Quantification of PV Power and Economic Losses Due to Soiling In

sustainability Article Quantification of PV Power and Economic Losses Due to Soiling in Qatar Amr Zeedan *, Abdulaziz Barakeh, Khaled Al-Fakhroo, Farid Touati and Antonio S. P. Gonzales, Jr. Department of Electrical Engineering, Qatar University, Doha 2713, Qatar; [email protected] (A.B.); [email protected] (K.A.-F.); [email protected] (F.T.); [email protected] (A.S.P.G.J.) * Correspondence: [email protected]; Tel.: +974-3009-3019 Abstract: Soiling losses of photovoltaic (PV) panels due to dust lead to a significant decrease in solar energy yield and result in economic losses; this hence poses critical challenges to the viability of PV in smart grid systems. In this paper, these losses are quantified under Qatar’s harsh environment. This quantification is based on experimental data from long-term measurements of various climatic parameters and the output power of PV panels located in Qatar University’s Solar facility in Doha, Qatar, using a customized measurement and monitoring setup. A data processing algorithm was deliberately developed and applied, which aimed to correlate output power to ambient dust density in the vicinity of PV panels. It was found that, without cleaning, soiling reduced the output power by 43% after six months of exposure to an average ambient dust density of 0.7 mg/m3. The power and economic loss that would result from this power reduction for Qatar’s ongoing solar PV projects has also been estimated. For example, for the Al-Kharasaah project power plant, similar soiling loss would result in about a 10% power decrease after six months for typical ranges of dust density in Qatar’s environment; this, in turn, would result in an 11,000 QAR/h financial loss. This would pose a pressing need to mitigate soiling effects in PV power plants. Citation: Zeedan, A.; Barakeh, A.; Keywords: photovoltaic (PV); standard test conditions (STC); Middle East and North Africa (MENA); Al-Fakhroo, K.; Touati, F.; Gonzales, soiling losses; dust density A.S.P., Jr. Quantification of PV Power and Economic Losses Due to Soiling in Qatar. Sustainability 2021, 13, 3364. https://doi.org/10.3390/su13063364 1. Introduction Academic Editor: Maria Malvon In this age of rapid technological advancement, conventional energy sources are being replaced by renewable energy resources for various economic and environmental reasons. Received: 20 February 2021 Solar energy is among the most widespread sources of renewable energy. This energy Accepted: 9 March 2021 is harnessed using solar photovoltaic (PV) cells. Solar power is also one of the cleanest Published: 18 March 2021 renewable energy sources. However, it is highly dependent on local climate conditions, which can vastly change a solar panel’s efficiency due to various processes, such as soiling Publisher’s Note: MDPI stays neutral losses [1]. Large amounts of soil accumulate on the surface of a solar PV panel in this with regard to jurisdictional claims in process. Dust accumulation is standard in areas with large amounts of soil, dust, or published maps and institutional affil- sandstorms, such as the Middle East [1]. In such locations, this site-specific phenomenon iations. can cause a power generation loss exceeding one percent per day [1]. Dust from agricultural emissions and industry emissions as well as engine exhaust, pollen, plant debris, fungi, mosses, algae, bacteria biofilms, bird droppings, and dust deposits of minerals are some of the many location-dependent contamination types that can reduce and scatter sunlight, Copyright: © 2021 by the authors. thus affecting the overall performance of solar photovoltaic cells [1]. Licensee MDPI, Basel, Switzerland. Dust accumulation on the surfaces of PV panels leads to a reduction in the power This article is an open access article produced by solar power systems [1,2]. Without a suitable mitigation technique to address distributed under the terms and these soiling losses, especially in desert countries, the economic losses accumulated over conditions of the Creative Commons several weeks can be a considerable hurdle to the viability of using solar power as a cost- Attribution (CC BY) license (https:// efficient and sustainable energy resource that can be meshed reliably in any hybrid energy creativecommons.org/licenses/by/ matrix. Moreover, the cleaning costs required to reduce dust deposition on solar panels 4.0/). Sustainability 2021, 13, 3364. https://doi.org/10.3390/su13063364 https://www.mdpi.com/journal/sustainability Sustainability 2021, 13, 3364 2 of 15 can be economically challenging [1–3]. As a result, the mitigation technique adopted must be not only be efficient but also financially feasible. Quantifying soiling losses in Qatar’s environment is essential in justifying the need for an economical and effective mitigation technique to overcome these losses. In addition, this quantification can later be used to evaluate the actual power and cost improvements resulting from the application of the proposed mitigation technique. Moreover, having an expectation about the amount of power decrease due to soiling is vital in planning and managing solar power plants and reliably incorporating solar power into conventional (or other renewable) power plants to meet the electricity consumption demands of the country. Taking all these factors into consideration, solar energy could be used more efficiently as a clean, sustainable, and reliable energy resource. An extensive literature review was carried out to study the effects of dust accumulation on solar PV panels and the economic impact of soiling losses. The review was organized to summarize the dependence of PV power production on solar irradiance and then illustrate the negative impact of dust accumulation on reducing the transmittance of transparent surfaces such as solar panel coatings, thus accounting for the reduction in output power of PV panels. This review is detailed in Section2 and is followed by a detailed examination of the economic impact of soiling losses, both on a global scale and on a regional scale in the Gulf area. In the methods and results sections, the soiling losses of PV panels in Qatar will be quantified in terms of energy and money, based on the analysis of the experimental data collected. Moreover, it is well established that the specific power and economic losses resulting from dust accumulation are region-specific. This paper will first prove that, indeed, in Qatar’s environment dust accumulation does result in significant losses in terms of power production and costs of solar power systems. Second, the authors will quantify these energy and financial losses, which justify the need for an effective mitigation technique. This quantification will be employed in a future study to design a PV mitigation technique based on nanomaterial hydrophobic coating. It will then be possible to identify the exact improvements resulting from the application of the proposed hydrophobic mitigation technique. 2. Literature Review 2.1. The Dependence of PV Power Production on Solar Irradiance A photovoltaic cell consists of two types of semiconductors: n-type and p-type. The p-type semiconductor has an electron vacancy or a hole, since it is made by adding gallium or boron atoms to the silicon atoms. Boron and gallium have one less valence electron to form all four bonds with silicon, thus leaving an electron vacancy. The n-type silicon is made by doping silicon with atoms having five valence electrons, such as phosphorus, thus leaving one free electron. A PV cell consists of a layer of n-type silicon next to a layer of p-type silicon. Near this p-n junction, a depletion zone forms where the electrons from the n-type fill the holes in the p-type. This leads to an internal electric potential that prevents further electrons in the n-type from filling holes in the p-type. When a photon falls on the PV cell it ejects an electron, which results in a hole or vacancy left behind. When this happens in the depletion region, the electric potential pushes the electrons to the n-type layer and the holes to the p-type layer. A wire from the other side connects the p-type and n-type layers; thus, the electrons flow from the n-type layer to the p-type layer through the depletion region and through the wire, creating a current as depicted in Figure1. The short-circuit current, measured in amperes (A), of a solar cell is linearly proportional to the light intensity, measured in watts per meter square (W/m2). This can be rationalized, based on the above model of the solar cell, as follows. The number of mobile electrons produced is roughly equal to the number of absorbed photons, and since current is linearly proportional to moving charges and light intensity is linearly proportional to the number of photons, the current produced is linearly proportional to the light intensity. However, the open-circuit voltage increases logarithmically with light intensity, and the Sustainability 2021, 13, 3364 3 of 15 output power will be the product of the current and voltage. Thus, it can be seen how solar cell power production is related to the light intensity reaching the solar cell using basic principles. The exact formulas depend on other parameters and usually differ from one solar panel to another, depending on its design, materials, and connection with other panels (out of scope). The general observation is that the output power of solar panels depends in a direct way on the light intensity reaching the panel, and this explains why dust accumulation reduces the efficiency and output power of solar panels by reducing Sustainability 2021, 13, x FOR PEER REVIEW 3 of 15 the light intensity reaching the panel. This effect is investigated in the next section in more detail and with supporting data. FigureFigure 1.1.Structure Structure ofof aa photovoltaicphotovoltaic (PV)(PV) cellcell ((left)left) andand thethe effecteffect ofof aa photonphoton falling on the PV cell (right(right))[ [4].4].

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