Standards Development

Scope

Background:

IEC 61400-12-1:2017 allows the use of remote sensing devices (RSDs), such as lidars and sodars, for power curve measurement. However, the scope of this guidance is limited to the ground based devices. The guidance in IEC 61400-12-1:2017 is being re-organised such that measurement methods are handled in a manner that is independent of the use case whose data requirements the methods ultimately fulfil. Furthermore, separate documents will deal with distinct approaches to measurement:

- The future IEC 61400-50-1 will address the guidance for met mast measurements currently described in IEC 61400-12-1:2017.

- The future IEC 61400-50-2 will cover the guidance already developed for ground based RSDs as described in IEC 61400-12-1:2017.

- IEC 61400-50-3 is currently being developed to provide guidance for the use of nacelle mounted lidars.

A distinct measurement approach not currently supported by the guidance described above involves the use of floating lidar. During the past 10 years, floating systems have been developed to allow lidars to be deployed offshore without the need to install a fixed platform. Guidelines and procedures for the use of such devices have been developed. These have often been developed on a piecemeal basis internally by companies using the equipment. In addition, pre-normative guidance has been developed by the International Energy Agency under IEA Wind Task 32, and by the Carbon Trust Offshore Wind Accelerator (OWA). Since floating lidars are now commonly available on the market and are already used by the industry in a number of roles, there is a need for a normative standard that provides a framework for the various methodologies and recommendations that are emerging. The proposed technical specification will fulfil this need 

Scope:

The aim of the proposed technical specification is to provide general requirements and guidelines to ensure that floating lidar wind measurements meet the level of quality and confidence required for the use cases they are currently deployed to support. The technical specification should be independent of the lidar technology and allow consideration of all existing types of floating lidar as well as those that may potentially be developed in the future.

This technical specification will primarily focus on floating lidar wind measurement in free stream conditions offshore, including use cases such as pre-construction resource assessment and site classification, and post-construction use cases that entail measurements in unperturbed flow, unaffected by the wakes or induction zones of wind power assets, such as power performance testing. The technical specification will provide guidance that is suitable for the use of floating lidar in the context of other use cases, but the current industry experience and expertise which the technical specification will codify is likely to be based on deployments which have supported the use cases described above. The guidance will include:

- Requirements on lidar technology,

- Requirements on the floating platform and system integration,

- Calibration and classification processes,

- Intermediate variable measurement uncertainty derivation,

- Mounting on the floating platform, system configuration, deployment, installation and mooring,

- Data filtering and analysis,

- Final variable measurement uncertainty derivation,

- Wind lidar data reporting.

The main expected challenge is to define requirements that will be specific enough to ensure coherence, repeatability and accuracy of measurements but that will also be generic enough to be independent of the floating lidar make and model and the specific use cases they have historically been deployed to support.

The primary use case envisaged by this technical specification is pre-construction wind resource assessment, as there are alternative methods suitable for post-construction use cases. Therefore this technical specification will focus in the first instance on providing floating lidar wind measurements in compliance to the requirements for pre-construction wind resource assessment, energy yield estimation, and site classfication.

Purpose

The purpose of this new technical specification is to provide a common method for all the stakeholders within the international wind energy community to use floating lidar for wind measurements in fulfilment of the data requirements of key wind energy assessment use cases, including, but not limited to, offshore preconstruction wind resource assessment and energy yield estimation, offshore site suitability assessment and classification, and offshore wind turbine power performance testing.

Using a floating lidar to support these use cases instead of a met mast represents a significant cost reduction and an increase in the database acquired to allow wind energy assessment calculations, even more if we consider a floating lidar is easy to move from one location to another, which is practically impossible with a met mast.

This new technical specification is intended to be used as a complement to the wind measurement techniques already being covered in the new organization of the IEC 61400-12 and IEC 61400-50 standards and technical specifications. As such it is expected to be used to accurately and fairly measure the wind to assess the incident wind resource, turbine loads, power performance, and/or noise.

The impact of this new technical specification is expected to be immediate since the technology is already used by many stakeholders but often requiring agreement between different parties involved in applications supported by the RSD deployment. This technical specification will provide a complete and generic methodology which will minimize the needs for specific agreement between the parties.

Therefore it is proposed to start the development of this technical specification as soon as possible and not wait for a final strategy of re-organisation of the TC 88 standards and technical specifications. The international offshore wind industry lacks a normative procedure and it would be appropriate to gather the available resources into an IEC standard or technical specification rather than individual national standards.