Monday, September 24, 2018

Remember "Paving Roads With Solar Cells"?

Remember a few years ago when people talked about using road and sidewalk surfaces for photovoltaic cells?  Well, a few experimental installations have been done and they really suck.

I know: what a surprise?  Who would have guessed? ... I mean besides the groups getting some gubmint money to install them.

A little thought by someone who has seen solar cells used properly will give a handful of reasons why it's a bad idea.   The most obvious one is dirt.  Roads get dirty, covered with snow drifts or wind driven sand, for example, and small amounts of light being cut off by dirt have large impacts on the efficiency of the cells.  Next most obvious is the mounting angle.  To be perpendicular to the light of the sun (max intensity and energy transfer), the cells should be mounted at the complement of the latitude.  In the areas where the sun is most intense, the cells would need to be 25, 30 or even 35 degrees from the vertical, or 55, 60 or 65 angles to the horizontal.  Cars can't drive on that.  Instead, they'll be at road grade, flat to within less than 20 degrees in most places.  Finally, they'll need to be mounted under glass strong enough to support the cars and trucks that travel that road.  Thick glass will further reduce the light converted to electricity. 

A study reported in the Herald Sun news from Australia goes over some results.  Warning for odd units ahead.
One of the first solar roads to be installed is in Tourouvre-au-Perche, northwest France. This has a maximum power output of 420kW, covers 2800sq m and cost €5 million ($8 million) to install. This implies a cost of €11,905 ($A19,230) per installed kW.

While the road is supposed to generate 800kWh/day (kilowatt hours per day), some recently released data indicates a yield closer to 409kWh/day, or 150,000kWh/yr.

....The road’s capacity factor — which measures the efficiency of the technology by dividing its average power output by its potential maximum power output — is just 4 per cent.
Oops.  For comparison, the Herald Sun reports on a solar panel installation in the Bordeaux region of France, in a place called Cestas.  This plant was designed with rows of solar panels carefully aligned at the proper angle towards the sun, not to be driven on.  It has a maximum power output of 300 Megawatts (300,000kW) and a capacity factor of 14 per cent.  At a cost of €360 million ($A581 million), or €1200 ($A1938) per installed kilowatt, one-tenth the cost of the solar roadway, it generates three times more power.

While it's not surprising that this insanity has spread to the US, it was a little surprising to me that a small pilot project was done in small town, Idaho, specifically Sandpoint, Idaho.
This is 13.9sq m in area, with an installed capacity of 1.529kW. The installation cost is given as $US48,734 (about $A67,000), which implies a cost per installed kilowatt of $A44,420 more than 20 times higher than the Cestas power plant. 
1.5 kW is a rather small project, so I'd have to guess some sort of "proof of concept", but at 20x the per-kW cost of the Cestas facility (and at a similar latitude as Cestas, 48N for Sandpoint vs. 45N for Cestas), clearly not a good use of funds.
And this is before we look at the actual data from the Sandpoint installation, which generated 52.397kWh in six months, or 104.8kWh over a year. From this we can estimate a capacity factor of just 0.782 per cent, which is 20 times less efficient than the Cestas power plant.
I should note that in the photo of the Sandpoint square road (and sidewalk!) you'll notice traffic lines, speed limits and other information from LEDs embedded in the roads.  While it's a nice touch, in the brutal reality of energy input/output they must be budgeted for.  It turns out the LEDs use 25% of the power the road generates. 

Final words to the Herald Sun:
That said, it should be pointed out that this panel is in a town square. If there is one thing we can conclude, it’s that a section of pavement surrounded by buildings in a snowy northern town is not the best place to locate a solar installation.

However, perhaps there’s a bigger point — solar roads on city streets are just not a great idea.


  1. Owwww! With efficiency that low, it can only be a government project!

  2. I remember this nonsense. A cousin of mine, an engineer who should have known better, was crowing that it was a 'game changer". I submitted to him my personal calculations, done on official envelope backs no less!, but he declined to agree, claiming the evergreen 'but when it's mature tech' argument, skimming over power of insolation per square meter (ok, I did it in SAE and then metric, as a check, but then doesn't everyone?).

    1. (ok, I did it in SAE and then metric, as a check, but then doesn't everyone?). Everyone does who comes from the country that put men on the moon.

      But seriously... It shouldn't be that hard to explain about the yield being ruined by the sunlight hitting the panels at low angles. It's the same mechanism that causes the seasons and every school kid knows that, right? Every engineer should be able to work out the trig.

      Now ask him how much power he thinks comes out of a panel under a foot of snow.

    2. It isn't just the low angles, though that is a problem... which is why they still sell mounts that tilt (for seasonal adjustments) and mounts that track the sun if getting the most efficiency is a big deal....

      The article mentions air movement. Solar panels are sensitive to temperature, being more efficient at lower temps. Panels are rated at 60 degrees. You can calculate how much energy loss per degree C. (Yes, some of us in America understand the metric system, and use 24hr clocks!)

      The article doesn't mention if they are crystalline or amorphous panels. (I would guess amorphous because they are meant to be walked on.) They are significantly less efficient that crystalline panels, at a slightly lower cost. You can walk on them, and roll them up.

  3. I drive by a spot, almost every day, where a painting company, or one of the trucks that lines the roads, had a minor accident. The road was covered with paint for several square yards (or meters if you want to keep the units consistent). It's just a matter of time before something like that happens to the road. Not to mention bird droppings, leaking transmissions and oil pans. Same for radiators, etc. I wonder what happens if someone in a muscle car burns a strip off his tires....

  4. Aesop:

    Solar LED lane and limit markers, embedded in the road: great plan.
    Solar LED flashing crosswalk markers and back-up signal lights: also great.
    Solar shelter with roof of solar panels over parking lots, and covering the rooftops of large ft² buildings: love it.

    Solar roadways: an idea so stupid only the government would do it.

  5. So what is the friction level of a glass road? Do they add friction modifiers to it? What does that do to the solar efficiency?
    This idea is so stupid it had to come from a stupid farm.
    What is it that ostensibly educated people can think it is a good idea to try to combine completely different items into a unit, and expect them to work as well as a single optimized one?

    1. There's a picture in the original article linked above. It definitely looks texturized, and I'm sure that less light gets through to the cells.

  6. How long before the glass becomes so scuffed up and marred that very little light gets through to the solar cells?

  7. The Chinese tried this on a section of highway. It was open for traffic for one day. They tore it out the next week. Thunderf00t on YouTube has a series on busting these things.

  8. But just think of all the money that the Right People will make from designing, building, and repairing solar highways!

    Solyndra, anyone? But then surely no project so pure as this would EVER be corrupted by frauds, liars, and traitors...

  9. I am sitting in my motorhome with a PV panel on the roof to power my computer. I got my first PV "cell" in 1955 as a 12 year old child. I have always liked/loved PV. All my life I have been teased by the stories in Popular Electronics and other similar outlets about the pending new breakthrough in PV; more efficient, cheaper, better, etc. And yet with a few improvements since 1955 PV is still not cost effective. I happen to be in the best place in America for PV (Las Vegas) and even here PV is simply not cost effective. Maybe it never will be. The ONLY purpose of commercial PV in the U.S. today is to "mine" tax money for PV companies and NOT to generate cost effective electricity. Period!

    1. I have a similar background, but I was 1 in 1955, so a bit behind you in age. I've played around with PV cells, built little solar powered radios and little projects, but never built anything big. The biggest thing I've built is the two panel, 40W panel project in the right side bar. I'd like to have about a 100Watt panel or two. One of my lessons learned from Irma is just how little power I have in my last resort backup (backup backup) - a 35AH AGM battery.

      There are times in the year when Florida is good for sun, but we're not as reliable as Lost Wages and the "Valley of the Sun" a bit south of you. We get too much clouds and rain to guarantee a battery system can get charged. Since one of my uses is for after a hurricane - guess what? - it's often cloudy.

      That's the problem in much of the country. Couple in bird droppings, and other dirt and it's rough to get 20% of the energy hitting the things. If I'm reading those figures right, the Idaho solar road got less than 1% of the energy coming in.

      It's so easy to overlook just how good power generation by natural gas is compared to PV, wind power, and all the "renewables".

    2. You're using the wrong metric to judge the worth of the item.
      Strict adherence to bottom-line accounting suggests that storing food is asinine, and you should just buy in bulk at CostCo, etc.

      So, just curious, how does that work for ya after a disaster?

      PV is for places where you can't get other energy at any price, and are beyond the grid, because it's down or non-existent.
      This is why you put it in places where you can't run a line for less than 2 limbs of your choice, or on a sailboat, or an RV.
      (No one has yet worked out an extension cored rated for 70MPH.)

      And for when a disaster, of any type, will make other options an unobtanium solution.

      Guys in the Keys last year had stored gasoline for their generators.
      Turns out 89 octane cut with 50% seawater doesn't run at 50% efficiency. Who knew?

      1 PV panel, even a dashboard trickle charger, under that post-hurricane scenario, gets you a charged cellphone, and a flashlight. Which is two devices better than you get with land power that's torn up for 100 miles, or a genny that won't run on half gas and half seawater.
      A few panels and a battery bank gets you the occasional use of a microwave, and a small RV freezer, and ice. In near-tropical heat and humidity, with no other fuel for cooking. You could even be running an electric bike or scooter forever, allowing you some form of transport, besides walking, when there's no gas.

      So...what's the over/under breakeven price on that per kWh when there's no other power?

    3. It's also a great boon in other ways, like when your Moonbeam governor encourages 10M illegals to move in, but you haven't cut a permit for a single new power plant ion 30 years, so even with the grid, you have rolling brownouts in peak use times.

      And when you carpet the roof with PV, you're not only either generating sufficient power then, you're also cutting the UV and weathering damage to the roof, protecting it from normal wear and tear for longer, and cutting solar gain in the hot months by an order of magnitude, so it's saving you money even when you're running off grid power.

      All of which adds to the bare cost return per kWh from just what the power generation alone is.

      I wouldn't do it in the Dakotas, but in the Sun Belt, using it is pretty smart for a host of reasons. Just not exclusively or primarily, unless you have no other viable choices.

      But before I'd spend government bux on PV roadways, I'd try biodiesel made from ground-up and rendered politicians and AGW radicals.


    4. Re: your first one, I went into a lot of this in detail in my "Hurricane Irma Lessons Learned" post a few days after the storm. And like I said above, I'd like to expand that 40W panel into something in the range of 100-200 watts.

      Hurricanes bring a strong downside for PV panels. It's often cloudy or raining for a day or two after the power goes out. Sometimes for a long time after the power goes out. Your battery bank should be charged and ready before your power goes out. (Battery banks need routine maintenance of charging and discharging in a controlled manner so they should always be ready).

      Our tendency for rain is one reason we're rated about half scale on potential for solar power; about half as available as the desert southwest and "four corners" region.

  10. I might add that this is my 4th motorhome and I never use the generator. They are nice generators, expensive, powerful, built in starters and I don't have to put gas in them because they get their fuel from the motorhome tank. I do use simple lawn lights. The type that has a small solar cell and a directed ability (like a spotlight). I used to have the Harbor Freight 45 watt panels on the roof but now I have a 100W panel and it allows me to use the lights, charge the computer and phones and run the pump and heating system. More than enough power. Still not "cost effective" but if you are boon docking and there is no AC it is practical and the one time expense is more or less worth it.