1. The levels shown are approximately to scale. It should be possible to arrange for continuously rising pipe between the cylinder coil and the solar panel.
2. The inverted U at the highest point acts both as an air bleed and as steam/pressure relief.
3. There is no one-way valve. I will include one if there is evidence of water flow in the loop when the pump is off. I don't really want to have one in case it interferes with the effective pump pressure or causes problems when draining the system.
2. Two similar thermistors are needed to perform the differential temperature function. Any approximately matched pair would do fine. The ones that I use are both about 100K at room temperature.
3. The capacitor SOT sets the time for which the pump remains operating after being triggered by the temperature difference. Its value will be chosen (see D3 above) by trial and error when the complete system is up and running.
4. The circuit was built on the board supplied by Maplin. Many of the kit components are used. The board needed several modifications on the print side. It would probably have been easier to build the circuit on strip board.
Norm, This is great and thanks for sharing details of your installation.
Your plumbing circuit design is very nice, and I especially like the clever multi-purpose vent pipe up at the panel which serves both as an automatic air bleed and pressure release. Should work a treat provided the levels are as shown and there is at least a few inches of fluid in the vertical section of the vent pipe, otherwise air could perhaps get drawn into the fluid.
Thanks also for sharing your pump controller circuit design - Copying this design should be in the reach of us mortals with minimal electronics expertise, and I particularly like the fact that it's broadly based on a £6 project kit available from Maplins.
The surface etching of the aluminium sheet so that matt black paint will adhere. Done using sodium hydroxide (caustic soda) soluion. "Buster" brand kitchen drain/plug hole clearer does the trick. Works for aluminium only. Aluminium sheet (about 1.5 sq metre) outside on ground close to drain. spray some water on it then about 5 or 6 capfulls of "Buster". Brush over surface several times. The reaction gives off hydrogen gas - the "Buster" contains some sort of perfume which stinks. Rubber boots are a good idea also have a hose or bucket of water close by. After 20 or 30 minutes of reaction, hose all away.
Photo shows reaction in process, the drain cleaner bottles and detail of the reaction.
Another sunny day and put the double glaze unit in front of the panel. No attempt (yet) to encase the whole unit. Photo is below. Guess its value is in reducing direct heat loss to the surrounding air. Wonder if a single glaze unit would be as effective. A single glaze unit would reflect, and absorb, less of the incident solar energy.
Noted the approximate temperatures of the water at the top and bottom of the heat accumulator. Weather was sunny with occasional light cloud. The panel faces near south. The solar panel delivered its heated water to the top of the bin. It was replaced by cooler water pumped from the bottom of the bin. The volume of water in the bin was 24 litres and the volume of the pipe on the solar panel was 1 litre. In the 4 hour period 10:15 to 14:15 the average temperaure went from 22C to about 52C. See the pic below. Guess that the 52C represents equilibrium of heat gain and heat loss. This may be improved when connected to a real DHW cylinder with its much larger volume. And when the solar panel has a draught excluding frame.
as you suggest, you will get better energy capture efficiency with the bigger tank as efficiency is highest when panel temperature (closely tied to tank base temp) is closest to ambient air temp. bigger tank should provide colder water to the panel for longer.
sealed collector box will help too. several people have suggested that single glazed is as good as DG. Attenuation of the light energy proportional to glass thickness. Try the DG first. You can always split the DG unit with a stanley knife and use the toughened panes for two panels later!
all looks good so far and thanks for posting up the details.
your sealant is for fireplaces as well so i presume high temp rated?