Two Solar Waterboiler projects

Many people in my region have photo-voltaic (PV) panels installed on the roof, and are still using a natural gas geyser for heating domestic hot water. It would be nice, if the solar energy could also heat the water, which can be done by using a simple (cheap) electric water boiler.

Simply replacing the gas geyser with an electric water boiler is a bad idea, since:

• the weather is not good enough to do that the whole year through - in the winter you will end up buying electricity, which is way more expensive than using gas to warm domestic hot water.
• once the water in the tank is used, you will have cold water and have to wait a few hours.

Installing them both, and manually switching between them per season is possible, but the switching is cumbersome, and financially not optimal.

Here we describe a solution to increase the solar energy self-consumption, and reduce the fossile energy (natural gas) usage by adding an electric waterboiler, which only heats water with excess electricity from the solar panels, and switches automatically between both systems (gas geyser and electric waterboiler).

This system is guaranteed to always use the cheapest source of energy, provides unlimited hot domestic water, and is future-proof, since it can be switched to choose manually between electricity and gas.

The implementation of this solution largely depends on the presence or absence of a home battery, and the other systems available in the house.
So, we discuss the following different solar waterboiler projects:

Project J

Solar panels with home battery, with natural gas, Home Assistant

Project M

Solar panels without a home battery, with natural gas, Domoticz