Dirty detail: Solar panels need water—How much is the question, as developers downplay… cleanings

[OKIsItJustMe]

http://www.lasvegassun.com/news/2009/sep/18/dirty-detail-solar-panels-need-water/

Dirty detail: Solar panels need water

How much is the question, as developers downplay frequency of cleanings

By Stephanie Tavares (contact)

Friday, Sept. 18, 2009 | 2 a.m.

Southern Nevada may pose more of a dirty little problem for some solar plant developers than they realize or are letting on.

Solar photovoltaic developers say not to worry about how much water their plants will use because they need only enough water to run the office bathrooms and wash the arrays of panels a couple of times a year.

But people who live near proposed plants or maintain solar panels in the desert guffaw at that last bit and are willing to bet the panels will need to be hosed down more frequently.

Dust on solar panels can decrease their efficiency by about 3 percent, solar photovoltaic experts said. The larger the solar array, the more electricity lost.

…

[aquart]

1. You dust with water?

[OKIsItJustMe]

2. I don't think it's that big a concern, however, from the article…

…

Solar photovoltaic developers say their plants don’t use much water, but “much” is relative. True, they use a fraction of what a water-cooled solar thermal power plant consumes annually — about a 16,689 gallons per megawatt for photovoltaics compared with 2.61 million gallons per megawatt for wet-cooled solar thermal — but a large photovoltaic array can still easily use more water in a year than an entire residential block.

…

[customerserviceguy]

3. Perhaps a system that recycles the water would work efficiently

It doesn't need to be potable water, it just needs to deal with dust. Yes, you'll have some evaporation losses, but if the washing is done at night, it will be minimized.

[joshcryer]

4. It would evaporate away, in non-trivial amounts in these locations. Non-water dusting methods...

...are probably more desirable.

[kestrel91316]

5. Why the blithe assumption that the panels will need to be "hosed down"????

Water wastefulness isn't necessary. I suspect a feather duster could manage the job.

[OKIsItJustMe]

6. Standard operating procedure

…

When NexLight disclosed plans for biannual cleanings at BLM scoping meetings, locals scoffed. If the dust on the cars in the parking lot was any indication, the developers would be cleaning those panels a lot more than twice a year. The dust in the Ivanpah Valley can be brutal under normal circumstances, residents said. But the area is also a popular spot for large multiday off-road races that can stir up even more dust.

The NexLight plants are planned smack dab in the middle of a popular off-road raceway, which the company proposes rerouting around the solar plant.

…

I wonder if mechanically pushing the “dust” off (i.e. “dusting” them) would involve a greater risk of scratching the panels…

[kestrel91316]

7. High-pressure air could blow it off.

[joshcryer]

8. Not with the right coatings, and non-stick coatings can stop dust from forming heavily...

...in the first place.

Introducing a blowing action to the panels could also 'shake' the dust off (see the Mars Exploration Rovers for an example).

If a solar field is using water for cleaning they should move to something else immediately.

It simply isn't *necessary*.

[OKIsItJustMe]

10. Seems sound in principle

However, they don't seem to be denying that they plan to use water.

Don't get me wrong. I'm a big fan of PV farms, but I was raised to play the “Devil's Advocate.”

Compared to a oil-fired boiler, the amount of water used here should be small, but not insignificant.

[joshcryer]

11. Well, that's why we should reign this in before it becomes a problem. We can't be wasting water!

We shouldn't even consider using water for this process. Water is relatively cheap (the cheapest commodity, in fact, due in part because it's necessary to sustain life). Using water can be seen as an effective means to keep the panels clean, and it can be seen as a cheap way to do it. We have to stop thinking monetarily, though. It might be "more profitable" in the short term to use water than it would be to install systems that clean these panels without it (maybe the panels *don't* have a scratch resistant coating, and adding it would add more cost to their production). Long term thinking is where we should start.

[kristopher]

12. That has nothing to do with why water is "cheap".

You wrote, "Water is relatively cheap (the cheapest commodity, in fact, due in part because it's necessary to sustain life)."

Actually the effect of water being necessary to life is the exact opposite - it gives water most of the value that it has. As to why it is "cheap", that is because it is generally abundant. The governing theory is called marginal utility:

The paradox of water and diamonds

The “law” of diminishing marginal utility is said to explain the “paradox of water and diamonds”, most commonly associated with Adam Smith<13> (though recognized by earlier thinkers).<14> Human beings cannot even survive without water, whereas diamonds were in Smith's day mere ornamentation or engraving bits. Yet water had a very small price, and diamonds a very large price, by any normal measure. Marginalists explained that it is the marginal usefulness of any given quantity that matters, rather than the usefulness of a class or of a totality. For most people, water was sufficiently abundant that the loss or gain of a gallon would withdraw or add only some very minor use if any; whereas diamonds were in much more restricted supply, so that the lost or gained use were much greater.

That is not to say that the price of any good or service is simply a function of the marginal utility that it has for any one individual nor for some ostensibly typical individual. Rather, individuals are willing to trade based upon the respective marginal utilities of the goods that they have or desire (with these marginal utilities being distinct for each potential trader), and prices thus develop constrained by these marginal utilities.

The “law” is not about geology or cosmology, so does not tell us such things as why diamonds are naturally less abundant on the earth than is water, but helps us to understand how relative abundance affects the value imputed to a given diamond and the price of diamonds in a market.

http://en.wikipedia.org/wiki/Marginalism#The_paradox_of_water_and_diamonds


The actual valuation in different circumstances is more complicated and involves several variables, but I think you get the gist.

[joshcryer]

13. I get the argument, but fresh water is 3% of our planetary reserves.

Here in Colorado we have political wars over water rights (McCain lost Colorado because he wanted to give its water to Arizona). If you ever lived in the midwest you'd know that "getting water" is nontrivial, and billions of dollars are spent in projects that pump it deep out of the ground and producing reservoirs for consumption. Yet I don't even have a extra water bill. The government gives out significant water subsidies to keep the price down, especially as we deplete our reserves.

[kristopher]

14. You get the argument "but"??

There is no "but".

You are completely wrong.

[IDemo]

9. Another possible option: electrostatic dust removal and/or repellent

http://findarticles.com/p/articles/mi_qa3957/is_200209/ai_n9136699/

[NNadir]

16. You mean solar power plants can consume as much energy as they produce for cleaning themselves?

This is sort analogous to the way that solar plants are unable to produce enough electricity to power all the computers devoted to saying how wonderful solar energy is.

http://www.eia.doe.gov/cneaf/alternate/page/renew_energy_consump/table3.html

[joshcryer]

17. Gotta admit, though, wind is *kickin ass* in these stats.

:hi:

[IDemo]

18. No

As stated in the article I linked, electrostatic deflection does involve high voltage but not high power. About what you'd experience touching a doorknob after walking across a carpet on a dry winter day.

[Javaman]

19. Yeah, and nuclear power doesn't use any water at all...

:eyes:

[XemaSab]

15. My old boss said this was a make-or-break factor for many projects

and siting power plants was his career.