Unlike other heating devices that produce heat through the combustion of fossil fuels, such as furnaces, heat pumps exchange heat from one space to another. ASHPs run on electricity and use a refrigerant to absorb heat from outside air and release it into an indoor space. They can also provide cooling by running in the opposite direction. ASHPs are the most common type of heat pump in residential buildings in the U.S.

A colorless gas compound with a characteristic pungent smell, made from hydrogen and nitrogen. Today, ammonia is mainly used to make fertilizer, cleaning products, and plastics, but is also seen as a promising clean fuel for maritime transport.

A process through which bacteria break down organic matter—such as animal manure, wastewater biosolids, and food wastes—in the absence of oxygen. Anaerobic digestion generates biogas, which is mostly methane (CH₄) and carbon dioxide (CO₂), with very small amounts of water vapor and other gases. The carbon dioxide and other gases can be removed, leaving only the methane.

Emissions of greenhouse gases (GHGs), precursors of GHGs, and aerosols caused by human activities.

Paid positions with on-the-job training and additional classroom instruction.

The process of converting biomass to biogas, a mixture of methane (CH₄) and carbon dioxide (CO₂) that can be used as a fuel. Also called biomass gasification.

The process of converting biomass to biogas while capturing the CO₂ produced for either sequestration or utilization.

A carbon-removal technique that depends on two technologies. Biomass is converted into heat, electricity, or liquid or gas fuels (“bioenergy”), and the carbon emissions from this bioenergy conversion are captured and sequestered (“carbon capture and storage”).

Liquid fuel produced from biomass. The two most common types of biofuels in use today are ethanol and biodiesel.

A combustible gas composed predominantly of methane that is collected from waste streams, such as landfills and manure lagoons, for use as fuel. As a fuel, it is virtually identical to conventional natural gas.

The combined negative carbon emissions when accounting for carbon that ends up in products like asphalt (i.e., product), or is not in state emissions inventories because it is used in international transport (i.e., bunkering). Together, these are referred to as CO₂ product and bunkering.

Technology that prevents carbon emissions from escaping into the atmosphere from power plant or industrial waste gas streams, and stores it in geological formations or utilizes it in clean fuel production.

A colorless, odorless, non-poisonous gas that is a normal part of Earth’s atmosphere. Carbon dioxide is a product of fossil fuel combustion as well as other processes. It is considered a greenhouse gas as it traps heat (infrared energy) radiated by Earth into the atmosphere and thereby contributes to the potential for global warming.

A standard way of measuring emissions that expresses the impact of each greenhouse gas in terms of the amount of CO₂ that would produce the same amount of warming. CO₂e is computed by multiplying the weight of the gas being measured (for example, methane) by its estimated global warming potential (21 for methane, for example).

A process in which carbon dioxide gas (CO₂) is removed from the atmosphere by deliberate human activities and durably stored in geological, terrestrial, or ocean reservoirs, or in durable products.

A fixed piece of equipment with an attached cable and plug for charging electric vehicles.

A market-based, technology-neutral portfolio standard that requires a certain percentage of retail electricity sales to come from non- or low-emitting sources.

Net-zero-emissions fuels that include hydrogen, ammonia, biofuel, and drop-in synthetic hydrocarbon electrofuels (produced with the Fischer-Tropsch process in this analysis).

In this study, clean vehicles refer to zero-emission vehicles (ZEVs) that are powered by alternative fuels, including electric vehicles and hydrogen fuel-cell vehicles.

When referring to transmission, co-location is the term for adding a new transmission line to pre-existing transmission infrastructure or adding a new transmission line adjacent to an existing transmission line. Co-location can help minimize land use and environmental impact.

The amount of electric capacity needed for conversion processes. These include hydrogen electrolysis, as well as Fischer-Tropsch and Haber-Bosch processes to convert the hydrogen to other fuels.

Changes in electricity usage by consumers in response to peak load periods to decrease demand on the grid and maintain electricity reliability.

Technology that removes carbon dioxide from the atmosphere.

Employment associated with the initial economic impact of a given investment or activity (e.g., changes in wages, production, or jobs).

A distributed energy resource that uses a battery to store electricity, providing flexibility to the power system and supporting the increased integration of renewable energy sources. The duration refers to the amount of time a battery can discharge electricity at its nameplate power capacity until it runs out. In this study, the DER1–Accelerated PV scenario deploys 1.5-hour duration distributed battery storage along with rooftop PV.

Small, modular, energy generation and storage technologies that provide electric capacity or energy near sites of use. Examples include rooftop solar panels and battery storage.

Solar PV (photovoltaic) systems that are generally small, connect to the distribution network (rather than the transmission network), and are either behind the meter or in front of it and connected to the low-voltage distribution network.

A type of distributed energy resource that consists of energy storage systems connected to the electricity distribution system and located close to the end consumers.

The physical equipment used to distribute electric power at voltages below 38,000 volts, including but not limited to poles, primary lines, secondary lines, service drops, transformers, and meters.

Daytime activity. In the context of renewable energy, used to refer to the shape of production of solar energy.

All the components necessary to transfer an engine’s energy to its wheels in order to make the vehicle move.

An electric resistance heater produces heat when an electric current passes through the resistance of a conductor. Electric resistance heating equipment can include baseboard heaters, electric furnaces, and electric wall heaters.

A battery-powered vehicle that runs on electric motors.

Electricity generation and consumption.

Electricity directly consumed by an end user.

The amount of electricity drawn from the electrical grid.

Electricity storage describes all technologies that can absorb electrical energy for later use as electrical energy. Capacity can describe the maximum amount of electricity able to be stored by either a single storage device or a fleet of storage resources.

Electrochemical storage involves various kinds of battery energy storage systems. These batteries convert chemical energy into electricity and vice versa.

Also known as an e-fuel, an electrofuel is synthetic carbon-based fuel typically produced from carbon dioxide and water, employing renewable electricity as the primary source of energy. The primary type of electrofuel represented in this study is Fischer-Tropsch liquids, which are produced by combining hydrogen derived from renewable sources with captured carbon.

In this study, electrolysis is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyzer. Hydrogen produced via electrolysis can generate zero greenhouse gas emissions if the electricity source used is renewable.

A system used to produce hydrogen through electrolysis of water that separates hydrogen and oxygen atoms using a direct electric current.

A natural digestive process in livestock that produces methane as a by-product.

A renewable alternative fuel produced from esters of fatty acids with physical characteristics similar to those of fossil diesel fuels.

Fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller, that pose health risks.

This process converts synthetic gas (syngas, a mixture of hydrogen and carbon monoxide) to produce hydrocarbon fuels that can be used as drop-in clean fuels for petroleum product substitution.

An appliance or device with power consumption that can be varied to shift electricity demand and restore balance to the grid during peak events.

Also known as smart vehicle charging, flexible vehicle charging means adapting the charging cycle of electric vehicles to both the conditions of the power system and the needs of vehicle users.

Chemical compounds that contain fluorine and are gases near room temperature. They come almost entirely from human-related activities and have no significant natural sources. F-gases are emitted through their use as substitutes for ozone-depleting substances (e.g., as refrigerants) and through various industrial processes. Many f-gases have very high global warming potential and can also have long atmospheric lifetimes.

A vehicle that runs on electric motors with electricity produced by hydrogen-powered fuel cells.

Fuel that is stored as a vapor, rather than as a liquid or a solid, such as methane, propane, or hydrogen. Gaseous fuels take up more space but weigh less per unit of energy than liquid or solid fuels.

The intended maximum output of a power plant or electrical generator. Also referred to as installed capacity or nameplate capacity.

A type of engineered sequestration where captured carbon dioxide is injected for permanent storage into underground geologic reservoirs, such as oil and natural gas fields, saline aquifers, or abandoned coal mines.

Geothermal heat pumps are highly efficient space heating and cooling technologies that run on electricity and take advantage of the naturally occurring difference between the above-ground air temperature and the subsurface soil temperature to move heat. Geothermal heat pumps are much more efficient than air-source heat pumps, but they are generally more expensive and require more invasive installation. Also called ground-source heat pumps.

A measure of how much energy the emissions of 1 ton of a greenhouse gas will absorb relative to the emissions of 1 ton of carbon dioxide (CO₂) over a fixed period of time, such as 100 years. Since different greenhouse gases can have different effects on Earth's warming, the GWP was developed to allow comparisons of the global warming impacts of different gases.

Physical equipment and generation resources at the scale of the electricity grid (compared to distributed energy resources that provide electric capacity or energy near sites of use). Also called utility-scale infrastructure/resources.

Total greenhouse gas emissions from energy, industrial processes, agriculture, and waste. Does not include any measures to remove carbon from the atmosphere, such as negative emissions technologies, land-use measures, and natural land sink. See also: net-zero emissions.

The primary method of producing ammonia from nitrogen and hydrogen.

Used to estimate the number of premature deaths, unscheduled hospitalizations, and other morbidity outcomes.

In this study, HDVs are defined as on-road trucks weighing over 26,000 pounds, aligning with the Federal Highway Administration (FHA)’s Class 7 and Class 8 definition. Long-haul vehicles travel more than 200 miles per day, while short-haul vehicles travel under 200 miles per day.

An electricity generation resource that produces a relatively high ratio of energy annually compared to its maximum theoretical energy output.

In this analysis, refers to gas furnaces with 99% efficiency. When an existing furnace reaches the end of its useful life, it can be replaced with a number of different technologies; one replacement option is a high-efficiency gas furnace.

Conductors that can withstand operating temperatures of up to 210 °C, thus carrying higher power compared to conventional conductors.

Alternating current is an electric current in which the direction of the flow of electrons switches back and forth at regular intervals, and is the form in which electric power is typically delivered to consumers. The voltage may be increased or decreased with a transformer, allowing the power to be transmitted through power lines more efficiently at high voltage.

Direct current is an electric current that flows in one direction, in contrast to the more common alternating current (see above). HVDC power systems are often used for transmission of bulk power over long distances because DC lines have lower losses and improved efficiency compared to AC lines.

These hybrid heating systems are made up of both an electric air-source heat pump (ASHP) and a gas furnace. The ASHP is the primary source of heat in most hours of the year, but the system switches to the gas furnace when the external temperature drops below a set point, because ASHPs perform at lower efficiency in very cold temperatures. Also called dual-fuel heat pumps.

Fuel that consists mostly of hydrocarbons. Hydrocarbons are highly combustible organic compounds consisting of hydrogen and carbon found in crude oil, natural gas, and coal.

A group of man-made chemicals composed of one or two carbon atoms and varying numbers of hydrogen and fluorine atoms. Most HFCs have 100-year Global Warming Potentials in the thousands. See Global Warming Potential.

The most abundant element in the universe and the lightest of all gases. Hydrogen occurs naturally on Earth only in compound form with other elements in liquids, gases, or solids. Hydrogen combined with oxygen is water (H2O), and hydrogen combined with carbon forms different compounds (hydrocarbons) found in natural gas, coal, and petroleum. Hydrogen can be produced—separated—from water, fossil fuels, or biomass and used as a source of energy/fuel that has a high energy content per unit of weight.

Refers to the use of hydrogen directly in end uses, such as fuel-cell vehicles, as opposed to the use of hydrogen in conversion processes, such as the Fischer-Tropsch process to produce liquid hydrocarbon fuels.

Land sink refers to natural ecosystems, such as forests, that remove carbon dioxide from the atmosphere naturally. Land-use negative emissions technologies (e.g., reforestation) increase the removal capability of the natural environment, and the additional capability is referred to as incremental land sink.

Employment associated with the supply chain connected to the initial economic impact of the original investment or activity (e.g., purchases of goods and services or business tax impacts).

Employment based on the additional household spending resulting from the direct and indirect employment that is generated from the initial economic impact of the original investment or activity (e.g., wages paid, household purchases, or household tax impacts).

Vehicles that are powered by burning a liquid, such as gasoline, diesel, biofuels, or a gaseous fuel, such as compressed natural gas.

A labor union or trade union is an organized group or association of workers who unite to make decisions about conditions affecting their work, including pay, benefits, working conditions, and more. Labor unions negotiate contracts with employers and engage in collective bargaining on behalf of their members to increase wages and benefits and improve workplace conditions.

In this study, LDVs are defined as on-road autos and trucks weighing up to 14,000 pounds, aligning with FHA classes 1 and 2.

Combustible or energy-generating molecules: all petroleum, including crude oil and products of petroleum refining; natural gas liquids; biofuels; and liquids derived from other hydrocarbon sources (including coal to liquids and gas to liquids).

In this study, MDVs are defined as on-road vehicles weighing between 14,001 and 26,000 pounds, aligning with FHA classes 4, 5, and 6.

A colorless, flammable, odorless hydrocarbon gas that is the major component of natural gas. It is also a source of hydrogen in various industrial processes. Methane is a greenhouse gas.

Any technology that removes carbon from the air and sequesters it. Examples include land-use measures that increase carbon storage in the natural environment (e.g., reforestation) and direct air capture.

In this study, net-zero emissions means that all remaining greenhouse gases released into the atmosphere from human activity must be offset by measures to remove carbon from the atmosphere.

One of a group of highly reactive gases known as nitrogen oxides (NOx). NO₂ forms from emissions from cars, trucks and buses, power plants, and off-road equipment. Natural sources of NO₂ include biological processes in soil, atmospheric oxidation of ammonia, volcanic emissions, and bacteria.

Compounds of nitrogen and oxygen produced by the burning of fossil fuels. NOx emissions are primarily caused by transportation (vehicles and trucks, as well as construction equipment and boats) and industrial facilities.

Emissions from greenhouse gases other than CO₂, including methane (CH₄), nitrous oxide (N₂O), and fluorinated greenhouse gases (F-gases: HFCs, PFCs, and SF₆).

Carbon dioxide emitted from sources other than the burning of fossil fuels, such as deforestation, soil carbon, landfills and wastewater, and permafrost.

Mixture of solid particles and liquid droplets found in the air. Particles vary in size, and those with a diameter of 10 micrometers or less are inhalable into the lungs and can induce adverse health effects. See also: fine particulate matter.

Capacity of electricity-generating equipment normally reserved for operation during the hours of highest daily, weekly, or seasonal electricity demand. Some generating equipment may be operated at certain times as peaking capacity and at other times to serve loads on an around-the-clock basis.

The maximum demand for electricity during a given time period (for example, a day, season, or year). Also referred to as peak load and peak demand.

Unlike greenhouse gas emissions, which contribute to global warming, pollutant emissions are chemical compounds that impact human health and the environment when released into the air or emitted by various sources.

Programs designed to prepare workers with the skills needed for successful entry into apprenticeship programs, usually targeting certain underrepresented populations or demographics.

The basic hourly rate of wages and benefits paid to a number of similarly employed workers in a given geography.

Pre-hire collective bargaining agreements negotiated between construction unions and construction contractors that establish the terms and conditions of employment for construction projects.

Installing new conductor wires on existing towers to increase the capacity of existing transmission lines.

The default gas heating technology that complies with existing building standards but not the highest efficiency standards. In this analysis, new reference gas furnaces are assumed to be 92% efficient.

An apprenticeship program that is approved and validated by the U.S. Department of Labor or a State Apprenticeship Agency.

Solar photovoltaic (PV) panels installed on rooftops and an example of a distributed energy resource.

Formed in the atmosphere through complex chemical reactions in which PM₂.₅ precursors such as nitrogen oxides (NOx), volatile organic compounds (VOCs), sulfur dioxides (SO₂), and ammonia contribute to the formation of secondary fine particulates.

Proposed class of nuclear fission reactors, with smaller capacities than conventional nuclear reactors, which can be built in one location (such as a factory), then shipped, commissioned, and operated at a separate site.

SO₂ is the predominant form of gaseous sulfur oxides (SOx) and largely comes from fossil fuel combustion in power plants and other industrial facilities.

Compounds containing sulfur and oxygen, such as sulfur dioxide (SO₂) and sulfur trioxide (SO₃).

Dictates the maximum electricity flow that can occur on the line in either direction in any hour.