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It won't be too long before we see tow trucks with built-in, V2V charging capabilities.

It is mobile devices like this, though, that make me wonder why businesses can't just install low-cost DC-DC chargers run off of batteries linked to their local power supply. Even a 250 kWh battery bank with a basic 240 V @ 40 A power hook up would be able to charge 10 to 12 EVs per day.
Let's see. 240V @ 40A would take about 8 hours to charge a Bolt. That's three Bolts per day. To get to 12, each Bolt only gets a 25% boost.

Put another way, 240V @ 40A = 9.6kW. Assuming 90% efficient, it would take about 29 hours to charge the battery bank.

This setup would only be good for a convenient boost. How much would you pay for a 25% boost? There would have to be a whole lot more EVs on the road for this to make economic sense for a business. If someone did this today, it would only be to make a statement.
 

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This setup would only be good for a convenient boost.
The idea is to get your car off the side of a busy highway. A half hour charge could get you 12-16 miles, hopefully to an actual charger. When they bring you a can of gas, the idea is that you will head to the nearest gas station, not continue on your trip.
 

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The idea is to get your car off the side of a busy highway. A half hour charge could get you 12-16 miles, hopefully to an actual charger. When they bring you a can of gas, the idea is that you will head to the nearest gas station, not continue on your trip.
I was replying to the idea of a 250kWh battery with a 240V/40A grid connection at some business location, not the portable solution.

I don't expect to see solutions like this at tow trucks until BEVs reach a critical mass. As noted by others, it's not that bad to just tow you to the nearest charger and leave you there.

I can also image the more adventurous drivers carrying one of these just for emergencies. Kind of like you see long-distance / off-road drivers carrying a jerry can of gasoline "just in case", despite having gas stations every 5 miles most of the time.
 

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Let's see. 240V @ 40A would take about 8 hours to charge a Bolt. That's three Bolts per day. To get to 12, each Bolt only gets a 25% boost.

Put another way, 240V @ 40A = 9.6kW. Assuming 90% efficient, it would take about 29 hours to charge the battery bank.

This setup would only be good for a convenient boost. How much would you pay for a 25% boost? There would have to be a whole lot more EVs on the road for this to make economic sense for a business. If someone did this today, it would only be to make a statement.
Yes, I should have been more clear. I'm talking about DC fast chargers run directly off of a 250 kWh battery, which itself is recharged off of a standard 240 V @ 40 A power connection. In other words, say four 50 kW DC chargers all hooked up directly to the 250 kWh battery with DC-DC converters. The 250 kWh battery is what would be charged off the grid with a 240 V @ 40 A (9.6 kW) charger.

Basically, starting with a full battery (250 kWh), you have enough energy to charge six to eight EVs with 30 kWh to 40 kWh sessions. The 240 V charger would be recharging that 250 kWh battery throughout the day, and at 9.6 kW, it should be able to nearly refill the 250 kWh battery in 24 hours (probably closer adding 200 to 220 kWh in a 24 hour period).

If the usage for the site was too high (i.e., draining the battery plus whatever it was recharged from the 240 V grid connection), the answer would be to add more battery capacity. In order for that to happen, you'd need to have 15 sessions a day averaging 30 kWh drawn. Adding a second 250 kWh battery would increase the max capacity to over 20 DC fast charging sessions per day. In order for that to happen, each 50 kW charger would need to be occupied and charging at full power for over 4 hours per day. All of that off of a 240 V @ 40 A power hookup that can be found or easily installed at most businesses.

Of course, now that I'm spit balling, I actually think the better configuration might be four of ChargePoint's CPE units linked together for a max output of 250 kW when one charger is in use, 125 kW each when two chargers are in use, and 62.5 kW each when four chargers are in use. :unsure: The idea with the faster chargers being, the sooner someone drains the battery, the sooner the battery can start trickle charging again.
 

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If the usage for the site was too high (i.e., draining the battery plus whatever it was recharged from the 240 V grid connection), the answer would be to add more battery capacity. In order for that to happen, you'd need to have 15 sessions a day averaging 30 kWh drawn. Adding a second 250 kWh battery would increase the max capacity to over 20 DC fast charging sessions per day. In order for that to happen, each 50 kW charger would need to be occupied and charging at full power for over 4 hours per day. All of that off of a 240 V @ 40 A power hookup that can be found or easily installed at most businesses.
Well, no, the answer wouldn't be to add a new battery on the same connection. You would need a new 240V/40A hookup for each 250kWh battery. As you said, that hookup can only provide maybe 200-220kWh in a 24h period. Adding more battery only will let you handle a short-lived (less than two days) burst, but to sustain that rate you need to double your connection to the grid.
 

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Well, no, the answer wouldn't be to add a new battery on the same connection. You would need a new 240V/40A hookup for each 250kWh battery. As you said, that hookup can only provide maybe 200-220kWh in a 24h period. Adding more battery only will let you handle a short-lived (less than two days) burst, but to sustain that rate you need to double your connection to the grid.
Sure, if you could establish that it was a sustained demand of over 20 cars per day, then more site power would be required. At that point, you'd also likely want on-site solar. I'd say that you'd want to reserve adding second 240 V @ 40 A circuit as a last resort, though in conjunction with a second 250 kWh battery, that would guarantee support for a sustained demand of 30+ cars per day and a peak demand of 40+ cars per day.

For me, this type of setup would make the most sense for travel corridors that typically see low loads most of the time with peaks on weekends and holidays, so the total battery capacity would the key issue. Even in California, with all of our EVs, seeing 30 cars per day outside of city centers would be extremely unusual.
 

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Fair. I guess most travel bursts are typically two days long (i.e. weekends). If the battery is sized to handle the weekend, then the grid connection really only needs to recharge them in the course of a week. I'm hoping to see more of these battery-assisted sites. With more experience, the industry should get pretty good at right-sizing them.
 

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Fair. I guess most travel bursts are typically two days long (i.e. weekends). If the battery is sized to handle the weekend, then the grid connection really only needs to recharge them in the course of a week. I'm hoping to see more of these battery-assisted sites. With more experience, the industry should get pretty good at right-sizing them.
I've definitely been seeing more battery assisted sites, though they are set up to be capable of a 100% constant load. The batteries are really only there to offset demand fees, as far as I can tell. I'd really like to find out how much energy storage the Envision Solar sites we have going in at California rest stops have. Whatever it is, it doesn't seem to be enough because the sites are down more often than not, and even during the daytime, the power is often limited to maybe what the solar panel arrays are currently gathering.
 

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VW mobile charging solution (360kWh) fed by a standard 30A power source. Max output is 100kW DC, and up to 4 simultaneous charge sessions.
I really like this because it solves two problems with one installation: EV charging and grid storage for intermittent sources of green energy. If stations like this could be widely deployed in conjunction with widespread EV adoption it could be a double whammy for fossil fuel consumption.
 
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