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Calculated plant data

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About calculated data points

Grid operators, plant operators, energy traders, or balancing service providers often want to know the potential available production of a PV plant in real-time. You can use the calculated data points in blue’Log for this.

The following values can be read via the Modbus interfaces Modbus power controland Remote Power Control:

  • Available active power

  • Available reactive power

  • Number of active inverters

  • Number of installed inverters

To configure the values, navigate to Power Control > Operating data > Calculated data points.

Available active power

The available active power Pavailable is a theoretical calculation of what can be produced by the PV plant based on the current weather conditions and irradiation.

  • Prerequisite: Master or standalone mode

  • You must define one irradiance sensor.

  • For a more exact calculation, you can set an inclination angle and include a temperature coefficient. This is required by some grid operators and in some countries.

Configure available active power
Configure available active power


Item

Designation

Description

1

Measured value

If a device offers several values, select the measured value of the sensor.

2

Inclination of irradiance sensor

If the irradiance sensor is not mounted on the module plane, correct its inclination angle here.

The correction is applied as follows:
Irradiance in module plane = Measured irradiance/cos(Inclination)

3

Temperature sensor

Assign the module temperature sensor that corresponds to this irradiance sensor.

4

Measured value

See item 1

5

Module temperature coefficient

The temperature coefficient of the PV module indicates the loss of performance measured in W per °C (reference: 25°C).

Refer to the PV module datasheet for this value.

Formula: Available active power

Pavailable = Pinst * [1/cos(inclinationi)] * [Gm/ 1000] * [1+(Temperature coefficient/100)*(Module temperature - 25)]

  • Pinst in W: Installed active power: sum of the nominal power of the installed power generating units (inverters). Configure this value under Plant data > Extended plant data/rating data.

  • Gm in W/m2: Irradiance in module plane.

  • If this theoretical calculated value is above the real maximum power of the PV inverters, the value Pavailable will be limited up to Pmax, AC.


Notes

  • In a future release, it will be possible to add multiple irradiance sensors with individual temperature dependencies.

  • VCOM users ONLY To explore more complex methods of calculating the theoretical available power, see the topic Simulation in the VCOM Cloud documentation.


Available reactive power

Grid operators want to know a plant’s reactive power capability to estimate its contribution to voltage stability. The available reactive power is the calculation of the potential reactive power that can be produced by the PV plant, taking into account the capabilities of the inverters and the current production.

For the calculation of Qavailable, you must define the following parameters:

Parameter

Description

Where to define?

Smax

Maximum apparent power of the power-generating system

Power control > Operating data > Plant data > Extended plant data/rating data

cos φmax

(Maximum) power factor of inverter

Power control > Operating data > Calculated data points > Available reactive power
Formula: Maximum active power Pmax, cos φmax

Pmax, cos φmax = Smax * cos φmax

Formula: Maximum reactive power Qmax:

Qmax = sqrt( S²max - P²max, cos φmax ) = sqrt( S²max * (1 - (cos φmax)² ))

Formula: Available reactive power Qavailable:

This depends on the value Psum,inv which is the sum of the inverter active power.

  • if Psum,inv < Pmax, cos φmax: → Qavailable = Qmax

  • if Psum,inv >= Pmax, cos φmax: → Qavailable = sqrt( S²max- P²sum,inv )

📗

Example

A PV plant consisting of one inverter, where:

Smax = 66kVA and cos φmax = 0.8.

The resulting available reactive power is shown as a function of the active power output in the graph below. For example, if the inverter is producing 30kW, it can potentially deliver 39 kVar of reactive power (available reactive power).

Reactive power as a function of active power output
Reactive power as a function of active power output


Number of installed inverters​

  • Sum of all connected inverters.

  • No configuration necessary​.

  • If the blue'Log XC is configured as a master, the number of inverters connected to slaves will also be considered.

Number of active inverters

  • An inverter is "active" once a threshold of current or power is exceeded​.

  • You can configure this threshold under Power Control > Operating data > Calculated data points > Number of active inverters.​

  • If the blue'Log XC is configured as a master, the number of inverters connected to slaves will also be considered.