Design and integration of an off-shore off-grid system and an on-land system for comparison on photovoltaic performance

Abstract

The purpose of this thesis research was to perform a photovoltaic (PV) performance assessment and comparison between a small-scale land-based PV system and an off-shore off-grid floating PV system. Also from this research design guidelines for off-grid off-shore floating PV systems were developed. The research experiment was carried out in The Netherlands, with one system floating in the North Sea and one system standing on-land. To be able to have a fair comparison two identical 4.32 𝑘𝑊 PV arrays were built simultaneously, consisting of two parallel strings, each with six 360 𝑊𝑝 bifacial PV modules connected in series. Each of the two systems was equipped with a monitoring set up consisting of temperature sensors, pyranometers, reference cells, power meters and an inclinometer for the off-shore system. Additional measurements concerning wind, wave and water temperatures off-shore were taken from the Royal Netherlands Meteorological Institute (KNMI) weather station Hollandse Kust Zuid Alpha (HKZA), which was situated in the same region of the North Sea. The two PV experimental set-ups were compared between 15th November 2022 and 1st January 2023. On the DC side being measured, the on-land PV system recorded 96.3 𝑘𝑊ℎ while the off-shore PV system recorded 93.4 𝑘𝑊ℎ, which was subject to lower irradiance levels. The performance ratio (PR) found off-shore during the period of research was 0.92 while on-land this value was 0.934 between the two PV strings, however these values should be re-validated due to a potential malfunction of the Hall effect sensors. The PR off-shore was higher than expected from literature for a similar system being simulated. With respect to module temperatures recorded off-shore, a low thermal variation was found when compared to on-land, with the average module temperature off-shore being 11.3 𝑜𝐶 higher than on-land during this period of research. Ambient temperatures as well as irradiance on the Plane of Array (POA) were found to have a larger influence on the module temperatures for the on-land system than for the off-shore system. Module temperatures throughout the PV array off-shore were found to be the equal. Additionally, four OFPV linear regression models derived from the empirical measurements were presented and compared with existing empirical FPV models found in literature, which were found to be subject to be site and design specific. Additional environmental effects on the module temperature concerning wind, wave and water temperatures were presented, highlighting the dominant effect of the water with respect to module temperatures. The off-shore floating PV system withstood waves of up to 3.4 meters while the system maximum tilts were found to be to be 13.33 𝑜 and 17.36 𝑜 for the X and Y axis of the PV floater respectively. No permanent soiling due to bio-fouling or salt deposition was detected after one month of measurements but dynamic soiling, in the form of bio-fouling, snow and water splashing were identified, with the latter being the most predominant. The work done through this thesis lays the foundation for further research and comparisons of off-shore floating PV systems. It is recommended to perform this comparison for a period of a complete year to yield annual conclusions.