Article 正式发布 Versions 1 Vol 28 (6) : 1186-1194 2019
Download
Research on Photovoltaic Performance Reduction due to Dust Deposition: Modelling and Experimental Approach;灰尘沉积对光伏性能的影响研究:建模与实验方法
: 2019 - 11 - 05
72 0 0
Abstract & Keywords
Abstract: Photovoltaic (PV) power generation technology is the main renewable energy utilization technology. However, dust deposition severely affects the PV power generation efficiency and decreases the production capacity of PV power plants. In this study, the factors affecting PV technology were divided into the following three types: occlusion, corrosion, and temperature rise. A dust-collecting PV model considering dust deposition and rainfall scouring was established; a PV performance index was proposed. By conducting experiments with different dust mass densities, it was found that the short-circuit current (SCC), open-circuit voltage (OCV), and PV output power of PV decreased with the increase in dust mass density. In the initial stage of dust deposition, dust exhibited the greatest effect on the performance of PV. In the later stage of dust deposition, the effect of dust deposition became stable. The initial 10 g/m2 dust decreased the PV output power by 34%. In addition, the conversion efficiency and fill factor (FF) decreased with the increase in dust mass density; both of them were exponential functions. When the dust mass density was low (less than 30 g/m2), the dust mass density increased by 10 g/m2, and the conversion efficiency decreased by an average of 3.4%. Finally, by conducting economic calculations, it was found that a PV power plant where dust has not removed for one year will cause 12% loss of power generation. 近年来,太阳能光伏技术被认为是解决世界能源危机的主要途径之一。光伏电站一般建在沙漠、荒地等开阔地区,四周无建筑遮挡,光伏表面非常容易受天气影响而被灰尘覆盖,发电效率也受到影响。研究首先阐述了灰尘对光伏发电造成影响的三个因素,遮挡效应、温度效应和腐蚀效应,在此基础上建立了粉灰尘沉积状态下光伏表面的热平衡方程,并提出了一种可行的光伏电池效率评价方法。最后通过现场测试,发现随着灰尘沉积密度的增大,短路电流和开路电压均减小。且在光伏积尘初期,灰尘对光伏发电的输出性能影响最大。当灰尘沉积密度为10 g/m2时,光伏最大功率降低了约34%。此外,灰尘沉积密度与光伏转换效率具有良好的非线性关系。随着灰尘沉积密度的逐渐增大,光伏转换效率逐渐降低。当灰尘沉积密度增大到一定程度时,光伏转换效率趋于稳定。最后,通过经济性分析,发现定期清洗光伏板具有显著的经济效益。
Keywords: photovoltaic technology, dust deposition, conversion efficiency, fill factor
1. Introduction
Nowadays, the energy consumption of world is huge; therefore, the utilization of solar energy technology is widely regarded as an important way to solve the energy crisis. As one of the solar energy utilization technologies, photovoltaic (PV) power generation technology has become an important part of social energy structure because of its high energy grade, convenient installation and maintenance, and strong regional adaptability. International Energy Agency (IEA) predicts that global PV installation will reach 115 GW in 2019. PV power plants are generally located in open terrain such as grasslands and desert areas. These areas are surrounded by open air, large wind, and sand; PV surfaces easily accumulate dust. The data show that dust can decrease the PV power generation efficiency by an average of 17% and even 40% in severe cases. A decrease in PV efficiency directly leads to a decrease in PV capacity, which in turn will affect economic efficiency. Thus, it is important to study the influencing mechanism of dust accumulation on PV.
 
Nomenclature
APV surface area/m2Qsolaramount of solar radiation received by the PV surface/W
B0maximum dust accumulation amount per unit area/g·m−2Qtempheat converted into PV and dust/W
B1dust accumulation rate constantQtranexchange of heat between PV and the outside world/W
BLamount of dust left on the PV surface before dust accumulates/g·m−2Rdust particle radius/m
Cratio of heat dissipation intensity of the sky to the direct radiation intensity reaching the ground/W·m−2Rsseries resistor/Ω
cdustspecific heat capacity of dust/J·kg−1·K−1Rshparallel shunt resistor/Ω
cpvspecific heat capacity of PV/J·kg−1·K−1Sarea of solar energy received by PV array/m2
dcoverage density of dust particles on the PV surface/g·m−2Tiduration of a rain/h
Ffloorview factor between PV with groundTdust accumulation time before the rain/h
Fskyview factor between PV with skyTairambient air temperature/K
f (t)density function of dustfallTbackback temperature/K
Grefstandard radiation intensity/W·m−2Tfloorfloor temperature/K
Hmonthly average total solar irradiation/kW·m−2TfrontPV front temperature/K
hbackconvection coefficients of the back of PV/ /W·m−2·K−1Tpvactual temperature of PV/K
hfrontconvection coefficients of the front of PV /W·m−2·K−1Treftemperature of the PV under the STC/K
I0reverse saturation current/ATskysky temperature/K
IDdirect radiation intensity of solar PV surface /W·m−2titime interval between two rains/h
Idheat dissipation of sky/W·m−2Voc (d)OCV at different dust coverage densities/V
IHTtotal intensity of solar radiation at the horizontal plane/W·m−2W0power generation of PV array/kW
Iph(ref)photogenerated current reference value/AGreek letters
IRintensity of ground-reflected radiation/W·m−2constant/V
ISsolar radiation intensity of PV surface/W·m−2pvinclination of PV/rad
Isc (d)the SCC under different dust coverage densities/Areftemperature coefficient of the solar cell
kcomprehensive efficiency of PV array ()transparency of dust to different wavelengths of light
Mamount of dust deposition on PV surface /g·m−2emissivity
Mdustamount of dust/g·m−2refefficiency of solar cell module under the STC
Mrainamount of dust washed away with rain/g·m−2angle of incidence of the sun/rad
mdustmass of dust/kgwavelength of electromagnetic waves
mpvmass of PV/kgtransmission rate
Pininput power to the PV surface/W1PV transmittances before PV surface dust accumulation
PmaxPV maximum output power/W2PV transmittances after PV surface dust accumulation
Qpowerelectrical energy produced by PV/Wdustdensity of dust particles/kg·m−3
Qrefamount of solar radiation reflected/W·m−2greflectivity of ground
Qradenergy of radiation/W·m−2Stefan–Boltzmann constant/W·m−2·K−4
qelectronic chargeabsorption rate of battery to solar radiation
Covering the PV surface to avoid dust will block the solar radiation and decrease the area where the PV surface can directly receive solar radiation. Mastekbayeva [1] studied the effect of dust on the transmittance of 0.2-mm-thick low-density polyethylene (LDPE) glass commonly used in PV. Dust accumulation on the LDPE glass affected the transmittance, and the decrease in transmittance depends on the dust density. In tropical humid areas, when the dust deposition density is 5 g/m2, the transmittance decreased by 11%. Elminir [2] conducted a seven-month experiment; for PV panels with a tilt angle between 0° and 90°, the dust density was distributed in the range of 15.84–4.48 g/m2. The transmittance decreased by 52.42%–12.38%. A study by Boyle [3] in the Front Range of Colorado showed that the transmittance of PV glass cover linearly varies with the bulk density of dust; dust per 1 g/m2 of mass density decreases the transmission by 4.1%. Sayigh [4] studied the effect of dust on the transmittance of PV glass cover in Kuwait. The results show that dust accumulation in 38 days decreases the transmittance of PV glass cover by 17%–64%. In addition, similar studies were reported in Refs. [5–7], etc.
Adinoyi’s [8] study in Saudi Arabia shows that the reduction in PV power output due to dust accumulation not only depends on the duration of PV exposure, but also on the frequency and intensity of dust, unless it is cleaned by rain or by human operation. Performance gradually decreases as dust is accumulated; six months of dust accumulation decreases the PV output power by more than 50%. Salari [9] studied the effect of dust deposition density on PV electrical properties; an increase in the PV surface dust density from 0 g/m2 to 8 g/m2 decreased the electrical efficiency by 26.36%. Saidan [10] studied the effect of dust on PV power generation. Experimental results show that dust decreases the maximum current by 6.9%–16.4% depending on the time when PV panels are exposed to dust-affected environments. After one day, one week and one month of leakage, the PV efficiency decreased by 6.24%, 11.8%, and 18.74%, respectively.
The accumulation of dust on a PV surface not only affects PV performance, but also causes economic loss. Gholami [11] showed that the energy reduction of 289 kWh during the 70 days of PV dust deposition experiment is 4.845 kW power capacity. In addition, in the absence of rain for 70 days, 57.800 kWh of clean energy per megawatt of electricity will be lost due to natural dust. This decrease in clean energy is equivalent to 3 hectares of forest absorbing carbon (32.7 tons). Tanesab [12] tested a 1.5 kW grid-connected PV system in Perth and found that the energy lost by PV caused by dust accumulation was 7.11 kWh/year. In addition, similar studies have been conducted on dust types and particle sizes. For example, Heydarabadi [13] studied the dust accumulation of PV with different dip angles. Oh [14] and Lu [15] studied the effect of dust particle size on transmittance; Darwish [16] studied the effect of dust type on PV efficiency.
These studies focused on the effects of dust on PV efficiency, including dust deposition, transmittance, and dust particle size. The thermal process analysis of effect of dust on PV is ignored, and the effect of dust accumulation on PV characteristic curves is described. In this study, the factors affecting dust are divided into three types: occlusion, corrosion, and temperature rise according to the cause of dust generation, and a mathematical model of dust deposition on PV is established. The dust mass density was set to 10 g/m2, 20 g/m2, and 30 g/m2. The effects of dust accumulation on the PV characteristic curve, conversion efficiency, and FF were studied. Finally, the PV power station in Hainan was selected for the economic calculation of dust accumulation effect on PV.
2. Methods of Dust Deposition on PV Panels
2.1   Influencing principles
The structure of PV panels is generally divided into five layers, from top to bottom: glass cover, upper ethylene vinyl acetate (EVA), Si-cells, lower EVA, and back tedlar layer. The glass cover is generally a transparent glass, and the light transmittance is high, generally above 91%. When a certain wavelength of incident light is irradiated onto the glass cover, a part of light is reflected by the glass, and a part of light is transmitted to the surface of battery through the glass to be converted into electric energy owing to the PV effect. When the surface of PV module is deposited with dust, the dust particles absorb and scatter the incident sunlight, thus decreasing the effective area of PV module panel and light transmittance and partial incident sunlight passes through the tempered glass. The uniformity of propagation changes, thus decreasing the power generation efficiency and power generation. The higher the deposition concentration of the dust, the lower the actual transmittance of PV module and the lower the output power.
Dust particles adsorb and combine with harmful substances in the air to form a certain acidity or alkalinity. The main components of surface layer tempered glass of PV modules are SiO2 and limestone. When these components are used for a long time under the action of acidic or alkaline environment, they will gradually corrode. Thus, the original smooth surface forms many small concave surfaces, and the overall roughness increases. When sunlight falls on the surface, the small concave surfaces form a diffuse reflection, thus decreasing the uniformity of solar radiation propagation in the PV module. Therefore, the energy of reflected light increases, and the energy of refracted light decreases, thus decreasing the radiation energy received by the solar cell. The photoelectric effect is weakened; the power generation efficiency is lowered; the power generation amount is decreased.
Accumulation of dust on the surface of PV module not only blocks the incident light, but also changes the heat transfer form of PV module. In the long-term use, the surface of PV module is inevitably covered with bird droppings, dust, and other obstructions, and these occludes form a shadow on the PV module. Because of the existence of local shadows, the current and voltage of some solar cells in the PV module increase, increasing the temperature of blocked part much more than the unblocked part and even the darkness of burnt out due to excessive temperature. Severe hot spot effect can even damage the entire PV panel. At the same time, the temperature of solar cell will increase during operation, and the dust deposited on the surface of PV module will block the heat transfer to the outside, forming an insulation layer, affecting the PV power generation efficiency. For every 1°C increase in solar cell operating temperature, the output power decreases by 0.35%.
2.2   PV dust accumulation model
PV surface dust is mainly attributed to gravity dust. Dust particles are heavier, and their particle size is mostly above 0.01 mm. The dust particles fall on the PV surface under the action of their own gravity. Particles with a particle size of less than 0.01 mm have insufficient gravity for falling and float in the air for a long time. These particles are accumulated on the PV surface by wind. In fine weather, the dust particles present in the
atmosphere increases their self-weight when the humidity increases and the speed of wind decreases. At this time, the dust particles floating above the surface of PV panel will continuously fall on the surface of PV panel to form dust deposits. In rainy weather, rain will wash away some of the dust particles on the PV surface, and the dust present in the rain will remain on the PV surface. The PV dust deposition process is shown in Fig. 1.
The accumulation of dust is related to factors such as dustfall and rainfall. The amount of PV surface dust can be expressed as follows:
(1)
where M is the amount of dust deposition on PV surface, g/m2. Mdust is the amount of dust, g/m2. Mrain is the amount of dust washed away by rain, g/m2.
In fine weather, the cumulative amount of dust per unit area of PV surface can be calculated using Eq. (2).
(2)
where BL is the amount of dust left on the PV surface before dust accumulates, g/m2. T is the dust accumulation time before the rain, h. B0 is the maximum dust accumulation amount per unit area, g/m2. B1 is the dust accumulation rate constant.
After the dust is washed by rain, the PV surface area gray model can be expressed as follows:
(3)
where f(t) is the density function of dustfall. qT is the runoff function. ti is the time interval between two rains, i.e., the rain cycle. Ti is the duration of a rain.
2.3   PV dust deposition thermodynamic model
When the PV surface is covered with dust, a part of the solar radiation received by the PV surface is reflected and absorbed by the dust. A part of the solar radiation passes through the dust to reach the PV glass cover plate, and a part of the solar radiation reaching the glass cover plate is received by the battery through the glass cover plate to generate a thermoelectric effect. A part of the solar radiation is converted into heat through heat convection and radiation to the environment, and a part of the PV temperature increases, as shown in Fig. 2. The heat balance equation of PV can be expressed as follows:


 
Fig. 1 Formation of PV dust deposition
(4)
where Qsolar is the amount of solar radiation received by the PV surface, W; Qtran is the exchange of heat between PV and the outside world, mainly including radiative heat transfer and convective heat transfer, W. Qpower is the electrical energy produced by PV, W; Qtemp is the heat converted into PV and dust, W.


 
Fig. 2 Schematic diagram of solar radiation transmission
The amount of solar radiation received by the PV surface can be expressed as follows:
(5)
where is the transmission rate, and the dust will affect the transmittance of glass cover. IS is the solar radiation intensity of PV surface, W/m2. is the absorption rate of battery to solar radiation. A is the PV surface area, m2.
can be calculated using Eq. (6).
(6)
where 1 and2 are different PV transmittances before and after PV surface dust accumulation. is the wavelength of electromagnetic waves; () is the transparency of dust to different wavelengths of light. R is the dust particle radius, m. dust is the density of dust particles, kg/m3. d is the coverage density of dust particles on the PV surface, g/m2.
Among them, the solar radiation intensity on the PV tilt can be expressed using Eqs. (7–10),
(7)
(8)
(9)
(10)
where ID is the direct radiation intensity of solar PV surface, W/m2. Id is the heat dissipation of sky, W/m2. IR is the intensity of ground-reflected radiation, W/m2. IHT is the total intensity of solar radiation at the horizontal plane, W/m2; is the angle of incidence of the sun, rad. C is the ratio of heat dissipation intensity of the sky to the direct radiation intensity reaching the ground, W/m2.pv is the inclination of PV, rad. g is the reflectivity of ground.
The electrical energy generated by PV can be expressed as follows:
(11)
where ref is the efficiency of solar cell module under the standard test conditions (STC). Tref is the temperature of the PV under the STC, K. ref is the temperature coefficient of the solar cell. Tpv is the actual temperature of PV, K.
PV is mainly exchanged in the form of radiative heat exchange and convective heat exchange with the outside world. This can be expressed as follows:
(12)
(13)
(14)
where Qref is the amount of solar radiation reflected, W/m2. Qrad is the energy of radiation, W/m2. hfront and hback are the convection coefficients of the front and back of PV, W/(m2·K). is the Stefan-Boltzmann constant, W/(m2·K4). Tfront , Tback , Tair , Tsky , and Tfloor are PV front temperature, back temperature, ambient air temperature, sky temperature, and floor temperature, K. Fsky and Ffloor are the view factors. is the emissivity.
The heat stored in PV and dust can be expressed as follows:
(15)
where cpv and cdust are the specific heat capacity of PV and dust, respectively, J/(kg·K). mpv and mdust are the mass of PV and dust, respectively, kg.
2.4   PV performance evaluation approach
Open-circuit voltage (OCV), short-circuit current (SCC), maximum power point voltage, maximum power point current, and peak power can be obtained from the I-U and P-U characteristic curves, as shown in Fig. 3. Different temperatures, radiant intensities, and occlusions can change the voltage and current of PV, resulting in a lower operating power of PV.


 
Fig. 3 Performance diagram of solar cells
OCV and SCC are important characteristic parameters of PV performance. They can be expressed as follows:
(16)
(17)
where Voc (d) is OCV at different dust coverage densities, V. Iph(ref) is photogenerated current reference value, A; is constant, 0.0259 V under STC. Gref is standard radiation intensity, 1000 W/m2. I0 is reverse saturation current, A. Isc (d) is the SCC under different dust coverage densities, representing the maximum current that can be generated and continuously output by PV modules, A. Rs is series resistor, Ω. Rsh is parallel shunt resistor, Ω.
Conversion efficiency is the most important indicator of PV modules. When PV is in normal operation, conversion efficiency is mainly affected by solar radiation intensity, occlusion, and temperature. The conversion efficiency is the ratio of maximum output power of PV to the input power incident on the PV surface.
(18)
where Pmax is the PV maximum output power, W. Pin is the input power to the PV surface, W.
Another important indicator for evaluating PV performance is the FF. This is used to characterize the quality of PV. Increased losses due to series resistance and leakage resistance will make FF smaller.
The FF of dust PV can be expressed as follows:
(19)
where q is electronic charge, 1.6×10-19.
3. Experimental Research and Results Analysis
3.1   Experiment description


 
Fig. 4 Schematic diagram of test instrument layout
3.2   Results
3.2.1   PV surface temperature


 
Fig. 5 Solar radiation and outdoor temperature


 
Fig. 6 Effect of dust on PV surface temperature
3.2.2   I -U and P-U characteristic curve


 
Fig. 7 I -U curve of PV under different mass densities


 
Fig. 8P -U curve of PV under different mass densities
3.2.3   Output power


 
Fig. 9 Solar radiation intensity and mass density on PV output power
3.2.4   Conversion efficiency and FF


 
Fig. 10 Effect of mass density on PV efficiency and FF
3.2.5   Economic effect
(20)
where W0 is the power generation of PV array, kW; S is the area of solar energy received by PV array, m2; H is the monthly average total solar irradiation, kW/m2; k is the comprehensive efficiency of PV array.


 
Fig. 11 Dustfall content and generating capacity
4. Conclusions
In this study, based on the factors affecting the occlusion, corrosion, and temperature rise of PV, a PV model was established, and PV experiments with different dust mass densities were conducted. The main conclusions are as follows:
The SCC and OCV of PV decreased with the increase in dust mass density. The effect of dust deposition on SCC was greater than the effect on OCV, and the reduction rate of short circuit current and open circuit voltage is the largest in the early stage of dust deposition.
As the dust mass density increased, the PV output power gradually decreased, and both of them were exponential functions. A dust mass density of 10 g/m2 decreased the PV output power by 34%. At the initial stage of PV dust deposition, dust had the greatest influence on the performance of PV. In the later stage of dust deposition, the effect of dust was gradually stabilized. Thus, it is recommended that when dust deposition remains in the early stage, cleaning the PV surface works the best.
The conversion efficiency and FF decreased with the increase in dust mass density, and both of them were exponential functions. When the dust mass density was low (less than 30 g/m2), the conversion efficiency and FF increased with the increase in dust mass density. With a rapid decrease, the conversion efficiency decreased by an average of 3.4% for every 10 g/m2 increase in dust mass density.
Acknowledgments
We extend our gratitude to the Funds supports of National Natural Science Foundation of China (Project No. 51590911), and the national key research projects (Nos. 2016YFC0700400), and the key research and development program of Shaanxi Province (2018ZDCXL-SF-03-01).
[1]
Mastekbayeva G.A., Kumar S., Effect of dust on the transmittance of low density polyethylene glazing in a tropical climate. Solar Energy, 2000, 68(2): 135‒141.
[2]
Elminir H.K., Ghitas A.E., Hamid R.H., El-Hussainy F., Beheary M.M., Abdel-Moneim K.M., Effect of dust on the transparent cover of solar collectors. Energy Conversion and Management, 2006, 47(18): 3192‒ 3203.
[3]
Boyle L., Flinchpaugh H., Hannigan M.P., Natural soiling of photovoltaic cover plates and the impact on transmission. Renewable Energy, 2015, 77: 166‒173.
[4]
Sayigh A., Al-Jandal S., Ahmed H., Dust effect on solar flat surfaces devices in Kuwait. Proceedings of the International Symposium on Thermal Application of Solar Energy, 1985, pp. 96‒100.
[5]
Garg H.P., Effect of dirt on transparent covers in flat-plate solar energy collectors. Solar Energy, 1974,
15(4): 299‒302.
[6]
Hegazy A.A., Effect of dust accumulation on solar transmittance through glass covers of plate-type collectors. Renewable Energy, 2014, 22(4): 525‒540.
[7]
Semaoui S., Arab A.H., Boudjelthia E.K., Bacha S., Zeraia H., Dust effect on optical transmittance of photovoltaic module glazing in a desert region. Energy Procedia, 2015, 74: 1347‒1357.
[8]
Adinoyi M.J., Said S.A.M., Effect of dust accumulation on the power outputs of solar photovoltaic modules. Renewable Energy, 2013, 60: 633‒636.
[9]
Salari A., Hakkaki-Fard A., A numerical study of dust deposition effects on photovoltaic modules and photovoltaic-thermal systems. Renewable Energy, 2019, 135: 437‒449.
[10]
Saidan M., Albaali A.G., Alasis E., Kaldellis J.K., Experimental study on the effect of dust deposition on solar photovoltaic panels in desert environment. Renewable Energy, 2016, 92: 499‒505.
[11]
Gholami A., Khazaee I., Eslami S., Zandi M., Akrami E., Experimental investigation of dust deposition effects on photo-voltaic output performance. Solar Energy, 2018, 159: 346‒352.
[12]
Tanesab J., Parlevliet D., Whale J., Urmee T., Energy and economic losses caused by dust on residential photovoltaic (PV) systems deployed in different climate areas. Renewable Energy, 2018, 120: 401‒412.
[13]
Heydarabadi H., Abdolzadeh M., Lari K., Simulation of airflow and particle deposition settled over a tilted photovoltaic module. Energy, 2017, 139: 1016‒1029.
[14]
Oh S., Analytic and Monte-Carlo studies of the effect of dust accumulation on photovoltaics. Solar Energy, 2019, 188: 1243‒1247.
[15]
Lu H., Lu L., Zhang L.Z., Pan A., Numerical study on polydispersed dust pollution process on solar photovoltaic panels mounted on a building roof. Energy Procedia, 2019, 158: 879‒884.
[16]
Darwish Z.A., Kazem H.A., Sopian K., Al-Goul M.A., Alawadhi H., Effect of dust pollutant type on photovoltaic performance. Renewable and Sustainable Energy Reviews, 2015, 41: 735‒744.
Article and author information
Download:
CHEN Yingya1,2
WANG Dengjia1,2,*
LIU Yanfeng1,2
DONG Yu1,2
LIU Jiaping1,2
Publication records
Published: Nov. 5, 2019 (Versions1
References
Journal of Thermal Science