Assumptions book

Consultation on draft assumptions book v2.0

Transpower is now consulting on an update to the assumptions book for benefit-based charges (BBCs).

The consultation period is two weeks commencing 7 October 2024, with submissions due by 5pm on Monday, 21 October 2024. This will be followed by a one-week period for cross-submissions. 

The draft assumptions book consultation package consists of the following documents:

Response to suggested areas for development in Jacobs’ assurance report

In its review, Jacobs suggested some potential areas for future development of the assumptions book. Two related to regularly reviewing information (i.e. geothermal emissions factors and CCGT availability), one to further development of the spreadsheet data book, and one to further investigation of generation capex costs. As suggested by Jacobs, we do not consider that these suggestions necessitate any immediate changes to the assumptions book. We have noted these suggestions and will investigate them further as we work towards our next update, anticipated for next year.

 

Current assumptions book

Key documents

About our assumptions book

Our benefit-based charges (BBC) assumptions book is designed to outline the assumptions and detailed methodologies Transpower intends to apply for allocating and adjusting BBCs – calculating starting benefit-based investments (BBIs) customer allocations for post-2019 BBIs and adjusting BBCs. The assumptions book covers both standard methods (price-quantity method and resiliency method) and the simple method for calculating starting BBI customer allocations for post-2019 BBIs. We have taken a relatively detailed approach to provide greater (up-front) certainty about how BBCs will be allocated and adjusted under the TPM. It is a living document that will be updated from time to time.

Additional information

The Electricity Authority's (Authority's) transmission pricing methodology (TPM) contains the structural and fundamental aspects of the transmission pricing regime that has applied since 1 April 2023. The TPM also includes a role for secondary documentation to help ensure consistent and transparent application at an operational level. Under the TPM’s requirements for BBCs, Transpower must develop, consult on and publish an assumptions book. Where Transpower proposes to depart materially from the assumptions book we will explain and consult on this when we consult on our application of the relevant BBC allocation or adjustment methodology.  We may not deviate from the assumptions book in any way that does not comply with the TPM or wider Code. The assumptions book will be consistent with the TPM and all aspects of the Code.  It is not intended to replicate, and cannot change, the fundamental and structural requirements for allocating or adjusting BBCs, which are specified in the TPM itself.

 

Previous assumptions book editions

Previous versions of the assumptions book have been used as a basis for the analysis for the following BBIs:

Assumptions book versionBenefit-based investment
V1.0CUWLP
V1.1

WUNIVM Stage 1a – HAM STATCOM

WUNIVM Stage 1b – OTA STATCOM

HVDC Pole 2 refurbishment

 

Assumptions book v1.1 – March 2023 

Key documents

Consultation process 

On 1 February 2023 we began consulting on a draft update (v1.1), which included benefit factors in Chapter 5 and corrected some errors in Chapter 2 and 3. On 10 February 2023, we reissued the consultation paper and draft updated assumptions book to show correct spill paths in the diagram below paragraph 90. This was a minor correction. Due to the impact Cyclone Gabrielle had on some customers, we extended due dates for submissions and cross-submissions by two weeks. Submissions were due by 5pm Monday, 6 March 2023. We did not receive any submissions. Consequently, the cross-submission period was cancelled.

Our consultation package included:

Assumptions book v1.0 – September 2022 

Key documents 

Consultation process

The consultation period was 4 weeks. Submissions were due by 5pm on Friday, 27 May 2022. This was followed by a 1-week period for cross-submissions. Cross-submissions were due by 5pm on Friday, 3 June 2022. We made changes to the assumptions book as a result of some of the feedback. 

Consultation package

The draft assumptions book consultation package included:

Submissions

Cross-submissions 

Online drop-in session

On Friday, 6 May 2022 at 1:30pm we hosted an online drop-in session. It was an opportunity for stakeholders to ask questions and seek clarifications about the consultation and the draft assumptions book itself. The session was recorded and transcribed  for interested parties unable to attend on the day.