Clean Energy Glossary
Definitions of common terms, acronyms, and concepts in renewable energy.
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Last updated: December 4, 2024
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.
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.
- Bifacial Solar Panel Solar
- 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 Factor Technical
- 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%.
- Community Solar Solar
- 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.
- Curtailment Technical
- 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.
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.
- Distributed Generation Technical
- 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.
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.
G
- 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
- Interconnection Technical
- 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.
- Inverter Technical
- 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.
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.
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.
- 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
- Net Metering Policy
- 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.
O
- Offshore Wind Wind
- 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
- PJM Markets
- 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.
- 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.
- 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.
- 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.
S
- Solar + Storage Solar
- 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.
T
- Tracker Solar
- 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.
U
- Utility-Scale Solar Solar
- 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.