This story features a Shell station in England that now offers only EV charging (no more gas/petrol sales). One sentence caught my attention:
The awnings over each charger are equipped with solar panels and can fully charge a Tesla Model 3 in about a half-hour, costing around $39.
Sounds optimistic, especially for England. Thus my question: Making realistic assumptions about insolation and efficiency, what area of solar panels would be needed to fully charge a Tesla in 30 minutes?
A Tesla Model 3 (Standard Range) has a battery capacity when new of ~60 kWh (57.5 kWh useable). Assume charging from 10% to 90% of capacity, so assume 45 kWh of energy required. At the most ideal circumstances (clear sky, highest azimuth angle integral) you’ve going to see a maximum of about 400 W/m2 of solar irradiance. Assuming the panels are clean and can optimally track the sun as is transits, that is going to give:
t=46~kWh / (0.5~h * 0.4~kW/m^2) = 225~m^2
or a square 15 meters on each side.
Making realistic assumptions about a typical English day, I think the answer is somewhere between 5X of that and an “awning” that would cover all of Cornwall. You hear a lot of people talk about England, Germany, or Sweden “switching” to solar as the primary means of generating electrical power indigenously without any real basis in reality. This is certainly a possibility in the sunny Mediterranean countries and the Balkans (although what they are going to do when a raging wildfire shades solar panels for weeks on end is another question) but for much of Central and Northern Europe solar is at best a supplemental and irregular source of power.
Stranger
I just wanted to add that depending on how you read the sentence in question, it isn’t making the claim it seems to.
Depending on how you parse it, it says each awning is equipped with solar panels, but as written it isn’t absolutely confirming that the solar panel is what’s doing the charge in a half-hour.
But looking at the nature of the article, I bet this is a deliberate ambiguity in the writing, to make it much more dramatic than it actually is. As far as I can tell, 30 minutes would be on par with the best proprietary Tesla Superchargers.
And that’s leaving out Stranger’s excellent math proving what a ludicrous claim it would be under even best case scenarios.
The only way this could actually happen (assuming that the awning size is not ridiculously large) would be if the solar panels charge a battery (or feed back into the grid) over a far longer period of time, which then dumps the charge into the car in half an hour.
Of course, even this will only work if each charger is little-used, such that it has a long period of time to charge the battery/feed into the grid, between each charging of a car. Again, this seems massively unrealistic.
This solar map suggests the PV output in London is about 1000kW/h/m2 per year.
If you assume an awning of about 30m2 per charging bay, totally covered in ideally positioned solar panels, that means 30,000kW/h/yr which using @Stranger_On_A_Train’s figure of 46kW/h per charge means each charging bay could charge 650 cars per year, or a bit better than twelve a week. Which is obviously far too few to be realistic.
Are you figuring in the efficiency of the solar panels? What’s a good solar panel output rate nowadays?
A more interesting take - my home charger will do 40A continuous, 240V so about 10kW and adds about 60km per hour to my Model 3. Depending on model of Supercharger, they are if I understand 350V and fast at about 150A to 250A. That can produce an addition of about 1,000mph to the battery. However, the closer it gets to full (or in my case, 90% on road trips) it’s slowly dropping down to, say, 200mph.
I agree, the ideal setup should be charging a bank of batteries 24-7 (12-7, give or take?) and it may be necessary to expand the solar array as the place becomes busier. At very least, also charge from electrical grid, a battery array could be used to reduce peak consumption in areas that meter by peak use too.
I remember reading about these “solar canopy” chargers in an article several months ago. At the time I believe they were targeted at businesses that wanted to allow employees to charge during a day, without the high electrical consumption - so providing the 10K level 2 charging. .
No @Stranger was using deliberately optimistic figures to show how ridiculous the story (if taken at face value) may be.
But there are very handy online calculators like this one which will give you realistic figures. Well, in theory.
No, I should have made it clear I was assuming 100% conversion efficiency which is not physically plausible. I think the maximum demonstrated conversion efficiency for an unconcentrated GaAs cell is about 25%, and the maximum theoretical efficiency of a cell with a single p-n junction is around 33.7% per the Shockley–Queisser limit for a 6000 K blackbody source. As @Princhester noted, I was just making the most generous assumption to make the calculation as favorable as possible, and more to the point to avoid looking things up and citing some source.
Stranger
The only way I see the numbers in the OP’s article working is if the fueling station is storing power in batteries they later use to charge a car. I would think it necessary that they are also using grid power to make that charging happen.
So, at best, the solar panels mitigate the cost to some extent and almost certainly are not charging a car in 30 minutes on their own.
100% guess. I see none of that mentioned in the article. But, I cannot see how it could be otherwise.
Journalism on such things is really poor so it does not surprise me that the author missed some crucial details.
Sounds like it’s just poorly written. It’s almost certainly a Level 3 charging station that supplements with solar but written in a way to make it seem like it’s powered strictly from the panels.
The 30 minute figure is the giveaway. That’s the typical figure they give for 20% to 80% charge from such stations.
Especially journalism that is actually a barely re-written press release, which was designed to mislead in the first place.
I wonder if the panels are powering the EVSE and that’s the basis for the statement which (deliberately?) implies the energy being pushed into your car is coming directly from the sun and into those panels. As we know, any panel that fits over the top of a charging station isn’t going to fully charge a tesla in 39 minutes. But it might be able to run the electronics and close some contactors connecting your car to the grid.
It just dawned on me that when they say awning, they’re not talking about something directly over an EVSE to give you a bit of protection from the weather when plugging the car in. They’re talking about the entire canopy you see over all the pumps at the gas station, which is a whole lot closer to a 15m square than what I was picturing. Maybe, at least in theory, their statement could be true (on a perfect day, for a single car at a time etc).
https://www.designnews.com/sites/designnews.com/files/Tesla%20Supercharging.jpg
As I said, the news item about a similar installation being advertised, was for single-stall installations and was Level-2 charging. Basically, say you used 50 miles of range getting to work, you plug into this and by quitting time the car is fully charged to the recommended 80%-90% level, at no cost to the employer (except the tens of thousands of dollars to install this thing).
Or you build the equivalent on your roof. I have a lot of friends who charge their cars and their entire house with their roof solar arrays. One guy is also paying his friend’s entire electric bill. (Net metering.)
Granted, they live further south than the UK, being in America. But they are in the northern tier of the US, in Massachusetts, New York, and Illinois.
sunlight is physically contains 1kW/m^2 at the equator, and good PV can then give 40% efficiency, so 400W … which is why they still want to find ways to improve efficiency…improving from 40% can make it far easier to use PV… But he used 400W as his starting point… the maximum kW/m^2 PV anywhere in the world.
That is absolutely correct, but Solar Panels are rated using STC or NOCT standards. Lets look at STC (Standard Test Conditions) from IEC 61538 :
Someone could have used the rated capacity and not factored in the degradation. In the renewable industry, we often get into questions like these because ultimately this is related to Government funding / taxation.
Please note that the battery rating of kWh is also a nominal value, measured under specific conditions, and may not give the same kWh @ England’s conditions. This is very common with power systems - for example a gas turbine rated for 25 MW is rated for sea level and certain temperatures.
Agree that reporting could be better but my guess is that it will take some time. If you look at Gasoline Car Mileage on new car stickers and the media, you’ll see them exaggerated too.
When I was living in Maine decades ago the local paper had a breathless article about how a guy was heating his “entire house” very cheaply with a modified washing machine. He had replaced the basket and agitator in a top-loader with a solid cylindrical bucket and had a second cylinder that fit inside. The space between the two was filled with oil and the agitator motor drove the two cylinders back and forth, the shear action on the oil heating it. A blower blew the warm air out the top of the washer cabinet.
I didn’t see how this was more efficient than resistive heating but when you read the article, it turned out he would use the contraption to heat his bedroom when he was in it, then trundle it into the kitchen while he made breakfast, then into the living room while he read the paper. He might have been heating the whole house but it was one room at a time.
You cannot talk about solar capacity without talking about capacity factor, which is dismal for solar. Especially so in the UK. And especially so in winter. And especially for awning installations, which are not at the right angle and likely not in the correct direction for efficiency.
The credulous media almost always reports on solar by using advertised capacity. “New 5 MW solar installation opens, powering up to X homes!” Then you find out that actual output (capacity factor) from solar in North America ranges from 24% in the best places to about 16% in the worst.
Here in Alberta, our solar returned 6.6% of rated capacity for the month of December. Solar is ridiculous in cold northern countries or countries shrouded in regular cloud cover.
He also built himself a fine car one piece at a time.
Stranger
Since resistive heating is 100% efficient, probably not.