I use a couple of bags to increase the insulation on my Hot Tank held in place with some old inner tubes. I have installed the longest electrical heater i could find a 27" one, and heat by excess electric diverted from our PV solar panels. I get sufficient hot water for our use for almost 8 months of the year before i have to use the central heating to top it up.
Although the tank is foam insulated its 20 years old and is not as well insulated as current tanks which have double the foam thickness.
Only downside to this is the earache from her indoors who complains that out hot cupboard aint hot anymore.
