Some contend that: In the interest of sustaining the world as we know it, we may have to learn to tread a bit more lightly, one step in this direction is to change our transportation to systems that consume less resources while fouling the air less. Others believe these alternative systems will just raise the cost of doing business and damage the economy. A number of alternative car propulsion systems have been devised, none as yet has been able to dethrone the the gasoline powered internal combustion engine as the dominant source of transportation power.

Here's a lay person's quick interpretation if the literature alternatives on car power systems and an estimate of their potential.

Gasoline Engines: Very good energy storage density, established infrastructure, "first there" advantages.

Diesel: The historical smelly, soot producing bad boy on the road, some remarkable advances in better mileage and lowered pollution have been made in diesel engine designs. Sustainable bio-diesel fuel produces lower pollutants, while reducing reliance in imported fossil fuel.

Gasoline/Hybrid-Electric: An higher efficiency Gasoline propulsion system, strategically assisting a reduced size, more economical gas engine with an electric motor, recycling potential energy of braking normally wasted as heat.

Electric Power: While the electric motor is an efficient propulsion system, in comparison to the internal combustion engine (which produces more heat than horsepower for the your energy) The storage system for the amount of electricity required to propel a ton of car is technically challenging. Uniquely to electric car efficiency equation, electric cars don't become lighter as the fuel supply is exhausted.

Plug-in Hybrid: Both an electric and a hybrid vehicle, the initial part of the day's mileage is powered by low cost, low night rate home electricity. The payoff for this solution to the electric car "Range Anxiety" issue seems to depend on a match of the driver habits and vehicle configuration, see the Chevy Volt discussion below. Some home brewed electric conversions using golf cart batteries have a gasoline powered portable generator stored under the hood as their "Range Anxiety" antidote.

LPG: Currently most popular alternative fuel in the world, liquefied petroleum gas, a by-product of the oil and gas industries is a natural hydrocarbon fuel made up of propane and butane, that produces lower CO2 that other fuels. Even in it's most dense liquid state petroleum gas has about 84% the energy density of gasoline, this and the harder to fit high pressure storage tank requirement make for a lower travel range. More popular in Europe, availability and tax/pricing often dictate the feasibility, over 10% of vehicles in the Netherlands are LPG powered. Studies have shown that dual powered LPG/Gasoline vehicles in the U.S. are operated mostly in gasoline mode.

CNG: Compressed natural gas (mostly methane): another low polluting big fuel tank energy source in plentiful supply in the U.S. As with LPG standard gasoline engine cars can be adapted to run CNG, usually with the trunk space used for the added tank.

LNG: (Liquidized natural gas) is the most dense form, providing about 60% of the energy density of diesel. The complexities of the cryogenic containment requirements make LNG uncommon in private vehicles use, but is an optimal form for special tankers.

Corn Ethanol: Widely declared by critics outside of the corn belt to be a break even at best energy scheme. Brazil's sugar can based ethanol is a more practical system, while ethanol produced from farming byproduct, like corn stalks, or algae would be the ultimate green solution.

Liquid Fuel Made From Coal: Synthetic gasoline, diesel fuel, methanol, etc. can be made from coal, allowing this plentiful energy source to be used by existing vehicle designs, this fuel synthesis process was used by Germany in WWII. Not currently cost effective and a renowned source of pollution, it would seem to not be in the running.

Hydrogen: While providing zero tail pipe emissions, some critics contend that is just shifts emissions to fixed power generation stations. Hydrogen is not as energy dense as gasoline, limiting range and requiring larger tanks. Though adaptable to the familiar filling station model, with fuel either trucked in or generated on site from electricity or natural gas. The standard hydrogen car configuration using electricity generated by fuel cell's rely on the strategic metal platinum which may be the ultimate limiting factor.

Compressed Air: A relatively low tech scheme that may be more sustainable than battery or fuel cell systems that rely on exotic metals. The energy balance sheet takes a big hit in the air compression part of the equation, there may be a 75% energy loss in the process of filling the more advanced air vehicle's carbon fiber tanks to 5000 psi.. Perhaps in a mad max future of exhausted resources, a vehicle like the steam engine sounding one with the extra dials and levers in the demo video below will make sense.

Water power: Certainly the most intriguing and fraught with fraud concept, buying the idea requires a certain kind of faith and ignorance of the laws of thermodynamics A number of schemes have been described, none proven to be practicable.There have been demonstrations of vehicles that appear to be powered by as small quantity of water. One recent Japanese company (now out of business) demonstrated a vehicle using a water-to-hydrogen 300 watt generation system, believed to use a reaction of water with the actual (and limited) energy source, a metal hydride.

You can find a comprehensive guide to alternative fuels at the U.S. department of energy, as well as mileage and pollution stats for most cars.

The production of Electric Vehicle (EV) test fleets was prompted in part by California's Zero Emission Vehicle (ZEV) legislation enacted in in 1990, it started with rather simple guidelines:

• in 1998, 2% of the vehicles sold would be ZEV
• in 2001, 5% of the vehicles sold would be ZEV
• in 2003, 10% of the vehicles sold would be ZEV

Manufacturers did take this seriously (for a time) the most well known production trial car the GM EV-1. of which 800 were produced between 1996 and 1999.

Be sure to Insure Your Hybrid.

In 2001 the requirements were watered down with:

• 2% ZEV required
• 8% Partial Zero Emission Vehicles (this politico speak is describing well smoged gas engines)
  

In 2002 the regulations were repealed after a federal injunction was brought against CARB

There have been allegations of backroom collusion, mis-information from car manufacturers and oil companies, and conflict of interest by the head of CARB Alan Lloyd, who had been made director of the newly formed Fuel Cell Institute.

Following word of the ZEV mandate repeal, manufacturers scaled back their alternate energy car programs, GM discontinued the EV-1 program, repossessing the cars without recourse, crushing all but a few crippled museum curiosities, prohibited from being driven on the road.

The distruction of the EV-1s, beloved by their uses prompted the production of the documentary: "Who Killed The Electric Car" in which blame is liberal spread among all parties involved, the arrested picketers suggest the GM surveys finding little interest in EVs may have been biased. The recent ups and downs in gas prices and the demonstration of usability of EV cars, lead by te marginally practical but oh-so-sexy Terla have inspired the movie's director to start a new project, "Revenge of The Electric Car" which is currently in production, his web site is loaded with electric car news.

California has a new set of ZEV regulations in place, now with a number of convoluted clauses and options allowing manufacturers to make their quota in a number of ways, perhaps reasonable, with the practical demonstration of the hybrid car potential unknown in 1990.

Bearing in mind the myriad of trade offs and alternatives available to manufactures to meet the quotas, the core 2009 CARB by Year ZEV Requirements are:

• 2009-2011 11%
• 2012-2014 12%
• 2015-2017 14%
• 2018+ 16%

Types of required and allowed vehicles:
ZEVs, Enhanced AT PZEVs, AT PZEVs and PZEVs

(Everything besides ZEV are "Partial Zero Emissions Vehicle" variations that range from well smog controlled gas burners, like the Ford Focus, to plug-in Hybrids, like the Chevy Volt)

You can get the details of the 2009 CARB regulations in the "ZEV Tutorial"

Right wing and some scientifically informed critics question the ultimate cost effectiveness of the new green car technologies, the Chevy Volt has been a recent target of critics.

Many pundits have cited the Carnegie Mellon University announced in March 2009 as being critical of the Chevy Volt's sort of battery range choices, although not specificity naming the Volt. Edmunds.com published the article: 'Study Says Chevrolet Volt's Battery Profile Is "Not Cost Effective"' While US News & World Report's headline declared: Study: Chevy Volt "Not Cost Effective in Any Scenario" The actual study may not have been quite so cut and dry.

A Carnegie Mellon press release references it as part of a more optimistic, diplomatic terms: Carnegie Mellon Researchers Find a Win-Win in Small-Capacity Plug-In-Hybrid Electric Vehicles. The press release goes on to say: "The core conclusion is consistent: For urban drivers who charge frequently—every 20 miles or less— plug-in vehicles with small battery packs sized for about 7 miles of electric travel per charge can reduce gasoline consumption, greenhouse gas emissions and lifetime cost. For those who can't charge often, large-capacity plug-in vehicles sized for 40 or more miles of electric travel will still reduce gasoline consumption and greenhouse gas emissions, but at a higher lifetime cost,''

The detailed 11 page "Energy Policy" paper "Impact of battery weight and charging patterns on the economic and environmental benefits of plug-in hybrid vehicles" now available for download, may not have been available to the authors of the critical headlines. The study concludes in part "the additional weight of a PHEV60 results in a 10% increase in operation-related costs and greenhouse gas emissions per mile relative to a PHEV7 or drivers who charge frequently (every 7 miles or less)." [PHEV60 being: a Plug In Hybrid Electric Vehicle with a battery range of 60 miles] They go on to note that nearly 50% of US passenger vehicle miles the detailed study examined 7, 20, 40 and 60 mile battery ranges. The conclusion mentions that 50% of US passenger car miles are traveled by vehicles driving less than 20 miles per day. GM based their target design on statistics indicting that 75% of cards are driven less than 40 miles a day.

A tool that anyone can use to estimate the lifetime cost the vehicle and fuel measured in Dollars, Barrels (of oil) and Tons (of CO2) is the The cost of Plug-in Electric Vehicles Calculator at the ProjectGetReady site. You select 2 vehicles to compare, along with cost of gas, yearly mileage and length of ownership figures.

The 54 minute Charlie Rose tour of the Volt labs and interview of designer Bob Lutz can be viewed on his web site. Some suggest that due to the lack of penetrating questions, it amounted to a free one hour commercial for Chevy.

The tour included a look at the EV-1 and Volt batteries compared side by side (Volt on the right). Battery weight being big issue in the cost effective calculation, the Volt battery is 1/3 the weight of the EV-1's, although in the interview Bob Lutz only mentions the 16 KWh Lead-acid version of the EV-1 battery pack, the last version of the EV-1 achieved considerably better mileage employing nickel-metal hydride batteries, efficient, although heavier than the Volt's Li-ion and labeled by Lutz as having environmental issues.

EV-1 battery: 540kg, 1200 lbs

• 1st version: 16.5 kWh, Delphi Lead-acid batteries, 55 to 75 miles per charge
• last version: 26.4 kWh, Gen.2 NiMH batteries, 75 mi to 150 miles per charge (this later battery was actually some 192 lbs. lighter than the led acid pack)
  

Volt Battery: 180kg, 400 lbs

• 16 kw, lithium ion batteries, 40 miles before auxiliary engine kicks in
  

More recently in a September 2009 web chat Bob Lutz Stated: "The Volt technology is very exciting, but costs will have to come down before it can become generalized, and U.S. fuel prices will have to rise to world levels", meaning $5 or $6 per gallon. industry pundits have estimate the cost of the Volt  lithium ion battery pack to be in the $16,000 to $20,000 range.

Hydrogen is the one fuel that can be consumed with zero emissions. It may be seen from a distant executive/politician office to be a direct replacement for gasoline, demonstrations showing a driver pulling into a station and filling their fuel tank suggests that oil companies and gas station operators would simply have to convert to hydrogen handling equipment.

The reality is hydrogen and gasoline have little in common, gasoline's great success stems from it starting as a free energy resource provided by nature, the only real costs are for the process of pumping and refining oil into gasoline. Though it's all around us, there is no natural pools of pure hydrogen that can be simply pumped out. Hydrogen is made in an energy intensive extraction process, effectively converting some other energy source into hydrogen. Natural gas, a limited natural resource seems to be most commonly used in the hydrogen production process.

The "Zero Tailpipe Emission" promise is a bit of a shell game, emission does take place at the hydrogen production plant.

It's unclear whether producing hydrogen in a central refinery is most cost effective, it's complicated and expensive to transport, a local filing station can produce hydrogen with a room sized apparatus using piped in natural gas, a relatively plentiful resource in the U.S. Honda has a design for a home refueling system that produces hydrogen to refill one's car as well as powering the house.

While modified internal combustion engines can run on hydrogen with low emissions, the standard model for zero emission hydrogen cars uses a fuel cell, (a technology used to power satellite) to drive the car's electric motor.

While hydrogen's lower energy density requires an oversize high pressure tank taking up trunk sized space similar to an LPG, CNG tank, the more serious obstacle to broad adoption is the fuel cell technology that converts hydrogen to electricity, still in the highly expensive developmental phase, some critics point out that platinum, a crucial element in the current designs, is found in only a few places on earth, the limited availability of platinum, also used in emission reducing catalytic converters may limit the ultimate availability of fuel cells.

Hydrogen, like electricity and less directly ethanol, is an intermediate energy form that must be created from a 'source' energy, either oil, coal, solar, hydro or nuclear. Electric car advocates point out that the hydrogen tank - fuel cell combination is the functional equivalent of an electric battery, both drive an electric motor in place of an internal combustion engine. While batteries have their disadvantages, weight and charge time, electric cars don't require a whole new production / distribution / storage infrastructure that hydrogen cars require.

Gasoline advocates point out that the majority of electricity is currently generated by dirty coal powered plants, a trade-off to lower foreign oil consumption. Electric motor smaller energy consumption may cancel out the higher pollution of fixed electric generation plants. (Electric car efficiency has been measured to be equivalent 100+ mpg gas mileage) Tesla motors has calculated the "Well to Wheel" efficiency of all stages of transmitting energy to their electric car's wheels. Using natural gas powered power plant electricity the combined energy consumption is 24% of the average U.S. gas powered car.

The most efficient electric generation plants, and hydrogen production and 'bottling' facilities have roughly the same efficiency of 60%.

The tank to wheel effeciency stats given by Tesla and Honda for various vehicles include:

• Conventional Gasoline Engine 19%
• Hybrid Compact Car 30%
• Optimal Diesel Operation 45%
  
• Hydrogen Fuel Cell FCX 60%
• Electric Car 70% to 85% (accounting for battery charge/discharge losses)
  

Very roughly estimating an overall hydrogen car efficiency of 36% (Generation 60% x fuel cell car 60%)

A natural gas powered hybrid car using a conventional ICE engine would have a fuel tank size similar to a hydrogen car's, it would have very low emission and would get an overall fuel efficiency of roughly 30%, not dramatically different from the more expensive and complex hydrogen car. Assuming the co2 emissions of a natural gas powered hydrogen plant and natural gas car are in the same ballpark, a natural gas powered hybrid car while not technological sexy, would be the safer be.

An approach, even more energy efficient than hydrogen would substitute a Natural Gas Fuel Cell, a simpler technology that operates at an efficiency similar to a hydrogen cell, eliminating the intermediate conversion step required for hydrogen. A Natural Gas Fuel Cell powered car ay prove to be ultimately more efficient than a plug-in electric car too, due to the lower efficiency of the average electricity generation plant in comparison to the Natural Gas Fuel Cell's, .

Seemingly found in the same fantasy land as the water powered car, air powered cars do exist. The big question: can they be economically and ecologically cost effective. Compressed air engines have been used in environments including mines and warehouses where exhaust gasses are unacceptable.

Guy Negre a former formula-1 race car engineer, suspected to be a schemer by some, is a strong proponent of applying the the zero pollution compressed air engine concept on a broader scale. Originally designed to run solely from compressed air stored in special carbon fiber tanks at 5000 psi, in small cars in the India market place. The multi-stage air compression system needed to fill such tanks is not at all energy efficient (performance of existing industrial compressors and the mathematical proofs given in the links below support this) though Negre described in description if a 1999 a Mexican taxi design that it would take $2 in electricity to fill the tank.

The most in depth technical analysis on the subject I have seen is in the responses to the story The Air Car - A Breath Of Fresh Air Or A Waste Of Breath ? at the Oil Drum

Here is a second series of responses to the air car issue.

Another write up showing a far out concept car design, with critical reader responces.

An A.P. article on the subject, quoted an expert: James Van de Ven, who who has studied compressed-air technology as a mechanical engineering assistant professor at Worcester Poly Tech, who said "air compressors allow you to recover only 25 to 30 percent of the energy used to compress the air. The rest is lost through heat, air leakage and other forms of waste"

Some theorists have suggested going as far as compressing the air in a cold geographical location, then shipping the tanks of air to hot geographical area for consumption. Air engines work best in warm environments, in fact generating cold air as a byproduct, a nice bonus in India, but a source of system freeze ups in Minnesota.

The compromise solution for eliminating most of the bulky storage tanks and inefficient high pressure compression is to create the compressed air on the fly with some variation of the steam engine boiler approach. A description of the compressed air engine design I once read indicated that the multi stage design used to make a more efficient compressed air engine could be adapted to make a, modern steam engine like propulsion system when the engine and boiler system are more closely integrated than the simple independent compressor and engine scheme described in earlier incarnations. The analysis suggested that dropping the catchy "Air Car" approach and embracing an "External Combustion Engine" design might be the most successful approach. The Stirling engine is a well known external combustion engine.

The newest incarnation of the air car, written up in 2008: 106 mpg Air Car to come to U.S. by 2010 uses a gasoline powered boiler to supplement the travel range. Again it seems unnecessary for a new engine design to come packaged in such a catchy press worthy package.Considering the designers track record, I may wait to plunk down my deposit until this car is a proven reality, here's hoping it is...