Oh, a kilowatt. Or kW. I see. So in electricity, a watt is a unit of power. It takes more power to light a room with a 100W bulb than it does with a 60W bulb. More power through the lightbulb, more light. A kilowatt is 1,000 watts. So ten 100W lightbulbs. Sort of.
A kilowatt-hour is the amount of energy we use when we push a kilowatt around for an hour. Light those ten bulbs for an hour, that’s 1kWh. Do it all night, that’s, um, more kWh. Depends on how long your night is. According to Wikipedia, so you know it’s true, the average US customer pays 12 cents per kWh. So ten 100W bulbs for an hours costs a bit more than a dime.
If I have a battery that holds, say, 95 kWh we can light those 10 100W bulbs for 95 hours. Or five of them for 190 hours. Or one for 950 hours.
This thing here:
Is a rolling 95kWh battery. It’s an Audi e-tron. It’s sitting in Boise, ID. We live near Seattle. It’s 500 miles. And we have a battery measured not in miles, but in kWh. Can we make it?
No.
Well, not in one fell-swoop, as they say. The key thing we need to know is, how many miles can you get per kWh. With a full charge, the car said it could go 250 miles. That’s 2.63 miles per kWH. Starting the car and running the A/C brought that quickly down to 212. Reviews on the web estimate 200 to 208. EVs (electric vehicles, if that wasn’t obvious) don’t let their batteries get below some threshold. Apparently a Tesla will use up to 90 percent or so of its juice. Rumor says Audi dialed that to around 20 percent. And they brag, a lot, about how little time it takes to charge the battery 80 percent. So let’s guess that they only use… 80 percent, or 76 kWh.
They also say owners get 1000 kWh free at ElectrifyAmerican charging stations and that amount of energy is roughly equivalent to 2,000 miles.
So… 2 miles per kWh. That’s 76 kWh (using the 20 percent floor) times 2m/kWh is right about 150 miles per ‘tank’. At 0.12 per kWh the cost is just over $9. That’s six cents a mile!
But what about getting from point A to point B?
First you have to find a charger every 150 miles. Ok, we have an app for that. The app lets you enter your start and destination addresses and details about your car (distance it can cover, how many miles you have remaining, when you start) and they find you chargers every, say 150s miles, along the route. Can any particular charger on the route get you the next, say 150 miles, down the road? Time for more math! You knew there would be math, right?
Keeping our 2m/kWh estimate, we need to get 75kWh into the car. If a charger produces 75kWh, it will take one hour to ‘fill the tank’. I’m making a boatload (technical term) of assumptions here about charge rates and the car’s ability to suck up the juice. But they match up pretty well with info Audi is advertising and publishing on the web.
Anyway, a 150kW charge needs a half-hour to add 75kW to the car. This exactly matches an Audi claim. That is, on a high-speed DC charger, you can add 80 percent distance in thirty minutes. Electrify America is Volkswagen (owns Audi) Corporation’s partial atonement for ‘diesel-gate’. They are investing $2B to build a (USA) nation-wide network of chargers. Their chargers will be 50kW, 150kW and 350kW units.
So, if we can find 150kWh chargers every 150 miles apart, we’re good to go. Let’s see… Maybe we can average 75mph on the highway. That’s two hours per leg of the trip. So we:
- Drive two hours
- Charge for one-half hour
- Drive two hours
- Charge for one-half hour
- Drive two hours
- Charge for one-half hour
- Drive for two-thirds of an hour
And we’re home! EA charges $0.30 to $0.35 per minute. That’s nine dollars per charge. This trip costs $27 for fuel not counting the top-off at the end of the trip. Plus one and a half-hour in time. My Q7 gets 20 mpg on the highway at almost $4 per gallon. That’s about a hundred bucks but less time.
None of this reduces my enthusiasm for an electric car. And the e-tron is a great car. Good size, between the Q5 and Q7, all-wheel drive, lots of luxury features, etc.
So, are we going to drive it or ship it? Driving would be a fun adventure. But other things going on at the moment argue against an adventure at this moment. If we do drive it, we’ll describe the trip here.
In the meantime. I’ve done some research on charging ports, which matter, that I might post here. Plus specifics about charger levels, home chargers, getting accounts with charger companies. etc. More to follow…