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Solar water heating panel covers

Solar water heating panel covers

Old Nov 15th 2023, 1:27 pm
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Default Solar water heating panel covers

While we were away over the summer our solar water heating system lost all pressure (I guess through overheating although our previous system managed OK)

Managed to get it topped up but looking to prevent it happening again.

I gather fitting solar panel covers while we are away may prevent that pressure loss.

I've seen them advertised in other countries but not Portugal.

Any suggestions?
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Old Nov 15th 2023, 10:37 pm
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Default Re: Solar water heating panel covers

First thing to be sure of is that you have the necessary antifreeze within the solar panels. You can get it from aki. This prevents the water in the panels from boiling! Here is a link
https://www.leroymerlin.pt/produtos/...1.html?src=clk
You need about a 1:4 mix. So if your panels have around 20 litres of liquid you need to have 5 litres antifreeze and 15 litres water.

We bought a proprietary 'solar cover' and it took about 2 years to totally disintegrate in the sun. It was a waste of time. So I did a bit of head scratching and....

What has worked is using artificial grass. This is also available from Aki. It comes in the right width to fit a panel and you can cut the length to match the panel.
https://www.leroymerlin.pt/produtos/...3.html?src=clk

It has proved to be very UV resistant as you might imagine. Get a few metres of good rope from a good hardware shop (not from a chinese shop) like the fishermen use, as that too is very weather resistant. Lay the grass mat (grass up) on the panel, loop the rope over the grass and under the panel several times to secure it. Then when you want to remove the grass mat, loosen off the loops and slip the mat off.
We live right on the coast so we have very significant winds and so far all has been well. I think the total cost for rope and grass was about €30, so not the end of the world if it does blow off and if it did, it is very unlikely to damage anything or anyone.
Hope that helps.



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Old Nov 16th 2023, 7:35 am
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Default Re: Solar water heating panel covers

Originally Posted by fergus
First thing to be sure of is that you have the necessary antifreeze within the solar panels. You can get it from aki. This prevents the water in the panels from boiling! Here is a link
https://www.leroymerlin.pt/produtos/...1.html?src=clk
You need about a 1:4 mix. So if your panels have around 20 litres of liquid you need to have 5 litres antifreeze and 15 litres water..

Isn't that 1:3? A 1:4 mix would be 4 litres antifreeze and 16 litres water..

Last edited by Rosemary; Nov 16th 2023 at 8:18 am. Reason: Corrected quote
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Old Nov 20th 2023, 7:24 am
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Default Re: Solar water heating panel covers

I wouldn't waste your money on the "branded" stuff. It's Ethylene Glycol, anti freeze. Pick up a few of the cheap anti freeze cartons from the supermarket, it's the same stuff. I bought some from Auchan the other week to top up, 5L was 3 euro something. Use it neat at that price too. Never use borehole water if you're not on town water.
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Old Nov 21st 2023, 6:41 pm
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Default Re: Solar water heating panel covers

You are right that it is anti-freeze and there is plenty of cheap stuff around. I do buy the 'branded' stuff as it is 'food grade' which means that should there be some contamination of the hot water by the anti-freeze, it shouldn't kill any of my family. I know the contamination is a very unlikely event and that no one is likely to ever be exposed to enough of it to become seriously ill. But for the sake of €30 a year, I get the 'branded' stuff and sleep easy.
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Old Nov 21st 2023, 7:10 pm
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Default Re: Solar water heating panel covers

How often does the anti-freeze need to be replaced?
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Old Nov 22nd 2023, 7:12 am
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Default Re: Solar water heating panel covers

The food grade antifreeze is a different chemical; glycol is very poisonous.
When you buy glycol (auto antifreeze/ anti corrosive/ anti boil) these days, it comes already mixed; you need to check the label. It's possible to buy stronger mixes, up to 50:50.
If anyone knows where to buy unmixed, I'd like to know.

Regarding replacement times; the glycol lasts forever, it's the anti-corrosion chemicals that need to be replaced when it's in a car engine.
Car engines have all sorts of different metals inside and are very corrosion prone, but solar collectors don't and aren't.

I don't know details on the food grade anti-freeze. That's mostly used on fresh water systems in cold countries when they're not used in winter, like campers and vacation cabins.


I think the idea to use artificial grass is brilliant!
For UV resistance you want nylon rope, not polypropylene. Check the label.
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Old Nov 22nd 2023, 8:20 am
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Default Re: Solar water heating panel covers

I use Blue Wallmate sheets. I dont cover all of both panels, maybe 80% of the glass area. Hold them down with wire (used rope one year, ((destroyed after 3 months of being away).
Did a check before going away (mid summer) and found that at 80% cover the water temp at tap was just above luke warm. Still use same panels after 3 years. Bit of a faff though, even tho panels are on a large flat roof. Dunno what I would do if on a sloping tiled roof as some are. DOnt trust the expansion valve. But the installer said it allows the hot water to recirculate back into the tank and is unlikely to explode !!
Maybe others know just how these work (its normal PT type rather than those used in Spain, which I think are different
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Old Nov 22nd 2023, 1:53 pm
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Default Re: Solar water heating panel covers

In my installation there is an expansion tank which absorbs the regular changes in pressure with no loss of liquid as the panels heat up.

Then there is a presure relief valve which opens to drain if the presuure gets really excessive to prevent the 'explosion risk'

I'm assuming my loss of liquid is from the second but may also be through the air vent at the top of the system when the liquid starts to boil?
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Old Nov 22nd 2023, 9:57 pm
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Default Re: Solar water heating panel covers

I am not an expert so what I am about to say may be wrong. If it is I am sure someone will let you know.

I believe the air vent is there to allow air to escape from the liquid that is in the panels and heated by the sun. If the liquid was to get sufficiently hot to start to boil, then the valve would also let this heated air out.

When you add liquid to the solar panels, you unscrew this vent completely and feed water into the panels via gravity. You know when the system is full of liquid when it starts to leak out of the smallish hole left by removing the vent. Then you replace the vent and close the 'feed' point on the panels.

The pressure relief valve is for the hot water cylinder. When it vents it is the water in the tank (not the solar panels) that is released, ejecting hot water which is then automatically replaced by the cold water feed. Once the pressure has reduced the valve closes. My experience is that this is more likely to happen when the hot water is not being used, for example when there is no one at the property, but the panels continue to heat the water.

If you cover the panels when you are away then you are unlikely to have this problem.
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Old Nov 23rd 2023, 6:26 am
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Default Re: Solar water heating panel covers

Originally Posted by fergus
I am not an expert so what I am about to say may be wrong. If it is I am sure someone will let you know.

I believe the air vent is there to allow air to escape from the liquid that is in the panels and heated by the sun. If the liquid was to get sufficiently hot to start to boil, then the valve would also let this heated air out.

The pressure relief valve is for the hot water cylinder. When it vents it is the water in the tank (not the solar panels) that is released, ejecting hot water which is then automatically replaced by the cold water feed. Once the pressure has reduced the valve closes. My experience is that this is more likely to happen when the hot water is not being used, for example when there is no one at the property, but the panels continue to heat the water.

If you cover the panels when you are away then you are unlikely to have this problem.
Yes the spring loaded valve on my system would do just that. But one problem as I see it, as my house is left unoccupied for 3 months mid summer (worst time for heating) is that icould never be sure it would actually work !! But even if it did it would put very hot water on the flat roof, which is bitumen and not tiles, and added to that the outlet is not suited to connecting a hose such that it could be directed into a rain water pipe...hence the palava of the panels to cover.
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Old Nov 23rd 2023, 7:31 am
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Default Re: Solar water heating panel covers

My pressure relief valve did allow me to attach a hose. I had thought that it would not but it turned out that it was the right size. There is some hozelock or equivalent fitting (1/4 inch I think) that, on my tank, allowed me to screw it into the valve, leaving the usual hozelock 'male' connection point. So I can easily push the hose pipe on to connect it and when I am there, squeeze sides and release to pop the hose pipe off. The hose pipe has lasted 5+ years in the sun but I expect to need to replace it in the next couple of years. But it was only €20 from lidl. I think it would also be pretty easy to feed the hosepipe into a water butt or similar so that you would have an indication if water had been released whilst you were away.
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Old Nov 23rd 2023, 7:47 am
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Default Re: Solar water heating panel covers

Here are some images of the set up on my system.
Pic 1 being the pressure relief valve that I assumed I would need to attach a pipe to....???
But maybe I should be using the safety outlet in pic 2......??





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Old Nov 23rd 2023, 9:28 am
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Default Re: Solar water heating panel covers

The solar collector (panel) and the tank itself are separate, the liquids never mix. The glycol in the collector gravitates upwards (heat rises), up into the tank above but inside a coil or heat exchanger passing the heat into the surrounding water. As it loses it's heat it cools, dropping out the other side and returning to the bottom corner of the collector (normally the return pipe runs down one side). The glycol level must fill not only the collector but the coil as well otherwise it can't gravitate over the top. Therefore the fill point is always at the top, above the coil. The safety valve here will release at 9 or 10 bar pressure and sometimes 90°C temperature too. If it's boiled over at some point it needs topping up.

The tank itself should also have a safety valve on the hot side which again vents based on temperature and pressure. To prevent boiling the tank, and as someone has already said it gets replaced by cold water from the cold in side.

It's also advisable to install a thermostatic down mix valve on the hot out. This avoids having 89°C water shooting out of your taps in the house and scolding whoever is washing their hands. It connects the hot out of the tank, the cold in, and creates mixed out. You can normally set what you want the maximum output to be, so say 60°C.
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Old Nov 23rd 2023, 2:05 pm
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Default Re: Solar water heating panel covers

On this pic you can just see the thermostat sitting at the top of the system. Installer told me to keep that at MAX !!!!


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