Help and advice please on re-use of solar hot water panels

[RoyInFrance]

Hello, Newbie here but I have some understanding of Solar PV, Solar hot water and Ground/Air source heat exchange and need advice about re-installing a solar Hot water installation at my holiday home in France (I live in the UK).
When the solar hot water system was removed from my Son's House I retained all the panels , Valves, pump and control unit with the hope of using them, instead of just having them thrown away.(No-one was interested in re-installing the system).
There are no local solar companies in France and all others I have spoken to only wish to sell me new systems and are not interested in advising how I can re-use/re-cycle the existing equipment, so I am looking for someone with knowledge to advise me if what I am planning will work and identify any errors in my plan.
The system was very simple, Glycol in the pipes pass through the black lined solar panels and feed into a coil inside the hot water cylinder. The system was sealed (no header tank) and pressurised with an expansion chamber. There were two temperature sensors and if the temperature in the panels was greater than in the hot water cylinder the pump started and the glycol moved through the system thereby transferring the heat into the hot water cylinder.
My house is in the south of France at 500 metres altitude and is very rural with only wood burning fires for heating. Currently, the hot water is heated by an electric immersion overnight to use cheaper rate electricity. In summer temperatures often reach 30C but in winter can go well below freezing.
We are mostly there in the good weather and rarely during the winter, I would not want to drain and refill the Solar Glycol system each visit so this system needs to be able to cope with both extremes unattended. We may visit more during winter when the Flue boiler and radiator system is added.
Attached is a brief diagram of the planned system.
Thank you

[J.P.M.]

Given what you describe of your situation and location, for all the complexity and age of the current system, unless you're into solar domestic water heating as a hobby that will turn into a part time job for (re)install/upkeep/maint., I'd think about scrapping the current system for the value of the copper and replacing it with a batch heater - simpler, easier for DIY and so maybe making DIY more appropriate - or a purchased batch system for more money (but still simpler).

Solar water heating is not rocket science. While indirect flat plate systems of the type you describe are workable, in spite of what you may think, they're often more complicated than necessary for the task at hand. They're usually overkill in terms of design that, depending on the application, can easily violate the KISS principle.

lMO, indirect systems like you have are overkill for the task and situation you describe, and unless you know what you're doing, reinstalling it will wind up wasting more energy than it produces.

While not suitable for every application, if you drain a batch heater for times then you're not around like in the winter, it may well be pretty much fit for purpose and mostly maintenance free while being rather easy to construct.

The performance of batch heaters in terms of output m^2 of effective area is similar to more complicated systems for a whole lot less hassle and expense.

Determine your loads, look at a website called builditsolar.com for ideas and scope the net for papers/nomographs/books on solar batch heating. For DIY, I'd look at investigating the type of batch heater that's little more than a 150l to 300l tank painted flat black and placed inside an insulated and foil lined box with a moveable top and front with glazing on the equator facing side and top.

Skill level requires simple carpentry and plumbing skills. Read/learn the info as described above for education as to a few details.

Having designed and built both (and other) types, my educated guess is that for the application your describe, a direct type DIY batch type tank heater will be easier to construct, less costly in terms of toil and treasure and a whole lot easier to maintain than reinstalling an indirect flat plate system.

Welcome to the neighborhood.

[LucMan]

Looking at your solar design it seems that you want to connect to your radiators for space heating. How many panels do you have?
If I remember correctly the south of France gets lots of sun in the winter and the temps are mild. If you have at least 128 square ft. of panels the system should work for spacing heating in your climate zone.
Your drawing indicates that the solar panels are connected to the center coil in the storage tank, that is incorrect. The solar panels need to be connected to the lowest coil, the center coil would be connected to your radiators. The radiators should be sized for 110 degrees F for your heat loss and constant circulation should be utilized.
No need to drain your glycol except if it starts to break down from overheating, so make sure solar rated glycol is used it is rated for higher temperatures.
Since you already have all the components have at it, it should be a fun project .
My cousin lives in Avignon.

[RoyInFrance]

Thanks for the replies'
J.P.M. First I know nothing about batch heaters but will research those. The copper pipes in the panels does not have much scrap value (all the pipework that used to link everything together has been scrapped) So really the whole project was about recycling instead of throwing away/scrap, but I will look at batch heating if it is low cost.

.LucMan,
The solar system is intended to only heat the hot water, not the radiators and would be mostly effective in the summer when no additional heating is needed in the house, but hot water is. The radiator system would only be in effect in cold weather when the wood burner was working using "wasted" heat in the flue. The wood flue boiler would also heat the hot water on these cold days.
It is a greater concern that on cold days with a little sunshine the pump would remove heat from the hot water cylinder into the panels, but I am not sure if this is a real risk. If it is possible to also have the DC pump controlled by sensors that only allow the glycol to circulate when panels are hotter than cylinder I would like that (but I need the whole solar system to work off mains)
Thanks for the nod about solar rated glycol.
The whole radiator system I will design with the plumber, specifying the flue boiler for the appropriate BTU for hot water and radiators. this is not a problem as he has done this before. It is all the solar stuff that he has no knowledge of.

A question still remains. The radiator system will mostly (not directly next to the flue boiler) use PB or PEX pipe (like Hep2O) . Can I use the same for the glycol filled solar system?

[J.P.M.]

Thanks for the replies'
J.P.M. First I know nothing about batch heaters but will research those. The copper pipes in the panels does not have much scrap value (all the pipework that used to link everything together has been scrapped) So really the whole project was about recycling instead of throwing away/scrap, but I will look at batch heating if it is low cost.

.LucMan,
The solar system is intended to only heat the hot water, not the radiators and would be mostly effective in the summer when no additional heating is needed in the house, but hot water is. The radiator system would only be in effect in cold weather when the wood burner was working using "wasted" heat in the flue. The wood flue boiler would also heat the hot water on these cold days.
It is a greater concern that on cold days with a little sunshine the pump would remove heat from the hot water cylinder into the panels, but I am not sure if this is a real risk. If it is possible to also have the DC pump controlled by sensors that only allow the glycol to circulate when panels are hotter than cylinder I would like that (but I need the whole solar system to work off mains)
Thanks for the nod about solar rated glycol.
The whole radiator system I will design with the plumber, specifying the flue boiler for the appropriate BTU for hot water and radiators. this is not a problem as he has done this before. It is all the solar stuff that he has no knowledge of.

A question still remains. The radiator system will mostly (not directly next to the flue boiler) use PB or PEX pipe (like Hep2O) . Can I use the same for the glycol filled solar system?

Understood.

If you're into DIY/recycling, and as for simplicity for batch type heaters, for mostly non freezing climates, what's often called a breadbox water heater is about as simple as it gets.

Think of constructing an insulated, foil lined box maybe 1m X 1m X 2m (or whatever size you choose, depending on the chosen tank size).

Hinge 2 adjacent long sides of the box and put the hinges on opposite long edges.

Place the box horizontally on its long side with the long axis parallel to the equator so that the top long side and equator facing long side can be opened and act as reflectors (using the insulation foil as reflectors).

Place a (recycled (?) but pressure tested) domestic water tank that's been stripped of its insulation and painted with flat black paint inside the box. Put the outlet connection at a higher elevation than the inlet and plumb through the east and west ends of the box.

Glaze 2 adjacent long sides of the box (the equator facing and top sides) and hinge the wood on those sides so they can be opened during the day to collect more sun.

Keep the lines short and insulated, put a check valve on the inlet and see builditsolar.com for lots of other details, alternate designs and ideas. Just take some of the advice with a grain of caution. There's a lot of good info that the site contains but there's also a lot of redneck engineering that goes on and it's not too well vetted.

I've built a couple of these things and for a mostly non freezing climate they're about as easy to make and about as trouble free as it gets which is probably helpful for the semi isolated situation you seem to be describing. The performance can be surprisingly comparable to closed loop, indirect flat plate systems which are much more complicated, particularly if you're big on reusing materials and using appropriate technology of the kind that (analogously) doesn't use a howitzer to kill flies.

Heating water is a "dumb" application. For a lot of reasons, it doesn't need to be complicated.

[LucMan]

Use a differential controller for the solar pump using line voltage. The differential controller will keep the pump off unless the panels are 10-15 degrees F warmer than the stored hot water, eliminating the possibility of the the pump cooling the storage tank.
Do not use PEX on this system use only copper or corrugated stainless steel. There is a high possibility of reaching stagnation temps and bursting the PEX at high temps with a pressurized system. Some PEX is acceptable if you convert to a drain back system but that would require a knowledgeable solar installer.

[RoyInFrance]

Use a differential controller for the solar pump using line voltage. The differential controller will keep the pump off unless the panels are 10-15 degrees F warmer than the stored hot water, eliminating the possibility of the the pump cooling the storage tank.
Do not use PEX on this system use only copper or corrugated stainless steel. There is a high possibility of reaching stagnation temps and bursting the PEX at high temps with a pressurized system. Some PEX is acceptable if you convert to a drain back system but that would require a knowledgeable solar installer.

Any advice on where to get the differential controller, possibly with pump and solar panel to drive both.

[LucMan]

I can't help you with that , do a search for 220v solar hot water differential controller (Caleffi, Resol), & solar thermal pump. ( Grundfoss or Wilo)

[RoyInFrance]

I can't help you with that , do a search for 220v solar hot water differential controller (Caleffi, Resol), & solar thermal pump. ( Grundfoss or Wilo)

220V ? Surely you mean 12V or am I being stupid. Thanks

[LucMan]

As I stated in a previous reply use a line voltage controller and pump, in France that would be 220v 50hz.

[RoyInFrance]

As I stated in a previous reply use a line voltage controller and pump, in France that would be 220v 50hz.

Apologies Lucman, I did not mean to question the advice. I am trying to keep this solar installation off grid i.e. not connected to mains as there is often interruption to mains power.
If no one is at the property when the mains comes back on the circuit breaker has already been tripped so the power does not return.
I understand that a solar PV panel generates DC which can be converted to AC but this is an additional expense and complication for the DC-AC converter.
Can I just use the DC power directly, or am I being too simplistic?

Perhaps I am solving a problem of over heating, which may not occur.
When no one is at the property I do not need the hot water heated, but does the system NEED to circulate?
During these unattended period If there is high solar activity I am concerned that there is a danger of the glycol in the panels overheating causing damage to the system if it is not circulated removing the heat, Do I need the glycol to circulate whenever the panels get hot?

Thanks again

[J.P.M.]

Apologies Lucman, I did not mean to question the advice. I am trying to keep this solar installation off grid i.e. not connected to mains as there is often interruption to mains power.
If no one is at the property when the mains comes back on the circuit breaker has already been tripped so the power does not return.
I understand that a solar PV panel generates DC which can be converted to AC but this is an additional expense and complication for the DC-AC converter.
Can I just use the DC power directly, or am I being too simplistic?

Perhaps I am solving a problem of over heating, which may not occur.
When no one is at the property I do not need the hot water heated, but does the system NEED to circulate?
During these unattended period If there is high solar activity I am concerned that there is a danger of the glycol in the panels overheating causing damage to the system if it is not circulated removing the heat, Do I need the glycol to circulate whenever the panels get hot?

Thanks again

From what you've described of your situation and goals so far, you're going to be better off with some form of passive solar water heating system of which bread box heaters are one type.

Why all the complication ?

[RoyInFrance]

From what you've described of your situation and goals so far, you're going to be better off with some form of passive solar water heating system of which bread box heaters are one type.

Why all the complication ?

Because I already have most of the equipment panels, pressure gauges, expansion vessels, etc. I even have a couple of 220V pumps .
I only need to buy a new hot water tank and pipework, which would be needed whatever method I choose.
Possibly a solar hot water differential controller which I am discussing with LucMan
Here there are 3 choices
1. If I can keep it all 12V DC I need a PV solar panel, with pump and controller (Independent of mains interruptions)
2. Run it all off mains, use the pump I have and only need the Controller, (could there be problems when no mains?)
3. Just PV panel and pump and it runs when the sun shines. (would there be enough sun to run the pump but not heat the water?)

Which of these is the better option OR not possible OR to be avoided I need the advice from experienced people such as yourselves

P.S. I will however be looking at the bread box heater as a method to warm our above ground pool but that is another project for another time.

Thanks to you both for your advice and comments.

[LucMan]

1. If I can keep it all 12V DC I need a PV solar panel, with pump and controller (Independent of mains interruptions)
2. Run it all off mains, use the pump I have and only need the Controller, (could there be problems when no mains?)
3. Just PV panel and pump and it runs when the sun shines. (would there be enough sun to run the pump but not heat the water?)

Which of these is the better option OR not possible OR to be avoided I need the advice from experienced people such as yourselves

P.S. I will however be looking at the bread box heater as a method to warm our above ground pool but that is another project for another time.

Thanks to you both for your advice and comments.

1- You can run off 12v PV with a solar panel and 12v dc pump = no control when the sun hits the panel the pump will start to run slowly reaching full speed when full sun hits the panel. This usually works for 1 small 32sq.ft serpentine panel or evacuated tube system. If you have flat plate standard header and tube panel or multiple panels it would be hard to find a dc pump to give you sufficient g.p.m flow rate to make this work.

2- This in my opinion is the most desirable option. If power is lost the panels may stagnate but that should not be a problem if the expansion tank is sized properly. The controller will just resume when the power comes back on, no reset required.
Or convert to a drain back system. This is the only type system that I install because of it's simplicity, no glycol, no expansion tank. Search for solar drain back system .

3- See #1

[J.P.M.]

Because I already have most of the equipment panels, pressure gauges, expansion vessels, etc. I even have a couple of 220V pumps .
I only need to buy a new hot water tank and pipework, which would be needed whatever method I choose.
Possibly a solar hot water differential controller which I am discussing with LucMan
Here there are 3 choices
1. If I can keep it all 12V DC I need a PV solar panel, with pump and controller (Independent of mains interruptions)
2. Run it all off mains, use the pump I have and only need the Controller, (could there be problems when no mains?)
3. Just PV panel and pump and it runs when the sun shines. (would there be enough sun to run the pump but not heat the water?)

Which of these is the better option OR not possible OR to be avoided I need the advice from experienced people such as yourselves

P.S. I will however be looking at the bread box heater as a method to warm our above ground pool but that is another project for another time.

Thanks to you both for your advice and comments.

You're most welcome. As for pool heating, don't use a batch heater. Doing so is is an ineffective use of the technology.
The most technologically appropriate way to heat most any reasonably sized swimming pool in a mild, sunny climate is to use an effective pool cover. For added heat if the pool cover doesn't keep the water adequately warm, use flat plate pool heaters made for the purpose for the final boost, but start with an effective pool cover.