Symbol | Definition | Page Links |
$$A_i$$ | Anisotropy Index [unitless] | Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model |
$$AM$$ | Air Mass [unitless] | Air Mass |
$$AM_a$$ | Absolute Air Mass [unitless] | Perez Sky Diffuse Model, Sandia PV Array Performance Model |
$$\theta_{AOI}$$ | Angle of Incidence [degrees] | POA Beam, Angle of Incidence, Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model, Perez Sky Diffuse Model |
$$DHI$$ | Diffuse Horizontal Irradiance [W/m2] | Global Horizontal Irradiance, Diffuse Horizontal Irradiance, Isotropic Sky Diffuse Model, Simple Sandia Sky Diffuse Model, Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model, Perez Sky Diffuse Model |
$$DNI$$ | Direct Normal Irradiance [W/m2] | Irradiance and Weather – Definitions and Overview: Direct Normal Irradiance, Global Horizontal Irradiance, POA Beam, Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model |
$$DOY$$ | Day of Year | Extraterrestrial Radiation |
$$E_0$$ | reference irradiance, typically 1000 W/m2 | Sandia Cell Temperature Model, Effective Irradiance, Sandia PV Array Performance Model, PVWatts |
$$E_a$$ | Extraterrestrial Irradiance [W/m2] | Extraterrestrial Radiation, DISC Model, Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model, Perez Sky Diffuse Model |
$$E_b$$ | beam component of plane-of-array irradiance [W/m2] | Plane of Array (POA) Irradiance, POA Beam, Sandia PV Array Performance Model |
$$E_d$$ | sky diffuse component of plane-of-array irradiance [W/m2] | Plane of Array (POA) Irradiance, Simple Sandia Sky Diffuse Model, Hay and Davies Sky Diffuse Model, Reindl Sky Diffuse Model, Perez Sky Diffuse Model, Sandia PV Array Performance Model |
$$E_e$$ | effective irradiance [unitless] | Effective Irradiance, Sandia PV Array Performance Model, PVWatts |
$$E_{POA}$$ | irradiance incident on the plane of the array [W/m2] | Plane of Array (POA) Irradiance, Faiman Module Temperature Model, Sandia Cell Temperature Model, PVsyst Cell Temperature Model, Effective Irradiance |
$$E_{qt}$$ | Equation of Time | Simple Models |
$$E{sc}$$ | Solar Constant | Extraterrestrial Radiation |
$$eta_{m}$$ | efficiency of PV module | PVsyst Cell Temperature Model |
$$f_d$$ | fraction of diffuse light used by PV module | Sandia PV Array Performance Model |
$$GHI$$ | Global Horizontal Irradiance [W/m2] | Direct Normal Irradiance, DISC Model, Global Horizontal Irradiance, Simple Sandia Sky Diffuse Model, Reindl Sky Diffuse Model |
$$I$$ | Current [amps] | Module IV Curve, Single Diode Equivalent Circuit Models |
$$I_0$$ | Saturation current | Single Diode Equivalent Circuit Models |
$$IAM$$ | Incidence angle modifier | Incident Angle Reflection Losses |
$$IAM_b$$ | Incidence angle modifier for beam component of irradiance | Incident Angle Reflection Losses |
$$I_D$$ | voltage-dependent current lost to recombination | Single Diode Equivalent Circuit Models |
$$I_L$$ | light-generated current produced within PV cell | Single Diode Equivalent Circuit Models |
$$I{M}$$ | current of module or array | Single Diode Equivalent Circuit Models |
$$I_{mp}$$ | current at maximum power | Sandia PV Array Performance Model |
$$I{sc}$$ | short circuit current | Sandia Model, Effective Irradiance, Sandia PV Array Performance Model |
$$I_{sc0}$$ | | Effective Irradiance, Sandia PV Array Performance Model |
$$I_{scr}$$ | | Effective Irradiance |
$$I_{scr0}$$ | | Effective Irradiance |
$$I_{sh}$$ | current lost due to shunt resistances | Single Diode Equivalent Circuit Models |
$$K$$ | glazing extinction coefficient | Physical Model of IAM |
$$K_n$$ | Direct Normal Transmittance | DISC Model |
$$K_t$$ | Global Horizontal Transmittance | DISC Model |
$$L$$ | glazing thickness | Physical Model of IAM |
$$Long_{local}$$ | Longitude of the observer | Simple Models |
$$Long_{sm}$$ | Longitude of standard meridian of observer’s time zone | Simple Models |
$$M$$ | air mass modifier | De Soto Model |
$$N_s$$ | number of cells in series | Single Diode Equivalent Circuit Models |
$$P_{AC}$$ | AC output power | Sandia Inverter Model |
$$P_{ACO}$$ | maximum AC power rating | Sandia Inverter Model |
$$P_{DC}$$ | DC input power | Sandia Inverter Model |
$$p_{in}$$ | normalized DC power | Driesse Inverter Model |
$$p_{loss}$$ | | Driesse Inverter Model |
$$P_{mp}$$ | maximum power point power | Point-value Models, PVWatts |
$$P_{mp0}$$ | | PVWatts |
$$PR_{AC}$$ | daily AC performance ratio | Performance Ratio |
$$q$$ | elementary charge (constant) | Single Diode Equivalent Circuit Models, Sandia PV Array Performance Model |
$$R_{av}$$ | mean Sun-Earth distance | Extraterrestrial Radiation |
$$R_s$$ | series resistance | Single Diode Equivalent Circuit Models |
$$R_{sh}$$ | shunt resistance | Single Diode Equivalent Circuit Models |
$$R_{sh,ecp}$$ | | PVsyst Model |
$$S$$ | total absorbed irradiance [W/m2] | De Soto Model, PVsyst Model |
$$SF$$ | soiling factor; ranges from 0 (no soiling)to 1 (complete soiling) | Effective Irradiance |
$$T_{0}$$ | reference temperature, typically 25 degrees Celsius | Effective Irradiance, Sandia PV Array Performance Model, PVWatts |
$$T_{c}$$ | cell temperature [°C] | Sandia Cell Temperature Model, PVsyst Cell Temperature Model, Effective Irradiance, De Soto Model, PVWatts |
$$T_{cr}$$ | | Effective Irradiance |
$$T_{local}$$ | local time | Simple Models |
$$T_{m}$$ | module temperature [°C] | Sandia Module Temperature Model, Faiman Module Temperature Model, Sandia Cell Temperature Model |
$$T_{solar}$$ | solar time | Simple Models |
$$U_{0}$$ | constant heat transfer component | Faiman Module Temperature Model, PVsyst Cell Temperature Model |
$$U_1$$ | convective heat transfer component | Faiman Module Temperature Model, PVsyst Cell Temperature Model |
$$V$$ | voltage [V] | Module IV Curve |
$$V_{DC}$$ | DC input voltage [V] | Sandia Inverter Model |
$$V_{DC0}$$ | DC voltage level at which AC power rating is achieved [V] | Sandia Inverter Model |
$$v{in}$$ | normalized DC voltage | Driesse Inverter Model |
$$V_M$$ | voltage of module or array [V] | Single Diode Equivalent Circuit Models |
$$V_{mp}$$ | maximum power point voltage [V] | Sandia PV Array Performance Model |
$$V_{oc}$$ | open circuit voltage [V] | Sandia PV Array Performance Model |
$$V_T$$ | thermal voltage | Single Diode Equivalent Circuit Models |
$$WS$$ | wind speed [m/s] | Sandia Module Temperature Model, Faiman Module Temperature Model, PVsyst Cell Temperature Model |
$$Y_{fAC}$$ | AC system yield | Performance Ratio |
$$Y_r$$ | ratio of plane-of-array irradiance to reference irradiance | Performance Ratio |
$$alpha$$ | absorption coefficient of PV module | PVsyst Cell Temperature Model |
$$alpha_{lmp}$$ | temperature coefficient for maximum power point current | Sandia PV Array Performance Model |
$$alpha_{lsc}$$ | temperature coefficient for short circuit current | Effective Irradiance, De Soto Model, Sandia PV Array Performance Model, PVsyst Model |
$$alpha_{lscr}$$ | | Effective Irradiance |
$$beta_{Voc}$$ | temperature coefficient for module; open circuit voltage | Sandia PV Array Performance Model |
$$beta_{Voc0}$$ | temperature coefficient for module; open circuit voltage at reference irradiance | Sandia PV Array Performance Model |
$$gamma$$ | temperature correction for Pmp | PVWatts |
$$Delta T$$ | temperature difference parameter | Sandia Cell Temperature Model |
$$varepsilon$$ | bins of clearness | Perez Sky Diffuse Model |
$$theta_A$$ | azimuth angle | Sun Position, Angle of Incidence |
$$theta_d$$ | declination of the sun | Simple Models |
$$theta_{el}$$ | solar elevation angle | Sun Position |
$$theta_{hr}$$ | hour angle | Simple Models |
$$theta_{r}$$ | angle of refraction | Physical Model of IAM |
$$theta_Z$$ | solar zenith angle | Sun Position, Air Mass, Angle of Incidence, Simple Sandia Sky Diffuse Model, Perez Sky Diffuse Model |
$$kappa$$ | constant | Perez Sky Diffuse Model |
$$lambda$$ | latitude of the observer | Simple Models |
$$tau$$ | weighted transmittance | Incident Angle Reflection Losses |