Simple guide to Good Quality CHP and the Quality Index value

Good Quality is the term used to describe CHP schemes that are considered energy efficient under the CHPQA assessment criteria. The Quality Index(QI) is the scoring system developed for CHPQA that provides a means of assessing the quality of CHP Schemes. SIMPLE GUIDE TO GOOD QUALITY CHP AND THE QUALITY INDEX VALUE Abstract This is a simple guide to ‘Good Quality’ CHP (GQCHP) and the Quality Index (QI) value scoring system. v2 March 2026 CHPQA Administrator chpqainfo@chpqa.com Introduction 1. Introduction The ‘Simple Guide To’ series is designed to assist Responsible Persons (RPs) in understanding various aspects of the CHPQA process. The content here is a simplified and condensed form of that found in the detailed Guidance Notes 10 and 24 - 27 which are outlined below and can be accessed online with the following hyperlinks. References are made to these and other guidance notes in the form “GNXX.X” which refer to paragraphs within the detailed guidance notes. In any cases of doubt, please refer to the detailed guidance notes as they are comprehensive and shall always take precedence. Detailed Guidance Notes: GN10 – Defining Good Quality CHP GN24 – Determination of Scheme Quality GN25 – Determination of CHP Qualifying Fuel Input GN26 – Determination of CHP Qualifying Power Output GN27 – Determination of Qualifying Power Capacity CHPQA Guidance Notes https://www.gov.uk/guidance/chpqa-guidance-notes Good Quality (GQ) is the term coined to describe CHP Schemes that are considered energy efficient under the CHPQA assessment criteria. The Quality Index (QI) is the scoring system developed for CHPQA that provides a means of assessing the quality of CHP Schemes. For Schemes to meet the definition of Good Quality they must meet a power efficiency threshold (20%) and meet or exceed a pre-determined QI threshold value (usually 100). Schemes that do not meet these criteria are described as ‘partially qualified’ and any fiscal benefits that they may be eligible for are scaled back. It is therefore in the best interests of an RP to achieve the Good Quality CHP criteria to maximise the subsidies/exemptions available, whilst also reducing the Scheme’s environmental impact. 2. What is considered ‘Good Quality’ CHP? There are two parameters CHPQA use for assessment of Good Quality CHP (GQCHP): QI and Power Efficiency. If these threshold criteria are met, Page 1 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? the fuel inputs and/or power outputs can be considered GQCHP and the Scheme is fully qualified. Subsidies and exemptions gained from certification under the CHPQA scheme are based on three metrics: Qualifying Fuel Input (QFI) Qualifying Power Output (QPO) Qualifying Power Capacity (QPC) If the relevant thresholds are met and the Scheme is considered Good Quality CHP, the Qualifying Fuel Input and the Qualifying Power Output are equal to their Total counterparts (see boxes below). When the thresholds are not met, some of the fuel input or power outputs are not considered as Good Quality CHP inputs or outputs, and qualifying metrics are scaled back from their Total counterparts (see Section 3). It is therefore in the best interests of an RP to achieve the Thresholds to maximise the qualifying values and hence maximise any subsidies and exemptions. Page 2 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? Existing and New Schemes are explained in the section below. Maximum Heat Output is based on operation at the heat output that is expected to be exceeded for the hours specified in the CHPQA Standard and further explained in GN27 depending on the use of the CHP heat output. 2.1. How is the Power Efficiency determined? Power efficiency is the Total Power Output (TPO) generated in MWh during the reporting period expressed as a percentage of the Total Fuel input (TFI) in MWh during the same period. Note: CHPTFI must be based on the Gross Calorific Value (GCV) or Higher Heating Value (HHV) of the fuel. 2.2. How is the Quality Index (QI) value determined? The QI methodology ensures validity across a broad spectrum of CHP plant and applications, considering all sizes, fuel and types of CHP technology. The QI formulae have been developed and tested based around a simple general form: Where heat efficiency is the Qualifying Heat Output (QHO) generated in MWh during the reporting period expressed as a percentage of the Total Fuel input (TFI) in MWh during the same period. Page 3 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? The QI value enables a simplified comparison of the overall power and heat efficiency of the CHP scheme compared to individual power generating and heat generating plants respectively. X is a coefficient related to alternative power supply options. Similarly, Y is a coefficient for heat generation, related to alternative heat supply options (boilers). The values of X and Y vary for different sizes and fuel types of Scheme and the date of certification. Refer to the relevant CHPQA Standard for full details and identification of the appropriate QI definition for a given Scheme. 2.1. Threshold Values The below table details the threshold values for Power Efficiency and QI that need to be met for the fuel inputs and/or power outputs to be considered Good Quality CHP input and/or output. The Initial Operation (IO) of a Scheme begins when the RP notifies CHPQA that the CHP Scheme has begun operating as a CHP. IO finishes and subsequently Annual Operation (AO) commences, once the Scheme has operated for a full calendar year. For example, if a Scheme were to begin operating in February 2019, its IO would finish on 31 December 2020, after it had operated for the full calendar year of 2020. Its AO would subsequently commence on 1 January 2021. A lower QI threshold is set for schemes in IO, to provide leniency on Schemes Page 4 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? that have just started operating, as they may encounter operational issues, or may have yet to connect all of their heat loads. Conversely, a stricter, higher QI threshold is set for New Schemes, as their performance is based on design conditions and so could be considered a best-case performance scenario. 3.What happens if the Power Efficiency and/or QI thresholds are not met? Schemes that do not meet the power efficiency and/or the QI threshold are still eligible for fiscal benefits, but the extent of that eligibility is reduced. Schemes that do not meet the Good Quality CHP thresholds are deemed to be partially qualified. Partially qualified Schemes are still certified under CHPQA, but only a portion of the fuel input and/or power outputs classify as being ‘Good Quality’. For most CHP schemes, the power efficiency achieved is consistent each year. This means that the amount of useful heat used is the biggest factor towards increasing the QI value. In simple terms, the heat-to-power ratio must be improved to meet the QI Threshold (QIth). Page 5 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? 3.1. How do I determine Qualifying Fuel Input (QFI)? The QFI is equal to the Total Fuel Input (TFI) for fully certified GQCHP schemes. However, for partially qualified schemes the QFI is the proportion of TFI that is qualified as GQCHP. The method to calculate the QFI for partially certified schemes is shown below: For example, if a Scheme achieves a power efficiency (ηpower) of 15%, which is lower than the threshold power efficiency of 20% (ηthreshold), and given the TFI is 100 MWh, the Qualifying Fuel Input (QFI) is determined as follows: 3.2. How do I determine Qualifying Power Output (QPO)? The QPO is equal to the Total Power Output (TPO) for fully certified GQCHP schemes. However, for partially qualified schemes, the QPO is the proportion of TPO that is qualified as GQCHP power output. The method to calculate the QPO for partially qualified schemes is shown below. Condensing/pass-out steam turbine based CHP schemes should refer to the method in GN26.6­ 26.7. Page 6 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? For example, a CHP Scheme with the performance characteristics in the below table would calculate their QI and QPO based on the following steps: The Quality Index (QI) must first be calculated in order to determine whether the QPO needs to be scaled back from the TPO. The CHP Scheme has not met the QI threshold of 100 (assuming that this is an Existing Scheme - see section 2.1 for definition). Its QPO must therefore be scaled back from its TPO. Firstly, the heat efficiency that would be required to meet the QI threshold should be determined: Page 7 © Crown Copyright 2026 What happens if the Power Efficiency and/or QI thresholds are not met? Then calculate the heat-to-power ratio between the new heat efficiency and the power efficiency: The QPO is determined as follows, given a QHO of 100MWh: Page 8 © Crown Copyright 2026 Further information 4.Further information 4.1. Further guidance See the accompanying series of ‘Simple Guide to’ guides and the detailed guidance notes here: https://www.gov.uk/guidance/chpqa-guidance-notes 4.2. Contact Us In the first instance, all queries on CHPQA should be directed to the CHPQA helpline, or emailed to the Administration team using the details below: CHPQA Helpline: • Tel: 01235 753004 • E-mail: chpqainfo@chpqa.com • Website: https://www.gov.uk/combined-heat-power-quality-assurance-programme Simple Guide to GQCHP & QI - V1.1 Page 9  Crown Copyright 2019