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Throughout the SolTrex site, terms that are defined in the glossary appear like this: energy. Clicking on that highlighted term pops up a window with the definition and related terms. The complete glossary is also included here.

Adjusted kWh
Monthly kWh measurements are sometimes adjusted to account for discrepancies between logged data and actual meter reads. Both the logged data and any adjustments are included in the Adjusted kWh figure.

Alternating Current (AC)
Electric current which repeatedly changes polarity from negative to positive and back again. The most commonly used form of alternating current does so in a sine wave pattern.

Amperage (Ampere, Amp, A)
A unit of electrical current (I). The relationship between power, current and voltage is expressed in the Power Equation, P=IV. The relationship between voltage, current, and resistance is expressed in Ohm's Law, V=IR.

Anenometer
A sensor that measures wind speeds.

Array
PV modules wired together in series and parallel to produce desired electrical characteristics. PV arrays connected to a single metering point constitute a system.

Azimuth
The orientation of a PV array relative to direction, in degrees, in which 180 refers to due South, 90 refers to due East, and 270 refers to due West.

Capacity
The maximum amount of power a system or its component parts is expected to be capable of producing over a short time period.

Cell
The basic building block of a PV system . Individual PV cells are wired together in series and parallel to make modules.

Current (I)
The flow of charge through an electrical conductor, usually measured in Amperes (A). The relationship between power, current and voltage is expressed in the Power Equation, P=IV. The relationship betwee voltage, current, and resistance is expressed in Ohm's Law, V=IR. In fluid systems current is analogous to the flow rate (measured, for example, in gallons per minute).

Datalogger
A device that records and transmits data sampled by sensors.

Direct Current (DC)
A one-way flow of charge through an electrical conductor. Current is caused by a flow of negatively charged electrons along a metallic conductor.

Energy
Usable heat or power. The amount (or average amount) of power produced, consumed, or delivered over a specified time period. Typically measured in watt-hours (wh), kilowatt-hours (KWH), or megawatt-hours (MWH).

Energy and Power
A good analogy for the relationship between energy and power is a car's odometer and speedometer. The odometer is similar to a PV system's KWH meter in that it tracks the amount of work accomplished (distance covered, kilowatt-hours produced) over some interval of time. This is a measure of energy. A car's speedometer is similar to a PV system's power output display in that it shows the rate at which work is being accomplished (speed of the car, kilowatts produced by the PV system) at a given moment. This is a measure of power. In fact, the mathematical relationship between distance and speed is the same as that between energy and power.

Expected Production
We use NREL's PVWatts Model v. 2 to estimate monthly and annual expected production for every system. PVWatts generates monthly expected production figures based on the system size (DC capacity), module tilt and azimuth, and location. We use each system's zip code as an input into PVWatts, as well as the model's default 77% DC-to-AC derating factor. PVWatts generates estimated monthly production based on Typical Meteorological Year (TMY) data on solar radiation, temperature, and wind speed. TMY data is derived from 30 years of historical weather conditions from 239 sites around the U.S. More information on PVWatts can be found by following the link below.

Facility
The physical location of a system.

Generation
The electricity generated by a system as recorded by a KWH meter, recorded in KWH or MWH.

Generation Attributes
Characteristics of generation not including the electricity itself. Examples of generation attributes include the type of fuel used (solar, wind, coal, hydro, etc.), the air emissions associated with the generation, and whether it qualifies as "renewable" or "green energy" under various state, regional, or national statutory, regulatory or voluntary standards.

Generator
The owner of a system and/or its generation or generation attributes.

Inverter
A device that converts DC electricity into AC electricity.

Inverter KWac (KWac)
A rating of the capacity of a system's inverter(s). The inverter capacity should be as large or larger than the System KWac, but is sometimes smaller than the System KWdc.

Inverter Wac
The rated AC capacity of an inverter, in Watts. Inverters are typically around 90% efficient, meaning they convert about 90% of DC input into AC electricity.

Irradiance
See Solar Radiation.

KWH Meter (Meter)
A type of sensor that measures and records energy production. When outfitted with a pulse actuator, it can transmit energy production data to a datalogger.

Kilowatt (KW)
A measure of instantaneous electric power consumption or production. Equal to one thousand watts.

Kilowatt-Hour (KWH)
The amount of energy consumed (produced) by a continuous load (generation) of 1 kilowatt over one hour. Equal to one thousand watt-hours.

Last Month Register kWh
The meter register reading recorded at the end of the previous period.

Locked kWh
The amount of energy production logged at the time production data was permanently recorded.

Logged kWh
The amount of energy production logged during the period.

Megawatt (MW)
A measure of instantaneous electric power consumption or production. Equal to one thousand KW.

Megawatt-Hour (MWH)
The amount of energy consumed (produced) by a continuous load (generation) of 1 megawatt over one hour. Equal to one thousand KWH.

Module
A group of PV cells wired in series and parallel to achieve desired electrical characteristics and packaged as a single unit. Modules are wired together in series and parallel to make arrays.

Module Wdc
The rated DC capacity of each PV module at standard test conditions.

New Register kWh
The sum of the Total kWh and the Last Register kWh columns.

Nominal Operating Cell Temperature (NOCT)
The PV cell temperature under standard operating conditions. Under most climatic conditions, PV cells in a module operate hotter than the ambient air temperature. The NOCT is an indicator of the temperature differential between PV cells and air temperature.

Ohm (R)
A unit of electrical resistance. The relationship between voltage, current and resistance is governed by Ohm's Law, V=IR.

Ohm's Law (V=IR)
An equation that expresses the relationship between voltage (V), current (I) and resistance (R).

Operator
The entity responsible for the operation, maintenance and/or management of a system and/or the disposition of its generation or generation attributes. This entity is usually, but not always, the same as the generator.

Peak/Rated kWac
The ratio of the peak kWac recorded divided by the the system's rated kWac. An indicator of system performance, as systems can generally be expected to operate near their peak at some point during. Low values do not always indicate a problem, as they may be due to poor seasonal sunlight conditions (e.g. near-horizontal arrays in northern latitudes during winter).

Photovoltaic (PV)
Literally, "light" (photo) and "electricity" (voltaic). The class of equipment used to generate electricity directly from sunlight.

Plane of Array
Refers to the orientation of a sensor - usually a pyranometer - to the same azimuth and tilt as a PV array in order to accurately measure the solar radiation actually available to the array.

Potential
The difference in electrical potential between two points in an electric circuit; measured in volts and expressed as the voltage (V). The relationship between power, current and voltage is expressed in the Power Equation, P=IV. The relationship betwee voltage, current, and resistance is expressed in Ohm's Law, V=IR.

Power
The rate at which energy is produced, typically expressed in watts (w), kilowatts (KW), or megawatts (MW). The relationship between power, current and voltage is expressed in the Power Equation, P=IV.

Power Equation (P=IV)
The equation expressing the relationship between power (P, in watts), current (I, in amps), and voltage (V, in volts). For example, a 20 amp breaker on a 110 volt circuit is designed to trip when loads on the circuit exceed 2,200 watts (2,200 watts = 20 amps * 110 volts).

Pulse Actuator
A device that opens and closes a circuit (or circuits) at a rate proportional to the rate of energy production sensed by a KWH meter. Also used in some anemometers and other sensors.

Pyranometer
A sensor that measures solar radiation.

Recording Intervals
The frequency of data storage by a datalogger. Typical values are 15-minute, hourly, daily, and irregular. For 15-minute, hourly, and daily intervals, sensors are sampled at the sampling rate throughout the interval, and the average of these samples is recorded every 15 minutes, hour, or day, respectively. For irregular intervals, the datalogger records only the time when some change occurs. This can substantially reduce the amount of data stored and transmitted.

Renewable Energy Credit (REC)
A tradeable certificate representing the generation attributes of energy derived from a qualified renewable energy source. In the U.S., formal markets for RECs are established in New England and Texas, and are developing elsewhere. Informal and voluntary markets are active or emerging in several other U.S. regions. RECs are also called renewable energy certificates, tradable renewable certificates (TRCs), "green tags", and other names.

Resistance (R)
The ratio of the potential difference (i.e., voltage) across an electrical component (i.e., a resistor) to the current passing through it. The relationship between voltage, current and resistance is described by Ohm's Law, V=IR.

Sampling Rate
The frequency of sensor sampling by a datalogger. Typically once per second or once per minute for environmental variables like temperature, but can be much faster (in the millisecond, or thousandth of a second, range) for some sensors.

Sensor
A device that translates a condition (temperature, sunlight) or event (kWh production) into electronic signals interpreted by a datalogger.

Solar Radiation
Radiant energy deriving from the sun. Measured in watts per square meter.

Standard Operating Conditions (SOC)
A standard set of conditions used for comparing PV module performance. The conditions are: ambient air temperature of 20ºC, solar irradiation of 800 w/m2, and wind speed of 1 m/s.

Standard Test Conditions (STC)
A standard set of conditions used for comparing PV module performance. The conditions are: solar irradiation of 1,000 w/m2 and cell temperature of 25ºC. Abbreviated on this site as "stc", as in "Module Rating (DCstc)".

System
All equipment used to generate electricity whose output is metered at a single point.

System KWac (KWac)
A rating of the AC electricity generating capacity of a system. This approximates the maximum expected AC output (peaking power) of a PV system under ideal conditions. Although there are many ways to calculate an AC system rating, for simplicity and consistency we multiply the System KWdc (the sum of the DCstc ratings of all the PV modules in a system) by 0.90 to obtain System KWac. This method is based on estimated wire and mismatch losses of about 4% and inverter losses of about 6%. Other factors, such as high temperatures, could also degrade the actual system KWac. For example, modules are rated at 20 degrees C, but experience a degradation of about 0.5% for every degree C above 20. In hot climates, modules can operate at very high temperatures and the effect of this temperature degradation can be quite high.

System KWdc
A rating of the DC electricity generating capacity of a system. In the case of PV systems, it is the sum of the rated module DC capacity (module Wdc) of all modules deployed in the system.

Thermometer
A sensor that measures temperature.

Tilt
The inclination of a PV array in the direction of the azimuth, in degrees, in which 0 refers to horizontal and 90 refers to vertical.

Total kWh
The sum of the Locked kWh and Adjust kWh columns.

Voltage (Volt, V)
A unit of electrical potential difference between two points. The relationship between power, current and voltage is expressed in the Power Equation, P=IV. The relationship betwee voltage, current, and resistance is expressed in Ohm's Law, V=IR.

kWh/Modeled kWh
A measure of system energy production over a month relative to the expected energy production using PVWatts v2 and average 30-year weather data.

Actual kWh
Actual kWh consists both of raw logged production data and any adjustments made to that data to bring it in line with physical meter reads at the site. Logged data most commonly differ from actual meter reads due to temporary communications problems between loggers and our servers. Both the logged data and any adjustments are included in the Adjusted kWh figure.