Further clarifications on the Medium Combustion Plant Directive

In January 2018 the Medium Combustion Plant Directive (MCPD) was passed into UK Law following the EU law that was passed on 18 December 2015.

In England and Wales special rules have been added for electricity generators (see below).

A Medium Combustion Plant (MCP) is a boiler, engine, turbine, generator etc. with a heat input of 1MW to 50MW. If it runs for <500 hours per year you must sign a declaration.

If it runs for >500 hours per year you must register, be tested and comply with emissions limits (particularly NOx) by:

  • New plant by 1 Jan 19
  • Existing plant >5MW by 1 Jan 25
  • Existing plant 1MW-5MW by 1 Jan 30

The exact limits are in the EU legislation (see “Sources” below.)

Electricity generators in England and Wales (but not Scotland) are covered by special restrictions “SCHEDULE 25B” which is applies many different rules to electricity generators and imposes some earlier deadlines. Also, generators can’t claim the <500 hours exemption like MCPs. There will be a NOx limit that will be difficult for diesel engines to comply with unless they fit or retro-fit scrubbing.

The only way to avoid the NOx limit completely is to follow the rules for a “back-up generator”. This is strictly defined as a generator operated for the sole purpose of maintaining power supply at a site during an on-site emergency can claim exemption from Schedule 25B by testing for <50 hours per year (unless there’s a special requirement for more testing) and also declaring they are exempt from the MCPD under the 500 hours rule.

New generators must comply with a NOx limit of 190mg/Nm3 by 1 Jan 2019.

A “Tranche A generator” which came into operation before 1st December 2016 has later deadlines, the same deadlines as the MCPD, to comply:

  • Existing plant >5MW by 1 Jan 25, with registration and testing in 2024
  • Existing plant 1MW-5MW by 1 Jan 30 with registration and testing in 2029

Any Tranche A generators >5MW with NOx emissions >500mg/Nm3 and operating for more than 50 hours per year may be covered by the 190mg NOx limits from 1st October 2019 or could limited under the Air Quality Standards Regulations 2010 which regulates local air quality.

However, Tranche A generators lose their status and have to comply with the NOx limit if they sign up to a balancing services (e.g. STOR) or Capacity Mechanism Agreement after 31st October 2017 that remains in force after 31st December 2018.

Tranche A generators which are only running for triad-avoidance need to be careful and watch-out for guidance when it is published by the Environment Agency – it is possible that they may reinterpret the law and try to impose the earlier deadline of 2019 by declaring triad-avoidance to be a balancing service when the electricity industry knows that is isn’t.

Generators which signed up to certain balancing services (e.g. STOR), Capacity Mechanism Agreement or FIT agreements between 2014 and 2017 get special favourable treatment and should check the Statutory Instrument carefully.

There is a catch-all at the end of the Statutory Instrument which says the regulator must ensure that the operation of the generator will not give rise to an exceedance of the limit values for nitrogen dioxide in the Air Quality Standards Regulations 2010 for England or Wales as appropriate.

Remember NOx test in Annex II of the EU MCPD defined to be diluted with air to maintain a 15% oxygen level and may give different results to a manufacturer’s data sheet.

Next Steps

Hopefully the Environment Agency will issue draft guidance in May and clarify some of the following points.

If we ignore the 2025 and 2030 deadlines for the time being, then the most risk of being caught with a deadline in 2019 is highest for:

  • New equipment (combustion plant, including power generators installed after 1st December 2016)
  • Existing power generators >5MW with NOx emissions >500mg/Nm3 and operating for more than 50 hours per year
  • Existing power generators that sign-up to balancing services or Capacity Mechanism agreements after 31st October 2017 that remains in force after 31st December 2018
  • Existing power generators who triad-avoid may possibly be caught if the EA broadly re-interpret the rule above
  • Anyone caught out by local air quality problems

These particular generators may want to take advice on their different options. For example, what would the cost and benefit be from retro-fitting NOx scrubbers or installing new gas or diesel generators before 2019? What would the cost and benefit be from claiming an exemption from this legislation?


England and Wales Legislation
EU legislation (especially p14-17 which are referenced by the UK legislation)
Scottish Legislation
EA Slides
DEFRA Consultation