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Ultra-supercritical steam cycle
The ultra-supercritical steam cycle is a Rankine power cycle operating above water's critical pressure, around 3,750 psia and above 1,100 °F, the most efficient commercial class of pulverized coal plants.
UltraBattery
UltraBattery is a hybrid energy storage device combining an asymmetric supercapacitor with a lead-acid battery in a single cell, developed by Australia's CSIRO under Lan Lam.
Ultralife Corporation
Ultralife Corporation (NASDAQ: ULBI) is an American manufacturer of lithium primary batteries, rechargeable battery packs, charging systems, and communications equipment, headquartered in Newark, New York and founded in 1990.
Ultranet (HVDC transmission project)
Ultranet is a 2,000-megawatt high-voltage direct current transmission line under construction in Germany, running about 340 kilometers from Osterath to Philippsburg, due operational at the end of 2026.
Umm Al Houl power plant
Umm Al Houl Power is a gas-fired power and desalination plant about 20 km south of Doha, Qatar, supplying roughly 30 percent of the country's electricity.
Umm Al Nar power station
The Umm Al Nar power station is a gas-fired cogeneration plant on Sas Al Nakhl Island near Abu Dhabi, producing electricity and desalinated drinking water since the 1970s.
Umm Al-Dalkh Oil Field
Umm Al-Dalkh is an offshore oil field about 25 km northwest of Abu Dhabi, United Arab Emirates, discovered in 1969 and producing since 1985, now operated by ADNOC Offshore.
Umm Gudair oil field
Umm Gudair oil field (أم قدير) is an onshore oil field in western Kuwait, discovered in 1962, operated by the Kuwait Oil Company, and counted among Kuwait's giant fields.
Umm Lulu
Umm Lulu, also written Umm al Lulu, is an offshore oil field in shallow Arabian Gulf waters about 30 km from Abu Dhabi, which produced first oil in 2014.
Umm Niqa oil field
Umm Niqa is a heavy oil field in northern Kuwait, operated by Kuwait Oil Company, producing about 22,000 barrels per day from the Lower Fars formation.
Umm Shaif oil field
Umm Shaif is an offshore oil field in the Arabian Gulf near Abu Dhabi, discovered in 1958 and the site of Abu Dhabi's first oil exports in 1962.
Umusadege oil field
The Umusadege oil field is an onshore field near Kwale in Delta State, Nigeria, discovered in 1974 and producing since 2008 under operator Midwestern Oil & Gas.
UN 38.3
UN 38.3 is the section of the UN Manual of Tests and Criteria that lithium cells and batteries must pass through eight tests, T.1 to T.8, before transport.
Unam oil field
The Unam oil field is a conventional oil and gas field in OML 67, offshore Nigeria south of Akwa Ibom State, producing under the NNPC and Mobil joint venture.
Unburnable carbon
Unburnable carbon is fossil fuel that cannot be burned if global warming is to stay below limits like 1.5 or 2 °C, a concept from Carbon Tracker in 2011.
Under-frequency load shedding
Under-frequency load shedding (UFLS) is a last-resort emergency protection scheme that automatically disconnects predetermined blocks of load when power system frequency falls below thresholds, arresting decline and preventing cascading blackouts.
Underbalanced drilling
Underbalanced drilling (UBD) is a drilling technique in which wellbore pressure is deliberately kept below formation pressure, letting reservoir fluids flow to surface and reducing formation damage.
Underground coal gasification
Underground coal gasification converts coal in place into synthesis gas by injecting an oxidant into a seam and igniting it, reaching coal too deep to mine.
Underground gas storage
Underground gas storage is the practice of holding natural gas in depleted oil and gas reservoirs, aquifers, and salt caverns, so surplus gas injected in low-demand periods can be withdrawn at peak.
Underground mining (soft rock)
Underground mining of soft rock extracts coal and potash deposits from beneath the surface, using continuous cutting machines and two main method families, room-and-pillar and longwall mining.
Undergrounding
Undergrounding is the practice of placing electric power lines below ground instead of on poles, improving reliability and reducing wildfire risk at much higher cost.
Undervoltage load shedding
Undervoltage load shedding (UVLS) is an emergency control measure in electric power systems that automatically disconnects selected loads when bus voltages fall below preset thresholds, arresting voltage instability and preventing collapse.
Underwater Compressed Air Energy Storage
Underwater compressed air energy storage (UWCAES) stores high-pressure air on the sea or lake bed, where water pressure keeps it at constant pressure for grid energy storage.
UNGG reactor
The UNGG reactor, short for uranium naturel graphite gaz, was a French gas-cooled power reactor design of the 1950s using natural uranium fuel and carbon dioxide coolant.
UNICA (Brazilian sugarcane industry association)
UNICA (União da Indústria de Cana-de-Açúcar e Bioenergia) is Brazil's sugarcane, ethanol, and bioenergy industry association, founded in 1997; its members produce over half the country's sugarcane.
UniEnergy Technologies
UniEnergy Technologies (UET) was a Mukilteo, Washington company founded in 2012 that made vanadium redox flow batteries for utility-scale energy storage; it went bankrupt in 2021.
Unified cell
The Unified Cell is a standardized prismatic lithium-ion battery cell developed by PowerCo, Volkswagen's battery subsidiary, announced in 2021 and entering production at Salzgitter, Germany in December 2025.
Unified power flow controller
The unified power flow controller (UPFC) is a FACTS device that independently controls active and reactive power on a transmission line by injecting a series voltage.
Uninterruptible power supply
An uninterruptible power supply (UPS), or battery backup, is a device that instantly supplies battery power when the main power fails, letting computers and data centers keep running or shut down safely.
Union Electric
Union Electric Company is an investor-owned electric utility founded in 1902 in St. Louis, Missouri, now doing business as Ameren Missouri and serving about 1.2 million customers.