Using excess power for water heating in off-grid systems

07 Dec 23

Using excess power for water heating in off-grid systems

For an Off-Grid system. when the batteries are full and we still have AC coupled PV power available, that power is lost. We could use that power and send it to a boiler or something similar. For this we are using a device from my-PV called AC-Thor.

In off-grid systems, once the battery is full, excess photovoltaic or wind power, which cannot be stored in the battery, can be used to generate hot water using the AC-THOR.

This is done by using the frequency shift feature of off-grid inverters.

When the battery becomes fully charged and the inverter increases the AC output frequency. The AC•THOR detects the rise in frequency and increases the heating power accordingly.

For how to use this with Victron Multiplus & Quattro inverters see more here

For Sunny Island inverters see here

The AC•THOR in off-grid operation

To increase the energy independence of his home, one of our customers optimised his off-grid PV system with the AC•THOR utilising it's frequency shift function in conjunction with a Victron Multiplus inverter system and standard PV string inverter connected to the inverter's output.

First, the battery is charged, and then the additional photovoltaic energy is directed to heating water.

While the house remains connected to the public grid, the PV system doesn't export surplus power to the grid. Instead, excess energy is stored in a battery storage system, effectively creating a micro-grid. When the battery storage reaches full capacity, it adjusts its frequency within a range between 50 to 60 Hz, based on user-defined settings. This frequency shift signals the PV inverter to shut down. The AC•THOR can detect this frequency change within the micro-grid and prevent the PV inverter from shutting down by quickly redirecting the excess power to the heating application after the battery storage is charged.

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The AC•THOR is a Photovoltaic-Power-Manager for hot-water and space-heating, providing linear control of electric heatsources depending on excess PV power and heat demand. It communicates via Ethernet with inverters, battery systems and smart home controllers and receives information on how much photovoltaic energy is available.




The AC•THOR 9s is a Photovoltaic-Power-Manager for hot-water and space-heating for use in 3-phase systems.