[fundatus]

> This will be a logistical challenge for the grid but absolutely fantastic for BYD owners in particular.

Interestingly BYD actually puts batteries next to these chargers that they charge "off peak" to minimise the strain on the grid. So often times cars will actually charge from that battery instead of directly from the grid.

[woadwarrior01]

One of the wonders of vertical integration.

[rogerrogerr]

Tesla often does this too.

[stymaar]

> batteries next to these chargers that they charge "off peak"

I don't think that's what they'll do. Charging off peak means being able to store the entirety of the energy demand for the power station in a battery, which is going to be very expensive (assuming 20 cars charge during peak hours every day, that'd mean having to swallow the cost of 20 cars worth of battery per charging station. Good luck getting a good ROI with that).

Instead I think they'll just use the battery so that they never drain the full power of a charge when a car is charging. Drawing a megawatt of current 5% of the time is putting lots of pressure on the local grid, and it can be mitigated by having a battery with the capacity of a car battery that you charge slowly during the whole day (including during peak hour) and discharge fast when a car is charging (for instance, if in average you have 2 cars charging for 5 minutes every hour, you can draw 166kW continuously instead of having bursts of 1MW consumption).

[alkonaut]

> if in average you have 2 cars charging for 5 minutes every hour, you can draw 166kW continuously instead of having bursts of 1MW consumption)

You definitely need to have that to not load the grid with 1MW, but the question still remains what the capacity of the battery is. A charger that promises a 5 minute 1MW charge BUT which can only do it once per hour and then falls back to 200kW doesn't seem as special as a charger that actually charges a car every five minutes.

It's convenient to get going in 5 minutes. But the time you REALLY want the charger to be quick is when you are third in line to charge at that charger.

[stymaar]

I was definitely using simplifying assumptions to get my point straight here.

Setting the actual parameters for such systems is an engineering job, I just wanted to illustrate that the goal isn't going to have the charging station off the grid during peak hours thanks to the batteries, and more about managing the burden you put on the grid.

[alkonaut]

Yeah that's why it probably needs to be more than 1 charge in the battery. Unless you do N back-to-back charges during peak time, the charger isn't utilized enough. And to do N back to back charges you need about N car batteries as buffer.

[stymaar]

If you have full usage of your charger, then batteries are pointless anyway because you have steady usage no matter what.

But it's not a realistic assumption, at the very least the driver has to park, get out of their car, plug the car, spend some time on the payment interface, then unplug the car and leave.

So even in the maximum theoretical scenario where drivers are lining up at the charging station, your charger isn't going above 80% utilization. Using a single car battery, you can save 20% in terms of connection to the grid (you “just” need a 800kW connection instead of a 1MW one), and you aren't nearly as much of a nuisance to the grid as if you were having constant ups and down of 1MW.

In practice there will a be a trade off between how much you save in connection infrastructure to the grid and how much you spend on batteries, and this calculation will depends a lot on the usage pattern.

[soco]

So do those batteries support fast charging AND fast discharging?

[mekdoonggi]

Yes. IIRC they are the same batteries in the cars.

[jannyfer]

Oh then that's like the battery swap idea but without the swapping!

[Tostino]

Generally fast charging has been a much harder nut to crack than fast discharge. If you have fast charging you necessarily have fast discharge in my experience.