A study on the performance of solar photovoltaic modules exposed to salt water

Abstract

The floating photovoltaic installation is a new concept which combines land-based PV technology with recently evolving floating system approach. A number of floating PV systems have been developed worldwide on various types of fresh water bodies. However, for countries like Malta, being in possession of marine territorial waters, one must take into account the potential effect of salt on the performance of solar modules, when implementing an offshore installation. While the effect of dust accumulation on PV panels is well-known, and is proven to significantly reduce their performance, even up to 50%, the consequence of salt build-up is still poorly understood. Since salt is not as opaque as dust, it is not clear how much it will shade or to what extent it would accumulate by repeated wetting of the panels. Salt water drying on solar panels, is one of the factors affecting floating PV performance, hence its impact was examined in this research. A sequence of tests were performed on monocrystalline modules which combined several factors that resulted in eight types of wetting treatments. The variations involved different salt solutions (seawater and saturated solution), inclination angles of photovoltaics (5° and 30°), as well as various types of wetting nozzles (fine mist and jet trigger sprayers). Auxiliary tests involved replicating the spraying procedure on glass sheets in order to check the level of opacity and percentage coverage of deposited salt layer. Moreover, tests were also conducted on microscope slides to examine light transmittance, thickness and morphology of salt crystals. To further analyse the impact of salt water on the performance of different PV technologies (polycrystalline silicon, amorphous silicon and CIGS modules), two types of setups have been constructed. One of the setups exposed the panels to a partial immersion and the other subjected them to the dripping procedure. Artificial deposition showed that seawater leads only to minimal traces of salt build-up that corroborates the findings of the earlier research, which revealed that shading from sea salt does not have such a pronounced effect. The surface of the glass samples treated with seawater, remained relatively translucent and thus a drop in the amount of light passing through the sample ranged only up to 3%. When it comes to the power output, the panels treated with seawater exhibited only a slight drop or no effect on the performance, and in some cases, improvements were also observed. However, based on the results of extended wetting with salt water, it was noted that the modules exposed to continuous contact with salt through immersion and water flow, suffered apparent losses in their performance. The percentage drop in power performance measured after a total of 30 days of immersion procedure ranged from around 14 to 28 %, depending on the PV technology. Whereas, the percentage reduction noted after completing a total of 30 days of dripping procedure varied from about 13 to 25 %, with the largest drop in the output exhibited by the CIGS panels. Therefore, it can be postulated that it is feasible to adapt the scenario of floating PV panels on the sea. Nevertheless, the key success of such venture is strictly linked to selection of adequate PV technologies and adoption of necessary measures to withstand the harsh marine conditions. The modules implemented at sea need to have a suitable protection from the water and/or be placed sufficiently high so that they will not often come in close contact with seawater.