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It’s finally here: Porsche puts wireless EV charging into production (electrek.co)
submitted 1 month ago by to c/electricvehicles@slrpnk.net
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[–] 6 points 1 month ago (9 children)

I wondered about this. I have "qi charger" in my car, on my desk, and on my bedside table, and all of them put out a fair amount of heat, so I knew there was loss, but didn't know it was in the 10% range. That's a lot!

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  • [–] 26 points 1 month ago* (8 children)

    10% is so low, that I doubt it's factual. For comparison, QI charging loses 20-30% in addition to what wired chargers lose. Here is an article with cited studies: https://www.engadget.com/2200186/wireless-charging-wastes-electricity-why/

    Moral of the story: plugging the phone in is worth it in the long run.

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  • [–] 2 points 1 month ago* (last edited 1 month ago)

    Add that to the fact that the "qi charger" in my car is very finicky about position. So, if I want to grab the phone to change music, take a picture, etc, etc while driving, then when I put it back in place I always have to fiddle with it to get it to start charging again. Whereas if it's plugged in to a wired connection, there is no fiddling about while I'm attempting to drive safely.

    The qi charger in the car, and on the desk at the office don't get a whole lot of use. The one by my bed, a disc with one functional side, always!?! is wrong side up when I try to connect it, sleepily, in the dark. Plug in is just easier to use. I appear to have convinced myself to swap it out with a wired connection.

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  • [–] 1 point 1 month ago (6 children)

    For phones, though, the absolute amount of energy is so low that a high percentage loss doesn't actually mean that much. A typical smartphone battery is about 15 Wh, so charging it literally every day for a year consumes 5.4 kWh. Doubling that won't make a noticeable difference to your energy consumption, the heat released in your home, your electric bill, etc.

    That's why small device chargers are engineered without much regard for efficiency. For that specific application, having long flexible light cables is better than making sure it squeezes every bit of efficiency out of it.

    For cars, though, even a 10% loss can make a difference.

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  • [–] 4 points 1 month ago (5 children)

    I would disagree. The difference might not mean much for a single household but looking at all mobile phones paints a significantly different picture.

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  • [–] 0 points 1 month ago (4 children)

    If everyone in the world population of 8.3 billion wasted that much energy per year (5.4 kWh), that would represent a global increase of 44.8 terawatt hours.

    Global energy use was about 177,000 terawatt hours in 2025 so that represents about 0.025% of total energy use.

    Consumer electronics, especially mobile devices, just don't use any significant amount of energy worth talking about, and has basically no effect on overall demand. Making them half as efficient wouldn't be noticeable on any scale.

    For comparison, a liter of gasoline contains 8.9 kWh of stored energy. There's probably a lot more to gain by just getting people to drive something like 5 km less per year, rather than trying to squeeze just a little bit more efficiency out of their phone chargers.

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  • [–] 2 points 1 month ago* (3 children)

    The gain may not be much but the cost is even less. Reaching for a cable costs a second more and would save around 10000 tons of coal per year (based on your calculation) if the equivalent of coal power plants were reduced by the same amount. It's not like using wired charging is any sort of effort that would outweigh the benefit.

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  • [–] 1 point 1 month ago (2 children)

    Reaching for a cable costs a second more and would save around 10000 tons of coal per year (based on your calculation) if the equivalent of coal power plants were reduced by the same amount.

    You can't have it both ways. If you're counting the energy consumption of 8.3 billion people consuming 15 Wh, 365 times, then you're also talking about "a second" for each, or 3 trillion seconds, or 95,000 years of time saved in exchange for that coal.

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  • [–] 2 points 1 month ago (1 child)

    The difference is, that one second is personal cost. The CO2 is socialized cost. If you have a different perspective on this, I understand. When I looked up wireless charging because it looked cool and saw the numbers, I decided to stick with cables and not buy any wireless charging hardware.

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  • [–] 1 point 1 month ago

    And I'm saying that this particular issue is completely inconsequential. Based on worst case scenario assumptions (fully discharging a 15 Wh battery down to 0% every day, waste heat equal to 100% of the charge, all electricity from coal), you're only using a 5.4 kWh per year, or about 2.5 kg of coal, about 4.6 kg of CO2 emissions.

    That's about 170g/6 oz of beef (27 kg CO2/kg beef). Commit to eating (or wasting) one less burger per year and you've made up for the worst case scenario, calculated using unrealistically large assumptions.

    Or that's 1.9 L/0.5 gallon of gasoline. Drive 25 km/15 miles less per year.

    More realistically, we're probably talking 80% charge per night, 80% efficiency, and an electricity mix that generates the US average CO2 emissions of 0.384 kg/kWh. That cuts it down to 3 Wh/day, 1.1 kWh/year, and about 0.42 kg of CO2.

    That's 16g of beef, or 0.17 L of gasoline.

    The real impact comes from changes around the bigger uses of energy. Focus on the things using many orders of magnitude more energy, within your control: transportation, climate control, food choices. Consumer electronics are less than a rounding error.

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