Solving the Soiling Problem for Solar Power Systems
2019; Elsevier BV; Volume: 3; Issue: 10 Linguagem: Inglês
10.1016/j.joule.2019.09.011
ISSN2542-4785
Autores Tópico(s)Solar Radiation and Photovoltaics
ResumoIn this issue of Joule, Ilse et al. have presented a comprehensive look at soiling losses seen in photovoltaic systems around the world and quantified the threshold allowable cost for some commonly proposed mitigation measures. Their analysis shows significant differences in economic feasibility of mitigation measures in regional markets based on their soiling rates. In this issue of Joule, Ilse et al. have presented a comprehensive look at soiling losses seen in photovoltaic systems around the world and quantified the threshold allowable cost for some commonly proposed mitigation measures. Their analysis shows significant differences in economic feasibility of mitigation measures in regional markets based on their soiling rates. That soiling is considered an important problem for the PV industry is an indicator of the success of the industry, coming from a technology with niche applications and considered by mainstream utility players as too expensive to be significant less than a decade ago, to being the largest source of new energy generation in the world today.1Jäger-Waldau, A. (2018). PV Status Report 2018. EUR 29463 EN, Publications Office of the European Union, Luxembourg. https://doi.org/10.2760/826496.Google Scholar When photovoltaic (PV) module prices were $4/watt, that was the main problem to be solved. Now, any problem affecting the field performance and long-term reliability of deployed PV systems is serious business indeed. As the PV industry was poised to make the transition to really large-scale deployment, forward thinkers in the industry began to anticipate the new issues of scale that would soon emerge and engage the international PV community to understand and mitigate those issues. Particularly, the formation of the PV Quality Assurance Task Force (PVQAT) was initially spearheaded by Sarah Kurtz of NREL (now at the University of California at Merced) and Michio Kondo of AIST in Japan, leading the first international forum in July 2011.2PV Quality Assurance Task Force. Accessed 11 Sep 2019.https://www.pvqat.org/about/.Google Scholar Task group 12 of PVQAT, focused on soiling, was created initially under the leadership of Lawrence Kazmerski in 2014, and it has grown to become the most active group in PVQAT, hosting an annual international workshop and frequent webinars. Ilse and several of his co-authors have been active participants.5Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Solar energy dust and soiling R&D progress. Literature review update for 2016.Renew. Sustain. Energy Rev. 2018; 82: 2504-2536Crossref Scopus (110) Google Scholar As noted by Kazmerski and others, the rate of new research in this topic area has accelerated in response to the explosive growth in the number, size, and site diversity of PV plants (see Figure 1). The much larger rate of publications for PV compared to concentrating solar power (CSP), despite the soiling effect being an order of magnitude more severe in CSP systems, is testament to the much greater financial stakes now for the PV industry. Kazmerski and his team published a comprehensive 2013 review of the prior work on the subject,4Sarver T. Al-Qaraghuli A. Kazmerski L.L. A comprehensive review of the impact of dust on the use of solar energy: History, investigations, results, literature, and mitigation approaches.Renew. Sustain. Energy Rev. 2013; 22: 698-733Crossref Scopus (611) Google Scholar which has since been periodically updated.6Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Dust and soiling issues and impacts relating to solar energy systems. Literature review update for 2012–2015.Renew. Sustain. Energy Rev. 2016; 63: 33-61Crossref Scopus (176) Google Scholar, 3Ilse K. Micheli L. Figgis B.W. Lange K. Daßler D. Hanifi H. Wolfertstetter F. Naumann V. Hagendorf C. Gottschalg R. et al.Techno-economic assessment of soiling losses and mitigation strategies for solar power generation.Joule. 2019; 3 (this issue): 2303-2321Abstract Full Text Full Text PDF Scopus (129) Google Scholar The availability of these exhaustive reviews of the literature has greatly facilitated efforts like this one by Ilse et al.,5Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Solar energy dust and soiling R&D progress. Literature review update for 2016.Renew. Sustain. Energy Rev. 2018; 82: 2504-2536Crossref Scopus (110) Google Scholar drawing on such a large number of sources. The soiling problem is a very complex interaction of airborne aerosols of varying composition and particle size distribution, local soil eroded by wind, electrostatic and capillary forces at the module surface,7Jiang C.S. Moutinho H.R. To B. Xiao C. Perkins C. Muller M. Al-Jassim M.M. Simpson L.J. Strong Attraction and Adhesion Forces of Dust Particles by System Voltages of Photovoltaic Modules.IEEE J. Photovoltaics. 2019; 9: 1121-1127Crossref Scopus (7) Google Scholar geometric features of the module surface texture and mounting (tilt angle, height above ground) and site (proximity to dust-generating sources, vegetation), rainfall, humidity, and more—so much so that it may never be possible to model soiling rates from these conditions with any useful degree of fidelity. In the face of this limitation, we are left with modeling based on empirical relationships and scaling of observed data, as is the case in the paper by Ilse et al.5Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Solar energy dust and soiling R&D progress. Literature review update for 2016.Renew. Sustain. Energy Rev. 2018; 82: 2504-2536Crossref Scopus (110) Google Scholar The automated extraction of soiling rates from PV plant performance data that has been developed by Micheli et al.8Micheli L. Deceglie M.G. Muller M. Mapping Photovoltaic Soiling Using Spatial Interpolation Techniques.IEEE J. Photovoltaics. 2019; 9: 272-277Crossref Scopus (17) Google Scholar can aid greatly in performing studies of the type presented here. Given the breadth of soiling research that had already been done, I was surprised at the time of my 2014 study9Jones R.K. Baras A. Al Saeeri A. Al Qahtani A. Al Amoudi A.O. Al Shaya Y. Alodan M. Al-Hsaien S.A. Optimized Cleaning Cost and Schedule Based on Observed Soiling Conditions for Photovoltaic Plants in Central Saudi Arabia.IEEE J. Photovolt. 2016; 6: 730-738Crossref Scopus (99) Google Scholar to find no prior published work on optimal cleaning schedules (although there may well have been unpublished similar work by PV plant operators). The present work extends a similar optimization formulation to a much larger dataset representing key global PV markets. The authors have reminded us in their paper that there are simple design measures that can mitigate soiling at little or no cost. In particular, it seems obvious that if trackers were designed to tilt ≥90°, most of the day’s accumulated soil could simply fall off, and this could be incorporated into tracker requirements in dusty locales at little or no cost. Vertical orientation of the modules at night would also eliminate dew formation on the surface that has been previously shown by some of the same authors to potentially contribute to permanent module damage through cementation10Ilse K. Werner M. Naumann V. Figgis B.W. Hagendorf C. Bagdahn J. Microstructural analysis of the cementation process during soiling on glass surfaces in arid and semi-arid climates.Phys. Status Solidi RRL. 2016; 7: 525-529Crossref Scopus (33) Google Scholar (the combination of mineral deposits with moisture cycles from dew leading to formation of strong adhesion bonds with the module surface). In understanding the results presented by the Ilse et al.5Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Solar energy dust and soiling R&D progress. Literature review update for 2016.Renew. Sustain. Energy Rev. 2018; 82: 2504-2536Crossref Scopus (110) Google Scholar in Figure S3, the efficacy of every mitigation must be assessed in opposition to the cost of cleaning, which is itself subject to potential improvements, and it behooves us to really work to reduce the cost of cleaning to the greatest extent possible. The water use for cleaning operations is frequently cited as a driver for needing non-cleaning mitigation strategies, but to put the water use in perspective, typical water consumption in a thermal-electric water-cooled plant is 1.8 L per kWh11Torcellini, P., Long, N., and Judkoff, R. (2003) Consumptive Water Use for U.S. Power Production. NREL Technical Report NREL/TP-550-33905. https://www.nrel.gov/docs/fy04osti/33905.pdf.Google Scholar; a water-conserving PV cleaning scheme using 0.5 L/m2 and a cleaning cycle of 14 days in a sunny locale uses only about 3(10−5) L per kWh, less than 0.2% of the water use in conventional power generation (even less with water recovery and recycling). In most cases, there’s simply no alternative to cleaning at least sometimes. And in some cases, frequent cleaning is mandatory to avoid cementation or fungal deposits that can result in permanent performance loss and shortened system life. It is analogous to reliability improvement in automobiles: they have been vastly improved over time, but we still have to periodically change the oil if we want a long engine life. Ilse et al.5Costa S.C.S. Diniz A.S.A.C. Kazmerski L.L. Solar energy dust and soiling R&D progress. Literature review update for 2016.Renew. Sustain. Energy Rev. 2018; 82: 2504-2536Crossref Scopus (110) Google Scholar provide a quantitative look at the main mitigation strategies currently being researched in terms of the bottom-line cost metric for specific locations throughout the world. The interplay between technology and economics therefore allows for a rational and targeted approach that can drive R&D in PV modules and systems in the years ahead. Techno-Economic Assessment of Soiling Losses and Mitigation Strategies for Solar Power GenerationIlse et al.JouleSeptember 26, 2019In BriefClean collector surfaces are crucial for the performance of solar power generators. Soiling—the accumulation of dust and dirt on photovoltaic modules or mirror surfaces—significantly reduces the energy yield and is a major problem that is far from being solved. Within this study, the impact of soiling on global solar power generation is quantified for the first time. Furthermore, the effectiveness and economic feasibility of various soiling mitigation strategies are analyzed, and future research and development directions are indicated. Full-Text PDF Open Archive
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