Connecting Load-Shedding Contactors

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Load shedding prevents battery deep discharge and controls the supply of energy to the loads. Load shedding provides the option of disconnecting specific loads from the system.

Load shedding is necessary for an off-grid system that is exclusively supplied with PV energy or wind energy.

The Sunny Island controls up to two load-shedding contactors depending on the state of charge of the battery. You can install two types of load shedding:

  • One-level load shedding
    If the battery state of charge limit has been reached, one load-shedding contactor disconnects all loads at the same time. Depending on the configuration, the load-shedding contactor closes when the battery has been sufficiently charged or when the stand-alone grid has been switched to an external energy source.

  • Two-level load shedding
    In two-level load shedding, there are two thresholds for the state of charge of the battery in order to control two load-shedding contactors. When the first threshold for the state of charge of the battery is reached, the first load-shedding contactor disconnects a group of loads. When the second threshold for the state of charge of the battery is reached, the second load-shedding contactor disconnects the remaining loads.

Load shedding in a multicluster system

One-level load shedding is integrated into the Multicluster-Box. The load-shedding contactor is controlled directly by the master of the main cluster via communication with the Multicluster-Box. If you install an additional load-shedding contactor in a multicluster system, it is controlled with a multifunction relay in the master of extension cluster 1. Additional load-shedding contactors cannot be controlled by the main cluster.

Load-shedding contactors in a cluster

If you connect load-shedding contactors to the master, limited operation is possible in the event of a disturbance. Slaves can control the load-shedding contactors less reliably in the event of a fault. In the event of a disturbance, the slave may wait for confirmation from the master.

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Connection of control cable for one-level load shedding (example)

Requirements:

Cable requirements:

  • Copper wire
  • Conductor cross-section: 0.2 mm² to 2.5 mm²

Procedure:

  1. Ensure that the load-shedding contactor only disconnects loads from the system. This ensures that the battery can be recharged from AC sources in the system.
  2. When connecting the load shedding, preferably use the multifunction relay Relay2. Since the default setting of Sunny Island uses the multifunction relay Relay2 for load shedding. Perform the following steps:
  3. If the multifunction relay Relay2 for load shedding is not available, use the multifunction relay Relay1 when connecting the load shedding. Perform the following steps:
  4. Enter the selected configuration into the table of the settings ( > Setting the Functions of the Multifunction Relays):

    5. Value

    Explanation

    One-level load shedding

    Setting for one-level load shedding. When the Sunny Island switches to an external energy source, load shedding is stopped and the loads are supplied by the external energy source. The battery is only charged with the excess energy.

    One‑level load shedding or the first level of two-level load shedding

    Setting for one-level load shedding or the first level of two-level load shedding. Load shedding is only stopped when the battery has been sufficiently charged.

    First level of two‑level load shedding

    Setting for the second level of two-level load shedding. Load shedding is only stopped when the battery has been sufficiently charged.

    Load shedding in the multicluster system

    Setting for additional one-level load shedding in a multicluster system. Load shedding is only stopped when the batteries of the extension cluster have been sufficiently charged.

  5. Repeat steps 1 to 5 for two-level load shedding. Connect the second load-shedding contactor to an unused multifunction relay.

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