Distributed Renewable Energy Operating Impacts and Valuation Study

Technical Value – Distribution System
delay specific upgrades required for future growth. Additionally, APS could allow capacity
upgrade deferrals only if the load would not exceed the equipment’s emergency rating when the
solar DE is not available due to cloud cover. APS design standards include an emergency rating
that allows loading most distribution equipment 10 percent over the planning rating. Without a
storage mechanism to maintain solar DE reliability during cloud cover, solar DE can only
provide dependable capacity within that 10 percent bandwidth to provide increased capacity
during normal conditions without overloading the equipment when the inverters have switched
off.
Deferral of transmission and distribution system upgrade projects is based on the dependable
capacity of solar DE during annual peak load. Determination of dependable capacity involves a
comparison of hourly solar output to hourly load for potential peak load days.
To test the feasibility of utilizing solar DE to defer a capital project, a constrained area was
analyzed where a capital improvement project has been identified to relieve an overloaded
feeder. As an example of a constrained area, a screening analysis of the Thompson Peak
Substation Feeder 10 project was conducted. Thompson Peak Feeder 10 is projected to be
loaded to maximum capacity in 2008, and a new feeder is planned to relieve it. Solar DE could
be used to reduce load to the planning level to postpone the upgrade. Loss of the solar DE due to
cloud cover during peak loads would increase loading back to the present operating level.
Solar DE can only be used to defer upgrade projects for feeders loaded between the planning and
emergency ratings. Additional growth on Thompson Peak Feeder 10 would result in the
equipment being overloaded if solar DE is not available and will require the upgrade until
storage is available.
The Study team also explored the possibility of implementing solar DE in a “greenfield” area of
new development with the idea that each customer would install the appropriate technology. To
review the impacts on a greenfield area, a feeder from the Deadman Wash Substation (Deadman
Wash Feeder 4) was analyzed. While the Deadman Wash Feeder #4 is not in a greenfield area,
which by definition would not have feeders, it is located in the Anthem master-planned
community, which was identified as a proxy for future development areas.
3.3.2 Modeling Description
The modeling effort to determine the potential for deferment of capex on the distribution system
consisted of three distinct components. The first consisted of determining the potential
dependable capacity for the distribution and transmission systems associated with solar DE. The
second consisted of a screening analysis of specific feeders and their actual loads with solar DE
production (specifically related to PV systems). The third consisted of reviewing impacts to
specific feeders utilizing EPRI’s DSS model (which included the Deadman Wash Feeder #4
analysis).
Dependable Capacity Modeling Effort
Figure 3-3 depicts an example of savings from solar DE by comparing peak load on a summer
day before and after installing significant amounts of solar DE generation. The example shows a
253 MW reduction in peak demand. This graph is intended as an example to illustrate the
implications of system load and solar DE coincidence, and is not meant to provide an actual
measurement of coincidence.
Distributed Renewable Energy Operating Impacts & Valuation Study R. W. Beck, Inc. 3-9