1:45  -  2:45

October 25, 2018

Grand Cypress B

302: 1-in-N Year Weather Selection for Design Day Analysis

Session Category :  Natural Gas 

Local distribution companies (LDCs), like CenterPoint Energy, need to know how much gas their customers will demand on their design day, which for CenterPoint Energy is defined as the highest volume of gas it expects to use in a single day. LDCs must design their natural gas distribution systems as well as procure enough third party pipeline capacity to meet the anticipated demand on design day condition.
One essential piece of this study is determining the design day weather event. Currently, CenterPoint Energy uses the coldest weather event in the past 30 years as the design day event. For most of our southern operating areas, that date is December 23, 1989. Using our current selection method, that date will no longer be able to be considered in 2 years. The next coldest weather event in the past 30 years is not nearly as cold as the one that occurred on 12/23/89.

Having a much warmer design day criteria puts a higher risk on meeting customer demand should an extreme cold day occur in the future. If a future peak day occurs which is much colder than the new design day weather condition, the company might not be able to provide enough natural gas to meet its customers’ demand. On the other hand, the company needs to make sure that it is not over-estimating design day demand in order to keep pipeline reservation fees reasonable.

CenterPoint Energy is working with Marquette University to provide the company with an in depth analysis by using advanced mathematical tools and sound statistical theories.
The method includes a probability calculation to come up with a 1-in-N year weather condition that will be specific to CenterPoint Energy’s operation areas. The soundness of the method is further supported by having been published in a professional technical journal publication. The company feels confident to begin using this as the design day weather condition for our planning purpose.
A lot of LDCs are also facing the same dilemma as what is the right design day weather selection. Hopefully this talk could share some insights as what they could look for.