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Comment by tony_cannistra | Hacker News Reader

As they mention in the article though, there are lots of applications that aren't space-limited but are structurally-limited (warehouses) in that they can't support the weight of solar panels without more engineering.

I did think it was strange that they obfuscated the W/m^2 statistic by only presenting W/kg and kg/m^2. I suppose focusing on watts per kilogram better aligns with a breakthrough in installations with poor structural support for heavy panels.

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In that case I suggest installing efficient panels in some large installation somewhere else. Like, a power company solar farm miles from your warehouse.

<digression> It's such a strange magpie impulse folks have to want solar on their house. Look at my stuff! I'm doing things!

From a societal point of view the efficient installation is in bulk, serviceable, unobstructed. A rooftop is comically not these things. </digression>

Sure, cut down a forest or buy ready land. Level the land, prepare drainage, and install racks to hold the films. Why do that when a warehouse roof is ready for solar to be deployed?

Or just put it on the parking lot?

The efficiency is so low on these, good luck. Covering a corner of the parking lot with standard panels is going to be cheaper and easier than doing the roof using these.

Covering a parking lot with anything let alone solar panels that require lots of electrical connections is not a simple job. Think of all the supporting posts and beams, footings that will take up space, wind load considerations, etc.

Simpler than doing it on a (low load rating) roof, where you also have to deal with an inability to drive to where you are doing things, have low maximum weight limits, have to worry about water tightness, etc.

Even better, if the contractor screws it up, it doesn’t burn the building down or cause massive water damage. Worst case some cars catch on fire. Much cheaper!

The advantage of solar on roofs is that solar doesn't need to be serviced often, and the solar panels actually protect the roof under it and will lower electricity use in the summer by keeping sun off the roof.

The disadvantage being that they add weight to the roof and are a significant source of wind load.

And pierce the supposedly waterproof roof (the entire point of a roof). And mounted at whatever angle the roof is built, instead of an optimal angle. And are in the most difficult place for maintenance and cleaning, so those things will be neglected.

And you need to replace the roof? Now what?

You could run cables down the roof and the outside outside of the wall which not particularly rare. Actually that's the case for one of the aerials on my roof. And piercing roofs isn't exactly uncommon. Aircon vents, chimneys, mountings for aerials etc. The thing with something like this is that it doesn't have to be an optimal solution which instantly solves all our problems, which is what a lot of people seem to demand when it comes to anything which is even vaguely green, it just needs to be cheap and easy and move us away from our reliance on fossil fuels. This, along with traditional solar, hydro, onshore and offshore wind, nuclear etc. all have their place.

ressources are not infinite and framing the problem as one of good being the enemy of perfect is disingenuous. Rooftop solar is a terrible idea when compared to the alternative - utility scale solar, installed at the right location, in the right way, with economies of scale; all while achieving everything you mentioned.

Rooftop solar has numerous problems, starting with structural considerations, scale, shading, imperfect angles, local grid congestion and so on. Why have everyone waste money on this when we could just install solar farms?

because even with the inefficiencies it more than pays for itself.

To bring it back: Governmental policy vs individual choice? If I, a consumer of electricity want to reduce my GHG impact, I can only lobby the source of my electricity so much. Rooftop solar might be less efficient than gridscale for the system, but it's something the individual can do.

Because we're not installing solar farms and are installing rooftop solar in many locations because land is limited and expensive and roofs aren't? Not everywhere has large amounts of empty land waiting to be built on

It’s not the holes for the cables that are the problem. It’s the anchor screws that mount the panels to the roof. If you’ve ever installed shingles on a roof you would know that you have to be careful to cover all of the nail heads with the next row of shingles and preferably use roofing tar as well to get a good seal. The anchor screws for solar are supposed to only go into the rafters below the roofing but anyone can tell you that is hard to do 100% of the time on an existing roof even if you are being meticulous and judging from the installs I’ve seen most solar installers aren’t.

> And are in the most difficult place for maintenance and cleaning, so those things will be neglected.

They don't need much service. And it's not like you need a helicopter to get there

> And you need to replace the roof? Now what?

That's one in 50 years event

Like yeah, if you have good amount of space that is otherwise unused go ahead, but realistically someone will want that space for a house or business, not a bunch of glassy squares, those can go on roof.

Or, in a utility solar farm, where they work well.

50 years? Where, Europe? With tile I’m guessing because in North America most people have asphalt roofs that need to be replaced every 15 to 20.

And get in the way of fire fighting[1].

[1]: https://brannredning.com/brann/brannen-asko-bygget/

Great in a sparsely populated country like the US, not so much in Belgium, Netherlands, South East England where such installations end up either on agricultural land or in places where housing is needed.

On the other hand, 100g/m² is too low for “simply unroll it on a roof”. A carpet so light will blow away in a storm, worst-case taking (part of) the roof with it (roofs often are fairly weak when pulled upwards or sidewards. That’s why solar panels on roofs sometimes are weighed down: it keeps the net force on the roof more or less downwards, even if the wind exerts an upwards force)

What would you use to attach these, and what would that weigh?

I see these end up on cars, sailing boats, etc, where I think weight and flexibility matter more, before ending up in high-volume applications.

On the plus side, the article doesn’t mention it, but I would guess recyclability for these would be higher because they don’t glue cells to glass.

Since it is fabric presumably you could just stick them down the same way you do with a felted roof. I guess you could even incorporate it into a felt roll.

It’ll need to be durable enough to walk on then.

Hell, durable enough for hail, gales, a foot of snow and ice.

Is this really practical for outdoor use at all? Most of us have really durable roofs, not some paper/plastic felt cover.

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