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Ford unveils C-MAX Solar Energi concept; “plug-in” hybrid not dependent on electric grid can fully recharge from sun

Ford’s C-MAX Solar Energi concept combines a rooftop solar panel with an off-board solar concentrator—essentially an inexpensive Fresnel lens canopy. The vehicle moves beneath the canopy during the day to maintain maximum concentrated solar irradiance. Click to enlarge.

Ford Motor Company announced the C-MAX Solar Energi Concept, a sun-powered hybrid vehicle that can deliver the efficiency of a plug-in hybrid without depending on the electric grid for recharging. Instead of recharging its battery from an electrical outlet, Ford C-MAX Solar Energi Concept uses a special Fresnel lens-based solar concentrator as a stationary canopy working with solar panels on the vehicle roof to recharge directly from the sun.

The concept vehicle uses a day’s worth of sunlight to deliver the same performance as the conventional C-MAX Energi plug-in hybrid (earlier post), which draws its power from the electric grid. Ford C-MAX Energi gets a combined EPA-estimated 108 MPGe city and 92 MPGe highway, for a combined 100 MPGe. C-MAX Solar Energi Concept, which will be shown at the 2014 International CES in Las Vegas, is a collaborative project of Ford, SunPower Corp. and Georgia Tech.

Ford C-MAX Solar Energi Concept. Click to enlarge.

SunPower, which has been Ford’s solar technology partner since 2011, is providing high-efficiency solar cells for the roof of Ford C-MAX Solar Energi Concept—about 1.5 m2 worth, according to Mike Tinskey, Ford’s Director, Vehicle Electrification and Infrastructure. Because the PV cells alone would generate only about 300W—insufficient to charge the vehicle’s battery—Ford turned to Georgia Institute of Technology for a way to amplify the sunlight in order to make a solar-powered hybrid feasible for daily use.

Researchers developed an off-vehicle solar concentrator that uses a special Fresnel lens to direct sunlight to the solar cells while boosting the impact of the sunlight by a factor of eight. The Fresnel lens is a compact lens originally developed for use in lighthouses. The patent-pending canopy-vehicle system tracks the sun as it moves from east to west, drawing enough power from the sun through the concentrator each day to equal a four-hour battery charge (8 kW).

With a full charge, Ford C-MAX Solar Energi Concept is estimated to have the same total range as a conventional C-MAX Energi of up to 620 miles, including up to 21 electric-only miles. Additionally, the vehicle still has a charge port, and can be charged by connecting to a charging station via cord and plug so that drivers retain the option to power up via the grid, if desired.

After C-MAX Solar Energi Concept is shown at CES, Ford and Georgia Tech will begin testing the vehicle in numerous real-world scenarios. The outcome of those tests will help to determine if the concept is feasible as a production car.

By tapping renewable solar energy with a rooftop solar panel system, C-MAX Solar Energi Concept is not dependent on the traditional electric grid for its battery power. Internal Ford data suggest the sun could power up to 75% of all trips made by an average driver in a solar hybrid vehicle. This could be especially important in places where the electric grid is underdeveloped, unreliable or expensive to use.

The vehicle also reinforces MyEnergi Lifestyle, a concept revealed by Ford and several partners at 2013 CES. MyEnergi Lifestyle uses math, science and computer modeling to help homeowners understand how they can take advantage of energy-efficient home appliances, solar power systems and plug-in hybrid vehicles to significantly reduce monthly expenses while also reducing their overall carbon footprint.



Various authors on here (including myself) have been ridiculed for suggesting this concept over the years. Good to see Ford are taking it seriously!


I agree,imagine the millions of people in sunny metro areas worldwide who commute a few miles a day from the 'burbs into downtown to work, the very worst way to use an internal combustion engine.

Something like this could make their entire work week journey zero carbon, you might not even need the collector if your commute is short and you dont whack on the air con!


Depending on the cost, this could work for me. I have a garage, so topping off at night would be easy enough. But I live in sunny Colorado, and park all day at work, in the sun. This approach could reduce the need for an oversized battery.


Google already has solar panel covered parking garages for their electric cars.

Will S

Interesting concept, but seems a little bit on the flashy side. Why not just have PV on the roof and be done with it?

And the simulation shows the car moving under the canopy as the sun is passing overhead - how is that accomplished?

8 times as much solar is going to more rapidly wear out the solar panels. This has been discovered in many other PV concentrator trials.

Finally, 8 times as much solar insolation hitting the roof would increase the heat load on the car by 8, which could be a summer disaster in most states.


It may be economically more advantageous to install the same very high efficiency solar units over open parking places. When equipped with (shared) e-storage units, many more BEVs and PHEVs could benefit with clean recharges.

Keeping the vehicle cooler would also reduce the energy required to cool it down.

Roger Pham

In the days that PV cells were expensive, solar tracking makes sense, to reduce the amount of PV cells used. Now, PV cells are real cheap, so the tracking mech. actually costs more than using extra solar cells to provide equivalent output.

IMHO, mount solar PV on the building or on top of parking lot cover and then use the electricity to charge the vehicle would be more practical than solar focusing and tracking mechanism. In this way, even PEV's parked in parking garage on lower decks can benefit from solar PV's mount on top of the building.

Bob Wallace

We need to be charging our EVs with wind power.

That will create a new market for wind during off-peak hours and make wind more profitable.

The extra profit will mean more turbines are installed.

And that, in turn, will make more cheap wind energy available during peak hours to lower our utility bills.

Put panels on rooftops. Use the power to lower peak hour demand.


The discussion on the power/energy of the system needs to be clarified. The power is hinted at being 8 kW, but surely that isn't correct because the Energi's battery is only 7.6 kWh, so that would mean a full charge in an hour--but the sentence also says it would take a full day to equal a four-hour battery charge. It can't be both! I would suspect something around 1 kW to get a full charge in 8 hours of sunlight.

@Will S, having solar panels on the roof doesn't increase the heat load on the car--the same amount of sunshine is hitting it. The PV will mean that more is absorbed than reflected from a conventional roof, but it certainly won't be anything like eight times higher.

Roger Pham

With 8-fold concentration of sunlight on top of the car's roof, surely the PV cells will be a lot hotter than without solar concentration. Remember how to start a fire using a magnifying glass to focus sunlight on top of leaves or paper?

Normally, stationary solar PV has a hollow channel on the bottom for convective airflow for cooling. When mounted on the roof of the car as in the photo, no cooling channel is shown and heating may be worse, especially the dark color of the panel.

william g irwin

I suspect it would be cheaper for someone who owns property in the sunbelt to put up a car port w/solar panels on top rather than carry the extra weight of the panels around or putting the concentrators on top of the car port. This would only help while at home during the day, which isn't useful unless this is driven by a work at home person. On the other hand, panels on the car allows slow charging anywhere if that is at all useful.
This concept would make more sense for an at-work parking lot, but again, put the cells on the car port.


One thing is for certain, if the Fresnel really does concentrate the light 8x, you won't see any vehicles ICE'ing your parking spot more than once. Can you imagine how hot it would cook a car that didn't have a PV array on its roof? On second thought, just how hot would the C-Max get, even if it does have a panel on its roof?

Bob Wallace

The area of the roof doesn't change. Only "one sun" is hitting the roof. A lens would only concentrate that energy on a small portion of the area, it wouldn't increase the total amount of energy/heat.

If high efficiency cells were used, say 40% efficient, then 40% of the energy would be converted to electricity and the car would be cooler than a highly absorbent black roof.

That said, I think this more of an attention-getter for Ford rather than a practical solution.


The area of the roof may not change but I believe the area that matters is that of the concentrator ( 4.3m x 5.3m = 22.8mxm ) which is considerably more than the 1.5mxm of solar panel on the car. The canopy is no doubt less than 100% effective and some of the light it is concentrating on the panels would have landed elsewhere on the vehicle anyway and some of that energy is being converted to electricity as opposed to heat. In spite of those mitigating factors I believe there is legitimate concern for heat build up near the panels.

The big expense in tracking devices of yore was in the motors and integration. In this case almost everything required for rudimentary tracking is already in the car. All they needed to add are some cheap sensors and some SW so it is almost free. Kudos to their engineers.

While we may see more implementations of solar panels as trickle chargers on EVs as well as ICEVs I would not expect to see this concept productized any time soon.


It's still possible to provide a reasonable number of daily "sunshine" miles without a concentrator car-port.

If you allowed a solar panel to extend from the roof over the windscreen and bonnet when parked, you could easily get 3.5 metres squared of panel over the car. (Of course it would retract before driving off!) The most efficient non-concentrating solar cells are ~38% efficient, which would give 1.33 kW peak from this area.

In an overcast location (eg the UK), that would give you an average of 2.9 kWh per day, which is equivalent to 14.6 electric-only miles per day or 5,300 miles per year.

However, in a sunny location (eg Arizona), you would get about 2.5x that, or 36 miles per day (~13,000 miles per year).

Of course you would get much more free sunshine miles in the summer than the winter, but it would still cut your annual fuel bill massively, and of course no need to plug in. Any surplus could be fed into the house or sold to the grid if the car is not being used.

Bob Wallace

Concentrating lenses would create hot spots. But they can't create energy. The net energy hitting the car would be the same with a lens or a metal top. It all comes down to how much energy is reflected, how much absorbed and how much converted to electricity rather than heat.

Super efficient solar cells are super expensive. I just don't think the math is going to work for Ford.

Wireless charging with solar panels on building roofs would make charging super easy and be most cost efficient.


Excellent practical ideal from 'clett'.

Another future possibility will be to integrate transparent flexible high efficiency solar panel over front-back windows, bonnet, roof and booth for 4M2 to 5M2. If not enough, the roof could open 'left and right, when parked, to double roof effective size and overall size of 6M2 to 7M2.

In sunny areas, that would be enough to power well designed BEVs, without having to plug them in, for up to 15,000 miles/year. Summertime surplus could be fed in the local grid or home storage system.


Solarizing carports and shading parking lots makes more sense than expecting PV-topped cars to be using particular lens-equippped parking spaces.  Use the grid to move power from the established parking areas to wherever users (vehicles or otherwise) happen to be.  That's what the grid is for.

The sunward sides of buildings can be solarized for the same purpose.

The real issue is matching demand to supply.  It would take many times the existing EV/PHEV fleet to absorb the current PV peak in several areas.  Supply that cannot be matched to demand should not be built, period.

Roger Pham

Good point, E-P. Matching demand to supply is important.
If the concentrator is capable of charging only one PHEV, then what happens if that person's commute is only 10 miles one way, thus draining only 1/2 of the usable charge of the PHEV? The rest of the day, the solar energy will be wasted. However, on cloudy days, the car may not receive sufficient charge.

However, if the solarized carport can charge many cars, as well as supplying excess power to the grid, then no solar electricity will be wasted. On cloudy days, the PV panels on the carport won't have enough power for all the plugged-in cars, and the cars will have to be charged from the grid's power.

Another disadvantage of this scheme is that the car must be able to move back and forth to keep the sunlight focused, thus taking two parking slots for one PHEV. This may not be acceptable in a busy parking lot, or will cost the owner double for parking fee.


Come on you two. No solar energy has to be wasted because electrified vehicles equipped with solar energy collectors will easily feed the excess energy to the GRID via wired or wireless connections and get credited for it.

One main advantage of having solar energy collectors on board your PHEV could be a much lesser need for an ICE range extender and reduced fossil fuel consumption. Also, less e-grid loading would lead to less CPP usage and cleaner air etc. .

However, having the solar energy collectors on the car ports, parking lots or on the vehicles would work and could supply most of the energy required for e-vehicles, specially with higher efficient units in sunny places.

Bob Wallace

I missed the canopy part in an earlier comment. The larger "gathering" area of the canopy would put more energy onto the top of the car.

If the cells don't convert that extra energy into electricity then the vehicle would likely get hotter than an ordinary vehicle.


It's more than silly to put a solar cell on a mobile vehicle, and require that it park itself under a static lens to be useful.  Mount the cell to the lens, and feed the vehicle through the grid.  Or don't bother with lenses, should they make no sense in context.

This has more than a few elements of agitprop.

Roger Pham

Thanks, E-P, for noticing the Emperor's New Clothes.

Since the law mandated handicap parking slots everywhere, the law can also mandate charging sockets in limited number to be available at every business and parking lot. This will help owners of PHEV-20 who has over 20-mile daily commute to avoid having to burn gasoline. Day-time charging will help absorb the daytime solar peak energy production and will allow higher penetration of solar PV.

It would be more useful that PHEV makers like Ford and GM would lobby for mandating charging sockets at work rather than expending effort at this concentrated lense scheme.


Ideally, future extended range BEVs could benefit from having on-board higher efficiency (35% to 50%) solar energy converters. Something like 8 KW to 10 KW could keep a well designed BEV going during sunlight hours, specially if a day long trip is started with a fully charged 85+ kWh battery pack?

Shorter range BEVs could be equipped with smaller on-board solar units (3 to 4 KW) and smaller battery pack (20 to 40 kWh).

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