Glossary of Energy Terms

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A B C D E F G H I J K L M N O P Q R S T U V W X-Z Acronyms

Note: No entries for Y or Z.

Letter P

PARALLEL PATH FLOW - As defined by NERC, this refers to the flow of electric power on an electric system's transmission facilities resulting from scheduled electric power transfers between two other electric systems. (Electric power flows on all interconnected parallel paths in amounts inversely proportional to each path's resistance.)

PARTIAL LOAD - An electrical demand that uses only part of the electrical power available. [See California Code of Regulations, Title 24, Section 2-5342(e) 2]

PARTICULATE MATTER (PM) - Unburned fuel particles that form smoke or soot and stick to lung tissue when inhaled. A chief component of exhaust emissions from heavy-duty diesel engines.

PASSIVE SOLAR ENERGY - Use of the sun to help meet a building's energy needs by means of architectural design (such as arrangement of windows) and materials (such as floors that store heat, or other thermal mass).

PASSIVE SOLAR SYSTEM - A solar heating or cooling system that uses no external mechanical power to move the collected solar heat.

PBR - PERFORMANCE-BASED REGULATION - Any rate-setting mechanism which attempts to link rewards (generally profits) to desired results or targets. PBR sets rates, or components of rates,for a period of time based on external indices rather than a utility's cost-of-service. Other definitions include light-handed regulation which is less costly and less subject to debate and litigation. A form of rate regulation which provides utilities with better incentives to reduce their costs than does cost-of-service regulation.


PEAKER - A nickname for a power generating station that is normally used to produce extra electricity during peak load times.

PEAK LOAD OR PEAK DEMAND - The electric load that corresponds to a maximum level of electric demand in a specified time period.

PEAK LOAD - The highest electrical demand within a particular period of time. Daily electric peaks on weekdays occur in late afternoon and early evening. Annual peaks occur on hot summer days.

PEAK LOAD POWER PLANT - A power generating station that is normally used to produce extra electricity during peak load times.

PEAKING UNIT - A power generator used by a utility to produce extra electricity during peak load times.

PEAT - A heterogeneous mixture of partly decomposed organic matter that has accumulated in a water saturated environment over a very long period of time. Peat geologically is considered a very young form of coal and has a heating value of 6,600 Btu/pound in situ. California has minor peat resources.

PETROCHEMICALS - Chemicals made from oil.

PETRODOLLARS - Money paid to other countries for oil imported to the United States.

PADD (PETROLEUM ADMINISTRATION FOR DEFENSE DISTRICTS) - The United States is divided by the U.S. Department of Energy into five PADD regions for planning purposes. The states within PADD V are Alaska, Arizona, California, Hawaii, Nevada, Oregon and Washington, which are linked closely by their oil supply network. Since very little petroleum product is export outside the district, PADD V is essentially a self-contained oil supply system with Alaska and California the main producers and California refining the majority of the crude oil consumed in the PADD.

PERM - The measurement of water vapor through different materials measured in perm-inch (mass of water vapor moving through a unit area in unit time).

PETROLEUM - Oil as found it its natural state under the ground.

PG&E - The acronym for Pacific Gas and Electric Company an electric and natural gas utility serving the central and northern California region.

PHOTOCELL - A device that produces an electric reaction to visible radiant energy (light).

PHOTOSYNTHESIS - A process by which green plants change carbon dioxide into oxygen and organic materials. The energy for this process comes from sunlight.

PHOTOVOLTAIC CELL - A semiconductor that converts light directly into electricity.

PIPELINE - A line of pipe with pumping machinery and apparatus (including valves, compressor units, metering stations, regulator stations, etc.) for conveying a liquid or gas.

POOLCO - Poolco refers to a specialized, centrally dispatched spot market power pool that functions as a short-term market. It establishes the short-term market clearing price and provides a system of long-term transmission compensation contracts. It is regulated to provide open access, comparable service and cost recovery. A poolco would make ancillary generation services, including load following, spinning reserve, backup power, and reactive power, available to all market participants on comparable terms. In addition, the Poolco provides settlement mechanisms when differences in contracted volumes exist between buyers and sellers of energy and capacity.

PORTFOLIO MANAGEMENT - The functions of resource planning and procurement under a traditional utility structure. Portfolio management can also be defined as the aggregation and management of a diverse portfolio of supply (and demand-reduction) resources which will act as a hedge against various risks that may affect specific resources (i.e., fuel price fluctuations and certainty of supply, common mode failures, operational reliability, changes in environmental regulations, and the risk of health, safety, and environmental damages that may occur as a result of operating some supply resources). Under a more market-driven power sector with a "power-pool" or POOLCO wholesale market structure, a portfolio manager would: aggregate and manage a diverse portfolio of spot-market purchases, contracts-for-differences, futures contracts and other market-hedging-type contracts and mechanisms.

PCBs (POLYCHLORONATED BIPHENYLS) - A group of organic compounds used in the manufacture of plastics and formerly used as a coolant in electric transformers. In the environment, PCBs are highly toxic to aquatic life. They persist in the environment for long periods of time and are biologically accumulative.

POWER - Electricity for use as energy.

POWER AUTHORITIES - Quasi-governmental agencies that perform all or some of the functions of a public utility.

POWER PLANT (Note: Two separate words, not one word.) - A central station generating facility that produces energy.

POWER PLANT ENTRAINMENT - A situation where small organisms carried along with the water drawn into the power plant are subjected to thermal, physical, or chemical stresses.

POWER POOL - An entity established to coordinate short-term operations to maintain system stability and achieve least-cost dispatch. The dispatch provides backup supplies, short-term excess sales, reactive power support, and spinning reserve. Historically, some of these services were provided on an unpriced basis as part of the members' utility franchise obligations. Coordinating short-term operations includes the aggregation and firming of power from various generators, arranging exchanges between generators, and establishing (or enforcing) the rules of conduct for wholesale transactions. The pool may own, manage and/or operate the transmission lines ("wires") or be an independent entity that manages the transactions between entities. Often,the power pool is not meant to provide transmission access and pricing, or settlement mechanisms if differences between contracted volumes among buyers and sellers exist.

POWER POOL - Two or more interconnected utilities that plan and operate to supply electricity in the most reliable, economical way to meet their combined load.

PPM (PARTS PER MILLION) - The unit commonly used to represent the degree of pollutant concentration where the concentrations are small.

PREFERRED DAY-AHEAD SCHEDULE - A Scheduling Coordinator's preferred schedule for the ISO day-ahead scheduling process.

PREFERRED HOUR-AHEAD SCHEDULE -- A Scheduling Coordinator's preferred schedule for the ISO hour-ahead scheduling process.

PREFERRED SCHEDULE - The initial schedule produced by a Scheduling Coordinator that represents its preferred mix of generation to meet demand. The schedule includes the quantity of output (generators) and consumption (loads), details of any adjustment bids, and the location of each generator and load. The schedule also specifies the quantities and location of trades between the Scheduling Coordinator and all other Scheduling Coordinators, and is balanced with respect to generation, transmission losses, load, and trades.

PRESSURIZED WATER REACTOR (PWR) - A nuclear power unit cooled by water that is pressurized to keep it from boiling when it reaches high temperatures.

PRIMARY FUEL - Fuel consumed in the original production of energy, before conversion takes place.

PROGRAMMABLE CONTROLLER - A device that controls the operation of electrical equipment (such as air conditioning units and lights) according to a preset time schedule.

PROPANE - A gas that is both present in natural gas and refined from crude oil. It is used for heating, lighting and industrial applications. See also LPG.

PROVIDER OF LAST RESORT - A legal obligation(traditionally given to utilities) to provide service to a customer where competitors have decided they do not want that customer's business.

PUBLIC ADVISER - A appointee of the governor who attends all meetings of the California Energy Commission and provides assistance to members of the public and interveners in cases before the Commission.

PUBLIC INTEREST GOALS -- Public interest goals of electric utility regulation include: 1) inter-and intra-class and intergenerational equity); 2) the equal treatment of equals (horizontal equity); 3)balancing long- and short-term goals that have the potential to affect intergenerational balance; 4)protecting against the abuse of monopoly power; and 5) general protection of the health and welfare of the citizens of the state, nation, and world. Environmental and other types of social costs are subsumed under the equity and health and welfare responsibilities.

PUHCA - The Public Utility Holding Company Act of 1935. This act prohibits acquisition of any wholesale or retail electric business through a holding company unless that business forms part of an integrated public utility system when combined with the utility's other electric business. The legislation also restricts ownership of an electric business by non-utility corporations.

PUMPED HYDROELECTRIC STORAGE - Commercial method used for large-scale storage of power. During off-peak times, excess power is used to pump water to a reservoir. During peak times, the reservoir releases water to operate hydroelectric generators.

PURPA - The Public Utility Regulatory Policy Act of 1978. Among other things, this federal legislation requires utilities to buy electric power from private "qualifying facilities," at an avoided cost rate. This avoided cost rate is equivalent to what it would have otherwise cost the utility to generate or purchase that power themselves. Utilities must further provide customers who choose to self-generate a reasonably priced back-up supply of electricity.

PURPA - The Public Utilities Regulatory Policies Act of 1978 (PURPA) is implemented by the Federal Energy Regulatory Commission and the California Public Utilities Commission (CPUC). Under PURPA each electric utility is required to offer to purchase available electric energy from cogeneration and small power production facilities.

PX - The California Power Exchange Corporation, a state chartered, non-profit corporation charged with providing Day-Ahead and Hour-Ahead markets for energy and ancillary services, if it chooses to self-provide, in accordance with the PX tariff. The PX is a Scheduling Coordinator, and is independent of both the ISO and all other market participants.

PX GENERATION - Generation being scheduled by the PX.

PX LOAD - Load that has been scheduled by the PX, and which is received through the use of transmission or distribution facilities owned by participating transmission owners.

PX PARTICIPANT - An entity that is authorized to buy or sell energy or ancillary services through the PX, and any agent authorized to act on behalf of such an entity.

A B C D E F G H I J K L M N O P Q R S T U V W X-Z Acronyms

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