Can anyone do the math for a fully solar powered Supercharger site?

[thegruf]

I keep hearing about the possibility for Tesla to do this, but don't know enough to do the math.

The reason I think it might become increasingly relevant is that with ever more "extreme" claims being made for charging speeds, the delivery of the power from the grid has to be a major limiting factor and huge cost.

Tesla again have the possibility to beat the competition down with the integration of in-house solar and powerwalls for charging.

But how much solar is needed and how many powerwalls for eg a 10 bay site?

 

[SDRick]

My hunch is the math and land required is not very pretty or we would be seeing solar powered super chargers,. I hope I am wrong since my ground mount solar powers my house and Tesla with zero paid annually to SDGE That math works great for me for now and as long as I have net metering.

 

[ewoodrick]

It's pretty simple. 100W panel for $100. Each is 40 in x 26 in.
A 120kW charger requires 1200 panels when each is producing full capacity.
Then you need to add some batteries for night and increase the number of cells to allow the batteries to charge. (Maybe 2-3+ more cells???) And this isn't including all of the ancillary electronics.

And if you arrange the cells in 30x40 cells, that's 100ft x 86ft for the original 1200 cells.

Multiply by 5 for a 10 bay Supercharger.

 

[swaltner]

Like everything, "It Depends". If you're talking about a supercharger site in the middle of summer located in the middle of nowhere in the Midwest (for example, western Kansas) that just has a couple people stop by each day for their cross-country travels, that could be covered by a relatively small 10-20 kW solar installation. If you're talking about supplying all the power for a busy location in California in the depths of winter, your numbers look a lot worse. As is the case for all SI units, the units pretty much tell you what needs to be done.

Your basic calculation is estimate daily kWh needs and then use PVWatts to calculate the size of the solar array that could supply that much power on average on a daily basis.

Getting the kWh/day demand for a site is where you're going to make a lot of assumptions (guesses for us, real data for Tesla). Example calculations could be as follows:

• Busy Location
• 80% busy from noon to 5:00 PM: average of 116 kW/supercharger pair * 5 pairs of superchargers * 5 hours = 3,625 kWh/day
• 50% busy from 5:00 PM to 8:00 PM and 9:00 AM to noon: 72 kW/pair * 5 pairs * 6 hours = 1,800 kWh/day
• 10% busy from 8:00 PM to 9:00 AM: 14.5 kW * 5 * 13 = 942 kWh/day
• Total: 6,367 kWh - That's 128 cars getting 50 kWh (partial charge) over the course of the day

• Mostly Idle Location
• 5 cars per day taking on 50 kWh/car = 250 kWh/day

Now visit PVWatts at PVWatts Calculator to design a system that could produce that much energy...

PVWatts data for California:
Need 2.45 MW of solar panels to cover that daily usage all year round - PVWatts says 2.45 MW (2,450 kW) of solar would generate 200,819 kWh in December. That's 6,478 kWh/day in December, but it also WAY over produces in summer - 14,609 kWh/day in July. 2.45 MW of solar using 325 W panels (77" x 39" or 20.85 sq foot each) would require 7,539 panels - That's 157,188 square feet or 3.61 acres (and that's without ANY gaps between the panels)

PVWatts for mostly idle site in Kansas:
75 kW site (230 panels at 325 Watts Each) would generate 377 kWh/day in July and 191 kWh/day in December. That would be almost 4,800 square feet for that many panels.

Those are the rough calculations that you need to do. You could adjust your assumptions on the utilization of the location; where the site is located in the US (average weather patterns influence solar production); if you're trying to cover the power demands on average, only during the summer (coming up short otherwise), in the winter (overproducing the rest of the year). Any of those changes could make wild swings to the amount of solar needed, but it's a large amount of surface area no matter what you do. While roof-top solar is a great match for the residential and many commercial locations, it doesn't really line up with how dense (peak kW/square foot) the power demands of a Supercharger site are. To make a meaningful dent on the energy or power demands of a Supercharger site, you need a LOT of solar panels.

 

[mswlogo]

Keep in mind that powerwalls alone can solve a lot issues as well by storing power during off peak to offset power demand during peak usage. How much waste that adds I’m not sure.

 

[SDRick]

To begin to answer the question accurately, are we talking grid tied or off the grid?

 

[thegruf]

@swaltner - thanks for your analysis. Seems like a good ballpark to me.
A small local field of PV required - doesnt seem too excessive, urban locations obviously more of a challenge.

I'm not sure whether solar can deliver the current though and presumably this is where Powerall type technology could boost peak power, plus offer storage for 24h operation. So how many powerwalls?

My line of thought really apart from the obvious eco aspect, is how much of an advantage does Tesla have over the competition by having all the technology in-house?

As for tied or off grid as per @SDRick comment - well I guess it is tied unless the grid (for security of supply) is not available.
But this also introduces further options to Tesla where a certain level of power is available at manageable cost, but to upgrade to bigger power might involve excessive charges from the utility maybe because a new sub-station could be required, so a part-part solution becomes highly attractive.

 

[arg]

But this also introduces further options to Tesla where a certain level of power is available at manageable cost, but to upgrade to bigger power might involve excessive charges from the utility maybe because a new sub-station could be required, so a part-part solution becomes highly attractive.

I think this was the original idea (back in 2012). With a 1-stall or 2-stall site, it can't actually service many customers in a day (arriving at random) without unacceptable queueing. If 1- or 2-stall is enough for your actual level of traffic, then it's going to be idle most of the time, and so a plausible amount of solar and/or use of the spare capacity of the existing (LV) electrical connection at the site is probably enough to cover the average power drawn across the day. Batteries then allow you to meet the peak demand.

However, the huge success of Model S soon outgrew the 2-stall sites. Once you get to a larger number of stalls, the average power is way above what can be done with on-site solar or the likely spare power at most locations - pretty much every supercharger in the US has a dedicated transformer (and probably most do elsewhere too, though it's less obvious).

Once at that level, you _could_ add batteries, or a field full of solar if there happens to be handy land nearby, but at that point it doesn't really make sense to regard these as resources dedicated to the supercharger - you are better off connecting them to the grid and selling the output to the highest bidder (which might be your own use for supercharging, but often won't be).

 

[Vogon]

In a previous life I was a solar expert (but retired for 8 years). What Telsa could/should do is install solar covered parking at all their charging stations and then grid tie the power the solar system generates to the grid. This would:
-reduce the carbon footprint for the charing stations (from the grid)
-promote/advertise their solar products
-provide those of us charging, shade or protection from the rain.
The footprint of the panels installed over the car does not generate sufficient instant power to charge the battery (especially at supercharging rates) but the solar panels are like magic; they generate power when the sun shines and feed that power into the grid.