Technical Yes, but really quite simple.
There are many different types of Solar Water Heater now coming on to the market offering various levels of performance and various configuration possibilities.
Pre heat vs. Primary system.
A pre heater configuration heats water in a separate secondary tank using solar energy and then feeds this pre-heated water into your normal electric primary geyser. The theory being that this can reduce the amount of work your electric geyser has to do and so save some money.
Whilst this method can provide some benefit, the down side to this is that the pre-heated water is only transferred to the main geyser when you draw water. This means that the water in the electric primary geyser must still be kept hot electrically. Therefore still using quite a lot of electricity to keep the water hot, overnight.
The power rating, i.e the Q factor, is still just as important as you still need to know if the solar collector can produce as much hot water as your will draw each day. If not the electric geyser will have still more work to do than just keeping the water hot.
A primary heating configuration on the other hand can be configured to allow the water in the tank to be hotter than required from solar input prior to the evening. Thus providing some additional energy to stay hot over night or at very least, reduce the amount of electricity required to do so.
Conclusion: Wherever possible one should opt for a Primary configuration