I have off peak hot water. So I lifted the cold water tank as high as possible in the roof. A hot water cylinder with heating coil has been installed below the hot water tank which takes the cold water in at the bottom and out at the top, which feeds warm water down to the immersion tank. A home made solar panel is fitted below the bath room window. Its made from 22mm coper pipe soldered to a back plate, paint it with matt black paint and second hand double glazing glass on to a custom made box, approximatly 4 * 5 ft. the water in the coil with its own feed tank can have anti freeze for the winter. Because the panel is below the cylinder no pumps or controls are needed. on a good day the water can reach 36 degrees. On a bad day who cares it will last years so it will save money because the heating bill is mainly from 10 deg to 50deg. scrap parts were mainly used. A new insulation blanket wont break the bank.