Distributed Renewable Energy Operating Impacts and Valuation Study

Technical Value – Distribution System
This section discusses the analysis used by the Study team to determine the value for each of
four potential sources of value: line losses, deferment of capital expenditures (capex), extension
of service life, and reduction in equipment sizing. The section includes a description of the
methodology used to determine value, a description of the various models utilized in that effort,
and a discussion of the modeling results. These modeling results are then presented for each of
the deployment scenarios described in Section 2 of this Report. A discussion of some of the
technical limitations associated with Solar DE on the distribution system is also included.
A description of how the four value sources roll up to provide an aggregate value for the total
distribution system is presented at the end of this section. Depending on the level of detail
required for the analysis, supplemental analysis and information may be presented in the
appendices to this Report.
The overall approach used by the Study team in this section included a combination of empirical
testing, system modeling, and reviewing information provided by APS, other electric utilities,
research institutions, and the stakeholder group. Empirical testing included utilizing existing
solar DE installations owned and operated by APS to test certain conditions. The energy
production from a large APS solar facility on a feeder, for example, was dropped momentarily
from the electrical system to study the effect on feeder voltage and harmonics.
System modeling included the development of customer load models, feeder load flows and
annual hourly system usage to simulate the impact on annual peak demand and energy losses
from a range of installed levels of solar DE technologies. The models were used to perform a
screening analysis for actual APS residential and commercial customers, as well as feeders and
substations, utilizing 2006 and 2007 load and weather data to estimate demand savings
associated with solar DE.
The residential and commercial customer screening analysis supported the analysis of the
potential value source associated with a reduction in equipment sizing. The feeder screening
analysis was used to evaluate potential solar impact to determine the level of solar DE required
to defer capex.
Since demand varies on an hourly basis, and solar output varies on an hourly basis — both
relatively significantly — an hourly analysis of loss savings was conducted. Projected annual
hourly system load profiles, with and without solar, were compared to determine annual energy
losses, as well as peak demand losses at the system level. The methodology and results for this
analysis are included in Section 4, which incorporates loss savings for both the distribution and
transmission systems.
Hourly projected solar DE data was used to calculate “dependable capacity” at the time of the
annual system peak load for the distribution and transmission system. This was use to determine
a targeted capacity deferment value at the system level for the distribution and transmission
systems (a slightly different calculation of “dependable capacity” was utilized for the generation
system described in Section 5). An average cost of distribution improvements per MW of noncoincident
load growth was used to calculate the value to the distribution system.
In addition, EPRI’s DSS tool was used to analyze the hourly impact of different levels and types
of solar DE deployment on a particular feeder to validate annual distribution loss calculations
and the effect on annual peak demand for capital deferment or possible equipment size reduction.
Distributed Renewable Energy Operating Impacts & Valuation Study R. W. Beck, Inc. 3-3