Can using CHG Mode be more efficient?

A few problems. One how to measure the amount of gas used by the CHG Mode accurately enough to do this experiment? Also, how to measure the amount of electricity generated is not easily measured. If we assume 6.5kWh from the wall is needed to fill -- to 100% SoC, then 1kWh of electricity is about 15.4% SoC. But this is assuming 100% of wall electricity goes to the battery which certainly is not true. Moreover, trying to measure the accurate amount of gas used to generate that 15.4% SoC gain is not an easy task.

I agree that driving conditions will affect the CHG mode efficiency. It is not a constant number of kWh generated per gallon of gas. We already know this because two data point one by me at 45mph and one by KYBlue at 75mph show wide differences in miles driven for gaining 1mile of EV range.

 

With HA, I tried to measure the number of kWh used during EV mode drive, but the number did not match what was fed from the wall (read by kill-a-watt meter) and what is reported on the dash (SoC). In the end, I could not tell what number to believe. The gas used is more of a problem as you know ECU is very optimistic in calculating mpg. I don't know if I can believe that number either. I can no longer use HA on my 2021 PP. The app refuses to link to an adaptor. So I will not be able to play with HA app anymore.

Even if the generator efficiency is constant, with other variables while operating CHG mode, the result would be totally different from one trip to another. Even if you can measure the precise amount of kWh generated with a precise amount of gas used when the car is PARKED, I don't know how you would use that number for the specific driving conditions without knowing how much change will occur under certain driving conditions compared to stationary CHG mode. Certainly, we are not expecting the CHG mode to generate the same amount of kWh of electricity from 1gal of gas used when comparing car stationery at 70F to the car going 75mph in sub-zero temp.

In fact, I am not sure if the generator efficiency is really constant all the time. With your example of a portable generator generating 8 kWh using a gallon of gas, this must be a spec given under certain testing conditions not always a constant number. If you put a lot of load into the generator, it certainly uses more gas than just sitting and running without any load. At least that's what I have observed with my portable generator.

 

The amount of regen has to be taken into the consideration I would think. With stationary CHG mode, there would be no regen. If the CHG mode is turned on when the car is going downhill, you would have additional kWh produced. How much difference would it make, I have no idea...lol

This I agree. Only if that is easily measured. But it's not. And extrapolating the data obtained from the stationary CHG mode to an actual real-world driving situation is going to be very difficult if not impossible. It is like EPA-rated mpg and EV range is a good starting point, but we all know that number does not apply to all driving situations in the real world.

Cursory online search finds many generator data. I am not a generator expert, so I don't have any data to back up his claim. Here are some numbers on Honda portable generators. The amount of gallons of gas used/kWh generated under high and low load seems to be large enough to be concerned if applicable for CHG mode.
Source: Generator Fuel Consumption Data - Thor Forums

Honda Inverter Generators:

900/1000 Watt Portable

• .21 gallons / kWh at 100%
• .38 gallons / kWh at 25%

1800/2200 Watt Portable (New)

• .16 gallons / kWh at 100%
• .26 gallons / kWh at 25%

2500/2800 Watt Portable

• .16 gallons / kWh at 100%
• .28 gallons / kWh at 25%

2800/3000 Watt Portable

• .17 gallons / kWh at 100%
• .24 gallons / kWh at 25%

 

I am with you on this. What we need is more empirical real-world data just like the real-world mpg data on Fuelly. But the experimental drive does not need to be elaborate. All we need to know are two factors under various real-world driving conditions as I mentioned before. The driving conditions between reporters do not need to be identical. In fact, it is better to have a wider range of real-world variations. An experimenter just needs to make sure the comparison between CHG/EV and HV is driven under very similar conditions. The rests are calculatable with the assumption that CHG/EV driving is identical to HV driving conditions in every other variable that affects the overall mpg.

 

I think you are over-generalizing. Your miles driven, mpg and miles/kWh do not apply universally to everyone for every trip. And even for you, it is not a fixed constant number every day. You are also assuming the amount of kWh generated under CHG mode is constant which I really think will change depending on the driving conditions. The question is, assuming that you drove 130miles round trip all on HV mode at 65mpg, then can you drive the same round trip under similar conditions using CHG/EV mode and get an overall mpg better or worse than 65mpg, that is the ultimate question to be answered. If the number difference is small or results in flip-flop each time, or the number of trials is small, then it will not give a definitive answer but the number difference is large or it is always resulting in one being better than the other, then that would be a good indication there is a real difference.

BTW, when your trip gets longer than 100 miles, the amount of HV portion increases if you restrict the distance of EV mode to only 80% of SoC. Therefore longer the trip, the less impactful the difference will be in either direction. To mitigate this problem you can keep repeating CHG/EV driving as many times as required to finish the travel without using any HV mode in the CHG/EV trip.

Here is my formula-based calculation for that hypothetical trip using mpg factor=0.5, EV gain factor=1.00. As you can see, using these factors, the CHG/EV vs HV has no difference. This means if the 65mpg you can achieve on HV mode is reduced to 32.5mpg under CHG mode, but each mile you drive on CHG mode generates enough battery charge to be able to drive 1EV mile, then you do not gain or lose at all.



Now, change the factor to mpg factor=0.6, keeping the EV gain factor=1.00. This means from 65mpg HV mode is now 39 mpg on CHG mode, but 1 mile of CHG mode is able to produce 1 mile of EV mode repeatedly to get full 65 miles of EV drive. You see overall mpg is better under CHG/EV. Can I really do this? I don't know without trying, but since I have seen with my one trial that EV gain factor of ~1.0 and mpg factor of ~0.6, I think I can.


But if the factor is really like mpg factor=0.6, and the EV gain factor=0.5 the KYBlue has seen on his trip, then the overall mpg will be better on HV mode. This may be the case under certain driving conditions, but without actually doing this trip twice, you never know.

 

Did you read my entire hypothetical trip calculation? You can repeat CHG/EV more than once to gain more EV range than single 80% SoC can supply. That alone will change your prospect. And again, the question is not specific to your trip alone. Maybe under your driving condition, it is not possible to get better efficiency using CHG/EV mode over pure HV mode, but that does not eliminate the possibility of CHG/EV mode getting better overall efficiency over pure HV mode driving under other conditions by other drivers. Again, just like Fuelly mpg collections, someone could get only 45mpg no matter how hard he/she tries does not negate the fact that someone else is getting 100mpg from the same make/model of car. And if we have enough people showing his/her own driving data, then we can get an overall average if in fact that CHG/EV mode can be more efficient than HV mode under certain circumstances.

 

Try your calculation with 40 miles total distance of the trip. With that short distance, you do not have to drive on HV mode at all if ~20 miles of CHG mode can generate enough kWh to SoC ~80% to gain ~20EV miles at 4 miles/kWh efficiency. if the mpg drop is less than 50%, then overall mpg will be better with CHG/EV mode. This is easily testable unlike the measuring gas used and kWh generated under CHG mode either at PARK or DRIVE.

 

Yes, it matters. If the CHG mode can produce kWh of energy to carry the car further in EV mode than HV mode would by the excess amount of gas used under CHG mode, then more CHG mode is used further it goes on EV mode, thus more efficient mpg (higher). Of course, it is also true for the opposite direction as well. That is, if the CHG mode excess amount of gas used can not produce enough kWh of energy for EV mode to beat the regular HV mode efficiency, then more CHG mode used less efficient mpg (lower).

However, all of this is assuming that the amount of kWh generated per gallon of gas used in CHG mode is always constant, which I really think is not the case. Also, the assumption is that EV efficiency and HV efficiency stay constant as well which is certainly is not the case. It simply depends on how much kWh CHG mode can produce under the driving conditions tested, and how far that kWh energy can carry the car on EV mode compared to HV mode used under the same condition. I think all three numbers, that is EV efficiency miles/kWh, HV efficiency mpg, and CHG mode generator efficiency kWh/gal are variables that change depending on the particular driving condition, thus can only be determined for a particular driver for a particular driving route and distance under particular condition by empirical testing.

Your number is correct, but maybe you are underestimating the efficiency of the PRIUS generator. After all, it is the same generator for the regular Prius which has only HV mode for all practical purposes. You keep stating as if beating a small gas engine Honda generator efficiency is an impossible task. But my rudimentary understanding is that a small engine gas generator efficiency is very low even for a HONDA.

1 gal of gas contains 33.70kWh equivalent of energy. 8kWh is only 23.7% efficiency. Isn't a larger electric generator much better than that? Again, I am not an expert in this area, so I might be way off, but maybe 13.8 kWh per gallon which is 40.9% efficiency isn't that hard to achieve? This may not apply to small engine generators, but I have read some articles saying over 90% efficiency is achieved by large industrial diesel engine generators.

The only way to test it is just to do the actual drive and compare as I proposed, or do as you say to measure the CHG mode generator efficiency at PARK, if you find out ways to measure the gal of gas used under CHG mode and also measure the amount kWh of electricity generated. I think driving is the easier way of two and it is an empirical real-world result. Your CHG mode generator measurement only applies to the PARK condition, and if the amount of kWh generated per gallon under CHG mode is not a constant number, then it only gives some reference point that may or may not be applicable to all driving conditions.

Try repeating the same condition drive with that segment you used CHG mode in HV mode and come back with mpg, Also, I need the miles of EV range gained for the total miles CHG mode you drove on this round.