Solar Panels loosing pressure

dennigerz

Hi, i had solar panels installed in my new build three years ago, but i constantly find myself having to top them up, because the pressure keeps dropping. When i top them up to 2.5bar on the pressure gauge in the morning i have to top them up again that night because they have dropped to 1 bar. Is this normal or have i a problem. I cannot see any visible leaks, but could a leak be the problem. Thanks

dathi

does your system have an outomatic air vent if it has it might not be solar rated and could be leaking due to high tempeteratures

dennigerz

Hi dathi, sorry for being thick on the matter, but what do you mean by automatic air vent? Thanks for reply

Micky Dolenz

You have a leak somewhere. as suggest check the aav, it may be fitted near the highest point, in attic.

dathi

as micky says look in attic should be a cylinder about 1.5 inches in diameter with a small nipple on the top with a screw cap if not you might have a leak out on roof where you cant see it. out of intrest have you tubes or flat plates and how are you re filling the system

RavenII

your expansion vessel may not have any, or enough air in it...when the fluid heats up it expands; a small discharge at the safety valve may have gone un-noticed. When it cools down the pressure has dropped off. Could also be the auto-air vent or a small leak of course!

Paragon Energy

Does this only happen on hot days or does it happen everyday without fail? If it only happens on hot days, it could well be a problem such as an expansion vessel failure and the system is releasing pressure via the pressure relief valve. You can check this by checking for glycol discharge from the PRV, usually piped from adjacent to the pressure guage.

Also how are you building the pressure back up with a pumping station? If the system is fed by feed pipe from a cold water supply valve, this is dangerous and against regulations. If this is so, I presume it has a non-return valve on it, but these can fail and you will have glycol flowing back into your water circuit.

You are best to have a solar engineer inspect the system.

heinbloed

Another question would be "who told the owner or installer that the pressure must be 3 bar?"
That the expansion vessels are delivered to be used with a difference of 30 meter hight between collector and vessel (continental conditions) doesn't mean the pressure of 3 bar is correct when used in a two floor home.

The higher the pressure the higher the stress on the entire system.
Plenty of jobs to be done .......but that was the intention of the subsidies, creating jobs.....

A closed ST system does not need to be pressurised at the highest point with more then 0.1 bar. To be on the safe side - the meassuring devices can be crude - bring it to 0.2 or 0.3 bar. But not more.

That the car tires are guaranteed to 10 bar doesn't mean that a driver with his marbels in the right place would actually pump them up to 10 bar....

Ask your installers why they're doing this, overpressurising the systems.

And filling up the pressure vessel/expansion vessel should only be done with nitrogene gas. Not with plain air. Air will diffuse through the membrane, gets into the closed system and will be discharged at the air valve. A rat race.

Paragon Energy

heinbloed wrote: »

Another question would be "who told the owner or installer that the pressure must be 3 bar?"
That the expansion vessels are delivered to be used with a difference of 30 meter hight between collector and vessel (continental conditions) doesn't mean the pressure of 3 bar is correct when used in a two floor home.

The higher the pressure the higher the stress on the entire system.
Plenty of jobs to be done .......but that was the intention of the subsidies, creating jobs.....

A closed ST system does not need to be pressurised at the highest point with more then 0.1 bar. To be on the safe side - the meassuring devices can be crude - bring it to 0.2 or 0.3 bar. But not more.

Very true.
Solar circuit pressure should be calculated individually for each installation and most are over pressurized. System pressure calculations should be on the basis of 1 bar plus 0.1 bar for every meter of head height from pumping station to top of solar collector, and the expansion vessel pressure should be set to 0.3 bar below the system pressure. This is to attract the pressure to release back to the PRV in case of a failure within the system whereas the expansion vessel is usually located close to the PRV.

Micky Dolenz

But surely on a pressurised system, pressure is equal across the entire system so location of PRV would be moot?

Paragon Energy

Micky Dolenz wrote: »

But surely on a pressurised system, pressure is equal across the entire system so location of PRV would be moot?

Pressure is equal across the system however, if there is a failure, you will want the pressure to release at the PRV. The pressure will be attracted to the weakest point first, i.e. the expansion vessel as this has the capacity to flex. This is also why it should be set to slightly lower pressure than system pressure. Most manifolds have the PRV built into them and the vessel is teed from this point. Should there be a failure within the system and usually this occurs due to the expansion vessel being either undersized or system pressure + expansion when hot is too great for vessel or PRV or indeed a failure within the vessel itself, the attraction is to PRV and not to another weak point in the system or at the opposite end of the system. If they are close to each other, the failure will go to the next weakest point, i.e. the PRV, usually at 6 bar pressure.
In my experience, these are the only times that I have seen the PRV blow off glycol.
Actually, I have seen other ones, where the glycol has been diluted so much that the boiling point has been lowered to 100C and therefore released by too much expansion. Incorrect sizing of solar circuit pipework can also cause this problem.

heinbloed

I have to correct the two previous posters. The pressure in a vertical, closed system is higher at the bottom and lower at the top.
The weight of the water's mass has to added.
A sample: if a closed system has between it's highest and lowest point 10 meters of height difference the pressure difference between the two points would be 1 bar. No matter how much additional pressure would be added to the system by the installer: the difference would be always 1 bar.

There is absolutly no need to pressurise a closed ST system to more then 0.1 bar when meassured at the highest point.

If using glycol in the system the water would boil at a much lower temperature than the glycol, note the boiling point as stated by the manufacturer.

Pressurising the system to an absurd pressure of 3 bar would NOT increase the guaranteed temperature to which the glycol is stable. But would increase the operating temperature of the system, putting the stability of the glycol at risk !

In a closed system the pressure should be low enough to allowe the water to evaporate (to steam-back) before the glycol gets towards it's critical temperature.

The highest temperarture is only seen at the thermal source, the solar collector. Therefore the pressure there should be as low as possible. To allow the water steam fraction to push back the liquid glycol/water fraction. Before it runs into the hot collector.
This is what solar installers call a "steam-back", the self securing mechanism of the system.
A steam bubble in the collector will save the anti-freeze from being demaged by heat. By hindering the liquid glycol/ water mixture to enter the collector in the first place.

"Keep away from naked flames" it says on the jerry can. On the glycol can it says: "keep away from high temperatures".

Plain knowledge on the continent. Well, here as well, the moonshiners (destillers) know that as well. But in the solar trade here we see most closed systems installed by amateurs who take it for granted that the pressure in the cold collector must be the same as in the delivered, new expansion vessel.
Which is fit for 10 storeys plus roof and basement, 3 bar and more of nitrogene filled in by the manufacturer.

So these amateurs pressurise the systems they install to 3 bar.
And have a job guaranteed for a lifetime. Unless someone informs the authorities/consumer organisations about this faulty and wrong practice....

Micky Dolenz

Good post, makes sense.

Paragon Energy

What a load of waffle!

That is absolute nonsense. So what you are saying is that the pressure at the pump station (should that be the location of the pressure guage is) should be in or around 0.1 to 0.2 bar pressure. Low pressure = low efficiency as then there is a lower the rate of transfer of heat and the higher the pressure the higher the rate of transfer of heat is.

Manufacturers (with teams of engineers) go to great lengths and costs of calculating and testing different system pressures in relation to their particular product. If there is a poor performance achieved from their calculations, then this will reflect on the overall sales, which is ultimately what they are after, God forbid they should make a profit! If a manufacturer informs me to calculate the pressure of the system in the previously mentioned manner, then that is what I will set the system to and so should everyone else. I will do so until you can prove that you know more than all the various manufacturers out there and the manufacturers bow to your greatness and advise me accordingly.

I thought this website was a forum for people who needed a bit of advice and could obtain it for free. DENNIGERZ had a problem with system pressure, which without seeing the installation, various people offered advice to what could be the potential problem. You however, seem to go into a waffle about low pressure systems, that I have never come across, apart from Drain-Back systems which are not pressurized at all. So what you are advising to the general reader is to lower pressure in all systems and go against manufacturers' recommendations. This can invalidate any warranty that maybe in place.

Good luck and thanks.

heinbloed

Paragon Energy wrote:

What a load of waffle!

That is absolute nonsense. So what you are saying is that the pressure at the pump station (should that be the location of the pressure guage is) should be in or around 0.1 to 0.2 bar pressure.

Nowhere did I or anyone else say that.

The cream on the solar installer's waffle is literacy and a profound understanding of the laws of physics and the economics behind the system.

If an installer listens to the manufacturer of a product only we would never have seen safety belts in our cars. The pressure created by physical impact on human bodies would catapult the insurance premia for car owners high into the sky.
If a ST installer does not know how to interpret the laws of physics then at least he or she could get some literature on the issue.

Check the www. for the term " solar thermal + steam back ".
And then buy some good books to which the web refers as well.


Paragon Energy wrote:

Low pressure = low efficiency as then there is a lower the rate of transfer of heat and the higher the pressure the higher the rate of transfer of heat is.

Now, this is absolutly new to me !

Who says so?

No ST system can harvest more than it recives from the sun. No matter how high the system's pressure is.
But let me know how you build your perpetuum mobiles, I'm all open to this storey (smiley).

The flow rate through the collector should be adjusted to the demanded Delta T Kelvin ( the temperature difference between entrance and exit of the collector). The lower the entrance temperature is in combination with a temperature lift which should be as low as possible (the low Delta T Kelvin !) the more efficient the collector works. Since a low temperature of the fluid guarantees a low thermal loss to the enviroment.
The hotter the collector gets the less efficient it works.

The pressure of the system IN THE COLLECTOR is simply irrelevant to it's efficiency.

Just the opposite could be experienced:

The higher the pressure in the collector the more likely the temperature in it will increase. Going above 100 dgrees Celsius, the boiling point of water,
will cut severly into the efficiency of the ST system.
Because the higher the temperature difference between the collector's content and the enviroment is the less efficient the collector works. See above.

But sure, some

Manufacturers (with teams of engineers) go to great lengths

to tell their installers something different, or don't they ?!

Which manufacturer has told something like this to his installers ?


It seems to me that the OP had an overpressurised ST system installed and no one has told him about the consequences.

Namely that this superfluous pressure will lead to a premature aging of the system.To leaks.

heinbloed

The OP wrote:

Hi dathi, sorry for being thick on the matter, but what do you mean by automatic air vent? Thanks for reply

Automatic air vents are air vents which let out air without someone opening them, without a person ' bleeding ' the system.

You see these vents at your boiler, at your central heating manifold and maybe as well on your radiators.
The old radiator air vents are manual, someone has to use a key or spanner and let out the air which diffuses into the system. These vents cost around €3.- each. The auto-vents (which do their job automatically without a helping hand) cost around twice that much.

At the solar station there should be such a vent. Either a manual one (your installer hasn't told you I think) or an automatic one. But ST vents are exposed to more stress compared to central heating vents, they cost a bit more.

And then there should be at least one more vent, preferable an intelligent automatic vent. At the highest point of the system.
Esp. when running pressurised ST systems an intelligent air valve (or air-vent) is to be prefered. Since these make a difference between steam and air: the glycol/water mixture stays in the system whilest air will be released.

This secondary valve should be installed at the highest point of the system. Since this is the point where air-bubbles will go naturally. And there they can be released.

The highest point of the system is usually (but not always !)
the collector. So if you can't see an air release valve installed there (between the inlet of the collector and the pipe leading towards it) then very likely there is none installed. Your installer saved on €200.- of material and got the job because he was cheaper.
But very likely he didn't even know about this device at all ....otherwise he would have told you that the system needs regular venting ('bleeding') as any closed water circulating system does.

Advising the consumer on the maintenance needed for the system (on any system/device, not just a ST system) is part of the job of selling. If he didn't do so you have a come back, the guarantee time starts only at the completion of the job. And informing the consumer on what maintenance must be done is part of the job. Similar to the check-book coming with a car or the user's manual purchased with a washing machine. As long as these things are not handed over to the consumer the guarantee time doesn't start.