Clean Energy Glossary

Definitions of common terms, acronyms, and concepts in renewable energy.

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A

AC (Alternating Current)Technical#: An electric current that reverses direction at regular intervals. Most homes and businesses use AC power. Solar panels produce DC power, which must be converted to AC by an inverter.
AgrivoltaicsSolar#: The practice of using the same land for both solar power generation and agriculture — crops grown beneath elevated panels, or livestock grazing around conventional arrays. Also called dual-use solar. Full explainer

B

BESS (Battery Energy Storage System)Storage#: A system that stores electrical energy using batteries for later use. Grid-scale BESS typically uses lithium-ion batteries and helps balance electricity supply and demand, integrate renewable energy, and provide grid services. Full explainer
Behind-the-MeterTechnical#: Energy resources located on the customer's side of the utility meter — rooftop solar, on-site batteries, or a generator serving a factory or data center directly — reducing or bypassing purchases from the grid.
Bifacial Solar PanelSolar#: A solar panel that can capture sunlight on both its front and back sides, increasing energy production by 5-30% compared to traditional monofacial panels. Commonly used in utility-scale installations.

C

CAISO (California Independent System Operator)Markets#: The organization that manages the flow of electricity across the high-voltage power lines in California. CAISO operates the wholesale electricity market for about 80% of California.
Capacity FactorTechnical#: The ratio of actual electricity output to maximum possible output over a period of time. Solar typically has a 20-30% capacity factor, onshore wind 30-45%, and offshore wind 40-55%. Full explainer
Capacity MarketMarkets#: A market that pays generators for committing to be available during peak demand, separate from payments for energy actually produced. PJM, ISO-NE, and NYISO run capacity markets; ERCOT is energy-only.
Community SolarSolar#: A solar power plant whose electricity is shared by multiple subscribers who receive credits on their utility bills. Allows renters and those without suitable roofs to benefit from solar energy. Full explainer
CurtailmentTechnical#: The intentional reduction of power output from a generator, often required when there is more electricity supply than demand. Renewable energy curtailment is a growing challenge as solar and wind capacity increases. Full explainer

D

DC (Direct Current)Technical#: An electric current that flows in one direction. Solar panels and batteries produce DC power. Must be converted to AC for most applications using an inverter.
Demand ResponseMarkets#: Programs that pay electricity customers to reduce or shift consumption during peak periods, treating flexible demand as a grid resource that competes with building new power plants.
Distributed GenerationTechnical#: Electricity generation from small, decentralized sources like rooftop solar, as opposed to large central power plants. Distributed generation is connected at the distribution level rather than the transmission system.
Duck CurveTechnical#: The duck-shaped daily net-demand curve created by abundant midday solar: demand minus solar sags in the afternoon (the belly), then ramps steeply as the sun sets and evening usage peaks (the neck). Full explainer

E

ERCOT (Electric Reliability Council of Texas)Markets#: The organization that operates the electric grid for about 90% of Texas. ERCOT manages the flow of electric power to 26 million customers and is largely separate from the rest of the US grid.

F

FERC (Federal Energy Regulatory Commission)Policy#: The US federal agency that regulates interstate electricity sales, wholesale electric rates, hydropower licensing, and natural gas pricing. FERC has significant influence over renewable energy interconnection policies.
Front-of-the-MeterTechnical#: Energy resources connected to the utility grid rather than a customer's premises — utility-scale solar farms, wind plants, and grid batteries that sell power through wholesale markets.

G

Grid ServicesTechnical#: Support functions that keep the grid stable — frequency regulation, voltage support, spinning reserve, and black-start capability. Increasingly supplied by batteries, which respond faster than conventional plants.
GW (Gigawatt)Technical#: A unit of power equal to 1 billion watts or 1,000 megawatts. The US has approximately 180 GW of utility-scale solar and wind capacity as of 2024.

I

InterconnectionTechnical#: The process of connecting a power generation facility to the electrical grid. Interconnection requires technical studies, grid upgrades, and regulatory approval. Interconnection queue backlogs are a major challenge for renewable energy deployment.
Interconnection QueueTechnical#: The waiting line of proposed power projects seeking permission to connect to the grid. US queues hold far more proposed capacity than the country's entire existing fleet, with multi-year waits dominated by solar, storage, and wind. Full explainer
InverterTechnical#: A device that converts direct current (DC) electricity from solar panels or batteries into alternating current (AC) for use in homes and the grid. A critical component of any solar or storage installation.
IRA (Inflation Reduction Act)Policy#: US legislation passed in 2022 providing approximately $370 billion in clean energy incentives over 10 years. The largest climate investment in US history, including tax credits for solar, wind, storage, and clean vehicles.
ITC (Investment Tax Credit)Policy#: A federal tax credit that reduces the cost of solar and storage projects by allowing a percentage of installation costs to be deducted from federal taxes. Currently 30% for projects meeting labor requirements under the IRA. Full explainer

L

LCOE (Levelized Cost of Electricity)Markets#: A measure of the average cost of electricity generation over a projects lifetime, including capital, fuel, and operations costs. Utility-scale solar LCOE is typically $25-40/MWh, making it among the cheapest electricity sources. Full explainer

M

MISO (Midcontinent Independent System Operator)Markets#: The organization that manages the electric grid across 15 US states and Manitoba, Canada. MISO operates wholesale electricity markets and manages transmission planning for one of the largest renewable energy buildout regions.
MoratoriumPolicy#: A temporary local ban on accepting or approving development applications — commonly imposed by counties or townships on solar, wind, battery storage, or data center projects while zoning rules are rewritten. Many are extended repeatedly or made permanent. Full explainer
MW (Megawatt)Technical#: A unit of power equal to 1 million watts. A typical utility-scale solar project ranges from 50-500 MW. One megawatt of solar can power approximately 150-200 homes.
MWh (Megawatt-hour)Technical#: A unit of energy equal to 1 megawatt of power delivered for 1 hour. Electricity prices are often quoted in dollars per MWh. Average US wholesale electricity prices range from $30-60/MWh.

N

Nameplate CapacityTechnical#: A generator's maximum rated output under ideal conditions, measured in MW or GW. Actual production depends on the capacity factor — a 100 MW solar farm does not produce 100 MW around the clock.
Net MeteringPolicy#: A billing arrangement that credits solar system owners for electricity they add to the grid. When solar produces more than needed, the excess is sent to the grid and the meter "runs backward." Policies vary significantly by state. Full explainer
NIMBYPolicy#: "Not In My Backyard" — shorthand for local opposition to nearby development. In clean energy, the label is contested: opponents cite property values, farmland, and character; supporters note the projects must go somewhere.

O

Offshore WindWind#: Wind turbines installed in bodies of water, typically the ocean. Benefits from stronger, more consistent winds than onshore locations. The US has significant offshore wind potential, particularly along the Atlantic coast.

P

PJMMarkets#: PJM Interconnection, the organization that coordinates the movement of wholesale electricity in all or parts of 13 states and DC. The largest competitive wholesale electricity market in the world.
Peaker PlantTechnical#: A power plant, usually gas-fired, that runs only during peak demand hours. Expensive per MWh and increasingly displaced by batteries, which serve the same role without fuel or on-site emissions.
PPA (Power Purchase Agreement)Markets#: A long-term contract between an electricity generator and a buyer, typically 10-25 years. PPAs provide revenue certainty for renewable projects and price certainty for buyers. Corporate PPAs are a major driver of renewable development. Full explainer
PTC (Production Tax Credit)Policy#: A federal tax credit for renewable electricity generation based on kilowatt-hours produced, as opposed to the ITC which is based on installation cost. Wind projects commonly use the PTC. Currently about $28/MWh for projects meeting labor requirements.

R

REC (Renewable Energy Certificate)Markets#: A tradable certificate representing the environmental attributes of 1 MWh of renewable electricity. RECs allow companies to claim renewable energy use even when purchasing power from the general grid. Also called Renewable Energy Credits.
RepoweringTechnical#: Replacing aging wind turbines or solar equipment at an existing site with newer, more productive hardware — reusing the land, grid connection, and permits while raising output.
RPS (Renewable Portfolio Standard)Policy#: A state policy requiring utilities to source a percentage of electricity from renewable sources. Over 30 states have RPS policies, with targets ranging from 10% to 100% renewable electricity by various deadlines.
RTO/ISOMarkets#: Regional Transmission Organizations and Independent System Operators — the nonprofit entities that run wholesale power markets and operate the high-voltage grid across multi-state regions. PJM, MISO, CAISO, ERCOT, SPP, NYISO, and ISO-NE cover about two-thirds of US electricity demand.

S

Safe HarborPolicy#: IRS rules letting a project lock in a tax credit's terms by starting construction — via physical work or incurring 5% of costs — before a deadline. Safe-harbor races routinely shape US solar and wind construction timing.
Setback OrdinancePolicy#: A local zoning rule setting minimum distances between energy facilities and property lines, homes, or roads. Large setbacks are a common tool for restricting wind and solar development without an outright ban.
Solar GrazingSolar#: Managing vegetation at solar sites with livestock — usually sheep — instead of mowing. The most widespread form of agrivoltaics, pairing land-lease income for ranchers with lower maintenance costs for developers.
Solar + StorageSolar#: A power plant combining solar panels with battery storage. Storage allows solar energy to be dispatched when needed rather than only when the sun shines, increasing project value and grid flexibility.
Special Use PermitPolicy#: A discretionary local approval (also called a conditional use permit) required for projects not allowed by-right under zoning. Public hearings on special use permits are where many county solar and battery fights play out.

T

TrackerSolar#: A mounting system that moves solar panels to follow the sun across the sky, increasing energy production by 15-25% compared to fixed-tilt systems. Single-axis trackers are standard for utility-scale solar in the US.
TransmissionTechnical#: The high-voltage network that moves electricity in bulk from power plants to load centers. Transmission scarcity is a primary constraint on US renewable growth — the best wind and solar resources are far from the cities that need them.

U

Utility-Scale SolarSolar#: Large solar power plants generating electricity for sale to utilities or wholesale markets, typically 1 MW or larger. Connected directly to the transmission or distribution grid. The fastest-growing source of new US electricity generation.

V

Virtual PPA (VPPA)Markets#: A financial contract that provides the economic benefits of a Power Purchase Agreement without physical electricity delivery. The buyer receives RECs and settles the difference between the contract price and market price. Popular with corporations.