A constant criticism of electric cars is their charging time. Despite all of their other advantages, charging takes noticeably longer than refueling a gasoline car and this difference make some people dismissive. When I leased a Volt for 3 years, charging time was a nonissue because it was parked in a garage with a charging station. Meaning my car recharged overnight while I slept, just like my phone and laptop. I rarely ever charged the car away from home, and it’s usually done more out of novelty than necessity.
But real issue or not, charge time is something that needs to be addressed for consumer acceptance. So technology has been developing to make electric car charging ever faster. The rapid pace of development also means a lot of competition, each claiming to be faster than the last. The latest round of news has General Motors proclaiming that they’re working on a 400 kilowatt charging system.
The big headline number of 400 kilowatts is impressive, but the engineers would dig deeper for an arguably a more impressive number: 96.5% efficiency. The publicity material focuses on economical and ecological advantage of wasting less energy, but it also makes adoption far more realistic. Wasting less power isn’t just good for the pocketbook and environment, it also means less power being turned into heat.
How much heat are we talking about? 96.5% efficiency implies 3.5% waste. So that 400 kilowatt charger is turning about 3.5%, or about 14 kilowatts, into heat. For comparison, cheap home electric space heaters usually top out at about 1500 watts, or 1.5 kilowatts. Meaning these car chargers need to deal with byproduct waste heat that’s roughly ten times that generated by a home heater whose entire purpose is to generate heat. That’s a lot of heat to deal with! Heat management is a concern for all the high speed charging stations, from Tesla to Volkswagon. It’s good to see progress in efficiency so our super high power charging stations don’t cook themselves or anyone nearby.