Are electric cars more energy efficient?



This analysis neglects the differences between the qualities of energy sources. Coal won't fuel a car directly, it's only good for making steam . Petroleum is more versatile. Electricity is the highest, most valuable form which can do almost anything except be stored cheaply in bulk..
jsw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I'm not sure what you are referring to.
To be clear, my point was that Iggy's original premise was flawed. He assumed no production or distribution losses on petroleum and inflated those losses on electricity.
In terms of btus dug from the ground and delivered to the transmission, it is probably a wash.
28% carnot efficiency * 85% production efficiency = 23.8% of the btu dug hit the transmission 33% production efficiency * 93% transmission efficiency = 30.69% for electricity delivered. If the charging and motor losses are 22.45% than it is dead even.
As to Iggy's question, "And how is it going to reduce CO2 emissions, if more CO2 needs to be burned as coal than would come from gasoline?"
Even if the EV is less efficient than gas engines, not all electricity comes from hydrocarbons but all gasoline comes from hydrocarbons. If the difference in efficiency is less than the percentage of electricity produced from hydro/nuke/solar/wind then it will result in a net reduction of CO2.
All that aside, I drive a 12yo pickup. But speaking as a person who owns a hundred different hammers, I say "Diversity is always a good thing and should be encouraged".
There's more than one way to skin a cat. That doesn't seem important now, but it's gonna be real handy when we run out of squirrels to eat.
Paul K. Dickman
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
whoyakidding wrote:

OK, will you mostly be doing short drives and then recharging from the line? If so, the cost to operate it looks really good! If you will be going more than 28 miles or so on a typical day's driving before recharging, then it starts to look really bad, and many cars on the road will actually do BETTER! It appears the Volt gets about 26 MPG on gasoline.
Take a look at the Honda Civic Hybrid. I get over 50 MPG in mixed city/hwy driving. I just did an 1100 mile round trip to a conference, with 600+ Lbs of junk in the car (plus me) and going 70 MPH on the highway in beastly heat, I got 46 MPG. If I ran a bit slower with less weight, I'd get 49 or so. The HCH is a LOT cheaper than the Volt.
Jon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Plenty of shorter drives and charging at least partly from solar panels I'll install.

CR got 37 combined if I remember right. I'm reading expect 35 and sometimes get 40 on trips. Example: http://gm-volt.com/forum/showthread.php?7512-My-First-Long-Drive Don't forget that some fuel only reports won't include recharge while driving. http://www.plugincars.com/chevy-volts-mountain-mode-vastly-underrated-yields-new-driving-strategies-107176.html http://gm-volt.com/forum/showthread.php?8720-MM-vs.-Normal-D-vs.-L I saw a report of high 20s that once adjusted for recharge equaled high 30s.

The Volt outweighs the Civic by about 30% but is quicker. Apples and oranges. Anyway a large part of my theory here is that I don't want to merely do what's cheapest for me.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
whoyakidding wrote:

This doesn't work. The Volt has an 18 KVA battery pack, I think. To get 18 KVA from a set of solar cells, you'd need the roof space of a good-sized commercial building. One face of a typical home will get you a couple KW for a few hours a day, so MAYBE a halfway charge overt a full day. A big enough solar cell array to perform a full charge on one day might cost MORE than the car!

37, 35, 40? Are these numbers range on electric power or MPG? The MPG numbers I've seen INLCUDE powering it electrically until the battery is depleted, THEN switching to gasoline, and counting the wall-power as free!

Yep, those batteries are heavy. But, my HCH experience is from 50K + miles in one. I'm certainly a satisfied customer.
Jon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Congratulations you are now qualified to work at the Chevy dealer I visited.

Think energy instead of power. The Volt's useable capacity is about 10kwh ($1 at average utility rate). It takes about 12 hours to charge from a standard 120V outlet or 3 hours from a standard 240V outlet.

Arf arf.

1800 sq ft square single story = single wall face 43.5 ft X 8' = 349 sq ft = about 3.4kw actual X 4 hours average (location dependant) 13.6kwh. Approximately enough to fully charge the car 7 days per week. Less required if you don't drive every day or use the full battery every day of driving. Example: if your commute is 20 miles round trip then you might only charge 3 times per week and could either live in Seattle or downsize the array to suit.

A full charge on a Volt requires about 13kwh. Note the hour part. http://gm-volt.com/forum/archive/index.php/t-5610.html Some approximate numbers off the top of my head: if one's daily mileage averages half the cars battery range then the array could be about 10 of these or the equivalent plus the usual grid inverter etc. http://www.sunelec.com/evergreen-solar-panel-195-watts-2800-vmp-b-p-1623.html Adjust size to suit owner's miles and location. I'm considering installing enough for the car and my home's use. PV is cheap right now so I may go overboard and shoot for running a net surplus.

The numbers I used were the gas only numbers.

Sample quote from one of the links I provided in the post you responded to: "The EPA officially gave the Volt a 35 city/40 highway mpg rating without using stored battery power, but in my experience that charge-sustaining fuel economy on the highway was closer to 43 mpg (yes, that's calculated without any grid-filled battery input)" This chart https://www.voltstats.net/ is also useful.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Jon, please include at least a sentence of the quoted text so we, anyone, will know WTF you're talking about. ;)
-- Always bear in mind that your own resolution to succeed is more important than any one thing. -- Abraham Lincoln
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 28 Jun 2012 20:33:39 -0700, Larry Jaques

Please pardon me for the brain fart. I had accidentally turned off quoted text and everyone's posts were showing up that way. First time in over a decade, too.
-- Always bear in mind that your own resolution to succeed is more important than any one thing. -- Abraham Lincoln
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6/27/2012 3:24 PM, Jon Elson wrote:

And, I don't have to subsidize it!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 26 Jun 2012 07:42:33 -0500, Paul K. Dickman wrote:
(...)

There's that 300 - million - year delay in turning biomass into oil, too. If time is money, that is a hell of a toll.
--Winston
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 26 Jun 2012 07:42:33 -0500, "Paul K. Dickman"

And ioncreases the relative efficiency of bunker fired plants.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ignoramus6950 wrote:

The source of the electricity used for charging has the greatest impact on the true efficiency and emissions as everyone else noted. What they forgot to note is that EVs do not consume any energy during stops or downhill grades, and recapture some energy during braking, both of which can further improve efficiency to a variable amount based on terrain and usage.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Planning the route and timing of your shopping trips does that too, with any vehicle.
jsw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Pete C. wrote:

My Honda hybrid does the same. As soon as you take your foot off the gas, the fuel is cut off and the intake valves are closed, allowing the engine to freewheel with low losses. As you slow for a stop, at 9 MPH the clutch drops out and the engine stops completely. When you take your foot off the brake, the engine is spun up by the assist motor and the valves are engaged. The motor assists acceleration to cover for the woeful power output of the semi-Atkinson cycle engine. The assist motor also absorbs energy to charge the battery during downhill grades and average braking. So, on Honda Hybrids, the brakes usually last the life of the car.
Jon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6/26/2012 6:08, Ignoramus6950 wrote:

That's simple. Just like any truly green electricity without CO2 emissions. Make the electricity with nuclear power.
However, in the cold or hot climate (most places:), one of the big problems with electric cars is AIR CONDITIONING, cooling or heating. In a normal gasoline powered car, there is extra heat to use for heating the car (here in winter at -20C). In the electric car, the extra heat has to come from electricity in battery, and we are talking about several kW.. Electric cars are cold cars in winter as the battery just simply can't handle the heating.. Also, you have to use power to cool it in summer, but that is less of a problem (less delta-T). Perhaps better heat insulation will solve this.
The second big problem is that it costs 10000-20000 usd per 5 years for battery replacement.. That makes a LOT for the USD/km cost.. Perhaps better battery technology will solve this.
The third big problem is TAXES. Nowadays here in Finland the gasoline costs about 1.7 euro/litre (0.70euro/litre for gasoline and 1.00 euro/litre government tax). If the electric cars come popular, there will definitely be a tax on "electric car electricity".. Perhaps put a kWh counter in each electric car and then pay X.XX USD/kWh electric car electricity tax.. Nothing will solve THIS.
Here the reasonable way to go at the moment is with CNG, compressed natural gas. Conversion of old car is about 2500euro. Cost of CNG driving is HALF the cost of gasoline driving, for fuel cost per km. However, the big threat is that government will also put a heavy tax on CNG (like on gasoline), so people are afraid to convert their cars. It takes about 2 years payback time for the conversion. Again, nothing will solve the TAX problem, especially poor predictability on changes of taxes.
IMHO.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I am fascinated by the idea of using CNG to run my vehicles. Especially the corporate trucks. If it could costs twice less, that would make a huge difference.
Say, my dump truck, rarely leaves a 50 mile area.
i
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ignoramus6950 wrote:

Not even close. A good Otto-cycle engine gets maybe 13% efficiency at near wide-open throttle. At typical mid-throttle operation, it is much worse, maybe 5-8%. A semi-Atkinson cycle engine like in my Honda Civic Hybrid does better at mid-throttle, as does a Diesel by eliminating pumping losses.
So, a standard gas engine is a lot worse than you might imagine.
Most of the electrical gear is WAY more efficient than that, hence small heat sinks and minimal cooling system are needed.
No, the losses in the electrical system are small compared to the incredibly poor efficiency of the typical gas engine. Any time you have the gas pedal less than floored, you are practically driving with the brakes on! Read up on "pumping loss" if you don't believe me.
Then, look at the VAST amount of heat going out the tailpipe, and the significant amount of heat going out the radiator.
Just being able to drive without these massive heat losses gives some idea of the efficiency of electric vehicles.
Compare the KWH energy loaded into the batteries of a typical EV against the BTU content of a tank of gas, you won't believe the numbers!
Jon
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Jon Elson wrote:

Modern gasoline engines have a maximum thermal efficiency of about 25% to 30% when used to power a car. In other words, even when the engine is operating at its point of maximum thermal efficiency, of the total heat energy released by the gasoline consumed, about 70-75% is rejected as heat without being turned into useful work, i.e. turning the crankshaft. Approximately half of this rejected heat is carried away by the exhaust gases, and half passes through the cylinder walls or cylinder head into the engine cooling system, and is passed to the atmosphere via the coolant system radiator[1]. Some of the work generated is also lost as friction, noise, air turbulence, and work used to turn engine equipment and appliances such as water and oil pumps and the electrical generator, and only about 25-30% of the energy released by the fuel consumed is available to move the vehicle.
At idle, the thermal efficiency is zero since no usable work is being drawn from the engine. At low speeds gasoline engines suffer efficiency losses at small throttle openings from the high turbulence and frictional (head) loss when the incoming air must fight its way around the nearly closed throttle; diesel engines do not suffer this loss because the incoming air is not throttled. At high speeds, efficiency in both types of engine is reduced by pumping and mechanical frictional losses, and the shorter time period within which combustion has to take place. Engine efficiency peaks in most applications at around 75% of rated engine power, which is also the range of greatest engine torque (e.g. in the 2007 Ford Focus, maximum torque of 133 foot-pounds (180 Nm) is obtained at 4,500 RPM, and maximum engine power of 136 brake horsepower (101 kW) is obtained at 6,000 RPM). At all other combinations of engine speed and torque, the thermal efficiency is less than this maximum.
In the past 3-4 years, GDI (Gasoline Direct Injection) increased the efficiency of the engines equipped with this fueling system up to 35%. Currently the technology is available in a wide variety of vehicles ranging from affordable cars from Mazda, Ford and Chevrolet to more expensive cars from BMW, Mercedes-Benz, VAG.
http://www.fueleconomy.gov/feg/atv.shtml
Only about 14%26% of the energy from the fuel you put in your tank gets used to move your car down the road, depending on the drive cycle. The rest of the energy is lost to engine and driveline inefficiencies or used to power accessories. Therefore, the potential to improve fuel efficiency with advanced technologies is enormous.
Improving IC Engine Efficiency
Todays efficiency situation:
FUEL 100%
PUSHING THE PISTONS 35%
OVERCOMING ENGINE FRICTION AND PUMPING THE AIR AND FUEL
(typical US driving condition) 20%

--
Steve W.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

My 1949 Aircraft Powerplant Handbook puts the typical engine output power at 29.5% of the energy in the fuel at cruise, 60% of rated power. http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption The R-3350 (B-29, DC-7) was better at 33.7%, close to the top of the range for the most efficient gasoline car engines. It used an exhaust power recovery turbine system that's much too complex and expensive for an economy car. http://en.wikipedia.org/wiki/Turbo-compound_engine
jsw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6/25/2012 11:08 PM, Ignoramus6950 wrote:

Ya'but does it make one FEEL good?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.