PV Solar Collector Performance - Equivalent One Diode

This object describes the performance characteristics of Photovoltaic (PV) modules to be modelled using an equivalent one-diode circuit. This model is also known at the 4- or 5-parameter TRNSYS model for photovoltaics.

Note: The number series and parallel-wired of Equivalent One Diode modules to be included in the model are defined on the Constructions tab under the Solar Collector header.

 

ClosedTechnical

 

Mathematically speaking, the EnergyPlus PV module employs equations for an empirical equivalent circuit model to predict the current-voltage characteristics of a single module. This circuit consists of a DC current source, diode, and either one or two resistors. The strength of the current source is dependent on solar radiation and the IV characteristics of the diode are temperature-dependent. The results for a single module equivalent circuit are extrapolated to predict the performance of a multi-module array.

 

The module employs a “four-parameter” equivalent circuit to model crystalline (both mono and poly) PV modules developed at the University of Wisconsin – Madison [2]. The values of these parameters cannot normally be obtained directly from manufacturers’ catalogs. However, the PV module will automatically calculate them from commonly available data. The PV module also includes an optional incidence angle modifier correlation to calculate how the reflectance of the PV module surface varies with the angle of incidence of solar radiation.

 

Equivalent circuit in the four parameter model

 

More detailed technical information can be found in the EnergyPlus Engineering Reference.

Name

This field contains the unique name for the photovoltaic module performance data. The name is used as an identifier.

Cell type

This field is used to describe the type of technology used in the PV module. There are two options available:

 

Cells in series

The number of individual cells wired in series to make up a single module. The typical number for a 12V crystalline silicon PV module is 36.

Active area

This field is the active area of the PV module in (m2 or ft2).

Transmittance absorptance product

This field indicates the transmittance-absorptance product at normal incidence angles for the PV modules. If the τ. α product is positive, that value will be used for all angles of incidence. If the value specified is negative, then the magnitude of the given value will be used for normal incidence and the IAM modifier correlation will be used for all other angles.

Semiconductor bandgap

This field is the semiconductor bandgap for the PV material. The bandgap for silicon is 1.12eV (electron volts).

Shunt resistance

This field is the shunt (parallel) resistance (in Ω) in the single diode electrical model of the PV. The shunt resistance is effectively infinite for crystalline silicon based PV modules and is finite for thin film and exotic metal modules.

Reference temperature

This field is the ambient temperature (in K or °F) at reference conditions. The value is usually 298K

Reference Insolation

This field is the radiation level (in W/m2 or Btu/h-ft2-°F) at reference conditions. The value is usually 1000 W/m2.

Module heat loss coefficient

This field is the heat loss coefficient (in W/m2.K or Btu/h-ft2-°F) for the array. The heat loss coefficient is dependent upon measures taken to actively or passively promote airflow over the array surface. The heat loss coefficient value is used only if the Integration and Cell Temperature Mode is set to “Decoupled Ulleberg Dynamic.”

Total heat capacity

This field is the heat capacity (in J/m2.K or Btu/ft2-F) of the modules in the array. It describes the module’s ability to store incident solar radiation internally. Such energy storage is manifested as a temperature increase in the modules that is considered to be undesirable. The total heat capacity value is used only if the Integration and Cell Temperature Mode is set to 2-Decoupled Ulleberg Dynamic.

Rated electric power

This numeric field contains the nominal electric power output to be requested from the panel. It is normally equal to the rated power output of the generator (in W). This value is used only for supervisory control and generator dispatch; the actual power output for each time step is determined by the generator models. This value affects how much a generator is loaded (i.e., requested electric power output) and can also impact the operation of an electric storage unit if one is connected to the associated Electric load centre.

Note: The Rated electric power is used for sizing the battery storage and inverters and does not define the maximum power output available from the panel.

For details in this input and its relationship with electric storage refer to Electrical Storage in the EnergyPlus Engineering Reference.

Availability schedule

Select the generator availability schedule. A schedule value of 0 indicates the generator is not available, while a schedule value > 0 indicates that the generator is available to operate.

Current

Short circuit current

This field is the short circuit current (in A) for an individual module in the PV array at reference conditions.

Module current at maximum power

This field is module current (in A) at the maximum power point and reference conditions.

Temperature coefficient of short circuit current

This field accounts for the fact that the module short circuit current is temperature dependent. The coefficient is given in A/K.

Voltage

Open circuit voltage

This field is the open circuit voltage (in V) for an individual module in the PV array at reference conditions.

Module voltage at maximum power

This field is module voltage (in V) at the maximum power point and reference conditions.

Temperature coefficient of open circuit voltage

This field accounts for the fact that the module open circuit voltage is temperature dependent. The coefficient is given in V/K.

Nominal Operating Cell Temperature

Nominal operating cell temperature test ambient temperature

This field is the ambient temperature (in K or °F) from the Nominal Operating Cell Temperature (NOCT) test. The value is usually 293 K

Nominal operating cell temperature test cell temperature

This field is the cell temperature (in K or °F) from the Nominal Operating Cell Temperature (NOCT) test.

Nominal operating cell temperature test insolation

This field is the insolation level (in W/m2 or Btu/h-ft2) from the Nominal Operating Cell Temperature (NOCT) test. The value is usually 800 W/m2.