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Comment by DropPanda | Hacker News Reader

This is very interesting and perfectly logical. I wrote a fairly recent report looking at a very similar question, and reached the opposite conclusion: night time charging is far better for the grid. That study however focuses on Sweden, where solar power only marginally impacts day-time supply.

Link to the study: http://urn.kb.se/resolve?urn=urn%3Anbn%3Ase%3Ari%3Adiva-5752...

If the western US has a surplus in mornings and afternoons, you guys really should invest in dynamic charging using electrified roads (commonly referred to as wireless inductive charging in California, but there are conductive solutions as well).

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Inductive charging seems like a horrible solution as it must surely be extremely inefficient? Also, if dynamic charging refers to charging while in motion, why would that be a good solution? It seems way more complicated and inefficient than charging while stationary, and personally owned cars are stationary more than 90% of the time.

Surprisingly, transmission efficiency (grid to motor) does not appear to be lower with inductive methods than conductive. Numbers above 90% should be expected. A bit lower for the dynamic (in-motion) solutions, but not so much that it’s a deal breaker. There seem to be much larger savings/costs elsewhere in the system that make transmission efficiency of less importance.

Cars that are stationary most of the time are a pretty good reason to put charging infrastructure on the only land they actually share - the roads.

This source (https://batteryuniversity.com/article/bu-412-charging-withou....) says efficiency is only 75-80% when charging inductively. Do you have any better sources for those 90%?

Witricity claims to have inductive charging efficiency that matches traditional plug-in level 2 charging:

https://witricity.com/newsroom/blogs/what-is-efficiency-how-...

It’s hard to get data from non-biased sources, given that there are no commercial installations yet.

Some numbers are thrown around here (static inductive): https://insideevs.com/news/425972/momentum-dynamics-wireless...

And here (dynamic inductive): https://www.greencarcongress.com/2022/06/20220614-electreon....

From what I have heard, the transmission efficiency of the dynamic inductive solution is quite sensitive to alignment and they still have some R&D left to do there.

Remember, when you charge your cell phone, you charge at ~15W (or less), so 80% efficiency is something like 3W of power loss. You can dissipate that pretty easily.

For a car charging, you're charging closer to 7-11kW. Dissipating 2.2kW (20% of 11kW) as heat is basically impossible. The inductive charging they're using for cars (which, are basically mostly prototypes at this point) are different and use much more closely coupled coils... so they can get better efficiency. Whether it works in practice, I don't know, but that's what companies are claiming who come out with these solutions.

I worry that my phone’s battery gets hotter while charging so it’s getting double damage when it comes to lifespan. Maybe we should add a fan to inductive phone chargers…

(Doesn’t help that 99% of people run a case on their phones, and I doubt the manufacturer’s inductive charging efficiency tests account for that)

> you guys really should invest in dynamic charging using electrified roads

The state of our roads is already atrocious. Electrifying them would make them worse (installing any significant amount of road would take away from repairing the existing issues), and also dangerous.

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