energy efficiency equivalent

[bystander]

I know we're not supposed to reply to news items directly in their own news items forums, so I'm discussing it here.

In this article:

Celebrities Autograph Segway HT to Benefit Environment at 'An Inconvenient Truth' (http://forums.segwaychat.com/showthread.php?p=113083)

an updated figure for "energy efficiency equivalent" has been stated.

It costs only 25 cents to charge up the Segway HT and it has an energy efficiency equivalent to 450 miles per gallon.

There still isn't a source on this, I assume it's the Segway, Inc. marketing dept.

What we don't know is what figure is being used for the following items:


Price of gasoline
Price of electricity
Electricity used for full charge
Miles traveled per full charge


Lots of variables there. We know the pair of Saphion packs stores 800 watt-hours, but don't know exactly how much it costs to fill them because the conversion efficiency of the charger is not explicitly stated.

Up till now, I've always thought I can get about 8 full charges per dollar of electricity spent. And if gasoline costs about $3.25 per gallon, then I should be able to charge 26 times for the price of one gallon of gas. 26 charges times 20 miles per charge = 520 miles. More than 450, isn't it?

If I only got 17.3 miles per full charge then the figure would be 450 miles, that makes it a valid estimate, allowing for various terrains and rider weights.

But if it's costing me 25 cents per charge, then $3.25 should only buy 13 charging cycles and give a rage of 13 x 20 = 260 miles. A lot less than 450, isn't it? My range would have to be 34.6 miles per charge, which seems unrealistic.

Or maybe I'm barking up the wrong tree. If one looks up the energy equivalent of one gallon of gasoline, it is around 37 KWH, but only assuming that one can fully convert everything without any conversion losses. 37 KWH is enough to fill a pair of Saphion packs 45 times, still assuming zero conversion losses.

Assuming 20 miles per charge, that would be 900 mpg. That's quite a bit more than the figure of 450 mpg. So there must be some sort of accounting of the energy conversion losses. It would seem that the total conversion loss is 50%. I suppose one could speculate that 25% is lost converting the gasoline to electricity and an additional 25% is lost when charging the HT's packs.

So 260 mpg is too low and 900 mpg is too high, but exactly how did they arrive at that figure of 450 mpg?

I'm not losing any sleep over this, just curious if anybody else has been wondering about the "energy efficiency equivalent" figure. Maybe there's some other way to calculate this figure.

I realize this is somewhat of an "apples to oranges" comparison anyway, because the different vehicle mass and typical speed difference of what's being compared.

Trivia: it has been estimated that the "energy efficiency equivalent" of walking or running is 235 mpg in gasoline energy terms (http://en.wikipedia.org/wiki/Fuel_efficiency#Fuel_efficiency_in_transportation) . And estimates for bicycling are between 650 and 1100 "mpg". Some even estimate 1500 mpg for bicycles, but I haven't seen those figures.

[macgeek]

I have known it takes 10 cents to charge Nimh batteries 8 hrs at 1.2 cents per kw/hr

so lets say its 15 cents for Li/oN same 1.2 cents per k/h

$3.50 gallon of gas devided by 1.2 cents

292 miles per 'gallon' on a seg

BUT

The seg goes 22 miles on a charge - so take 15 cents devide it by 22 miles
so its 6/8ths of a cent per mile

Jonathan

[citivolus]

It comes from the energy density of gasoline. The problem is that energy density is based on mass. According to http://hypertextbook.com/facts/2003/ArthurGolnik.shtml the energy density is about 45 MJ/kg. Using a rough swag at the gasoline volume density of 3.2 kg/gal that makes 144 MJ/gal. Converting MJ to kW•hr requires the following conversion, 1 J = 1 W•s. 1 kW•hr = 3600 kW•s = 3.6 MW•s = 3.6 MJ.
The last bit is 144 MJ/gal • (1 kW•hr / 3.6 MJ) = 40 kW•hr/gal.

Now the density of gasoline varies a little with temperature and formula. The energy density varies depending on additives like ethanol and formula so using any accepted value is fine.

Another thing it doesn't take into account is the fact that the best gasoline engines are only about 30% efficient and diesels can get near 40% before any losses associated with a vehicle.

hyperphysics has a calculator
http://hyperphysics.phy-astr.gsu.edu/hbase/gaseng.html

HTH

Jonathan, 1.2 cents / kw•hr ?!?!?!
Who do you get juice from?

[bystander]

For cost per mile, I think I'm experiencing somewhere around 0.6 cents per mile (city tax not included) -- 10% more with the tax. The uncertainty of my calculation is not very good though, it may be off by 20%. Still, that would be only 0.79 cents per mile (tax included), or 17.4 cents per full Saphion charge.

So why the claim of 25 cents per full charge? that would make the cost per mile at 1.13 cents. Maybe they've figured in a higher local tax rate or worst case KWH rate.

It can be challenging to know how much money it costs to charge the HT with great precision, because I don't have equipment to monitor precise AC current draw over time.

Another big issue is the fact that the majority of my charges are partial, as I like to keep the HT "topped-up". Since one doesn't know with any great precision is already in the packs (when only partially discharged), one doesn't really know how much is added unless has some kind of data-logging equipment installed where the charger plugs into the wall.

It seems to me the HT could keep track of all of this, maybe users can get access to the data on a future firmware upgrade or future model.

[bystander]

...Another thing it doesn't take into account is the fact that the best gasoline engines are only about 30% efficient and diesels can get near 40% before any losses associated with a vehicle.

I wonder if more people realized that 75% of the money they spent on gasoline was wasted, whether there'd be more demand for higher efficiency vehicles.

Back when gas was under a dollar, the point was moot. But now, is there enough interest to create the demand that will eventually make higher-efficiency vehicles less expensive?


---naah! probably not. . . . . .

[SegwayUtah]

I'm guessing that the calculations are based on "reasonable worst-case scenario" (like energy prices in New York City or Urban California). The 25 cent figure is probably the updated figure for rising energy costs and the double-range Lithium batteries.

Chris

[Desert_Seg]

I have been looking at this at length and it is one of the questions I have written down for the dealer conference.

Now, while all the above calculations are good to know, they, unfortunately, operate within a vaccuum. The energy used by the Segway is directly related to the mass onboard the Segway, the terrain on which the Seway is riden, the method used to ride the Segway (start / stop, non-stop, etc), AND both the temperature and air-density during the ride.

We all know the cost of fossil fuel bears a direct relation to the 450Mpg figure but what about those countries that use fossil fuel to generate power? Or Nuclear Energy? Ach, what about wind power.

The reality is that this 450Mpg figure is a great marketing ploy that likely has some great numbers behind it. It is a great selling point and I believe that with the upwardly mobile fuel prices the distance traveled is probably greater.

Each dollar increase in the price of a barrel increases the value of a Segway proportionally....but boy does it hurt if also rely heavily on your car.

Steven

[cmonkey]

I have a slightly inaccurate (alternative way) of looking at mileage.

Very few people actually know what they're paying for electricity, I sure don't. And I'm not about to do the kilowatt hour gas mass energy equivilent conversion math. (yet)

But, from what I've seen, the cost to charge/run a seg is about a penny a mile.

I look at it this way...

Someone asks me the mileage question, and I'll in turn ask them how much they paid for their last gallon of gas.

Then I tell them that for what they paid for that gallon, I can go X miles.
$3.50/Gal = 350 miles.

Now, marketing math aside, I've found that with this simple comparison folks are more apt to think about the Segway's capabilites because now they're thinking about their wallet! It's a much more direct connection.

And I can take this a step further.... neener, neener, my seg gets 600miles to the gallon :D. You see, I also happen to have a weekend gas guzzler that eats 100 octane fuel. This fuel costs me $6/gal. So, for what I pay for a gallon of gas for that beast... I can go 600 miles on my seg.

I've had the 'eneregy equivilant' conversation with people, and they look at me like I'm going to spontaneously sprout pocket protectors out of every orifice! Yes I'm a nerd, but I'm not going to prove it every chance I get.

For the sake of simplicity, I've found the way to most people's brains, is through their wallet, so, that's where I direct the conversation. The result is that I can see the gears turning as people ponder their commuting alternatives.

I wonder how far I could 'go' on a gallon of dragster fuel?
Happy Gliding!
Dave@600mpg

[KSagal]

Someone did briefly mention my following point.

Gallons of gasoline converted to kilowatts is nice, but that is like bench horsepower ratings on engines. Nice but not always applicable.

My car weighs over a ton, so hauling my 210 butt around is not so significant to it's efficiency. My Seg weighs less than half my weight, so the same cannot be said...

I will only claim the equivalent of 450 miles per gallion when I am doing that fat guy in the speedo thing that is common of French beaches.

When I am wearing my normal clothes, and have my seg cargo bags full of electronic crapola, I only claim the equivalent of about 417 miles per gallon.

[citivolus]

Now that I've actually thought about it, I think the out of pocket comparison is much more useful than bothering with esoteric energy calculations. Why go to the inconvenience of installing mammary glands on a leverage enhancing device?

Oh Karl, thanks for painting an all too clear picture. :eek:

mental note: stay away from French beaches.

[macgeek]

"karl your carrying grapes in the wrong place"

Oh Thats his speedo

:)

Jonathan