How to calculate effective electricity+gas consumption of a plug-in hybrid car? - Page 1
Forum section: electronics / general

author: Greybeard
author_rank: Frequent Contributor
timestamp: May 13, 2025, 09:46:29 pm
content: I'm looking for a way to calculate the effective electricity and gasoline consumption of my new plug-in hybrid electric car.I used to simply fill up my old car to the top and divide the liters consumed by the distance driven since the last fill-up - that's the old tried-and-true method.That works out to liters per 100 km (I know Americans do it the other way around and calculate miles per gallon - that's not the problem).With a hybrid car, I see two problems:1. Charging with electricity and gasoline never happen at the same time. I might even charge with electricity several times before needing gas, or vice versa, depending on how I use the vehicle.2. I actually don't know which part of the distance since the last fill-up was driven with electricity and which with gasoline.Unfortunately, my onboard computer doesn't provide this data.It only displays kWh per 100 km and liters per 100 km since the last engine start, but not the distance traveled on electric or gasoline since the last engine start.Has anyone here already thought about this hybrid-specific problem?Perhaps there's a simple solution that I just haven't found yet.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 13, 2025, 09:57:49 pm
content: It's not so easy to even define separately since the hybrid element makes the gas engine more efficient.But a procedure could be this:1) Run down the battery then measure gas consumption by itself in the standard way.2) Track gas + electric use over a long distance including multiple fill-ups of both gas + multiple charges (to avoid effect #1)3) Now calculate "electric kilometers" = kilometers driven - (gas used liters / (liters/km gas)4) And now electric km / kWhr will give you a number measured in km/kWhr.

author: Greybeard
author_rank: Frequent Contributor
timestamp: May 13, 2025, 11:11:09 pm
content: EDIT (I did not understand your point 1 correctly):If I understand you correctly, your number one method is to always fill up the battery and gasoline at the same time.Since my car's electric range is only about 60 km, I had to do that every 1-2 days.But that would be too much work for me. Of course, you could simply add up several battery charges until the tank is empty and then refilled.Then I would at least have an average value for the electricity and fuel consumption over that period.But that wouldn't be very accurate, since the gas station is several kilometers from my garage, where I usually charge the battery.Unfortunately, I can't follow your points 3 and 4 (maybe I'm too stupid or just too tired).Another problem also arises:As you already wrote, the electric motor supports the combustion engine when accelerating or at higher speeds, and vice versa, the combustion engine charges the battery when it's almost empty.As a driver, I usually notice little or nothing of all this.Since I can't possibly differentiate between the fuel types this way, I guess I have no choice but to add everything up once a month or quarter (or year?), so that an error caused by an additional or reduced tankful (electric or gasoline) isn't as serious.(That would be your method #2 ?)

author: ejeffrey
author_rank: Super Contributor
timestamp: May 16, 2025, 02:10:10 am
content: My plan was just to find how efficient is the gas engine when run as just a normal non-plugin hybrid. Then find the total system consumption under "normal" use and say all the benefit above what it would do as a regular hybrid is due to the electric system.Let's say you measure it as getting 40 miles per gallon as a hybrid if you never plug it in. Now imagine you drive 1000 miles using 10 gallons of gas and 200 kWhr electric. As long as you fill both at the very end that's fine. The hybrid alone would have only make 400 miles, so you had an effective 600 miles electric travel at 3 miles/kWhr.That's not a true electric efficiency rating, it's rather measuring how much better the plug in aspect makes the rest of the system. But that's as close as you can get.

author: Greybeard
author_rank: Frequent Contributor
timestamp: May 16, 2025, 10:33:01 pm
content: It is much more complex than I initially thought.