CHP Tool Documentation

Introduction to New Tool

The ADE Research CHP Marginal Emissions Tool has been rebuilt to deliver enhanced precision, accessibility, and relevance for users. The original Excel-based tool relied on static data, last updated in 2022, when coal was part of the grid fuel mix. This outdated approach used a weighted average of carbon intensity, assuming a mix of coal and CCGT as marginal plants. With coal now removed from the grid mix and CCGT most likely acting as the marginal plant, the new tool offers a more accurate, real-time solution.

This entirely web-based platform uses daily NESO data on CCGT generation proportions and balancing action carbon intensities, enabling precise calculations of marginal generation and emissions. It also integrates next-day carbon intensity forecasts for both regional and national grids, empowering users to plan operations based on upcoming grid conditions.

A key feature of the tool is its ease of use. Users only need to enter their profile once. Using a unique code, they can retrieve their profile at any time and access updated results without needing to re-enter data, saving time and reducing errors.

Key Features:

• Web-based platform for convenient, browser-based calculations.
• Real-time NESO data integration for precise marginal generation and emissions calculations.
• Next-day forecasts for regional and national grid carbon intensities.
• Dynamic updates that replace static, outdated data for greater accuracy and relevance.
• Profile retrieval using a unique code for streamlined usability.

Benefits:

• Enhanced precision through real-time data and improved methodology reflecting CCGT as the dominant marginal plant.
• Future-proofing with next-day carbon intensity forecasts for proactive planning.
• Increased accessibility, eliminating the need for file attachments.
• Streamlined workflow and reduced user input requirements with reusable profiles.
• Greater relevance by aligning with the modern grid’s dynamics and removing outdated coal-based assumptions.

This rebuilt tool empowers users with the insights they need to optimise their operations, reduce carbon emissions, and adapt to the evolving energy landscape.

Overview

The ADE Research CHP Marginal Emissions Tool provides a robust framework for analysing carbon emissions savings from Combined Heat and Power (CHP) plants. By comparing emissions under specific operational conditions to the highest carbon emitter, it supports evidence-based decision-making for decarbonisation efforts.

Leveraging year-to-date and forecasted data from National Grid ESO (NESO), the tool ensures precision and adaptability. Its methodology incorporates CHP plant types, fuel properties, operational efficiencies, and usage patterns to deliver accurate and tailored outputs.

Inputs: Key Parameters

1. Plant Type

Specify the type of CHP plant, such as gas turbines, reciprocating engines, or organic Rankine cycles. Each type has unique performance characteristics that influence emissions profiles.

2. Fuel Type

Select the fuel utilised by the plant, such as natural gas, butane, or blast furnace gas. Emission factors vary by fuel type and are critical for accurate carbon output calculations.

3. Output (MW)

Enter the plant’s electricity generation capacity in megawatts (MW). This forms the basis for calculating energy output and emissions.

4. Efficiency

• Electrical Efficiency: Define the plant’s capacity to convert fuel into electricity. Custom values can be entered, or defaults applied based on plant type.
• Heat Efficiency: Include the efficiency of heat production, either as a custom value or default based on plant characteristics.

5. Region

Indicate the plant’s location to enable the use of region-specific carbon intensity data from NESO.

6. Usage Pattern

Define generation in one of four ways: total hours, percentage of hours, total MWh, or using prefilled operating profiles for each of these periods. Choose an operational profile:

• Annual: Consistent operation throughout the year.
• Seasonal: Adjusted operation for heating and non-heating seasons.
• Monthly: Specify unique patterns for each month.

Outputs: Key Metrics

1. CHP Carbon Intensity

Carbon dioxide emissions (in gCO₂/kWh) for the CHP plant’s electricity generation.

2. Marginal Plant (CCGT) Carbon Intensity

The carbon intensity of grid electricity, focusing on marginal generation needed to meet demand fluctuations.

3. CHP Total Emissions

The annualised total carbon dioxide emissions from the CHP plant (in tonnes of CO₂).

4. Grid Total Emissions

The emissions that would result from generating the same energy through grid-connected alternatives.

5. Emissions Difference

A comparison of CHP versus grid emissions. Positive values indicate CHP is less carbon-intensive, while negative values suggest the grid is more efficient.

6. Marginal Emissions

• CHP Marginal Emissions: Additional emissions during partial load operation.
• Grid Marginal Emissions: Emissions from marginal grid electricity.
• Marginal Emissions Difference: Indicates whether CHP or the grid has lower marginal emissions.

7. Regional and National Forecasts

Projections for carbon intensity across regions and the UK, aiding strategic planning.

Methodology

The tool calculates emissions using the following principles:

• Fuel Emission Factor: Quantifies CO₂ emitted per unit of fuel burned.
• Plant Efficiency: Accounts for energy conversion efficiency.
• Grid Carbon Intensity: Utilises NESO’s live and forecasted data to reflect real-time conditions.

Example Calculation:

If a CHP plant consumes 1 unit of natural gas with a fuel factor of 0.18 tCO₂/MWh and operates at 40% electrical efficiency, the carbon intensity is calculated as:

CHP Carbon Intensity = (Fuel Used × Emission Factor) / Efficiency.

This result is compared against the grid’s carbon intensity to determine relative performance.

Marginal Generation Calculations

1. Key Inputs

• Total Grid and Gas Generation: Extracted from NESO’s API.
• FPN (Final Physical Notification): Represents total grid carbon intensity at the start of the settlement period.
• BOA (Bid-Offer Acceptance): Denotes additional or reduced grid carbon intensity during the settlement period.
• Emission Factors: Predefined values for different fuel types.

2. Defining Marginal Generation

Marginal generation is derived as:

Fraction = (BOA - FPN) / (CI^m - FPN)

Marginal Generation = Fraction × G

For CCGT, assumed as the marginal generator:

• The fraction of total generation attributed to the marginal plant is estimated by comparing forecasted to actual carbon intensity. If the actual carbon intensity (BOA) is higher than the forecast (FPN), that surplus is attributed to a greater share of CCGT. Conversely, if BOA is lower, it suggests reduced dependence on CCGT as the marginal source.
• This calculation assumes that changes in carbon intensity beyond the baseline are attributed to CCGT as the marginal source.

3. Calculating Marginal Emissions

The marginal emissions are determined as:

Marginal Emissions = (BOA - FPN) × Total Generation MWh.

4. Spreadsheet Integration

• Carbon Intensity of Balancing Action: Used to compute marginal generation and intensity.
• Historical Fuel Mix: Provides total generation from each fuel type on the grid for each half-hour settlement period.

5. Example Calculation

For a settlement period:

• FPN Carbon Intensity: 250 gCO₂/kWh (0.25 tCO₂/MWh)
• BOA Carbon Intensity: 350 gCO₂/kWh (0.35 tCO₂/MWh)
• Total Generation: 1000 MWh
• Marginal Plant (CCGT) Carbon Intensity (CI^m): 394 gCO₂/kWh (0.394 tCO₂/MWh)

Fraction = (350 - 250) / (394 - 250) = 100 / 144 ≈ 0.694

Marginal Generation = 0.694 × 1000 = 694 MWh

Interpretation:
The additional generation is primarily attributed to CCGT as the marginal plant due to the observed increase in carbon intensity (BOA > FPN).

Detailed Logic of Key Outputs

1. Marginal Generation

Assumption: Changes in carbon intensity between the Forecast/Planned (FPN) and the Actual Balancing (BOA) are attributed to a single “marginal” plant, typically a CCGT. An increase in carbon intensity (BOA > FPN) implies a greater share of marginal generation from CCGT; a decrease implies reduced use of CCGT.

Formula:

• Fraction of Total Generation attributed to marginal plant:
  Fraction = (BOA CI – FPN CI) / (CCGT CI – FPN CI)
• Marginal Generation (MWh):
  Marginal Generation = Fraction × Total Grid Generation

2. Marginal Emissions

Once marginal generation is known, marginal emissions are calculated as:

Marginal Emissions = Marginal Generation (MWh) × CCGT CI

3. Effective Electrical Efficiency

Assumption: Useful heat from CHP displaces a stand-alone boiler, typically assumed to be 80% efficient. This “credit” is factored in to produce a higher effective electrical efficiency.

Formula:

η_eff,el = η_el / (1 – (η_th / 0.8))

where η_el is nominal electrical efficiency and η_th is the heat efficiency. The 0.8 represents the assumed boiler efficiency.

4. Carbon Intensity of CHP

Assumption: The CHP’s total CO₂ emissions per unit of electricity is derived from its fuel CO₂ factor and its electrical efficiency.

Formula:

CHP CI = (Fuel CO₂ Factor) / η_el

Units must be consistent (e.g., if the fuel factor is in kgCO₂/kWh, η_el should be dimensionally compatible). Alternatively, if total CHP CO₂ and total output are known, it is simply Total CO₂ / Total MWh.

5. Total Emissions Calculations

• CHP Emissions:
  Total CHP Emissions = CHP CI × CHP Electricity Output (MWh)
• Reference Emissions (e.g. CCGT):
  Emissions_Ref = CHP Electricity Output × CCGT CI
• Emissions Difference:
  Δ Emissions = CHP Emissions – Emissions_Ref

6. Key Assumptions

• Fuel Type & Emission Factors: Each fuel has a predefined CO₂ intensity (e.g., 0.18 tCO₂ per MWh of gas). The tool applies an approximate conversion factor (1.1) when shifting between HHV/LHV bases.
• Boiler Efficiency: An 80% (0.8) figure is assumed for the stand-alone boiler that CHP heat displaces.
• CCGT as Marginal Plant: In most modern grid conditions (post-coal phase-out), CCGT is the primary marginal generator.