Quantifying the Air Pollution Exposure Consequences of - Houston ...

II.A.1.b Hypothetical DG Cases
Hypothetical DG sources represent two location types and two classes of DG
technologies. Because an important niche for DG is to provide on-site power to large,
commercial buildings, we considered units installed at the city halls of the eleven most
populous cities in California. We chose city halls for siting because they are easily
identifiable landmarks and are typically located in the downtown core. The second type
of hypothetical DG source is co-located at the site of each existing unit.
While DG is arguably not limited to any certain capacity (tens of megawatts could
be locally used at large industrial sites), most electricity users’ demands are less than 1
MW. Thus, the DG technologies modeled are typical of those below 1 MW capacity. We
consider technologies most likely to have been installed before CARB’s 2003 emission
standard as well as ones certified as meeting CARB’s 2003 and 2007 emission standard.
Internal combustion engines (ICE) and turbines are both mature technologies that
represent the largest fraction of installed DG in the US and California (CEC, 2001c; EPA,
2003a). The two most popular fuels for ICEs are diesel and natural gas; natural gas is the
most popular fuel for turbines. Thus, the three technologies representing the pre-2003
fleet of installed, small-scale DG are diesel and NG ICEs and natural gas turbines (GT).
CARB has certified seven DG products for meeting the 2003 and/or 2007
standard, all them small-scale (< 1 MW) (CARB, 2004a). Three microturbines meet the
2003 standard and four fuel cells meet the 2007 standard. Thus, microturbines and fuel
cells are modeled in our post-2003 and post-2007 cases. While the approved fuel cells
can operate at both high and low temperatures, we model low temperature fuel cells
because these are the most mature technologies (Energy Nexus Group, 2002).
Table 5 summarizes attributes of the hypothetical DG cases.
II.A.2 Location and Background Information of Cases
II.A.2.a Existing Units
In all, 37 existing units met the inclusion and selection criteria: 25 central stations,
6 cogeneration plants and 6 DG units (> 1 MW). Combined, these units represent 32% of
the in-state generation capacity of California (CEC, 2001a) and 17% of 1999, Californiaowned
generation 9 (CEC, 2004a). As can be seen in Figures 3-5, these plants are located
in most air basins in California. Tables 6-8 reveal that the cases selected represent a total
of nine fuel types (including one coal plant), five combustion technologies, and six
nitrogen oxides control technologies. The size (capacity) of the plants varies widely, from
the largest combustion-based central stations in California (2000+ MW) to systems
barely greater than 1 MW. The smaller systems generally utilize “opportunity fuels” such
as landfill and digester gas and wood waste. The cases also vary widely in capacity
factor, which indicates that these plants are used across the load duration curve, i.e., in
peaking, baseload and load-following modes. We model the plants as if they were all
baseload. Future work could address the sensitivity of our results to the hour of operation.
9 1999 California generation includes California utility-owned shares of nuclear, coal and some firm
contract generation in other states (CEC, 2004a).
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