Following the successful first part of the article on optimizing the heating of hot water (TUV) using a bivalent heat source, a common question has arisen: how to solve this in the case of a boiler with a single coil?
The main problem with heating water in a boiler with a single coil is that solar energy cannot be fully utilized. At night, the boiler heats up using "night current," and during the day, not much energy can enter the boiler because it was heated at night. The boiler has its internal thermostat, a knob with which you set the temperature. If the water temperature exceeds the desired limit, the heating thermostat simply turns off and no longer heats, even if we have enough solar energy.
What to do about it?
The theoretical solution is to split the limit temperatures into two. One will be set as the comfortable temperature, and the other as truly hot water. We will heat the boiler from the grid to the comfortable temperature (e.g., 48°C) and to the truly hot temperature (65°C) only from excess, spot prices, etc...
But practically?
Finally, in the Solar Station project, I reached support for the so-called AddOn. It extends the existing Solar Plug Pro Mini with a temperature sensor.
The installation should be performed by an experienced electrician (or a handy DIYer).
A newly purchasable SOLAR PLUG PRO MINI AddOn can be bought for the already connected SOLAR PLUG PRO MINI. We include the temperature sensor in the package.
We connect both products by snapping them together. Be careful with the connection PINs (I awkwardly bent one).
We connect the temperature sensor according to the diagram - VCC (red), DATA (yellow), GND (black).
We place the temperature sensor into the boiler coil. There should be a place for the sensor. Try to place the temperature sensor as deep as possible. Continue to connect the Solar Plug Pro Mini according to the instructions – there is no difference here.
After proper connection, just press the RESET button on the Solar Station, and it will configure everything. The temperature from the sensor will now appear on the Solar Plug tile.
Now you just need to set the correct switching logic in the form:
In the Solar Plug Pro Mini, temperature conditions are now also displayed. Choose the combination rule "ANY matches" – this means that the relay will switch on if one of the conditions is met:
- The battery charge reached 90%
- The sensor temperature dropped below 48°C
As a bonus, you can also combine the rules with spot pricing, e.g., if it is one of the 3 cheapest hours of the day.
The relay will thus switch on if the battery exceeds 90% and remain switched on as long as the battery is charged. The boiler heating will continue until the internal thermostat temperature is reached. I recommend setting it to the maximum temperature. In the case of an ugly or winter day, the relay will maintain the temperature in the boiler at48°C – from the grid.
Of course, a similar method can also apply to underfloor heating by a direct heater, etc. The temperature sensor can have two conditions – temperature drops below (for heating) or temperature rises above (for cooling with AC).
