Guidance: Specified generator: when you need a permit

Natural Resources Wales

September 1
11:36 2022

A generator is a combustion plant that generates electricity, including:

  • engines
  • gas turbines
  • boilers that operate as a combined heat and power combustion plant

A direct drive and heat only combustion plant is not classed as a generator. But its still a medium combustion plant (MCP).

Definition of a specified generator

The term specified generator covers an individual generator or a number of generators if theyre:

  • on the same site
  • operated by the same operator
  • for the same purpose (generating electricity)

Generators are still classed as operating for the same purpose if theyre:

  • using different fuels or technologies
  • under contract for a capacity marketing agreement or to provide a balancing service

If you have more than one generator on your site youll need to aggregate your generators into a specified generator. Youll need one permit for the site.

Use this guidance to work out:

  • if your generator is excluded from specified generator controls
  • the specified generators capacity
  • whether the specified generator qualifies for transitional arrangements
  • the deadline for applying for the environmental permit
  • how to aggregate your generators into a specified generator

Generators affected by Medium Combustion Plant Directive (MCPD) controls

Both the MCPD and specified generator regulations can apply to generators.

If your site includes a medium combustion plant that generates electricity you must check if your generator:

  • is excluded from both specified generator and MCPD controls if its excluded from one but not the other youll still need to apply for a permit
  • is required to meet both specified generator and MCPD controls youll need to apply for the environmental permit with the stricter controls and earlier deadline
  • is already permitted under the Environmental Permitting Regulations but must also meet MCPD requirements

Check using the guidance on Medium combustion plant: when you need a permit.

Excluded generators

These generators are excluded from specified generator controls. For a MCP that generates electricity you must also check if the MCP is excluded from the MCPD controls.

Chapter 2 or 3 Industrial Emissions Directive (IED) installation

Generators that are part of an IED installation under chapter 2 or 3 are excluded.

However, the regulators will use the MCPD and specified generator requirements to inform the site-specific best available techniques. These are the minimum standards they will apply. See how to meet MCPD and specified generator requirements for IED chapter 2 installations.

Nuclear safety role

Generators that have a defined nuclear safety role under a nuclear site licence issued by the Office for Nuclear Regulation are excluded.

Emergency backup generators

From 1 January 2019, a backup generator only used to provide power at a site during an emergency is excluded. However, it is a MCP and requires a permit by the appropriate deadline.

Using a backup generator for the following is not classed as emergency use:

  • providing a balancing service (whether procured or not)
  • demand side response operations such as triad avoidance or fast frequency response

For an on-site emergency, theres no restriction on the total number of hours:

  • a backup generator can operate for operators must try to reduce the period and frequency of emergency use
  • black start backup generators can operate for

Number of hours you can test backup generators

You must not carry out more than 50 hours testing a year for each backup generator. You must get agreement in writing from your regulator if you want to increase this limit. The regulator can exclude commissioning time within the written agreement.

For each backup generator, you must record the number of hours you test during the year. This is to demonstrate that you meet the exclusion criteria.

If you exceed the limit of 50 hours testing a year without written agreement the regulator will take appropriate enforcement action.

Data centres

Data centres that use an on-site emergency backup generator when the transmission frequency is unstable are excluded. This is provided the generator is not part of a formal agreement or contract.

How to test backup engines

When you test backup engines you should:

  • stagger the tests if you have multiple backup engines
  • keep testing times and frequency to the minimum just enough to demonstrate reliability at the appropriate load
  • only test when you expect low ambient nitrogen oxides (NOx) background, such as not during peak traffic periods
  • use the electricity generated from the test on your site
  • install backup generators away from sensitive receptors (not below windows or venting onto car parks) and terminate the exhaust flues vertically, making sure there are no obstructions

Offshore generators

Generators operated offshore are excluded.

Gas storage and unloading platforms

Generators installed on a gas storage or unloading platform are excluded.

Research and development testing

For the requirement in England see the Environment Agencys Regulatory Position Statement Operating a schedule 25B, Tranche B specified generator for research and development: RPS 220.

Mobile generators

The owner of the mobile generator is responsible for its compliance with specified generator controls.

Specified generator controls do not apply to a mobile generator that is designed to move or be moved (on roads or land). However, the controls do apply if it:

  • generates electricity for the national transmission or distribution system to cover a specified generator thats out of operation
  • performs a function that a static generator could do

The regulator will decide whether a mobile generator is operating as a static generator. They will look at:

  • the nature of the activity the operators doing and other equipment theyre using
  • whether the site is relatively permanent or transient
  • how long the generator is in a single location if its in place for 6 months or more the regulator will consider it to be functioning like a static generator and the controls apply
  • whether the site is finished or parts of it are under construction

Mobile generators used for planned maintenance or emergencies

Specified generator controls do not apply when the mobile generator is used for planned maintenance or emergencies. These are examples of maintenance or emergency use from different sectors:

  • water utilities emergency use or when replacing assets such as pumps and electrical infrastructure
  • IT and telecoms routine maintenance activities of data centres or telecom switch sites
  • general building maintenance activities such as low voltage and high voltage switchgear upgrades and replacements
  • running electricity transmission and distribution during an emergency or planned maintenance

Mobile generators on construction sites

Specified generator controls do not apply to a mobile generator used on a construction

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