Distributed Renewable Energy Operating Impacts and Valuation Study

Section 5
Figure 5-1: Coincidence of Solar DE Output with the APS System Load Shape, Solar DE at 10% of Peak
8,000
1,200
Demand
7,000
243 MW Peak
Reduction
1,000
Demand After Solar
Solar Resources
Hourly Electric System Demand (MW)
6,000
5,000
4,000
3,000
2,000
713 MW Solar
Capacity
800
600
400
Hourly Solar DE Production (MW)
1,000
200
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Hour Ending
0
Transmission and distribution planning is usually concerned with the peak demand placed on the
electric facilities; therefore, an analysis of the coincidence of the solar DE capability at the time
of the peak on the electric facilities is sufficient to determine the impact of solar DE capacity.
However, power supply planning is concerned with the ability of a given resource portfolio to
reliably serve the total system load – not just at the time of the peak but across all hours of the
year. The capability of solar DE resources to displace power supply resources must, therefore,
be determined through a different analysis than that used for the transmission and distribution
analyses.
Determining Power Supply Capacity Reliability
Power supply planning is typically performed such that resources are added to meet a given level
of capacity reserves above the forecast peak demand, or reserve margin. In the case of APS, the
planning reserve margin is 15 percent. While a planning reserve margin reflects a reasonable
rule-of-thumb for long-term planning purposes, the 15 percent reserve margin is actually derived
through a more rigorous analysis of the quantity of resources needed to maintain a minimum
level of reliability to serve customer loads. The electric industry has adopted several similar
methods to compute such reliability metrics; generally they are all related to a specific measure
of how likely a utility will be able to serve the loads of its customers.
5-6 R. W. Beck, Inc. Arizona Public Service