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The Electrek site has an article on Tesla's new mobile supercharger that uses a container-sized battery to supplement fixed Supercharger locations during peak travel times, but the headline is "Tesla deploys new mobile Supercharger powered by Megapack instead of diesel generators".
The automaker is using its smaller "Urban Supercharger" stalls all around the flat trailer on which they also installed a large Megapack.
Interestingly, owners are reporting that the stalls are capable of delivering 125 kW, which is not quite comparable to the new Supercharger V3, but it is impressive power for a mobile station.
[...] This is awesome. Way better than Tesla's previous mobile Supercharger stations, which were often powered by diesel generators.
However, Tesla still needs to charge those Megachargers, but they can potentially connect them to better energy sources than diesel generators.
It will be interesting to see if Tesla starts using more of these.
An obvious question is, which is more efficient--charging a big battery (one hopes from an efficient and clean power source) and then using that battery to charge a bunch of cars, or, charging the cars directly from a diesel generator (which can be pretty efficient, but nothing like a big fixed power plant)?
Are there any Tesla owners here? Have you come across a diesel supercharger, and how did it feel to hook your cool, quiet car up to a noisy, smelly monster?
(Score: 5, Informative) by PhilSalkie on Monday December 09 2019, @06:42PM
Two Model S here - P85D and P100DL, I've put about 70,000 miles on them so far, most of that distance road trips. Over 400 supercharge events at more than 70 locations east of the Mississippi, never saw a temporary Supercharger setup or a diesel generator supplying power - and never had to wait more than 10 minutes for a charging spot, and that only about twice. (There's an awesome website called "Teslafi" that logs all that driving and charging info for you.) House has 13KW of solar panels, and any electric power we buy is wind generated, so the day-to-day short term driving is all artisinal, locally sourced electrons. US electrical grid's around 27% coal, 35% NatGas, less than 1% diesel - and that mix is using less coal every year. Overall less coal here on the East coast, but I've seen analyses that suggest that even a battery EV charged from 100% coal generated power is still cleaner overall than a gasoline or diesel vehicle. Most people don't think of the large amount of energy expended in refining and transporting liquid fuels - it doesn't come out of the ground as gasoline, but natural gas requires very little refining (there's actually a separation process that splits off the more profitable fractions like butane and propane - but you literally could stick a pipe into a well and run a generator from it, no refining required.) Coal's no picnic to transport, but it's pretty much dig it up, move it to the power plant, and burn it, and the efficiency of a coal plant (in the mid 30% range) times the line losses getting the power to your actual car's battery beats a gasoline car's 20-30% times the losses incurred in fractional distillation (essentially vaporizing all the liquid and re-condensing it), energy involved in creating and adding octane modifiers and detergents, and the energy of transport required to get it to your gas station. Another way to think of those equivalences is by the market price you pay - if I pay $0.10 / KWh for electricity (US national average) to feed my 2.5 mile / KWh electric car, that's roughly equivalent to a 45 MPG hybrid paying $2.00 / gallon for gasoline - so (less the amount of governmental subsidy which may or may not be pouring down the throats of big oil or big solar) basic market rates say that electric propulsion's more efficient than gasoline or diesel, because I can't fuel a gasoline vehicle as cheaply as I can recharge a car. (And an electric vehicle requires no oil changes, has minimal brake wear, requires less general maintenance overall, and when the battery gets old enough that it's no longer usable for powering a vehicle, it'll still work well enough to be used as a house power battery.)
As for Megapack usage, the large current demand of supercharging a car has impacts on the local grid and on the cost of the electricity to the charge system vendor (Tesla, in my case, or Electrify America, or ChargePoint, etc.) Commonly, the more current you draw at one instant (the "Demand Load"), the higher the rate you pay for power _For The Entire Billing Period._ That is, if you never exceed an instantaneous draw of, for example, 50 KW, you may pay rate X for one KWH. If you ever exceed 50KW in a month, you may pay 1.5X - if you ever exceed 100KW, you may pay 2X. (These numbers are all negotiable items when large companies buy lots of power from suppliers - but there's definitely going to be a boost in price at some demand load.) You can get better rates if you let the power company communicate with your equipment and tell it when it can run - that's one way utilities can get away with not having enough generation to run every possible air conditioner in the city, they have certain large users they can contact and say "hey, back off on your usage for the next two hours" when there's a projected increase in power demand.
I was involved in installing some 3MW diesel gensets at an Air Force base - they had crazy peak demands due to large test equipment on-base (things like starting up a giant wind tunnel's fan motors.) The USD 10 Million+ that was spent on the generators, fuel tanks, pumps, etc. was expected to be recovered in six months' time due to the ability of those generators to be started _before_ the wind tunnels, then ramp up to soak up the peaks, then shut off. The savings would be entirely in the demand load differential - not having to pay N times the normal rate because the base drew an extra couple MW for 30 seconds when they started up the fans. The expectation was that the generators would run less than five hours per month.
So, if you put a large battery pack at a Supercharger station, you can program it to suck up power when cars are _not_ charging, then provide it when they're drawing the most load - my car might draw 110 KW for ten minutes, then slowly drop down to 50 KW, or as low as 25 KW if I'm eating lunch nearby and having the car fill up all the way. Having a local power buffer like a Megapack limits the demand load on the grid, which keeps Tesla's electric bill lower. It also smooths out the demand presented to the power generation stations, which might keep the utilities from needing to start up peaker plants to handle the sudden changes in load. Lots of utilities are now looking at exactly that on a grand scale (check out the Hornsdale Power Reserve in Australia) - they install huge battery packs to store excess power when it's available (or when it's cheap, or both) and release it when it's needed most. That "power rate arbitrage" can make huge amounts of money for the owner of the battery system - spot pricing for electricity is notoriously variable, primarily because large plants are slow to spool up, and small peaker plants are inefficient and expensive to own and run because they cost a lot but don't run very often.
Interestingly enough, lots of large buildings have been doing much the same thing with their air-conditioning loads for many years - they freeze large amounts of water at night in "Ice Build" rooms deep in the building, and use that ice as a heat sink during the day when power is more expensive and there's more load on the HVAC system. This is primarily because utilities have large amounts of excess generation ("Base Load") capacity at night, when few people are using power, and therefore power is artificially cheap. Once more solar power generation is installed, industries can and will take advantage of power price fluctuations during the day to store power - either in batteries, in ice build rooms, or by running energy intensive systems only when power is cheap. (Think of a large machine that shreds junk cars. You probably don't have to run that 24/7 - maybe only ten hours a week. If you choose to run it the ten hours that power's very inexpensive, it's a win for you, and helps balance the grid's usage.)
Most of the power rate infrastructure (at least in the US) isn't designed for the information age - it's older equipment, and there's not much ability yet for a consumer to, for instance, heat their water or charge their electric car when it's cheapest for them and best for the utility. The communications infrastructure is in place, but the power switching equipment and regulatory structure is not. I can't plug my water heater in to the internet and set up some sort of time/price based billing - yet - but that day's probably not too far away.