How to make use of 100+ evacuated solar tubes (without copper collector)

[rogerdw]

Hi guys, I'm new here, just came across the forum yesterday.

I'm interested in solar pv and inverters etc ... but recently came across a heap of (cheap) evacauted solar tubes and was trying to work out if I could make use of them.

I quickly discovered that they have no collector in them ... if that's what you call the copper tube and bulb that sticks out the top to transfer the heat to a manifold.

That straight away limits the options of course ... but interested in any suggestions as to how they could still be put to work.

In my searches I came across people who have fitted copper tubes down the centre to allow air in ... which then heats as it flows back out between the tube and the inner face of the glass.

Some have used a spiral type device to force the air to spend a bit more time in the tube so it collects more heat ... but these were all pretty basic experiments, so very hard to know whether that extreme was worth the trouble.

If anyone has any ideas I am all ears as it seems like too good an opportunity to pass up. Thanks.

 

[svetz]

Interesting!
What are the dimensions of these evacuated glass tubes?
Any coatings on them? Are they smooth cylinders or do they have attachment points?

 

[Woody]

Here’s some links on what is an evacuated solar collector.

Figure 1. Operating principles and essential parts of a conventional...

Download scientific diagram | Operating principles and essential parts of a conventional evacuated tube solar collector: 1-manifold header, 2-heat pipe head, 3-heat pipe, and 4-vacuum glass tube. from publication: Design and Numerical Study of the Novel Manifold Header for the Evacuated Tube...

www.researchgate.net

Evacuated Tube vs. Flat Plate Solar Hot Water Systems - Which Is Best?

Not sure which solar hot water system is best? Get in touch. Sun City offers quality flat plate solar hot water systems & evacuated tube solar hot water systems

suncityhotwaterplumbing.com.au

Components Of Evacuated Tube Solar Collector And How It Works

Components Of Evacuated Tube Solar Collector And How It Works - Download as a PDF or view online for free

www.slideshare.net

Sounds like you just have the glass tubes. The third link shows the other parts that make the collection system function. If you just have the glass tubes, you’re missing a lot.

So with just the glass tubes you can make a small solar tube stove. Kluge together a make shift solar water heater. YouTube has some videos on doing this. Search for “solar oven vacuum tube” and/or “solar tube heater”.

Perhaps these videos are what you want to try to build:

The second link is about a home made creation and you can see all the parts you need to make a working collector system. For me, unless you’re friends with a plumber, it would be better just to purchase a fully functional collector than pay for all those individual parts and then build the collector.

 

[rogerdw]

Interesting!
What are the dimensions of these evacuated glass tubes?
Any coatings on them? Are they smooth cylinders or do they have attachment points?

They are 1.8 metres long 65mm OD and 43mm ID and are like a thermos flask with one tube inside the other with a vacuum between them.

The outer tube is clear and the inner tube has a black coating which absorbs the heat. They are longer versions of what Woody shows in the videos below.

Normally they come with a "heat tube" which is a copper tube with a bulb at the top ... with a small amount of acetone or other liquid sealed inside ... which evaporates when hot and transfers the heat to the bulb.

There is usually also a metal tube or folded metal that transfers the heat from the inside of the glass to the heat tube.

The bulb then transfers the heat to a manifold and is collected that way.

The tubes have no mounting points other than they sit in a plastic or rubber cup at the closed end where the nipple is (where vacuum was drawn from) ... and the other end held captive in the housing at the manifold end.

 

[rogerdw]

Here’s some links on what is an evacuated solar collector.


Sounds like you just have the glass tubes. The third link shows the other parts that make the collection system function. If you just have the glass tubes, you’re missing a lot.

So with just the glass tubes you can make a small solar tube stove. Kluge together a make shift solar water heater. YouTube has some videos on doing this. Search for “solar oven vacuum tube” and/or “solar tube heater”.


The second link is about a home made creation and you can see all the parts you need to make a working collector system. For me, unless you’re friends with a plumber, it would be better just to purchase a fully functional collector than pay for all those individual parts and then build the collector.

Thanks for the links Woody, I've been reading up on all them for a while.

Yes, you are correct, it's only the tubes that are available with no heat tubes unfortunately.

What has my attention is the price ... 100+ tubes for $100.

I can buy heat tubes from ebay etc ... but tubes plus freight for just 10 is expensive ... and I'd still need the additional copper finned section to contain each heat tube.

Of course if I knew the result was going to be worthwhile I'd cough up the dough ... but for basic experimenting I'm a bit more cautious.

I had seen the second video you linked to but not the first ... that is definitely a method I can try out.


I had bought just 10 to play with and am impressed with the results so far.

Late Sunday arvo I put two on the back lawn propped up at about a 10 degree angle.

Ambient temperature was 20° C and sun was nice and bright but behind broken clouds.

Only took a little while for the temp inside the ends to get to 30° C ... and then I left the probe in the end ... effectively blocking it so the heat couldn't get out.

It took about 20 mins before the temp was up over 70° C ... and off the scale of my probe. 5.30pm.

I found some 10mm diameter, thin walled plastic sleeving and slid down to the bottom and blew into it ... but the restriction of the creased tubing made it hard to get much flow before I ran out of breath.

So I blew in air from the air compressor ... and the resulting air was pretty impressive. Couldn't hold my hand in front because it was like a hair dryer.

I expected the compressor air to cool the whole thing down pretty quickly ... but it held up remarkably well and took quite a while to start coming down.

Took several minutes to drop to 60° ... then another 5 or 6 mins to get to 30°. Pretty hefty airflow though.

The following mildly sunny day had the inside temperature up as high as 194°C !!!

 

[Jo67]

How about building a solar food steamer (a cooker that can steam food) https://solarcooking.fandom.com/wiki/Solar_Steamer

By the way, you do not need have this copper pipe (called heat pipe) in the middle of the glass tubes. you can just fill the tubes with water. You just cannot pressurize the system because the glass would not tolerate it.

 

[rogerdw]

How about building a solar food steamer (a cooker that can steam food) https://solarcooking.fandom.com/wiki/Solar_Steamer

By the way, you do not need have this copper pipe (called heat pipe) in the middle of the glass tubes. you can just fill the tubes with water. You just cannot pressurize the system because the glass would not tolerate it.

Thanks for the link and your reply Jo67.

I had seen reference to the food steamer some time ago, but it seems the company behind it are no longer around ... but I haven't played with heating water directly yet ... I must try that.

I have made considerable progress with an air heating system that uses 18 tubes and is temporarily plumbed up to my lounge room window. It can produce up to 1,500 watts of heating energy in good conditions ... and I'm sure it could double that in the middle of summer, though I wouldn't need the heat then.

My plans are to fit a 54 tube system up on the roof and use it to heat our home during winter. With the tests so far, I can see us being able to reduce our wood burning by at least 30% ... maybe as much as 50%.

You can see the progress over on thebackshed forum in the solar thread ... https://www.thebackshed.com/forum/ViewTopic.php?FID=10&TID=13675&LastEntry=Y#169384

 

[sunshine]

My plans are to fit a 54 tube system up on the roof and use it to heat our home during winter.

Heating tubes are good at heating small volumes to a high temp but are not comparable to other cheaper methods that use a larger surface area when required temperature differences are lower and volume is greater.

 

[rogerdw]

Heating tubes are good at heating small volumes to a high temp but are not comparable to other cheaper methods that use a larger surface area when required temperature differences are lower and volume is greater.

You are probably correct, but don't forget I scored 140 odd tubes (including 4 or 5 stands and a heap of reflectors) for $100 ... and three inline exhaust fans for $50.

At times I have wondered how it would have compared to a 'normal' solar air heater with soda cans or flywire ... but I'm becoming more and more happy with how this is performing as I begin to understand how it works and what makes a difference in it's operation. That's why the plan to scale it up times three.

What would be the best/cheapest/easiest method in your opinion ... coz this clearly is not likely the easiest ... and if you had to pay retail for the tubes, definitely not the cheapest either.

 

[sunshine]

What would be the best/cheapest/easiest method in your opinion

Home heating is probably solars biggest weakness, Always coldest when the sun isn't shinning and any storage solutions don't have the capacity when scaled down to house size. Here it is 11pm. 5 days from the start of winter and the temp is 16C. No heating, just another jumper when it gets colder.
Keep going with your solar tubes. I have 50meters of polypipe under glass but the price you paid for the tubes puts them ahead.
When I go behind my pv arrays and feel the heat I can not see why all the rooftop arrays dont get boxed in with extract fans directing heat into the house in winter (reversed in summer)

 

[rogerdw]

Home heating is probably solars biggest weakness, Always coldest when the sun isn't shinning and any storage solutions don't have the capacity when scaled down to house size. Here it is 11pm. 5 days from the start of winter and the temp is 16C. No heating, just another jumper when it gets colder.
Keep going with your solar tubes. I have 50meters of polypipe under glass but the price you paid for the tubes puts them ahead.
When I go behind my pv arrays and feel the heat I can not see why all the rooftop arrays dont get boxed in with extract fans directing heat into the house in winter (reversed in summer)

Yes, agreed, it is a pain. But that's why I wanted to at least try and make a bit of headway during the day while there is a little sun.

My wife struggles with the cold, so over the last few years I've put a lot of time and effort into keeping a wood heater going 24/7 during the cold season.

My thoughts were that if I could add some heat during the day ... heat soak the place ... I could get away with burning less wood.

This device has only been operating about 2 and a half weeks ... and it has only been a couple days where I actually stoked up the fire during the day. I definitely have been burning wood overnight still ... but if I can keep this up ... I believe I can reduce my wood consumption by one third or more. Of course the real cold is yet to come with winter ... but I'm also learning how to drive this thing to get the best out of it.

I was interested to read your thoughts on collecting heat from behind your PV panels, because there is a guy over on thebackshed who has been talking about doing the same thing (Davo99) ... but he hasn't been getting any real support and I don't think he has tried it yet. May be worth discussing it with him.

How well is your polypipe collector performing? What size is the container .... and do you have any figures on heat gain or equivalent power?

Like I mentioned earlier, I definitely wouldn't be going down this path if I'd had to pay retail for the tubes ... it would have been something else as cheap as I could make it.

The following is the results from today and I am more than happy with them. I keep imagining it with 3 times the output and I think I could make some serious inroads with that. May have to shut it off on good days.

 

[sunshine]

How well is your polypipe collector performing? What size is the container

50m of 20mm PEX mains pressure poly coiled up, zipped tied oblong/rectangle, on top of aluminium composite board, 6'x4', ex for sale sign, painted black for extra heat absorption (,,,and to cover up the ''property of....''), Under glass still in the aluminium frame from its former use as a sliding door. Sits on top of a guinea pig cage. There is a million similar variations on ytube. Was used to pre-heat the water going into the hot water system. Very effective under full sun

In your situation replacing the poly with black painted corrugated steel sheeting just to heat air would be the most cost effective, Maybe 1kw/hr of heat from the theoretical 2.5 possible.