Solar water heating

Solar Water Heating Installation

I had wanted to do this for years! The complexity of double tanks and a primary circuit with antifreeze was daunting – until I came across ‘Solartwin’ – a freeze tolerant direct system. Cold is taken from the feed to the hot water tank and hot is returned to the top of the water tank. It is driven by a 12v pump powered by a photovoltaic panel. The system is therefore self regulating – the stronger the sunlight the greater the flow rate – and entirely independent of mains electric power. I mounted it on the wall above the roof of my garage’ at the Southern end of the house. The intended position is on a tiled roof. This gave me a better direction.

The panel is mounted on 3 frames made from 4×2 softwood, half lapped joints (Picture 1) mounted above the roof with 5 masonry screws to each frame (2). The end frame is braced by a diagonal strut to the wall. The silicone rubber pipes pass through the wall in a sleeve of polythene pipe, itself within 20mm rigid black conduit. This enabled the insulation to be firmly clamped by cable ties (4) either side of the wall. On the outside is uv resistant ‘armaflex’ insulation as supplied by Solartwin. The pump is suspended by an elastic strap to reduce vibration (5) and the pipes are plumbed into the system in the loft, above the hot water tank, for ease of access. I have fitted valves to allow isolation of the system.

The photovoltaic panel is mounted higher up the wall. It is planned to mount it a little further from the wall as shown in the main picture, and to angle a few degrees further west facing to get the remaining heat out of the system as the sun begins to move off the panel, and to reduce pumping in the morning until the panel has warmed up more. The system really needs some hysteresis and I plan to experiment with a 1fd capacitor.

A 12v 5w zener prevents overdriving of the pump.

I used MultiMonti masonry screws ( from which were an easy way to fix the frames to the wall. There are 5 to each frame which should make the panel gale proof. I avoided fitting the frames to the flat roof because it is not actually flat and I did not want to break the membrane and compromise water tightness. Screwfix also supplied the stainless steel screws used to mount the aluminium mounting brackets to the frames and to the panel. Although the panel looks large it is not unduly heavy and it was an easy job for two to get it into place.

The mounting angle from horizontal is 50 degrees – designed to be optimal at around the equinoxes.

On a sunny day in mid June when the system was first running it heated a full tank to 70oC.

For reading about this and other forms of renewable energy I strongly recommend ‘Renewable Energy’, Editor Godfrey Boyle, Oxford, ISBN 0-19-926178-4.