alt.energy.renewable

On Oct 22, 4:17 pm, Retired VIP wrote:
> On Sun, 21 Oct 2007 22:29:47 -0700, "bsr3...@ "
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> wrote:
> >On Oct 21, 10:09 pm, Retired VIP wrote:
> >> On Sun, 21 Oct 2007 17:09:56 -0700, "bsr3...@ "
>
> >> wrote:
> >> >On Oct 10, 1:55 pm, Eeyore
> >> >wrote:
> >> >> BobG wrote:
> >> >> > Actually looks pretty slippery. .25KWhr per mile perhaps?
>
> >> >> In a flat country like Holland maybe ?
>
> >> >> Graham
>
> >> >I did a google for "road horsepower" and the first link was for a
> >> >Toyota MR2.
>
> >> > /
>
> >> >A test by Car & Driver put it at hp @ 50 mph. That would be 14*.
> >> >746= KW, which is what would be needed to cover 50 miles.
> >> > /50 = .20888 KW hr/mi. An efficiency of 85% would not be
> >> >unrealistic and would give .20888/.85 = .246 KWhr/mi. This thing
> >> >looks like it probably has a lower CD than an MR2. BTW that hp
> >> >was broken down into
>
> >> >Friction and tire losses @ 50 mph ..... hp
> >> >Aerodynamic drag @ 50 mph ............. hp
>
> >> >Bruce
>
> >> I think you missed something here. According to your figures, it will
> >> take just over 200 watts to move the car at 50 mph for one mile.
> >> That's not the figure given of 14 hp, that's more like 1/4 hp expended
> >> to move one mile. You have to expend that power at a constant rate of
> >> 14 hp or kW. Look at it another way.
>
> >Read it again. That is 200 watt hours. Yes, a 1/4 hp motor should be
> >able to move the car 1 mile in an hour. And a 1 hp motor could move
> >it 4 miles in an hour. And a 2 hp motor could move it 8 miles in an
> >hour. And a 14 hp motor could move it 50 miles in an hour. A watt is
> >energy per unit of time, same as hp. A watt hour is a unit of energy,
> >as would be a hp hour. Spread that energy out over a long period of
> >time and the power is low, but the amount of work that can be done is
> >the same.
>
> So 4 hp would move the car 16 miles in an hour (16 mph). A 8 hp motor
> would move the car 32 miles. A 16 hp motor would move the car 64
> miles. And it would take a 32 hp motor to move the car 128 mph. Holly
> smokes, my car should be able to travel at well over 400 mph using its
> 120 hp motor. Do you see something wrong with this progression?

Sure, I made it linear rather than exponential to keep things simple.
The further you get from the 50 mph starting point the further off you
will be. The point was that 1/4 hp would move the car 1 mile in an
hour. That's traveling 1mph for an hour.

> A watt is a unit of power without regard to time. A wHr is a unit of
> work. 10 watts isn't the same as 100 watts but 10 watts applied to a
> device for 10 hours will do the same amount of work as 100 watts
> applied for 1 hour. The same is true of horsepower, it's a
> measurement of power not work. A hpHr is a measurement of work.
>
> So, if it takes 14 hp to move a car at 50 mph without regard to time.
> It will take 14 hp to move that car at 50 mph for one minute or one
> hour. The only difference is the amount of work done, not the amount
> of power needed.
>
> So, his figure of 200 watts to move a car at 50 mph is wrong.

It was 200 watt-hours to move the car one mile in 1/50 hrs. If you
want to go 50 miles in an hour it will take 50 times that.

> Jack
>
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