Amber Control

I am exporting renewable power to the grid, because our house is not using all the renewable power that is available, and I would like to use more in the house.

Sorry, the Amber Switch cannot help here – they are not designed for grid-connected systems.


I am not using all the available renewable power in an off-grid wind or PV power system because the batteries are full. What are the benefits of the Amber Switch?

  • Heating fuel savings and improved building comfort, by meeting more room heating or water heating requirements from renewable power.

  • Increased Feed-In Tariff revenue (where available), by increasing the total renewable energy that can be generated and used.

  • Reduced mechanical wear and tear on wind turbines, by keeping them loaded up.

  • Ensure that only surplus renewable energy, not valuable battery-stored energy, is used for heating.

  • Indicator LEDs showing when surplus renewable energy is and is not available.

  • Several Amber Switches can be used in one system - the in-built randomised delays make sure they switch at different moments, and they can be prioritised using different frequency settings. They are particularly suitable for large systems with long distances between generators, batteries and loads.

What kind of power system can the Amber Switch be used with?

Off-grid renewable power systems where the renewable generation is AC-connected (also known as AC-coupled), and the battery inverter-chargers shift system frequency to signal a high state of battery charge.

There are numerous Amber Switch installations in off-grid power systems using the SMA Sunny Island inverter system.

  • The Sunny Island battery inverter raises the system frequency when the batteries are full. This normally signals Sunny Boy or Windy Boy inverters to reduce their power output, to avoid overcharging the batteries – SMA call this “Frequency-Shift Power Control (FSPC)”. If additional loads are switched on (e.g. by the Amber Switch responding to the rise in frequency), then some of the surplus renewable power is diverted to useful applications (such as water heating or space heating) instead of being lost.

  • Victron's Multi and Quattro inverters can also be set up to use frequency shifting with AC-coupled generation.

What kind of power system is likely to be unsuitable for the Amber Switch?

  • Off-grid battery-inverter systems which operate at constant output frequency.

  • Off-grid battery-inverter systems which use DC dump loads to avoid overcharging batteries (it may be possible to make Amber Switches work with this type of system, with careful design).

  • Off-grid battery-inverter systems which use a diesel generator with a very wide / high range of operating frequency in normal operation.

  • Grid-connected renewable power installations.

What does the Amber Switch do?

It is basically an extra, automatic switch which switches a load on or off. It switches its load on when the system frequency is above a certain setpoint, which is above the normal system frequency, after a relatively short, variable time delay. It switches its load off when the system frequency is below the setpoint, again after a relatively short, variable time delay.

With the Sunny Island battery inverter system, high frequency (usually) means that the batteries are full, but that renewable energy is still available. Amber Switches, responding to the frequency rise, can switch on useful loads (such as water heating or space heating), to make use of some of the surplus renewable power.

What type of load can be controlled by an Amber Switch?

Heating loads are ideal. Good examples are immersion heaters and storage heaters.

The controlled load might be switched often, so fan heaters, anything with a motor, and devices that are sensitive to frequent on-off switching should not be connected to an Amber Switch.

The amount of surplus renewable power that is available is going to vary all the time - does the Amber Switch use exactly the amount of surplus renewable power that is available?

No, it just switches its load on or off. So if the load that it controls is 1kW, then the Amber Switch will either add 1kW to the total overall system demand, or remove 1kW when it switches off.

If the controlled load is more than the available power, the Amber Switch will probably cycle the load on and off. This shouldn’t be a problem with a heating load. It still makes sure that some of the available renewable power is not lost.

If the controlled load is less than the available power, the controlled load will be switched on, and the Sunny Island inverter may still raise the system frequency to avoid overcharging the batteries.

What size load should be controlled by an Amber Switch?

Amber Switches are best installed with loads that are likely to be a fraction of the available surplus power. For example, if a house has a 5kW off-grid PV system, but the daytime load is normally only about 1-2kW, then there could be ~3kW surplus power available. Three Amber Switches could each switch a 1kW heater. If their frequency setpoints are adjusted correctly in relation to the Sunny Boy PV inverter settings, then approximately the correct amount of load should be switched on when there is surplus PV power.

Will the Amber Switch switch its load on when there isn’t surplus renewable power?

It is possible. If the frequency in the power system is above the Amber Switch’s setpoint, it will switch its load on.

The Sunny Island increases the system frequency if there is surplus renewable power. There are other reasons why the system frequency might be high, and the Amber Switch will switch its load on regardless in these circumstances.

How can the Amber Switch help with system start-up?

When a generator or power system is first started, the Amber Switch detects when the frequency is above its setpoint, and then waits for its variable delay before switching its load on. This reduces the amount of load that the generator has to pick up in one step. This can be helpful if there are large loads with motors (e.g. freezers) which take a lot of current to start up. The Amber Switch will wait a few seconds before switching on.  


How / where should the Amber Switch be installed?

The Amber Switch is installed on the AC side of the power system (in contrast to some other controlled loads, which are installed on the DC side of PV / wind / battery systems).

Each Amber Switch is wired into the electrical circuit between the power supply and one controlled load. It is wall-mounted.
What is the largest load that can be controlled by an Amber Switch?

The maximum current that can be controlled by an Amber Switch is 15A. This equates to just above 3kW on a 230V system.

The Amber Switch can be used to control an AC contactor, and therefore indirectly switch larger loads, circuits, or three-phase loads.

Can the frequency setpoint be adjusted?

There are 7 frequency setpoints available for 50Hz systems. These can be set during installation, using dip switches inside the Amber Switch case.

Is the frequency setpoint accurate?

The Amber Switch is not a precision device. There is a slight variation in the actual frequency at which the switch will start its time delay countdown, due to manufacturing variation. Some variability is designed into the time when it will switch on or off after it has sensed that its frequency is above or below its setpoint – this is designed to avoid several switches all switching at once.

These two factors mean that the switch is likely to switch on when the frequency is a little way above its setpoint, and switch off when the frequency is a little way below its setpoint.

Frequently Asked Questions

Frequently Asked Questions