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Ford's solar charging robocar design

One of the silly ideas I see often is the solar powered car. In 2011, I wrote an article about the solar powered robocar which explained some of the reasons why the idea is anti-green, and how robocars might help.

I was interested to see a concept from Ford for a solar charging station for a robocar which goes further than my idea.

In the Ford proposal, there is a special garage with sun exposure and a giant Fresnel lens, which can focus light on a solar panel on the car parked in the garage, effectively a solar concentrator based PV system. The trick is that the car is able to move during the day, so as the sun moves (or rather the Earth and the garage turn with respect to the sun) the car adjusts to put the panel in the beam of the Fresnel lens. They predict they could get 21 miles of range in six hours of sunlight. That's a bit over 5kwh, meaning the panel must generate just under a kw during those 6 hours.

Normally 1kw of solar panel is quite large, and the roof of the garage is large to make this happen. The downside is this would make the panels really, really hot, which reduces their efficiency and frankly, could be dangerously hot and also wear out the panels and roof quickly. (We would need to see what temperature parameters they plan for.)

In the end, this system still falls into the pitfalls that make a green solar powered car a contradiction in terms. To be green, you must use all the power panels generate. When this car is not in the garage, its panel will produce minimal output, since as it moves about its day it will park in shade or at the wrong angle to the sun, and the panels will be horizontal. The only way to properly exploit panels is to have them at the very least facing south in a permanently sunny spot, tilted to the latitude (or sun-tracking) and combined with the grid, so every single joule they generate is put to use.

There is a minor win for solar on a vehicle, which is when you are driving, the energy is never stored, and thus battery weight can be slightly lowered and there are no storage or transmission losses. However, unless you are going to make something like the cars that compete in the solar races, this doesn't make up for the waste of having panels whose output is mostly unused. Toyota figured out a good use for a panel on the Prius -- it runs the ventilation fan, whose demand matches the sunlight and heat of the day. Every joule of that panel is used, and keeping the car cool saves on AC when driving. Had the panel fed into the hybrid battery, its output would be thrown away most of the time when the battery was not low.

As I noted in my earlier article, robocars could make better use of solar panels because they could arrange to always store themselves in the sun, pointed in the right direction, and could even go find connection stations to feed their power back to the grid if the batteries were not low. (You need some robotic ability to connect to the charging station without a human, and ideally without the 10% loss of inductive coupling but even that is tolerable.)

In that world, you could put up Fresnel or other concentrating charging stations which cars could seek out to make the best use of their panels. However, these cars are now consigned to never being garaged or parking in the shade, which is not really what we're looking for.

This does have the advantage of not needing to plug in, though inductive charging stations are also something robocars would move themselves to. If the vehicles are used off-grid, this would be somewhat more valuable even if on-grid the panels (concentrated or not) should just feed that grid.

There's another downside to the heat of this system. In the summer at least, you then have to spend a fair bit of energy cooling the car down. The extra energy gained from sitting in the sun might be lost in cooling if the wait was modest. A cooling fan is a good idea while in the sun.

In other News

Michigan has passed its law regulating the testing of robocars there. It's being touted as a way to "save jobs" by preventing the flight of automaking innovation to other locations. It's going to be a tall order. The Detroit car companies are opening labs in silicon valley, in part because it's very difficult to recruit the very best people to come live in Detroit, no matter how cheap the housing is -- and you can have a mansion in Detroit for the price of a shack in San Francisco. If Michigan wants to retain its car dominance, it will need to do even more.

Several announcements planned for CES. Delphi will be showing off their latest work, which is more ADAS related. Bosch will be showing off their prototype cars, and presumably Audi and others will return.

Results from the Ann Arbor V2V test bed are expected soon. The original plan was for the DoT to propose regulations demanding V2V in all new cars in 2013. They missed that deadline, of course, but many expect something very soon. Results of this testbed are expected to be crucial. I predict the results will be lukewarm when viewed through the robocar lens -- which is to say, the V2V systems will only have been found able to prevent a tiny number of incidents which could not also be detected with advanced sensors directly on the cars. They may not publish that number, as there are incentives to make the test report as a success.


I have to agree on the solar panel on a car idea.
Even with a robocar's ability to find strong sunlight to park in, the amount of energy recovered would never make it worthwhile.
The increase UV damage to the paint and interior alone would offset any gains, not to mention the increased cost/weight/complexity for such a small advantage.
If solar is cost effective in the area the car operates, then put it on the building the car parks in.
If robocars and the johnny cab concept are so successful that the car never parks during the day, then solar panels are still going to be largely ineffective unless in ideal conditions.
I assume this is just typical corporate greenwash and that Ford engineers don't believe in it any more than you do.

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