ABSTRACT
The soiling effects on solar photovoltaic modules and solar water pumps are of great concern in countries with large generation potential for solar energy. Previous studies indicate that soiling affects the PV performance. No previous studies on soiling impacts in Nigeria as well as their influence on solar water pumping have been conducted. In this project, the cumulative effects of dust accumulation were investigated for a period of 90 days. Two sites in Lagos; Mushin and Ojuelegba were selected. The soiling impact affected key performance metrics and this was used to conduct a comparative analysis between clean and soiled panels as well as modules at different tilt angles and location. The results indicate that cumulative soiling considerably reduced the power output of the soiled panel as compared to the cleaned one (12% reduction).
Low tilt angle was also found to promote dust accumulation (11.9% less for module at 10 ). Soiling was found to reduce the efficiency of the module from 10.5 % to 7.26% (15 tilt angle) and 6.3% (10 tilt angle) for the first 25 days and this further reduced to 4% (15 tilt angle ) and 4.22% (10 tilt angle). Soiling losses were found to increase with cumulative dust adherence over the study period and were affected by the tilt angle. The fill factor was also affected by soiling.
The cleaned module had a FF = 0.81 while the soiled module had FF= 0.70(13% less) in the first month and 0.52 (34.8%) in the last month. Soiling was also found to cause significant loss in rectangularity of the I-V curves and this increased with more dust accumulation. Dust accumulation was affected by the location. The Ojuelegba site recorded lower power, efficiency and increased soiling losses as compared to the Mushin site. The pump performance was found to reduce with increase in soiling over the entire study period. Dust accumulation significantly reduced flow rate and maximum head and altered the shape of performance curves (Q-H curves). It is recommended that a correction factor be introduced when designing and sizing PV panels in Nigeria and regular cleaning to reduce these effects.
CHAPTER ONE
INTRODUCTION
Background to the study
Solar photovoltaic (PV) is one of the most important renewable energy in the world. It is becoming a principle source of power in grid and off grid systems all over the world. In terms of installed capacity, it is ranked third after hydropower and wind. As of 2014, the global installed capacity was 177 GWh (International Energy Agency, 2014). PV therefore represents one of the next generation renewable energy sources due to its high reliability during the day and prevention of global pollution, climate change and reduction in greenhouse gas emissions. (Bayod-Rújula, Ortego-Bielsa, & MartÃnez-Gracia, 2010).
The performance of PV modules depends upon the geographical factors (longitude, latitude, and solar intensity), the environmental factors (temperature, wind, humidity, pollution, dust, rain, etc.) and the type of PV technology used. These factors affect the intensity of sunlight energy which in turn reduces the efficiency and power output of the PV.
Most commercial solar cells have an efficiency that ranges between 15-20%. Various technologies such as mono-crystalline, polycrystalline, thin film and transparent solar cells have varying efficiencies and performance curves which are also affected by the environmental conditions. Most researches on solar PV have focused on increasing efficiency through changing the tilt angle, increasing the exposure using sun tracers and sun tracking systems and reducing the impact of temperature. Dust, shading, bird droppings and other factors which considerably reduce the performance and efficiency of most PV cells in most parts of the world have not received considerable attention.
Dust is one of the major environmental factors affecting the performance of PV cells. These are minute solid particles with diameters less than 500 µm accumulating on the PV. The air quality is considerably aggravated by suspended particles that may be directly emitted from both human and natural processes or formed in the atmosphere. These particles include sand, silt, soil, clay, minerals, pollutants from factories and vehicles and chemicals (Ramanathan & Feng, 2009). They also include particulate matter (PM) consisting of finely subdivided solids or liquids such as dust (e.g. particles deriving from civil construction activities), fly-ash, smoke, aerosols and condensing vapors (Mani & Pillai, 2010).
