solar - direct or indirect

[JPC]

has anyone here had experience with solar and if so, would a direct solar, like http://www.solartwin.com/ be better that an indirect one, like most on the market, seemingly.

the advantage i see with the direct one is a cylinder swap is not required, hence saving money for the customer

any thoughts

 

[muggles]

Direct is a nasty way of doing it IMHO, here's why:

1) There's virtually no control over hot water tempterature; as long as the pump's running the water will keep heating up on a hot sunny day, even they admit they've seen it get to 87ºC. And you can't switch the pump off because the water in the panels will boil, turn to steam and then all hell will break loose. Proper indirect solar systems use glycol which won't boil, so you can switch the pump off when the cylinder's up to temperature.

2) They pump the water into the top of the cylinder to keep it hot at the top, which is all very well but when you come to draw water off there's a conflict of flow directions. This is overcome by piping the panel in above the drawoff connection, but as it's pumped and not a standard gravity system I can see there's potential issues with it. They also seem to require you to run the open vent, which is combined with the pumped solar bit, vertically off the top of the cylinder, which doesn't comply with modern water regs.

It's also interesting to note that Solartwin have been refused membership to the Solar Trade Association, they have speel on this but read into it what you will...

I'd say get the customer to spend the extra money and have a proper twin-coil indirect system.

 

[Agile]

has anyone here had experience with solar and if so, would a direct solar, like http://www.solartwin.com/ be better that an indirect one, like most on the market, seemingly.

the advantage i see with the direct one is a cylinder swap is not required, hence saving money for the customer

any thoughts

Some people will buy anything.

A quick search comes up with:-

Solartwin incompetent technology!!! said,
March 22, 2008 @ 11:42 pm

I attended BPEC Solar Thermal training in Bedford college. All the instructors telling us, Solartwin is a scamer. Using plastic soft pipe in the circulation loop. something is going to melt badly if the collector does WORK. If NOT melt, then the panel is NOT working.

The flatplate panel they make worse than any flat plate from China. Shame for them to say, made in UK and patent!!!

they even dare to publish the video on youtube.com (see the quality of there system for yourself)
http://youtube.com/watch?v=eIk9oi9WZ-4[/color]

 

[JPC]

a couple of opinions saying its not so good...i can see water getting to hot, good point.
from watching the utube video link from agile..it seems rather expensive at £2000 ( they reckon thats the trade price)

hmmm seems indirect might be better then

any more comments

 

[AMEdinburgh]

Looking on Ebay will give you lots of smaller and more economical companies and their websites for further reading. When I looked, it was going to take a very long time before it would pay for itself and only then if it didn't need any money spent in the interim. However this is based on Scottish weather. Going to go for a new efficient gas boiler, though with gas prices rising too I might revisit the issue and left appropriate pathways for pipes and wires in the build in case.

Also explored the grant and indeed applied successfully for one to find cost to me appeared to inflated mysteriously by the value of the grant compared to me buying and having installed a system, meaning it was of no benefit whatsoever.

 

[Kev F]

im off to do the course at bedford soon so hopefully will be told the same. I thought that on direct cylinders you still had to use chemical as temp can get to over 100 degrees c, am i wrong? was told you have to use chemical all the time

 

[Paul Barker]

no you don't need chemical except to protect from frost if not a drain back system.

Mustn't solder in a drain back it could melt if panel gets hot when pump notactivated or if pump fails..

I plan to make my own flat plate collector and use some (maybe 3) of the cylinders taken out of houses so I have plenty of storage to maximise use of UV when it is available.

Will probably circulate the cylinders' water round panel and pass dhw through the 3 secodary coils (inverted cylinders so coil is at top) at mains pressure if that doesn't warm it sufficiently I'll add a plate a pump and a flow switch.

Use a standard heating pump on slowest speed with a choper circuit to further slow pump speed down by providing interrupted 230v. (pumps prefer rated voltage but don't mind if it is chopped on and off).

 

[oilman]

Try this for an alternative.

 

[Agile]

Mustn't solder in a drain back it could melt if panel gets hot when pump notactivated or if pump fails..

Not exactly, the whole concept os a drain back is that if the panel ow water gets too hot then the water will drain back thus isolating the hot panel from the system inside teh house.

The only problem arises if the pump jams on for some reason and continues to extract heat from the panel with the water has reached boiling point.

I am having a lot of difficulty finding any ready made panels suitable fro drainback.

Tony

 

[Norcon]

This one is interesting.........
http://www.hoval.co.uk/docs/GB/PDFs/SolKit(250,500)may.pdf

Note the use of the sparge pipes to ensure a more even energy transfer and the change over valves from top to lower section.

 

[Agile]

I dont see any prices there and the whole style of the details and designs are for a very expensive product.

For solar to be viable the cost has to come down significantly. panels about £360 inc VAT for example.

Currently solar is severely over priced!

Tony

 

[PDrawmer]

To get the best out of solar, you need to be able to extract as much heat as possible.

The solartwin design takes the output from the panel and pumps it into the hottest part of the storage tank. Since you can only extract energy from the system when the input from the panel is hotter than the storage, this means that their system will only work when the sun is HOT and the water is less than operating temp.

A more conventional solar system will heat the bottom of the cylinder so that in less than ideal conditions solar can still provide benefit by pre-heating the DHW.

In any case most effecient solar systems can make the DHW much hotter than required in conditions of low use and high sun. To take advantage of this, a TMV should be inserted in the DHW take off to prevent scalding, and some sort of heat dump circuit should be incorporated to get rid of excess heat in extreme conditions.

 

[Agile]

In any case most effecient solar systems can make the DHW much hotter than required in conditions of low use and high sun. To take advantage of this, a TMV should be inserted in the DHW take off to prevent scalding, and some sort of heat dump circuit should be incorporated to get rid of excess heat in extreme conditions.

If you had studied solar systems then you would know that the control circuit turns off the pump when the temperature gets too high.

You dont dump solar energy! You just let the panels stagnate.

Tony

 

[PDrawmer]

Sorry, I forgot it was a drain down system.

Still think it's not the best idea.

As an aside, I'm suprised at the number of flat panels being marketed when the evacuated tubes are so much more efficient.

 

[Norcon]

Agile wrote

You dont dump solar energy!

Actually you can !.
A "hybrid" ground source heat pump loop integrated with a solar collector.
So the ground becomes the heat dump and a thermal store in effect.
Some installers supplement the GSHP system with solar thermal collectors which will reduce the required size of the ground loop and increase heat pump efficiency by providing higher building loop temperatures than could be attained by the ground heat exchanger alone.
They didn't teach you that on your solar course.
Thats a high tech method of course. Many utilise simple radiators as heat dumps on solar systems similar to solid fuel heat dumps.

If you had studied solar systems then you would know that the control circuit turns off the pump when the temperature gets too high.

The supplemental solar collector loop includes a photovoltaic (PV) panel for powering the recirculating pump. When the evacuated-tubes cannot collect enough solar heat to add to the ground loop, the PV panel will not have enough power for the recirculating pump. This provides automatic recirculation control without the need for a separate electronic controller. By being suitably sized to match the pump motor and solar thermal array, the PV panel IS the controller.

panels about £360 inc VAT for example.

Navitron supply a 10 tube solar panel - high efficiency 47mm double wall evacuated tube solar collector for £320 including vat and delivery.
At that kind of a price why would any diyer want to cobble one together ?.

Hoval wrote

Not viable and uneconomical”, that‘s the preconceived
opinions shared by many about solar energy.

Sound familiar ?.