Being vertical in configuration with a surrounding diaphan¬ ous casing it can receive sun radiation from any direction and can therefore be easily located.

The solar heater is of upright configuration as shown in Fig¬ ure 1 which is a cross section drawing of it. It has an up¬ right tank and is placed in a sunlit location such as a roof¬ top and it has it's outer surface dark coloured to act as the absorber 1.

The invention is comprised of an outer surrounding cylindric¬ al water jacket which encompasses a central storage tank 2. The water jacket is made up from two cylinders with prefer¬ ably domelike lids, one 3 fitted over the other 4 which is just slightly shorter in height and diameter. Both cylinders can be fixed to the base 5 and this container shall be here¬ after referred to as the outer container 6, Water held in the narrow cavity of the outer container 6 will become heated by sun radiation onto it's outer wall the absorber 1. A central storage tank hereafter referred to as the inner con= tainer 2 which is shorter and narrower than the outer contain¬ er 6 has interconnecting open-ended pipes at the top 7 and the bottom 8 ideally located centrally and which induce a thermo- siphon flow when the container 6 water is hotter than that in the inner container 2. The heated water entering the inner con¬ tainer 2 through the top interconnection 7 as the cooler water is expelled through the bottom opening 8.

The cavity between the inner and outer container can be filled with insulating material 9, the only contact points being the interconnection top 7 and bottom 8 and where the inner contain-

-_.

/ er 2 becomes attached to the base 9.

SUBSTITUTE SHEET

In order to minimise reverse thermosiphoning the top in¬ flow pipe 7 can protrude about one third of the depth of the inner container as indicated 10.

To negate heat transfer loss at the connection between the two containers the inflow pipe 7 can be circumscribed by another pipe 11 of wider diameter and covering the part of the inflow pipe that protrudes into the inner contain¬ er 2 and the cavity between them can be filled with insul¬ ating material 12.

The absorber 1 is encased by a diaphanous and preferably translucent cover 13 which is usually cylindrical with a domelike lid 14. The translucent effect can be obtained by using a transparent material with a prismatic or similar pattern. The diaphanous cover 13 & 14 admits and reflects sun radiation from any angle onto the absorber contained within it as well as mitigating heat loss besides contain¬ ing heat. The translucency of the covering obscures the absorber 1 so that the appearabce is enhanced. Water from the mains supply usually enters the outer con¬ tainer 6 close to the bottom 15 and the heated water is drawn off from the top strata of the inner container 2 through a pipe 16 which has an open end at it's top and which can extrude through the bottom of the inner contain¬ er 2 and through the base 17.

Auxillery heating can be provided and one means is by us¬ ing an electric immersion heater 18 which can be fitted in¬ to the top of the inner container 2 and set above the open¬ ing of the inlet 10 in order to prevent heated water from reverse thermosiphoning as much as possible. The temperature of the water heated by the immersion heat¬ er 18 can be controlled by a thermostat fixed onto the top of the inner container 2 but this is not shown in the ill¬ ustration and electrical wiring can be passed down through the insulation 9 to a terminal 19 on the base 17. Holes through the top of the outer container which have sealed rims 20 & 21 nrovide access to the immersion heater 18 and thermostat and a third such hole prevents the re¬ lief valve 23 from making contact with the outer contain-

er 6 as the relief valve is fitted into a pipe which pro¬ trudes through the opening provided. The holes in the top of the outer container 6 all have insulated plugs that fit into them and the immersion heater plug and the thermostat plug have lids which conduct heat. Two or more of the described solar water heaters can be interconnected by joining the outflow pipe 16 from one to the inner container 2 of the other usually to a connection provided at the bottom of the tank 24.

Three alternative methods of preventing reverse thermosip¬ honing are as follows:

(1) A valve comprised of a small receptacle containing a liquid which has a low boiling point and the receptacle is immersed in water in a small container usually fixed top centre on the outer container 6 so that when heated by sun radiation the liquid will boil causing the receptacle to float and in doing so will unplug the top thermosiphon in¬ let 7 .

(2) A light sensor which electrically operates a solenoid which in turn works a plug type valve which opens the inf¬ low thermosiphon pipe when activated by sunlight.

(3) A solenoid which operates a plug type valve which opens the thermosiphon inlet and controlled by a thermostat which in turn is operated by sun radiation heat.