for the huge western region, the Western
Electricity Coordinating Council (WECC),
which I have split up into the subregions
because of their significant differences in
characteristics. The four WECC subregions
are WECC California (CAMX), WECC North-
west (NWPP), WECC Southwest (AZNM)
and WECC Rockies (RMPA).
Figure 3 shows, for each grid area
(and U.S. average), the average annual
emissions rate for all power plants as well
as the average annual emissions rate for
non-baseload plants. The latter is gener-
ally a more appropriate yardstick because
new distributed generation sources will
usually displace intermediate grid gener-
ation capacity rather than baseload units
– which are generally either nuclear units
or relatively efficient fossil fuel plants.
Several observations are appropri-
ate. First, the average emissions rate for
U.S. power plants is about 1,000 lb of
carbon dioxide equivalent per megawatt-
hour of electricity (CO2e/MWhe). For a
sense of perspective, a large natural gas
combined-cycle power plant will emit
about 800 lb CO2e/MWhe. Second, the
average non-baseload emissions are over
1,500 lb CO2e/MWhe, nearly twice that
of a gas combined-cycle plant. Third, the
lowest emissions are in California and
New England, but even in these regions
the non-baseload emissions rates are
about 1,000 lb CO2e/MWhe.
Grid emissions have implications for
electric-driven systems including technology that is of increasing interest for sustainable energy infrastructure, particularly
heat pump systems such as geoexchange
(aka “ground source heat pumps” or
sometimes “geothermal”). Geoexchange
taps low-temperature heat in the earth by
circulating a liquid through underground
pipes. Shallow earth temperatures vary
depending on location, depth and season
but typically range between 50 degrees F
and 60 F. Electric heat pumps are used to
upgrade the heat to a useful temperature.
The efficiency of heat pumps is measured
as coefficient of performance (COP), i.e.,
the ratio of useful thermal energy produced (heating or cooling) to the electric
energy consumed. Heating COPs depend
on heat source and sink temperatures and
the specific machine design but are usually in the range of 3.0-4.0.
Figure 4 shows the CO2 equivalent
emissions per million Btu (MMBtu) of heat
resulting from the use of heat pumps,
assuming a heating COP of 3. 5. These
emissions are substantial in most regions,
with emissions per MMBtu of heat in five
regions (based on non-baseload power)
FIGURE 2. U.S. Environmental Protection Agency eGRID subregions.
Source: U. S. Environmental Protection Agency, June 2018 ( https://tinyurl.com/ydhant9m).
FIGURE 1. U.S. Environmental Protection Agency eGRID regions.
Source: U.S. Environmental Protection Agency, September 2015 ( https://tinyurl.com/y92ka6qz).
ASCC...... Alaska Systems
FRCC ...... Florida Reliability
HICC....... Hawaiian Islands
MRO ....... Midwest Reliability
NPCC .....Northeast Power
RFC.......... Reliability First Corp.
SERC ...... SERC Reliability Corp.
SPP.......... Southwest Power Pool
TRE.......... Texas Reliability Entity
WECC.... Western Electricity