Should I use up my EV daily for work?

You need to do the math and compare your cost per mile for gas vs electricity in your situation.
For me I’d need to get 80+ mpg for gasoline to be less costly than electric.

 

^^ +1 ^^
Unless you have insanely expensive electricity, you're wasting money if you come home with unused EV range. (Assuming you went far enough to use it up.)

 

Since you live in CA, I assume your gas price is very high. Depending on what rate of electricity you are getting, and how efficiently you can drive on your daily commute is going to affect the economic.

I made an Excel spreadsheet to do the calculation for my daily commuting. I live in NE where gas price is relatively cheap but the electric rate is extremely high. For me, driving pure EV cost more than driving HV. However, when I mix HV and EV and get my EV efficiency up (shown by high miles/kWh), I can get better economy and less gas used than pure HV. The result for my 35 miles of daily commute is that it is better to drive HV mixed with EV at high miles/kWh and use about 50% of charge everyday than depleting 100% EV miles at low miles/kWh or driving all HV everyday. This was especially true for my winter driving condition when I need more heating. The difference is quite big, max ~$50 saving in 80 days compared to using up EV, or ~$30 saving compared to using HV only, as you can see on the screen shot of the spreadsheet. I can achieve this saving without using much more gas than using max EV drive (24 gal vs 20.8 gal).

What is your gas and electricity cost in your area? I can generate the comparison similar to mine for you.

 

With your electric rate, it is going to be easy to say EV drive is far more economical than HV drive. I would try using up all the battery charge at the highest attainable mile/kWh possible.

Assuming 100 miles commute and charging only at home, using $3.40/gal gas and $0.13/kWh elec. My spread sheet gives those numbers. You probably do not have as much of seasonal fluctuation as I do. Your number maybe mostly summer time, and AC use may affect the EV efficiency bit more.

Winter Conditions 4 mo (80days drive) HV 53 mpg, EV 4.5miles/kWh, or Full Range HV/EV is based on 8miles/kWh
MAX EV cost $453.80 gas (gal) 113.58
MAX HV cost $513.21 gas (gal) 150.94
Full Range HV/EV mix drive $355.01 gas (gal) 84.53

Summer Conditions 8 mo (160 days drive) HV 60 mpg, EV 5.5miles/kWh, or Full Range HV/EV is based on 8miles/kWh
MAX EV cost $767.62 gas (gal) 186.00
MAX HV cost $906.67 gas (gal) 266.67
Full Range HV/EV mix drive $321.48 gas (gal) 149.33

Full Range HV/EV is based on 8miles/kWh of EV efficiency and use all the EV range during trip by mixing HV and EV. It is not easy to attain if you do all >70mph highway drive, but with much slower drive I am currently averaging ~8miles/kWh.

 

And THAT is the only answer that he really needs.

Asking the question at all seems a bit odd.
Why would someone buy a Prime in the first place if you didn't already know that running EV as much as possible is saving you money ??

Given his stated mileage, the best thing would be to charge at BOTH ends, if he could get a reasonable price on electricity at the "work" end.

 

Well, I have been asking that question for 2.5 years now. That's because, if he lives in NE and pays the same price for gas and electricity as I do, he would be spending more by driving EV compared to driving HV all the time. With my shorter distance of commuting it is more economical to drive part EV mixed with HV without depleting the battery charge than drive straight EV discharging all battery charge or straight HV not using battery charge at all. It is also as ecological as maxing out EV drive in terms of gas usage. Turns out even if my electric rate is reduced by 40% to a national average, for my commuting, it is still cheaper overall to drive only partial EV with very high miles/kWh rating, than use all the battery charge at lower efficiency.

Everyone's situation is different. It is not a simple question to answer.

 

I don't know how the heat works in the Prime compared to the PIP. But you should use some gas when you want to get the car heated up, in winter.
Also, to try and be the most optimum I think you want to save a few miles going to work to use at the end of your commute to work and the start to go home when you are on city streets. Try a few different methods and see what uses the least gas, but always use all EV.

Mike

 

On your commute you could try to use up some of your EV during the city miles and the rest on your slower parts of the highway/in highway traffic. Or put it in EV Auto and see how it uses up your charge (it keeps it in EV until about 72mph, then switches to HV).

"Using HV on freeway" assumes you will use all EV up before you get home, since HV is more efficient on the highway (as compared to HV in city).

I have a 40-50 mile commute one way. I do some shorter drives around work sometimes. And then I usually drive around 10 miles going out in the evening. Charging for me during off-peak is about half price compared to using gasoline. I can't charge when I get home from work, because it's peak pricing. So what I do is run it in EV until I get on the highway (about 2 miles, like you), run it in HV on the highway till I get to work. At work, if I drive around, I do it all in EV, so the ICE doesn't have to turn on. I drive home mostly in HV mode on the highway, but I use up some of my EV on the slower parts of the trip (like where the speed limit is 55 instead of 70, or if there's traffic). I try to get home with about 35% charge remaining. Then when I go out at night, I use up that 35% without having to turn on the ICE for the short trips. That's basically my plan - only turn on the ICE on long trips. Use EV on short trips to save wear on the engine. Try to end the day with as close to 0% charge. Charge at night for cheaper rates.

 

You don't need to turn on the ICE to get heat in the winter. Just don't use the defrost button. But it only gets down to like 30 degrees here, not like a real winter.

 

True, but from the number's I've seen, very rarely should EV be more expensive than HV, with the most common places where it might are islands (Hawaii, Puerto Rico, etc).

 

That may be true for many places on paper by simply comparing pure HV and pure EV. If the driving distance is always less than the max EV range, then the comparison is straightforward. But for a distance longer than the max EV range, it is not as easy to come up with the best strategy to minimize the cost and the gas usage. On top of this, the gas prices are fairly volatile. The electricity rate is regionally and/or seasonally affected. I have not had the same electric rate from month to month. When it comes to analyzing the cost for the use of EV drive in given drive case like my commuting, as I commented above, even if my electricity is at the national average of $0.13/kWh and current gas price of $2.40/gal, my numbers show it is less expensive to drive HV mixed with EV rather than driving purely on gas or max out the EV range.

 

How do you figure that you can get 8 miles/kwh on EV and still get the same 50 for HV? Wouldn't using mostly EV on the efficient sections bring down the average for HV if you're using it on all the inefficient sections of the drive? If you have data to back it up, that would be really interesting and potentially be a big deal for maximizing efficiency. Although I think it's rate for me to do a long enough drive to use all the EV range and also make good use of HV mode. Most of my driving is within or just slightly over the EV range.

The heat pump works well above freezing. It's very efficient and I don't think it changes the EV vs HV calculation too much. Below freezing I'm not sure. It can have a big impact on EV range. But using the heat makes the engine run longer than it would otherwise, so you'll likely see lower mileage. I still use the heat pump extensively rather than switch to HV, even down to the minimum temperature or in a snowstorm where I need to blast the heat the whole way. The worst I've seen is about 16 miles of EV range blasting the heat on my commute in a snowstorm. EV driving is cleaner, so even if it costs slightly more it's worthwhile to me. I pay for "100% wind" power, so in theory my electricity usage is more sustainable than using gas. In practice it's hard to wrap my head around how that works, because it all comes from the same grid, but I think it helps. The car is so cheap to drive whether on gas or electric that the cost of fuel hardly matters to me.


Another consideration for HV vs EV is letting the engine warm up. I think it's not the best for the engine to let it run for just a short time on a regular basis. It will always complete the warm-up cycle unless you turn the car off before it's done, but the warm up cycle the minimum, not necessarily enough to get everything fully up to operating temperature. For example if I have just slightly less EV range than I need to make it to my destination, I might use HV the whole way. But maybe it doesn't matter too much?

 

Yes, there are some guess works at play here. As you know it is not easy to determine the real HV portion of mpg on PRIME when EV mode is mixed in. But if I can keep the EV range fairly constant for the same distance commute, in my case total ~35 miles, the overall mpg displayed on the car should be proportional to pure HV mpg regardless of how EV portion is mixed into the 35 miles. Compared to the monthly log data from the first year Nov-Jan to this winter Nov-Jan, I am getting almost the same monthly average mpg yet vastly different miles/kWh. During my first winter, I never used HV/EV switch at all. I just drove EV until the car ran out of EV SOC then rest was just HV. During those days I determined my true EV range in my winter was ~20miles on continuous EV mode drive. This winter, I was always switching HV/EV during my commute, but have a set point when I do the switching, so the sum of the segments I have the car in EV mode can be calculated. This distance is about 20 miles in total. So, having a similar EV distance in the same 35 miles commute route and resulting similar overall mpg must mean HV portion of mpg is also very similar.

 

My point about using HV when you want heat is more the case where your total trip length is going to be beyond the EV range anyway.
This way you are getting the advantage of the ICE waste heat and can use the battery EV range for driving.

Mike

 

If you are in SoCal and SCE is your electricity provider, then the $$/mile is about the same whether you drive in EV or HV,
It's about $0.05/mile whether driving HV or EV mode.

 

OP said he is paying "gas is btw $3.39 and $4, depending on if I make it to Costco: I’m using SCE time of use which is a flat .13 cents during the night which is when I charge". At that rate, EV is much better choice at ~$0.034/mile. In comarison HV for gas at $3.39/gal will be at ~$0.063/mile.

 

Wonder why OP couldn't figure that out when he had all the data he needed to calculate $$/mile. ???
I just drive and don't think too much about this. And charge the battery as often as possible.