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Comment by brianbreslin | Hacker News Reader

A few things to point out: 1. putting solar on the ground means that it is less efficient (cars blocking rays) than raising it above the roadway and providing shade to the roadway. 2. Dirt on the panels makes them less efficient, roads are dirty 3. Expensive to fix. It is cheaper to fix asphalt than photovoltaic.

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Agreed, it seems that the economics simply don't add up. The article is also particularly deceptive, as it claims that 4 metres are enough to power one household, and 1km to "light a settlement of 5000 people". However, that means just powering the streetlights of a settlement of 5000, as 1000/4 = 250 only. It's interesting at least as an example of environmental action purely driven by an attempt to get cheap political support (pun intended). I wonder if such an experiment could at least drive further research and innovation.

I doubt that 4 meters of solar roadway would be able to power a household after 6 months of normal use (not to mention that the placement of solar panels on the road is such a stupid idea that it beggars belief).

I think you can ignore the effect of shadows from cars. If you look at satellite images of highways, the percentage of the road covered by cars is actually quite small (<5%, by length, I would estimate.) The reduced efficiency due to not orienting the panels at the optimum angle will be much greater.

https://www.civicsolar.com/resource/effect-array-tilt-angle-...

Solar panels are connected in series to improve efficiency and reduce costs of inverters. Single panel under shadow degrades the whole set. It behaves as a resistance.

But it's still only 5% resistant to the 95% providing electro motive force.

Which is why you add bypass diodes. If you don't have bypass diodes, and have enough other cells in series, you can actually burn out a section of panel by casting a shadow on it.

That's a poor comparison, it's not about efficency at any one stage, it's a question of total cost vs total gain. If the cost of this road surface over it's lifetime is less than traditional road surface plus the equivelent solar cells over there lifetime then it's a good idea.

It won't be. Tarmac is an incredibly well-designed material to use for roads. Glass + silicon is not (to put it mildly). Not to mention that the sheer cost of solar panels makes this a ludicrously expensive project (why didn't they just make a solar farm instead and save some of the money to pay for tarmac -- it's a much better way to spend your money).

It is a pity they will probably find out after 1,000 km, and not after, say, 1 km.

Tarmac is cheap and easy to apply, other than that it's a poor road surface. In heavy use coupled with poor conditions Tarmac can need resurfacing in as little as 5 years (10-20 is more common). Worse, it can significantly increase fuel consumption for heavy vesicles as the road surface deforms.

Concrete is better for fuel consumption and can last 2-4 times as long, but needs regular gaps for heat expansion which can cause noise issues and poor ware patterns. It's also far more expensive and end of life roads often spend long periods in poor repair.

Glass is actually a fairly competitive surface. Though, to expensive for most uses, people have used to for see though driveways etc.

> Tarmac is cheap and easy to apply, other than that it's a poor road surface. In heavy use coupled with poor conditions Tarmac can need resurfacing in as little as 5 years (10-20 is more common). Worse, it can significantly increase fuel consumption for heavy vesicles as the road surface deforms.

Yes, but because it's cheap this isn't a big problem. Not to mention that glass will not last 5-20 years on a highway. It is much softer than the stones and other crap which will be scraped against it with car tyres. It will start to crack when it's hot. It will lose any grip very quickly (thus making it a public safety hazard) and won't function as a useful solar panel much faster than it will stop working. A driveway and a highway are very different problems to solve.

> Concrete is better for fuel consumption and can last 2-4 times as long, but needs regular gaps for heat expansion which can cause noise issues and poor ware patterns. It's also far more expensive and end of life roads often spend long periods in poor repair.

Yeah, concrete is good as well. I forgot to mention it.

> Glass is actually a fairly competitive surface. Though, to expensive for most uses, people have used to for see though driveways etc.

See above. I don't agree. And I don't see why people are trying to convince themselves that it isn't a stupid idea.

I don't think it's a good idea.

However, it's the kind of problem begging for a good solution. One option would be an ablative surface like asphalt where glass chunks are suspended in a clear resin. Probably a health hazard. Another is to only add panels down the center of a lane, which might push a marginal solution into feasibility.

Given that asphalt construction is made out of mostly waste materials, is nearly 100% recyclable, can be patched in-situ, requires very little maintenance, requires very little skill to install/maintain, and is much more durable than glass, there's no way the TCOs are even remotely comparable.

Asphalt is a product from crude oil; as such it's got finite supply and is likely to go up significantly in costs over time. It's actually used on roofs which are becoming less common for various reasons and breaks down in sunlight.

PS: Nothing says they need to use glass, just a cheap durable and translucent substance.

OK, can you name a cheap, somewhat durable, and translucent substance that's not glass?

The typical translucent substances people use in practice are various kinds of glass, plexiglass (not durable; scratches up a lot), transparent ceramics of various sorts (generally not cheap), gems like sapphire (not cheap, especially for large-scale applications). Anything I'm missing?

Lacquer wood finish comes to mind, though tar is hardly durable. Not 100% on the specifics but people already use concrete sealant on roads so traction and cost wise it's in the ballpark.

Don't forget Silicon is really quite tough so your really looking for something that can sit outside for 20 years vs. trying to protect fragile components.

Silicon is not necessarily tough in the sense of https://en.wikipedia.org/wiki/Toughness -- it really depends.

The hard problem in road surfaces is not the sitting outside for 20 years. Glass, even cheap crappy glass, handles this last just fine; see windows in houses. The hard problems are dealing with repeated time-varying mechanical stress and dealing with thermal expansion (windows can play fast and loose with this by leaving expansion space around the glass inside the frame).

Crystal silicon not steel, but it's reasonably close to concrete. And concrete is the high end road surface vs. asphalt.

Crystal silicon [.6 - 1.3KIc (MPa · m1/2)] https://lirias.kuleuven.be/bitstream/123456789/355152/1/Ther... (Page 12)

Concrete [0.2-1.4 KIc (MPa · m1/2)] https://en.wikipedia.org/wiki/Fracture_toughness

Asphalt is nearly 100% recycled.

It is beyond stupid on so many levels only a politician could love it. The sad part is how much money politicians can waste without oversight, especially on dubious expenditures. They would get so much more bang for their buck putting up a solar array along the highway.

However this really sounds as if the politicians bought a bill of goods and simply could not comprehend they don't understand the issues. As in, they are the smartest people they know so they are incapable of being sold a bill of goods that are bogus.

Politicians generally aren't the bumbling idiots us computer enthusiasts would like to imagine they are.

I prefer to look at it this way: effectiveness of their ideas is one of the least important things they optimize for. They're driven by constraints that have little to do with actual value to society.

In other words, if it does appear idiotic for all the technical reasons, it would follow other reasons are at play. (Call me a cynic, but "pork-barrel" immediately comes to mind.)

Perhaps not, but it's also quite rare for a minister to be a domain expert in his portfolio.

That's just the start. How about, the worst possible case for transmitting power to where its needed - a huge line. A real solar plant can be put where demand is. Also, the angle of the cells is necessarily straight up. Works on the equator, sucks every other place on the planet. And so on.

This is an example of stupid thinking - "Roads are flat; solar cells are flat; lets combine them!" It ignores all the other requirements for a good (efficient, positive return) solar installation.

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