bremidon t1_j2378i2 wrote
Reply to comment by hacktheself in ELI5 why do electric vehicles have one big battery that's hard to replace once it's expired, rather than lots of smaller ones that could be swapped out based on need (to trade off range/power/weight)? by ginonofalg
You need to actually take a deeper look before being quite so confident.
You are semi-correct though: it *is* a conscious choice. You are just completely wrong on the reasons.
Here are the real reasons:
- We do not have enough batteries. We need every single battery we can make to be in a car, not sitting around somewhere doing nothing.
- Swapping stations are bulky and expensive. It is *much* more efficient and effective to use the same amount of space and money to make chargers than swapping stations. We are not talking 10 or 20% better, but more like 10 to 20 times better.
- Your "5 minutes" only works if you compare a single car charging to a single car swapping. Because you cannot have so many swapping stations, you are going to end up with queues, and that will drastically change things up. Even just a 4 car queue is going to put charging and swapping on fairly level ground.
- There are legal issues surrounding the batteries. If you bought them, then what happens when you get new ones swapped in? What if you deliberately swapped out defective batteries just to get better ones? If you don't own them, how does that work? Who is responsible for the batteries currently in your car?
I want to make clear that none of these things are unsolvable, but they *are* major headwinds. We are having trouble building out just a charger network; waiting for a swapping network would delay things by at least 10 years or more.
Only the first one is guaranteed to be solved, more or less on its own. In 5-10 years we can strike it from the list. The last one is probably the next easiest, but I expect it will take at least 10 years for all the legal difficulties to wind their way through courts.
The middle two are tough, though. As charging times keep coming down and the ability to charge at home keeps increasing, the use case for swapping gets smaller and smaller. Perhaps it will end up being a thing in some bigger cities, but it will probably never be the standard.
Bonus Reason: Because of all of the previous reasons, it is less expensive (and makes the car lighter and safer) to make the batteries part of the structure. So unless someone can quickly solve all those earlier points, the carmakers are going to all gravitate towards swapping being physically impossible. This reduces the use case for creating a swapping system and the whole idea simply collapses in on itself.
ginonofalg OP t1_j23m1r0 wrote
Great insight. Thanks!
maowai t1_j250g9f wrote
Chargers are also much, much more mechanically simple than some sort of machine that would swap out your 1000lb battery for you. Electrify America already has trouble keeping their chargers working. Imagine how bad it would be if it was machines with 500 moving parts instead.
hacktheself t1_j23ubhw wrote
you made highly erroneous assumptions.
the claim of 10-20x efficiency for chargers vs swappers is intriguing
a swap station is bulkier and more expensive to build but at the same time is capable of continuously charging more batteries in parallel and testing all the batteries at the same time
additionally if you have five cars queueing for one 5min swap that’s 20min for the last car; if you have five cars queueing for four fast chargers, even if that fast charge is 10min, average wait time per vehicle is longer and that assumes full high speed delivery of fast charge which is dependent on multiple factors
this latter phenomenon is parallel to the walk left-stand right concept commonly used in escalators except statistically speaking standing on both sides moves everyone faster, both in teens of average speed and throughput and increases escalator reliability since the steps aren’t unevenly worn
the final bullet point is a good one, and there are multiple possible answers but a reasonable one is that access to the battery network is subscription based as in you pay a monthly fee for the batteries
additionally against your final point: swappable batteries aren’t structural but the frame around them most assuredly is, just like how the battery box at least should be structural but the batteries themselves cannot be for safety reasons
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