Anyone have a calculator that shows at what gas/electricity prices it makes sense to use which fuel?

[cmwade77]

I am by no means a solar contrarian, and don't want to start a firestorm.
But... Solar power is far from free until the cost of the array has been completely offset by your energy savings.
This process takes time. Dave included the caveat (ignoring amortization), but it is definitely a little misleading for anyone to claim they "drive for free" because they have solar panels.

That depends, if the solar panels are added to existing construction, I would give that to you, but since solar is required in our neck of the woods for new construction, it could simply be considered part of the cost of the house, so this is a tricky one to answer.

 

[cmwade77]

I have a Google Docs spreadsheet that has a pretty detailed setup and you can base it on your vehicle and you can also set the gas vehicle you wish to compare to, although that does require a bit more manual input of the combined MPG.

But, the link is here:
https://docs.google.com/spreadsheets/d/1OkQW8LRKbJSwApoYhrJY4nx4r3qu8cdaCpwwDSzLYT0/edit?usp=sharing

I have pre-populated it with some of my past charging data.

NOTE: I have not included free charges in this, so the overall cost per gallon is a lot lower than this, but this gives a good idea of what can be accomplished. You will also notice that there are several sections for the more popular networks, these are designed (where possible) to allow you to directly import the files as the various services export the data.

I am sure there are many improvements that need to be made, but hopefully it gives a nice starting point.

 

[MrFixit]

but since solar is required in our neck of the woods for new construction

Hum, I was unaware that there was a requirement anywhere for solar on new construction...
Where is this "neck of the woods"?

 

[cmwade77]

Hum, I was unaware that there was a requirement anywhere for solar on new construction...
Where is this "neck of the woods"?

California now requires most new construction to have solar, additionally, most new construction requires EV charging stations.

 

[Landshark]

Add battery backup to a solar array and the picture gets more complicated.

We had a system installed in 2012 with batteries and 2 inverters to run a 240V well pump and holding tank pump, among other circuits, during power outages. To us, there is value in that, in addition to offsetting some of our electricity usage. In fact, having backup power was more important than feeding juice back in to the grid.

At the time, rebates and credits offset nearly 70% of the cost. That’s better than the Clarity, which was about 40%. It was a solution to a potential problem, and it has been used. The idea of free electricity or a break even date are of no concern.

 

[Mark W]

To further help with this analysis, do we know the MPG breakdown for highway vs. City? And also the Miles/kwh difference between stop and go city and 65-70 mph? The reason I ask is that, the highway driving experience between EV and HV mode is nearly the same to me. But for stop and go local driving the EV is experience is MUCH better. I won't use HV for local driving, even though currently it would save me some money.

 

[MrFixit]

do we know the MPG breakdown for highway vs. City? And also the Miles/kwh difference between stop and go city and 65-70 mph?

There can be a lot of variables here, and you can try and customize an analysis for your particular scenario if you want. But, even within an individual's case, there will be variability.

In my opinion, the generic analysis (graph that shows $2.00 per gallon is roughly equal to $0.15 per kWh) is all you need to do this simple trade. If you try to be any more 'exact' than this, you may be engaging in "Analysis Paralysis". Trying to save every possible penny is a false economy particularly because secondary effects like extra wear & tear on the engine with gas kick in and cloud the precise answer anyway.

 

[JCA]

Honda claims 42 mpg. I usually get closer to 50. Take 45 as a pessimistic average guess. 45 miles is close to a pessimistic electric-only range, too. Your easy napkin-calculation is to divide the price of a gallon of gas by the 17 kWh of a full charge.

A gallon of gas near me costs $1.68. Divided by 17 kWh that's 9.8¢ for even prices. However, given my electricity is free, it never makes sense to get that gas unless I'm going beyond electric range

Just one correction -- the battery pack may be 17 kWh, but the car doesn't allow all of that to be used. Driving to 0 EV then fully charging for another (estimated) 45 EV miles typically takes 14-15 kWh from what I and others have measured. So your breakeven power cost is more like 11.2 - 12 cents/kWh.

As others have mentioned it can vary a lot based on your driving too -- more higher speed highway miles might lower MPG a little, but MPkWh a lot, whereas more slower speed driving might raise MPG a little but MPkWh a lot.

 

[Landshark]

There certainly are a number of variables. The greatest seems to be EV range in various temperatures. I believe we’ve had reports of EV range as low as 25 miles in cold weather and as high as 65 or more in warm weather. Whereas gasoline produces more consistent results, perhaps in the 35-45mpg range.

Another factor to consider after the pennies per mile has been determined, is total miles driven. A penny per mile over 10K miles is a $100 difference. If you’re burning gas to save $100/yr that’ll get spent on a couple of oil changes. Now, $.10/mile over 10K miles would be a $1000 difference. That’s something to consider.

And let’s face it, this car is much more likely to suffer a costly gizmo failure than an ICE failure.

 

[Mark W]

There can be a lot of variables here, and you can try and customize an analysis for your particular scenario if you want. But, even within an individual's case, there will be variability.

In my opinion, the generic analysis (graph that shows $2.00 per gallon is roughly equal to $0.15 per kWh) is all you need to do this simple trade. If you try to be any more 'exact' than this, you may be engaging in "Analysis Paralysis". Trying to save every possible penny is a false economy particularly because secondary effects like extra wear & tear on the engine with gas kick in and cloud the precise answer anyway.

That's fine, and I agree, but I would still like to know the differences. Not so much for the exact calculation of which is cheaper.

 

[Landshark]

That's fine, and I agree, but I would still like to know the differences. Not so much for the exact calculation of which is cheaper.

At 70-80 mph in HV the car (my car) gets ~36mpg. Three 700 mile trips in 10 hours each, that’s the number. Coincidentally, it also gets about the same range at those speeds in EV. That indicates that a gallon of gas is equal to a full charge at those speeds.

In stop and go, rush hour, commuter, around town traffic, EV range has been from 50-65 miles, in warm weather, mostly above 60 degrees. I cannot provide data for driving in those conditions in HV, as it is always less costly, and preferable, where I drive to operate in EV for that type of trip. HV is only deployed for trips that exceed EV range.

I believe you would need to establish the EV range and MPG that you obtain given your driving conditions and habits and then use those figures to determine a fuel of choice.

The Clarity has a remarkable ability to produce a wide variety of results depending on who owns the vehicle.

 

[MrFixit]

OK, thinking about this some more, and using some of the experience conveyed by @Landshark , here is an attempt to incorporate driving style into the break-even analysis...

The global assumptions are these:
1. A full charge is 14 kWh (nominal vehicle buffering)
2. Nominal temperatures (no heat, A/C impact would be small)

Three conditions are shown with these assumptions:
City - EV range 55, HV mileage 44 mpg
Mixed - EV range 47, HV mileage 42 mpg
Highway - EV range 36, HV mileage 36 mpg (70-80 mph). 55-60 mph would be more like 'Mixed'

Here is the resulting plot: