Since I last posted, I've made more progress on the solar panel project (which is just as well, as I'm not doing anything else!) One job that I had thought might be beyond me was fitting a new electric socket into the cupboard where the pump is. I've never tackled mains electricity before, and didn't really know where to start. However, browsing through the Readers Digest DIY manual (as you do), I found nice clear instructions for taking a spur from one socket to supply another. That's exactly what I needed - I could use the socket across the hall that we'd been plugging the extension lead into. Far better to have the wire running under the floor than over it. All I had to do was lift the floor...
In one way, that wasn't too bad as I'd laid that bit of floor myself, so knew where I was with it. On the other hand, the pipes set into the floor had been connected up since then. At least they were flexible plastic, so should cope with having the board gently eased up. I did just that and, after a slight setback when I discovered that the wires to the socket went up, not down (so no hole in the floor beneath them), the job went entirely to plan, and I now have a new double socket in the cupboard. I also tidied up the wiring in there and added a switch for the pump. First I had to find a switch, which came to light when I took the coats off the coat rack before soldering just above them. There was a thermostat on the wall, no longer in use (obviously).
That must have a switch in it! I thought. I took it to pieces and discovered not only a switch that's normally on, push button for off, but also a wiring diagram. Perfect. This enables the pump to be switched off with the solenoid valve left open, which is necessary for draining the system. In addition to a switch, the pump now has a connected earth wire. Yes, I know.
I've connected up all the plumbing. This included a few solder joints, most of which were done twice, though in my defense, I was dodging hail showers at the time, and re-doing the leaky connector over the coat rack that I hadn't quite fixed last time I tried. I'd expected the compression joints to be relatively easy, but even they threw up a few challenges. One pipe running down the side of a radiator wouldn't go past the plug I'd put in the other corner, but luckily I had a flatter one in a different corner, so could swap them around. In spite of writing
Make sure 1st and 2nd boxes are close enough together for flexi-hose on my list, they weren't, but I solved that by bending the solid pipe instead of cutting it to only just longer than the box. When I went to raid the old radiators for bleed valves, I found that most of them had the grub screws missing. I don't know how that happened - I don't remember taking them out. I used a cap in place of one bleed valve - it works almost as well. Finally, I nearly destroyed two nuts trying to tighten a joint that I'd failed to put an olive in. Luckily, I checked.
Having made all the connections, I needed to fill the system to check for leaks. That meant going up into the loft, which meant a ladder that I discovered, on first climbing it, wasn't very firm on the floor. That is, the floor is dusty and the ladder slipped. I caught it before it went too far, but came down quickly and resolved not to go up again without someone to hold the bottom. Ian being out at work, I called on a neighbour, who kindly came round and held the ladder for me, and was quite interested to see the rest of the system too. Much to my surprise, not to say delight, there were no leaks. Not one.
The next step was to replace the plain water in the system with an antifreeze* mix. I'd originally thought of mixing it up in a watering can then pouring it into the header tank in the loft. Unfortunately there wasn't enough headroom above the tank for that plan to work. When Ian got home from work I asked for his input on the problem. He thought a bit then said,
I do have that 12 volt pump and hose that I used to use for biodiesel. Maybe we could pump it up there. I have a spare battery, too. While he went off to fetch those things, I continued to search for inspiration on the internet. Surely other people have solved this problem? Well yes, but most of them solved it at the design stage, incorporating
charging valves into the system for this very purpose. Then I came across the following very useful advice:
you could try this "cheapskate" approach:I wasn't sure whether our pump could deliver that kind of pressure, but filling through the drain would be a lot easier than getting the pump within reach of the header tank. It had to be worth a go.
Make no connection whatsoever to the water main. Use a 5L house-plant sprayer (Hozelock). Remove spray head, fill container with antifreeze water mix, attach hose to system drain and pump. The pump will easily deliver up to 3 bar.
It worked, just about. We ran the system pump to help it, and there was lots of running out to open bleed valves, then close them again in case the antifreeze all escaped as well as opening and closing the drain to take liquid in, then not let it out again. This required a lot of coordination between the two of us. The pump didn't quite manage the last litre and a half, so Ian took that up to the loft in a jug, and I think we may need to top up with a bit more water, as there are distinct gurgling sounds when the pump's running. However, we now have all the panels connected up and full of antifreeze, ready to go. The controller is doing its thing, and reporting slightly more information than it was last time I wrote about it.
In addition to sensors in the panel and in the tank, I now have one on the pipe just before it goes into the tank. Ideally, this should be at about the same temperature as the panel when the pump's running, but as you can see, it's considerably lower. That means we've lost almost 20°C between the panel and the tank. Not good. Insulation is needed.
I started insulating the pipes around the panels, but I need to improve on this. I'll do more when the weather's better.
For the next stage of their journey the pipes cross the conservatory. I had an idea that since they're running under a transparent roof, maybe they could absorb some more sunlight on the way. It's probably a daft idea, but I persevered. Using an offcut of the roof itself, I made thee sides of a box.
It is possible to bend polycarbonate cold, but only if you can take it a lot further than the angle you need, to allow for spring back. I couldn't do that, so had to apply heat. This meant waving a blowtorch at a piece of plastic I was holding in my hand. I managed not to burn myself, which is quite remarkable considering how often I burn myself on the oven. The other day I even managed to burn my finger on one of the solar panels. Yes, it did get that hot!
To go inside the box, I taped up some of the thin insulation for behind radiators and pleated a few layers between the pipes, and some more around them. Just the top was left open to the sunshine. When I say open, I mean covered by twin-wall polycarbonate roofing.
I'm not entirely convinced by this, but it has to be better than it was. If nothing else, it's a lot tidier.
Items remaining on my list are:
Insulate pipes and
touch up paint on window frames, both of which are waiting for better weather,
screw down window on first box, which I'll do when I'm quite sure the system doesn't need bleeding any more,
fix blinds to boxes, which can wait, as it's only needed if we go away in the summer, and possibly not even then,
figure out clock for controller and
program data logging, the first of which I spent quite a lot of time on today, and one I added yesterday,
calibrate sensors. When I checked first thing, the display reported that the panel was at -2°C but there was no sign of frost, so it's evidently not accurate. I had meant to do this before I taped the sensor to the back of a solar panel, but I forgot.
As for figuring out a clock, this is so I can record temperatures and keep track of when they occur. People usually use an external, battery powered clock for this, but it is possible to make the Aruduino keep track of time and date after taking a time signal from a PC to start it off. I spent a long time looking up how to do this (it's here, if you're interested), then this afternoon our electricity kept flicking on and off, reminding me why the external clock's a good idea. I guess I'll be getting one of those then. That means more soldering. Hmph.
So there we are, nearly finished. The only remaining job that's going to make a difference to the effectiveness of the panels is adding insulation, and I'm well on the way with that. All I need now is some sunshine.
* I spent far too long considering what kind of antifreeze to use. Our system has the unusual feature of two walls of copper between the solar loop and the drinking water. This means I'm not constrained to use non-toxic antifreeze (if you have only one wall of copper separating them, you should use propylene glycol, which is food safe, in case there's a leak. Otherwise you might end up poisoning your drinking water), so could consider other alternatives. Methanol has a low freezing point, low viscosity, and an even higher specific heat capacity than water. It would be absolutely ideal if it weren't for - and I found this fact very frustrating - its tendency to evaporate, filling the space with poisonous, explosive gas. I settled for car antifreeze in the end, which is pretty much where I started from.