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250 concepts · 176 concept relationships · counts derived from the ontology registry

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Published concepts 46

  • KilowattPublished

    A kilowatt is a unit of power equal to 1,000 watts.

    GS-CONCEPT-007 · Measurement · Source event as of June 25, 2026
  • Kilowatt-hourPublished

    A kilowatt-hour is a unit of energy equal to using one kilowatt of power for one hour.

    GS-CONCEPT-008 · Measurement · Source event as of June 25, 2026

  • Solar system size is the rated power capacity of a photovoltaic system, commonly expressed in kilowatts.

    GS-CONCEPT-009 · Measurement · Source event date unavailable

  • Annual solar production is the amount of electrical energy a photovoltaic system generates over a year.

    GS-CONCEPT-010 · Measurement · Source event date unavailable

  • Solar irradiance is solar power incident on a surface per unit area at a particular time.

    GS-CONCEPT-032 · Measurement · Source event as of September 25, 2025

  • Peak sun hours express daily solar irradiation as the equivalent number of hours at a reference irradiance of one kilowatt per square meter.

    GS-CONCEPT-033 · Measurement · Source event as of January 1, 2011

  • Photovoltaic shading loss is the reduction in modeled or measured photovoltaic output associated with solar radiation blocked from modules by surrounding objects or terrain.

    GS-CONCEPT-034 · Measurement · Source event as of September 1, 2014

  • Solar array azimuth is the compass direction toward which the array surface faces, expressed under a stated angular convention.

    GS-CONCEPT-035 · Measurement · Source event as of September 25, 2025

  • Solar array tilt is the angle between the photovoltaic array surface and the horizontal plane.

    GS-CONCEPT-036 · Measurement · Source event as of September 25, 2025

  • Photovoltaic module efficiency is the ratio of module electrical power output to incident solar power under stated test conditions.

    GS-CONCEPT-037 · Measurement · Source event as of May 5, 2026

  • A photovoltaic temperature coefficient describes how a specified module electrical characteristic changes with cell temperature relative to stated reference conditions.

    GS-CONCEPT-038 · Measurement · Source event as of August 1, 2004

  • Inverter clipping occurs when available direct-current photovoltaic power exceeds the inverter's ability to convert and deliver alternating-current power at that moment.

    GS-CONCEPT-039 · Measurement · Source event as of September 1, 2014

  • Photovoltaic system loss is a modeled or measured reduction between an identified reference energy and delivered photovoltaic energy attributable to specified loss mechanisms.

    GS-CONCEPT-040 · Measurement · Source event as of September 1, 2014

  • Photovoltaic performance ratio compares delivered system energy with a reference yield based on in-plane irradiation and installed capacity over the same period.

    GS-CONCEPT-041 · Measurement · Source event as of December 17, 2023

  • Photovoltaic capacity factor is electrical energy generated over a period divided by the energy that would result from operating at the stated rated capacity throughout that period.

    GS-CONCEPT-042 · Measurement · Source event as of December 17, 2023

  • Photovoltaic degradation rate describes the change in a system or module performance metric over time under a stated method and period.

    GS-CONCEPT-043 · Measurement · Source event as of April 1, 2012

  • Battery energy capacity is the amount of electrical energy a battery system is specified or demonstrated to store under stated conditions.

    GS-CONCEPT-044 · Measurement · Source event as of December 1, 2023

  • Usable battery capacity is the portion of stored energy made available between the system's allowed upper and lower state-of-charge limits under specified conditions.

    GS-CONCEPT-045 · Measurement · Source event as of December 1, 2023

  • Battery power rating is the rate at which a battery system can charge or discharge electrical energy under stated operating limits.

    GS-CONCEPT-046 · Measurement · Source event as of December 1, 2023

  • Battery depth of discharge is the fraction or percentage of a stated battery capacity that has been withdrawn relative to a defined full condition.

    GS-CONCEPT-047 · Measurement · Source event as of December 1, 2023

  • Battery round-trip efficiency is delivered discharge energy divided by charge energy over a defined charge-and-discharge test boundary.

    GS-CONCEPT-048 · Measurement · Source event as of December 1, 2023

  • Battery state of charge estimates the energy remaining in a battery relative to a defined available or rated capacity.

    GS-CONCEPT-049 · Measurement · Source event as of December 1, 2023

  • Battery cycle life is the number of defined charge-discharge cycles completed before a specified performance endpoint is reached under stated test conditions.

    GS-CONCEPT-050 · Measurement · Source event as of December 1, 2023

  • A photovoltaic production estimate is modeled electrical energy output for a specified photovoltaic system, location, weather dataset, period, and set of assumptions.

    GS-CONCEPT-066 · Measurement · Source event as of September 25, 2025

  • Photovoltaic specific yield is energy generated over a period divided by the photovoltaic system's stated rated capacity, commonly expressed as kilowatt-hours per kilowatt.

    GS-CONCEPT-067 · Measurement · Source event as of September 25, 2025

  • NREL PVWatts reports plane-of-array irradiance as solar irradiance at the array plane.

    GS-CONCEPT-121 · Measurement · Source event date unavailable

  • NREL SAM lists global horizontal irradiance as a weather-data element for photovoltaic modeling.

    GS-CONCEPT-122 · Measurement · Source event as of April 16, 2025

  • NREL SAM lists direct normal irradiance as a weather-data element for photovoltaic modeling.

    GS-CONCEPT-123 · Measurement · Source event as of April 16, 2025

  • NREL SAM lists diffuse horizontal irradiance as a weather-data element for photovoltaic modeling.

    GS-CONCEPT-124 · Measurement · Source event as of April 16, 2025

  • NREL documents albedo as ground reflectance in PVWatts V8 model inputs.

    GS-CONCEPT-125 · Measurement · Source event date unavailable
  • Bifacial gainPublished

    NREL documents bifacial-model inputs for rear-side irradiance and module bifaciality in SAM.

    GS-CONCEPT-126 · Measurement · Source event as of April 16, 2025

  • NREL PVWatts defines the DC-to-AC ratio as a positive model input with a default value of 1.2.

    GS-CONCEPT-127 · Measurement · Source event date unavailable

  • NREL PVWatts documents inverter efficiency at rated power as the inv_eff model input.

    GS-CONCEPT-128 · Measurement · Source event date unavailable

  • NREL SAM identifies module-voltage mismatch as an electrical loss input on the detailed-PV model Losses page.

    GS-CONCEPT-129 · Measurement · Source event as of April 16, 2025

  • NREL PVWatts defines soiling as a reduction in incident solar irradiance from dust or other seasonal module-surface soiling.

    GS-CONCEPT-130 · Measurement · Source event date unavailable

  • DOE FEMP defines PV availability as the percentage of time a system is operational and capable of delivering power when the solar resource and grid are working.

    GS-CONCEPT-131 · Measurement · Source event as of May 20, 2026

  • NREL SAM documents Annual Energy and Energy Yield as photovoltaic performance metrics.

    GS-CONCEPT-132 · Measurement · Source event as of April 16, 2025

  • NREL documents weather-corrected PV performance methods that use calibrated irradiance and measured environmental inputs.

    GS-CONCEPT-133 · Measurement · Source event as of 2013

  • NREL Standard Work Specifications calls for system performance benchmark data in photovoltaic owner documentation.

    GS-CONCEPT-134 · Measurement · Source event date unavailable

  • Nominal operating cell temperature (NOCT) is a PV module’s measured cell temperature under the defined NOCT test conditions of 800 W/m² incident irradiance, 20°C ambient temperature, and 1 m/s wind speed.

    GS-CONCEPT-135 · Measurement · Source event as of April 16, 2025
  • PyranometerPublished

    NREL's weather-corrected performance guidance uses a calibrated pyranometer to measure horizontal irradiance.

    GS-CONCEPT-136 · Measurement · Source event as of 2013

  • NREL's weather-corrected performance guidance uses calibrated reference cells or modules to determine plane-of-array irradiance.

    GS-CONCEPT-137 · Measurement · Source event as of 2013

  • NREL's weather-corrected performance guidance uses a shielded thermocouple or equivalent RTD surface-mounted on a module to measure module temperature.

    GS-CONCEPT-138 · Measurement · Source event as of 2013

  • DOE FEMP says power-conditioning equipment such as inverters often include metering and instrumentation that report parameters to a monitoring system.

    GS-CONCEPT-139 · Measurement · Source event date unavailable

  • DOE FEMP says a PV monitoring platform may receive utility control signals for setpoints such as curtailment of power delivery.

    GS-CONCEPT-140 · Measurement · Source event date unavailable

  • NREL reports low-irradiance losses of photovoltaic modules as a module-efficiency behavior considered in PV energy-performance analysis.

    GS-CONCEPT-141 · Measurement · Source event date unavailable
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