If you have surplus solar power, you can easily use it to produce hot water. Often, the yield during summer and transitional periods is sufficient to become independent of fossil fuels. The immersion heater, also known as a heating rod, is screwed directly into the hot water storage tank. If this is not provided for, adapters are available to install the immersion heater into the inspection cover. Outputs in the range of 2-3 kW are often sufficient to produce hot water for the entire household during the day.
How the immersion heater works
An immersion heater consists of an electric heating element, similar to those found in washing machines. It also features a temperature sensor that measures the water temperature and a safety temperature limiter (STB) that switches off the immersion heater in the event of overheating.
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When power is supplied to the immersion heater, it heats up to the preset temperature; once this is reached, the immersion heater switches off automatically. If the immersion heater is operated exclusively with PV surplus, it is recommended to set the desired temperature higher than that of the heating system. This ensures that the regular heating system only activates when there is insufficient sunlight. For example, you can set the heating system to 45 °C and the immersion heater to 65 °C, resulting in a 20 °C temperature buffer that can be used during the night.
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Limescale typically forms during hot water production; therefore, you must adhere to the manufacturer's specified maintenance intervals. If the STB triggers, it may be due to excessive calcification. Descaling is recommended in such cases.
What do I need to consider regarding the connection?
In principle, electrical work may only be performed by a qualified electrician; there is a risk of fatal injury. The images provided are connection examples only and not an electrical wiring diagram.
It is essential to ensure that the maximum power of the immersion heater does not exceed the capacity of the switch.
The installation of the immersion heater must be carried out by a heating installer. Improper installation can lead to building damage.
Control via a Shelly Plug
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The simplest installation of the immersion heater can be achieved via a Shelly Plug or another supported smart plug. The immersion heater can only be switched on and off.
Control via a Shelly Plus 1PM
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As an alternative to the Shelly Plug, the heating can also be controlled via a Shelly Plus 1PM. It is essential to always consider the maximum power of the immersion heater and the relay. The immersion heater can only be switched on and off.
Control via 3 Shelly Plus 1PM
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If you have an immersion heater with 3x 230V connections, you can connect it via 3 Shelly Plus 1PM devices. The advantage is that each phase can be controlled individually. This allows you to operate a 3 kW immersion heater in 1 kW increments, thereby achieving even higher self-consumption. It is essential to always consider the maximum power of the immersion heater and the relay.
Setting up the control
First, you must set up the Shelly and connect it to the internet and the Shelly Cloud.
Afterward, you can connect the Shelly to our app.
During setup, ensure that you enter the correct nominal power. The nominal power corresponds to the connected load of your immersion heater, or 1/3 of the nominal power when connected via 3 Shelly devices. As soon as the surplus exceeds the set nominal power, the immersion heater is activated.
In the electricity meter settings, you can use the grid feed-in buffer to define the minimum power to be reserved as a buffer for the building or the amount of grid import allowed before a switch turns off.
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If your grid feed-in buffer is, for example, 200W, then at least 200W will always be exported to the public grid. If the grid export is less than 200W, the switch will turn off. If the grid feed-in buffer is, for example, -500W, grid import is permitted. The switch will only turn off once more than 500W is drawn from the grid. This allows you to adapt the control to your individual needs and system dimensions.