ing wind farms has grown, with concerns
expressed regarding aesthetics, impacts
on migrating birds and other issues. Wind
is an intermittent resource and is less predictable on an hourly basis than solar.
It is worthwhile taking a look at the
variability of the solar resource. Solar irradiance varies not only from one location
to another (e.g., more solar resources in
the western part of the U.S.) but also on
an hourly basis – not just in its obvious
absence during nighttime but also in significant seasonal variations, with much
lower irradiance during winter. This is
illustrated in figure 7, which shows average hourly irradiance in four cities during the months of January and July. These
seasonal variations have important implications for both the usable solar capacity
as well as solar energy production on a
seasonal basis.
Increasing deployment of solar is having a growing impact on the power grid, as
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FIGURE 6. Comparison of greenhouse gas emissions from heat pump
use and net emissions from combined heat and power assuming non-baseload grid emissions (lb CO2e/MMBtu heat).
Source: Compiled using calculations based on non-baseload grid emissions per
figure 4 and calculation of net CHP emissions as explained in figure 5.
extracted in winter, the ground will gradually warm up). Thermal imbalances can
be mitigated to some extent by installing
more boreholes and/or by natural dissipation of excess thermal energy if the
ground has high heat conductivity.
Chiller heat recovery is a thermodynamic thing of beauty. We want to harvest
the heat that is produced in chillers. The
size of the opportunity depends on the
extent to which there are simultaneous
heating and cooling loads (or near-simul-taneous, since hot water and chilled-water storage can help optimize the system). A full analysis of hourly climate and
load data is essential. It is a highly case-specific opportunity.
Recovering heat from raw or treated
sewage also requires a hard look at hourly
conditions. Sewage flows vary signifi-
cantly on a daily and seasonal basis, and
temperatures vary seasonally. Sewage
heat pump capacity must be optimized
for the site-specific conditions. Another
key factor is the location of resources:
How far away are the sewer mains or sew-
age effluent pipes?
SOLAR AND WIND
The costs of solar photovoltaic and
wind power have come down dramatically
in the past 10 years, and their deployment
has grown significantly. Use of these
resources, both on the grid and behind
the meter, can and should grow further.
Solar PV and wind are increasingly being
deployed as utility grid resources. These
renewable resources, particularly solar, are
also being incorporated into microgrids or
other customer-side installations as important carbon reduction strategies.
Wind is a location-specific resource,
based on local meteorological conditions.
Most wind capacity resides in large, grid-connected wind farms. As deployment of
wind energy has grown, resistance to sit-
FIGURE 5. Comparison of greenhouse gas emissions from heat pump
use and net emissions from combined heat and power assuming
average grid emissions (lb CO2e/MMBtu heat).
Source: Compiled using calculations based on average grid emissions per figure 4.
Calculation of net CHP emissions as follows: CHP greenhouse gas emissions were
calculated assuming a 5 M We reciprocating engine with a heat rate of 8,750
Btu/k Whe and a power/heat ratio of 0.98. Net CHP emissions were calculated by
deducting grid emissions avoided by generating electricity with CHP rather than
grid resources. The net emissions were then divided by the heat produced by CHP.
FIGURE 5 FIGURE 6
(150)
(100)
( 50)
0
50
100
150
Greenhouse
gas
emissions
(lb
C O2 e
/M
MB
t
u
h
ea
t)
eGRID subregion
Emissions resulting from heat pump use based on non-baseload grid emissions
Net emissions from CHP based on non-baseload grid emissions
(250)
(200)
(150)
(100)
( 50)
0
50
100
150
Greenhouse
gas
emissions
(lb
C O2 e
/M
MB
t
u
h
ea
t)
eGRID subregion
Emissions resulting from heat pump use based on average grid emissions
Net emissions from CHP based on average grid emissions
FIGURE 5 FIGURE 6
(150)
(100)
( 50)
0
50
100
150
Greenhouse
gas
emissions
(lb
C O2 e
/M
MB
t
u
h
ea
t)
eGRID subregion
Emissions resulting from heat pump use based on non-baseload grid emissions
Net emissions from CHP based on non-baseload grid emissions
(250)
(200)
(150)
(100)
( 50)
0
50
100
150
Greenhouse
gas
emissions
(lb
C O2 e
/M
MB
t
u
h
ea
t)
eGRID subregion
Emissions resulting from heat pump use based on average grid emissions
Net emissions from CHP based on average grid emissions
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