2023 Prius Prime EV Range

In our climate, after a snowstorm, if the packed snow is not melted by a sufficient amoun of salt and pavement is not dry before nightfall, it becomes slick ice most of the time. The snowstorm may be over, but the morning after is almost always more dangerous and treacherous conditions to drive. I would much rather drive on fresh snow than packed-ice-turned-to-ice following the snowstorm. Fortunately, a true black-ice event caused by nighttime rain covering the road then freezing on the surface or real freezing rain which will freeze as soon as a supercooled raindrop hit any hard surface is a rare event, but black-ice caused by melted snow that did not completely dry and refreezing following a snowstorm happens frequently.

 

Here is my write-up on the PP recharging the traction battery by regen alone in the hill descent experiment. See my conclusion here: Battery Charging After Depletion? | Page 2 | PriusChat

I can not say that I did not use the friction brake at all on the first descent, but I was very careful not to use it. Most of the braking was done by regen on B mode. Still, on my first ascent, I used 42% SoC and gained back only 23% on the descent. That's only 55% back, nowhere close to 80%-90% regen capability @Gokhan is claiming. However, it is only a single data point. Certainly, the "Your Mileage May Vary" clause must be inserted here.

 

I know what efficiency is. However, I have no idea in what context you are using it. You need to define something precisely before you can expect others to know what it is. Are you referring to the efficiency of the ICE? Are you referring to the charging efficiency? How can you even measure total EV efficiency, as you have no idea what the aerodynamic force, rolling resistance, etc. are. Go ahead and precisely define what you are talking about.

Of course, it is not going to work on steep hills. I said 80–90% efficiency for regenerative braking for both very gentle acceleration and very gentle deceleration. A steep hill is a good fraction of the gravitational acceleration g, which is not gentle acceleration or deceleration. This is probably why the other poster is seeing poor EV mileage because he is not accelerating and decelerating gently enough.

 

A hill ascent and a hill descent are very high acceleration and very high deceleration, respectively—a good fraction of the gravitational acceleration g. There is no way regenerative braking can be efficient in these conditions. To have 80–90% regenerative braking efficiency, you need to both accelerate very gently and decelerate very gently. For the Prius Prime, this is like 0 to 30 mph on a flat road in 15 seconds or so. The same goes for braking for a red light. This is how I get 6.9 miles/kWh in city driving.

 

Why don't you just video the Soc on the dash next time you do the gentle acceleration and deceleration on a flat road on EV mode. You can easily demonstrate it by documenting the SoC change on those conditions. If you start say with 50% SoC and start accelerating on a flat road hopefully without other traffic and no sudden stops, you can record how far down the SoC will dip before you start decelerating. If it dips to 30%, then with regen you should be back to 46-48% SoC when you come to a stop if regen efficiency is 80-90%. I would try it myself, but I am still carless, as you know. LOL

 

I watched the miles/kWh as a function of time, which gives you a far better idea of what happens when you accelerate and decelerate than simply looking at the SOC.

LOL Carless, yes, perhaps you can buy a new Prius Prime this December so that you can benefit from the nearly maximal rebates and the federal tax credit. Don't you need a car to go the gym and such?

 

I do not follow your reasoning that miles/kWh reading demonstrates the regen efficiency better than SoC reading. You are saying 80-90% regen, so why not SoC showing that 80-90% re-gain is the easiest way to show and prove that number?

Well, I am not so sure of maximizing the saving by waiting until the end of the year. For one thing, the current rebate is not likely to be sustained until the end of the year. And I highly doubt Toyota will be giving the same amount of rebate on the upcoming 2022 model. But buying a new car now may not be a smart thing to do either. I don't need a daily driver for my commuting at least until September possibly much later. We have another car my wife was driving. A Pathfinder Hybrid is certainly not as fuel-efficient as PP, but it can haul 2 times more stuff than PP. For our current needs for driving, it serves better than PP. We go shopping less time now for more stuff. Double the cargo of PP, half the number of trips of PP works out to be roughly the same amount of gas used/month.

 

Please go first. You claimed 90% regenerative braking efficiency in the Prime before I challenged such high figures. Show us how your claim meets your standard. How you defined it, and then the calculations for how you figured 90% in your experiments.

After that, then I'll proceed with my "definition" per your request.

Please show the math for how these observations lead to a calculation of 90% regenerative braking efficiency.

Because?

 

It is harder to judge the regenerative-braking efficiency by simply observing the SOC because cruising also drains the SOC. Unlike the SOC, which is a state or static variable, miles/kWh is a rate or dynamic variable. In fact, miles/kWh is the rate of change of the SOC. When I cruise, the miles/kWh will remain constant around 6.9 miles/kWh. When I very gently decelerate, it will go up to 7.0 miles/kWh or higher. When I very gently accelerate, it will drop to 6.8 miles/kWh or so. When I go back to cruising, it will go back to 6.9 miles/kWh. Therefore, I can easily tell that the regenerative braking is at least 80% and perhaps 90% efficient for very gentle acceleration combined with very gentle deceleration.

I like buying a Prius Prime in December because: 1. You are getting nearly the maximal rebates on the current-year's model. 2. You have the least amount of wait for the federal tax credit. 3. You are getting the newest model year, which saves you a lot from depreciation.

 

I just explained it to @Salamander_King.

Why cannot you have efficient regenerative braking on a steep hill? There is a limit to the current that you can recharge the battery with. Also, acceleration becomes less efficient when the current increases.

 

No, you were just waving your hands and making a claim without a solid definition or calculation.

Then pick a hill shallow enough to not exceed the battery's regenerative charge current limit.

A Prius with driver weighing 3600 pounds, descending a 5% grade at 60 mph, would regenerate at what rate -- 21.5 kW, less air drag and other parasitic losses? That is under the 27 kW regeneration battery charge limit of my Gen3 Liftback. The Prime should have a higher limit than its previous Liftback.

If you go just 30 mph to reduce air drag losses, that should allow for more than a 10% grade.

 

I am not going to spend effort to make an accurate calculation, which requires special hardware and testing. I have no interest in and motivation for that, not to mention time.

I told you what I see on the miles/kWh display for my driving style, and it is convincing enough for me. miles/kWh wouldn't fluctuate around a constant value as I went through traffic lights if the regenerative braking wasn't over 80% efficient for my driving style. Observe your own miles/kWh as a function of time and report it. Also, post your EV DTE, and let's see it. The other poster is getting much lower miles/kWh than I do, and obviously his driving style and/or A/C use are quite different than mine. That's all there is to it.

 

Which miles/kWh display are you looking at? DM2 or Daily Eco Diary? Or are you looking at instant miles/kWh on the split-screen gauge? But it does not have a numerical display, so it can't be the gauge. DM2 is average since the last reset and Eco Diary is the average for that day, either way, the display does not show exclusive miles/kWh values for your accelerate, cruise, and decelerate segments of your trip. If you had the DM2 reset right before starting the trip, or you are looking at the Eco Diary on your first trip of the day, you will be able to see the change in "average" miles/kWh for the total trip, but still, that's not specific to the accelerate, cruise, and decelerate segments of your trip. In comparison, SoC change is very specific to before, during, and after the accelerate, cruise, and decelerate segments of your trip, which is better to show the 80-90% regen if that is true.

IIRC, the 2021 model came out earlier this year than the previous one. I have a feeling that the 2021 rebate will end earlier this year. I am just trying to maximize my saving by not spending money on a car until I absolutely need to buy one. Also, I want to wait as long as I can to have more choices on my next car. New BEVs and PHEV are on the horizon, I may have a better choice than PP. The longer I wait, the more new models to choose from.

 

It is the eco diary, which resets everyday.

With the SOC, I don't have an accurate way of judging the rate of change of the SOC because the precision is only a whole percent. The change in SOC during acceleration and deceleration is only a fraction of percent, which cannot be measured by the SOC display. With the miles/kWh in the eco diary, it is the rate, which measures the change in the SOC, even though it is not an instantaneous rate but the average rate for the day.

 

You don't need to know the rate, if your claim of 80-90% regen is true, then all you need is an instant value of before, during, and after the accelerate, cruise, and decelerate segments of your trip. Besides, no one, except a few Toyota engineers, knows the actual logic used to calculate the miles/kWh number on the Eco Dialy. As it is the average of that day, if you did only one contiguous EV mode trip on that day, that will be the only data used. But you can not assign specific miles/kWh value to any segment of the trip on that day. In my experience, the miles/kWh number can changes vastly from one day to the next day even though a very similar trip was driven under very similar conditions, whereas SoC changes are much more consistent under similar trips and driving conditions.

 

But the SOC doesn't have enough precision to report small changes in it. It would work if it were reported to 0.1% precision, but between the cruising, accelerating, and decelerating, I don't know how to extract the specific SOC changes for those three things with only 1% precision being available.

miles/kWh in the eco diary is very simple. It measures the miles and kWh for a given day and divides them. It is updated every ten seconds or so. You can easily see how much it changes during acceleration and deceleration.

 

That's why I suggested finding a flat road without much other traffic and no sudden stops or acceleration to do the experiment I suggested. All you need is a distance long enough to drive to use 20% SoC during acceleration and cruise on EV. That would be less than 7 miles. If that is too long, I think 10% SoC is OK, although the margin of error would be bigger. Again, if I had PP, I can do it myself very easily. The street I am on is fairly flat and very little traffic. I can drive starting from the front of my house and accelerate gently until I use 10% of SoC, then decelerate gently until it comes to a complete stop. If the regen is 80-90% efficient, the SoC should be back to within 1-2% below the starting SoC.

BTW, here are pics showing the typical variations of Eco Dialy reported daily average miles/kWh. They are 4 days of my commuting of the same route under very similar conditions.
in winter


and in fall

 

I am not sure if it's that simple. For one thing, while the miles driven on EV mode may be measurable, the actual kWh used from the traction battery can not be verified. One question I have is this. Is it a net kWh used? If that is the case, on a day I did EV mode drive to regenerate SoC back to % where I started or gained more than I started, the Eco Diary should show either an error (divide by 0) or minus number (net gain of kWh), but it doesn't. Instead, it shows 99.9miles/kWh for that day. Conversely, when I did not drive the car at all but used traction battery on idling in EV mode, the display should be 0 miles/kWh but it sometimes showed a small number like 0.4miles/kWh. There were other anomalies that I could not explain by the simple math of miles driven on EV mode/net kWh energy used from the traction battery on any given day.

 

I don't have an explanation for all your anomalies, but tonight I have verified that regenerative braking is close to 100% efficient, perhaps the actual number being around 90%, for very gentle acceleration and very gentle deceleration. I watched my miles/kWh, and I always gained back what I lost during acceleration after regenerative braking. Toward the end of the trip, it fluctuated between 6.7 and 6.9 miles/kWh, and I finished at 6.9 kWh. My A/C load was 2%.

If you aren't getting good numbers in city driving, you haven't mastered driving the Prius Prime, and you are using the brake pedal incorrectly, which is not allowing efficient regenerative braking. It could also be that your A/C load is too high.

If you don't believe my numbers, I will post my EV DTE after next time I fully charge my Prius Prime.

 

Again, I don't think you can use the daily average miles/kWh number on the Eco Dialy to make an estimate on the regen efficiency. But since you are adamant about that point without a clear explanation, I am going to let it go. I still think you should try the SoC experiment to see if it re-gains your claim of close to 100% regen efficiency.

Unfortunately or fortunately, I have no way or no need to learn how to drive in a city. I live in a rural village without many city amenities including heavy traffic and numerous traffic lights. The closest city (of about pop 10K?) is 50 miles away. When I was driving PP on regular basis on my commute, I was getting over 30miles of contiguous EV range from a single charge during warmer months on average of 6-9miles/kWh, but that number plummets during winter to an average of ~20 EV miles or 3-4miles/kWh. For me, city drive and highway speed are not enemies, it is the bitter cold in winter that kills overall EV efficiency.

I do believe your EV range and HV milage, what I am questioning is your statement of regen efficiency of "close to 100%". BTW, by "EV DTE" do you mean the Guess-O-Meter EV range? If so, that number has absolutely no meaning in terms of regen efficiency. I had a peak number of 48.5 miles on GOM. And @PiPLosAngeles had shown us the pinned 50.0 miles on GOM that would not get any higher even though his estimated EV range was longer than 50 miles.