Motor and charger efficiencies

[davidrools]

This one's for the geeks (I know who you are). I was bored at work last week and started putting together a spreadsheet to calculate relative efficiencies and costs of driving the Aptera vs. other vehicles. Feel free to take a look at the attached spreadsheet. I'm sure I've probably made some significant errors so feel free to correct. I should probably annotate to show my derivations, so I'll do that soon if anyone's interested.

There are two variables that I'm not sure how to estimate but have a pretty significant impact on the results. They are:

Aptera efficiency! How many watts does it take to drive a mile? This of course varies with driving behavior (cruising speed, hard acceleration, etc.) so I have three lines to bracket/center different scenarios. I calculated the ideal case based on the claimed 120 mile range using an 80% discharge of a 10kW battery (8,000W/120miles=67W/mi) with 100% drain getting a little worse 83.3W/mi. I also tried to back calculate the efficiency based on Aptera's claims of "$1 or $2 of electricity to charge overnight" which of course depends heavily on commute distance and driving style. Anyway, any ideas on that spec would be helpful.

Also, the charging efficiency may come into play since not all the juice you pay for will make it into the batteries. I'm sure its a relatively small loss, but it would surely add up over 10 years of nightly charging. I just don't have a clue as to what number to plug in there (100% eliminates the consideration all together)

Thanks!

In case you can't or don't want to bother unzipping/opening the Excel file, it basically lets you punch in the price of electricity and gas, lbs of CO2 produced from gas or electricity, mpg of cars to compare, and # of miles you drive in a week, then it outputs the weekly and monthly cost of operating each car, cost and CO2 savings over other cars, and equivalent mpg and gas price for the Aptera.

Here's a Google Doc (http://spreadsheets.google.com/ccc?key=pqbAfu8laph4aLj_HXZIPKg&hl=en) if you're into that thing :) (choose File -> "Copy Spreadsheet" to save it to your account and play with your own numbers!)

[GCustom]

only changing your price of gas to what I'm afraid it may be when I hope I'll manage to snag an Aptera, 4.109, my yearly savings are expected to be $673.11 with about 2700 lbs of CO2 saved.
Thanks

[KarenRei]

No geeks that I know of on this forum ;)

Electric motors and chargers vary in terms of efficiencies, but in practice, you can expect an electric car to average 85-90% (in optimal conditions, they're as high as 95%), and I think 90-95% would be a reasonable number for a charger.

80Wh/mi is about right for 55mph. I've done a number of calculations and they all come out to about the same thing. It's something like 115 Wh/mi for top speed (85mph), although I'm a lot less certain about that number.

Li-ion batteries are virtually lossless in terms of charging. batteryuniversity.com says 99.9% efficiency. Compare that to NiMH and their 50-70% efficiency :) Lithium phosphate batteries are not traditional li-ions, but I wouldn't expect any significant efficiency changes. Traditional li-ions also leak about 5% a month (compared with ~30% for NiMH)

Are you including maintenance in your spreadsheet? That's a biggie in vehicles.

Also, if this is a full economics calculator, the number you want is *not* payback period (time for the extra cost of purchasing an Aptera vs. a gasoline vehicle to be paid off). What you want is either IRR (Investment Rate of Return -- given a period of time, what sort of interest rate do you make on your investment over that time) or mortgage length (given an interest rate, how long does it take you to pay off a mortgage on the amount extra you paid for the Aptera).

[futura]

This one's for the geeks (I know who you are). I was bored at work last week and started putting together a spreadsheet to calculate relative efficiencies and costs of driving the Aptera vs. other vehicles. Feel free to take a look at the attached spreadsheet. I'm sure I've probably made some significant errors so feel free to correct. I should probably annotate to show my derivations, so I'll do that soon if anyone's interested.


Nice work (first time I've used Google Docs). If you're in an annotating mood you might consider dropping in the equation used by X-Prize for MPGe http://autoblog.xprize.org/ . With a few other variables the Typ1-h folks can play along at home and we can more easily see how Aptera stacks up against the competition. When I use your numbers with the MPGe formula I get 85, 136 and 507 MPGe for "lead foot" etc.

Cheers.