PV panels, batteries, inverters are only part of an energy saving plan. You cannot expect a return on your money in the short term
The geyser-type electric water heater consumes 70% of the electrical energy in the house
Therefore it would make sense to replace this with something more efficient
We have a superb South African product called "Geyserwise Plus" which will accurately monitor the water temperature in your tank, can switch the geyser on and off at pre-determined periods, always depending on the current water temp at the time and also switch on a pump to aid hot water circulation from a solar collector
I have given talks to U3A and similar clubs, explaining how it works, since many people don't have a clue
In summer, a 10-tube evacuated tube solar water panel can heat 150 litres of water by 50 deg in 4 hours, often reaching temperatures of 80 deg
So if the GW is set to switch on the geyser at 16h00 and the thermostat is set to 55 deg, it will not come on at 16h00 since the water is hotter than 55 deg
If you have a 200 litre geyser and have a 3-minute shower after dark, the water will probably only drop by 15 deg and will still be warm enough in the morning for another shower. Therefore the GW must not, in summer, turn on the element in the morning since by lunchtime the sun will have heated the water
Another consideration is a heat pump. This is basically a fridge in reverse and extracts heat from the local environment to heat water. About 300% more efficient than a geyser element
Other energy saving tricks are led lamps, insulation, draft exclusion and double glazing. Even lined curtains make a difference