Hacker News Reader

Comment by meric | Hacker News Reader

Roads are quite a good place to place solar panels, logistically speaking. Yes they are 30% less efficient, but they are also closer to where the electricity will be used, and the marginal opportunity cost of real estate is zero since road use is retained. You don't need new land and you don't need to worry about transporting power at great distances. I'm glad such experiments are being conducted to see how well this idea performs in practice. It's good they started with bike lane as opposed to truck roads. It will give them opportunity to iterate on the panels resiliency.

View on HN

US roads are home to several critical subterranean infrastructures: water, sewer, electrical, natural gas, and internet. Our roads are constantly being cut open, trenched, and patched to do maintenance and repairs to these systems.

In the US, we have large amounts of unused space on top of our buildings. Placing panels on the top of buildings puts the electricity near its consumption point and reduces building cooling costs.

The issues with placing solar panels on roofs is the high cost of installation. I would guess the cost of installing panels on busy streets would be similar to the cost of installing them on rooftops.

Rooftop is great for medium and low density residential. Higher density residential and industrial and it starts to get difficult.

The municipality here is in the process of disposing of their ~30 MW power plant (mostly coal + oil peaker), that serves ~20,000 people. Rooftop would handily meet summer needs, winter heating is another question (there is space, it would be too costly). A nearby mill has a 100 MW natural gas plant and occupies considerably less area than is served by the municipal plant.

US power plant data is here: http://www.eia.gov/state/maps.cfm

>Higher density residential and industrial and it starts to get difficult.

Rooftop solar may not be profitable for individual building owners, but is still likely to be a good thing across the community. A more "socialized" model where the costs are borne and the generated power reaped across the grid, rather than per-building, makes more sense. Particularly since we're talking about this as an alternative to solar panels in roads.

> Our roads are constantly being cut open, trenched, and patched to do maintenance and repairs to these systems.

At a glance, it looks like the solar road system uses semi-modular panels. That could possibly make road work much easier than it is on asphalt, which requires a ridiculous array of equipment to cut away the offending area before work begins, then lay down an entirely new replacement section once work is complete.

The main purpose of roads is to handle vehicle traffic. Here I see solar panels covered with glass and I just don't get it how it can be used for anything else but to generate hype. Even if the glass was somehow more damage resistant than asphalt there is still the question of grip. And even if you invented transparent asphalt to put the panels beneath, it would only be trasparent for a day or two, until dirt accumulates. They are probably cleaning this 70m strip every day but can't do the same for the entire road network.

Part of the experiment is to test the traction surface. They had a problem with a bicyclist slipping, so they switched from stick-on surface to spray-on surface.

The article says they use an angled surface and natural precipitation to keep the glass clean. I can only imagine how much dirt builds up on a highway over a day. A similar complication would be dirt or sand being blown onto the roadway by wind, or washed there by rainfall.

Not sure why you are being downvoted, but I thing your comment makes a lot of sense, and I'd like to know why some think otherwise.

The economics of solar panels in roads are horrible, given current technology.

Here's an excellent engineering analysis of this exact project: https://www.youtube.com/watch?v=HOZBrHqTJk4

I wrote a comment there. Panels on roads, if they can suffer being driven on well, can be economical when rooftop spaces run out. Rooftops are only sufficient for 25% of Netherland's electricity demand. I notice now there is a couple of inaccuracies but they are only minor ones financially. The benefit from saved real estate is too big.

Local council governments may have access to its road real estate, but have no legal right to install panels on roofs. Netherland land value, per square meter, is €4,907. There is a local property tax is 0.05% - 0.3%. (http://www.shelteroffshore.com/index.php/property/more/prope...), and a wealth tax of 1.3% per year. Assuming 1.4% total taxes per square meter, the revenue received by the government is €68 per square meter. Since building the solar panel on the road means they don't have to build solar panels on real estate that can generate tax revenue, the benefit is €10 of generated electricity, plus the €68 of tax revenue that is preserved (assuming all municipal building rooftops are exhausted, already). That makes a payback of €78 per year. In 15 years, this would equate to €1170, compared to building a solar array on free land. The savings would be even greater compared to the local government renting rooftops to place solar panels.

Logistically speaking, there's a nightmarish level of complexity introduced here. Put a country's food distribution network on top of its energy production system? Put solar cells where you know they'll be constantly driven over by heavy machinery? Replace some of the most durable materials known to man (asphalt and concrete) with glass encased electronics?

These things aren't impossible, but it's such an uphill battle that I wouldn't hold my breath. (http://jalopnik.com/why-the-solar-roadway-is-a-terrible-idea...)

I gather from their website that the solar panels are embedded on top of the concrete roadway, so it would seem to have the same strength.

Durability, not strength. Asphalt is very durable and it fails in predictable ways, it's difficult to design glass that fails gracefully. Yes, it's a surmountable engineering challenge but this project has more than it's fair share of things that fall in the "technically not impossible" or "we'll figure it out later" categories.

Asphalt is cheap, but not really that durable. 3-5 years in you generally see some cracking and should start matence. 5-7 years you generally need some patches and 15-20 you need to replace the surface. Though that's assuming good conditions and reasonable traffic patterns in some areas you need to resurface within 10 years. Concrete on the other hand generally lasts twice as long.

From a material perspective glass is much closer to concrete than asphalt. Ex: http://en.m.wikipedia.org/wiki/Glass_brick the point being glass withstands sunlight and the elements without issue, it's being driven on that's going to be an issue. And luckily that kind of stress is much easer to simulate in a lab vs weathering.

PS: That or ice which can handle heavy loads with little issue.

Point granted, we use asphalt because it's a cheap and I should know better. I would still expect it to last longer than wildly complicated solar panel/computer/light displays that have many more modes of failure.

For this to work you have to do several things to the glass at the same time, none of which come easy: make it strong, make it hard (probably need to get to 8 or 9 on Moh's hardness scale), make it tough, and have it grip rubber as well as asphalt does even when it's wet. Considering scratch resistant and grippy compete with eachother this is not looking hopeful.

Yea, I don't think this is a good idea yet. However, train tracks might be a good option if you could get it durable enough but where having traction issues. The ~1m distance between rails is generally just wasted space and the US has ~400,000 miles of rail if say 20% efficiency over 1/2 of that distance that's ~320GWh per day which is a fair bit of power.

The advantage being rail lines need to trainsport electricity for electric trains, so you get dual use from those power lines.

That's still bundling something fragile with infrastructure that carries heavy machinery. Transporting electricity is a solved problem, we can put a solar farm in the middle of nowhere with current technology. And if we're looking for land that's already owned we could put solar cells underneath long range transmission lines 1000x easier than we could embed them in roads or in train tracks.

Thick pices of tempered glass are vary durable and could easily outlast asphalt as a road surface. Right now the decreased efficiency makes this a non starter, but long term if solar keeps getting cheaper it may become a reasonable supplement to the power grid.

PS: Bullet resistant glass is surprisingly clear dispite how thick it is.

I wonder what the stopping distance is on this glass?

Not as big as wet glass or icy glass ;)

Materials scientists do fascinating things with glass, but making it competitive with rocks for road surfaces seems like a waste of effort.

Personally I think Elon Musk's solutions for this problem (decentralized clean power generation) are a bit more compelling, especially the part about putting solar panels on our rooftops instead of in our roads.

http://fusion.net/story/129075/elon-musk-reminded-everyone-l...

Is it important that they started with bike lanes and not full roadways? A bicycle vs. a delivery truck present radically different loads to the roadway.

The road is much wider, and pose greater disruption to transport during installation - If the experiment fails because it can't even take bicycle loads, and bicycle wear and tear, there would be bigger waste. If 70m works (physically, politically, economically), do 100m. If 100m works, go for 500m. If that works, do a 50m prototype on a road. Something like that.

It would also be far more costly. As roadways have way higher requirements then bikes.

Strangely enough, glass lasts a very long time in terms of actual time from the perspective of geologic longevity. Pieces of glass will tell humanity's story long after buildings and roads crumble to dust. I understand that shards resting peacefully and a pathway that is used constantly are very different things, but I never cease to be amazed at the strength of glass and how much it has strengthened in my own life time. Just a thought.

In a country with sun nearly all day, on a bike path (not a road), run in a place without shade trees or houses. So they got a few KWH. If instead of a mile of 'solar bike path' you made a proper installation anywhere along that path in an empty lot, you'd do better, it would be cheaper, transmission costs would be less, and on and on.

This fixation on "we're already using land area for roads; solar panels need land area; lets combine them!" is not an engineering decision - its politics and public relations.

Comments to the article are not so enthusiastic:

- 25% more solar exposure in the area this april--should be considered, too

- with the frost, the glass-like surface turned into a frictionless slide

Roads, bike lanes, etc are all terrible places to put solar. Look at the difficulties people have with floor heating via hot water pipes, which is a simpler problem to solve and despite that is still problematic.

Reply on news.ycombinator.com