Total carbon cycle must be included
Coal-generated electricity emits the highest amount of CO2 per kWh. Depending on the variety of coal used, it is just below one kilogram of CO2 per KWh. But this amount does not include the total GHG that coal is adding to our climate.
When comparing alternative energy sources, it is obvious that we should compare total costs, from cradle to the grave, as the saying goes, or Life Cycle Costs. Too often we do not do a similar analyses when the total carbon cycle is involved. We need to consider the total coal emitted in the process, from the beginning of the coal extraction to final electricity generation.
A recent study* indicates that the total carbon emissions of coal is not just the one kilogram per kWh of the power plant, but we must add between 7% to 17% for the cutting of the mountains, for coal transportation, and the removal of trees when the coal is extracted from mountain tops.
[*Nature, Feb. 10, issue. P. 1002]
[Modern natural gas plants emit about one half as much per unit of electricity.]
Similarly, we have to compare the CO2 emitted during fabrication, installation and maintenance of alternative energy systems. For example, when we consider photovoltaic systems we do not include the amount of CO2 emitted during the manufacturing process. PV is the worse "green technology" as far as CO2 emission is concerned.
Past analysis indicates that it took some 8 years to payback the electricity consumes in the manufacturing, system fabrication and installation of roof-mounted silicon PV systems. It takes a considerable amount of electricity to make the pure silicon panels for current technology PV. Because fabrication cost is important many of the PV silicon panels are made where electricity is very cheap, where electricity is generated by coal power plants! A high percentage of PV silicon is made in Germany and China. Germany uses coal to produce 50% of its electricity, and 80% of China's electricity is generated by coal.
Even if we assume that higher production led to higher manufacturing efficiency of silicon, the CO2 payback can still be in the region of 4 to 5 years. The silicon panels are just 30% of total costs, and considerable amount of additional material and transportation are involved in making and installing a roof-mounted PV system. The amount of CO2 generated by the total the PV life-cycle is almost never included in the analysis of PV net generation of electricity. And in addition, the amount of electricity produced by PV systems is hidden and rarely discussed in order to hide its very high cost per kWh produced, which is the highest of all low-carbon technologies, including nuclear power.
Wind energy has very little CO2 foot print per kWh, and nuclear power has even less than that. But remote new green plants would require long transmission lines with their own CO2 "cost." This is typically not a very high contributor when you divide the initial GHG contribution over the 50 years of typical life of transmission lines.
In all cases of green technology and other reductions of GHG we need to determine and tell the true story, or our ability to reduce GHG emissions would be grossly over estimated.
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