In tropical and temperate marine climates, the cooling influence of water in floating PV systems can be improved if a suitable system configuration allows for more wind to flow through the modules and the water surface. This is one of the key results of a recent research project carried out by the Dutch Organization for Applied Scientific Research (TNO) and the Singapore Solar Energy Research Institute (SERIS).
Scientists from both organizations jointly tested floating solar arrays in the Netherlands and Singapore for irradiance-weighted average temperatures (IWATs) and compared the findings with those of ground-mounted installations and rooftop PV systems.
The test field in the Netherlands was situated in the province of South-Holland on an inland lake close to the sea. The testbed in Singapore was at the Tengeh Reservoir with a 1 MW floating solar array. Two types of floating structures were evaluated in the former: one with a small water footprint and an open structure (NL1), and one with a large water footprint and a closed structure (NL2).
Three separate systems have been studied in the latter: an array with a wide footprint and a closed structure (SG1), a system with a medium footprint and a closed structure (SG2) and an open-structure free-standing system (SG3).
The efficiency and temperature behaviour of the arrays NL1 and NL2 were compared with those of two ground-mounted reference installations. They were named NL 3 and NL 4 by the researchers. The energy yield of the three systems in Singapore was also contrasted with the yield of the free-standing rooftop PV system (SG4).
The measurements showed that the IWAT of the NL1 system in the Netherlands, which was the best performing system, was 3.2 C lower than that of the nearby reference system. The best performing device in Singapore was the SG3 series, which exhibited an IWAT of 14.5 C lower than its reference system. Besides, within the PVsyst program, the calculated heat loss coefficients of the various systems have been used to model the annual yield of floating systems and reference arrays in a typical meteorological year.
The best performing device in Singapore was the SG3 series, which exhibited an IWAT of 14.5 C lower than its reference system.
“The determined median heat-loss coefficients of the best-performing systems NL1 and SG3 are with 57 W/m2 per kelvin and 55 W/ m2 per kelvin, respectively, almost identical,” the researchers concluded. “When the coefficients of heat loss of all systems are divided into a constant value and a wind-dependent value, and these values are used to model the specific yield of all systems, it can be concluded that the greatest part of the cooling effect of FPV systems can be attributed to higher wind velocities above water compared to land.”
They also claimed that the open-structure floating systems that allow for wind under the modules can provide a coefficient of heat loss that is up to 22 W/m2 per kelvin higher than the reference systems.
In “The cooling effect of floating PV in two different climate zones: a comparison of field test data from the Netherlands and Singapore,” which was recently published in Solar Energy, the scientists identified the floating PV systems and their results.
Source – here