US solar groups advance soiling analysis to reduce seasonal risks

PV plant operators are demanding more sophisticated dust accumulation analysis to inform construction and operations decisions and new research is linking weather models and predictive analysis to reduce downtime, leading industry experts said.

Plant operators are investing in soiling mitigation early in the development process. (Image credit: TzahiV)

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As the performance of PV plants continues to improve and operations and maintenance (O&M) practices become more important, soiling has become a key area of research to leverage further gains.

U.S. plant operators are increasing upfront O&M spending in the development phase in order to improve plant reliability and optimize predictive maintenance strategies.

Soiling data helps owners identify causes for lower output during certain times of the year and plan how often panels should be cleaned to limit energy losses.

New techniques to mitigate soiling are set to improve U.S. plant performance and provide even greater cost benefits in emerging higher risk markets such as the Middle East and North Africa (MENA), where scientists believe soiling could be responsible for 50% of power losses.

The US National Renewable Energy Laboratory (NREL) is currently developing predictive soiling rate analysis using environmental data and operators are installing new technology on site.

California's Pacific Gas & Electric Company (PG&E) plans to install and begin testing prototype monitoring equipment to measure soiling impact before the end of this year,” Alvin Thoma, PG&E’s director of Solar Operations & Maintenance, told PV Insider.

“PG&E currently does not have sufficient instrumentation installed for ongoing measurement of soiling impact. However, this certainly is an area of interest for us,” he said.

The use of preconstruction measurement stations, which provide data on the composition and behaviour of soiling particles, has risen rapidly.

“If you look back just like three or four years ago, we wouldn't have any soiling [measurement] stations deployed in pre-construction, before the plant is built,” said Ann Gaglioti, CEO at Groundwork Renewables, a California-based company providing meteorological measurement services to support solar and wind project development. “Now I would say that 80% of our stations have pre-construction soiling stations on them.”

US plants

Soiling mainly reduces the transmission of light through the covered glass of PV modules, decreasing power production. Dust can also affect durability and reliability of tracking systems used in some PV power plants, thus raising maintenance costs, Lin Simpson, senior scientist at the National Renewable Energy Laboratory (NREL), told PV Insider.

Because soiling is a very localized phenomenon, and its impact on power production can vary greatly from site to site, there is currently no U.S. national or regional data on average soiling losses available.

Power plants near agricultural or industrial areas are more prone to register higher soiling rates in the U.S., according to specialists. Gaglioti said pollen can also be a potential concern, in Eastern U.S. for example, and a report by Vaisala consultancy last month said summer wildfires in the south west-- which have increased in number-- have dented plant performance.

For PG&E, soiling is a seasonal issue, with more significant impacts occurring in the summer when wind tends to kick more dust from agricultural fields to the power plants, Thoma said.

Clean Power Research, a California-based research and consultancy company, is currently studying ground data to quantify typical soiling rates in different areas of the state, as part of a broader project for the California Energy Commission.

“We are in the process of developing that number (average of soiling losses) so we can report it to the California Energy Commission,” said Skip Dise, product manager. Clean Power Research expects it to take at least six months before the data can be reported to the commission, he said.

New predictions

Soiling measurement systems have improved significantly in the last few years following improvements in data collection technology, new methodologies to calculate soiling ratios and new software which can process soiling data to estimate output reductions, Justin Robinson, Technical Director at Groundwork Renewables, said.

“Today we can make accurate and informed decisions on how to manage these assets from an operational perspective, and also to more accurately model energy production during project financing,” he said.

New research projects are set to further improve performance by providing more sophisticated analysis of environmental data.

NREL is currently developing predictive soiling estimations and loss models using environmental parameters, through a project funded by the U.S Department of Energy (DOE).

“Preliminary results suggest a strong correlation between PV soiling loss and measured atmospheric particulate levels combined with precipitation,” said NREL's Simpson. “If these results as well as other correlations are validated, then weather models that predict these types of environmental factors may become useful to help improve seasonal soiling loss estimates.”

Information on soiling can generally be obtained in production data that PV power plants are already collecting and NREL is working on developing methods to extract this info automatically, so that this information can be used to help develop improved soiling mitigation strategies and technologies, Simpson said.

By Anna Flávia Rochas