I've lived "off the grid" for seven years. There's NO power lines within 3 miles of my house. And your premise is a very good one. As I've experimented with a variety of solar electric topologies, one thing is very clear: the storage media is a major, and short lived, component. The problem with a fixed solar mount on a car roof is that the efficiency just isn't there. Better to spend the money on more starge media and charge that media up during the day to be used to recharge the car's batteries during the night.
Fixed solar installations like some businesses in teh US Southwest have installed make sense for recharging a car at work, and the parking structures shade cars from the sun in any case.
and be sure to check out the comments. More than before, I am convinced this is just a classic high-profile PR stunt to get attention at CES, and easily fool those gullible, "trend-hungry" journalists--and it worked! No engineer would see it as having any viability, not even close to it. Problem is that when these concepts fall flat, as they were inevitably destined to do, they cast a shadow (pun intended) on legitimate related efforts.
I've also lived off-the-grid for the past 9 years and I totally agree with the points in this article. However, I will throw out one small point in favor of the concept. With more and more electronics installed in the car, or potentially plugged into the car these days, it's nice to have a modest power source that doesn't require the car to be running. Dead batteries would be a thing of the past! I've often wished for an integrated solar charger for my car, but granted, this usage doesn't require or even justify a lot of fancy technology.
It's gratifying to see an article that debunks mindless hype. Efficient, sleek vehicles, with skinny tires, i.e. vehicles with far less frontal area than the oafish C-Max, require roughly 12 HP to travel at 50 mph. This used to be a very informative statistic provided in vehicle reviews, by Car and Driver magazine. Too bad they quit publishing that parameter. When they did publish that number, as I recall, 12 HP was the best I ever ran across. Pigs like SUVs barely managed 24 HP, for 50 mph.
So, even an efficient vehicle would need 8,948 Watts to run at 50 mph. Basically 9 KW. Hardly a couple hundred.
Solar cars are successfully being raced across the Australian outback, but these have disproportionately large solar arrays, light carbon-fiber bodies, and are operating in an area where insolation is substantial. They are a long, long way from providing what was implied in the WSJ article you referenced. (Which I note describes the car as a "hybrid" and claims a full-charge range of 620 miles, of which only 21 are battery-only. I assume that the unmentioned full tank fueling the gasoline engine provides the other 599.)
A video outlining the Ford concept is available here, and it tells a slightly different story than what the media ran with. In particular, Ford explicitly states that the car's solar panels alone (1.5 m2) will not recharge the batteries in a day. Instead, you would use a canopy of Fresnel lenses (kind of like a carport with a transparent roof) that the car parks under during the day. The car itself moves to track the sun beam the canopy generates. The concentrated solar energy is said to fully charge the battery in a day.
I suppose that if you were stuck in the desert far from the electric grid that this solar car might be able to leapfrog its way to civilization a few miles at a time at night after spending the day recharging, but otherwise it seems totally impractical. Especially in the cloudy Pacific NW where I live.
I saw the original article and I was also very sceptical. They claim 8x the power of normal solar cells when the vehicle is parked under a carport roofed with a big fresnel lens. The car automatically moves to position itself optimally at the area where the lens directs the sunlight to.
That's all possible, and quite clever, but I'd question whether any known solar panels will deliver 8x the power if they receive 8x the insolation due to the lens, and someone else raised heating issues - being as the cells are dark and not that efficient they'd heat up (and hot solar cells are inefficient too).
And yes. even if it did work as stated, with good sunlight every day, it would not give anything like a full charge for a practical daily journey.
I drive a LEAF, and it is solar powered. But indirectly of course. I have 6kW of solar panels on my home roof. The electricity produced is put back on the grid. Thanks to net metering I get credit for that and help produce power during higher demand times of the day. Then I charge my car at night when demand is low. Eliminates thestorage problem for now. I hoping the organic/inorganic flow cell batteries solve that significant problem.
My LEAF gets 4 miles per kWh on average with about half my driving on the highway.
In December, the solar array produced 25 to 70 kWh per week (The snow is NOT helping, the array is at a low roof angle so it doesn't slide off, takes a while to melt.)
I use about 30kWh per week driving, so plenty of excess to help power my home. I'm hoping that in the other three seasons most of the house power is covered too.
Thanks to rebates (50% from utility, 30% tax) I'll pay about $8,000 or less for the system. It should payoff in 5-10 years depending on how fast electric rates rise, and meanwhile I'm not driving my car on coal.
Somehow the author has his head in the sand. 15% is not the max efficiency for even cheap cells these days. Concentrators are typically over 30%. Does anybody check these articles before publishing them?
@rtapl123 The last (relatively expensive) panels I bought were a little less than 15% efficiency. Sunpower panels ar about 16% while Sanyo panels are around 17.25% efficient. The cheap panels are a lot lower efficiency. Concentrators are an interesting option, but it's pretty easy over power a panel - especially during winter cold.
@Henry, rtapl. I went back and watched the Ford video again. They claim 1.5 m2 of panels and 300W output - that's 200w / m2 or 20% efficiency.
The "Carport" is shown as 4.3 x 5.3 m = 22.8 m2 of concentrator lens, that's 15.2 times the area of the panels, and they are claiming an 8x increase in power as result. Considering the difficulty in precisely positioning the car, that's probably reasonable, but I'd still question whether you can drive any solar panel that hard? And that's a big carport for a small car, I wish my garage at home was that big...
Again taking their figures, not ones I've estimated, that gives 300W x 8 x 5 hours - 12 KWH. Depending on the driving, that would give up to a bit more than an hour of driving per day. So it would be feasible for shortish commutes.
I'm a big fan of solar electric. But the systems issue of the Ford solution makes the "solution" a non-soution for most of the vehicles in use. Here's why: 87.7% of workers drive their car to work, and 77% drive alone. Less than 30% of all workers work other than a day shift (health care workers are 30% while management is 8%). So more than half of cars driven to work are at the workplace during the day. Unless you are a shift worker, the canopy buys little (at best a 1 day charge for the work week assuming the car isn't driving the 24 hours before the first work day).
@NewStandard....maybe not totally practical but I do like the idea of putting solar energy directly into the car, not as you say via other dubious sources. However I wonder about the Fresnel lens - probably made via petrochemicals?
My main reaction to this concept was that if this fancy new Fresnel lens improves the output of solar panels enough to be worth the cost, just forego putting PVs on a car roof and instead use this concept on conventional fixed panels everywhere else.
I actually don't mind some petrochemical items that have durability. It's the throwaway stuff that's smothering us. We are awash in plastic with no plan for a sustainable path out. Not to mention frivolous, one-use burning of fossil fuels that has destabilized the planet. But those are other topics.
Guys, don't forget that what matters is not watts (power) directly, but watt-hours (energy). Let's take some figures from the above posts. Assume that the solar cells generate a base 375 W in normal sunlight. Assume the car would be in the sun for 5 hours a day. That's 1875 Watt hours. Let's give Ford the benefit of the doubt and go with their claimed 8x boost with their fresnel lens, though I'm sceptical. That brings it up to 15000 watt hours, a respectable amount.
Bert estimated 9 KW to run a small vehicle at 50 MPH. So our charge would do that for about an hour and a half - practical for short journeys, maybe, but that is under ideal conditions. Under real conditions I don't see this as more than a top-up solution. Can anyone poke holes in my math here?
the fresnel lens will at most concentrate the light - it does not increase the total incident light - so if you still only have 1kW (or in fact quite a lot less) per square metre of car roof to play with - the lens makes no difference to that. What the lenses can do is make a very concentrated spot of light which may get you a better conversion factor depending on the technology, but you are not going to get more power out than was incident to start with.
(BTW incoming power from the sun is called insolation - but this is too easily confused with insulation!)
So if you store 12 hours of sunlight (if you live near the equator) and only drive the car for a very short time you might get enough energy assuming your storage is very efficient, but this can only work if the car is VERY light. Most American cars are seriously heavy - unless you get the car down to being a 200kg or less then this is a non-starter (quite literally)
Today converter don't have a 50% conversion ratio but more around 80% to 90%
It's not the 1.5m² of the solar cell surface you have to take into account, it's the canopy surface (around 20m²) that will be concentrated onto the car roof top.
The solar cells used there are multilayer type that can convert that amount of concentrated solar energy to electricity. Ford says 8x concentration, so not all of the 20m² equivalent surface will be converted, but more around 10m² with 20% ratio.
Those cells are already working as prototype with real 8x factor, but there's still the self-heating issue to take care of.
Nothing magic here.
So you can full-charge a car battery in one day... if the battery is not too big. If you want a bigger car and/or longer range then it will work for 50% of the full charge, that's is still good to have.
The stupid thing in this business model is that you'd better have 50m² of standard solar cells on your house roof top and charge your car with them, it will be cheaper.
Using the large fixed area of the roof of the house (or garage) would enable the vehicle to be charged when it is there and the house to obtain cheap power when the car is away. The additional area makes more power available (and you're spared the Fresnel lense contraption for your car). You also gain a longer lifetime for the solar panels to pay back the investment and generate savings.
&jeremybirch - thanks - do you think you could increase the output of your panels by 8 times with a lens? That's fairly key to making this work. And a typical parking space is 4 x 3 metres - thats 12 square metres - assuming 15% solar cell efficiency and 50% conversion losses that's 4.5 KWH in a 5-hour charge, not 15 KWH as in my workings. I'm pretty dubious of Ford's figures.
I think the lens system allows for slightly increased conversion efficiencies ie of the power incident on the active part of the solar cell more is converted into electricity. But it is still only 30% at best I think. Even if the efficiency was 100% (and I really think the laws of thermodynamics are well and truly against that) you still have the area limitation ie you only capture light from the area of the top of the lens and presumably you don't want to make the top of the car significantly larger so you are stuck with a few square metres at most - the lens concentrates the light incident upon it, it does not suck it in from a larger area.
In large solar thermal systems using lens or mirrors to concentrate you can get 80% efficiency BUT you need to concentrate the light by 5000 times and the running temperature is around 1300 kelvin (1000 centigrade) - see http://en.wikipedia.org/wiki/Concentrated_solar_power
For concentrated PV it may eventually reach 50% efficiency - but not sure how practical it is to mount them on the room of a car - see http://en.wikipedia.org/wiki/Concentrated_photovoltaics
No holes to poke, but I do wonder if the numbers look any better if you assume 25-30mph, say for city driving. (Heck, if I were stuck in the desert I would be happy with 10mph.) Wind resistance is much less than half, I think. Yes, of course in a city it is more difficult to come by direct sunlight.
@majortom84 - if you are looking at start-stop city driving I think the consumption would go up if anything - though you do have zero consumption at traffic lights and hopefully regenerative braking helping a bit. In suburban or industrial areas you could have parking lots covered in carports with fresnel lenses but in inner cities it would be more difficult.
Believe me, I have thought of that, as a gag gift to buy co-workers. At one time, I actually collected various used envelopes I received and sorted them by size, figuring I could use these cast-offs as raw materials; I was also going to ask friends for theirs. Thus, my BOM cost would be zero!
But relaity got in the way: who gets much mail these days? So I would have to buy the envelopes--and that changes the pricing structure.
As a product, the used envelopes will also have a privacy issue unless you cut off the fronts. You'd probably make more friends providing the whole envelopes to stamp collectors. As an engineering gag gift (where the pun will be appreciated), stapling together new envelopes with your explanatory binder would still cost less than they could be sold for.
My personal method of creating unlimited amounts of scrap paper (without the catchy "back of the envelope" moniker) is to take every sheet of scrap used 8.5" x 11" paper with a blank back (from junk mail, printing, bills) and fold / tear it in half twice. I stack these quarter sheet pieces of scrap paper on my desk at home and at work (and on the notepad on my car dashboard). Unlimited scrap paper for free. Once the backs have been used, they finally get recycled.
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