And you'll get all the rocks from the semi in front of you thrown onto your hood.
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And you'll get all the rocks from the semi in front of you thrown onto your hood.
Trying to estimate how the Semi Megachargers would function / be designed.
Looks like the loads will be huge (probably >1MW, and that's just for one connection!) and for short duration (~30 min charge, "peaky") -- which means very expensive to get that power from a utility hook up. Both from just capacity of hookup (1MW connection to grid will be expensive, and peak charges for that amount of electricity will be crazy)
So the obvious solution, as many have noted, is pull from large banks of PowerPacks instead of the grid. The PowerPacks could have a much smaller, near constant "trickle charge" from the grid (plus extra from solar) which would help control costs.
How these could differ from existing Superchargers however, can be interesting. Superchargers are built of stacks of many car charging (AC->DC) modules, and charge essentially directly from the grid (AC from Grid -> DC Car Battery).
If Megachargers will be essentially powered solely from PowerPacks, then they don't need the large amounts of AC-DC converters ($expensive$) that Superchargers use. PowerPack (DC) -> Semi Battery (DC). Not only is this more efficient (less conversion losses) but it would mean the cost of building these charging stations is pretty close to just the cost of the PowerPack + their (smaller) hookup to the grid.
Does this make sense? Am I missing something important? Anyones thoughts on the architecture of the Megachargers?
EDIT: Probably won't be more efficient in terms of conversion losses -- just changes where the conversion step occurs.
Looks like the loads will be huge (probably >1MW, and that's just for one connection!) and for short duration (~30 min charge, "peaky") -- which means very expensive to get that power from a utility hook up. Both from just capacity of hookup (1MW connection to grid will be expensive, and peak charges for that amount of electricity will be crazy)
So the obvious solution, as many have noted, is pull from large banks of PowerPacks instead of the grid. The PowerPacks could have a much smaller, near constant "trickle charge" from the grid (plus extra from solar) which would help control costs.
How these could differ from existing Superchargers however, can be interesting. Superchargers are built of stacks of many car charging (AC->DC) modules, and charge essentially directly from the grid (AC from Grid -> DC Car Battery).
If Megachargers will be essentially powered solely from PowerPacks, then they don't need the large amounts of AC-DC converters ($expensive$) that Superchargers use. PowerPack (DC) -> Semi Battery (DC). Not only is this more efficient (less conversion losses) but it would mean the cost of building these charging stations is pretty close to just the cost of the PowerPack + their (smaller) hookup to the grid.
Does this make sense? Am I missing something important? Anyones thoughts on the architecture of the Megachargers?
EDIT: Probably won't be more efficient in terms of conversion losses -- just changes where the conversion step occurs.
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Kipernicus
Model S Res#P1440
The risk is if a Convoy of trucks shows up, are there enough PowerPacks to charge them all at once? Or even in rapid succession?
Would not be good to have to wait for the PowerPacks to "trickle charge" up again. (I realize that in this case "Trickle" may be a few hundred kW but still it would be a long time for a semi)
Would not be good to have to wait for the PowerPacks to "trickle charge" up again. (I realize that in this case "Trickle" may be a few hundred kW but still it would be a long time for a semi)
Would have to see the numbers to determine which would be more efficient in terms of $$$, over-sizing battery packs to deal with events like that, or simply a massive grid connection with associated fees for direct from grid charging. I expect it will be somewhere in the middle of those two.
I think the Megacharger is just four superchargers. Perhaps by the time Tesla semi is actually released superchargers will be 200kW. So a megacharger would be 800kW. That number seems to work.
But trucks doing regional distribution won't need the full megacharger. They will charge overnight. It is going to be mid next decade before long range trucks are EV. These trucks will have batteries and chargers well advanced from todays products.
The displacement I am referring to is simply the ratio of fuel efficiencies. It is not the primary heat content that you are looking at. A diesel drivetrain has very low efficiency relative to an electric drivetrain. Something around 25% to 90%.
The idea of displacement is that we are substituting one fuel for another given the relative efficiencies of respective vehicles. So have Tesla Semi take the same load along the same route same driving conditions and speed. If the diesel consumes 100 gallons and the electric consumes 900 kWh, then this is a displacement ratio of 9kWh/gal. Note that if you begin with the heat content ratio of 37.8kWh/gal, multiply this times a 24% relative efficiency of 24% = 22%/90% to get to a displacement ratio of 9kWh/gal.
BTW, the reason why I am interested in the replacement ration is that I am primarily interest in energy economic, not physics or engineering. I want to be able to model how much demand for fuel commercial vehicles can displace with electricity as an economic substitute. For example, global diesel demand is about 27.5 million barrels per day. How much electricity would need to be generated per day just to reduce this by 1mb/d. Assuming 9kWh/gal, we would need 378 =9×42 million kWh per day, 378 GWh/d or 138 TWh/year. Very useful to know. Now we can size up how much solar or wind would produce this, about 100GW solar or 50GW wind. Or how much battery capacity is needed in the commercial fleet. If commercial vehicle cycle about 70% of their battery per day, then the fleet needs about 540 = 378 / 70% GWh of capacity. If the average Tesla Semi had 800kWh, then 675k trucks would have that 540GWh capacity sufficient to displace 1mb/d of diesel demand. So one gets an appreciation for the scale of opportunities here involved with taking market share from the oil industry. The displacement ratio is key to understanding impact accross multiple industries. It this displacement ratio is more like 10 than 9 kWh/gal, then the scale of batteries, heavy EVs, and renewable energy contributions need to be about 10% greater to achieve the same impact on oil, and this makes the economics 10% harder to realize. I believe this is why Tesla has put so much care into improving aerodynamics and other efficiencies. We're not just replacing fuels, we are decreasing consumption of total primary energy, and that is what drives a fundamental shift in energy economics.
Put another way we can consider the response of oil and commercial vehicle makers. Tesla is claiming to shave $0.25/mile off the cost of trucking assuming diesel at $2.50. With enough scale, the price of diesel may need to come down to close the gap. Suppose this 25c/mile gap is based on 5 mpg. Then the price of diesel would need to come down $1.25/gal to $1.25/gal for diesel to remain price competitive. Likewise diesel truck makers might need to increase fuel efficiency from 5mpg to 10mpg to stay price competitive at the same price of diesel or find other ways to cut costs. The likely response is that both fuel prices will come down while truck makers improve fuel efficiency and cut other costs. The oil industry will be challenged by both the price competition for fuel and demand lost to higher efficiency diesel trucks. The upshot for consumers is that cost of delivered goods will come down. A similar situation exists for natural gas and coal. They must price compete with each other inbthe electricity market. This keeps natural gas under $4/mmBtu. But both must also compete with wind and solar which are declining in price each year. This I believe is what keeps gas in this country near $3/mmBtu. This is super for consumers. The next step is for commercial EVs to open up price competition between diesel and industrial power rates. As diesel is forced to price compete with natural gas, coal, wind and solar, the price of oil will decline. Natural gas is probably the best measure of the price of energy. One mmBtu of natgas can produce about 125 kWh which via a Tesla Semi can displace about 13.9 gallons of diesel. That is, 1 mmBtu of natural gas can displace 1.8 mmBtu of diesel. Diesel at $2.5/gal is about $19.4/mmBtu. So here we have price competition that will both bring down the price of diesel which is 6x the price of natural gas while reducing primary energy and the emissions that result from combustion. That is we'd all prefer to breath the emissions of 1 unit of natural gas to 1.8 units of diesel while saving money on energy. The fact that some of this natgas can also be displaced by emission free renewables is icing on the cake.
Sorry about using your post as a pretext for launching into a discussion of energy economics, but these are thoughts I wanted to update anyway with newer information.
I would just add that they want solar to be the primary source, not the grid. So mostly you have DC solar to DC battery (semi and stationary) happening. Still trickle in grid power as needed to maintain stationary battery SOC. So some AC to DC, but max power can be just a fraction of peak charging rate.
No a Megacharger should be closer to 1600kW. 400 mile charge in 30 minutes. Stated usage is <2kWh/mi. So 400 miles would be ~800kWh which would take a charge rate of 1600kW to achieve in 30 minutes. (So a Megacharge is closer to 12 Superchargers.)
And that assumes no charging taper.
If they are going to give an 80% charge to a 1MWh battery in 30 minutes, they'll need more than 1.6MW. Maybe 8×250 kW.
Remember Musk saying 350kW charging was child's play.
Even charging 16 trucks 8 hours over night, you'll want 1.6MW combined. So overnight charging let's you go slower per truck, but per fleet you've got massive parallel charging happening.
So I'm thinking large fleets will want their own Megachargers onsite even for overnight charging. If you need 4MW or more for parallel charging, why not have the ability to charge 3 at 1.6 MW each? It would give you more logistical options to charge trucks quickly when needed.
Problems I see with that approach:
1. Fault tolerance: if one inverter goes bad, there is no way to isolate it. You need another 8 contactors to split them off.
2. Short protection/current sharing: if one pack is less healthy, and the motors all call for power, one pack could end up providing too much and blowing its fuse.
3. Wiring: this requires a buss bar with 4x the current handling. All intermediate wiring needs to handle 4x the fault current die to parallel packs. Including the current interrupt rating on the fuse.
Why not leave each pack and motor as a separate unit?
EDIT: 4: Fault handling: with 4 pack connected, who handles an inverter short? Currently, the pack will pyro its fuse if the draw is too high, but with 4 packs, one inverter could pull 50% of max from each and no fuse would blow, unless the inverters also get pyro fuses.
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Quit assuming anything, that's your problem in this. The numbers I provided are the ones you need to use. energy used is energy used regardless of how much makes it into forward motion. If a Telsa uses 2kwh/mile not all of that 2kwh is actually used for forward momentum but you're still counting it. You need to do the same for the diesel., If a truck gets 6mpg it had to use an entire gallon or 37.9kwh of energy to travel that distance, the 25% efficiency is irrelevant because it still used the whole gallon of diesel(37.9kwh)
Assuming 6mpg you need to use the number 6.32kWh/mile when making the diesel/EV comparison. If you want to replace 1M barrels of oil(42M gallons) you need to replace it at a rate of 2kwh for every gallon of diesel. So you'll need 84million kWh (84GigaWatts) of electricity to replace 1million barrels. In doing so you'll save 4.32kwh for every gallon saved or 181,440,000 kWh saved in efficiency or a net reduction of 478,627bbls a day.
It can be "primarily solar", indirectly, by building utility scale solar power stations where possible (in addition to as much solar as they can fit at their charging stations) and selling that direct to the grid, and then essentially buying "their" power from themselves through the grid (even if the actual electrons in question might have been motivated more directly by a non-solar plant closer by, if they generate a net solar output to the grid as big or bigger than what they take in, they're offsetting their power usage accordingly to be "powered by solar").
Plus, they can potentially choose to undercut their power plant competition and force grid rates lower, which if they (and others) can keep building utility scale renewables cheap enough, could effectively drive some of the non-renewables out of business, causing the entire grid to get cleaner. This of course depends on lots of grid scale storage to make up for the loss of various traditional peaker and base load plants, but over a long enough time span it should be doable. They could essentially use economics to both take a profit and force the grid to be cleaner, helping to further push us into a cleaner future.
They could probably build a few more solar panel gigafactories and not even sell the capacity to anyone else, just go into utility scale solar as their own customer (of panels) selling power into the grid, not as a loss but low enough to force change. Of course, that requires insane levels of capital investment up front and long payoff periods (the average cost of solar per kWh might be quite low over the lifetime of a utility scale project, but you still have to finance the construction up front... ), so I wouldn't expect them to become the #1 player in the energy sector overnight, more like 10-25 years...
mmd
Active Member
Can someone explain why we 're comparing to 6 mpg diesel trucks when 12 mpg and 13 mpg trucks are already out there for several years? By 2020 or whenever Tesla will launch its trucks, you can bet diesel trucks will improve even more.
Is The BulletTruck What Semis Will Look Like In The Future?
greencarreports Jan 2014 said:
Here is Daimler's supertruck with 12 mpg back in the ancient ages.
Daimler Unveils SuperTruck; 12-MPG Semi Is More Than Twice As Fuel-Efficient
Anyone wants to do the math with real competing trucks?
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Not sure where the guy got 3/gallons an hour idling. A big truck uses about half a gallon idling. diesels are compression ignition so they only need just enough fuel to keep the crank moving. bobtail a truck will get about 10mpg at 60ish mph. that's 6 gallons an hour. You're telling me that just sitting there it only uses 50% less fuel than propelling 20K lbs down the highway.
Either way trucks can come equipped with APUs that use maybe a gallon of fuel a night, There are some places popping up around the country that have stalls for trucks to park where A/C and power can be pumped in for a fee. I'll use about 1500w/hr just sitting around and 1500-2000w inverters are the most widely used in trucks. The EV semi will celestially help reduce fuel burn at idle but not 3gal/hr.
mmd
Active Member
No surprise there
Elon and his top commanders are famous for pulling numbers out of their re** to fit the stories..Rest assured they sing differently when they talk to real truckers, not just the masses who took the blue pill.
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