Solar Panel - anti freeze

[croydoncorgi]

Don't forget there are TWO distinct types of solar system: pressurised and drainback.

Sounds like yours will have to be presurised because there's no practical way of draining it back with the panels set low. (The idea of drainback is that the panels stay empty except when actually generating heat. That way, there's reduced risk of overheating and freezing. That's over-simplifying it but you'll get the idea.)

A pressurised system keeps fluid in the panels all the time but depending on the design, may need to be pressurised to PREVENT the fluid in the panels from boiling OR assumes that boiling WILL occur and can withstand the pressure when it does.

Having a system that is designed to vent automatically when it boils sounds like a recipe for disaster! What happens when (not if!) the vent gets blocked shut? Bang, probably. What happens when the vent jams open? Do you like paddling in glycol?

 

[ChrisRoberts]

What type of solder are U using? I've been to job where the solder has melted/failed. We use the flexible stainless. It's prelagged it's expensive but worth it.
Why don't U look on ebay. there is kits on there for about 700 quid.

 

[rikki]

I've looked at drain back systems and they seem very sensible for roof-top fixtures that are above the cylinder, but again they need all the electronics that can go wrong.

My system isn't presurised - it's like an (old fashioned) open vented system. I am hoping that I haven't oversized my collector, so that it won't regularly come to a boil, but it may well turn out to be unworkable because it boils too easily in the summer.

The problem with the solder failing sounds bad. I was assuming that being filled with water would keep the system below 110, but maybe that's not the case.

 

[ChrisRoberts]

My system regulary peaks at 180C. Look at getting some of the flexible stainless steele pipe work, this stuff comes prelagged and is the best.

 

[Biggles..]

As a rough guide the solar collector should be sized at 1square meter for every 50litres of hot water.The longer the pipework from the cylinder to the panel the better for minimizing stagnation.
For soldered joints either braze them or if you are not able to compression fittings will be just fine.
For lagging use armaflex, its what most MI recommend as itis rated at 150deg.

 

[dave93]

Rikki, if still around would be fascinating to hear how you have gone on with this - if indeed your blind system did prevent boiling in the summer.

Is a solar system with a vent much more dangerous than with a conventional boiler in an unvented system - the vent could get blocked and the boiler thermostat could fail (maybe modenr boilers have so many backups solar has none in some cases)??

I suppose there should be some consideration in the antifreeze about toxicity just in case the heat exchanger corrodes? So I think car antifreze (ethylene glycol) is a really bad idea - propylene glycol used in most solar apps is not so bad but still nasty (and what about all the anitcorrosives used in normal systems)?
_________________________________
Lynda, modertor

Riki stopped posting in January.
Also please read forum rule 20

 

[Agile]

There are a few misconceptions going on here! Or were as this thread is about 9 months old!

Firstly and the most obvious, motor antifreeze is ethanol but this degrades if its overheated.

Solar systems use propanol which is much better.

This system seems to have no protection against stagnation apart from boiling off the system water. Thats NOT normal solar practice !!!

Only compression or brazed pipe joints should be used on solar as the temperatures reached can melt the solder.

Anyone can fit solar systems at the moment and when they do so then these problems can arise.

Tony

 

[dave93]

this thread is about 9 months old!

It was my fault! I just search for what I'm looking for and ask on that thread. In a way that is a better system than asking some of the same questions on a new thread isn't it? But Rikki has probably gone - I just would have been interested to find out how he got on - wish people woudl give reports when they've finished as well as when they are posting looking for info ...

There are a few misconceptions going on here . . .
Firstly and the most obvious, motor antifreeze is ethanol but this degrades if its overheated.

I think that this is a dangerous statement. Motor antifreeze is not ethanol. Ethanol is normal "drinking" alcohol and is moderately toxic. Motor antifreeze is (well its main ingredient is) most often ethylene glycol, and it is highly toxic. Sometimes motor antifreeze is propylene glycol, which is used because it is less deadly, although I believe it doesn't perform as well for motor use.

Perhaps the point you wanted to make is that propylene glycol does not degrade when exposed to temperatures likely in a solar system in the same way that ethylene glycol does - of that I don't know off hand, but either way it is a bad idea to use normal car antifreeze in a solar system!

Just wondered about what considerations there were about using chemicals in "primary" pipework in case there was a mixing (I believe propylene glycol is still dangerous in more than small amounts although I have seen one solar company saying that they use "food grade glycol" implying it is safe which I doubt in the amounts present in solar systems)

Agile, what are some correct ways to account for the water "flashing to steam"/stagnating in a gravity solar system, or is it just improper to fit a gravity solar system? Pressurising the system would be one I suppose as already suggested, are there others? Longer pipework as lcgs suggested seems to be just a way of losing heat so the water going into the collector is cooler - and on a par with Rikkis idea of the blind?? (If Riki tested it on a very hot summer day then surely there isn't so much problem is there? If he has a vent then is it dangerous or just inconvenient if there is stagnation?)

I think one of the manufacturer sites I read seemed to suggest that you could install a gravity system without sensors or any valves as it was self regulating in some way, but I can see how it could continue to heat and heat the cylinder to a dangerous state on a really hot sunny day.

(With some electric pumped systems the manfs says they cannot possible be allowed to be without a pump so the pump must be dc and have a battery back up in case of power outage - but then what if the pump dies???!!!)

(Not quite sure the answer is letting only qualified professionals do it as sadly with other jobs in my house in recent years the quality of workmanship is on a rapid downward spiral - it seemed to be better in the days with less regs- the supposedly qualified people have done some horrible things in my house that would not be "normal practice" - well, it is normal sadly - its correct practice we are looking for. And anyway, surely better if a householder (and tradesmen of other trades than the one in question) understands fully the dangers of the systems they are living with and a good way to find out is to build them themselves - i.e. strange how unvented HW cylinders are subject to regs but vented aren't - yet you could turn a vented into unvented if either connected up improperly in the first place, or you damaged/blocked the vent pipe - ok you could say everyting in house has to be regulated but someone could do somethign stupid to electrics/plumbing etc in the course of decorating or just messing around in their house .)