Solar Panel

A solar panel (also known as solar module or photovoltaic module/panel) is an assembly of solar cells. Solar objects are typically parented to inverter or inverter_dyn, but can also run headless with internal default voltage/current placeholders (with warnings).

A minimal model could be created via:

object solar {
    panel_type SINGLE_CRYSTAL_SILICON;
    SOLAR_POWER_MODEL DEFAULT;
    efficiency 0.2;
    parent inverter1;
    area 2500;
}

Properties

Table 1: Solar Properties
Property name Type Unit Description Default
pvc_Pmax_calc_simp_mode bool n/a If true, PV-curve max power is approximated as pvc_U_m_V * pvc_I_m_A. TRUE
t_ref_cels double degC Reference cell temperature for PV-curve equations. 25
S_ref_wpm2 double W/m^2 Reference insolation for PV-curve equations. 1000
pvc_a1_inv_cels double 1/degC PV-curve temperature coefficient for current term dI. 0
pvc_b1_inv_cels double 1/degC PV-curve temperature coefficient for voltage term dU. 0
pvc_U_oc_V double V PV open-circuit voltage parameter. 0 (auto-derived in PV_CURVE mode if needed)
pvc_I_sc_A double A PV short-circuit current parameter. 0 (auto-derived in PV_CURVE mode if needed)
pvc_U_m_V double V PV voltage at maximum power point. 0 (auto-derived in PV_CURVE mode if needed)
pvc_I_m_A double A PV current at maximum power point. 0 (auto-derived in PV_CURVE mode if needed)
MAX_NR_ITERATIONS int16 n/a Maximum Newton-Raphson iterations for PV_CURVE solver. 32767
x0_root_rt double n/a Initial guess offset ratio for Newton-Raphson root search. 0.15
DOA_NR_ITERATIONS double n/a Newton-Raphson degree-of-accuracy threshold. 1e-5
panel_type enumeration n/a Panel technology. Values: SINGLE_CRYSTAL_SILICON, MULTI_CRYSTAL_SILICON, AMORPHOUS_SILICON, THIN_FILM_GA_AS, CONCENTRATOR. SINGLE_CRYSTAL_SILICON
SOLAR_TILT_MODEL enumeration n/a Tilt/irradiance model. Values: DEFAULT, SOLPOS, PLAYERVALUE. DEFAULT
SOLAR_POWER_MODEL enumeration n/a Power model. Values: DEFAULT, FLATPLATE, PV_CURVE. DEFAULT
a_coeff double n/a Module temperature correction coefficient a. -2.81
b_coeff[s/m] double s/m Module temperature correction coefficient b. -0.0455
dT_coeff[mmdegC/kW] double mmdegC/kW Module temperature correction coefficient dT. 0.0
T_coeff[%/degC] double %/degC Maximum-power temperature coefficient. -0.5
NOCT[degF] double degF Nominal operating cell temperature. 118.4
Tmodule[degF] double degF Module temperature used in legacy power calculations. Computed
Tambient[degC] double degC Ambient temperature used in model calculations. 25.0
wind_speed[mph] double mph Ambient wind speed (used in FLATPLATE mode). 0.0
ambient_temperature[degF] double degF Ambient air temperature input. 77
Insolation double W/sf Effective incident irradiance. 0
Rinternal double Ohm Internal resistance (legacy placeholder). 0.05
Rated_Insolation double W/sf Rated insolation value used in scaling. 92.902
Pmax_temp_coeff double n/a Temperature coefficient for power output. Panel-dependent (set during init)
Voc_temp_coeff double n/a Temperature coefficient for open-circuit voltage. Panel-dependent (set during init)
V_Max double V Maximum operating voltage of the PV module. 27.1
Voc_Max double V Maximum open-circuit voltage of the module. 34.0
Voc double V Current open-circuit voltage value. 34.0
efficiency double unit Conversion efficiency from insolation to DC power. Panel-dependent (defaults from panel type)
area double sf PV array area. 0
soiling double pu Array soiling factor. 0.95
derating double pu Panel derating factor. 0.95
Tcell double degC PV cell temperature. 21.0
rated_power double W Rated array power (Max_P). 0 (auto-derived if omitted)
P_Out double kW DC power output to inverter. Computed
V_Out double V DC output voltage to inverter. Computed
I_Out double A DC output current to inverter. Computed
weather object n/a Optional climate object reference. auto-discovered if available
shading_factor double pu Irradiance scaling factor for shading. 1.0
tilt_angle double deg PV array tilt angle. 45
orientation_azimuth double deg Cardinal azimuth (0=N, 90=E, 180=S, 270=W). 180
latitude_angle_fix bool n/a If true, tilt is set from climate latitude. FALSE
default_voltage_variable double n/a Hidden placeholder voltage for headless operation. hidden
default_current_variable double n/a Hidden placeholder current for headless operation. hidden
default_power_variable double n/a Hidden placeholder power for headless operation. hidden
orientation enumeration n/a Orientation type. Values: DEFAULT, FIXED_AXIS (others reserved/not implemented). DEFAULT

Example

object solar {
    parent inverter1;
    panel_type SINGLE_CRYSTAL_SILICON;
    SOLAR_POWER_MODEL FLATPLATE;
    SOLAR_TILT_MODEL SOLPOS;
    orientation FIXED_AXIS;
    tilt_angle 30;
    orientation_azimuth 180;
    shading_factor 0.95;
    efficiency 0.2;
    area 2500;
}

Orientation

Type of panel orientation. The documented and implemented operating modes are DEFAULT and FIXED_AXIS.

  • DEFAULT: ideal-tracking style insolation path.
  • FIXED_AXIS: uses fixed tilt_angle and orientation_azimuth with the selected SOLAR_TILT_MODEL.

ONE_AXIS, TWO_AXIS, and AZIMUTH_AXIS are enum placeholders but are not implemented for runtime calculations.

object solar {
        orientation FIXED_AXIS;
}

This orientation uses ideal insolation. Insolation is calculated by 

Insolation = solar_flux * shading_factor

where the value for solar_flux comes from mapped climate calculations when weather/climate data is available. Without climate data, the model falls back to static behavior and warns.

  • FIXED_AXIS - When orientation is set as FIXED_AXIS, weather, tilt_angle, orientation_azimuth, SOLAR_TILT_MODEL, and shading_factor are all used to calculate the solar radiation.

  • ONE_AXIS - Placeholder only; not implemented

  • TWO_AXIS - Placeholder only; not implemented
  • AZIMUTH_AXIS - Placeholder only; not implemented

Solar Tilt Model

Underlying solar position and tilt model used to calculate irradiance on the panel. Implemented model types include DEFAULT and SOLPOS for fixed-axis calculations, with PLAYERVALUE for player-driven insolation workflows.

object solar {
    SOLAR_TILT_MODEL SOLPOS;
}

  • DEFAULT - The incident solar radiation on a tilted array is calculated using algorithms from Solar Energy Thermal Processes by Duffie and Beckman (1974).

  • SOLPOS - The incident solar radiation on a tilted array is calculated using algoirthms from the [NREL SOLPOS] page and from "Modeling Daylight Availability and Irradiance Components from Direct and Global Irradiance" in Solar Energy volume 44, number 3 by Perez et al.

  • PLAYERVALUE - Bypasses internal tilt-position calculations and expects externally provided/played values (for example Insolation, ambient_temperature, wind_speed).

Model with DC Bus Model

The solar panel, when properly interfaced with an inverter_dyn object in grid-forming mode, will provide DC bus changes and some minor transient detail. A behavioral model of PV cell is adopted here, the advantage of this model is that it only needs parameters of output characteristics of PV cell such as open-circuit voltage (\(U_{oc}\)), short-circuit current (\(I_{sc}\)), voltage and current at maximum power operating point (\(U_m\) and \(I_m\)).

The formulas which describe the behavioral model are given as below:

Table 2: Behavioral Model
\(\displaystyle{}I=I_{sc}\left[1-C_1\left(\exp{\frac{U-dU}{C_2U_{oc}}}-1\right)\right]+dI\) (1)
\(\displaystyle{}C_1=\left(1+\frac{I_m}{I_{sc}}-\right)\exp{\frac{-U_m}{C_2U_{oc}}}\) (2)
\(\displaystyle{}C_2=\left(\frac{U_m}{U_{oc}}-1\right)\left[\ln{1-\frac{I_m}{I_{sc}}}\right]^{-1}\) (3)
\(\displaystyle{}dU=-b_1U_{oc}(t-t_{ref})\) (4)
\(\displaystyle{}dI=I_{sc}\left[a_1\frac{S}{S_{ref}}\left(t-t_{ref}\right)+\left(\frac{S}{S_{ref}}-1\right)\right]\) (5)

Where \(S_{ref}\) and \(t_{ref}\) are light intensity and temperature in standard environment (\(S_{ref}=1000\frac{w}{m^2}\), \(t_{ref}=25^{\circ}C\)), \(S\) and \(t\) are real light intensity and temperature, \(a_1\) and \(b_1\) are parameters that used to revise the output characteristics of PV panel in different environment. \(a_1\) and \(b_1\) are set zero in this instance.

A real PV panel has been modeled according to the formulas above, the output parameters of which are given in Table Table 3:

Table 3: Output Parameters of Behavioral Model
PV Panel Variable Units Value
\(\displaystyle{}U_{oc}\) V 1005
\(\displaystyle{}I_{sc}\) A 100
\(\displaystyle{}U_{m}\) V 750
\(\displaystyle{}I_{m}\) A 84

In GridLAB-D™ simulation, the PV panel is modeled as a controllable current source, with the light intensity (\(S\)), temperature (\(t\)) and voltage of PV panel as inputs. The output of the model is the current of PV panel.

The P-V curve of this PV panel is given in Figure 1, the maximum power is about 1400kW and the voltage at maximum power point is 850V. (\(t=25^{\circ}C, S=600\frac{w}{m^2}\)).

P-V Curve of PV Panel
Figure 1: P-V Curve of PV Panel