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Calculated plant data (without HEMS)
Available power
The two values "available active power" and "available reactive power" can be read via the Modbus interfaces "Modbus Power Control" and "Remote Power Control". To configure the values, navigate to Power Control > Operating data > Configuration calculated plant data:
Configure calculated plant data
Available active power
Description
The available active power is an estimate of what can be produced by the PV plant based on the current weather conditions/irradiation.
The available active power Pavailable is calculated using the following formula:
Pavailable = Pinst * Gm * 1/(1000 W/m2)
in which
Pinst in W: installed active power (Sum of the nominal power of the installed power generating units (inverters)). This value must be configured under Plant data > Extended plant data/rating data.
Gm in W/m2: irradiation in module plane (The irradiation in module plane is obtained from a sensor which must be selected. If the sensor is not mounted in the module plane, the measured value can be corrected by configuring the inclination (angle between the module plane and the mounted sensor)
Please note: Several other definitions of “available active power” exist, and VCOM also provides such a value.
Use case
Grid operators, plant operators, direct marketers, or balancing service providers want to know the potential production of a PV plant.
Available reactive power
Description
The available reactive power is an estimate 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.
The following parameters must be defined for the calculation of Qavailable:
Parameter | Description | Where to define? |
|---|---|---|
Smax | Maximum apparent power of the power-generating system | Plant data > Extended plant data/rating data |
cos φmax | (Maximum) power factor of inverter | Configuration calculated plant data > Available reactive power |
Psum,inv | Sum of inverter active power | Automatically aggregated by the blue'Log |
Calculation of maximum active power Pmax, cos φmax:
Pmax, cos φmax = Smax * cos φmax
Calculation of maximum reactive power Qmax:
Qmax = sqrt( S²max - P²max, cos φmax ) = sqrt( S²max * (1 - (cos φmax)² ))
Calculation of available reactive power Qavailable:
if Psum,inv < Pmax, cos φmax: → Qavailable = Qmax
if Psum,inv >= Pmax, cos φmax: → Qavailable = sqrt( S²max- P²sum,inv )
Use case
Grid operators want to know a plant’s reactive power capability in order to estimate its contribution to voltage stability.
Example
A PV plant consisting of one inverter in which Smax = 66kVA and cos φmax = 0,8.
The resulting available reactive power in 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
Number of available inverters
The number of installed and active inverters is now available via
Modbus Power Control interface
Remote Power Control interface
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 the threshold of current or power is exceeded.
The threshold can be configured via the user interface
Number of active inverters
Number of installed inverters
No configuration necessary