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Comment by walrus01 | Hacker News Reader

The cost of building that steel structure that will hold up against maximum in 100 year wind forces isn't cheap. Large PV panels make very good sails. The trusses look basically the same as you'd see in a large agricultural barn, horse riding arena, etc. Putting the PV panels on empty bare land at a height people can walk around and work with would be considerably less costly.

I would very much like to see a total dollar figure for the example "roof trusses over the canel" structure vs. how many panels it can hold.

It's already true that the ground mounting costs and labor to assemble the ground mount are a huge part of building a large scale PV system.

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The UK has covered some water reservoir with floating PV panels.

The article mentioned trialling several systems for covering California canals, I didn't see "floating" mentioned, although:

  Project Nexus tests not one, but three different solar canal models. 

  ... accordion-like retractable panels are positioned low across the narrow canal, ready to roll up at a moment’s notice.

might come close.

Floating panels have the issue of having to flex and perhaps bottom out (if water diverts to parallel canal for maintenance) on a dry canal - but there's less need for heavy steel trusses and a lower wind profile.

> Putting the PV panels on empty bare land at a height people can walk around and work with would be considerably less costly.

What empty, bare land?

If its really empty and bare, there is a reason for it and that reason is probably a problem for building and maintaining PV, and otherwise you have to add the loss of the alternative uses of the land to the cost.

In the context of California, land that is not suitable for agriculture because it can't be irrigated, even though it's flat and somewhat accessible by road. California has plenty of it, go drive around near Twenty Nine Palms and you'll see it...

Ok, now ask yourself why that area hasn’t been covered with solar panels yet…

Now measure the wind at twenty nine palms

And the moment you start building large structures on it everyone and their dog is going to show up and NIMBY it.

Spoken like someone who has never been to the mojave. This is the home to the largest wind turbine installation in the country. But again, if the worry is the solar panels acting like sails, probably not a great site given that wind.

And nonetheless, people show up and NIMBY projects in the Mojave desert! https://www.latimes.com/environment/story/2024-09-06/califor...

Sorry, the largest wind power installation in the western hemisphere, not just the US, is SunZia in New Mexico (5.3MW).

> What empty, bare land?

Have you been to Death Valley, my friend? All of Southeastern California is empty, barren land. Death Valley, Mojave Desert, etc.

> Have you been to Death Valley, my friend?

Well, no, but I’ve been close and I can imagine some features of the area that might have impacts on cost of construction and ongoing maintenance that are related to why it was empty land even before it was a National Park (and I can think of additional problems with California trying to build solar generation in a national park—different ones under the current federal administration than would be historically normal, but either way it would problematic.)

If you look at the city of Mojave, Calif. on Google Maps (satellite view) you can see massive solar farms all around it. There is plenty of space for expansion. There is no need to use a national or state park. (To be clear: Mojave Desert is far away from the city of Mojave!)

Guess how fast the wind blows across the surfaces. There's a reason why these places currently host massive wind turbine farms.

The wind and blown sand is something to behold. But large stretches are getting solar panels, yes.

    > The cost of building that steel structure that will hold up against maximum in 100 year wind forces isn't cheap.

I'm surprised by this comment. (Is this area known for strong winds?) If your comment is true, wouldn't all warehouses using the same type of standard "bents" also be very expensive? I doubt it.

    > Large PV panels make very good sails.

A quick Google search tells me:[1] "Most modern solar panels can withstand winds of up to 140 miles per hour." For all of the things I have read about large commercial solar panel installations, never once did I read anything about the risk of wind tearing off PV panels. If this were really a serious threat, wouldn't we see regularly local news stories about large PV panels "flying" away in big wind storms? And, yet, I never saw one.

[1] https://www.makemyhousegreen.com/green-guides/can-solar-pane...

> I'm surprised by this comment. (Is this area known for strong winds?)

Areas of the central valley are legendary for strong winds. A large stretch of the aqueduct (200km?) runs along the valley's West edge. So does the interstate highway I5.

The I5 has frequent high wind advisories. In the area around Pacheco Pass there are frequently gusting cross winds between 55 and 70km per hour. I use the I5 as my reference here, because I have spent many hours of my life driving it in these conditions.

> If your comment is true, wouldn't all warehouses using the same type of standard "bents" also be very expensive?

What makes you think building a warehouse in earthquake country is cheap?

> For all of the things I have read about large commercial solar panel installations, never once did I read anything about the risk of wind tearing off PV panels. If this were really a serious threat, wouldn't we see regularly local news stories about large PV panels "flying" away in big wind storms? And, yet, I never saw one.

The statement about solar panels making very good sails obviously true. Everything thin and flat makes a good sail.

PV panels don't go flying away because people spend a lot of money attaching them to the ground. They're expensive systems, and any installer that didn't make sure they were bolted down effectively, would be sued out of business after the first windstorm.

You can meet code requirements on rocky ground with relatively small concrete block anchoring systems. The cost of the blocks plus the metal pipe structure for a ground mount system is typically 10% or so of the total system install.

If you're on excavatable ground, the cost goes up a little (paradoxically, way more concrete is required to meet code).

There are also companies do this sort of thing with earth anchors/helical ground screws, which are VERY fast to install, but tend to cost more than the concrete. Nice that they can be (re)moved, though.

    > The I5 has frequent high wind advisories. In the area around Pacheco Pass there are frequently gusting cross winds between 55 and 70km per hour. I use the I5 as my reference here, because I have spent many hours of my life driving it in these conditions.

This is a classic bullshit HN reply. Literally, Brandolli law rules here!

My original post said that most panels with installation are good up to 140 mph (or 225 kmph). Your example is less than half my examplle.

    > The statement about solar panels making very good sails obviously true.

Ok, please provide five+ example from local news that shows poorly tied solar panels flying away in a wind storm. The "obvious" thruth: You cannot.

To my eye if you were putting up a few hundred or more of those steel structures, and it didn't require a redesign of the canal retainment around it, it could be built quite economically.

Every extra pylon structure built, especially the first dozen, will be cheaper and easy to produce and install.

You know where the wind blows really damn hard in California? Virtually any open field you can imagine putting these otherwise. Mojave for example is damn windy. That is why they currently host massive wind installations there.

I'm well aware of that, thanks. Ground mount PV is still going to be considerably less costly than this. Partly because it's easier to build, partly because it has many competing companies that sell the basic aluminum rail/hot dip galvanized steel mounting pieces, partly because you can use relatively low cost contractors to do work like install its footings and bolt it together.

Having stuff at ground level that can be reached by people on foot or on a 6 foot step ladder also makes doing the electrical work a lot less costly.

Part of the point is reducing evaporation.

>Having stuff at ground level that can be reached by people on foot or on a 6 foot step ladder also makes doing the electrical work a lot less costly.

I mean sure, but compared to say having that technician in a dingy boat, its more costly in the sense you need a dingy boat. But this doesn't seem insurmountable. Maybe you don't even need a dingy boat. Maybe just a long 2x12 would be fine or some other scaffold platform you can just drag around. There's also something to be said about this solar array being where the land is already being used, and some greenfield solar array going in, well, greenfield areas that might be ecologically more sensitive.

Tell me you've never built a ground or roof mount PV system without coming right out any saying it... Wow. You took a look at the photos in the original URL and think that a person can stand in a small boat and wire up the backside of the panels? I'd love to obtain some of what you're smoking because it must be some incredible stuff.

You tell me one reply up a ground based system can be repaired by a technician with a stepladder and somehow a longer step ladder with a solid platform doesn't work for what is effectively just a slightly taller ground based system? Please explain.

Have you ever put a stepladder in the center of a dinghy and tried standing on it? I don't think you'd like the results.

It’s not empty or bare - there is a water canal right in the middle of it.

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