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By Geoffrey Styles on Jan 20, 2014 with 22 responses

A Solar Car for the Masses?

Tags: Ford, solar, solar car

Ford’s Solar Car Isn’t Just A Toy

It’s car show season again. I’m not sure I’ll have time to take in the DC Auto Show later this month, but if I do, the entry I’ll be keenest to see won’t be the new Corvette “supercar” or the Acura TLX prototype, as much as those speak to my love of cars. Instead it’s the Ford “C-MAX Solar Energi” concept, an unlikely marriage of electric vehicle (EV) and solar photovoltaic panels (PV). The car previously debuted at this year’s Consumer Electronics Show in Las Vegas.

This isn’t the first time a carmaker has put solar panels on the roof of a car, even if we exclude competitions like the Solar Car Challenge and many other efforts to test how far or fast one-off solar vehicles designed by engineering students or enthusiasts could travel. However, I believe this is the first time an “OEM” has added solar panels to a production car for the purpose of providing a significant fraction of its motive power.

Fighting Physics

The biggest hurdle that any attempt to power a car with onboard solar panels must overcome is the low energy density of sunlight at the earth’s surface and the relatively low efficiency of current solar panels, which are much improved over past versions. A typical EV requires 0.25-0.33 kilowatt-hours (kWh) of energy to travel one mile. 1.5 square meters of solar panel on the roof of a vehicle would receive on average only about 6 kWH per day in much of the US, assuming it was stationary and never parked under a roof or tree, and much less in winter. That’s enough to travel up to 20 miles, or the equivalent of less than half a gallon of gasoline in a typical hybrid.

The clever part of Ford’s solar design is its recognition that the rate of self-charging from the car’s rooftop wouldn’t be sufficient to liberate its owner from the gas pump without help in the form of an “off-vehicle solar concentrator.” This is essentially a glass carport that focuses the sun’s rays on the car’s PV roof and, according to the write-up in MIT’s Technology Review, works with the car’s software to move the car during the course of the day to keep the roof in the brightest area. That maximizes the amount of energy stored in the car’s battery, yielding enough for the daily needs of a fair percentage of drivers.

Fighting Cost

It’s not immediately obvious that combining two of the most expensive energy technologies of today — EV and PV — represents a good strategy for making them competitive with the status quo, particularly given the likelihood of relatively stable gasoline prices for the next few years and the significant improvements being made in the fuel economy of conventional cars, for which 40 mpg highway is no longer considered remarkable. The ordinary hybrid version of the C-MAX is rated at 43 mpg combined city/highway, and the plug-in version on which the solar prototype is based is rated at 100 mpg-equivalent on electricity alone.

I have no idea what Ford would charge for the solar option, should it eventually build the car, but it’s a good bet that it would be a significant multiple of the roughly $300 cost of the solar panels. Even without the Fresnel-lens carport, integrating PV into the car’s roof in a durable manner, together with the changes to the car’s power management hardware and software, are unlikely to come cheap.

Nor is it obvious that putting solar panels on a car’s roof is the best way to provide renewable electricity for vehicles. As Technology Review notes, Tesla is pursuing high-voltage (thus rapid) recharging facilities powered by stationary solar arrays, thus removing the constraint on effective PV area. It’s even simpler for many EV owners who want to avoid “exporting” their car’s emissions to fossil-fuel power plants to sign up for 100% renewable power from their local utility.

Thinking Bigger

It’s no secret that EV sales have been disappointing, initially, for various reasons. The latest figures for the US indicate that EVs, including plug-in hybrids like the non-solar C-MAX Energi, accounted for sales of just under 100,000 vehicles in 2013, or 0.6% of the US car market, compared to nearly 500,000 hybrids, at just over 3% of total sales of 15.5 million. If the US Congress eventually pursues tax reform along the lines suggested by outgoing Senate Finance Committee chair Max Baucus (D-MT), then the federal EV tax credit of up to $7,500 per car, which has helped push EV sales to current levels, would be in jeopardy. Carmakers should be thinking seriously about the long-term value proposition for EVs on their own merits.

That’s where a car like the C-MAX Solar could shine. Once technology-hungry early adopters and the greenest consumers have been satisfied, the mass market will be seeking cars that compete on mainstream measures of convenience, cost and performance. In that light, even a Tesla that can be recharged to half its battery capacity in around 20 minutes via the company’s network of Superchargers falls short, compared to a gasoline car that can be refueled in under 3 minutes. No recharger on earth can deliver energy to a car at the effective rate of a gas pump, without dramatic changes in battery technology.

Yet the C-MAX Solar can do something that no other type of car can do: make its own fuel, in a car that can also be refueled conventionally at any gas station, anywhere. That could provide a unique selling point, enhancing the convenience of cars in a totally new way, rather than requiring compromises on convenience as other EVs do.

Conclusions – A Step Toward Better, Faster, Cheaper

I’ve long believed that the transition from fossil fuels to low-emission energy technologies has been hobbled by its dependence on government subsidies and would accelerate when those technologies can delivery attributes that outperform on measures of “better, faster, cheaper.” Ford’s solar prototype must still demonstrate that it can become a real production car, rather just than a car show concept. If it does, it could be an important step towards making EVs attractive to average consumers without requiring thousands of tax dollars in incentives. That could help create the basis for a truly sustainable transition to a new energy economy.

  1. By MikeM on January 20, 2014 at 9:37 pm

    Oh my, oh my!

    So “1.5 square meters of solar panel on the roof of a vehicle would receive on average only about 6 kWH per day in much of the US”?
    Maybe so. But it wont deliver all that insolation as electrical power. Aren’t we forgetting a little detail here, namely solar panel efficiency?

    Sunpower’s E20/327 panels are about 1.5 square meters and, being ~20% efficient (high BTW), only deliver 0.327 kilowatts, and that only under standard test conditions.
    Be a really, really long day of sunshine to come anywhere near 6 kWH per day!

    Hence the need to lurch the car back and forth under a Fresnel lens to focus and boost the energy collected.
    Can’t wait to see the color of those fried solar cells after a year of that treatment.
    (BTW panel efficiency drops when a PV panel gets hot. Drops even more when it gets the magnifying glass treatment).

    Don’t really want to quibble and carp here, but this project sounds more like junior high school than MIT.

    Oh, and lets talk about the cost – anybody?

    • By S Morris on January 21, 2014 at 1:52 pm

      Thanks Mister Snark

      • By MikeM on January 21, 2014 at 1:57 pm

        You’re welcome Mr. SnarkBuster!

    • By Geoffrey Styles on January 22, 2014 at 9:23 am

      Yipes! Let’s do the math right this time. The solar map suggests an average of 4.5 peak-sun hours a day in the US, so 350 W x 4.5 hrs gives us unconcentrated collection of only 1.6 kWh, or only enough juice for around 5 miles. And yes, that’s why they need the Fresnel lens and the “lurching” to get a useful amount of range from solar.

      Thanks for spotting my careless error!

      • By Robert Rapier on January 22, 2014 at 9:55 am

        I didn’t run through your calculation, but I had done a similar exercise a few years ago and concluded that a similar situation might get a car a charge worth 8 miles on a good day.

  2. By exdent11 on January 21, 2014 at 9:25 am

    In the late 1840s , London, which had been putting up with stinky summers for centuries, suddenly had some summers when the stink was so great and terrifying that the government finally had the support of the public to spend money on the first major sewage system. It took an environmental crisis for change to happen!
    Conversion away from fossil fuels could happen quickly if the public became convinced by ever more severe weather events that climate change is a threat. Cost is not the only factor ; fear is another.

    • By Veritasortruth on January 21, 2014 at 1:57 pm

      “Conversion away from fossil fuels could happen quickly if the public became convinced by ever more severe weather events that climate change is a threat.”

      A statement of breathtaking stupidity. Rarely have I read a statement as dumb as this, even on the Internet. This makes me wonder about what type of a background you have. You obviously know nothing about energy.
      Just how would you be able to fly in a 747 without jet fuel derived from fossil fuels? And that’s just the beginning. You have absolutely ZERO basis for your comments. The anology to London in the 1840 isn’t even close to what you are proposing.

      • By exdent11 on January 21, 2014 at 3:15 pm

        You have little imagination . Consider the country’s reaction to 9/11 ; when a threat to our security was perceived and reacted to.
        We spent close to 3 trillion dollars for homeland security and two wars without any thought of cost. Conversion rapidly to renewable energy is just a matter of will if fear is the driving motivation and not economics. My point, which is the same as the Pentagon’s , is that climate change is a huge national security risk.
        To Paraphrase , General Douglas MacArthur once said democracies are very inefficient at reaching consensus but very good at implementation once a consensus is reached .
        By the way, 747s are already testing biofuels [ not from crude oil ] and the Air Force and Navy are using biofuels in fighters …you twit !

        • By Veritasortruth on January 21, 2014 at 7:48 pm

          The whole infrastructure of the United States is built upon fossil fuels; petrolem, coal, and natural gas. What could possibly replace these items in the near term or even middle-term future. Biofuels take more units of energy to produce than what they generate. This is a negative energy transfer ratio. This is why they are not used unless they have heavy subsidies. There simply isn’t enough biofuel to replace oil, coal, and natural gas. There isn’t enough land and there certainly isn’t enough water. As we speak California (I live here) is in the midst of a very serious drought. By the summer CA will ration both water and power. So much for renewables. The “pilot” program that the Air Force has with bio and synthetic fuels is built on hideous subsidies. No one could afford to fly with what the airlines would have to charge with bio-fuels. Way too expensive.

          • By exdent11 on January 21, 2014 at 8:18 pm

            You are very thick. My point [ again ] is that there are other factors besides economics , security for example, that can drive rapid mobilization to new technologies. Wars do that and so would climate change if more and more violent weather events convince people there is serious problem. The author, Mr Styles, is only considering the economic contingencies which I see as a flaw because it excludes the main reason the government is pushing these technologies.

            • By Geoffrey Styles on January 22, 2014 at 9:31 am

              Go back to the legislation that authorized the generous tax credits for EVs, and further back to decades of federal support for PV, and you’d see that climate change was only one factor in the first case, and hardly figured in the second. The main concern motivating US energy policy since the 1970s has been energy security. Climate is a recent and still controversial factor. Our perspective on energy security is in the midst of a sea-change, as a result of the shale revolution, and it’s not at all clear that such legislation could be passed from scratch today, if it weren’t already in place.

            • By Tom G. on January 26, 2014 at 12:12 pm

              Very well said Geoffrey:

              There is no way to win an argument between two well informed individuals when it comes to talking about the future. We can only talk with some authority about things that “have happened” or are “currently happening”. Discussing “what might or should happen” at some future date probably involves the use of a crystal ball and mine broke months ago, LOL.

              While I actively support and believe that renewable energy systems will someday ["someday" is undefined] provide MOST of our energy needs; even then, I believe ["believe" is an opinion] a combination of energy solutions would be advisable. What is the old saying – never put all your eggs in the same basket or some words to that effect, LOL

              Have a great day everyone.

            • By Robert (Electricman) Weekley on May 17, 2016 at 6:09 pm

              Wow! If a broken mirror is good for 7 years bad luck, I can only imagine how many years bad luck a broken Chrystal Ball might bring! /giggles

              are a couple good references to see where we were recently, and were we are now, Globally!

              Closer to home . see and in a different perspective, see:

              Nice graphics (expand to see, or see article above.):

  3. By Russ Finley on January 23, 2014 at 8:44 pm

    I pulled in next to one of these a week ago at a charging station. I had never heard of a C-Max, so I looked it up on the internet. Appears to be the Ford version of a Prius Plug-in.

  4. By bingleybong on January 25, 2014 at 1:57 pm

    Dosen’t the whole concept fail? – just bulid a grid-connected solar car port (or indeed just some panels anywhere) and plug the car in. Looks like the result of one of those brainstorming sessions where the solution occured well before the problem.

    • By MikeM on January 26, 2014 at 10:37 pm

      Bingo! Elegant simplicity – especially if you are setting up your house for solar anyway.

      Oh, wait! You’d still have the horror of dealing with that nasty charging cable and its big ugly plug! Not at all classy, I’d say.

      Back to the drawing board!

      • By Tom G. on January 27, 2014 at 11:51 am

        Oh, wait! Inductive charging is now available. No more charging cable or ugly plug.

        Did I mention; no more broken nails for the ladies either, LOL.

        • By Geoffrey Styles on January 31, 2014 at 8:58 am

          Don’t ignore the power losses inherent in inductive charging.

          • By Tom G. on January 31, 2014 at 1:45 pm

            Hi Geoffrey:

            I don’t usually forget the 3-15% efficiency loss associated with inductive charging since it does exist. However, to me that would be a very small price to pay for my spouse not breaking a fingernail. Some recently married people may not yet fully understand the social ramifications of something like a broken fingernail, LOL.

            Have a great day.

            • By Geoffrey Styles on January 31, 2014 at 4:07 pm

              I’ve seen higher estimates, but even at 15%, that’s an effective 17+% increase in well(or mine)-to-wheels emissions. I understand the convenience and household harmony benefits–wouldn’t discount that for a minute–but for a technology currently touted for its environmental benefits that seems like a steep price for avoiding a plug.

            • By Tom G. on January 31, 2014 at 7:37 pm

              One example of inductive charging technology that Siemens is developing. Still your point is valid even at 90% efficiency.


              “Upscaling the technology for electric vehicles could put to rest many of the concerns people have over range anxiety or finding a place to charge, and they could be installed in all sorts of places – at stop lights, for example, or in mall parking lots. Siemens says the ideal distance for charging is between 3 to 6 inches. The charging efficiency is as high as 90 percent.”.

  5. By ben on January 26, 2014 at 10:35 am

    I’m highly suspect on the C-Max as a production car, but the point of exploring the use of readily available platforms for solar power is practical exercise. Economics and not government fiat will be the final arbiter as to whether it’s a viable proposition. There is, however, genuine merit in expanding our horizons on how existing transportation systems can benefit from innovations directed toward greater efficiency AND performance. Fortunately, technology offers a pathway toward these twin goals. The future has never looked more promising that both of these objectives will be met in the years just ahead. In the interim, we must pursue transitional strategies while resisting the rejection of existing techniques just because they appear to buttress a longstanding dependence on fossil fuels–a dependence that will not change anytime soon despite the rancor accompanying ideological protestations.

    Wishful thinking is not a sound basis for public policy, and we a have too long witnessed the eventual outcome of the policy process yielding little more than electoral massaging than substantive change achieving meaningful goals. In the coming session of Congress, we will presumably witness more of the hand-wringing that partisan wrangling that has left the average American with precious little appetite for Washington politics. Regrettable as this may be, at least it reinforces a practical outlook that change is largely the province of creative, problem-solving efforts in the minds, garages and new ventures of the private economy, which happens to be a much more dependable repository of trust and confidence than the machinations of politicians and those who manipulate them for narrow self-interests in the name of “progress.”


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