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Efficiency test of my 2024 Prius Prime: Gasoline vs Electricity in my first week. (lemmy.world)

submitted 4 months ago by [email protected] to c/[email protected]

56 comments fedilink hide all child comments

cross-posted from: https://lemmy.world/post/22892955

The Prius Prime is a dual fuel vehicle, able to run 100% on Electric, or 100% on gasoline, or a computerized blend in-between. This presents me a great opportunity to be able to do a direct comparison with the same car of an EV engine vs an ICE engine.

Toyota computer claims 3.2mi-per-kwhr.

Kill-a-watt (https://en.wikipedia.org/wiki/Kill_A_Watt) claims 2.2mi-per-kwhr.

Additional 1.5% losses should be assumed in the wires if you wish. (120V drops down to 118V during charging, meaning 2V of the energy was lost due to the resistance of my home's wires).

Level 1 charger at home (known to be less efficient).

Toyota computer claims 53miles-per-gallon (American Gallon).

I have not independently verified the gallon usage of my car.

295 miles driven total, sometimes EV, sometimes Gasoline, sometimes both.

30F to 40F (-1C to 4.5C) in my area this past week.

Winter-blend fuel.

12.5miles per $electricity-dollar (17.1c / kw-hr home charging costs)

17.1 miles per $gasoline-dollar ($3.10 per gallon last fillup).

If anyone has questions about my tests. The main takeaway is that L1 charging is so low in efficiency that gasoline in my area is cheaper than electricity. Obviously the price of gasoline and electricity varies significantly area-to-area, so feel free to use my numbers to calculate / simulate the costs in your area.

There is also substantial losses of efficiency due to cold weather, that is well acknowledged by the EV community. The Prius Prime (and most other EVs) will turn on a heater to keep the battery conditioned in the winter, spending precious electricity on battery-conditioning rather than miles. Gasoline engines do not have this problem and remain as efficient in the winter.

I originally wrote this post for /c/cars, but I feel like EVs come up often enough here on /c/technology that maybe you all would be interested in my tests as well.

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[–] [email protected] 0 points 3 months ago (1 children)

Nice info! A few notes:

Volts are not energy. Volts are a component of electrical energy. The drop in voltage is because of the additional load on the circuit that the charger represents. Energy losses come out as heat. If something gets hot while it's doing its job and its job is not to heat things it means that it's got a loss of energy somewhere. I'd bet that the charger warms up in use, and the loss is likely greater than the 1.75% loss that you were thinking you had with the voltage sag.

L1 charging is less efficient for a few reasons, but the biggest increase you get in efficiency from the L2+ charges is time. Triple the charge rate gets you full in an afternoon rather than overnight. But then you can parlay that into cost savings by timing your charge to off-peak times and charge up on cheaper electricity, if it is available in your area.

Electric cars do have an easily measurable range drop in cold weather for the reasons you outlined. Gas cars really shine in cold weather because not only do they not perform measurable worse in terms of range when the thermometer drips, but they also make their own heat, ALL THE TIME. In electric cars you have to use battery power to heat both the battery and the cabin, which is yet another drain on range. But, that gas combustion heat is loss in the summer when you're not using it. Like the waste from your charger, but this time it also comes with emissions.

[–] [email protected] -1 points 3 months ago

Oh yes.

But a wire's resistance is purely ohmic (or damn near a pure resistance, very little inductance or capacitance to discuss).

So seeing a voltage sag of 120V (original) to 118V across the 11 Amps my charger pulls means we can calculate the resistance to be 0.2Ohms.

The rest of the 118V to the charger and the car is the usable power. After all, the current is constant (11Amps).

Power = Voltage * Current.

With 2V * 11Amps being wire waste (22W in the wires in my home), and roughly 1298W delivered to the actual charger

Additional losses are clearly evident (winter, battery heater, air conditioner etc. etc.) later. But the 22W of wire-heat waste / 1320W of power drawn from my power meter (where my electric bill is calculated) is the 1.5ish% loss of this element.

So the 1.5W is literally the loss in my homes wires, before accounting for the charger itself heating up.

It sounds like you know all this but just want to clarify and double check.

[–] [email protected] 0 points 4 months ago (4 children)

Thanks for this. Are you planning to take more measurements during a warm season? It would be interesting to see how close the electric system comes to petrol in more favourable conditions/climates.

[–] [email protected] -1 points 4 months ago* (last edited 4 months ago)

Of course! I plan to keep this car for around a decade, so there's plenty of opportunity next year to experiment again.

Between the heater during charge + the heater during driving (!!!), we are getting hit twice by the cold weather efficiency demons.

[–] [email protected] -1 points 3 months ago* (last edited 3 months ago)

2.87mi/kwhr is the final number for 50F test.

That's +38% range. Or conversely, a 28% drop during freezing conditions. Or 72% efficiency near freezing compared to 50F.

Measured from Kill a Watt and therefore still a L1 charger that may have other inefficiencies.

Huge differences between 50F and 30F. Very curious indeed

[–] [email protected] -1 points 3 months ago* (last edited 3 months ago)

L2 charger at work returned 3.4mi/kwhr !!!!!

L2 charging at 50F (and below) is clearly way more efficient than L1 charging.

With this, I can safely say that L1 chargers should be avoided if possible.

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[–] [email protected] 0 points 4 months ago (1 children)

I have a question about these dual fuel cars, gas has a shelf life and can mess up your engine if you let it sit for too long. Would this become an issue if you only make short, electric drives in the car?

[–] [email protected] -1 points 4 months ago* (last edited 4 months ago)

Yes but there is an easy solution. Just fill up with 2 gallons, rather than 10 gallons.

Now you have the 100mi backup gasoline (why you bought a PHEV, right?), but still do EV every day. Every few months hit the HV button and burn off that fuel and fill up another 2 gallons.

That being said: Prius Prime dual mode has 0-60 time of 6.6 seconds. When both engines are on your acceleration is amazing, on both low end 0-30 EV) and high end (ICE engine covers 30-70mph).

So you want to be in auto mode (aka: use both engines mode) anyway for optimal driving experience.

And now that I know that gasoline is cheaper in the winter anyway, maybe I push that 'use both engine' button more....

If you ever need the 500mi gas tank for a long trip, just spend 5 minutes at a gas station. It's not like our gas tanks are locked behind 20+ minute chargers or whatever.

[–] [email protected] 0 points 4 months ago* (last edited 4 months ago) (1 children)

I get £0.09 /kwh for overnight charging. I spend about a fifth as much on electricity for my car each month than I spent on petrol on my previous car.

Why does your car calculate your petrol efficiency but not your electrical efficiency? Sometimes hybrid cars are sold as being more fuel efficient, so report the fuel efficiency of the gas by including the electricity-fueled miles in when calculator the gas efficiency. (Toyota haven't historically been terribly enthusiastic about electricity.)

[–] [email protected] -1 points 4 months ago* (last edited 4 months ago) (1 children)

My overall miles per gallon was 85mpg including electricity.

The 53mpg is within other tests (ex: consumer reports), and is within expectations.

Why does your car calculate your petrol efficiency but not your electrical efficiency?

On the contrary. I don't trust Toyotas EV efficiency figure of 3.2mi/kwh because I'm measuring 2.2mi/kwh from the wall.

Are YOU measuring the electrical output from the wall correctly? The cars battery has a figure but it's after the efficiency losses in the cable, heater and other such figures. My calculation includes all the losses except voltage sag in wires (1.5% estimate)

[–] [email protected] 0 points 4 months ago* (last edited 4 months ago) (39 children)

I'm calculating money I was charged by my electricity company actually during charging hours versus miles I actually drove. (The amount of electricity my house uses at that time of night is small and ignorable.) I'm trusting the milometer, but I think that's reasonable. It isn't claiming it's further to work than my previous car did!

In any case, it was almost five times as expensive on petrol as it is on electricity in my usage, and even if you adjusted the figures slightly it wouldn't make a difference. And the pure electric car is so much more fun to drive, with so much more oomph than any other car I ever drove. I love it.

I still think it's weird that you're not calculating your own gas efficiency. Toyota have a vested interest in you thinking they're doing a great job of that. I don't know why you're trusting their figures for gas but you're supremely skeptical about their figures for electricity. Why would they be so inconsistently honest with you, and why are you so inconsistently skeptical?

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[–] [email protected] 0 points 4 months ago (2 children)

12.5miles per $electricity-dollar (17.1c / kw-hr home charging costs)

17.1 miles per $gasoline-dollar ($3.10 per gallon last fillup).

UK figures:

Right now my electricity price is 6p/kWh, but the wind is rather high today (Storm Darragh). Still there are tariffs that guarantee 7.5p (9¢) overnight for car charging. That gives 24.3 miles per $electricity.
Petrol is ~£1.40 a litre here ($5.30 per US gallon). So, 9.8 miles per $gasoline.

[–] [email protected] 0 points 4 months ago (1 children)

How is that rate possible? My UK (Octopus) electricity rate is 23.44p/kWh. The energy price cap is 24.5p/kWh. There cannot be anyone out there offering a price of 6p/kWh - I suspect you are looking at your gas price (where 6p/kWh would be about right)

[–] [email protected] 0 points 4 months ago (1 children)

No. Electric. My price changes every 30 minutes.

I wrote that message this morning when the price was low. Now at 5pm the price is nearer 40p. Obviously you don't charge a car at peak prices.

Over the last 4 weeks I've averaged 18p/kWh. That's mainly by making sure I do things like charge the car when it's cheap.

My rate is very variable, but the figure I used is the off-peak rate on a rate designed for EV owners that gives cheap overnight electricity.

My gas price is 5.9p/kWh which also changes, but day by day. Today is average.

[–] [email protected] -1 points 4 months ago* (last edited 4 months ago)

I did read about wind energy making night time costs very low for some areas of the UK. Thanks for the graph, it helps me understand it.

In my state in the USA, I have a choice between one price at all times (17c, all taxes and surcharges included) or a on-peak/off-peak pricing structure of 28c on-peak and 12c off-peak.

Not as extreme as your every 30 minutes of change but if I squint I can kinda-sorta see my price differences kinda lining up with yours.

My lows aren't as low and the highs aren't as high. They are also multiple hours long of on peak vs off peak.

[–] [email protected] -1 points 4 months ago* (last edited 4 months ago)

Interesting. The internet suggests 22p/kwhr is the UK average ($0.27/kwhr in US dollar)

I do have a time of use program that I could take advantage of to drop my night time / off peak prices. But my on-peak prices go up so much that even with the EV I'm not saving any money.

I'm only going to drop from like 17c to 12c if I switch to the EV time of use program, or a change of like $1.70/night worth of charging to $1.20/night (10kwhr per typical day of travel)

Do UK citizens pay generation + transmission + taxes like we do in the USA?

8p/kwhr (10c/kwhr) is very close to the time of use / night time charge generation costs of my area. However, there are still local tax, surcharges, and transmission I have to pay for that would take that up to 17c when it's all accounted for.

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