IEEE Power & Energy Magazine - March/April 2015 - 64

SCE's SPVP: Deploying 200-Plus MW of Distribution-Connected PV
The Solar Photovoltaic Program (SPVP) of Southern California

supported the adoption of solar PV, CSI's program was focused on

Edison (SCE) is a utility-run program that facilitates the installa-

smaller installations while the SPVP focused on larger, utility-scale

tion of utility-scale solar PV into the distribution grid. The pro-

PV installations. The SPVP boasts one of the largest rooftop sys-

gram defined utility-scale systems as those measuring between

tems in the United States, with a rating of 10 MW dc. Focusing on

500 kW and 10 MW; most installations are located on rooftops.

larger installations has helped to achieve cost reductions. The first

The program is split into two parts: utility-owned installations

SPVP installation cost US$5.07/W dc while the final installation in

and independent power producer (IPP)-owned installations.

2013 was just US$2.85/W dc. The utility-owned portion has a total

The utility-owned portion of the program has completed instal-

of 25 sites: 24 rooftop sites and one ground mount.

lations totaling 91 MW dc as of 2014 (see Figure S1). The IPP
portion will run through 2015 and install a total of 125 MW dc.

To keep costs low, the PV panels were either monocrystalline or polycrystalline and were situated at a 5-10° tilt. The

The program began in 2010 with three goals: supporting Cali-

500-kVA inverters used were primarily sourced from Satcon

fornia renewable mandates, driving down the cost of solar PV,

Technology Inc. To interconnect the sites, the installations were

and maintaining a cost-effective procurement mechanism on

first studied using engineering software to determine system

behalf of ratepayers. Although the California Solar Initiative (CSI)

impacts and necessary mitigation techniques. Some of the systems were so large they required primary-side reconductering

SPVP Utility-Owned Installed PV Capacity

3/2011
5/2011
7/2011
9/2011
11/2011
1/2012
3/2012
5/2012
7/2012
9/2012
11/2012
1/2013
3/2013
5/2013
7/2013
9/2013
11/2013

Installed Capacity MWDC

100
90
80
70
60
50
40
30
20
10
0

to prevent thermal overloads. The sites were interconnected
under the Wholesale Distribution Access Tariff (WDAT). The
WDAT allows for distribution-connected generators to participate in the wholesale energy market. WDAT requires telemetry for CAISO market participation and a separate telemetry
system for distribution grid operators. The operators required
near-real-time power flow information connected to the utility SCADA system as well as remote-disconnect switches in
case of emergency. The sites were spread out over the SCE service territory, so remote terminal units (RTUs) were strategically placed so as to cluster site communications and minimize
costs. Sites where RTUs were placed also received weather stations that recorded ambient temperature, panel temperature,

figure S1. The installed capacity of PV systems
installed under the utility-owned portion of SCE's
SPVP.

✔✔ fault current contributions and impacts on circuit

protection.
In addition, levels of acceptable impact and the operational limits of the modeled distribution circuits were developed. Some operational limits, such as ANSI C84.1 Range A
voltage limits, are generally accepted by the distribution utility industry (although conservation-oriented voltage reduction policies can lower the upper bound) and can be used to
determine the specific PV system impact limit for PV impact
studies. Other metrics reflecting the impact limits are harder
to determine and may be different for different utilities. For
instance, the acceptable impact on automatic voltage regulation equipment operation varies considerably from utility
to utility, due to the fact that utilities implement differing
voltage regulation strategies. SCE typically uses only automatically switched capacitors for voltage regulation within
64

ieee power & energy magazine

barometric pressure, humidity, and irradiance. These weather
stations have been critical elements of solar PV performance
research efforts at SCE and its partner institutions.

its distribution circuits. Switched capacitors typically have a
larger voltage control deadband than voltage regulators, so
more voltage variation (due to the resource variability of PV
systems) may be acceptable than would be for utilities that
tightly regulate the voltage on their distribution circuits using
multiple voltage regulators and load tap changers at the substation. In these types of cases, instead of setting a specific
impact limit, the general impact severity or magnitude was
focused on in the modeling study process to simply show
the impact and let utilities' interconnecting utility-scale PV
systems determine their specific impact limit internally.
Quasistatic time-series analysis-sequential load flow
solutions with the slow time dynamics of voltage regulation
equipment and PV system variability modeled-was used to
investigate the operation of the study circuits at a one-minute
time scale. Additionally, a high-penetration PV impact study
march/april 2015



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