

#### *2.4. Water Savings Capability and E*ffi*ciency of the System*

The water savings capability of the FPV system investigated in this study has been estimated to be 90% of the volume of water corresponding to the surface covered by the FPV. This assumption is supported by previous studies that found that covering water surfaces with pontoon-based FPV could reduce the evaporation losses by more than 90% [38,91]. Thus, the resulting values are extremely conservative as here the FPV covers the entire water surface and is not a tilted FPV mount as in [38,91]. When planning an FPV installation on a water surface, the percentage coverage of the water by the solar systems depends on the type of activities that are being performed on the body of water. According to the World Bank Group, the FPV system should not cover more than 50% of the water surface if used

for fishing and not more than 60% if the water body is not used for fishing [60]. Therefore, a sensitivity analysis will be run on the coverage percentage to investigate the energy production and water saving capability of the foam-based FPV system in this study from 10% to 50% in 10% increments because Lake Mead is used for fishing. Then, the water saving capability is estimated by multiplying the water evaporation rate and the surface coverage. The result is adjusted by 90%. The cost of water saved annually is estimated using the average water cost in Nevada where Lake Mead serves as a clean water source. The cost of water according to Las Vegas Valley Water District ranges from USD 0.35/m<sup>3</sup> to 1.37/m<sup>3</sup> for a family size residential home, according to the size of the installed water meter [92]. On the other hand, the wholesale electricity rate of the power produced at the Hoover Dam, located in Nevada, is USD 0.02/kWh [93,94]. These values are used to estimate the lowest and highest potential energy revenues of the foam-based FPV system.

#### **3. Results**
