Distributed Renewable Energy Operating Impacts and Valuation Study

Section 3
The EPRI tool was also used with sub-hourly data to simulate short-term load changes due to
inverters switching off line and the resulting effect on feeder voltage.
3.2 Reduction in Losses
3.2.1 Methodology
Solar DE provides electricity at the site of application and therefore reduces the load needed to
be served by a centralized power generating facility. A reduction of load at the site of a solar DE
application results in energy savings due to the energy generated by the solar DE and a reduction
of generation at a centralized facility. This reduction in load also results in a reduction in the
electricity losses that occur during delivery of electricity from the centralized generating facility
to the load. This is referred to as line losses. If less electricity is required to be transmitted to a
specific location, then there will be a reduction in the line losses associated with that reduction in
power transmission.
The discussion and analysis associated with the value of the energy savings associated with the
generation of energy from solar DE is provided in Section 5 of this Report. Because the
distribution system and transmission system are inextricably linked when discussing line losses,
the results of the analysis for line losses are presented in Section 4.
In addition to energy losses, there are demand losses that occur at the time of a peak load.
Similarly to the energy, a reduction in peak current (or load) results in reducing peak demand
losses proportional to the square of the reduced load. The demand losses affect the system
capacity that is required to be built from the centralized generating station to the customer’s
meter.
3.2.2 Modeling Description
System Loss Model
As mentioned above the modeling, analysis, and results for the system level energy losses,
including the distribution and transmission, is discussed in Section 4. The system energy loss
model is also used to calculate the annual peak demand loss reduction due to solar DE. The
distribution specific portions of the modeling efforts undertaken for this Study are described
below.
Feeder–All Distribution Feeder Model
APS and the Study team performed analysis on specific distribution feeders to understand the
effect of peak load reduction on distribution demand losses. APS models distribution feeders
using ABB’s Feeder-All software to perform load flow studies that evaluate conductor loading,
voltage drop, and losses at specific load levels. Only the main three-phase lines are modeled in
Feeder-All; therefore, results do not include loading or losses on single-phase taps, distribution
transformers, or customer service conductors. APS and the Study team performed load flow
analysis on some of the distribution feeders to determine the relationship of feeder loading to the
losses on the main three-phase lines.
3-4 R. W. Beck, Inc. Arizona Public Service