One would think that paying about $300 to receive a bit of bad news about electric-vehicle charging would be counterproductive. But the fine folks at Teslarati believe that truth is beauty, and they're willing to pay a little extra for the straight dope.

There are always losses when taking power from the grid and shoving it into an EV's battery pack. The question is how big are these losses. Teslarati calculated digital read-outs from the dashboard of their Tesla Model S all-electric sedan and found that Tesla builds in about a nine percent efficiency loss when it comes to recharging the car. But the blog thought the Tesla couldn't know exactly what was transpiring between the wall and the battery, so it footed the bill for about $300 to install a digital submetering unit from EKM Metering.

With a little calculation, Teslarati was able to figure out after a couple of recharging rounds that the efficiency loss per recharge was closer to 15 percent than nine percent. That means that, instead of paying about 48 cents on the dollar relative to filling up an economy car (factoring in the AAA average price of $3.66 per gallon), Tesla owners are paying about 52 cents on the dollar. Not much compared to paying upwards towards $100,000 for the vehicle itself, but, hey, every cent counts, right? Get all of the details here.


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    • 1 Second Ago
  • 11 Comments
      Teslaliving
      • 6 Months Ago
      Kill-a-watt doesnt work with a NEMA 14-50 outlet. Only good for smaller stuff. Actual EKM meter was only $90. The enclosure was another $40 and then the electrician (I wasn't comfortable doing this on my own) was $150. There's no break even on the thing. Its informative only. No payback, pure expense. I just wanted to know and I was willing to pay $300 for that knowledge. My point was $300 is pretty expensive, you could drive over 5,000 miles for the price I paid for the meter+install. In other words its not worth it unless you're really curious. http://teslaliving.wordpress.com
      DarylMc
      • 6 Months Ago
      In the USA are figures for vehicles CO2 gram emissions per mile readily available? It's common for vehicle manufacturers in the metric world to supply CO2 gram emissions per km figures. Fortunately everyone uses kWh to measure electricity use. I don't know the current figures here in Australia but a largely coal burning country makes about 1kg of CO2 per kWh. The figures in the article puts Tesla Model S at nearly 20kWh per 100km. So 20kg of CO2 for 100km or around 200 grams of CO2 per km. VW E-UP, a much smaller car is claiming around 12kWH per 100km. So still around 120 grams of CO2 per km. I know because I own a gasoline UP that it claims around 100 grams of CO2 per km. VW XL1 is claiming around 7kWH per 100km Around 70 grams CO2 per km. I mention this purely to highlight the importance of a clean grid to achieve the benefits in CO2 reduction by using electric vehicles. Charging efficiency should probably be a high priority if the goal is CO2 reduction. Along with improving the grid.
      Dave R
      • 6 Months Ago
      Not new news, LEAF owners have long known that the dash efficiency readout is about 87-85% of the energy used to charge from the wall when L2 charging and another 5% worse or so when L1 charging. Given than vampire drain on the Tesla still isn't completely fixed, the difference probably goes up if you don't drive your Tesla much. Still good to see people use these meters - ideally every single circuit breaker in the house would be monitored.
        Dave R
        • 6 Months Ago
        @Dave R
        Oh BTW, if you're only going to bother to measure a single circuit like the Teslarati guys did, you can buy an old-school refurb utility style meter and socket for about $35 instead of the $200 they spent from places like Hialeah Meter. Doesn't look as cool, but if you're not going to use the advanced features of the EKM you can save quite a bit of money.
          GoodCheer
          • 6 Months Ago
          @Dave R
          Or a Kill-a-Watt. The ultimate measure is Wahh-hours through the meter per miles driven. This report does not indicate whether/how that number is changed by this finding.
      paulwesterberg
      • 6 Months Ago
      The EPA mpge figure on the sticker already accounts for charging loses.
      2 wheeled menace
      • 6 Months Ago
      So it's about as efficient as the ebike charger i've been using for 4 years. No surprise. They could design a charger that is 90-95% efficient, but the cost would be thousands of dollars more tacked onto the car to produce it. Would people pay the premium? doubtful.
        DarylMc
        • 6 Months Ago
        @2 wheeled menace
        Voltage conversions certainly need to be addressed. Fortunately for us Australians who were late to the party with this thing called electricity we have a 240/415v system. I think there is the possibility that soar DC, direct to batteries will prove a good thing.
      Rotation
      • 6 Months Ago
      Can someone make any sense of this guy's break even calculation? How can you ever break even on this meter since it doesn't improve efficiency? 'Assuming a $0.167/kWh electricity cost and 325 Wh/mile, the cost of the meter plus installation would require 5,380 miles of EV driving to break even.' He seems to be calculating the point at which you would have spent as much on electricity as this thing costs. But I don't see how that's any kind of break even, you haven't recouped the cost of the meter.
        Naturenut99
        • 6 Months Ago
        @Rotation
        It's only if you have the deep OCD for numbers. That even after having those numbers doesn't change anything. Why he tried to calculate a payback is ridiculous. Like you said, it can't save you anything. It's also a very small difference.
          Naturenut99
          • 6 Months Ago
          @Naturenut99
          That's coming from someone who does like spreadsheets.