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Power-User

Join Date: Jan 2011
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How Much Petrol Is A Watt Hour Worth?

09/09/2014 5:26 AM

I got a new battery for the electric bike so I was wondering how much petrol this is worth. The battery is is 222 watt hours. Petrol is 8.76KWh per liter. 1 kwh = 1 divided by 8.76 which = 0.1141 liters per kwh. So, 1 watt hour = 0.1141 divided by 1000 which is 0.0001141 litres for 1 watt hour.

Source is http://hypertextbook.com/facts/2003/ArthurGolnik.shtml

I am rubbish at maths so is this correct to say that 1 watt hour is 0.0001141 litres of petrol?

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#1

Re: How much petrol is a watt hour worth?

09/09/2014 5:35 AM

How far do you get with your batterie?

seems if you have a use of 10 liters per 100 km you can get

.

.

wait

.

.

math

.

.

o jerry can

.

you do it!

.

.

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#2

Re: How much petrol is a watt hour worth?

09/09/2014 6:05 AM

According to that, the battery is worth ~0.025 liters.

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#3

Re: How much petrol is a watt hour worth?

09/09/2014 6:22 AM

For a full comparison, the effectiveness of the engine that turns petrol into miles is missing from the analysis, as in the effectiveness of the electric motor that does the same.

Please indicate why the calculation matters.

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Power-User

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#4
In reply to #3

Re: How much petrol is a watt hour worth?

09/09/2014 6:55 AM

1

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#6
In reply to #4

Re: How much petrol is a watt hour worth?

09/09/2014 7:17 AM

Okay, now the battery is worth ~0.075 liters.

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Power-User

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#5
In reply to #3

Re: How much petrol is a watt hour worth?

09/09/2014 6:57 AM

It matters so that I can easilly do MPGe conversions on my electric bike. I am looking at the thermal energy content of the battery and the petrol. You would imagine the comparison as burning the petrol vs connecting the battery to a heating element. But in reality the useable energy of petrol is much lower when you consider how little of it actually moves the vehicle.

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Guru

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#7
In reply to #5

Re: How much petrol is a watt hour worth?

09/09/2014 11:53 AM

It's like a tiny tank that holds 75 ml of petrol, but it's pretty cheap petrol. Electric bikes don't need that much energy to get around and they're loads of fun.

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Power-User

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#14
In reply to #7

Re: How much petrol is a watt hour worth?

09/10/2014 2:15 AM

Brilliant fun. They can out accelerate all but the most elite of ricers.

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Guru

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#8
In reply to #5

Re: How much petrol is a watt hour worth?

09/09/2014 1:04 PM

"when you consider how little of it actually moves the vehicle."

Well if that is a consideration, you must give us an energy efficiency for the petrol engine you want compared to your electric bike.

My girlfriend can move her car 40 miles on a gallon, while I can only move my truck 18 miles.

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Power-User

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#9
In reply to #8

Re: How much petrol is a watt hour worth?

09/09/2014 4:11 PM

Well, typically engines are 30% efficient. To get mpge worked out I would need to connect a watt meter to the bike.

As for the truck and car, 40mpg is quite bad. My car gets 72. As for your truck, are you driving an 18 wheeler?

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Guru

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#21
In reply to #9

Re: How much petrol is a watt hour worth?

09/11/2014 9:32 PM

My truck is a Dodge Ram 2500 with a Cummins diesel engine.

I don't think I could pull a 32' offshore boat with a car that gets 72 mpg.

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Power-User

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#22
In reply to #21

Re: How much petrol is a watt hour worth?

09/13/2014 4:22 PM

My car is a Citroen C1 with a 998cc engine.

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#10
In reply to #5

Re: How much petrol is a watt hour worth?

09/09/2014 9:05 PM

So, how does 222 WH compare in price to 75 ml of petrol there?

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Power-User

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#13
In reply to #10

Re: How much petrol is a watt hour worth?

09/10/2014 2:14 AM

222wh of lipo costs £75. 222wh of petrol is 17 pence I think. It is about £1.40 a litre for petrol in Scotland.

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Guru

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#18
In reply to #13

Re: How much petrol is a watt hour worth?

09/10/2014 8:16 AM

I actually meant 222wh of electricity.

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Power-User

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#20
In reply to #18

Re: How much petrol is a watt hour worth?

09/10/2014 10:57 AM

That would be 3.37 pence

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#16
In reply to #3

Re: How much petrol is a watt hour worth?

09/10/2014 4:32 AM

....and the cost plus "life" (how many recharges) of the battery.....

The equation is incomplete without also the cost of the car, maintenance and repair costs and life expectancy.....and and and....

Also, battery life is reduced if the charger is used too often as all batteries have a maximum number of recharges, but very difficult to assess....this is affected by usage and temperature to name but two....

Not forgetting "How "clever" is the charger?

I go with 2000 recharges (but could be more or less!) for my ePed and my laptop batteries.....it appears to be very aproximately right or near enough for Government work......

My laptop battery was used by another for 6 months, since I have had it, charged once and removed....

The ePed battery is about 4 years old and has covered around 15,000 Kms, still giving full capacity....45-65 Kms per charge.....old style 10 amp battery, 250 Watt motor I believe....

Best of luck to all......

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Power-User

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#17
In reply to #16

Re: How much petrol is a watt hour worth?

09/10/2014 5:25 AM

I compare using the electric bike to using my car. 72mpg from the car is the best I have managed. I hate using the car. My bike has 1110 watt hours of lipo batteries which are mollycoddled on an expensive charger and charged from solar power only. I never store them charged. They are always stored at 3.83 per cell every day when I am finished using them. They are charged to a maximum of 4.07v per cell. I am confident that I will get many years of use from them. It was about £350 for all the lipo's I got.

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#11

Re: How Much Petrol Is A Watt Hour Worth?

09/09/2014 10:41 PM

I can add some real-world data here.

I have now been driving an electric Humber Vogue for over a year. It has a 3 phase motor and Vector VFD running it with Lithium Iron Phosphate batteries - no transmission.

I get around 120 Wh/km which is on par with EVs of the same weight.

Before conversion it got 12l/100km - not very good but we'll get to that.

My battery pack is 12kw/h and I only allow 80% of that - so 9.6kw/h. I get 80km range on that 9.6kw/h. (Thats would be 100km if I used all the capacity.)

From these figures, one litre of petrol is equivalent to 1kw/h of electric power.

But the Vogue 1600cc petrol motor with it's 3 speed Borg Warner was not economical , so lets make that 6l/100km for a modern power plant. Then we get one litre of petrol equals 2kw/h.

Hope this helps.

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Power-User

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#15
In reply to #11

Re: How Much Petrol Is A Watt Hour Worth?

09/10/2014 2:18 AM

It must have been quite easy as old cars are very simple without all that engine wiring to get out. Old meets new. I like that conversion. Just replace that battery with a load of high discharge rate lipo and bolt two warp impulse 9 motors together with a Soliton 1.2 megawatt controller. The last time I did an mpge calculation was on my old bike and it was over 1000mpge

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Guru

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#12

Re: How Much Petrol Is A Watt Hour Worth?

09/10/2014 1:29 AM

Watts is = (F*d/dt); Nm/s -- Power, which is the rate of energy.

Energy = (F*d/dt)* dt = F*d = 1Joules or 1Newton-meter = (3600)Watt-hour)You have a heat value of petrol on data sheet (maker) per liter as KJ/liter.

It should not be a problem converting. Only that, at carnot cycle, best efficiency of the machine would only be at 30% of the heat per liter.

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#19

Re: How Much Petrol Is A Watt Hour Worth?

09/10/2014 9:54 AM

To my way of thinking I guess it comes down to this question.
Do you want some sort of theoretical value simply for paper and pencil comparison
or
Do you want actual side by side knowledge of the difference in range and performance between the battery and the petrol.
The first will give your math skills a work out and probably yield very little in the way of practical information.
The later will give you actual comparative data.
Plus, you can add into your results real world factors like hills, heavy feet, traffic, temperature changes etc.
So its up to you
You can either tool around the countryside doing "research". wink wink nudge nudge
or

You can sit in your study or shop doing math.

Have you considered the "pub regenerative effect?"

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Commentator

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#23

Re: How Much Petrol Is A Watt Hour Worth?

09/29/2014 10:35 PM

Think of it this way:
Most cars are exactly like turning on 20 single-bar radiators.
Most electric cars are like having a car with 5 litres of petrol.

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