Over the past decade, rising energy demand, increasing climate change and volatile oil prices have forced people to get more electricity from renewable sources. The abundance of solar resources and the increasing efficiency of photovoltaic (PV) modules have made solar energy fast becoming a cost-effective source of power generation.
According to IRENA, the use of solar photovoltaic systems in electricity production is gradually expanding (480GW of photovoltaic systems have been installed worldwide) and will continue to be an essential renewable energy source in the coming decades.
According to the “Energy Outlook 2019” report released by the IEA, renewable energy generation will be led by solar photovoltaics, which will increase by 50% between 2019 and 2024.
As projected by IRENA, Australia will have the highest share of solar generation in 2050, at nearly 40%, followed by the US at 33%; South Africa at 32%; and Japan at 30%. The growth of solar PV is bound to create more jobs and income generation opportunities for all stakeholders.
It can be seen from the “Global Photovoltaic Power Generation Potential” in the figure below: Compared with other regions or countries, the potential of the Middle East, Africa and Australia is obviously outstanding. Because of this, many projects have been carried out in this land rich in radiation resources.
According to the 2020 Solar Outlook Report by the Middle East Solar Industry Association (MESIA), the Middle East and North Africa region will have more than 20GW of photovoltaic projects in the next few years.
The electrical energy output of a PV module and its lifetime depend on various aspects. Some of these issues are related to the module itself (type of PV material), while others are related to location and environment (solar energy, temperature, pollution, clouds, and occlusions).
Like other semiconductor devices, PV cells are very sensitive and their efficiency decreases with increasing temperature. Battery temperature is affected by various factors such as ambient temperature, wind speed, radiation drop, type of material making up the solar panel, etc. The extent to which temperature affects photovoltaic modules depends on the type of semiconductor used.
The deposition of foreign particles on the surface of a solar photovoltaic array module is called “fouling”. This dirt could be sand, salt, bird droppings, snow, or any other deposit on the panel. Such deposits affect the photon absorption of the solar cell by reducing the light transmission through the glass cover of the module. As the contamination increases, the conversion efficiency is gradually lost, thereby reducing the energy yield of the module and the entire array, which we call “fouling”.
The figure below shows the susceptibility of various regions of the world to dust storms. We can find that the regions and countries with the highest radiation globally also have high pollution potential. Although they are best suited for building large PV plants (from a solar radiation point of view), they must clean the PV panels efficiently and more frequently than plants elsewhere.
Reducing power loss due to dust is critical for solar power plants operating in arid regions. These areas have high concentrations of aerosols and frequent sandstorms, making it easier for dust to accumulate on panels.
In the Middle East, power generation losses due to dust buildup on photovoltaic panels can exceed 40%, while daily losses due to atmospheric dust deposition can exceed 6%. Dust deposits can cause significant performance degradation in some locations. Although several cleaning and prevention methods have been investigated, there is still a gap to a solution with low maintenance costs and minimal water and energy consumption.
Photovoltaic panels on two rovers NASA has sent to Mars are often covered in Martian dust, drastically reducing their power generation. However, the rover can only use strong wind dust removal as an alternative to other mechanical cleaning methods.
The risks and rewards for the owner and operator are tied to the performance ratio of the plant. Solar plants take up a lot of physical space, which is why they are often built in remote areas that meet minimum radiation levels.
Contamination is a serious problem for photovoltaic panels installed in harsh arid climates where dust storms are common. In response to this situation, the photovoltaic panel cleaning market has grown rapidly and become an integral part of solar technology.
Initially, most solar systems were installed in areas where rainfall was sufficient to clean the surfaces of photovoltaic panels. However, even in areas with heavy rainfall, pollution can seriously affect solar yields.
Cleaning of solar panels, although not standardized, has involved the application of various techniques, including manual, semi-automatic and fully automatic cleaning modes. Some factories use cleaning brush equipment powered by tractors or other vehicles; others prefer to use cleaning robots to clean the panels. Power plants can choose the appropriate cleaning method according to different parameters and budgets.
In terms of cleaning technology, the cleaning of solar panels can be divided into “dry cleaning” and “wet cleaning”.
As the name implies, “wet cleaning” is the use of water and associated chemicals to remove deposits from solar panels. This method is more suitable for areas with abundant water reserves and high rainfall. But according to the PI Berlin AG research institute, few large power plants consider water washing as the best solution for cleaning photovoltaic panels.
“Dry cleaning” is a way of cleaning without water. It cleans the panels by using motorized brushes or pressurized air. Various reports and studies done in desert-like environments suggest that dry cleaning is the best cleaning option for arid climates.
Global electricity demand will continue to grow, and renewable energy will become more widespread. If you want to use solar photovoltaic modules to generate electricity, you must clearly understand the relationship between the loss caused by pollution and temperature and the geographical location of the factory, so that you can take corresponding measures to solve these problems. For large photovoltaic power plants in arid environments, dry cleaning seems to be better than wet cleaning.