Tuesday, December 3, 2013

You Do The Math - Which is the "green" car?

Lately I've been hearing about hybrid supercars, first on TV, then online.  The Porsche 918 Spyder hybrid is claimed to reach 78 miles per gallon combined city and highway, but only in eco mode.  Otherwise, you're using the 600 hp gasoline engine combined with the 127 hp front motor and 154 hp rear motor and doing 0 to 60 in 2.5 seconds while getting maybe 1 mpg. 

Porsche 918 Spyder hybrid

Assuming you only use that power to occasionally zip down the entrance ramp of the interstate and actually merge at highway speeds, then maybe you would get 78 mpg for it's lifetime.  But, would this be "green"?  After all, the Spyder will run you about 845,000 dollars, which is a bargain compared to the 1.2 million dollar McLaren P1 and 1.2 million dollar Ferrari LaFerrari.

2013 Ford F150
Are these hybrids greener than the 17 mpg Ford F150 pickup or the 55 mpg Toyota Prius?  I see ads locally where I can get the F150 for $16,000 and the Prius for $30,000.  Which of these 3 uses less energy?

Toyota Prius Z4

Well, let's see.  The Ford F150 weighs 4000 pounds, much of that is steel. Steel turns liquid at about 2500 degrees Fahrenheit a couple times in its trip from iron ore to finished product.  Then it's annealed (heat treated), sometimes more than once, to various temperatures hot enough to turn you into dust.

But, the Prius is a 3000 pound machine, some of that is steel, too.  The rest is plastic, aluminum and glass.   Glass also melts around 2500 degrees.  Thankfully, plastic is cheap, being made from oil, and melts at low temperatures.  Those heavy lead batteries?  Eh, a couple hundred pounds, and melts below 900 degrees with soldering tools anyone can buy.   Pffft.

Steel and iron melt between 2300 and 2700 degrees Fahrenheit
Supercars may be made of carbon fiber and aluminum, but those materials cost more money and energy to make.  Aluminum uses massive amounts of electricity to relieve the alumina molecule from the burden of it's three oxygen atoms, leaving pure aluminum.  This means it gives between 5 and 7 times more money at the recycler than steel gives.  Ever heard of the phrase "Time is money"?  Since the dawn of the industrial revolution, when machines started doing our work and making our products, the phrase has been "Energy is money".

Many times in a product's life it is melted or close to melting.

Today, we'll do the math to see what uses less money, and therefore, less energy.  Let's assume gas prices stay at $3 a gallon, thanks to Canada's oil sands and the US's shale oil.  Heck, gasoline will probably drop to $1 again.  Global warming here we come, eh?

Steel can be recycled, thus eliminating the need to melt/process iron ore.
Cost in fuel for 100,000 miles:

Vehicle mpg  gallons dollars
F150     17  5,882   $17,647
Prius      55  1,818    $5,454
918       78  1,282     $3,846

Fuel plus purchase price for 100,000 miles

Vehicle    gas       purchase   total
F150    $17,647   $16,000      $33,647
Prius      $5,454    $30,000      $35,454
918        $3,846  $845,000   $848,846

Cost per mile:
F150    $33,647/100,000 =   33.7 cents
Prius     $35,454/100,000 =   35.5 cents
918    $848,846/100,000 = 8.49 dollars

The Ford F150, with the V-8 that gets 17 mpg, is the green vehicle.  Go figure.  And I ride a 60 mpg motorcycle that costs me 22 cents a mile, and a bicycle that costs me 10 cents a mile.  I ride the bicycle 600 miles a year to the grocery store and post office!  For someone like me to admit a F'ing pickup, which kills twice as many car occupants as cars do in side impact, the most evil, God-foresaken vehicle on the road, is the green vehicle...   you know it's the truth.  Sorry, did I say F'ing?  I meant F150.

Steel parts inside ceramic molds glow orange hot.

How about after 200,000 miles, which will be cheaper?  Well, the Prius needs a few thousand dollars in batteries after 100,000 miles or so, but the F150 needs thousands of dollars in repairs and upkeep as well.  Tires cost twice as much, and that alone could cost $3000 more in 200,000 miles.

Bearings in wind and hydro power generators are also made of steel.
Oil and filters costs twice as much, having your rotors turned cost twice as much...  In fact, everything costs much more.  V-8 vs four banger.  Do you do rings and valves after 150,000 miles?  That costs twice as much, too.  Fuel pumps and filters costs twice as much.  Let's be nice an ignore repair costs, giving the F150 a head start.

Cost in fuel for 200,000 miles:

Vehicle mpg  gallons dollars
F150     19  11,765   $35,294
Prius      55    3,636   $10,909
918       78    2,564      $7,692

Fuel plus purchase price for 100,000 miles

Vehicle gas       purchase   total
F150    $35,294   $16,000     $51,294
Prius    $10,909    $30,000     $40,909
918        $7,692  $845,000   $852,692

Cost per mile:
F150    $51,294/100,000 =   51.3 cents
Prius    $40,909/100,000 =   40.9 cents
918    $852,692/100,000 = 8.53 dollars

Metal parts before expensive machining, annealing and polishing.
So, the Prius is greener long before it hits 200,000 miles.  But, at what point does the Porsche 918 become greener than the Prius?  That point would be miles, m, in the equation below.

845,000 + (m/78*3) = 30,000 + (m/55*3)
815,000 = (m/55*3) - (m/78*3)
815,000 = 3m (1/55 - 1/78)
815,000 = 3m (1 / 186.5)
(815,000 / 3 * 186.5) = m
50,671,739 = miles

So, if you and your heirs drive 20,000 miles a year, the Porsche will break even with the Prius after 2,534 years.  Or more, if those super-huge, super-wide, low profile, sport compound, Z rated tires on the 200-plus mph Porsche cost more than the Prius's skinny, little, fuel efficient, high miles, H rated tires (115 mph).  And I'm sure they do!

Finally, the connecting rods in your engine are cast, machined and annealed.

Car & Driver magazine


Andy Austin said...

Greener ? or cost efficient?

The environment not to mention the roads would be safer if we all drove a Prius... or would they ?

WoodHugger said...

They sure would. The DOT did two studies 10 years apart, and found that smaller pickups and SUVs kill twice as many car occupants as large cars do. (Both large cars and small trucks are about 4000 pounds, in this case.) And as the pickups and SUVs climb in weight, which they do, all the way to 7200 pounds for the Hummers and 8000 pounds for some ford Excursions, they kill 4.5 times more car occupants! This is as bad as driving drunk. Therefore, these heavy, tall vehicles should be illegal.

WoodHugger said...

Cost efficient is the same as greener. That's the whole point of this particular dollar-to-dollar comparison.

WoodHugger said...

I forgot to add insurance. If the pickups and SUVs do twice the killing, they probably do twice the damage, so liability would be higher.

Just imagine if human life was insured for what it's worth. Say a million dollars? Consider a lifetime of employment and paying taxes. And taking care of your parents when they get old. This adds up! Is it affordable to insure all the vehicles on the road for the 20,000 or so deaths a year caused by multi-vehicle collision?

20,000 times a million = 20 billion
20 billion / 200 million drivers = $100. (Each year)

Of course, pickups and SUVs would cost double that of cars, so $200 divided into 1/3 and 2/3 is $67 for cars and $133 for the light trucks.