[SoCalGuy]

I've been thinking quite a bit about the electric vehicle movement and the anticipated fleet of options we'll have in the next few years. I think everyone of us on this forum want to move toward more eco-friendly, energy responsible vehicles. So as I was thinking today, is the Karma really a green vehicle?

When we think about eco-friendliness or energy efficiency, a large portion of the equation isn't just absolute emissions for emissions sake, but rather the efficiency with which we use stored energy. In other words, if an ICE converts 30% of the contained energy of gasoline into useful mechanical energy, there's plenty of room for improvement taking an ICE from 30% to 50%+. The same is true for electric vehicles. Just because EVs don't use gas, doesn't mean they can't be equally as inefficient as their ICE counterparts. If the associated emissions and poor energy efficiency from the coal-fired plants that generate the electricity to power our EVs is equal to our greater than that of an ICE, we're really no better off.

So that brings me to the next point - lighter cars, all else being equal, are more efficient than heavier cars. So I ask this: is the Karma, at 5,300lbs, a greener vehicle than a Toyota Corolla or Honda Civic at roughly 2,500lbs? Even the Maserati GranTurismo, Quattroporte, and Porsche Panamera Hybrid are 1,000lbs lighter at 4,300lbs! (The upcoming Tesla Model S is expected to be around 3,800lbs - I know, I know, its not a direct comp to the Karma, but still should be a reference point!)

The A123 20kwhr battery in the Karma weighs in at about 606lbs. So even excluding the battery, the Karma still weighs 4,700lbs, a fair bit more than the larger engined pure sports cars. The 2.0L EcoTec ICE from GM only weighs about 330lbs (for reference, the Panamera's V6 weighs around 404lbs). Where is all this extra weight coming from?

Is the Karma really a green vehicle? It always strikes me as odd that we need 3,000-5,000lbs of stuff to propel and move 200-800lbs or people. Thoughts welcome!

Cars that weigh less than a Karma:
Chevy Volt: 3,781lbs
Porsche Panamera 4,123lbs
Tesla Model S 3,800lbs
Aston Martin Rapide 4,378lbs
Bentley Continental 5,181lbs
BMW 7-series 4,344lbs
Honda Pilot 4.310lbs
Acura MDX 4,550lbs
Audi Q7 4,850lbs
Audi A8 4,436lbs
Audi R8 3,715lbs
Ford Explorer 4,872lbs
Jaguar XJ 4,331lbs
Lexus RX 4,178lbs
Maserati Quattroporte 4,962lbs
Mercedes S-Class 4,455lbs

 

[Fabulist]

I think about this issue hierarchically. At the highest level, the question is whether using electrical power is inherently more efficient that burning fossil fuel. My sense is that the answer to this question is "YES". The numbers I have seen in various studies generally say that if you start with the energy content of crude oil and carry that through the various steps of refining, transporting, delivering, and burning in a car to produce power, you end up with about 25% of the original energy. With electrical cars, the efficiency is much higher, above 50% by some accounts, since you are moving electrons around rather than actual heavy liquids, and the grid, the charger, and the battery each waste 5% or less of the energy input, as opposed to fuel pipelines and trucks that use up a lot more of the energy to carry the fuel around.

The Karma itself can aslo provide us with an example of this. The battery in the Karma and the engine-generator output about the same amount of energy (around 150KW or 200HP). Using Fisker's range numbers and the generally used figure of 36.6KWH/Gallon of Gasoline, we can see that in Sport mode, the Karma uses 9.5 Gal * 36.6KWH/Gal to go 250 miles which works out to a consumption of 1.39 KWH/Mile using Gasoline. In Stealth mode, you use 20 KWH to go 50 Miles which works out to a consumption of 0.4 KWH/Mile. Since the Karma's weight and the drive train are exactly the same in both modes, the only difference would be the efficiency of the gasoline engine/generator vs. the battery charged from the grid. As always, your milage may vary

The next level of the hierarchy would be the car itself. Obviously a car that had the same power as the Karma but weighed 1000 pounds less, with everything else being equal, would have much better performance. but that really is a function of material science more so than drive train. Like you, I am actually a bit surprised that the Karma weighs as much as it does, particularly since, unlike the Panamera or GranTourismo, the Fisker has no transmission. I can only guess that the two electric motors plus the generator attached to the engine up front must be contributing to the mass since the body is made mostly from Aluminum.

My view is that the Fisker can be a green vehicle, despite the mass, if your driving pattern falls within a certain portion of its envelope and you manage the power sources for economy. The driver has a huge influence of the car's efficiency. If you are a fan of the British TV Show Top Gear, you may have seen the episode where they raced a BMW 325 against a Toyotal Prius for 10 laps at high speed around their track and the BMW actually got slightly better milage. The same will undoubtedly be true with the Karma. If you leave it in Sport mode and flog it at full power all the time, you will not get very good efficiency. But if you stay in stealth mode for the slower portions of your drive and use the sport mode for limited high-speed runs, you could end up using very little gasoline.

-- Fab.

 

[kabalah70]

Plus, while ICE could become more efficient through use of technology to reduce their carbon footprint, it would require, more than likely, that expensive engine modifications or more likely the purchase of a new car to partake in those improvements.
With an electrically powered car, I improve my carbon footprint at no significant cost to me with the same car, when the power grid converts to using more and more solar, wind, and other renewable energies.

 

[SoCalGuy]

I think about this issue hierarchically. At the highest level, the question is whether using electrical power is inherently more efficient that burning fossil fuel. My sense is that the answer to this question is "YES". The numbers I have seen in various studies generally say that if you start with the energy content of crude oil and carry that through the various steps of refining, transporting, delivering, and burning in a car to produce power, you end up with about 25% of the original energy. With electrical cars, the efficiency is much higher, above 50% by some accounts, since you are moving electrons around rather than actual heavy liquids, and the grid, the charger, and the battery each waste 5% or less of the energy input, as opposed to fuel pipelines and trucks that use up a lot more of the energy to carry the fuel around.

The Karma itself can aslo provide us with an example of this. The battery in the Karma and the engine-generator output about the same amount of energy (around 150KW or 200HP). Using Fisker's range numbers and the generally used figure of 36.6KWH/Gallon of Gasoline, we can see that in Sport mode, the Karma uses 9.5 Gal * 36.6KWH/Gal to go 250 miles which works out to a consumption of 1.39 KWH/Mile using Gasoline. In Stealth mode, you use 20 KWH to go 50 Miles which works out to a consumption of 0.4 KWH/Mile. Since the Karma's weight and the drive train are exactly the same in both modes, the only difference would be the efficiency of the gasoline engine/generator vs. the battery charged from the grid. As always, your milage may vary

The next level of the hierarchy would be the car itself. Obviously a car that had the same power as the Karma but weighed 1000 pounds less, with everything else being equal, would have much better performance. but that really is a function of material science more so than drive train. Like you, I am actually a bit surprised that the Karma weighs as much as it does, particularly since, unlike the Panamera or GranTourismo, the Fisker has no transmission. I can only guess that the two electric motors plus the generator attached to the engine up front must be contributing to the mass since the body is made mostly from Aluminum.

My view is that the Fisker can be a green vehicle, despite the mass, if your driving pattern falls within a certain portion of its envelope and you manage the power sources for economy. The driver has a huge influence of the car's efficiency. If you are a fan of the British TV Show Top Gear, you may have seen the episode where they raced a BMW 325 against a Toyotal Prius for 10 laps at high speed around their track and the BMW actually got slightly better milage. The same will undoubtedly be true with the Karma. If you leave it in Sport mode and flog it at full power all the time, you will not get very good efficiency. But if you stay in stealth mode for the slower portions of your drive and use the sport mode for limited high-speed runs, you could end up using very little gasoline.

-- Fab.

Fab,

Thanks for your comments. I don't know that I agree that in a gas-powered car, you're getting 25% of the original energy content of the fossil fuel since I recall that most modern ICEs get around 30% or so energy efficiency of the energy content of the gas itself, which itself has required energy to produce from crude oil. At the same time, I'd argue the same is true for EVs - in most parts of the country, fossil fuels comprise the primary source of electricity (over 85% of the US energy supply comes from fossil fuels). So we'd need to factor in energy efficiency at the coal-fired plant (which I've been told is on the order of 70-80% for modern plants), and then factor in loss due to transmission - which is greater than 5%. Long distance transmission is around 6.5-7.0%, then you must factor in substation transmission loss, which is around 1-3%. Overall, you're looking at roughly 8-10% loss from original power source.

All that aside, lighter cars - regardless of the propulsion architecture and irrespective of the driving pattern - are going to be more efficient than heavier cars - that's just physics. It would be great to do a weight audit on the Karma vs. a Panamera or something else and see what are the big, heavy components of the car and determine the main culprit of the obesity.

 

[ct-fiskerbuzz]

Thanks for your comments. I don't know that I agree that in a gas-powered car, you're getting 25% of the original energy content of the fossil fuel since I recall that most modern ICEs get around 30% or so energy efficiency of the energy content of the gas itself, which itself has required energy to produce from crude oil. At the same time, I'd argue the same is true for EVs - in most parts of the country, fossil fuels comprise the primary source of electricity (over 85% of the US energy supply comes from fossil fuels). So we'd need to factor in energy efficiency at the coal-fired plant (which I've been told is on the order of 70-80% for modern plants), and then factor in loss due to transmission - which is greater than 5%. Long distance transmission is around 6.5-7.0%, then you must factor in substation transmission loss, which is around 1-3%. Overall, you're looking at roughly 8-10% loss from original power source.

Hmm, well. In practice, 30% would be remarkable. In theory, an ideal Otto cycle engine could have a thermodynamic efficiency of about 63% with a compression ratio of 12:1 (see MIT course page on Otto cycle efficiency), but in practice it is nowhere near this high, most cars use 9.5:1 or 10:1 (12:1 requires high octane gasoline, if using gasoline for fuel) and actual well-to-wheel efficiency is roughly 15 to 20% (see UW mech.engineering course page—there is a table at the end).

As for the electric energy, well, "it's complicated" Roughly half of the electric energy in the US is from coal, with the other half coming from nuclear and hydroelectric (slightly more nuke than hydro). The next biggest fraction is wind, at about 2%, and other renewables (excluding hydroelectric, which is renewable, but competes with recreational, agricultural, and flood-control uses of the same water, making the details horrifically messy) come it at under 1%. See the Sankey diagrams on https://flowcharts.llnl.gov/. But there is a huge hitch here: these values are highly time-dependent, both time-of-day and time-of-year. Peak power is largely from natural gas. Baseload power is mostly coal and nuclear (depending on location). Hydroelectric predominates in the Pacific Northwest (WA, OR, ID) and makes up a bigger fraction of both baseload and peak in California than in most other (non-PNW) states.

If you do get your baseload from coal (as I do: Utah is heavily coal-powered, although natgas is sneaking in to the mix, along with fast-growing but still overall-tiny wind), your coal-fired generators are not 70% efficient, but rather more like 35%. New combined-cycle gasifying coal plants can be as efficient as new natural gas combined-cycle plants, which have a theoretical thermal efficiency of just over 60%, but generally do well to hit 50% unless it is cold out.

The best local generation technology is "distributed cogeneration", also known as "combined heat and power" (CHP), "combined cooling, heating, and power" (CCHP), "building cooling, heating, and power" (BCHP), and various other acronyms. A gas-fired CCHP system providing an office tower with electric power, hot water, and chilled water can run about 80% efficient pretty much year round. A system that needs more hot water and/or hot air (e.g., a greenhouse, or a hotel with a lot of hot water needs for laundry) can get 85 to 90%. Unfortunately, CCHP costs a bit more up front, and if you have been involved in this sort of project, you know that most people would rather spend $250,000 now and $100,000 per year in operational costs than spend $350,000 now and $50,000 per year in operational costs, even though they come out ahead in the third year. So most people go for the inefficient centralized power plant, which makes it someone else's problem.

EHV transmission (the long distance AC and DC power lines) aim for a worst-case loss of about 3.5% (half of what you listed), but yes, when you add in step-up and step-down and local transmission and distribution, you're looking at 8 to 10% loss in many cases ... dropping a 35% efficient non-combined coal plant down to 31.5%. Again, distributed cogeneration avoids most of this loss.

Most of these are not factors that we, as individuals, can control in any way. Nonetheless, despite the Karma's weight, its estimated mileage when running on the petrol engine shows you how relatively efficient it is for a car in its class. A similarly powerful Mercedes, BMW, or Jag will be doing well if it gets 18 mpg. Factor in the fact that even with coal power, your well-to-wheels efficiency is two to four times higher than that of most gasoline-powered cars and when you look at equivalent luxury marques your Karma is probably roughly 1.5 to five times "greener", depending on where you are (in the USA), what time of day you charge it, and how far you go on electricity vs gasoline.[hr]
Let me add a note: although I quote UW's "15 to 20% well-to-wheel" efficiency for cars, the Sankey diagram has 25% for transportation. This is also a well-to-wheel number, but it includes long-haul trucks and trains, which are more efficient than the average automobile (trains in particular are much more efficient).

 

[kabalah70]

I am lazy today, but I am curious if it is more efficient to do a smaller step down to 220v than to step down to 110v. Would be nice to see some world standards that everyone follows. Perhaps the travel gadget industry is too powerful a lobbyist considering all the jobs they would lose if we did away with travel transformers and plug adapters. Lol.

 

[Fabulist]

Would be nice to see some world standards that everyone follows. Perhaps the travel gadget industry is too powerful a lobbyist considering all the jobs they would lose if we did away with travel transformers and plug adapters. Lol.

I think the travel gadget industry's power has already started to wane since most electronic devices use power adaptors that can accept any AC mains voltage in the range available in the world, plus the 12V DC available in cars, and 15V - 18V DC power available on airplanes. As long as you can plug it into the weird shaped plug at your destination, your charger can spit out the right voltage at the right current for your computer and handheld device. So if we keep putting switching power supplies in more and more devices, local voltage will eventually become irrelevant.

-- Fab.

 

[kabalah70]

http://in.answers.yahoo.com/question/index?qid=20100320195836AARjFCU

That's what I thought I remember power losss = Current squared times resistance. Therefore, for the same power requirement a higher voltage results is less loss, hence the whoel reason for high voltage power lines. Therefore, it would be nice if everyone switched to 220v. I had also heard with the increase in electrical accessories for automobiles, there was some talk of swtiching to a 42v system. That would rock as well.[hr]
http://in.answers.yahoo.com/question/index?qid=20100320195836AARjFCU

That's what I thought I remember power losss = Current squared times resistance. Therefore, for the same power requirement a higher voltage results is less loss, hence the whoel reason for high voltage power lines. Therefore, it would be nice if everyone switched to 220v. I had also heard with the increase in electrical accessories for automobiles, there was some talk of swtiching to a 42v system. That would rock as well.