Chinese evacuated tube solar collectors

Kevin_in_Denver_2

Has anyone ever seen an importer for the Chinese evac. tubes?
The guys at NREL are saying that they cost less than U.S. flat plate collectors

Mike T., Swampeast MO

Here's a source from British Columbia

Chinese are supposedly installing these by the millions of square feet while we spend billions and wage war to subsidize big oil.

RadPro

Vacum tube solar collectors

Again the key word here is to be wary of any and all cheaper solar STUFF in general as it may not perform or last to your expectations and then all parties are unsatisfied. Flat plate collectors will perform the same effic. wise about 50 percent of the time... the rest of the time the Vac tubes shine. I'M really pleased with mine...Paul

Mike T., Swampeast MO

Considering their domestic consumption, "seconds" may be used for export...

Constantin

I wonder though...

... how the this outfit offers tubes and inserts as replacements. In other words, the tubes are allegedly field-servicable by consumers, which raises an interesting question re: the longevity of the vacuum inside. I'm also a bit skeptical that this system can sustain -30°C conditions for any length of time.

But all-in-one solutions like this are a great solution for warmer countries... just mount it on the roof, like the cold-water cistern, let gravity do the rest.

However, as far as the usage of solar systems in China is concerned, I couldn't agree more. It's pretty funny to think that 75%+ of world hot water solar is now being installed just in China.

hr

In the book \"Lessons Learned\"

from 1977 to Today, the author, Tom Lane, cautions against the less expensive imported evac tubes you mentioned. He shows several pictures of clouded, and hail damaged ones. Think I would spend a little extra for a better grade.

hot rod

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Mike T., Swampeast MO

Not \"Funny\" at All

As an "emerging" nation, it's no surprise that they use somewhat reasonable alternatives when traditional fuels are in high demand.

Kevin_in_Denver_2

e-tube durability

All the tubes I've seen are relatively thin walled. On the other hand, the cylidrical shape is inherently very strong.

Is somebody making a thicker tube?

Kevin_in_Denver_2

freeze protecting

Constantin,
You're right, there is literally no way to reliably freeze protect this system.

The vacuum tubes won't freeze. The tank won't freeze solid in most climates because of its large thermal mass. The water pipes to and from the tank will most certainly freeze.

I think Mark Eatherton has seen a lot of hail damaged e-tubes around here. When you tilt them up at 70 degrees or so, however, hail shouldn't hurt them.

Bob W._3

I know of a physics professor who will be importing solar technology from China (he is from Taiwan). If you care to email me at rjwinz@hickorytech.net I will ask him what products he will be importing and let you know.

Tim_31

China & Solar

I would never rely on a solar sysytem that has built in heating elements as freeze protection. What are you gonna do when there is a power failure in the winter?

There are much simpler (US made) systems that don't use fancy evacuated tubes. Efficiencies are comparable. Solar should be kept simple.

Interesting note about China: In the next 12 years China will build more homes than we currently have in this entire country. The materials they use to build those homes will help decide the fate of this entire planet. If they choose sustainable, renewable materials we should likely be OK. If they use lots of concrete, or other energy intensive materials, we had better look out.

Tim_31

Slow Down

Don't bring up things like "war" or "facism" on this site or you will get "erased".

It's happened many times before.

Mike T., Swampeast MO

Sorry.

Have toned it down...

hr

I think China

is perfectly capable of turning out top notch stuff. The B&G iso valve flanges are as good, maybe better, than valves from Italy, or even the U.S. for that matter. I think a lot of B&G castings are now imports.

I think it all comes down to what you ask for. If you request a cheap spin off, that's what you get.

If you give them specs and material quality data, I suspect their machinery and labor force is capabale of world class work.

Have you seen the stuff coming from LG, a large Korean manufacturer? Everything from AC units, electronics, home appliances. Pretty nice stuff from what I have seen.

It's a global economy these days, better get used to.

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Steve Ebels_3

The Viessmann E-tubes

Look substantial, as is anything else they have brought to the market. Of course being Viessmann, they are not the cheapest around.

Kevin_in_Denver_2

value engineering

The design of this Chinese tube explains how their costs are low.

Weight usually means more cost, and this design is quite light compared to a flat plate. A 4x8 sheet of glass must be thick. The aluminum extrusion to support it also must be thick enough. The absorbers are roughly the same weight, but the tube doesn't need any additional insulation or a backing sheet.

The European tubes are nice, but they have a glass-to-metal seal that adds cost.

I'm impressed with the producibility and cost goals of the Chinese collector. The system, however, needs tweaking for freeze protection before we can buy it.

Jimmy Gillies

Kevin

I have started installing this type of solar unit here in Scotland, in effect I've bought five units and will be fitting my first this week.
I know the frost protection thing may be an issue, but we are fitting a high spec control system that will monitor that, also the 'header' is well protected - ever for Scottish weather.
Of course it's a risk using equiptment that cheap. However, equiptment for our trade is like a hair cut 'cost has no reflection on the outcome'
Kind regards.
Jimmy.

[Deleted User]

Chinee Ejacurated Tube Correctors...

can be seen here...http://www.js-solar.com/

BTW Kevin, we are back on the solar installation biz.

ME

Kevin_in_Denver_2

supply pipe freezing

Jimmy,

Whatever you do, use freeze tolerant supply & return pipes. Then the worst case scenario is merely a collector loop that is clogged with ice and won't collect heat. Heat tape to thaw the pipes out is probably unnecessary.

PEX and polybutylene are generally freeze tolerant. NREL testing is showing that the KITEC brand is not. Apparently the aluminum inside is too brittle to handle many cycles.

jerry scharf_3

I own some

Kevin,

There is a company out of New Zealand, Apricus, that designs and sells them. They are manufactured in China. In talking to them, cost was part of the issue, and China has some of the best set-ups for large evacuated parts around. They had hard times with others building a folded double wall tube 1.6m long (concern over an unusual part meant higher costs.)

The design of their tube is different than the thermomax, the heat pipe is not inside the vacuum. There is a double wall like a glass thermos bottle, and the heat pipe sits inside the whole thing. So you can lose and replace the glass without replacing the heat pipe. (If you think about how many glass thermos bottles are made in China, you can see why they have good manufacturing facilities. These have largey disappeared in the west with the popularity of stainless steel thermos bottles with higher margins.)

The importer I dealt with was Sunwise Solar out of Maine IIRC, but their wharehouse is in Denver. There is also a distributor in Oregon, but their focus is more on packaged systems.

There were a couple things that impressed me about the system. One was the easier maintenance in the case of a broken tube. Another was the impact of the double wall tube on the performance. Because of the refraction of adjacent tubes, they get a flatter top of the daily output curve and slightly greater overall gathering capability.

With natural gas prices going through the roof, this may pencil out a whole lot better than it did when I decided on it a year and a half ago. It's better to be lucky than smart.

hope that helps,
jerry

F. Garing_2

The company that makes the chinese evac tubes is Sunda. the sample I received looks fine. They make several styles of evac tubes. One style ,larger diameter than the thermomax ,one same size. The collector point does'nt have the check valve like themomaxs tubes, so you need to deal with a stagnation loop. I heard that the tube is german designed ,made in china. the american distribitor is Sun Spot Solar in Delaware water gap, pa .there are several installs in my area ( crested butte co ) I guess working fine . I have only installed the viessmann package (3) and the thermomax brand (2). the evac tubes are definitety less expensive (approx $1500) hope this helps

David Woycio

temps

Better watch those temps. Hot summer days can do wonders to non-metallic piping. Haven't drank the Kool-aid yet for the evacs. I've seen quite a few and am not impressed. I think the flat plats deliver more bang for the buck in reliability, ease of installation, and servicibility. Plus when installed correctly they look similar to sky lights and blend with the roof well.

We have been installing these same collectors for over 23 years and they just don't break. We service quite a few systems in Colorado and when an area goes through a hail storm we replace very few collectors from breakage. The roofs take a bigger hit than the collectors.

Not sure how the evacs. would hold up. If the tubes did not break then the reflective surface would certainly be compromised.

THE very biggest detetent for us is the fact that these systems are not drain-back water compatable. Glycol, expansion tanks, high pressure, pressure relief valves, pressure guages, pressures bypasses, high limit recirculation...etc., are items that keep us in the service business.

Looks like we'll be busy for the next 23 years.

jerry scharf_3

dumb question

Metro Man,

What makes these system not compatible with drain-back? As long as you have a pitch in the header and the piping, why wouldn't they drain back? Is the problem with the heat pipes themselves?

I live where the levels of freezing we see are simply not a problem for the well insulated evac tube system, so I'm not so smart about this.

I do believe that bang for the buck is almost certainly better for panels. We don't get the strength of sun you do in the winter, so evacs help us.

jerry

Jimmy Gillies

PEX pipe and solar

Kevin,
I wouldn't use any PEX type pipe on solar. There is a twin stainless steel pipe that's pre-insulated with Armaflex (it's called Solar Metal Flex).
I've not had a chance to check it out yet or have a look on their web site.
We will be using copper with anti-freeze, well insulated.

I would like to use a drain back system - as it's a low maintenance system, but was told it was not suitable for evacuated tube systems?? Like Jerry I'm not sure why?

Just as a wee foot note, we are paying £260 for a 20 tube panel here in the UK.
Thanks to everyone for a very interesting thread.
Regards.
Jimmy Gillies (Scotland)

David Woycio

evacs

The beauty of a drain-back water system (other than the efficiency) is the fact that you can shut it down with no wories. Just un-plug and all the water drains-back to your storage tank.

Evacs. are a different animal. The 700-900 deg. that the system can generate in full sun with no fluid for exchange will cause serious out-gassing and an eventual loss of the vacume. A heat dump of some type is recommended by the manufacturer to reduce this.

Thermomax and the chineese collectors CAN be used in a drain-back set-up but designing in a heat dump to me sounds like a waste of energy. When a flat plate system is off the solar collectors can stagnate without these issues.

The Viessman collectors use the the thermomax tubes but a waffle stlyle header that may not be suited for drain-back.

Also on a larger system when using evacs. in a drain-back system I would be very concerned with thermal shock. For example if the storage tank was cool (say around 60* F), no sun until mid afternoon, then full sun. The evacs. would heat very quickly, the pump would evergize, and water would flow. What would be the delta-T for that last collector in the end of the array? BOOM!

I have energized a 48 - 4' x 8' flat plat solar system in the middle of the afternoon with 80 deg. feed water temps. The system made a hell of a lot of noise and shot steam into the stroage tank for about 20 minutes but eventually quieted down and ran fine.

Don't think you could do that with an evac. set-up.

jerry scharf_3

thanks for explaining more

MM,

I've never run the tubes without water in the header, so I have no idea how hot they get. The company says that they shouldn't stagnate, but can withstand the 450+F heat that stagnation will cause. I don't know where they got that number from, but it's something that I just kind of have to believe them on. I have no plans to test it!

As for the thermal shock, I'm not sure what's so different from what you describe in the flat plate setup. You turn the water on and it is fairly likely in the case you describe that there will be likely to produce steam, probably much hotter than with a flat plate. (my mind is swimming at the thought of that steam, it could be well above boiling.) But the header in the Apricus setup is sitting in dense glass wool and is separated from the glass tube, so thermal shock to the header and heat pipe are not transmitted directly to the glass as stress. So I don't see the glass going BOOM. Now the pipes may be a different story...

Your basic point is well taken and they may not be the right mix with drainback. I do have a useful place to dump extra BTUs, so it's not such a problem for me.

jerry

RadPro

My thermomax pics

David Woycio

evac. temps

I got the 800-900 deg. F stagnation temp. from my thermomax notes. It is a high enough temp. to respect. They are VERY concerned with the potential loss of vacume at those temps.

Can't remember the old evac. tubes sold in the 80's but the system was a drain back set-up. The controller would shut down the solar circ. pump when a very high delta T was detected. This happened alot (usually when a cloud was overhead then full sun) and used to drive me crazy thinking of all the wasted btu gain

Where are you dumping your excess heat?

Kevin_in_Denver_2

Pex, cost, etc.

Jimmie,

You're right, plastic is a bad choice for just about any collector loop. So scratch my suggestion.

I'm trying to work out your costs, so I'm assuming the 20 tube array is 5 feet by 4 feet. If true, your cost is $22/ft2, or about 1.6 times the cost of flat plates. Does your price include all the system components?

If you are using glycol antifreeze, you may need to provide some sort of heat dissipation for those summer vacations. It's very hard to do that passively and fail-safe.

I'm not trying to dampen your enthusiasm for solar. Thanks for sharing your experience, please tell us more about how the system works. Some of us like MM and ME went through the whole learning curve 23 years ago, and we might be able to help you avoid some of the pitfalls.

If you're using a packaged system, here's an applicable quote from Tom Lane's book: "Some excellent collector manufacturers have poorly designed complete systems. Do not assume that a collector manufacturer has put together a good system with good components - no matter how long they have been in business. Their heat exchanger or pumping package may be inadequate."

I think it's sad, but still true. Now is the time for real hydronic manufacturers to provide more foolproof, plug and play type systems. Viessman is in the game, but their system doesn't seem to be nearly as trouble free and simple as our home grown flat plate drainback systems. We need something that acts more like an appliance than a custom pipe and control system.

Jimmy Gillies

Dumb down a bit.

Kevin,
You got to dumb down a bit for me, please. Sorry, I'm not sure if you maintain the China evacuated tube panel is 1.6 cheaper than flat plate? Cause we pay a lot more here for flat plate. Being Scottish, I have very deep pockets and short arms - so cost is a VERY big factor. No, the price of £260 is for the panel only.

We have installed a lot of flat plate panels with drain back systems in the past and they're very good. Here is a link detailing the control systems we use and the twin SS pipe I spoke of above: www.seconsolar.com

We will be using: a sealed system(with 12Ltr expansion tank)with the evacuated tube panel, a Deltasol BS(as can be viewed at the above link)controller, a twin coil S.S. 210Ltr indirect hot water tank and 240V circulator.

Lastly, thanks for highlighting the point regarding summer holidays. I will ensure our customer is made aware of that.
Thanks again.
Jimmy.

David Woycio

Kevin

Kevin,
Are you currently working in the solar field in the Denver area?

Kevin_in_Denver_2

cost, etc.

I was a local solar engineer/installer (P.E.) until '83. Then 12 yrs product design/mfg. engineer at Norgren (pneumatics).
Now I'm an urban real estate redeveloper looking to incorporate some solar in new homes.

Jimmie,

My calculations are showing that you're paying $22/ft2 for the e-tube collectors. We pay about $14 for flat plate.

Cost definitely drives system design, and costs vary around the globe.

Back to e-tube closed loop antifreeze systems. We had a NREL solar home tour last weekend, and there was such a system (Thermomax tubes I think). It was installed by the homeowner, who is a Phd. scientist at NREL. I asked him if he had the option of drainback freeze protection for the system. He said yes, and that it could be the best way to avoid summer overheating. I didn't ask about the thermal shock problem (which could be a deal killer)

Then he described what may happen with his closed loop system: when the tank high limit is reached (170F) the collector pump stops. He thinks that the e-tube condensers will be so hot that the antifreeze solution in the manifold will vaporize and push all the liquid out into the expansion tank. He says that could be good, because if the antifreeze liquid is overheated for extended periods, it becomes acidic. Well if this occurs, it will be very noisy, because as MM can tell you, a boiling collector loop is scary loud. I don't think it will puke fluid, though, because the collector loop relief valve was set to 150psi.

RadPro

Re thermomax and overtemp evacuated tubes.

ALL of the regular thermomax are self limiting in temp based on tube design(amount of alcohol in tube) that is spec'd out on purchase. The Thermomax /Solarmax tubes (see my other posting for the picture)will continue to heat well past the boiling point as an open loop system with glycol. As you will see in the Pic mine are angled up to 55 Degrees which help them self limit in temp in the summer. Oh I should mention that flat plates collect heat just as well but lose alot more before it gets transfered to your fluid. Also poor /cloudy overcast days dont heat worth beans it doesn't matter what type of panel...Paul

RadPro

Overtemp

The solar storage tank should also be sized as large as possible so overtemp does not happen, or you need to dump heat, or use tubes that self limit, or put panels at an angle to self regulate..Paul

Kevin_in_Denver_2

Thanks, Paul

I didn't understand how the Thermomax (Viesmann) tubes self limit before... http://www.thermomax-group.com/PRODUCTS/SOLAR/technologyT.htm

It seems to be a great solution. Unfortunately, they're the expensive ones!

BTW, a high angle won't work that great, because folks take vacations in December too. E-tubes hardly care about the ambient temperature.

jerry scharf_3

Dumping

> I got the 800-900 deg. F stagnation temp. from

> my thermomax notes. It is a high enough temp. to

> respect. They are VERY concerned with the

> potential loss of vacume at those temps.

>

> Can't

> remember the old evac. tubes sold in the 80's but

> the system was a drain back set-up. The

> controller would shut down the solar circ. pump

> when a very high delta T was detected. This

> happened alot (usually when a cloud was overhead

> then full sun) and used to drive me crazy

> thinking of all the wasted btu gain

>

> Where are

> you dumping your excess heat?

jerry scharf_3

Dumping

the excess into the hot tub. We keep it cool and then kick it up to use it, so there is always room for some more BTUs.

At 800F and contact between the glass and the heat pipe, I can only imagine you worry about the vacuum.

thanks,
jerry

Jimmy Gillies

Thanks Kevin

You have explained it very well in lay mans terms. I forgot to say our systems will have a pressure relief valve set at 3Bar(42psi).
Also we will inform our customer about overheat in the summer months, in fact most people that have solar like to keep an eye on the digi temperature display, this makes them feel good cause they're saving a few pounds or perhaps that's just a Scottish thing??
However that customer is English, so they will be unable to read the temperature dial without a Scotsman to help them!!!
Thanks very much Kevin for your help.
Regards.
Jimmy.

RadPro

Solar is my cup of tea

every day the sun shines the heat keeps coming in.Everyone should be doing this especially in this day an age with the high energy costs.But I've always said its not for everyone but it is for most people.There is far less btu's to be had in the winter here due to less sun in reply to your question...see picture.

Kevin_in_Denver_2

150 psi relief valve is recommended

See, at some point there will be an extended mid-day power failure, or the collector pump will fail, or a sensor will fail to turn it on. Stagnating e-tubes will definitely blow a 42 pound relief valve. They will also blow the 75 psi valve as recommended by Tom Lane, but his collectors need that protection.

Just make sure all the components in the collector loop are rated 150 psi minimum.
Then your worst case scenario is some pipes banging, not several gallons of oily fluid on the floor and a non-functioning system.

Do keep in mind that I have no experience with e-tubes, I'm extrapolating from my flat plate work. The 150 psi valve recommendation comes from what I've seen installed on 25 year old, still functioning systems.

RadPro

solar pump

runs off of the sun with a Pv panel so you do not hook your system up to hydro..therefore eliminating this potential problem.