My goal was to completely convert the charging pump of the hot water solar system to solar power. Since it is clear that if hot water is generated by the solar system, it must also be possible to generate enough electricity for a circulating pump.

To test, I connected 3 pieces of 90W PV modules to an MPPT controller and stored the energy gained in a Power Queen 12.8V LiFeP04 100Ah battery. The charging pump is then supplied with energy (230V AC) with a power of approx. 100W via a 600W inverter.
However, no unnecessary current should be drawn from the battery when the system is at a standstill. Therefore, the inverter, which is switched on by my freely programmable heating control, is controlled via two additional relays. First the inverter is connected to the battery and then the inverter is switched on with the second relay (pull-in delay).

If the battery should be empty despite everything, the pump will continue to be operated with mains power via an additional relay control.

As an additional task, I have converted my heating distributor so that the inverter is also switched on automatically in the event of a power failure, and the heating controller can continue to do its work. A small UPS system supplies the heating controller and other connected devices with power between the switchovers from the mains and emergency power.

Since you have to pause for a few seconds when switching between the two voltages (mains and emergency power supply from the inverter) so that the two voltages don't come together.

Obviously, another task can then be added. I had to classify my system into important and unimportant consumers. In the event of a power failure, only the solar charging pump and the associated switch valve (switching between boiler and buffer storage charging) should remain in operation in order not to unnecessarily load the battery. The other pumps that are available for heating the winter garden do not have to work in the event of a power failure. After some time of brainwork and with a good circuit diagram, I was able to do that satisfactorily. The important and unimportant devices are supplied with voltage via a plug-in distributor.

It would also be possible, should the inverter of the 12V system be defective, to immediately switch to a second system. But only by hand. Since I still have a 24V PV system with a 25.6V LiFeP04 battery from Power Queen. Which of course also supplies other devices and pumps with solar power.

So I can already say that I can make ends meet without mains power for some time. Of course, the PV system will be expanded and a second (super) battery from Power Queen will also be purchased.

(c) 2022 VoWa Jan.023