The 7% transmission loss factor may be optimistic for the US. Generally transmission loss is significantly higher in the US than many other countries because transmission distance is much larger in the US than those countries. Following is information I gathered in 2009 which was directly related to electricity from coal but as to most factors is equally applicable to US electricity generation generally, whether coal, natural gas, or nuclear. I hope all the links are still active.
DOE - CO2 Report
In the United States, about 40.5 percent(6) of anthropogenic CO2 emissions was attributed to the combustion of fossil fuels for the generation of electricity in 1998, the latest year for which all data are available.
Coal has the highest carbon intensity among fossil fuels, resulting in coal-fired plants having the highest output rate of CO2 per kilowatthour.
CO2 emissions from coal-fired electricity generation comprise nearly 80 percent of the total CO2 emissions produced by the generation of electricity in the United States, while the share of electricity generation from coal was 51.0 percent in 1999 (Table 3).
Fossil Fuel Power Plant
Subcritical fossil fuel power plants can achieve 36–38% efficiency. Supercritical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 4,400 psia (30 MPa) and dual stage reheat reaching about 48% efficiency.
Older nuclear power plants must operate below the temperatures and pressures that coal fired plants do. This limits their thermodynamic efficiency to the order of 34–37%. Advanced designs, such as the Advanced gas-cooled reactor and the Supercritical water reactor, operate at temperatures and pressures similar to current coal plants, producing comparable efficiency.
Newton
. . . this ideal maximum [thermodynamic] conversion efficiency is never achieved, so a
generous estimate would be 50%. In addition, the "true" cost is a much more complicated calculation. The "true" cost takes into account the cost of mining and transporting the coal, and the operating costs of the generation (plant cost, salaries, environmental costs, and so on). The bottom line is that the conversion of coal into electricity is very inefficient.
Estimate of 30% efficiency of 30%, or 9% efficiency, for transforming the heat energy of the coal into electrical energy and transmitting it to your home – [does not include the energy used in mining, transporting, and handling the coal before it is burned]
Fossil Energy
DOE estimates: only a third of the energy value of coal is actually converted into electricity, the rest is lost as waste heat.
Energetics
DOE: America operates a fleet of about 10,000 power plants. The average thermal efficiency is around 33%. Efficiency has not changed much since 1960 because of slow turnover of the capital stock and the inherent inefficiency of central power generation that cannot recycle heat.
Transmission Losses
the overall losses between the power plant and users can easily be between 8 % and 15 %,
Comparison
In any country, the network, through losses, is the biggest consumer of electricity. In Europe, these losses amount to 4-10% of electricity generated, with an average of 7%.
THEN END USE EFFICIENCY
No one disagrees that carbon-based electric generation works to provide electricity. What rarely is discussed, however, are the tremendous inefficiencies and wastes inherent in that form of electric generation, and the “costs†of those wastes to society and the environment.
America operates a fleet of about 10,000 power plants. The average thermal efficiency of these power plants is about 33% (DOE). In the US line losses range between 8% and 15%. So, starting with a pound of carbon-based fuel (or any energy producing fuel, including nuclear), net delivered energy to the end user ranges between 18-25% of the energy contained in the pound of fuel.
But even these figures do not relate the “true†cost of electricity produced from fuel-based power plants. The “true†cost must also take into account the cost of extracting, mining and transporting the fuel, the operating costs of the generation, and the costs of disposal of the waste products. The bottom line is that the conversion of fuels into electricity is very inefficient. And for those who have a concern about CO2 emissions, well, carbon fueled power plants, especially coal are exceptionally “dirty.â€
One also could argue that conversion of wind or solar into electricity also is inefficient (line losses are inherent in the US electric power grid and would apply on average to any form of electrical energy distribution). Average efficiency of wind turbines (energy output in watts/energy in wind) is about 35% (theoretical limit is about 60%), a little better than that of solid fueled power plants. Average solar electric efficiency (energy output in watts/divided solar energy delivered) ranges between 12-18%, although DOE reported in 2006 that new cell technology achieves efficiency slightly in excess of 40%, much better than solid fueled power plants.
The inefficiencies in wind or solar systems (as well as hydro-electric), however, do not share many of the “true†cost elements of solid fueled plants, such as extracting, mining and transporting the fuel, the costs of disposal of the waste products, and CO2 emissions. In these respects wind and solar systems are not only more efficient, but also they are environmentally “clean,†as compared to solid fueled plants, a fact well-recognized.
The bottom line clearly is that the “benefits†of solid fueled electric power generation come at a considerable cost, and efforts to improve the generation of electricity from wind, solar and hydro are extremely important.