MikeFTis has kindly shared with me details of the solar thermal system he has been developing, and it occurred to me that our discussions would make an excellent case study / discussion point on the development of a DIY flat panel system connected directly, i.e., without a heat exchanger, to the water tank. There are lots of features of his project which make this interesting, e.g., a non-ideal house orientation, using materials scavenged or otherwise readily available, his care to ensure the flow from the panel is as smooth as possible, his technique for increasing his shower water pressure in an old house, etc.
Mike has just retired and lives in Yorkshire. I reckon he hasn't too far to go with both the design and build of his solar water heating system - It won't take much more before he has useful amounts of hot water in his hot water tank.
The amazing thing is that he has done all this from the memory of a solar water heating book he read 30 years ago, plus of course a liberal dose of common sense.
Mike has kindly agreed that I can post up details of his system and extracts of our correspondence. He may even post up a few notes himself as we go along(?) Anyway, I'll do the easy bit to start out, and load up some pictures of his work in progress so far. We will then discuss those elements of his design that may need further refinement and at the same time highlight the good features of what he has done already.
the panel made so far has an area of about 0.6 sq metre, perhaps suitable for 25L of hot water per day.
the panel was made to this size for 2 good reasons:
(a) this was the size of the available materials. Of critical importance if you are recycling, repurposing, upcycling, etc.
(b) small panel is easily managed/lifted by one person. this is another important point if you are trying to do much of the work yourself and don't want to risk destroying your neighbour's conservatory and/or breaking your neck.
the intention is that more panels of a similar size will be added over the development of the project.
yet another interesting feature of the panel position is that it's fairly easily accessed. don't be put off building your own solar water heating system just because you are afraid of climbing on a roof!
a panel can be sited almost anywhere provided there's space for it and it can be faced somewhere other than north of east or west, and provided the panel is within 15-20m of your hot water tank.
the panel seen here is not ideally sited. Being on an east facing wall is not optimal but still worthwhile. Remember, from a direct east or direct west orientation, you can still capture 80% of the solar energy available from a panel facing directly south. this is because just less than 50% of your light energy is diffuse, i.,e., bounced off clouds etc. The DIYer need not therefore be too concerned about not having an ideal orientation , and can regard any site as potentially suitable provided the panel will not be pointed or faced anywhere north of east or west. So, Mike has demonstrated that we should not be put off by not having a south facing roof or wall!
Panel inclination: Mike is considering changing the inclination of this panel, as a vertical is not ideal. 35-55 degrees is fine. Even a small amount of tipping out at the base will improve this panel's ability to collect energy. Further panels he adds will be inclined somewhere in the range 35-55 degrees.
On a separate matter, Mike's conservatory/glass lean-to at back or side or house is always a good idea as this helps heat the house passively during the day and reduces heat loss overnight.
Pipework. Here we can see a few good features of solar panel pipework:
(a) Drain cock at the lowest point, facilitating easy drain down.
(b) continually rising pipe work from the panel up to the collection tank.
Mike had ensured the pipework continually rose from his panel(s) to his collection tank because he intended to rely on thermosysphon rather than a pump. (Pumped systems offer more flexibility regarding the relative heights of the panels and how water tank, whereas the panel in a thermosyphon system must be below the hot water tank). Now, whilst it now looks like thermosyphon won't function too well for Mike (reason for which will become apparent in later postings), and a pump will now be required after all, where the panel is located below the tank, the principle of continually rising pipework from the panel can still be good practice irrespective of whether you are building a thermosyphon/gravity system or a pumped system:
(a) Will help the pump to do its work (the thermosyphon effect will assist the pump), and (b) will reduce the opportunity for airlocks and will encourage air bubbles to rise to a higher point in the system where they can be vented or caught in an air trap and bled. ...
..further details on Mike's system to follow later in the weekend...
Mike has raised the cold water header tank in his loft. This is a good idea because it will (a) for 'direct flow' connection of solar panels to a tank it gives a greater height range at which the panel or panels can be fitted. This is because with 'direct flow' (no heat exchanger in the tank), the water in the solar panels is pressurised by the CW water tank, and, as water always finds its own level, you are normally restricted to having to fit your panel below the top of the water level in the cold water storage tank.
(b) give good shower pressure without having to resort to shower pumps. in older houses, built in days when when baths were the norm rather than showers, the CW tank was normally placed low in the loft resting on the loft joists. Shower pressure, with a shower head just a few feet below the CW tank, is normally woefully inadequate. By raising the CW tank a foot or two, this shower pressure problem is resolved.
Now we get to the minor refinements of the plumbing layout.
Currently, and not shown in the above picture of the plumbing in the loft, Mike has the panel plumbed directly into the cold tank. The idea was that the panel would preheat the cold water.
The logic with preheating a CW tank is that, assuming a regular use of HW in the house, there will be a regular running of the hot taps etc and this will draw somewhat preheated cold water (not so cold water) into the base of the tank. The boiler or immersion will then not have to do quite as much work to bring the preheated water up to showering/bathing temps, thereby saving on some of the electric/oil/gas usage
Whilst this would have worked and the preheating theory is sound, if you can install a sufficiently large solar panel area to match the size of the HW tank, it is generally better to try to get your panels to heat the water in the hot water tank rather than preheat the cold water in the loft.
There is an insulation and heat loss issue with preheating a loft tank - One can generally insulate the HW tank better than a loft tank, and the loft tank is exposed to colder temperatures in winter. There is also a 'delay' problem with a preheating arrangement, i.e., having to use hot water from the HW tank before any preheated water in the CW tank makes it into the tank. Finally, another factor against preheating a CW tank is that, in modern houses, CW tanks are plastic and are not designed for regularly holding very hot water.
In summary, it is better practice to try and heat the water first in the tank from which you will be drawing hot water. For these reasons Mike now intends to replumb his panel(s) so that they feed his hot water tank directly.
Next problem is that Mike's HW tank is boxed-in in the bathroom and is almost inaccessible for additional plumbing. The proposal then is to make the solar panel connections up inside the loft as per the attached diagram...
"....liked the idea of initially running the pump off a transformer and timer - both spare and laying around the house - so no capital cost there either !!!
Have set timer to come on for 6 hours from just after dawn (east facing remember) to just after mid day - initial thoughts are that flow be too fast for water in panel to gain much heat - so have just changed setting on timer to 15 mins on 15 mins off - will monitor over next few days
NEARLY all joints are water tight - just got a bit of weeping from bottom compression joint where flexi pipe meets outlet thru wall - so nothing to do with pump AND in my experience (and with a little luck) compresion olives have a habit of mending thenselves after a short while