Load Estimation Methodology
Companies affiliated with the Northeast Utilities System have been involved with retail access load estimation procedures since 1996, when the first pilot program began in New England and since March 1998 when retail access began in Massachusetts. WMECo’s approach draws upon this experience, as well as regional work groups.
Supplier Hourly Load Determination
The daily load determination process results in estimated hourly loads for each Supplier for the previous day using interval data and customer billing information. These loads are reported to ISO-NE by 37 business hours from the day of dispatch. On a monthly basis the estimates are refined by incorporating actual usage data obtained from customer meter readings as well as additional interval readings that may now be available.
There are several components in the daily load determination process:
- Select Load Shapes
Load profiles are generated for each customer within the WMECo service
territory. Actual hourly load data are utilized for customers that have
interval recorders installed. For all other customers, daily class profiles
are estimated utilizing representative historical load research data
developed from samples designed to meet DPUC regulatory standards.
- Aggregate Usage Information
A "usage factor" is calculated for each customer. This usage factor
reflects the relationship of each customer’s actual meter read cycle
usage to the average usage of customers in their respective class developed
from the sample data over the same period.
- Develop Preliminary Estimates of Hourly Loads
A preliminary estimate of each Supplier’s hourly loads is produced by
scaling the appropriate class profiles, relative to the associated usage
factors, and including any telemetered data. Each Supplier’s loads will
then be aggregated across the classes for a Supplier’s daily profile.
- Incorporate Non-Pool Transmission Facility (Non-PTF) Losses
Non-PTF Losses are added to each supplier’s load. Losses are 2.33% for
primary customers and 5.16% for secondary customers.
- Reconcile to System Loads
The Suppliers’ preliminary hourly loads are compared to the Company’s
actual hourly metered loads (as metered at the PTF boundary or interconnection
point with the distribution company network). The difference, or residual,
is allocated to Suppliers proportionally to the estimated portion of
the Suppliers’ loads.
Monthly Reconciliation Process
The monthly reconciliation process, which utilizes the same methodology as the daily load determination process, incorporates the most recent customer usage, which is available after monthly meter readings have been processed. This process also includes actual hourly demand information from the non-telemetered interval recorders that have been processed subsequent to the initial estimate. Revised Supplier values for the calendar month are reconciled to the revised system values for the same time period. Any residual is allocated proportionally to the estimated portion of the Supplier’s loads. The resulting energy values are reported to ISO-NE within 90 days from the end of the calendar month.
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