Electric Vehicles (EVs) – FreeJoule's Blog

Cabin Preconditioning

How much energy does it take to have a toasty warm cabin before getting into the car and driving off? Here is a view of energy consumed (kWh) and rate of energy (kW) to precondition the cabin (not battery) in 43 degree (6 C) ambient temperature garage. 20 minutes and 1 kWh later the car is warm and ready to go. It cost me 14 cents to warm the car while parked in the garage and plugged into my Juicebox Level2 charger. I also avoided losing about 4 miles of range since I didn’t have to use the main battery to warm the cabin while driving.
If we get another cold spell and the garage gets into the 30’s, I’ll re-test to compare the energy consumption at lower temperatures.

precondition graph

precondition table

First week with a fully electric car

After 1 week with the 100% electric BMW i3 I calculated and compared the energy costs to my previous gas car and our existing gas minivan.

In one week:
I saved $68.76 vs. driving the premium unleaded fuel BMW 335i.
I saved $49.64 vs. the regular unleaded fuel Toyota minivan.

Calculations:
Total miles driven: 478
Electricity cost including taxes and other fees: 0.1364 cents per kWh
Gas cost: $3.40 per gallon of premium unleaded fuel
Gas cost: $2.64 per gallon of regular unleaded fuel
Both gas cars average 19 MPG

What I actually paid driving the 100% electric BMW i3:
Electric used from all charging sessions: 123 kWh

As an added bonus, I’ve produced zero emissions during driving AND electric charging. I switched my electric generation provider to 100% renewables years ago.

Fuel Costs Per Mile – EV’s vs. Gas

Here is a quick comparison showing only fuel cost differences between gas and electric cars. This does not include any maintenance savings or other benefits of EV’s. Comparing Gas cost of two different MPG rated cars versus the average MPkWh rated electric car. This assumes home charging the EV with typical electric rates after all taxes, generation, distribution, and other fees in Pennsylvania.

Charts use the average efficiency of 3.27 Miles per kilowatt-hour (MPkWh) of an EV with electrical rate of $0.1364 cents per kWh. For Gas, $2.453 per gallon taken from today’s average in PA from www.gasbuddy.com

You can see from the graphs below, a 30 MPG gas car will cost Double the EV costs for every mile driven. A 19 MPG gas car such as a minivan will cost more than Tripple! EV saving are even higher since maintenance is minimal with no oil changes, no brakes (regenerative braking basically eliminates brake wear), and minimal moving parts to break.

Calculations for charts above:

Quantifying EV Energy Consumption

I want to better understand the energy consumption of electric cars. I’m not even going to discuss the EPA’s MPGe (miles per gallon equivalent) ratings for electric cars. I completely ignore this figure. I will never drive along in my pure electric car thinking… “I’m averaging 95 MPGe on this trip to the beach!” Especially when everything related to the EV will be in kilowatt-hours (kWh). Sizing of the car battery pack is in kWh. I’ll charge the car at home, then pay the electric bill which is based on kWh. Also while driving the car it will show instantaneous watt-hour per mile consumption.

I want to think in electric / energy terms and have a good understanding of relational consumption. The easiest way to understand energy consumption is to relate it to stuff we already understand. Charging a cell phone, a 60 watt light bulb, a 1400 watt coffee maker etc. We all have a pretty good idea of how much power these devices consume. Let’s relate this knowledge to EV’s.

Consider the energy consumption of the following cars. The kWh rating per 100 miles is pretty common to find now. Based on that number we can calculate the Watt-hours per mile:

watt-hour = 1000 × kilowatt × hour
abbreviated: Wh = 1000 × kW × h