Water heater:

Estimate your daily hot water consumption. Around 50 liters per person is the average, which is usually mixed with cold water as it is used (60-70% hot water mixed with 30-40% cold). The demand for hot water varies by household, depending on use of things like spa baths, dishwashers, clothes washers, and the water efficiency of those appliances.
The more people in the house, the bigger the tank. If your dishwasher draws on hot water (instead of heating its own), count it as an additional person. Similarly, if your washing machine draws hot water from the tank, it needs to be taken into consideration.
It’s great that you are considering making the switch to solar. Here you will find a wide variety of information designed to answer all your questions about putting solar power, solar hot water or a heat pump in your home.