Electricity

We estimate:

• 0.1 pounds of CO2e per kilowatt hour from wind and solar, mostly manufacture and placement
  
• 0.3 from nuclear, mostly fuel processing
• 1.0 from hydroelectricity, mostly vegetation in reservoirs decaying to methane (3 to 11 for reservoirs in forests)
  
• 1.8 average from US grid (or see "Nations" tab for over 100 other countries)
• Spreadsheet shows the steps of the calculations

Carma.org estimates the greenhouse gases directly released by burning fossil fuels at power plants. They convert these various greenhouse gases into pounds of CO2 with an equivalent ability to warm the earth, CO2e.

We increase their fossil fuel numbers to cover CO2e emitted while getting the fuel to the plant based on US ratios, and losses distributing the electricity to customers, based on US and European ratios (p.168).

We add to the fossil fuel numbers some estimates of CO2e from hydroelectric reservoirs, nuclear fuel processing and disposal, and solar cell and wind turbine production (below).

The US has 5 main electric grids, with much sharing inside, and little outside. CO2 output depends on your grid, not your state's plants, which may provide little of your power. For example Idaho has mostly low-CO2 hydroelectric plants, but gets over half its electricity from the Western grid, which emits much more CO2. A map of the main three grids calls them "Interconnects:" Eastern (covers from the great plains to the east coast), Western, and Central Texas (ERCOT-Energy Reliability Council of Texas). The other two grids are in Alaska and Hawaii.

Solar cells need substantial energy for manufacture, resulting in some CO2e, although in the long term they could use solar energy for manufacturing and have even less CO2e. Depending on type of solar cells, and assuming they generate electricity for 30 years the CO2e to make and install cells and distribute the power is 0.06 to 0.13 pounds per kilowatt hour. If they only last 20 years, emissions would be 50% higher.

Wind turbines on land need concrete, steel and some land clearance, resulting in 0.11 pounds CO2e per kilowatt hour, most of which cannot be replaced by wind-generated power. This assumes a useful life of 20 years. Wind turbines at sea might need less concrete and land clearance, but more CO2e for installation and maintenance. Wind turbines also have the environmental harm of killing birds and bats, especially along ridgetops during migrations.

Wave energy: We have no data yet on the CO2e used to manufacture & maintain wave energy systems. California has summarized some environmental risks of taking energy out of waves, such as changes in location of sand, shore dwellers and bottom dwellers, Developing Wave Energy In Coastal California .

Nuclear electricity creates CO2e at each step of fuel preparation and for long term defense of spent fuel.

Hydroelectricity: Hydroelectric reservoirs convert some of the carbon in the area they flood to methane. Methane has 25 times as much global warming effect as CO2, so hydroelectricity which converts carbon to methane can have major global warming effects.

Defense of electric generators. Aside from a small calculation for nuclear waste above, the fuel estimates exclude CO2e for military defense. Some have argued

(a) the US military spends (and so releases CO2e) heavily to defend oil supplies, and

(b) large hydroelectric dams upstream of cities have been and are military targets.

For example dams on the Ruhr were attacked in World War II, and two army divisions defend the Three Gorges Dam (Guardian, Dai Qing, Sino Daily, River at the Center of the World by Winchester 1997 and 2009).

The Brazilian dams used to derive CO2e here seem unlikely to be military targets, so we have not included military CO2e. If one studied dams upstream of major cities, such as the Ruhr or Three Gorges, some military CO2e could be included.

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