Keep solar panels clean from dust, fungus

Renewable energy sources such as wind and solar are making major strides in terms of number of installations, amount of energy generated, reliability, and cost. It’s obvious that wind turbines, for which there are many moving parts, need periodic maintenance, but what about photovoltaic (PV) systems?

PV systems are commonly perceived as maintenance free, as they operate silently without motion, unless they are tracking panels. Tracker mechanical issues are small compared to those of wind turbines with tall towers, huge blades, and various heavy-duty bearing assemblies. However, the reality is that there is an easily-overlooked potential problem with PV panels, whether it’s a simple rooftop system or a much-larger PV farm: dust and dirt accumulation. We’ll call it “dust” as a catch-all label (Figure 1).

photo of a rooftop solar PV system on a house
photo of a solar PV farm with many panels

Figure 1 Whether it’s a modest and simple rooftop installation (top) or a larger PV farm (bottom), unavoidable dust and dirt buildup impacts efficiency of the solar panels. Source: The Verge and Duke Energy

The accumulation and buildup of dust in various forms is inevitable. It lingers in the atmosphere from multiple sources and settles on solid objects or drops directly; it can also be caused by factors such as rain, air currents, temperature change, humidity, locale, birds, leaves, and more.

How much degradation in photovoltaic output does it cause? Typical numbers range from a few percent per year to around 10%, and there are sandy desert areas where it can be much higher, approaching 50%. Should users of PV systems worry about dust buildup? As is often the case, the answer depends on who is asking the question and who is answering it. A look at various websites revealed advice ranging from, “Don’t worry, it’s no big deal” to, “Yes, it is a problem.” Part of the answer variability is due to the fact that while the year-to-year impact may be acceptable, the cumulative effect over several years can be truly significant if you do the compounding math.

A National Renewable Energy Laboratory (NREL) story, “Scientists Studying Solar Try Solving a Dusty Problem,” examined the dust issue and provided some perspective. In an effort to better understand and quantify the situation, researchers at NREL have been studying the problems with data collection from various field-test arrangements (Figure 2).

photo of a researcher inspecting a soiling detector unit for PV panels at an NREL outdoor test facilityFigure 2 Researcher Matthew Muller looks over the detector unit for soiling spectral transmittance (DUSST) multi-unit soiling detector at an NREL outdoor test facility. Source: NREL

The way the dust and debris can settle on the PV cells differs case-by-case. For example, as PV panels cool down at night and attract morning dew, the minerals in the dust can morph into a “cement-like” substance that is hard to remove and won’t be blown away easily. And where does it land? On an adjacent PV panel. In other cases, the pollen may become a starter bed for hard-to-remove fungus growth. Even rain can be counterproductive in some settings.

The issue of keeping it clean is part of the broader issue of requiring ongoing maintenance for products. Let’s face it: no one likes to have to do it. As electronic-based systems replace many previously-mechanical implementations, especially for consumer products, the need for such maintenance has gone down to very little or none at all. We’re conditioned to think that these all-electronic products with few or no moving parts don’t need routine maintenance—and that often is the case—but PVs show the harsh reality. The average homeowner with PV cells on the roof isn’t thinking about an annual washing, especially if doing so requires more than a simple hosing.

It’s not that manufacturers don’t recommend it. My basic, no-frills, above-stovetop microwave oven has a “change filter” LED that comes on every 3-5 months, reminding me to spend $15 for a replacement filter, which slips into a convenient slot with no tools or disassembly required. I was afraid at first that the oven would refuse to work if I ignored the indicator and did not replace that filter, but it turns out the LED is a suggestion, not a mandate: you simply hold the associated keypad button down for a few seconds, and the indicator goes out.

Have you had to design while also taking into account the expectations of users of your mass-market consumer product for very little or even no regular maintenance? How did you “enforce” that maintenance need if it really existed? What happened if users chose to ignore it, as I did with the filter of the microwave oven?

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.

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