Glossary

Energy storage mediates between variable sources and variable loads. Without storage, energy generation must equal energy consumption. Energy storage works by moving energy through time. Energy generated at one time can be used at another time through storage. Electricity storage is one form of energy storage. Other forms of energy storage include oil in the Strategic Petroleum Reserve and in storage tanks, natural gas in underground storage reservoirs and pipelines, thermal energy in ice, and thermal mass/adobe.

Measure of the energy or power capacity of a battery relative to its volume (kW/L, kWh/L)

Although electricity is a clean and relatively safe form of energy when it is used, the generation and transmission of electricity affects the environment. Nearly all types of electric power plants have an effect on the environment, but some power plants have larger effects than others.

The United States has laws that govern the effects that electricity generation and transmission have on the environment. The Clean Air Act regulates air pollutant emissions from most power plants. The U.S. Environmental Protection Agency (EPA) administers the Clean Air Act and sets emissions standards for power plants through various programs such as the Acid Rain Program. The Clean Air Act has helped to substantially reduce emissions of some major air pollutants in the United States.

The effect of power plants on the landscape

All power plants have a physical footprint (the location of the power plant). Some power plants are located inside, on, or next to an existing building, so the footprint is fairly small. Most large power plants require land clearing to build the power plant. Some power plants may also require access roads, railroads, and pipelines for fuel delivery, electricity transmission lines, and cooling water supplies. Power plants that burn solid fuels may have areas to store the combustion ash.

Many power plants are large structures that alter the visual landscape. In general, the larger the structure, the more likely it is that the power plant will affect the visual landscape.

The two coal-fired power plants of the Crystal River North Steam Complex in Crystal River, Florida

Source: Ebyabe, Wikimedia Commons author (GNU Free Documentation License) (public domain)

Fossil fuel, biomass, and waste burning power plants

In the United States, about 61% of total electricity generation in 2021 was produced from fossil fuels (coal, natural gas, and petroleum), materials that come from plants (biomass), and municipal and industrial wastes. The substances that occur in combustion gases when these fuels are burned include:

• • Carbon dioxide (CO₂)
  • Carbon monoxide (CO)
  • Sulfur dioxide (SO₂)
  • Nitrogen oxides (NOx)
  • Particulate matter (PM)
  • Heavy metals such as mercury

Nearly all combustion byproducts have negative effects on the environment and human health:

• • CO₂ is a greenhouse gas, which contributes to the greenhouse effect.
  • SO₂ causes acid rain, which is harmful to plants and to animals that live in water. SO₂ also worsens respiratory illnesses and heart diseases, particularly in children and the elderly.
  • NOx contribute to ground-level ozone, which irritates and damages the lungs.
  • PM results in hazy conditions in cites and scenic areas and coupled with ozone, contributes to asthma and chronic bronchitis, especially in children and the elderly. Very small, or fine PM, is also believed to cause emphysema and lung cancer.
  • Heavy metals such as mercury are hazardous to human and animal health.

Power plants reduce air pollution emissions in various ways

Air pollution emission standards limit the amounts of some of the substances that power plants can release into the air. Some of the ways that power plants meet these standards include:

• • Burning low-sulfur-content coal to reduce SO₂ emissions. Some coal-fired power plants cofire wood chips with coal to reduce SO₂ emissions. Pretreating and processing coal can also reduce the level of undesirable compounds in combustion gases.
  • Different kinds of particulate emission control devices treat combustion gases before they exit the power plant:
    • Bag-houses are large filters that trap particulates.
    • Electrostatic precipitators use electrically charged plates that attract and pull particulates out of the combustion gas.
    • Wet scrubbers use a liquid solution to remove PM from combustion gas.
  • Wet and dry scrubbers mix lime in the fuel (coal) or spray a lime solution into combustion gases to reduce SO₂ emissions. Fluidized bed combustion also results in lower SO₂ emissions.
  • NOx emissions controls include low NOx burners during the combustion phase or selective catalytic and non-catalytic converters during the post combustion phase.

Hunter Power Plant, a coal-fired power plant south of Castle Dale, Utah

Source: Tricia Simpson, Wikimedia Commons author (GNU Free Documentation License) (public domain)

Many U.S. power plants produce CO₂ emissions

The electric power sector is a large source of U.S. CO₂ emissions. Electric power sector power plants that burned fossil fuels or materials made from fossil fuels, and some geothermal power plants, were the source of about 32% of total U.S. energy-related CO₂ emissions in 2021.

Some power plants also produce liquid and solid wastes

Ash is the solid residue that results from burning solid fuels such as coal, biomass, and municipal solid waste. Bottom ash includes the largest particles that collect at the bottom of the combustion chamber of power plant boilers. Fly ash is the smaller and lighter particulates that collect in air emission control devices. Fly ash is usually mixed with bottom ash. The ash contains all the hazardous materials that pollution control devices capture. Many coal-fired power plants store ash sludge (ash mixed with water) in retention ponds. Most of these ponds are unlined and pose risks to ground water. Several of these ponds have burst and caused extensive damage and pollution downstream. Some coal-fired power plants send ash to landfills or sell ash for use in making concrete blocks or asphalt.

Nuclear power plants produce different kinds of waste

Nuclear power plants do not produce greenhouse gases or PM, SO₂, or NOx, but they do produce two general types of radioactive waste:

• • Low-level waste, such as contaminated protective shoe covers, clothing, wiping rags, mops, filters, reactor water treatment residues, equipment, and tools, is stored at nuclear power plants until the radioactivity in the waste decays to a level safe for disposal as ordinary trash, or it is sent to a low-level radioactive waste disposal site.
  • High-level waste, which includes the highly radioactive spent (used) nuclear fuel assemblies, must be stored in specially designed storage containers and facilities (see Interim storage and final disposal in the United States).

Electric power lines and other distribution infrastructure also have a footprint

Electricity transmission lines and the distribution infrastructure that carries electricity from power plants to customers also have environmental effects. Most transmission lines are above ground on large towers. The towers and power lines alter the visual landscape, especially when they pass through undeveloped areas. Vegetation near power lines may be disturbed and may have to be continually managed to keep it away from the power lines. These activities can affect native plant populations and wildlife. Power lines can be placed underground, but it is a more expensive option and usually not done outside of urban areas.

Source: EIA
Last updated: November 23, 2022

Grid parity happens when our use of alternative energies like solar costs less than, or equal to, the price of using power from conventional sources such as coal, oil and natural gas (i.e., fossil fuel).

Grid Services: Benefits, Opportunity, and Value-Staking

Grid services provide dynamic load control to support the electric grid including shedding, shifting, and modulating loads. Modulating loads provide ancillary services (e.g., frequency regulation) and voltage control.  Grid services support the generation, transmission, and distribution of electricity by providing value through avoided electricity system costs (generation and/or delivery costs).

Grid Services include the value-stacking of a range of power generation, energy efficiency and load management solutions including but not limited to the following:

• Providing capacity services and energy shifting: System operators must ensure they have an adequate supply of generation capacity to reliably meet demand during the highest-demand periods in a given year. This peak demand is typically met with higher-cost generators which are almost exclusively used to serve peak demand, such as open cycle natural gas turbines; however, energy storage systems can also be used to ensure adequate peaking generation capacity. System operators can also improve the ability of variable renewable energy (VRE) plants to reliably contribute to peaking capacity by pairing VRE with energy storage, which can enable these resources to shift their generation to times when they are most needed. Storage systems may not need to be sited with VRE generators (known as co-location) in order to provide such benefits, and there are pros and cons to such co-location that must be carefully considered before siting storage systems.
• Providing fast-response ancillary services: Many forms of energy storage, most notably batteries, are capable of rapidly and accurately changing their charging and discharging rates in response to external signals. By quickly changing their output, these storage resources can provide valuable ancillary services that system operators use to help balance short-term differences between demand and supply. These ancillary services are particularly important in systems with large amounts of variable renewable energy generation, as system operators must be able to respond to unexpected changes in energy supply. Currently, ancillary services are predominantly provided by conventional generators. Using cost-effective and system-appropriate energy storage projects to align supply and demand through the provision of ancillary services increases the flexibility of the power system and helps reduce both the curtailment of renewable energy resources and spinning reserve requirements from conventional resources.
• Transmission and Distribution Upgrade Deferral: The electricity grid’s transmission and distribution infrastructure must be sized to meet peak demand, which may only occur over a few hours of the year. When anticipated growth in peak electricity demand exceeds the grid’s existing capacity, new investments are needed to upgrade equipment and expand network infrastructure. Deploying energy storage can help defer or avoid the need for new grid investments by meeting peak demand with energy stored from lower-demand periods, reducing congestion during periods of stress on network infrastructure and improving overall transmission and distribution asset utilization.
• Black Start: When starting up, large generators need an external source of electricity to perform key functions before they can begin generating electricity for the grid. During normal system conditions, this external electricity can be provided by the grid. After a system failure, however, the grid can no longer provide this power, and generators must be started through an on-site source of electricity. On-site energy storage such as a lithium-ion battery storage system can provide this service and avoid fuel costs and emissions from conventional black-start generators. As system-wide outages are rare, on-site energy storage can provide additional services when not performing black starts.
• Behind-the–Meter Applications: Battery storage systems that are interconnected behind-the-meter (BTM) can provide services for individual electricity consumers as well as services ‘upstream’ at the distribution- and transmission-levels. ‘Customer-facing’ services can broadly be categorized as (1) Bill savings; (2) Increased PV self-consumption; and (3) Backup power.

1) Bill savings: retail tariff elements determine how a customer is charged for electricity consumed from the grid and consequently determine the extent to which energy storage systems can help to reduce their electricity bills. Flat volumetric tariff elements that charge the same rate for energy consumption from the grid ($/kWh) regardless of when the energy is consumed provide little to no opportunity for energy storage to help customers reduce their bills. Time-of-use energy charges, which charge different rates for consumption during different parts of the day, and demand charge elements, which charge customers based on their maximum instantaneous consumption ($/kW) during a given period, offer opportunities to reduce bills with energy storage by shifting demand to different periods.

2) Increased PV self-consumption: Production from customer-sited solar PV systems and energy demand may be poorly aligned depending on customer demand patterns. This may mean solar PV energy that exceeds customer demand is either curtailed or exported to the power system, depending on restrictions on the customer’s interconnection agreement. Depending on how solar PV exports are compensated, this may represent a lost financial opportunity for the customer. Energy storage can help customers address the mismatch between their demand and PV generation by storing excess PV energy and discharging to meet demand after PV generation has tapered off.

3) Backup power: Energy storage, especially if combined with a generating source like solar PV or when interconnecting with multiple distributed energy resources (DER) in a micro-grid setting, can meet the energy needs of customers in the case of grid outages. This can be critical for essential infrastructure by, for example, ensuring power to an emergency shelter or hospital during a storm. Uninterrupted power can also be critical for sensitive industries that would suffer significant consequences from even brief interruptions.

• Allows storage system owner to claim a tax credit equal to a fixed percentage of eligible project costs, for example, 10% or 30%.
• Percentage can adjust downward over time
• Accelerated depreciation can lower your tax bill as well.

The systematic application of evidence based principles and methods from educational technology and the learning sciences to create engaging and effective learning experiences, support the difficulties and challenges of learners as they learn, and come to better understand learners and learning.

• A contract between the creditors (public or private) and a borrower such as banks or other commercial loan institutions that the Federal government will cover the borrower’s debt obligation in the event that the borrower defaults.

A local electrical grid with defined electrical boundaries, acting as a single and controllable entity. It can operate in grid connected and in island mode. A ‘Stand alone microgrid’ or ‘isolated microgrid’ only operates off the grid and cannot be connected to a wider electric power system.

A miniaturized version of a microgrid that supplies power to a single house or even a single load. It connects generating sources and provides distribution in the structure in an island or grid-like mode. By contrast, microgrids are larger versions that serve more than one building or much larger buildings.

• Provides ongoing payments to system owner based on the system’s actual kilowatt-hour production

• Tax credit for every kWh of renewable energy produced
• Earned over time with energy production (e.g., 10 years)

A prosumer is someone who not only consumes energy, but also produces it themselves using distributed energy sources such as solar. Prosumers also take energy monitoring into their own hands and can optimize their energy usage and reduce costs by becoming as efficient as possible.

Total possible instantaneous discharge capability (in kilowatts [kW] or megawatts [MW]) of the battery energy storage system (BESS), or the maximum rate of discharge that the BESS can achieve, starting from a fully charged state

Ratio of the energy charged to the battery to the energy discharged from the battery

The battery capacity as a percentage of its maximum capacity at a given time

Amount of time storage can discharge at its power capacity before depleting its energy capacity

• Eliminate or reduce the following taxes

1. Sales Taxes
2. Taxes on imported equipment
3. Property taxes on value of solar system

• Reduces initial cost of installing a renewable energy generation, storage or energy efficient system

Virtual power plants, generally considered a connected aggregation of distributed energy resource (DER) technologies, offer deeper integration of renewables and demand flexibility, which in turn offers more Americans cleaner and more affordable power.