Electricity (kWh) Fuel Consumption and MPGe - Fuelly Forums

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Old 03-06-2012, 02:16 PM   #1
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Electricity (kWh) Fuel Consumption and MPGe

Currently, there is no way to add electric fuel consumption in kWh. Without this, plug-in hybrid electric vehicles, which use both gas can appear to have very high MPG since the electricity consumption is not taken into account. Please consider adding electricity/kWh consumption to the site, so that there can be some reasonable comparison of fuel consumption efficiency between gasoline only, gasoline/electric vehicles, and even electric vehicles.

I did see this thread about this topic.

One of the concerns was how to compare to MPG. The EPA uses MPGe, where the energy content of a gallon of gasoline is used to compare with electricity. Wikipedia explains how to do the conversion as well as additional details.
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Old 03-06-2012, 10:05 PM   #2
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One problem is that the entire Fuelly system is based around the idea of a real world fuel-up. So with traditional vehicles you have to make a special trip to a station and fill up your tank. That's a natural time to record your consumption. It's something people have been doing with a piece of paper in the glove box since cars have existed. There's a natural rhythm to it.

We don't know the natural rhythm of electric vehicles yet. If you plug in your vehicle every night, do you enter your kWh every day into Fuelly? Does the vehicle report kWh usage, or is it a plug in the wall? Do you get that info monthly from your electricity bill? Maybe that's a natural interval to record consumption. And is your car electricity usage listed separately, or do you need to estimate it? Maybe a website can help with that or maybe it's not necessary.

These are questions we can find answers to, but we currently don't have enough information largely because we (the big we—society) haven't established these patterns yet. We are in an information-gathering phase on this. We're listening to what people who have electric vehicles are saying.
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Old 03-06-2012, 11:57 PM   #3
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Yeah, we would be happy to add something to Fuelly if it were easy and possible to track all your electricity usage. Neither of us founders have a plug-in or Volt car to test this stuff out on. If anyone owns one and can describe how they track their own data, I would love to hear it.
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Old 03-07-2012, 03:52 AM   #4
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I have a question that is somewhat on topic. Home battery charger stations are not 100% efficient with regards to the electricity they use from the grid versus the electricity they deliver to the vehicle battery. Depending on the charger unit, voltage, and the ambient temperature, that efficiency can change significantly, numbers I've heard range from 80% to 90% efficient just depending on the ambient temperature.

Do the chargers and/or vehicle take this into account when they report how much electricity has been used? I would think that if the vehicle were reporting the kWh/mile, it would NOT report this and would over-rate the electric efficiency by 10-20% or more. But if the charger itself were reporting, it might take this into account.

Seems like if this extra power was not logged, it would be equivalent to logging fillups on Fuelly by using the vehicle computer's fuel economy estimator instead of the gas receipt and odometer reading. Onboard fuel economy averages are often optimistic, but few of them read as much as 20% high. That seems grossly misleading to me.
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Old 03-07-2012, 01:48 PM   #5
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For recording electricity usage, there's a few ways of ways I can think of:

1) From the Prius Plug-in Owner's Manual, the kWh charged is displayed on Multi-Information Display while a charger is connected. I believe (don't quote me on this) that this is for the charge, so it would be recorded per charge (which would probably daily or even multiple times a day).

2a) Some electric utilities offer the option for a separate time-of-use meter for EV charging, so that EV charging can be charged at a discounted rate. This could be recorded at whatever interval the owner decides to go look at the meter or from the electric bill.

2b) A watt meter such as a Kill-a-Watt or Watts Up could be used to serve the same function as 2a.

3) Some EV/PHEV record this data automatically and sync it to a website, so there may be a way to sync the data or export the data as CSV.

As for taking into account charging efficiency, I think the Prius Plug-in display does that, but I'm not sure. A Tesla owner has posted that the Tesla Roadster does. I would imagine that all EV/PHEVs do display the amount from the wall, otherwise there would be discrepancies compared to the electricity bill that would have to be explained.
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Old 03-08-2012, 01:01 AM   #6
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Even if the car only displays internal KWh usage (the volt does), its easy to convert that to the wall, and my guess is that anyone using fuely is smart and and dedicated enough to do that. A full charge is 12.9 from the wall (measured with a kill-a-watt) so its not hard do the math, even for a partially charge.

I use voltstats.net to track my usage and have a CSV file from which i compute my actual uages.. I'd be glad to share it.

There is a different issue with PHEVs like the Volt. Fuely's model of only reporting after a few tanks is tough. I last filled up in october (2750 miles ago), and still have a 1/4 of a tank..

Without KWH its misleading and even with it gas usage will be unstable for quite a while.
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Old 03-11-2012, 05:22 AM   #7
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I don't see why there is a concern about a "natural rhythm". Charging is the (PH)EV equivalent of a gas fuel up, so the most basic method is to record per charge. However, with charging, the driver has the additional flexibility of accumulating the data over several charges with a power meter, either built into the car or external to the car.

Even with gasoline fuel-up, the rhythm varies between drivers and circumstance. The driver can refuel when the tank is almost empty, or more frequently based on personal preference, preparation for a long trip, or anticipation of rising gas prices. Some drivers don't fill-up all the way, instead charging a certain dollar amount or number of gallons in a fuel-up. Charging is no different and the rhythm can vary between drivers and circumstance as well. Fuelly actually doesn't care about the rhythm of a gasoline fuel-up and records them and calculate MPG fine without any consideration for it.

Not including electricity is actually a problem to this concept of rhythm. In the pathologically worst case, a PHEV can go indefinitely between gasoline fuel-ups or indefinitely without charging. However, it must do at least one or the other, at which point recording the gasoline fuel-up and or charge provides data points for calculating MPGe.

Anyhow, I'm not sure how it is any different than a gasoline fuel-up. The things recorded are for gasoline and electricity fuel-ups are:

odometer reading odometer reading

gallons kWh

price/gallon price/kWh

Calculating MPGe is also a documented formula.

Finally, I'm not sure I understand the "information-gathering". Was such information gathering necessary to have Fuelly record gasoline fuel-ups and calculate MPGe? Perhaps if you could be more specific about what information you need, (PH)EV owners could help supply it.
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Old 03-11-2012, 05:32 AM   #8
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"Even if the car only displays internal KWh usage (the volt does), its easy to convert that to the wall..."

So you are saying that the wall charger station displays the current converter efficiency for each recharge cycle? Since the efficiency changes significantly, you are making a gross assumption unless the charger itself displays it for your.
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Old 03-11-2012, 10:13 AM   #9
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What I mean by rhythm is that the fuel-up process provides the perfect time to record consumption. It's a process that takes time out of your day, and it's easy to add the step of recording to that process. People have been doing it for years.

If you come home every night and plug in your car, it's not a separate process like driving to a specific fueling station. That's all I meant by that. And no, we didn't need to gather information because people have been recording their gas mileage at fuel-ups for years and years. Fuelly is a mirror of that process. People are just starting to plug their cars in every night. So we need to get a sense of how and when people want to stop and record that activity. It's not intuitive to me that you would jot down your usage whenever you unplug or plug in your vehicle. (And then take the extra step of going to a website to record it as well.) So we want to get a sense of what we should mirror here if/when we add a system for tracking kWh.
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Old 03-12-2012, 06:20 AM   #10
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BDC, "wall charger station" is a misnomer; the correct term is Electric Vehicle Supply Equipment (EVSE). This name more correctly reflects the fact that all it is is a smart cord which has safeguards to only supply power when properly connected and disconnect if it detects a hazard. Any losses in the EVSE are negligible. The actual charger is built into the vehicle and determines the charging efficiency.

As for what should be mirrored, perhaps I'm missing something. How would the system change for tracking kWh depending on how/when people stop and record their electric fuel-ups?
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