Umair Gaines
Calculating electricity emissions is a complex process that involves several factors. Firstly, one must determine their electricity consumption, which can be done through on-site electricity meters or by estimating based on the size of the organisation and applying an electricity intensity assumption. Then, it is necessary to find the appropriate emissions factor, which varies by location and is influenced by factors such as weather, fuel prices, fuel availability, and the balance between demand and supply. This factor is typically provided by government entities, such as the UK Department for Energy Security and Net Zero or the US Environmental Protection Agency. Additionally, it is important to consider the Global Warming Potential (GWP) values for non-CO2 gases, as different gases have varying warming impacts in the atmosphere. Finally, with the total electricity consumption, emissions factors, and GWP values, calculations can be performed to determine the organisation's carbon footprint and make informed decisions about energy use and emissions reduction strategies.
| Characteristics | Values |
|---|---|
| First Step | Gather information on your organisation's electricity consumption |
| Methods | Use electricity meters on site, refer to your bill, or estimate consumption based on the size of your organisation |
| Consumption Unit | Kilowatt-hour (kWh) |
| Country-specific Factors | UK: Conversion factors from the UK Department for Energy Security and Net Zero; US: Grid electricity carbon factor from the US Environmental Protection Agency |
| Global Warming Potential (GWP) | Carbon dioxide has a value of 1, methane has a value of around 25 |
| GWP Sources | Intergovernmental Panel on Climate Change (IPCC) 6th assessment |
| Location-based Approach | Reflects the connection between grid electricity demand and emissions; emissions vary by sources of electricity (fuel prices, availability, demand, supply, etc.) |
| Location-based Emission Factor | Calculated as emissions (CO2e) from grid electricity supply divided by energy generated (kWh) |
| Market-based Approach | Uses emission factors tailored to the reporting organization's electricity purchases and contracts |
| Residual Emission Factors | Consider imports and exports of renewable energy attributes, higher carbon fuels, and inter-grid trading |
| Calculation Tools | Greenhouse Gas Equivalencies Calculator, eGRID (Emissions & Generation Resource Integrated Database) |
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What You'll Learn
Calculating electricity consumption
One method is to use electricity meters on-site. You can calculate a month's consumption by subtracting the previous month's reading from the current month's reading. This will give you a value in kilowatt-hours (kWh), the standard unit for electricity consumption. You can use this method for different time periods, such as quarters.
If you don't have access to an electricity meter, you can estimate your electricity consumption by measuring the size of your organisation in square metres or square feet and applying an electricity intensity assumption. These assumptions can be found through organisations such as the Chartered Institution of Building Services Engineers (CIBSE) and Better Buildings Partnership (BBP) in the UK, and the Commercial Buildings Energy Consumption Survey (CBECS) in the US.
Once you have your electricity consumption value in kWh, you can calculate your electricity emissions. This will depend on your location, as emission factors vary by country and state/province. For example, in the UK, you can find the country-specific grid average electricity emissions factor within the conversion factors provided by the UK Department for Energy Security and Net Zero. In the US, you can find the grid electricity carbon factor from the US Environmental Protection Agency, which also varies depending on your location within the country.
Additionally, you can use online calculators, such as the Greenhouse Gas Equivalencies Calculator provided by the US EPA, to estimate your electricity-related emissions. This calculator uses regional emission factors and enables users to input their residential or commercial zip code to obtain more accurate emissions estimates.
Furthermore, when calculating electricity consumption, it is important to consider the various sources of electricity consumption. For residential homes, the Energy Information Administration (EIA) found that air conditioning, space heating, and water heating are the top sources of electricity consumption, accounting for 43.5% of energy usage. To reduce consumption, one can consider lowering the temperature on the water heater, using energy-efficient appliances, or switching to LED light bulbs.
Additionally, to calculate electricity consumption in kVA, you can use the formula Amps multiplied by Volts = VA. For example, 50A and 120V gives 6000VA, or 6kVA.
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Location-based emission factors
The location-based emission factor is expressed as kg CO2e / kWh and is calculated by dividing the emissions (CO2e) from electricity generation, including on-grid generation, imports, and exports, by the energy generated (kWh). This factor considers the collective impact of electricity consumption within a specific region or country.
There are three types of location-based emission factors: subnational, national, and multinational. Most electricity consumers fall into one of these categories, depending on the scope of their electricity grid. For example, in the United States, electricity is supplied through multiple subnational grids, each with its emission factors published by the Environmental Protection Agency (EPA).
The fuel mix and emission factors are typically published annually by suppliers, as required by electricity market regulations in some regions. If not readily available, specific emission factors can be shared with data aggregators for publication. Residual emission factors, which are calculated after accounting for all claims on energy generation, tend to be higher than the grid average due to the inclusion of higher-carbon fuels.
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Market-based approach
The market-based approach to calculating emission factors for electricity focuses on a company's purchasing decisions and the specific energy contracts it has in place. This method allows organizations to calculate emissions using provider-specific factors from their electric utilities. It reflects how a company's energy choices, such as investing in renewable energy or choosing a green energy tariff, can reduce its carbon footprint.
In practice, data on provider-specific emission factors may be unavailable or challenging to obtain. In such cases, the market-based method uses the same energy production and emissions data as the location-based method for any energy not tracked by a contractual instrument. Companies without contractual instruments can track their kWh consumption from grid electricity, usually found on utility bills.
When provider-specific emission factors are available, they offer a more accurate calculation of emissions compared to applying an average regional factor. For example, a company buying energy on the open market can request its supplier to provide an emissions factor specific to the energy mix, which is then used to calculate emissions. In the US, for instance, if an organization buys energy directly from a power plant, the associated emission factor should be applied instead of the national or regional grid average.
The market-based approach also considers the use of renewable energy instruments such as Renewable Energy Certificates (RECs) or Guarantees of Origin (REGOs). These certificates represent a company's investment in renewable energy, and by purchasing them, businesses can lower their reported emissions. The GHG Protocol requires companies to report their Scope 2 emissions using both location-based and market-based methods, providing a comprehensive view of their environmental impact.
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Country-specific emission factors
In some cases, countries or regions may have their own electricity emissions factors. For example, in the United Kingdom, the UK Department for Energy Security and Net Zero provides conversion factors. In the United States, organisations can refer to the US Environmental Protection Agency for their grid electricity carbon factor, which can vary depending on the specific location within the country.
The AIB publishes Production Mix factors that represent electricity generated within a country, and the EEA (Europe) publishes similar emission factors. While these factors do not account for imports and exports, they can be used when Grid Mix factors are not available. Additionally, the GHG Protocol permits the use of these factors. When a subnational or regional emission factor is available, it should take precedence over the national factor.
Fuel mix or emission factors are typically published annually by each supplier, often as part of electricity market regulations. These factors can be found in the API, or specific emission factors can be shared with data platforms for publication. Residual emission factors, which result from the fuel mix remaining after claims on energy generation, tend to be higher than the grid average mix as they include higher carbon fuels.
Calculating country-specific emission factors can be complex, as it involves considering imports and exports of renewable energy attributes. Additionally, emission factors can vary within a country, with marginal emission factors representing emissions from fossil-fired generation and baseload emissions. These factors are used to estimate the emission impacts of energy efficiency and renewable energy programs on the electricity grid.
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Global Warming Potential values
Global Warming Potential (GWP) is a simplified index that estimates the potential future impact of emissions of different gases on the climate system. It is a relative measure of how much heat a greenhouse gas traps in the atmosphere over a specific time period compared to carbon dioxide (CO2). By definition, CO2 has a GWP of 1, and other gases are measured relative to it. GWP depends on a gas's radiative efficiency (its ability to absorb infrared radiation relative to CO2), its decay rate (how quickly it leaves the atmosphere relative to CO2), and the timeframe considered. For example, methane has a GWP of 25, meaning it is 25 times more warming than carbon dioxide. However, over longer periods, its GWP decreases to 27.9 for 100 years and 7.95 for 500 years because it has a shorter atmospheric lifetime than CO2. The GWP of a substance also depends on the number of years over which the potential is calculated.
The Intergovernmental Panel on Climate Change (IPCC) provides the most recent global warming potentials, with values published in its Sixth Assessment Report. The UN climate panel also provides conversions for billion metric tonnes of CO2 equivalent (GtCO2eq), million metric tonnes of carbon dioxide equivalents (MMTCDE), and grams of carbon dioxide equivalent per mile or kilometre (gCO2e/mile or km).
The GWP definition is based on emissions, and the radiative forcing capacity (RF) is the amount of energy per unit area and time absorbed by the greenhouse gas that would otherwise be lost to space. The GWP of H2O, for example, is negligible because anthropogenic emissions are removed via precipitation within weeks, limiting their concentration in the atmosphere.
When calculating the GWP of a greenhouse gas, the value depends on the absorption of infrared radiation by the gas, the wavelength of absorption, and the radiative efficiency of the gas. A high GWP correlates with a large infrared absorption and a long atmospheric lifetime.
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Frequently asked questions
An emission factor for electricity is a rate, usually expressed as kg CO2e / kWh, that is used to calculate the emissions resulting from the generation of electricity supplied into the grid.
The emission factor for electricity can be calculated by dividing the emissions (in CO2e) from the generation of electricity supplied to the grid (including on-grid generation, imports, and exports) by the energy generated (in kWh).
To calculate the emission factor for electricity, you will need data on the total emissions and total energy generated within a defined geographic boundary (typically a country) and during a defined time period (typically one year).
There are several tools and resources available to help calculate emission factors for electricity. For example, the Greenhouse Gas Equivalencies Calculator uses the Emissions & Generation Resource Integrated Database (eGRID) to provide regional emission factors for electric power. Additionally, organizations like the AIB and EEA publish Production Mix factors that represent electricity generation within specific regions or countries.
