We have a new set-up of 2 x 30 x 58mm solar thermal panels, a log boiler and a 2000 litre akvaterm solar plus tank. The house is as yet unoccupied so no hot water is being drawn from the tank.
The problem is that we do not appear to be capturing any worthwhile heat from the panels. The tank temperature was around 30C from a trial burn of the boiler. The panels were connected up and in a week of mostly sunny south coast weather the temperature has only risen to 32C.
When the sun is shining, if I go into the loft immediately below the panels and feel the flow and return pipes they are warn to the touch, but certainly not too hot to touch, and the temperature difference between them is marginal. Looking at the controller, the sensor at the panels will be indicating between 80C and 115C but the flow leaving the panels is only hand hot.
Clearly I can see that if the temperature going into the coil is not much more than 32C, then the tank itself is never going to get above that temperature.
I realise that with such a big tank it could easily take 2 weeks of sun to heat it up, but nothing is happening.
Any ideas gratefully received, thank you.
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Comments
When you say do you mean flat panels or tubes? i.e. 60 58mm diameter tubes.
You can roughly work out what you would expect to happen from the W/m^2 [input] x m^2 [panel area).
To get the W/m^2 input hunt around on Weather Underground for a local weather station that has a proper solar meter.
But I suspect that the controller is not talking to the pump from your description.
Check that there are no valves turned off (on some pump stations the pressure gauges are actually valves/taps and need to be turned open/vertical).
Does the pump station/controller display indicate that the pump should be on?
Have you tried using the pump station/controller's manual mode to operate the pump manually?
Is power getting to the pump?
Are the pipes filled with water and at the right pressure? Sometimes a large air lock can prevent pumping.
http://www.navitron.org.uk/store/solar-panels-hot-water/water-heating/evacuated-tube-panels/sfb-al-slimline-30-tube-58mm-solar-panel
Say 1 kW from each of the panels in good but not perfect conditions. Tank heat capacity ~= 8 MJ/K so 0.00025 °C/s or 0.9 °C/h or a couple of degrees per day at this time of year.
In normal operation the flow from the panels should be only a bit warmer than the tank contents - the panels should only raise the temperature of the fluid by a few degrees (maybe 10°C or so) on each pass.
If the panel temperature sensor is right (does it drop in cloudy weather and at night?) then it sounds like there's no flow. I'd agree with crosbie that it could be something to do with the programmer settings but it's more likely an airlock. Can you feel/hear the pump running?
The pump is working, insofar as I can hear it cut in and out and the controller display shows it switching on and off. It cuts in at around 55C panel sensor temperature.
Yes, there are 60 x 58mm tubes.
The plumber has filled the system with water/glycol and he seems to think it is all operating OK, his explanation being that even if the panels indicate over 100C, the fact that water is circulating means that it will knock that temperature right down. After a whole week of sun and without drawing any hot water and barely a rise in tank temperature, I disagree with him.
This has been going on for longer than a week, but a week ago because the insulation on the pipes between the panels had melted and the panel temperature was 155C, I asked him to investigate and he released an airlock, which has stopped the panels getting that hot, but in my view has not fixed all the problems.
I have done a few calculations of what I would expect in terms of energy capture and it seems to me that 10 sunny days at this time of the year should take the tank from 10C to 80C, give or take. 2C in 6 days, even allowing for losses, must be wrong.
And clearly to get the tank to high temperature, the flow must be high temperature and it isn't, even at midday with clear skies.
The supply from the panels should be close to the panel temperature, e.g. 90C, if the panels are 95C. So, if the pump has been pumping and the input to the solar coil (I assume you're using the coils fitted to the Solar Plus) is still 30C, then either a valve is closed or you have an airlock (or insufficient fluid).
Sure, the return temp will be something like 31C, but the supply should burn your hand.
Forget calculations. It sounds like there's a far bigger problem than mere economics. You have no flow.
If all else fails get at the top of the panels when it is cloudy and with helper inside let a slug of water out by partly undoing panel unions
At 155 °C the absolute pressure of steam would be 5.5 bar
http://www.engineeringtoolbox.com/saturated-steam-properties-d_457.html
so the gauge pressure (above atmospheric) would be 4.5 bar. A typical solar thermal system has a pressure relief valve set to 3.5 bar, I think.
A friend's flat-plate system which was installed by an incompetent plumber [¹] with plastic pipes right to the panels blew (pipes burst spraying out super-hot water - luckily nobody was in the way) at, IIRC, 130 °C and 3 bar while he had the electrics switched off to work on something else on a sunny summer's day.
As an experiment I put one of my tubes out in bright sunshine with the top of the heat pipe wrapped in insulation (an old work glove and some scraps of mineral wool then wrapped in a black plastic bin liner to prevent wind cooling). The top of the heat pipe got to 195 °C so 155 °C sounds quite a likely temperature for the manifold on a bright spring day with no cooling whatsoever. 195 °C discoloured the plastic bung which fits the heat pipe into the tube. I'd not recommend leaving this system in this state for too long if you can possibly avoid it even at the cost of getting a new plumber.
[¹] I was present for the first installation attempt but they had the wrong fittings for landscape/portrait so I didn't see the plastic pipes used when it was eventually installed otherwise I'd have said something.
Ed, Yes, I am sure that all that was left was steam and glycol, but since then the plumber refilled the system and that seems to be keeping the temp down to a max of 120C at the panels, but I don't know where the heat is going - not into the tank!
Yes I have the solar Plus system.
Presumably, at the moment, your circuit pressure gauge reads 0 bar when there's no sun?
Here's a suggestion for next steps:
0) Get your money back. :-)
1) Do a visual search for leaks, e.g. wet joints.
2) If no visible leaks, do a fluid pressure/leak test (night time).
3) Consider fitting a Spirovent - automatic air bleeder.
4) As owlman suggested, do the commissioning process (use pure water until the problem is sorted).
5) Manually operate pump. Check for flow.
6) Once you've assured that flow occurs, double-check the controller's programming.
7) Establish that during sunny weather, hot panel water is pumped and arrives hot at the coil input to a cool store.
8) Add glycol.
9) Monitor solar circuit pressure over following weeks, ensuring it does not significantly drop below required level.
In order to trace the fault here are a few questions:
1. What type of pipework does your system have from the collector to the pump station.
2. What type of fittings are used with that pipework?
3. Does your pump station have an AAV (automatic air vent) fitted? many do.
The pipework is all copper with brass fittings.
Not sure about the automatic vent, but just been out there now, on what is probably the hottest, sunniest day we have had so far (my 5.25kWp PV is chucking out a steady 4.8kW) and the temp reading from the tank has edged up a few degrees, BUT there are rather alarming loud cracking/banging noises emanating from the roof. Could that also indicate some air and is it likely to do damage. I can't get the plumber on site until Wednesday.
I guess it's not a convenient option to cover the panels with an opaque (preferably reflective) blanket of some sort? It might be if you had a velux near the panels?
Is there a pressure relief valve (and an expansion vessel) in the circuit?
I trust such a thing isn't currently disabled (if a valve is incorrectly shut - which may also be preventing normal flow).
There can be some expansion/creaking noises, but in normal operation they're fairly gentle and you'd have to be in the roof to hear them. Sounds like your noises are somewhat severe, and your alarm is probably warranted.
Unless you know exactly what you are doing, it may be safest not to visit the loft and investigate until the sun's gone down.
Presumably though, your solar controller/pump station is not in the loft and is accessible, probably near the heat store?
Hopefully you can read the circuit pressure and panel temperature?
If you have it built into the pump station, (look at the instructions), it may be called "air stop" and it'll look like a 3 or4" brass cylinder with a few extra bits sticking out.
Failing that do as crosbie said, and fit something like a Spirovent or other good quality air eliminator/separator. They often come with bleed nuts and can be placed somewhere on the system that's more convenient, rather than on the roof.
The system may be sucking in air through the compression fittings so you'll need to check that. My check list would be:
1. drain system and reserve the glycol.
2. fit AAV if not fitted
3. fill with water pressurise, and check for leaks
4. drain and refill with glycol and re commission.
Due to the noises I called the plumber who came and topped up the system.
It would seem that as you rightly say there is a small leak and air is getting in.
Hopefully we can now get it working properly
Thanks again
The plumber should visit the system during the next sunny day and check it's operating correctly. Did they not do this after commissioning the system the first time?
They should also let you know how to monitor the circuit pressure (assuming it's a closed circuit) to nip in the bud anything like this problem happening again.
It is on the boiler room wall, about 5 feet above the ground and with the little vent pointing downwards. Having looked online, it would seem that it should be mounted in a horizontal pipe run, not a vertical one and that it should be higher up in the system - even between the panels. Is this correct?
Thus you get the model appropriate to your pipe run, whether horizontal or vertical.
As I understand it, it should be mounted on the hot/output side of the panels, which should be the highest point in the system - where air tends to rise to (and cause airlocks).
It may also function elsewhere in the circuit, but may not be quite so effective.
In my case, the output from the panels rises slightly into my loft and it is there where my Spirovent is. And I must say it is very effective - when I fill the panels I have only a tiny pocket of air at the manual vent on the other upper panel.
The pump doesn't necessarily have to be advertised as variable speed, given controllers can effectively vary a pump's speed by modifying the voltage that goes to it - a bit like dimmer controls for lights, but specially designed to be kind to pumps.
You can get special 'high efficiency' pumps with special speed control inputs that some controllers can output to, but they are more expensive.
The auto air valve is a waste of time anywhere except high up in the system even then there need to bleed valves at the top of the panels though with mains pressurised full flow filling these are sometimes get away without.
Simply recharging the pressure does not mean that system is full of water, there can still be an air pocket (and probably is above the air vent, I fact there must be unless it is being full flow filled.
Get some in who understands how to fill a solar hot water system.
The problem is akin to having upstairs rads with no bleede screws on them!
Spirovents cannot ameliorate leaks. Even if a Spirovent is at the top of the system it can't prevent an airlock if the circuit isn't pressurised. It can only let air out (but not steam) if there's pressure to push it out, and the air actually goes past the Spirovent, i.e. there isn't an airlock higher up that prevents circulation past the Spirovent. So, if there's a leak somewhere, you'll still get an airlock. The Spirovent is there to make filling easy, and to eliminate the small amount of air that will come out of solution over time, during operation, which would otherwise cause noises/mini-airtraps.
I look forward to hearing Aviatrix tell us:
1) His plumber has demonstrated circulation occurs (by flow meter, or temperature change).
2) Circulation occurs automatically when the panels are significantly hotter than the bottom of the store.
3) The leak has been found and rectified.
4) The location and orientation of the Spirovent has been remedied.
5) The circuit pressure (>1 bar) is consistent every day (early morning or late evening) for at least a month.
6) The heatstore is heating up nicely, and has anyone got any suggestions for heat dumps? ;-)
http://alphathermalsystems.com/media/catalog/product/pdf/2010_ATS_SolarStation_FlowCon_FA.pdf
The Spirovent air eliminators are also good, I have one on my CH system.
http://www.spirotherm.com/sites/default/files/Solar-1_0.pdf
But as we've pointed out the leak needs fixing first.