3.3.3 Electric Power Generation
Electric power generation accounts for about 20% of GHG forcing, mostly from carbon dioxide, with some from nitrous oxide and ozone. Most power stations today (excluding nuclear and hydroelectric) use either coal or natural gas as the fuel. Fuel switching from coal to natural gas reduces the emissions of carbon dioxide per BTU of energy produced. Due to plentiful supplies, environmental air pollution regulations and low prices, most new U.S. plants and many outside the U.S. are natural gas fired (30). Recent price increases in natural gas may change this trend.
Generating some electricity by renewable forms of energy using wind-powered turbines and photovoltaic solar cells is possible today, but is too expensive relative to fossil fuels (72, 73) to be used on a large scale. Wind power is also handicapped by the fact most of the U.S. wind fields are in sparsely populated rural areas far away from the electrical grid (74). Electric utilities have shown little interest in reshaping the network of transmission lines to accommodate wind-generated electricity, let alone properly maintaining and upgrading the existing distribution network. The recent deregulation debacle in the U.S. has made fundamental changes in power transmission even more unlikely, although a massive power outage in the eastern U.S. on August 14, 2003 has temporarily put this issue front and center.
There is little additional available hydroelectric capacity in the U.S., but other countries like China are continuing to exploit this energy source (e.g., the Three Gorges dam project). Nuclear energy suffers from cost and waste disposal problems and a perception that the plants are unsafe or easy targets for terrorists.
Fuel cell production of electric power is also being considered with one option being smaller dispersed units as part of a distributed power grid in place of large 250-500 MW power stations. The smaller the power unit, however, the more expensive it will be to remove the carbon dioxide (75).
The problems with fuel cells and nuclear and renewable energy have lead the U.S. DOE, other similar agencies in the world and the power generation industry to conclude that the direct combustion of coal and natural gas will continue to be the primary method of production of electric power for many decades to come. For this reason, most of the interest is in building more efficient plants based on the direct combustion of these fuels. Later, the conventional wisdom holds that within say 25 years, a new generation of plants will be built that use carbon management to control emissions. Under this scenario, carbon dioxide from power plant emissions will be captured and disposed of as a waste much like sulfur dioxide is today.
Carbon management makes sense for the 5000 fossil fuel powered electric generating stations in the U.S. (76) and roughly 20,000 in the world and for some 3X that number later in the century, assuming the plants will be large enough to make the process economical. The number of sources is relatively small and the quantity of emissions per source large compared to the 700 million vehicles and hundreds of millions of businesses and residences that produce GHG emissions.
The problem is that the existing technologies for removing carbon dioxide from gas streams that could be applied to power plant emissions were developed in the 1930’s for removing high (>20%) levels of carbon dioxide from natural gas, a product with a market value. The low levels of carbon dioxide (3-12%) in power plant emissions (77), coupled with the fact that it has no economic value on the scale on which it would be recovered, means that the amount of energy required to capture it (absorption in an amine solution under high pressure), regenerate the capture solution and compress the gas prior to disposal is prohibitively expensive, an estimated $100-300 per metric ton of carbon equivalent (the way in which carbon dioxide disposal costs are calculated). This is enough to add 30-60% or more to the cost of electricity (78-80).
In 2000, the U.S. DOE had a stated goal of reducing this cost to $5-10/ton with a target date of 2015 for new technologies that met this target to be perfected and with implementation to begin shortly thereafter at all existing and new stations (80, 81). The implementation of carbon management using these technologies was predicted by the U.S. DOE to reduce U.S. carbon emissions by 145 million metric tons of carbon per year and global emissions by 270 million by 2030 (82). However, since global GHG emissions may approach 10 billion tons as carbon by 2030, this carbon management program, even if successful, would have little impact on reducing GHG forcing (52).
