Number of Solar Panels to power a Level-2 EV charger?

Thread Starter

b3an

Joined Feb 12, 2024
16
I am working on a project for my intro to engineering class. We are theoretically designing a EV charging station powered by solar panels. I found an example level 2 charger that says it is 9.2kW at 240V AC Lowes, and a solar panel which is 400W at 43V a1solar. How many solar panels would I need to power this charger? Is it basic math 9200W/400W? or is it more complicated?
 

crutschow

Joined Mar 14, 2008
34,681
Is it basic math 9200W/400W? or is it more complicated?
It's definitely more complicated.

That formula works for 100% efficiency with a noon-day sun directly on the panels.
You need to factor in the overall efficiency of converting the DC solar panel output to the 240Vac, plus how long during the day do you want that power to be available?
 

Thread Starter

b3an

Joined Feb 12, 2024
16
plus how long during the day do you want that power to be available?
This is just a freshman level class, so I don't want to get too crazy with it haha. But we are just theoretically designing a kind of rest stop/ 7-Eleven to charge EVs. So would ideally want 24-hour availability. I am just trying to find a rough estimate of how many solar panels needed per level-2 charger.
 

WBahn

Joined Mar 31, 2012
30,242
I am working on a project for my intro to engineering class. We are theoretically designing a EV charging station powered by solar panels. I found an example level 2 charger that says it is 9.2kW at 240V AC Lowes, and a solar panel which is 400W at 43V a1solar. How many solar panels would I need to power this charger? Is it basic math 9200W/400W? or is it more complicated?
That gets you in a very, very rough ballpark and sets a minimum number of panels. If your theoretical budget or space or other constraints is already exceeded by that, then you are done and know the project isn't feasible. A better ballpark figure would be twice that, but it is still ballpark.
 

WBahn

Joined Mar 31, 2012
30,242
This is just a freshman level class, so I don't want to get too crazy with it haha. But we are just theoretically designing a kind of rest stop/ 7-Eleven to charge EVs. So would ideally want 24-hour availability. I am just trying to find a rough estimate of how many solar panels needed per level-2 charger.
It's impossible to say what is expected and what is too crazy without knowing a lot more about the course and the assignment. Having said that, the more research you do and the more issues you at least identify, the better the grade you can expect.

If you want 24/7 availability for the charger, you have a lot of other issues that need to be considered. How are you going to power the charger at 2 am? How are you going to deal with extended periods of cloudy days? What about the difference between winter and summer at whatever location you are going to theoretically install this at? How do you take into account the changing angle of the sun over the course of the year? These, and more, are pretty basic issues that should be identified and dealt with, at least approximately, even by someone doing this as a high-school level assignment. There are other issues, such as the effect of temperature on system performance, that might be identified as considerations, but can reasonably be left as things yet to be accounted for in the actual design.

Starting from an example of a charger found online is not a bad starting point, but what if that particular charger is overkill? Or substandard? A bit of research time should be spent on finding out just what is actually required to be considered a Level 2 charger is almost certainly time well spent -- if nothing else it let's you put that information in your report and confirm that the charger you have chosen for your system actually qualifies.
 

Thread Starter

b3an

Joined Feb 12, 2024
16
It's impossible to say what is expected and what is too crazy without knowing a lot more about the course and the assignment. Having said that, the more research you do and the more issues you at least identify, the better the grade you can expect.

Thank you for your insightful feedback. At this stage, we are primarily focused on gathering rough estimations and brainstorming ideas. Our group project is currently in the design phase, and this current assignment is structured to initially emphasize the generation of ideas, sketching potential designs, and estimating costs.

We are aware that in-depth research into energy calculations, materials, compliance with codes, comprehensive cost analysis, and model development is crucial. However, this deeper dive into the technical aspects will follow our current phase. At the moment, our goal is to lay a foundation of ideas and basic understanding, from which we can build more detailed and researched plans.

Your points about the 24/7 availability of the charger, power sources during off-peak hours, weather considerations, and seasonal variations are indeed vital. These factors will be addressed more thoroughly in the subsequent stages of our project. I really appreciate your input
 

crutschow

Joined Mar 14, 2008
34,681
Definitely want battery storage units for our design, I feel that would be very beneficial for night hours.
So the next question to answer is, on average, how many cars do to want to charge in a 24 hour period, and how much charge per car will be taken.
Note that a 9.2kW Level 2 charger only adds about 30 miles of charge per hour to a typical EV, since their "mileage" is typically a little over 3 miles/kWh.
 

Thread Starter

b3an

Joined Feb 12, 2024
16
So the next question to answer is, on average, how many cars do to want to charge in a 24 hour period, and how much charge per car will be taken.
Note that a 9.2kW Level 2 charger only adds about 30 miles of charge per hour to a typical EV, since their "mileage" is typically a little over 3 miles/kWh.

Since this is theoretical, we're thinking about 20 - 30 EV chargers and have it run like your typical gas station. My interpretation of the project goals are being able to make a Bill of Materials, do an analysis of costs and energy calculations, look into codes/standards for charging stations, and design sketches which will become 3D models.
 

BobTPH

Joined Jun 5, 2013
9,132
Just for some perspective, my home solar system has 23 400W panels ( coincidentally, total 9200W).

Averaged over a year, it produced 23KWh per day. So, basically, each panel is producing about 1KWh per day.

So if you want to power 20 chargers, with each providing 10 hours of charging per day at 9.2KW you will need:

9.2 x 20 x 10 or 1840 panels.

And a ridiculous amount of battery storage. The cost would be in the 10’s of millions of dollars.
 

crutschow

Joined Mar 14, 2008
34,681
we're thinking about 20 - 30 EV chargers
As BobTPH noted, that's not even close to feasible.

Did you not understand what I said about the amount of energy you need?
You will be hard pressed to support even one charger with a practical number of panels.
You'll get an F in you engineering class if you don't do a feasible engineering design for this project.
Engineering is determining what can realistically be done, not just thinking about what pie-in-the-sky thing you'd like done.
 

WBahn

Joined Mar 31, 2012
30,242
Since this is theoretical, we're thinking about 20 - 30 EV chargers and have it run like your typical gas station.

My interpretation of the project goals are being able to make a Bill of Materials, do an analysis of costs and energy calculations, look into codes/standards for charging stations, and design sketches which will become 3D models.
I don't think I've ever seen a gas station with twenty pumps, even the big over-the-road gas stops seldom have more than about a dozen (which is not to say that such stations don't exist, they might).

But that's fine. You can start off with whatever goal you want, but just because it's only on paper doesn't absolve you of the need to, at some point, bring things into the world of the possible. So you need to determine how many chargers are at least within a reasonable realm of being practical in all respects.

Doing a cost analysis is fine, but that is not what decisions are based on. Consider the following -- you own a business and have two opportunities available to you to expand your business. The first will cost you $100,000 and the other will cost you $200,000. Is that enough to make your decision? What if the first will generate $8,000 in revenue in each of the next ten years, but the second will generate $80,000/yr over that same ten years. Things look a lot different now, don't they.

This is why the pie-in-the-sky crowd keeps talking about how the solution to the EV range issue is to treat the batteries the same way that we treat BBG propane tanks where you pull in and just exchange your drained batteries for a set of charged ones. Sure, on paper it looks great and the only hurdle would seem to be getting batteries standardized and modular, which seems like something that should be very doable. But it completely ignores the very huge difference between propane tanks and battery packs. With a tank, the store is taking the risk of selling someone $30 worth of propane and, occasionally, giving them a good tank and getting a bad tank in exchange. But that is a pretty rare event and the tank costs them something comparable to what they charged for the propane, so they build the expected cost of replacing bad tanks into the price for the propane. If 1% of the tanks they get are bad (and that's on the high side), they only need to add in about 30 cents to the price to cover it.

But now if you try to do that with EV batteries, you are going to charge someone for, say, $15 for the charge but are accepting the risk that the $10,000 battery pack they are getting in exchange is good. If 1% of those are bad, they need to add $100 to the cost of the charge in order to cover it. Who is going to take that risk? Who is going to pay $115 every time they stop for a charge? Yet this idea still gets pulled out and pushed on a regular basis.

Don't fall into that trap with your project. You need to consider not only how much it will cost to install the system, but you also need to consider how much revenue it will generate over its expected lifespan. Those solar panels and the batteries and everything else aren't going to last forever.

Then you need to compare that to some reasonable alternative. For instance, if I have the option to invest $100,000 in something that will produce revenue of $20,000/year for five years and have a salvage value of $40,000 at the end of that lifetime, so at the end I have $140,000 from my original $100,000. Is that a good investment? Consider the alternative of parking it in a Certificate of Deposit at 5% for five year. That may only generate about $5,000/year in interest, but at the end of the five years I still have the entire $100,000 as well as all of the interest (which totals out to about $128,000). On paper, it seems like the first option is a better investment than than the CD since I expect to end up with about $12,000 more, but that doesn't take into account risk. The CD is guaranteed to be worth $128,000 at the end of the term -- it is a secured, insured, investment. What if there is a 20% risk that the equipment will fail after four years, making it only worth $5,000 as salvage. If that happens, I would only generate $85,000 from my $100,000 investment. Taking that into account, my expected return is not just $120k and that CD is looking pretty atractive.

Any kind of analysis like this involves assumptions and estimates and simplifications. For instance, unless there is some strong basis to do otherwise, it is often assumed that the equipment will have no salvage value at the end (and sometimes it is assumed that not only does it not have any salvage value, but that you might actually have to pay to have it removed/recycled/whatever).

For a project like you are doing, you don't need to get carried away. Make major simplifications and reasonable assumptions based on very cursory research. The very fact that you are even attempting to do the analysis will likely set you head and shoulders above your peers.
 

MrAl

Joined Jun 17, 2014
11,565
This is just a freshman level class, so I don't want to get too crazy with it haha. But we are just theoretically designing a kind of rest stop/ 7-Eleven to charge EVs. So would ideally want 24-hour availability. I am just trying to find a rough estimate of how many solar panels needed per level-2 charger.
Hi,

Wow, 24 hour operation, do you happen to live in Alaska? :)
Yes, battery storage, but you are talking a HUGE project with high cost. Consider calculating the number of battery cells you would need to supply power for maybe 18 hours of the day with only 6 hours of charging when the weather is overcast. A few days of cloudy weather and there is little power available unless you have an extraordinary number of panels.
What happens is after the first cloudy day the available power drops somewhat, then after the next cloudy day the power drops more, etc., etc. When a sunny day finally comes it's a blessing, but until then you may not have much power to do anything with.
There are other issues that come up too.

Are you talking about building 20 charging stations that can supply power 24/7 that work solely on solar ? Yikes, that's a project for sure.
 

crutschow

Joined Mar 14, 2008
34,681
This is why the pie-in-the-sky crowd keeps talking about how the solution to the EV range issue is to treat the batteries the same way that we treat BBG propane tanks where you pull in and just exchange your drained batteries for a set of charged ones.
What "pie-in-the-sky crowd" are you referring to.
I've never heard of a serious proposal to do that.

The range issue is pretty well resolved with EVs that now have over a 250 mile range, and with there being numerous high-power DC charging stations along major highways, that can charge their battery to 80% in 20 minutes.
That's not much longer than I usually take on a trip to get gas, go potty, and eat a snack.
 

WBahn

Joined Mar 31, 2012
30,242
What "pie-in-the-sky crowd" are you referring to.
I've never heard of a serious proposal to do that.

The range issue is pretty well resolved with EVs that now have over a 250 mile range, and with there being numerous high-power DC charging stations along major highways, that can charge their battery to 80% in 20 minutes.
That's not much longer than I usually take on a trip to get gas, go potty, and eat a snack.
How 5-minute battery swaps could get more EVs on the road
Battery swapping station for electric vehicles: opportunities and ...
The pros and cons of EV battery swapping plans | Popular Science
Why charge an EV when you can just swap its battery?
Ample raises $160 million on the promise of battery swapping
Battery Swapping: a Promising Future for Electric Vehicles
A Comprehensive Review on Electric Vehicle Battery Swapping Stations ...
Ample's next-gen battery swap station cuts swap times to 5 minutes
Battery swapping - Wikipedia
A Fully Charged EV Battery in 5 Minutes? This Automaker Says It ... - PCMag
The Current State of EV Battery Swapping - NIO
Battery swapping station for electric vehicles - ifm
EV Battery Swaps: Now as Fast as Filling Your Tank - CNET

And that's just from the first page of Duck Duck Go searching for "EV battery swapping stations".

Tesla was pushing it hard at one point about a decade ago, charging $80 for a swap (about $105 today -- so right around that $115 dollars I came up with as a WAG in my post), and then abandoned it when customers mysteriously didn't want to pay $80 to get about $10 worth of electrical energy and swap out their hugely expensive battery in their brand new Tesla and for one that they had no idea how good a shape it was in. Gee, imagine that.

Now, there are some instances where this approach makes sense -- particularly where you have a fleet of vehicles and are swapping out batteries you own for other batteries that you own. It actually has always been common in large warehouses for electric fork lifts and such.
 

MrAl

Joined Jun 17, 2014
11,565
What "pie-in-the-sky crowd" are you referring to.
I've never heard of a serious proposal to do that.

The range issue is pretty well resolved with EVs that now have over a 250 mile range, and with there being numerous high-power DC charging stations along major highways, that can charge their battery to 80% in 20 minutes.
That's not much longer than I usually take on a trip to get gas, go potty, and eat a snack.
This has been talked about a lot in the past. Of course it takes some serious commitment, but there are a lot of advantages.
First, the battery is swapped out so with the right machinery it could be really fast. Maybe even faster than pulling up to get gas.
Then, there is the fact that the owner of the car does not have to own the battery, but rather 'rent' it. That means no huge cost to replace the battery.
After that, the owner does not have to worry about charging at home, which takes a lot of energy.
Probably the best advantage overall is that the charging does not have to take place on site. The batteries can be charged remotely and then shipped to the recharge station. That's a HUGE advantage because then the charging locations can be more easily constructed and melded into the current infrastructure, much better than in every location.
A disadvantage of course is that the charging stations would have to be a lot bigger to be able to store the battery packs. If 1000 customers pull up in one day, they would have to be able to store over 1000 battery packs, which are kind of big. Another one is the price control, which could be governed mostly by each location.
The biggest problem is probably how to get manufacturers to agree to using a universal battery pack. That's probably going to be hard to do.
 

BobTPH

Joined Jun 5, 2013
9,132
don't think I've ever seen a gas station with twenty pumps,
To be fair, a gas fill-up takes what, 3 minutes? So if an average charge takes an hour, an EV “gas” station with 20 chargers would have the same capacity as a gas station with one pump.
 

nsaspook

Joined Aug 27, 2009
13,420
Since this is theoretical, we're thinking about 20 - 30 EV chargers and have it run like your typical gas station. My interpretation of the project goals are being able to make a Bill of Materials, do an analysis of costs and energy calculations, look into codes/standards for charging stations, and design sketches which will become 3D models.
Once you do the calculations, it will be easy to see that a transition to a EV requirement is not something that can or will happen with just solar. We will need massive base load generators of some type like nuclear fission plants to supply the transportation grid.
 

WBahn

Joined Mar 31, 2012
30,242
To be fair, a gas fill-up takes what, 3 minutes? So if an average charge takes an hour, an EV “gas” station with 20 chargers would have the same capacity as a gas station with one pump.
Fair enough, though that underscores even further the challenges involved.

Another related factor that is usually overlooked is that one of the reasons that we have such an extensive gasoline/diesel infrastructure is that it makes economic sense for small stations to exist with just a couple of pumps. Gas stations make very little money off of fuel sales, particularly after shrinkage effects. But they are willing to have the two pumps because it brings foot traffic through the door and it is the sale of candy and soft drinks from those quick stops that make it worthwhile. But for that to work, you need quick turn around. With EV charging, you either need LOTS of charging stations or you need to offer people stuff that is commensurate with being stuck there for an extended period of time (or some combination of the two) and draws a commensurate larger amount of money out of them. But the former is extremely expensive and requires a LOT more space than most small stations will have, can obtain, or can afford, and the latter is problematic because while people may occasionally be willing to spend the ten to twenty times as much money as they would at a 7-Eleven when they get gas, they aren't going to be willing to do it every time they get gas. In fact, the total amount they are willing to spend on non-gas items is probably not going to be much higher than it is now. Which is not to say that there aren't opportunities for shifts to happen. Places that people go for extended periods of time already and that already have large lots available, such as grocery stores, could become a focus for charging stations. But there's still that cost factor.
 
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