Ways to clean rooftop solar panels – wherever you are

Home-based owners of solar panels do it tough in the planet’s many dry places. Rain can do a good job of removing dirt build-up from solar panels, but if there’s not enough rain, what’s the best way to clean your solar panels? While there are some good ways, some of those on offer have hidden pitfalls.

Solar cleaning and arid places

Studies show that in areas with long dry periods, energy output lost due to dirt build up dilutes the return on investment, significantly reducing the benefit of going solar. These studies, conducted in Spain, Egypt, India, Malaysia and the USA (to name just a few), show losses in some cases of up to 85%, and average losses of 35% are common. And losses can reach those levels within five weeks of cleaning.

Common Cleaning Options

Panels can be cleaned manually or automatically, using low pressure or high pressure water, or wet or dry brushing. All are effective in the short term, but can present long-term problems.

Manual Cleaning

DIY Cleaning

The safest method for cleaning your panels is low-pressure water, such as a standard garden hose spray nozzle. As a home owner, you can do this yourself, but you need to be on the rooftop – hosing rooftop panels from the ground is not effective, and uses large amounts of water. With water available set to become a key climate change issue, water efficiency is a key criterion. On the rooftop, there are obvious hazards, such as falling or slipping.

Because of the hazards, it’s generally thought to be a job for a contractor with the appropriate safety equipment. However, for the average home owner the costs of contractor cleaning (typically $AU150 per wash in Australia) makes it viable only on an annual or twice yearly basis. Yet annual cleaning is only slightly better than not washing at all.

Overall, the studies show that it’s best to wash weekly.

Brushes, sponges and high pressure water sprays

The two most common methods of manual washing present hazards to the solar array itself. Brushes, sponges or other physical means have the potential to scrape abrasive dirt particles across the panel, scratching the surface coating and in the end reducing its clarity – and therefore its power output. Using high pressure water (i.e., water blasters) carries the risk of water penetrating electrical junctions.

Another factor is that with manual washing there’s little control over the amount of water used, and that’s an issue in dry regions.

Automatic Cleaning

Cleaning Robots or Machines

A wide range of cleaning robots and machines has been developed, largely for solar farsm and other very large installations. They’re way too expensive for the small-scale solar owner, although viable (if still expensive) for solar farms where efficiency is a critical factor. Almost all use either rotating brushes (either wet or dry) or high pressure water, and therefore introduce the same hazards as manual cleaning. They may even cause more damage than manual cleaning, because the brushes are held to the surface of the panel by more than human action, and often rotate at high speed, and because the level of automation means that the cleaning is done far more regularly.

Those that have been developed to use a wet wash technique may also haver been developed without water efficiency as a priority criterion, meaning that excessive water use is a potential issue too.

Also, large solar arrays are split into multiple rows, and cleaning across these rows presents a challenge, which is addressed in one of several ways:

  • Separate machines are fixed to each row (increasing the cost)
  • The machine is physically moved from one row to the next (leading to labour costs and the need for lifting equipment for safety.
  • The cleaning equipment is mounted to a vehicle, which moves from one row to the next (leading to labour costs and vehicular hazards)

Automatic Low Pressure Spray Cleaning

This system uses micro-irrigation nozzles to direct a spray of water across the panel area. It offers low capital costs, no labour costs, no safety hazard, and no chance of panel abrasion or damage to electrical connections.

However, because the nozzles are designed with irrigation in mind, they spray across a large area, and there is consequently a lot of overspray; because they spray into the air in the region of panels, much water can also be lost to the wind. Also, water distribution is uneven, with some panel areas getting more spray than others. This means that either some of panel areas receive more water than is needed for cleaning (therefore wasting water) or some areas will receive too little water to clean them thoroughly; either outcome is undesirable.

Spray cleaning does offer a unique side-benefit: in regions with plenty of water, it can also be used for cooling the panels, which can increase energy output by between 10 and 20%, and can minimise overheating, a known potential cause of solar panel failure.

However, there is no practical option available for small-scale solar installations.

SolarClear: Cleaning Solution

These issues made us realise there must be a better answer, and prompted us to design and create one.

SolarClear® is the result. It’s an automatic low-pressure water cleaner like the spray cleaners, and shares all the benefits of low pressure sprays. However, instead of inefficient spray nozzles, it uses a cascade water delivery system, which delivers water just to the panels and uniformly across them, eliminating water waste. It simulates a short, heavy shower of rain. It’s fully automatic, with almost no need for upkeep, and can pay for itself in as little as 9 months.

We’ve designed SolarClear® to be suitable and affordable for even small installations in the domestic Australian market and conditions. However, we plan to make it available to solar farms and the international market in the near future.

At this stage, we’re in the process of crowdfunding to assist us get this product manufactured.

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