Mass production of electricity is not found in nature. A primary energy source must therefore be used to produce it. In almost all production units, a turbine drives a generator using (simplified) dynamo principles invented by Faraday at the beginning of the 19th century. Wind, ocean, or river currents; artificial waterfalls; and water vapor can all be used to power the turbine. Water vapor is the most common, but the environmental challenge is emitting the least amount of CO2 when heating the water.
A nuclear plant emits less than 10 grams of CO2 to produce one kilowatt hour (1 kWh = 3.6 MJ), but a coal-fired plant releases between 800 and 1,000 grams! Today around 35 % of the world's electricity comes from energy sources which emit low amounts of CO2: around 10 % from nuclear energy, 20 % from hydroelectricity, and a very small percentage from other renewable energies (wind, solar, tides, geothermal). The rest consumes coal (close to 40 %), natural gas (close to 20 %), or petroleum (8 %). In reality, these proportions vary enormously from country to country: this is known as a country's energy mix. The environmental balance of an electric road transportation system will therefore greatly depend on the local form of energy generation. The future certainly lies in the spread of small, decentralized production units using renewable energy sources such as photovoltaics or wind turbines.
French or Brazilian mix
The electric energy's production costs greatly depend on the country's energy mix, which are extremely variable from one country to another. The same is true for the price of a ton of CO2.
There are only trace levels of hydrogen in the earth's atmosphere. It must therefore be produced using raw materials such as water or natural gas.
Hydrogen production via water electrolysis represents only 4 % of world production due to its high cost: between 4 and 9 times the cost of gasoline. Its environmental balance depends on the way the electricity is produced. If it comes from nuclear or renewable energy (Canada is focusing on its extensive hydroelectric resources), electrolysis' very positive environmental balance could compensate for its higher cost relative to conventional reforming processes, especially if the cost per ton of CO2 emissions increases.
There may also be an increase in individual power plants using renewable energy sources.
The only industrial method for hydrogen production today is steam reforming of natural gas water vapor (48 % of production), gasified coal (18 %), or naphtha (30 %) produced from hydrogen and carbon monoxide, which quickly oxidizes into CO2. Hydrogen is used in large quantities in a number of industrial processes such as the desulfurization of petroleum-based fuels or the production of ammonia. Hydrogen is liquefied for transportation in large quantities. There are certainly pressurized gas pipelines, but they become much less cost-effective as distances increase.
The production of one ton of hydrogen from natural gas emits 9 tons of CO2, and 19 tons when it comes from coal. Under these conditions, a Capture and Sequestration System (CCS) is essential, which increases the cost (already 2 to 3 times higher than gasoline).
We can obviously reform natural gas from biomass in the same way, with a very positive CO2 balance, but the process is extremely expensive and collecting the feedstock at such a large scale would likely be difficult.
Another possible method in the long term is "splitting" water vapor at the very high temperatures present in fourth generation nuclear reactors or even fusion facilities. This could greatly improve output.
Hydrogen produced by electrolysis
g CO2/kWh electricity
kg CO2/kg H2
* The efficiency of electrolysis is taken as 80 %
** Hydrogen provides 33 kWh/kg
Hydrogen from steam reforming
Quantity of hydrogen
Quantity of CO2 kg
Energy per kg of hydrogen
gCO2/kWh which hydrogen will provide
Whether hydrogen is produced by electrolysis or steam reforming, it's the primary energy source which determines how much CO2 is produced. In both cases, the capture and sequestration of CO2 is necessary when the primary source is coal or natural gas.
Capture and sequestration of CO2
The process involves capturing CO2 at the point source, possibly transporting it, and then storing it in adapted natural reservoirs for several hundreds of years. Capture is obviously unthinkable for moving vehicles, but perfectly suited to large stationary facilities.
In total, these point sources produce more than 60 % of the total global CO2 emissions. Several capture technologies are currently in the industrial demonstration phase. The second step, transportation, can be done via pressurized pipelines. However boats are a better choice over very large distances. Lastly, CO2 can be stored either in geological formations (oil or gas fields, deep saline aquifers, unmineable coal seams), or deep in the ocean (it is then dissolved in water). Geological storage seems to be the most technologically feasible and long-lasting solution (the CO2 remains trapped), but it depends on the availability of appropriate sites. For example, the company Statoil re-injects CO2 that has been separated from methane into the Snøhvit natural gas field, off the coast of Hammerfest in Norway. Deep ocean storage is not definitive, even if it seems to last several centuries. We still don't fully understand the possible consequences (acidification of the ocean) and the necessary technology is still being researched.
Europe, the United States and Australia have all launched large-scale programs to test the feasibility of the entire range of CCS technologies by 2015-2020. The current estimated cost is calculated as 50 to 100 dollars per ton of stored CO2.
In 2013, hydrogen produced by steam reforming costs two to three times more than gasoline for the same quantity of energy. Hydrogen produced by electrolysis is even two to three times more expensive than that, except in countries with extensive hydroelectric production such as Canada.
Of course, production is not the only issue...the electricity and hydrogen must be transported to recharging stations that are close to vehicles. The creation of massive infrastructures to distribute electricity and hydrogen played a major part in the success of electric vehicles. However that requires significant investments.
A number of countries have implemented incentives or taxes on fuels and vehicles to reduce greenhouse gas emissions, again to varying degrees. Energy costs therefore only partially reflect real costs but are reflections of political will.