Solar Panel - anti freeze

[rikki]

I'm building a solar collector to heat my DHW. It's sited on a roof over my outhouse and has monotonic increasing 28mm pipework up to a cylinder on the first floor (i.e. it will gravity feed). The cylinder is 350 litres with a coil at the bottom for the solar circuit, and a second coil halfway up connected to the boiler. The collector has 8mm risers soldered onto copper sheet and painted black, under a glass surface. There is an aluminium venetian blind between the glass and the copper plates that can be used to regulate the system in very hot summers.

The two main problems with this type of system are

1. Too much heat. In greece this summer I noticed that virtually every house has a 1m^2 collector, but then they get plenty of sun all the time. To make a system viable in the UK you need 6 m^2 for spring and autumn. To overcome this I've put the venetian blind in so that I can "shut-off" half the collector in the summer. It's also why I've installed such a large DHW cylinder.

2. Freezing. If we get a one-in-50-year winter I can drain down the collector to protect it from deep freezing and bursting all the pipes, but for normal winter conditions the friendly people at CAT and Greenpeace say "use antifreeze". Does anyone know how much I should use? I've tried mixing some CH protector fluid 1:10 with water and putting it in the deep freeze over night, but it froze! Would brine work - or would that be too corrosive?

 

[Biggles..]

The glycol mix for solar systems usually comes premixed but can be done seperate, if mixing seperate you need a refractometer to check the glycol content. Also you need to check the ph and the viscosity. Easier to buy premade solution.

 

[rikki]

I've been looking at motor antifreeze - goes down to -59. I've calculated the volume of my solar circuit (incl. header tank) at 10 litres so I was going to buy a 5 litre bottle from Halfords and be done.

 

[billington]

you can order solar panel antifreeze at plumb centre outlets

 

[micky p]

yeah Glycol is your one.

 

[Birmingham_Spanner]

I went to Viesmann last week for a look at their solar heating product and they sressed very strongly that teh cylinder should be lower than the collector. Theirs is a pumped system but might be worth considering.

The glycol in their systems is supplied ready mixed to add when commissioning and i'm sure you can buy at plumb centre as already said.

I guess another advantage of a pumped system is that the pump can be activated in severe weather to reduce the likelihood of freezing.

Your venetian blinds sound like a fantastic idea. I hadn't realised util last week that the collectors will flash to steam and "stagnate" meaning that you have to wait until they have cooled (over night) until they can be operated again. The blinds may cure this. Better get the idea patented quick!!!

I can't quite see how a gravity fed system will work as the Viessman gear comes with a load of restrictive non-return valves and an expansion vessel with pressure relief valve etc. I guess you have done your home work though, I would love to hear of how it operates once you have it up and running.

 

[Paul Barker]

I would pump it. Crikey there are so many perfectly good Grundfoses litering my garden. I'm such a steptoe.

 

[Paul Barker]

My uncle, who I love, but man is he eccentric, once had an idea to collect the suns rays with a large reflector which tracks the position of the sun in the sky and conscentrates the energy. This was long before people had satalite dishes which track satelites. In the days of modern electronics it should be easy enough to track the sun. You could point the concsentrated energy at a boiler heat exchanger.

In other words do you really need a 1:1 surface area collector? Can you not focus the heat with reflectors into a smaller area and use a more efficient collector?

Anyone with some land could build an aray, thermister sensers would switch the hydraulics to the collector/s which are drawing the most heat. Or use one which moves, using thermisters to sense point of greatest heat and an old XT or similar computer to proces the information and continually move the dish to track the rays.

Amaising the manufacturers are still farting about with single point panels, they really need to get better at collectingh renewable energy if it is ever going to be viable.

 

[micky p]

My uncle, who I love, but man is he eccentric, once had an idea to collect the suns rays with a large reflector which tracks the position of the sun in the sky and conscentrates the energy. This was long before people had satalite dishes which track satelites. In the days of modern electronics it should be easy enough to track the sun. You could point the concsentrated energy at a boiler heat exchanger.

In other words do you really need a 1:1 surface area collector? Can you not focus the heat with reflectors into a smaller area and use a more efficient collector?

Anyone with some land could build an aray, thermister sensers would switch the hydraulics to the collector/s which are drawing the most heat. Or use one which moves, using thermisters to sense point of greatest heat and an old XT or similar computer to proces the information and continually move the dish to track the rays.

Amaising the manufacturers are still farting about with single point panels, they really need to get better at collectingh renewable energy if it is ever going to be viable.

This is one of the reason why they designed the vacuum tube collectors as they have more tolerance with the angle and trajectory.

 

[sm1thson]

This is one of the reason why they designed the vacuum tube collectors as they have more tolerance with the angle and trajectory.

-and a lot smaller with less to go wrong! (than a sun tracking system)

 

[rikki]

The sun-tracking systems have been around for a century or so, and worked on clockwork. There's a huge one in Switzerland (I think) that can focus so much energy at a point that it reaches temperatures hotter than any furnace on earth.

 

[rikki]

My main reason for wanting a gravity feed system is that it removes the need for all the sensors. If the collector is above the cylinder then you need sensors to tell when the water in the collector is hotter than in the cylinder. Then you need a pump (and power for the pump). My system needs no sensors since the gravity feed will ONLY work when the water in the collector is hotter, and it doesn't need a pump.

 

[micky p]

My main reason for wanting a gravity feed system is that it removes the need for all the sensors. If the collector is above the cylinder then you need sensors to tell when the water in the collector is hotter than in the cylinder. Then you need a pump (and power for the pump). My system needs no sensors since the gravity feed will ONLY work when the water in the collector is hotter, and it doesn't need a pump.

yeah but how do you control it when the cylinder is upto temp? What happens when the panels flash to steam you will have seriously hot water.

Viessmann have been desgining solar heat systems for approx 25 years and IMO there desgin is the best. Sealed system with panels above the cyclinder so when they flash to steam the steam cannot get down to the cyclinder and cause damage. (Unless you use there Vitosol 300 tubes which have a safety shut off valve on them at 140 deg C)

i can understand what you are trying but i think it needs to be pumped. the amount of energy you are saving will be far more than what a low energy pump will use.

If fact Viessmann say there new control unit can modulate the pump according to the temp of the panels allowing it to slow down the flow rate so that it has a better chance of picking the heat up. Quite clever i thought.

 

[rikki]

It sounds like they've got a really good system. My solutions to having too much heat are:

a) a really large cylinder (350 litre) so that it can store a lot of energy.

b) a venetian blind over half the collector so that in hot months (June, July, August) I can reduce the size of the collector; and

c) a header tank + vent so that if the panels boil there is an escape for the steam, and a refill (on a separate pipe).

On (b) above, I am having 6 square meters of collector, which should be about right for Spring and Autumn, and being reduced to 3 in summer.

 

[billy bob]

The design of a Viessmann system is no different to all the other reputable solar manufacturers, Schuco, Wolf, Genersys all work the same way as the Viessmann, it is common practice, it is not something Viessmann designed