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Comment by hoopd | Hacker News Reader

Really? On their website[0] they claim their glass surface doesn't require snow removal because the heating elements melt it and as such asphalt roads have a cost of snow removal that apparently comes for free with these.

However, it takes more energy to melt snow than to push it to the side[1] which they simply ignore and that makes me question what other things they're leaving out in order to tell a good story. I'd really like to see the numbers crunched for how many snowy days a year will cause the system to consume as much energy as it produces.

[0] - http://solarroadways.com/snow.shtml [1] - https://what-if.xkcd.com/130/

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It takes moe energy to melt snow than push it to the side? This is northwestern Europe, where the snow never gets more than a few centimeters deep, and the temperatures never go more than a few degrees below freezing. I could definitely see heating a surface by a few degrees being cheaper than bringing a plow or other snow clearing machinery out to some path.

Now, northern Canada would probably be a different story.

Can confirm, in the Netherlands on bike lanes black ice is a much bigger problem than snow. Heating should work fine against black ice while shoving isn't very effective.

The enthalpy of fusion for water is 335 J/g. The specific heat capacity of ice at -10C is 2.1 J/(gK). So the major part in melting the water isn't heating it until it melts - it is the melting itself that is expensive.

That said, I do see some value in solar ways in the space savings.

Why not awnings over the bike path? This can be done in ways that look awesome and do not ruin the scenery and the view from the bike path. Thin film collectors in the form of tarps suspended from poles would make the installation cost commensurate with installing light poles. You'd need significant R&D in the aerodynamics, etc. However, you already need significant R&D for collector roadways, and you're starting out with an inherently disadvantaged design.

It takes moe energy to melt snow than push it to the side?

Physics. We're talking the energy of phase change vs. mechanical energy. They're both factors of the mass. The XKCD what-if calculations apply just as well to varying amounts of snow. It will always take less energy to push it aside than it does to melt it.

If you are thinking about saving the cost of the equipment and driver, then that's fine. However, physics again rears its ugly head, and you are not going to be making the power to melt the snow from the roadway itself. What you are proposing is to embed all roads with heating elements, which is clearly very wasteful by the calculations in the links in the gp post. Embedding all roads with resistive heating elements is the last thing a country that wants to reduce its carbon footprint should do.

However, that does not compute the cost of having to drive over with a shoveling machine, let alone the cost of building and maintaining a shoveling machine, or the cost of calling workers at 4pm to show up to drive the shoveling machine....

Moreover, and perhaps more importantly, it doesn't snow that often in the Netherlands, so our dearly bought shoveling machine is now idling 359 days of the year - it will still be deprecated and replaced after 10 years though.

Environmental science lives in the real world ;-)

So the resistive heating elements that will add significant cost the the production of the panels will be embedded in the bike paths and are only useful 6 days per year?

Wow, you actually are posting that as if I hadn't mentioned that issue in the gp post.

"If you are thinking about saving the cost of the equipment and driver, then that's fine."

I can't tell if this is intellectual dishonesty or poor reading comprehension.

I notice their site doesn't show any pictures of snow melting.

Snow melting systems that work are available.[1] The power requirements are well understood, and the documents linked have tables and calculation rules. The second document[2] is for electrically powered snow melting.

The big win on power consumption is good controls. Both a snow sensor and temperature sensors are needed, or huge amounts of energy go into heating cold, dry concrete.

[1] http://www.viega.us/xbcr/en-us/Viega_S-no-ice_Snow_Melting_S... [2] http://www.pentairthermal.com/Images/EN-RaychemElectroMeltSn...

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