See the Tabbed Pages for links to video tutorials, and a linked list of post titles grouped by topic.

This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.

Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".

Wednesday, November 3, 2010

Electric Cars: Global Warming Fallacy, Until…

Summary:  Electric cars are being introduced in the American market.  They are touted either overtly or by suggestion as being emissions-free, or pollution-free, by the manufacturers and by industry commentators.  The batteries in electric cars must, however, be recharged using electric power from the electricity grid.  Therefore, greenhouse gases such as carbon dioxide, CO2, produced in the generation of electricity in fossil fuel-powered generation plants, are being released as a result of recharging the electric car.  Because of this, it’s a fallacy to consider that use of electric cars avoids production of greenhouse gases.  Rather, the source of greenhouse gas production is merely shifted from many distributed sources, the large number of motor vehicles on the road, to fixed point sources, the fossil fuel-burning generation plants.  Yet the need to eliminate all sources of greenhouse gas production remains.  Electric cars will only solve the global warming problem when all electric power originates from nonpolluting plants.

Introduction.  Electric cars are beginning to be offered in the American car market, as well as world wide.  The Nissan LEAF is an all-electric vehicle, equipped with battery storage for electric power and responsive electric motor.  Nissan suggests its range is about 100 miles, with a possible range as high as 138-162 miles, before the battery runs out.

Tesla Motors offers the all-electric Tesla, in two models.  The Roadster is stated to be extremely responsive and powerful, with a driving range of 245 miles per charge.  The Model S is slightly less powerful, and is stated to offer three different batteries with a range of up to 300 miles per charge.  Production is to begin in 2012.  The cars are rechargeable from virtually any electric outlet.  They are stated to be a “zero-emissions” car, although elsewhere the web site specifies, more accurately, that there are no tailpipe emissions.

The Mitsubishi iMiEV is an all electric minicar.  Its internet pages say it is a “zero-emissions vehicle”, but admits, more precisely, that when taking account of CO2 emissions from electric power plants, it produces less CO2 than a comparable gasoline powered minicar. It has a range of about 100 miles, and is rechargeable at electric outlets.  It’s thought to be available late in 2011.

GM is offering limited numbers of the Chevy Volt, powered by an electric battery that can be recharged while driving by an on-board gasoline powered electric generator, and at rest from an electric outlet.  Chevrolet states that it is emissions-free for most commutes.  The battery is rechargeable at electric outlets.

Electricity Production in the U. S.  The electric cars mentioned above rely completely or to a large extent on recharging depleted batteries by plugging the car into the electric grid.  In the U. S. about 69% of the electricity presently consumed is generated from fossil fuel-burning power plants.  A pie chart of electricity generating sources as of 2009 is shown here.

Source: http://en.wikipedia.org/wiki/File:2008_US_electricity_generation_by_source_v2.png, representing data given in a table provided by the U. S. Energy Information Administration

Recharging Electric Batteries Produces Greenhouse Gas Pollution.  The information in the graphic shows clearly that much of the electricity needed to recharge the batteries of electric cars originates by processes that expel greenhouse gases into the atmosphere.  For this reason it is incorrect to characterize electric cars as being operated in an emissions-free or a pollution-free manner. 

Relative Efficiencies of Operating Gasoline vs. Electric Cars.  The efficiency of a fossil fuel-driven engine or apparatus (fossil fuels include coal, petroleum and its products such as gasoline, and natural gas) is a measure of the amount of useful work or energy obtained from the heat energy released upon combustion when the fuel is burned.  The rest of the energy is wasted as heat.  (See the diagram at http://en.wikipedia.org/wiki/File:Heat_engine.png and related discussion at http://en.wikipedia.org/wiki/Heat_engine.)

It is generally agreed that a gasoline-powered automobile operates at about 15-20% efficiency (see Note 1).  Burning gasoline in the internal combustion engine of a car thus produces large amounts of greenhouse gases (about 80% of the total CO2) that are essentially of no use in moving the car down the road.

Of fuels used to generate electricity, coal is preponderant.  Coal, when burned, yields less heat energy for the amount of CO2 released than any other fossil fuel.  This means it is worst among fossil fuels in production of greenhouse gases.  Coal-fired generating plants have been used for at least a century.  Those in service presently in the U. S. are thought to have an efficiency, in terms of useful electrical energy derived from the heat released on burning the coal, of about 33% (see Note 2); the rest of the energy is released as unusable heat.  The U. S. Department of Energy is sponsoring research to try to increase this to 50% efficiency (see Note 3).

The next most significant fuel is natural gas.  Burning natural gas releases about 40% less greenhouse gas to the atmosphere to yield a given amount of heat than does coal.  Many natural gas-fired electric generating plants currently in service are gas turbine engines, not unlike the jet engine on an airplane.  Such natural gas power plants have somewhat higher thermal efficiencies than coal-fired power plants.  More recent versions of natural gas power plants are called combined cycle generating plants.  They build in a second phase of power generation that captures some of the excess heat to generate more electricity in an additional generating component.  The efficiency of combined cycle natural gas electricity plants can be up to 50% (see Note 4).  Research may push this to about 58-60% efficiency (Note 4).

Operating Electric Cars from Fossil Fuel-Derived Electricity.  We may conclude from the above comparisons that it is moderately more efficient to recharge batteries to power electric cars than it is to run gasoline-driven conventional cars.  It must be mentioned, though, that drawing power from, and recharging, the batteries also involves losses in  efficiency, as considerable waste heat is produced at this stage.  Only about 75% of the power stored in a battery is actually transferred to the wheels of an electric car (see Note 5), and there are comparable losses in recharging the battery from the grid.  As noted above, fossil fuel plants provide 69% of the electricity in the country.  Thus significant amounts of greenhouse gases are released into the atmosphere in operating electric cars.

Non-fossil fuel electricity sources are not expanding in the current energy environment in the U. S.  No new nuclear plants or hydroelectric dams have been added for many years, and few are on the drawing boards.   Renewable sources such as solar and wind turbines are either static or growing only quite slowly.  The New York Times reported recently that so far in 2010 the growth of wind turbine installations in the U. S. has fallen drastically, at least partly because of the economic recession.

Electric Cars Necessarily Produce Greenhouse Gases.  On the other hand, power generation by fossil fuel plants is expanding at similar rates as in past years.  Therefore the electricity that will be used in the foreseeable future to drive electric cars will continue to come from fossil fuels.  In other words, electric cars will continue to be responsible for producing greenhouse gases for their operation for the indefinite future.  This contradicts any statements by electric car manufacturers that their products do not add greenhouse gases to the atmosphere.

Conclusion: In order to justify electric cars, generating electricity must move to CO2-neutral technologies. Only then will electric cars contribute meaningfully to minimizing global warming.  Previous postings on this blog have emphasized the necessity of not adding any new atmospheric CO2 in order to minimize global warming (see Note 6).  Sale and use of large numbers of electric cars will provide pressure to move to CO2-free generation of electricity.  Solar power (both solar heating and photovoltaic panels) and wind power must be promoted by federal incentives and in the private sphere.  (While there is considerable interest in carbon capture and geological storage for fossil fuel plants, especially for coal, this technology so far is unproven and unavailable.)

*          *          *          *



Source: http://www.fueleconomy.gov/feg/atv.shtml

Electrical Generation Efficiency—Working Document of the NPC Global Oil & Gas Study, 18 July 2007  http://www.npc.org/Study_Topic_Papers/4-DTG-ElectricEfficiency.pdf.

Note 3. Electrical Generation Efficiency—Working Document of the NPC Global Oil & Gas Study, 18 July 2007  http://www.npc.org/Study_Topic_Papers/4-DTG-ElectricEfficiency.pdf

Note 4. Electrical Generation Efficiency—Working Document of the NPC Global Oil & Gas Study, 18 July 2007  http://www.npc.org/Study_Topic_Papers/4-DTG-ElectricEfficiency.pdf


3 comments:

  1. I believe that electric cars are essential in slowing down global warming. I do not agree with the fact in the article that electric cars will produce more green house gas emissions. There are many other sources of electricity that could be used such as solar power, wind turbines, and dams that could aid in the production of electricity to power the cars and they do not produce green house gasses. In this article (http://www.afdc.energy.gov/vehicles/electric_emissions.php) you can see that green house gasses emitted from the electric cars are significantly less than the conventional cars.

    ReplyDelete
  2. This comment has been removed by a blog administrator.

    ReplyDelete