United States
                 Environmental Protection
                 Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
                 Research and Development
EPA/600/SR-96/130
November 1996
&EPA     Project Summary

                 Demonstration of the
                 Environmental  and  Demand-side
                 Management  Benefits of
                 Grid-connected  Photovoltaic
                 Power  Systems
                 Edward C. Kern, Jr. and Daniel L. Greenberg
                   This project investigated the pollut-
                 ant emission reduction and demand-
                 side management potential of 16 pho-
                 tovoltaic (PV) systems installed across
                 the country in 1993 and 1994. The
                 project was sponsored by the U.S. EPA
                 and 11 electric utilities. This report pre-
                 sents analyses of each system's ability
                 to offset emissions of sulfur dioxide,
                 nitrogen oxides, carbon dioxide, and
                 participates, and to provide power dur-
                 ing peak load hours for the individual
                 host building and the utility. Results of
                 simulations of battery storage systems
                 powered by each  PV system are also
                 presented.
                   The analysis indicates a very broad
                 range in the systems' abilities to offset
                 pollutant emissions, due to variation in
                 the solar resource available and the
                 marginal emission rates of the partici-
                 pating  utilities. Use of dispatchable
                 storage would reduce emission offsets
                 due to energy losses in charging and
                 discharging  the batteries.  Each
                 system's ability to reduce building peak
                 loads was dependent on the correla-
                 tion of that load to the available solar
                 resource. Most systems operated in ex-
                 cess of 50% of their capacity during
                 building peak load hours in the sum-
                 mer months, but well below that level
                 during  winter peak  hours.  Similarly,
                 many systems operated above 50% of
                 their capacity during utility peak load
                 hours in the summer months, but at a
                 very low level during winter peak hours.
                 The addition of dispatchable  energy
                 storage significantly increases  each
                 system's peak  load  matching ability,
                 raising  capacity factors to  100% for
 most systems during the utility's high-
 est load hours.
   This Project Summary was developed
 by the  National Risk Management Re-
 search  Laboratory's Air Pollution Pre-
 vention and Control Division, Research
 Triangle Park, NC, to  announce key
 findings of the research project that is
 fully documented in a separate report
 of the  same title (see Project Report
 ordering information at back).

 Introduction
   Photovoltaic (PV) conversion of sunlight
 to electricity has become substantially less
 costly and  more efficient in recent years.
 Since its first application in the space pro-
 gram in the 1950s,  the  cost of PV mod-
 ules  has fallen approximately 70% per
 decade, and module manufacturers con-
 tinue to make progress in reducing costs
 further.  Although technological innovation
 has been responsible for much of the de-
 cline in  costs, an international market for
 remote,  off-grid power, growing at the rate
 of 20 to 30% annually,  has resulted in
 expansion  of module production capacity.
 This, in  turn, has led to production econo-
 mies which have driven module prices
 down still further.
   Despite these cost reductions,  modules
 remain the dominant factor in the cost of
 a  grid-tied  PV power system accounting
 for approximately 70% of the total. The
 power converter (inverter), necessary for
 transforming the direct-current (DC) power
 output from a  PV array to grid-synchro-
 nous alternating-current (AC) power, is an-
 other significant component of system cost,
 accounting for about 15% of total cost.
 Because the market for grid-tied AC power

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from PV systems has been relatively small,
there has been little progress in reducing
the cost of the inverter.
  However this project and  other similar
projects  are  increasing  the  demand  for
inverters,  and will likely  result in techno-
logical improvement and cost reduction.
The remaining cost components of  PV
systems are the array mounting structure,
wiring, and switchgear, collectively referred
to as the balance of system (BOS).
  Although electricity generated  by PVs
remains too  expensive to compete with
conventional  power  sources  in most grid-
connected applications, there is a growing
niche of  cost-effective applications (most
of them remote from the power grid) which
will expand as the cost of PV power falls.
A 50% drop in module prices is expected
within the decade which  has the potential
to greatly expand the grid-connected mar-
ket. Against this background of falling costs
is a heightened public awareness of the
threats to environmental quality posed by
the by-products of electricity production.
The most notable  concern  today is the
possibility that emission of carbon dioxide
(CO2) resulting from  the combustion of
fossil fuels may lead to climatic changes
on a global scale. As a result of this height-
ened concern  regarding environmental
quality, many consumers have shifted their
consumption  patterns, and some  are will-
ing  to pay  premiums for products that
have lower environmental impacts.  Sev-
eral recent  surveys  suggest  that  about
half of electric utility customers would  be
willing to pay a $10 monthly premium  for
electricity generated  by renewable  re-
sources. Given this context, it is very likely
that the domestic market for grid-tied  PV
power systems will  expand  substantially
within the next decade,   and continue to
grow rapidly.
  The potential environmental  benefits
from PV power generation are quite large.
If PV systems were installed where pos-
sible on the rooftops of the U.S. inventory
of residential, commercial, and industrial
buildings, they could produce roughly 20%
of the Nation's electricity. Currently, fossil
fuels used for electric power generation in
the U.S.  account for approximately 34%
of the CO2, 67% of the sulfur dioxide (SO2),
and 37% of the nitrogen oxide (NOx) emis-
sions into the atmosphere  from  control-
lable sources within  the U.S.
  In September 1991 the EPA issued a
solicitation for the installation of  grid-tied
PV systems  with the goal of measuring
their environmental and demand-side ben-
efits. Ascension Technology  developed a
proposal  in  response to  this solicitation,
with the support and participation of utili-
ties across the nation.  Eleven utilities sup-
porting the proposal to EPA were (1) New
England Electric System (NEES) with ser-
vice areas in  Rhode Island, Massachu-
setts, and New Hampshire; (2) New York
State Electric  and Gas (NYSEG)  in up-
state New York; (3) Northeast Utilities (NU)
with service areas in Connecticut, Massa-
chusetts, and New Hampshire; (4)  Atlan-
tic  City Electric (ACE) in southern New
Jersey; (5)  New  York  Power  Authority
(NYPA) with customers throughout New
York  State;  (6) Arizona  Public Service
(APS) in central and  northern Arizona; (7)
Wisconsin Public Service (WPS) in  south-
eastern Wisconsin;  (8) Northern States
Power (NSP) with service areas in Minne-
sota, Wisconsin, Michigan, and the  Dako-
tas; (9) Pacific Gas and Electric (PG&E),
serving most of northern  California; (10)
the City of Austin  Municipal Utility (COA);
and (11) Southern California Edison  (SCE)
serving much  of  southern California.  In
addition to the geographic diversity of the
service areas  represented by these utili-
ties, their pollutant emission characteris-
tics also  proved  to  be  quite  divergent.
Ascension Technology's partners from the
PV industry were  Siemens  Solar  Indus-
tries,  which  provided PV modules, and
Omnion Power Engineering Corporation,
which provided the inverters.
  EPA awarded the contract for this project
to Ascension Technology in the third quar-
ter  of 1992. The final system design effort
began shortly thereafter, and the first sys-
tem was installed  and  operating in April
1993. Ten of the systems were operating
by the end of  August 1993, and the last
was completed by mid-January 1994.
  Monitoring of each system began con-
currently  with initial system operation, al-
though the "official data start date" was
delayed where there were initial technical
problems  with  either instrumentation  or
PV system hardware.  At each site, 15-
minute average values of solar irradiance,
ambient temperature, PV system  power
output, and  building  load were  recorded
and stored  for subsequent retrieval  by
modem. Monitoring of  each site (for the
purposes of this study)  continued through
September 1994.
  Emission rate and load data provided
by  each participating utility were used in
conjunction with the data collected from
each  system to conduct analyses  of (1)
the emission offsets resulting from opera-
tion of the PV systems; (2)  the ability of
each PV system to reduce the peak  power
demand of the building on which  it was
installed;  and (3) the chronological  corre-
lation of each  PV system's power  output
to the respective  utility's  peak  loads. In
addition, a model was developed to simu-
late the operation  of each system in con-
junction with dispatchable battery storage.
This simulation shifted each system's daily
generation to the utility's daily peak load
hour(s), thus increasing the peak load cor-
relation and reducing emission offsets (due
to  battery  charging  and  discharging
losses).
  Chapter 1 of the full report is a general
introduction to  the  project.  Chapter de-
scribes the design,  installation, and cost
of each  system.  Chapter  describes the
data acquisition system and presents data
collection  and review procedures. System
performance  history  is described gener-
ally  in Chapter  (details are  provided  in
appendix D). Chapter discusses the model
used to simulate  the  behavior of the PV
systems with  dispatchable  battery  stor-
age. The  marginal emission rate models
developed for each participating utility are
described in Chapter 8, as are the site-by-
site  emission offset estimates. Chapter 6
discusses each  system's  impact on the
load of the building  it  is installed on, and
utility-level load matching results are pre-
sented  in  Chapter  7.  Conclusions  from
this project are summarized in Chapter.

Procedure

System Design
  Designs were developed for nominal  4-
kW "building  block" PV systems for this
project, capitalizing  on the project staff's
experience with roofmounted PV arrays  in
prior projects. The majority of the project's
sites  use  either one system (4 kW) or a
group of three systems (12 kW total).  Note
that the nominal system size refers to the
inverter AC rating. The actual  power out-
put  of the PV systems  under standard
operating  conditions  (1000 W/m2  irradi-
ance (full sunlight) and  an ambient  tem-
perature of 20°C) is  limited by the PV
array to multiples of 3.5 kW AC.
  PV arrays were configured using 12 PV
panel assemblies. Each PV panel assem-
bly  contains seven  modules,  electrically
wired  in series. A  PV  source circuit  is
formed with four PV panel  assemblies,
wired in series. A 4-kW PV array consists
of three PV source circuits.
  Both pitched- and flat-roof installations
utilize Ascension Technology RoofJack PV
array supports,  which  have been used  to
install  more than 1  MW of PV systems.
PV  arrays are held in  place by ballast on
flat  roofs; this approach requires no roof
penetrations to hold down of the PV ar-
rays. System design  details were devel-
oped in close cooperation with Siemens
Solar Industries of Camarillo, CA, the PV
module supplier. Omnion Power Engineer-
ing  was selected as the supplier of power
conditioners.  The PV systems were de-

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signed to accommodate the specifications
of the 4 kW-rated Omnion  Series 2200
unit.

System Installation
  System installation began in April 1993,
and was complete by the end of January
1994, although  instrumentation and hard-
ware  problems delayed the initiation of
monitoring  at  some  sites.  The  systems
were  installed  on a variety  of residential,
commercial, and  industrial  buildings.  In-
stallation costs for each system varied by
system size (4-, 8-, or 12-kW) and a num-
ber of site-specific factors. Table 1 sum-
marizes the size and  cost of each system.

PV System Performance
History
  Of the 16 PV systems installed by this
project, all  but two suffered  events during
the study period which temporarily limited
system output or prevented generation al-
together. Inverter-related problems were
the most vexing of the generation-limiting
events. In  all,  27 inverter-related events
resulted in a generation loss  of 12,740
kWh,  approximately 9% of the combined
generation  of these systems over the rel-
evant time  periods.
  As  a result of the  inverter-related  out-
ages  experienced  in this project, the in-
verter manufacturer made several design
changes and  increased  product testing
across their full line of inverters.  In addi-
tion, they extended the product warrantee
for the EPA project installations.
  Snow cover was also  a frequent cause
of PV system outages for those  systems
located in  northern locations or  at  high
Table 1. System Size and Cost
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Utility
NYSEG
NU
ACE
ACE
NYPA
APS
APS
WPS
WPS
NSP
PG&E
COA
APS
SCE
SCE
SCE
Size
kW
12
4
12
4
4
8
4
12
4
4
12
12
4
4
4
12
Total
Cost'
101.9
36.0
105.0
31.1
35.2
64.2
31.3
101.0
31.2
38.0
104.9
97.5
32.2
30.9
31.1
96.7
Cost*
per
AC
Watt
9.69
10.26
9.98
8.87
10.04
9
8.94
9.61
8.91
10.83
9.40
9.27
9.19
8.81
8.89
9.20
' Costs are in $1,000s
altitude. Of the systems in such locations,
the estimated energy loss as a result of
snow cover ranged from less than  1% to
16% of measured annual generation.
  A variety of other outages occurred dur-
ing the study period, not all of which have
identified causes. Of those "other" out-
ages for which a cause was identified, the
most frequent was, by far, fuse failure in
the DC disconnect switch.  Such failures
occurred 17 times at 11 sites. It was de-
termined that the original fuses in the DC
disconnect switches  did  not have  the
proper surge  rating. As they failed, they
were replaced by "slow-blow" fuses which
were  rated for  600 V DC.  None of the
replacement fuses has failed to date.

Battery Storage Model
  Where peak loads  do not  coincide with
peaks  in  the available solar resource, the
value provided by a PV system can some-
times be  greatly enhanced by the addition
of dispatchable battery storage. Although
some energy is lost both in charging and
discharging a battery  array,  the ability to
dispatch  energy generated by the PV sys-
tem during utility peak loads (or, for that
matter, the peak loads of a  transmission
line or distribution feeder)  allows the PV
generation  to be used to reduce genera-
tion by a utility's highest operating cost
units,  which are typically used only during
peak periods.
  To  investigate the  degree to  which
dispatchable  battery  storage would  im-
prove  the ability of each  PV  system to
offset load  during utility peak load hours,
a simple model  was developed to simu-
late battery charging, discharging, and dis-
patch.  The approach taken  was to maxi-
mize the contribution of each PV system
during the highest  utility load  hours  of
each  day, by simulating the daily opera-
tion of each  system's  inverter(s)  at  its
(their)  peak capacity for as  long as pos-
sible.  The duration of operation each day
was determined  by the amount of energy
actually generated each day and the AC
rating  of the  inverter.  The  addition  of
dispatchable battery storage affects both
pollutant  emission offsets (due to battery
charging  and discharging losses) and the
system's operation during utility peak load
hours.

Results

Pollutant Emission Offsets
  Models of marginal emission rates (i.e.,
emission rates of load following units) were
developed for each utility based on utility
provided  data. The hourly emission rates
of SO2, NOx, CO2, and particulates were
then combined with hourly PV system gen-
eration data  (and  simulated  PV/storage
dispatch  data) to determine hourly emis-
sion offsets.
  Annual emission offsets are presented
in Figures 1 through 4. Annual SO2 offsets
ranged from 4 g/kW to 16 kg/kW of sys-
tem rating under standard operating con-
ditions (SOC) (1000 W/m2 irradiance and
20° C ambient temperature).  NOx offsets
ranged from 110 g/kW to 8.7  kg/kW. The
range in annual CO2 emission  offsets was
from 700 to 2,300 kg/kW of system rating,
and that  for particulates was  20 g/kW to
600 g/kW  annually.  The  lighter shaded
area in each  figure is an estimate of the
pollutant  offset  achievable by a  PV sys-
tem with average  insolation,  using aver-
age U.S. emission rates based  on  data
collected by the Energy  Information Ad-
ministration for 1993.
  The extreme  variability in these results
is due to two factors: (1)  variability in the
local solar  resource and  (2) variability in
utility marginal emission rates. Factor (2)
is far more influential than (1), as can be
seen by  comparing the range for CO2 to
those  of  the other  pollutants.  Since there
are currently no mitigation measures in
place for CO2, variation in utility CO2 emis-
sion rates  is due  only  to the  relatively
small  (about 2:1) variation in  the carbon
content of fuels used and variation in the
heat rates of the power plants. The range
of the highest to lowest  annual  offset is
relatively small (3.3).  For  the other pollut-
ants, variations  in the  pollutant content of
the fuel as  well as inter-utility differences
in  installed  pollution mitigation equipment
give rise to the tremendous  differences
between  utility emission  rates which  un-
derlie  the differences  in emission offsets
described above.
  The  results of  the PV-powered
dispatchable  storage system  simulations
indicate  that  pollutant offsets would be
reduced  by at  least 25% were storage
added to these  systems.  This is largely
due to energy losses in charging and dis-
charging  batteries,  but is also influenced
by marginal emission rates which are typi-
cally lower during  utility peak load hours
when cleaner, more efficient power plants
are often used to follow load.

Building-Level Load Reduction
  Each   PV system's ability  to provide
power  during  building peak  load  hours
was analyzed by comparing each building's
net (of  PV  generation) and  gross  load
duration  curve  (LDC). The LDC  is  con-
structed  by sorting all  load values for  a
given period in descending order, and plot-
ting each value against  its rank in  the
sort. Differences in a building's  net and
gross  LDC for the highest  load values

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                                             Annual Sulfur Dioxide Offset
                    20
                    15
                 i
                 i
                    10
                 I
                                          nn
                        1   23   456   78   9  10  11   12  13  14  15  16  17


                                                   Site Number
Figure 1.  Annual SO2 offsets.
                    10
                                            \   Annual NOX Offset   |
                  I.

                  i
                  §
                  c  4
                        1   2   3  4   5   6   7   8  9   10  11  12  13  14   15   16   17


                                                   Site Number
Figure 2. Annual NO offsets.

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                                                        Annual Carbon Dioxide Offset
                           2500
                           2000
                       £
                           7500
                       |  7000
                            500
                                  7    2345   6   7    8   9    10  11   12  13   14   15  16   17
                                                                  Site Number
Figure 3.  Annual CO2 offsets.
                                                            Annual Particulate Offset
                            0.8
                            0.6

                            0.2
                                  1    23456    7    8   9   10   11   12   13   14   15   16   17
                                                                  Site Number
Figure 4.  Annual particulate offsets.

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indicate the PV system's ability to reduce
building peak loads.
  As one would expect, reductions in net
building load were  generally higher in the
summer months and lower in the winter
months, with the difference being particu-
larly pronounced for systems installed in
northern  states. Most  systems  reduced
the building's LDC by more than 50% of
system AC rating during the  highest load
hours in the second and third quarters of
the year. In the winter months, PV output
during  building  peak load hours  dropped
below  10% of  rating for some  systems,
although many systems in  the  southern
and western states performed as well or
even better during winter peak load hours.
  Two general conclusions may be drawn
from the analysis. The first is the relatively
self-evident conclusion that, if reduction of
customer net demand is the primary moti-
vation for the installation of a PV system,
it is critical to investigate the correlation of
building peak  loads to solar irradiance.
The set of host buildings participating in
this project included some with loads which
were very well  matched to the solar re-
source as  well as some  for which  the
match  was  very  poor.  The systems in
Ashwaubenon,  Wl, and Scottsdale,  AZ,
are examples of systems which  reduced
host building LDCs by  a substantial frac-
tion of their SOC rating. The highest loads
in these buildings occurred during midday
hours,  when  the solar resource peaks.
The  systems in Barstow, CA,  and Den-
mark, Wl, on the other hand had very little
effect on the host building's LDC, despite
ample solar resource. Many of the highest
building loads at these sites occurred near
or after sunset.
  The  second  general conclusion to be
drawn from the  data is that the generation
by  a  PV  system during an  individual
building's  peak load hour provides little
information regarding that system's ability
to reduce the building's peak monthly load,
or to reduce demand charges. Even if the
system generates at full power during the
monthly peak, there may be hours during
which building  load is  slightly  below  the
monthly peak  and during which the  PV
system operates at a much lower level. In
such cases there may be very little change
in the building's net LDC and correspond-
ingly small changes in  demand charges.
The  monthly peak load will  have simply
been shifted to  another hour.

Utility Coincident Peak Load
Reduction
  Each PV system's  ability to  provide
power  during utility peak load hours was
analyzed by simultaneously sorting hourly
PV generation  data and hourly utility load
data in descending order, with utility load
level determining the sort order.  The re-
sult was a utility load duration curve with
a value of PV generation for each corre-
sponding hour on the LDC. A "cumulative
average PV capacity factor curve" (CACF
curve) was then created by dividing each
hourly PV generation value by the system's
capacity rating (resulting in hourly capac-
ity factors) and then averaging each hour's
capacity factor with the capacity factors of
all hours  higher in the sort-order (i.e., all
hours  in  which  utility load was  higher).
The  resulting curve illustrates  the  PV
system's  average capacity factor for the
highest n load hours, where n is  read off
the ordinate.
   By  plotting this curve on the same axes
as the normalized LDC, one can deter-
mine for each point on the LDC, the aver-
age PV system capacity factor for all hours
up to  and  including that  hour.  For  ex-
ample, the CACF curve in Figure 5  indi-
cates that the PV system's average  ca-
pacity factor during the utility's 10 highest
load  hours was about 40%. CACF curves
were  calculated using both measured PV
system performance data and the perfor-
mance data generated by the dispatchable
storage simulation.
   Charts displaying the utility LDC  and
the PV system's CACF curves (both with
and without storage) were created  for each
calendar quarter during the study period.
An additional chart showing the same data
for the 100  highest load hours encoun-
tered  during  the study period was  also
                             created. These charts provide a measure
                             of each PV system's peak shaving capac-
                             ity.

                             Load Reduction Without
                             Storage
                               Not surprisingly,  load matching for PV
                             systems  installed  in northern states  is
                             greatest in the spring and summer months,
                             with the capacity factor during the highest
                             load hours typically  averaging above 40%.
                             Several  of these sites achieved capacity
                             factors well in excess of 60% of their SOC
                             rating  during  the highest  load  hours  in
                             these  months. The northern systems in-
                             variably generated  little or no power dur-
                             ing winter peak hours, most or all of which
                             occurred at night.
                               Utility peak loads in the southern and
                             western parts of the U.S. invariably oc-
                             curred during the summer months  when
                             the  solar resource  is  greatest,  although
                             these  peaks  consistently occurred in the
                             mid- to  late-afternoon.  Most of the sys-
                             tems installed in these regions  operated
                             at capacity factors in excess of 40% dur-
                             ing the highest load hours  in the summer
                             months. Some systems consistently oper-
                             ated at capacity factors above 60% during
                             these  hours.  The one exception to this is
                             the system in Flagstaff, AZ,  which  oper-
                             ated  at  only  about 30%  capacity factor
                             during the peak load hour.  This low  result
                             is most  likely explained by the fact that
                             the load and  weather patterns in Flagstaff
                                   Third Quarter 1993
                0.9
^
o
•a  0.8
£,

! °-7
o
i>  0.6
Q.
                                              System load
                            Cumulative average
                            capacity factor
                                                             10,000
Figure 5.  Example utility load duration and cumulative average capacity factor curves.

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are quite different from those  in Phoenix
which  is about  1  mi  (1.6 km)  lower  in
elevation and 140 mi (225  km)  south.
Loads  in the Phoenix area probably domi-
nate the APS system load.
  As did their counterparts in the Midwest
and  Northeast, systems  in the southern
and western states typically operated at a
lower level  during winter  peak hours. Ex-
cept for systems in southern California,
systems in  the West operated at or near
a zero  % capacity factor during  peak hours
in the first quarter of the year.

Load Reduction With Storage
  Except where  the  power  output  was
limited by a system outage, results from
the storage simulation indicate that stor-
age  can provide system  operation at the
full  inverter rating during the  peak load
hours  in the summer  months at all sites.
In regions (such as the NU service area)
where  peak utility loads are highly corre-
lated to the solar resource, the addition of
a dispatchable storage  system may do
little to improve  the  PV system's load
matching capability,  since it will already
be quite good. Systems in northern states
are much less able to provide  power dur-
ing  peak load  hours in winter due to their
limited  solar resource and  snow  cover.
Even with  storage, some of  these sys-
tems were  unable  to  provide power  at
more than a few percent  of inverter rating
during  winter peak  load  hours. However,
daytime generation at other northern sites
was sufficient to allow inverter operation
well  in  excess of 50% of inverter rating
during  winter peak hours.
  Unlike many systems installed in north-
ern climates, the addition of dispatchable
storage to systems  installed in the  south-
ern and western states would  allow them
to operate at high capacity factors  during
winter  peak hours. The results of the simu-
lation  indicate that  most  of the systems
installed in  this part  of  the  U.S.  would
operate at or near 100%  of inverter rating
during  the highest winter  load hours.
  It  is important to recognize that these
results are substantially determined by the
storage charging/dispatch  algorithm.  An
algorithm which stores generation from 1
or more days and dispatches  only when
load exceeds  a  predetermined threshold
(as opposed to dispatching during the peak
hours of each day) might substantially im-
prove the load matching characteristics of
all systems.

Conclusions
  This project has provided an initial dem-
onstration of the effectiveness of grid-con-
nected  PV energy  systems  in reducing
the pollutant emissions of electric  utilities.
The broad range  of emission  offsets
achieved by these systems reflects differ-
ences in both the available solar resource
at each site and  differences  in emission
rates among  utilities. The results  demon-
strate that  the latter factor is far  more
important in determining the pollution miti-
gating  potential of a  PV system  than is
the former. Given current and projected
costs of PV systems, it is unlikely that this
technology will  be employed solely for its
pollution mitigating potential. While  there
is certainly  substantial value in this poten-
tial, PV's environmental benefits must be
considered in  conjunction with the  other
benefits provided by the technology for
grid-connected  applications to  be  consid-
ered cost-effective. These benefits include
conventional  energy and power benefits
as  well as more  subtle and  less  well-
recognized advantages over central-sta-
tion generators.
  The  report documents case studies of
the peak load reduction benefits,  for utili-
ties and for individual customers  at sites
across the  country. While PV will not pro-
vide substantial power during peak load
periods at  every location, it will at many,
with or without storage.  If a PV system is
interconnected  on the customer  side  of
the meter, this translates into energy- and
demand-charge savings. On the utility side
of the  meter, distributed generating re-
sources such as PV which provide power
during  peak load hours can defer costly
and under-utilized additions to generation
and transmission capacity. In addition, ev-
ery kilowatt-hour generated by a PV sys-
tem reduces  utility fuel and variable  op-
eration and maintenance costs.
  As the electric utility industry enters the
world  of retail competition, the high cost
of providing power  during peak hours is
likely to be  much more clearly reflected in
the prices paid by consumers. The  value
provided by resources such  as PV that
generate power during such times is there-
fore likely to increase substantially for cus-
tomers that cannot alter their consump-
tion  patterns,  and for utilities hoping  to
retain such customers.
  Retail competition at the generation level
will also bring the costs of maintaining the
transmission and distribution (T&D) sys-
tem  under closer scrutiny.  Already,  sev-
eral studies have demonstrated that such
costs are not homogeneous across a ser-
vice area, but are typically highly differen-
tiated. Communities in which  load growth
necessitates an increase in the power de-
livery capacity  of  local distribution  re-
sources may have T&D  costs many times
the average for the  utility service area.  In
such  areas  distributed generating  re-
sources such as PV might  defer or elimi-
nate the  need for T&D capacity additions,
to the degree that they are able to provide
power at the time when the existing  distri-
bution system is stressed.
  In  addition to its environmental,  energy,
and capacity benefits, PV technology pos-
sesses a variety of characteristics which,
although less easily quantifiable,  contrib-
ute additional real  value.  Among these
are (1)  its reliance  on  a limitless,  indig-
enous resource, which could reduce grow-
ing  dependence  on imported oil;  (2)  its
modularity and speed of  installation, al-
lowing generating capacity to be  added
as needed rather  than tying  up  large
amounts of capital in  conventional power
plants, the need for which may not materi-
alize; (3) the relative ease of  siting PV
power plants, as opposed  to the permit-
ting hurdles and public opposition that utili-
ties typically encounter in  attempting  to
site conventional  power plants and trans-
mission   lines;  and  (4) its  ability to fulfill
consumers' desire  for  non-polluting, re-
newable  resources,  which may have stra-
tegic value to  utilities in addition to envi-
ronmental benefits.
  Taken collectively, the benefits  of grid-
connected  PV  power  may already out-
weigh its costs in some applications. As
PV costs continue to decline, the range of
such  applications is certain to grow, but
much work remains in  the effort to fully
quantify  the benefits of the  technology.
Projects such as the one this report docu-
ments are an essential component of that
effort.

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   E.C. Kern, Jr. and D.L Greenberg are with Ascension Technology, Inc., Lincoln
     Center, MA 01773.
   Ronald J. Spiegel is the EPA Project Officer (see below).
   The complete report, entitled "Demonstration of the Environmental and Demand-
     side Management Benefits of Grid-connected Photovoltaic Power Systems,"
     (Order No. PB97-117618; Cost: $41.00, subject to change) will be available only
     from:
           National Technical Information Service
           5285 Port Royal Road
           Springfield, VA 22161
           Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:
           Air Pollution Prevention and Control Division
           National Risk Management Research Laboratory
           U. S. Environmental Protection Agency
           Cincinnati, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information (G-72)
Cincinnati, OH 45268

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