Determination of PV soiling rates at various locations around the world
Photovoltaic Systems have become one of the main suppliers of electricity in today’s world. Research in materials has greatly increased the efficiency of solar panels in the recent years. But, one overlooked factor that degrades the efficiency and performance of the solar cells is the deposition of dust on the panel glass. This phenomenon is called soiling. Soiling of photovoltaic panels by definition is a process by which airborne particles deposit and accumulates on solar panels, creating an impact on the performance of the PV energy system. The accumulated dust particles greatly reduce the transmittance of the glass covering thereby reducing the power output of the PV panel. This accumulation of dust depends on various environmental factors such as temperature, humidity, rainfall etc. The characteristics of the dust particles greatly depend on the geographic locations too. For instance, the location at which the panels are mounted has a construction site or a busy road nearby can have dust particles of cement and carbon respectively. Therefore the soiling rates differ from location to location. PV panels which are left without cleaning for several days may have permanent stains of dust due to mixture of dust particles with rain water. Hence, proper cleaning of the panels is required to improve the power output of the panels. In order to determine a proper cleaning frequency, the soling rate of that particular location is important. This study analyzes the soiling rates of different locations around the globe based on literature that has been reported in the recent years.
Keywords: photovoltaic panels, dust accumulation, soiling losses
There is an ongoing conflict between fossil fuel vs. solar energy; it might be considered that the predominant resources (oil, coal and natural gas) on which the present world economy depends, may be completely out of existence in upcoming few years. In reality, these are the conventional sources of energy while wind and solar energy contributes only some two or three percent of the world energy capacity. Solar power is a much more optimal and reliable source of energy than fossil fuels in terms of environmental impacts. The best known technologies used for the conversion of solar energy to electrical energy is Photovoltaic (PV) modules comprising of solar cells which converts energy from sun into direct current (DC) with the help of semiconductors. There are many environmental factors which influence the performance of PV module such as wind speed, solar radiation, ambient temperature, humidity and dust.
One factor which is generally not considered in operation of a PV plant is the soiling on the exposed surface of the PV panel. Soiling of PV panels reduces its power output thereby reducing the efficiency of the whole plant. Soiling is the deposition of the dirt, dust and other particulate matters on the surface of the PV modules due to its exposure to outdoor environments for long periods. In places where it rains with high precipitation rates in rainy seasons, soiling losses decreases, but places with little rains can show increased soiling rates due to cementation of dust that occurs on the panels. The intensity of light reaching the solar cells tends to decline as the amount of dust deposited on the surface of PV modules increases. Thus, it is necessary to find a modern method of cleaning that would be inexpensive, less energy consuming, ecological and especially automatic.
In this work an extensive literature survey is done to find out the Soiling losses at different places around the world. After the data collection part, the soiling rates at the locations are calculated. The collected data are updated in the world soiling map.
Objectives of the Research
- The main objective of this work is to determine the soiling rates at various locations around the world.
- To put the collected data into a map with data points. Clicking on any pin on the map will give the soiling rate of the pinned location.
For a solar installation at a particular location it is very much important to do its maintenance. Hence optimal cleaning frequency has to be determined to make efficient use of water, man power and other resources. This World PV Soiling Map will allow people to know the amount of dust deposition in their location and thereby can determine the optimal cleaning frequency for the PV panels.
The entire data which was collected from literature was put into a table for the ease of readability. The data are shown below as images.
The table has the following fields such as authors of the paper, location in which the experiment is performed, the location’s latitude and longitude, type of the panel studied, max. Soiling rate and remarks or the brief summary from the paper from which the soiling rate is calculated.
World PV Soiling Map
Now a days, many countries around the world with adequate amount of sunlight are developing different technologies and putting their efforts for installation of PV modules. The MW installations can afford to do soiling experiments, but for the rooftop systems, it’s very expensive to do such experiments. Hence, there is a need to create a common database for the PV community to understand the soiling loss rate in different geographical locations. This will help in further installations in different locations with appropriate requirements of tilt angles, cleaning frequencies and temperature requirements. There are lot of tests, studies and experiments done and reported regarding the losses caused by the dust accumulation on the PV modules which is collected and compiled at one webpage.
The data that was collected from journals and conference papers published in years 2015, 2016, 2017, 2018, 2019 throughout the world discussing the soiling loss rates are all marked in the map. The most important point which is considered for the selection of the above discussed literature is that the tests were done on panels on which the dust was accumulated due to outdoor exposure and were studied for a particular duration and tilt angle similar to the latitude of the particular location. The literature in which indoor dust deposition was carried out on PV panels has been excluded. In the literature works studied, there was comparison of output parameters between a clean panel which was cleaned daily during the experiments and a dusty panel which was never cleaned during the study period. This was the type of experiment in general which was carried out for all locations with slight variations. The parameters considered in different papers for calculating the soiling loss rates are: reduction in power, energy, transmittance, short circuit current, efficiency and performance ratio. Based on the data collected for the literature a database table was formed and also the data was into the form of the above described map.
RESULTS AND DISCUSSION
The end result that is obtained is the World soiling map which contains various pins pointing to different locations around the globe. Clicking on any one of the pin will provide information about the location, the maximum site soiling rate, the reference from which the soiling loss data was calculated and the remarks about the site soiling can be seen. For instance, a pin pointing to a location in Saudi Arabia is clicked and it can be seen from the below figure that the location to which the pin is pointing is Jazan City, the max. site soiling rate at this location is found to be .092%/day.
It can be seen from the remarks section is that the efficiency had reduced by 10.4% due to accumulation of dust for three weeks at a tilt angle of 30 deg. Further if the tilt angle was increased to 55 deg the reduction in efficiency was only 9.7%. This shows that the soiling losses are less if the panels are tilted at higher tilt angles. But it is a general practice to mount the panels at a tilt angle similar to the latitude of the location in which the panels are going to be installed. Similar to the above example there are 36 locations for which maximum soiling rate has been updated in this map.
Solar installations require periodic cleaning and maintenance activities so that maximum power from the installation can be obtained. Hence determination of optimal cleaning frequency becomes crucial for efficient functioning of the solar installation. In order to determine the cleaning frequency, the soiling rate at that particular location is essential. Therefore, this detailed literature survey would allow owners of solar power plants to know the amount soiling occurring in the site location and thereby help them decide the optimal cleaning frequency of their installation. This survey would also allow people to know the reduction in solar power generation in their plant due to the effect of soiling and help them reduce the causes of soiling.
I feel very grateful to get selected for the Indian Academy of Sciences’ Summer Research Fellowship Program (SRFP 2019) and pursue my internship project at Indian Institute of Technology, Mumbai. I am very grateful to Indian Academy of Sciences for giving me this golden opportunity and this had surely been a great learning experience to me to work in such a renowned institute.
I express my sincere profound gratitude to my guide, Prof. Anil Kottantharayil, Dept. Electrical Engineering, IIT Bombay. It has been an honour to be his research intern for 8 weeks. I sincerely thank him for his excellent guidance, support and motivation in every step throughout my research and during the whole period of my project.
I specially thank Ms. Sonali, for her valuable support, patience, critical comments and detailed review during the period of my project. She is the one who always inspired me, was always willing to help and give her best suggestions.
At last I would like to express my deepest sense gratitude to my Principal Dr. AbhaiKumar V., my HOD Dr. Baskar S., Dr. Rajan Prakash, Mr. Varatharajan and Dr. Geethanjali for their support and motivation without which I would not have been able to participate in this internship.