Comment by jaclaz | Hacker News Reader

Comment by jaclaz | Hacker News Reader

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Any actual detail?

A "normal " sodium street lamp is (was) usually 250 W while a "modern" LED lamp is usually 50-70 W, and typically posts are 25-30 meters apart.

So, you have (roughly) 200 W "excess" per post, you need 35 lamps to leds replacement to make 7 kW and this would mean 35 posts at 30 meters each = roughly 1 km in length.

How many (electric) cars will be parked along this 1 Km stretch of a street? I would say as much as 200 (once the conversion to electric will be 100%).

But even supposing that each lamp post can actually house several 7 kW outlets, enough to cover the 30 m stretch, let's say 6 outlets as each car will take 5 meters along the road 5x6=30, the cable for the single car (or at the most two) parked right in front of the post will be a "normal" length but to get to the farthest ones you will need a 20 m cable, not exactly handy to carry around or to store.

And anyway you are now at around 6x7=42 kW of power per post (as opposed to the original 250 W) and - per kilometer, one side of the street only - you are around 35x42= 1470 kW (as opposed to the "current" 35x0.25=8.75 kW.

You're right, I've done a bit more research into this. The company in question (Ubitricity) are uprating lampposts to 25A single phase at 240V, so 6 kW per post. Even though sodium (and earlier flourescent) lighting never used anything like that much current, I can't find a source to confirm whether or not the lampposts were originally rated at 25A or lower.

On your calculations of how many cars can charge at once, I would keep it simpler and say that a row of parallel parking typical in UK cities, there is one street lamp for every 5 cars. 50 kWh charge overnight, approx 300 km range for every fifth car.

Supposing 100% EV adoption - well, already not everyone drives themselves to work/kids to school in UK cities (where most on-street parking takes place) - but if they do, and have charging at work plus some nearby rapid charging, that should do the trick, assuming a typical commute by road isn't more than 50 km each way. It's certainly in the ballpark.

As I see it, as long as the amount of (electric) cars will be a fraction of the total, it can be managed, but as soon as the amount will increase this "lamp post" approach won't work and something different will be needed.

A practical example is the following:

1) you use 20% battery per day

2) you get home at 20:00, with battery at 60%

3) you find the "right spot" near the lamp post free

Now, do you "risk" postponing the recharge one or two days or you "fill it up to the brim" right now?

And, then, let's say that after 4 hour recharge you will be at 100%, will you at 24:00 unplug and move the car (to allow someone else to recharge)?

Or will it be possible (at 24:00) for the owner of the car parked right after yours to unplug your car and connect his/her own?

And why should he/she wait until 24:00, and not unplug yours when he/she arrives at 20:15?

Most probably, at least when the numbers are small, there may be some form of "rechargiquette" but I doubt it would last for long.

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