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Comment by walrus01 | Hacker News Reader

I'm honestly curious what is the big challenge with keeping large arrays of ground mounted panels clean in Pakistan. The prevailing wage for unskilled labor for a 6 day a week, 45-hour work week for one laborer to clean panels is probably about $250-300 a month (USD equivalent, in rupees) in that area. That would be a good wage compared to construction work or farm work in that region.

With some basic equipment like rolling carts with sprayers and squeegees on extension sticks, how many individual 72-cell sized panels (1.99 x 0.99 meter size) can one person clean in one day? Multiply by probably 4 to 6 full time staff positions.

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Quoting the Wikipedia page cited above:

> It required one litre of water to clean, each of 400,000 installed panels. A total 15 days cleaning cycle required, 124 million litres of water enough to sustain 9000 people, while rain in Cholistan desert is rare and far between. Providing such huge amount of water in desert terrain, became a challenging and daunting task for management team. Besides, the manual cleaning methods allowed setting of dust before it was re-cleaned.

This seems kind of like a bullshit excuse where they just didn't really want to fix the issue. There are a number of waterless cleaning systems that have been available for years, for example [1]. Additionally, why the hell would you throw away the water used for cleaning? Filtering the dust particulate out of the water is pretty straightforward (hell, you can go from muddy to fairly clean water with nothing more than a cotton t-shirt), then you reuse it to clean more panels. 1L/panel with even basic reclamation is ridiculous.

[1] https://www.youtube.com/watch?v=wdidbRQaUEY

Agree. They could probably just have people walk around with blowers to blow the sand off.

I would suggest that blowing off sand with a strong airstream would scratch the solar panels, further reducing their efficiency. Or maybe there's other problems; in any case, I find it somehow ignorant to assume that nobody in the Pakistani government has ever heard of or considered a blower (or a broom).

I assume they have heard of blowers and probably knew sand would be a problem with this install. My take away is that project was a bad faith effort to serve as a strawman against renewables for oil. This is an engineering problem not a technological problem of solar panels. Having skipped over it implies questionable motivations.

Would those be a gasoline powered blowers ? ( ͜ʖ)

Perhaps a step down transformer that directly feeds a dyson blade style blower at one of the edges of each panel. More up front equipment and infrastructure cost but no employee wages. However I'm sure this is full of holes due to cost multiplied by number of solar panels and the number of transformers needed. It is also only able to clean only during the day assuming no battery or pumped hydro storage.

What about solar powered golf carts with blowers?

I wonder how much of the 1L evaporates.

During the night and very early morning, probably very little.

Evaporation often happens at night because of the temperature differences.

> Evaporation often happens at night because of the temperature differences.

I'm not sure the phrase 'temperature differences' exhibits a profound understanding of evaporation.

If a location gets 45c (as per GP's reference) during the day, this doesn't necessarily speak to night time temperatures.

I'll note that Bahawalpur's temperature profile is available at:

https://weather-and-climate.com/average-monthly-Rainfall-Tem...

For the three hottest months of the year the average lower temperature is around 25C, which suggests quite a low evaporation rate overnight.

It would be great if you could provide some more detailed insights.

What about a fleet of automated drones/machines which clean the panels by blowing air? I don't know, but it seems like physically scrubbing the panels would take more machinery (heavier), more moving parts (break down more easily), and the scrubs themselves would have to get replaced & careful not to be abrasive (not sure how much the panels "care" about it though). These "dusters" could run off the excess power too. I read somewhere else in this thread that one problem was the solar park would occasionally over-produce - maybe the fleet works whenever there is an overproduction, or after a certain amount of time has passed (we _must_ clean them now and can't wait until the next time of overproduction).

If you're going to clean things via physical automation, you could probably work out the energy cost involved ~reasonably well over time.

You can a have a quadcopter drone clean every panel with a soft brush/microfiber cloth and return to base at recharging station and repeat.

Have a swarm of these and cleaning will not be an issue.

but maybe they can use seawater for cleaning?

Would the salt be abrasive & damage the panels/coating decreasing efficiency?

I would imagine another challenge is the transporation costs. The nearest fresh water source appears to be Sutlej River ~18 KM straightline. The nearest seawater source appears to be the Arabian Sea, ~800 KM straightline.

The cost to a problem like this would never be labor as that can be trivially automated if it ever gets costly enough. Water is expensive at these scales.

That being said, it's probable that there could be solutions here. Automated scrubber/blower might be able to get most of the efficiency back without the cost (whether integrated into the panel or a robot on a track). Could potentially use any water more judiciously too when needed (moisten a scrub rather than blasting it with water). Don't know enough about the project but I would hope the domain experts responsible for the project would have considered something I only thought about for 30 seconds & there are reasons that they don't do that.

> Would the salt be abrasive & damage the panels/coating decreasing efficiency?

I imagine some glass coating should be cheap enough and efficient solution to implement.

> The nearest seawater source appears to be the Arabian Sea, ~800 KM straightline.

Sure, such plant has to be constructed near seawater source.

According to the Wikipedia article cited it takes 30 people 10-15 days to clean all 392,158 panels fully. That sounds like $100,000/y in raw wages but it seems to be limited by water supply more than raw labor cost. The dust being cited as 40% of the panel efficiency loss and not always being an issue depending on the season also drives some of that RoI down, looks like a good portion of the loss is due to the heat as well. By far the biggest costs seem to have been with corruption from choice of renewable source to choice of contractor vs operation of the actual installation.

You're off by a factor of 10 based on wages for cleaners in Pakistan which is about $1/hr.

http://www.salaryexplorer.com/salary-survey.php?loc=164&loct...

Using the average number from that source you get 356,000 PKR yearly * 30 people = ~$64,000, even using the low end from that site is only a factor of 2 off not 10. The numbers were actually based of the high end from above in the chain "for one laborer to clean panels is probably about $250-300 a month (USD equivalent, in rupees) in that area. That would be a good wage compared to construction work or farm work in that region." which corresponds very well to the high end from your source of 540,000 pkr.

This comes out to ~$97,000 which is how I came up with about $100,000/y.

Just to note this isn't something you do for just one month per year if that's how you came to a factor of ~10.

My apologies, I read your original statement of raw wages as being for the 10-15 days you were talking about, rather than yearly wages.

And there are also many PV cleaning robots available. This is not self-driving car stuff, it's off the shelf technology.

Windshield wipers are a mature and cheap technology that seems applicable.

They are designed to clean water off glass. I've never lived in a dessert area so I may be wrong, but I expect they're not great for cleaning large amounts of dry dust and dirt off at least without using huge amounts of water.

I'd adapt it, of course. Not literal store bought wipers.

Some kind of brush is probably what you need for dust.

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