Have there been advances and now alternatives to immersion water tanks and heaters ? I have electric only and rarely heat hot water unless I have guests ! What else is out there as a viable alternative for hot water heating as you need it ? Thanks
Not sure that you will find anything much cheaper than an immersion for hot water.
An electric shower heats as you use it.
Undersink water heater.
If it is very rare to need the hot water the small instant on demand heaters may be best.
However perhaps if you prefer retaining a larger store of hot water rather than instant on demand heat at point of use, have a look at https://www.sunamp.com
This heat battery takes up much less space than a traditional cylinder, can be heated at lower cost via a solar diverter (like immersion element) or external heat pump etc. The thermal losses are much less than a traditional hot water cylinder.
Google “Instantaneous Water Heater”. They sound like a good solution for your requirements.