The Truth About Deionized Water (aka Spotless Water) on Solar Panels

Did you know highly purified water is not healthy to drink? For similar reasons, it's not healthy for solar panels either.

Spotless water on solar panels sounds great, or is it? The advantage of spotless water is obvious, after all, who wants to see mineral stains after the water dries up? But there's one key fact that is often missed: spotless water, or deionized water, is actually corrosive. Yes, you read that correctly, however slight, it is corrosive.

The reason why is that as minerals are removed from water during deionization, the PH balance of the water goes from alkaline to acidic, in fact, this science paper from the National Institute of Health (NIH) mentions the corrosive effects of deionized water. Why should you care? Almost all solar panels are encased in aluminum frames. And it's not just aluminum - tin, iron, copper, and steel are all negatively affected by corrosion, which means you also have to think about the mounting brackets, footers, conduits, and grounding wires that will all be soaked with deionized water, including the gutter. Will deionized water cause catastrophic damage with one soaking? Unlikely. Thinking long term though, do you really want to soak these components with something partially corrosive, multiple times a year, especially if you want it to last 25+ years?

How do you know this is simply marketing and nothing more? Look at any manufacturer guideline on maintenance and cleaning. Not one of them mentions spotless water.

You might ask, why do companies advertise spotless water? Many companies who clean panels also clean windows. For windows, mineral stains are more obvious, and since most windows have vinyl frames, corrosion isn't an issue. In other words, spotless water makes sense for windows. As these window cleaners ventured into solar panel cleaning, they assumed the same benefits for solar panels and marketed this as an advantage. How do you know this is simply marketing and nothing more? Look at any manufacturer guideline on panel maintenance and cleaning. Not one of them mentions spotless water. Not QCells, not Canadian Solar, nor Vsun, Tesla, JA Solar, etc. If spotless water was helpful to the panels even a little, you would think at least one of the makers would mention it. None of them do:

• Canadian Solar: "If the panel has become soiled, wash with water."

• JA Solar: "You can choose to clean solar panels by washing them with water. This method is simple, effective, and will not cause damage to the solar panels."

• QCells: "To physically clean solar panels, use only a soft cloth and lukewarm — not hot — water to wash the panels gently, then let them air dry."

• etc.

At Interstellar, we prefer to follow manufacturer guidelines, and we assume they know their products better than window washers. We can mitigate mineral stains by applying a gentle squeegee to get most of the water to run off, and the slight mineral marks do not in any way affect solar panel efficiency, it is entirely aesthetics.

For unbiased, scientific information on this subject, Google "science paper deionized water corrosion". Some other references:

• Study the Effect of Deionized Water on The Corrosion Of Some Household Alloys at Different Temperatures, April 2018, Dhofar University

• Tin Corrosion Induced by Corrosive De-Ionized (DI) Water, 1999, International Symposium for Testing and Failure Analysis

Excerpt:

"Very highly purified water such as De-ionized (DI) water tends to become very corrosive once exposed to the atmosphere. This “Hungry Water” as known in the water purification world is known to be a major source of corrosion [1]. The DI water was responsible for corrosion of tin during autoclave and formed thin whiskers of solder. These whiskers created a leakage path between the leads causing the devices to fail for pin to pin leakage."