Solar Evac Tube question

Mark Eatherton

Tube failure explained

They lose their vacuum, become foggy and their performance drops significantly.

They are failing in Summit county and Stemboat that I am aware of. Probably more, just noticed.

ME

hot_rod

show me some 30 year old evac tubes

I have asked maybe 1000 solar installers that question over my travels and training seminars in the last year. I've yet to see or hear of one evac tube array sill operating after 15- 20 years.

I hear and see flat panels installations with 25- 30 year track records, on a weekly basis, including my own.

I know Corning, Sanyo, Phillips, Owens-Illinios were all building and selling evac tubes over 20 years ago, where are all these tubes?

It's easy to claim a 20- 30 year, even lifetime life expectancy, but in reality???

If in fact tubes fail and have to be replaced, even under warranty, there is still a labor cost and shipping involved. Rumors have it are some tubes are failing prematurely (in less than 5 years) and this must enter into that payback calc.

The failures we are hearing about, on this list are in Aspen, Steamboat, Phoenix, Wisconsin and the Vail area. In some cases the entire tube arrays have been replaced (under warranty) in the first year.

I've not seen too many flat plate collectors fail to harvest. Certainly not due to a vacumn loss in the glass or heat pipe tube.

I just don't see the facts to backup the longevity claims on the tubes. Do you have any data?

Not trying to slam one type of collector, or brand, I'd just like to see some real life data or actual installations with the track record you are claiming.

www.solarishot.com has some good data comparing tubes to flat panels, in real time and in cold climates, upstate NY. I am more apt to believe real life data to marketing claims.

hr

Pat_35

Number crunching

Flat Plates are affected by outside air temp. Evac tubes are not and they work 360 degrees. Flat Panels are 180 degrees.Heat loss with flat panels, non with evac tubes.
----
Not considering the initial investment, with an energy savings with any type of equipment of $50 per month has a savings of over $11,000 in 10 years. You have to include inflation of 4% per year and fossil fuel price increase of at least 10% additional per year. That is a savings of $600 per year and 14% return on money saved.
Over $50,000 in just 20 years. Flat panels or evac tubes.
Year Balance
1 $601.14
2 $1,285.30
3 $2,065.24
4 $2,954.38
5 $3,967.99
6 $5,123.51
7 $6,440.80
8 $7,942.51
9 $9,654.46
10 $11,606.08
11 $13,830.94
12 $16,367.27
13 $19,258.68
14 $22,554.90
15 $26,312.59
16 $30,596.35
17 $35,479.84
18 $41,047.01
19 $47,393.60
20 $54,628.70

Unknown

This is "hand waving", a heavily loaded comparison. You're giving a historically worst case on fuel, practically, worst case on inflation, practically, and best possible case ever on return on investment... that's even better than the typical "best scenario" of 12% return on investment for good, safe stock investment portfolios as promoted by "Dave Ramsey", the money guy. Maybe you should call him up with investment tips!

Further, while all you say about evacs are true relative to flat plates, that's not the point: actual measurements and ratings show that all the advantages of evacs are not helpful under peak collection periods, and those collection periods are when you get nearly all of your solar benefit. So being better at gaining or keeping heat, when it's marginal collection time anyway, is not of nearly as much benefit as the evac proponents like to pretend it is.

Not to slam evacs totally, they are fine technology, but they are not superior in the real world to flat plates in most cases. Just different. If you can't get your panels oriented properly, you are in a poor solar climate, you can't get up on the roof with panels easily.. these types of things point to evac tubes.

I enjoy numbers more than most, but come on, let's not load all the dice.

Pat_35

Thanx---

I appreciate your input. We all need to learn this business with all its twists and turns. I will get some data for you.

We sell about 6 Evac panels or systems per month during the 3 warm seasons. Maybe one flat panel system per year. The only tubes we sell are SRCC rated and are made in Germany or China. These quality tubes are not made in the USA yet... unfortunately. They are designed and assembled in New York.

These evac systems are in place in Europe for many years. I will get back to you with any info I get about tube life spans.

We have had no failures in the past 4 years with any evac tubes. Are your folks saying the tube vacuum is failing? Since there is no HTF fluid in the tubes.

Pat

Ron Huber_2

Fail

If you do not know how they can fail, than you haven't been installing them for very long.
You are arguing here with guys who have been around the block a few times,the attachments are of a 120 tube system I did around 94 or 95, the 30 tube around the same time, they had a 5 year warranty then, best tube on the market then, they both failed within a year and a half out of warranty. Flat plates I installed as a rookie in 1977 are still on roofs. Again, both have their place in the mix, but you have been brain washed by your manufacturer, the tubes are not the "new" "advanced" technology that you seem to believe they are. Take a look at the tubes on my house, 215 year old house with marginal roof insulation. The snow has melted off the roof before it has melted of the panels, days after the snow storm, you have to add that to your calculations. Send me your email address and I will send you the study in Germany on the side by side comparison of plates and tubes, some of the factors in their calculations included the result of frost and snow on evacuated tubes.

Ron Huber_2

Failures

Here are some pics of tube systems I did around 94 or 95, both failed within a year and a half after the 5 year warranty, at the time that was the best warranty you could get for tubes, these were Thermomax. The other pic is of my system 3 days after a snow storm, no snow on the roof,but panels still have snow. This is something that nobody factors into the performance calcs. The German study did factor this in an actual side by side performance, send me your email and I will forward this report to you. rhuber@metrocast.net I hope that we can all learn here, I cannot remember when I first started "lurking" on the wall, but it is a great place to share info.

Pat_35

BTUs vs cost

Inflation is steady 4% for many years. Fossil fuel prices have doubled in the past 6 years. A 14% annual savings from ANY alternative energy is realistic. If you spend $ 6,000 for a SRCC solar house heat system, you get $2,000 tax credit. Payback in about 4 year with a $50 per month energy savings. That is at least $10,000 savings in your pocket in just 10 years. If fossil fuel does not go up 10% per year, then a little less. The consumer is still ahead.

Our Flat Panels cost $33.50 per sq ft, and put out 182 BTU's per sq ft per bright solar hour.That is 18.4 cents per BTU.

Our Evac Tubes cost $ 54.30 per sq ft, and put out 233 BTU's per bright solar hour. That is 23.3 cents per BTU.

That shows FP are less expensive and more efficient in warm sunny areas.

When it is 15 degrees below zero, the evac panels are not affected and work perfect.

The big issue in this discussion is that there is opinion that evac tubes fail often. I have not seen that with our systems but it is a good question. The qualitiy has improved of course over the years.

Bob Gagnon plumbing and heating

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Bob Gagnon plumbing and heating

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Bob Gagnon plumbing and heating

Pat

You said the price of fuel has doubled in the last 6 years, what about the price of oil being half of what it was last year? There are drastic price drops coming for electricity too. I had 2 tubes lose their vacuum within the first couple of months, then I had a tube lose its vacuum after about two years. The latest failure, the heat transfer bulb broke off at the neck, at the top of the tube, see attached picture. I have a steep 65 degree tilt to collect the maxium winter sun and to keep the snow off the tubes, but even with this tilt they shouldn't have broken off, are they all going to start to break? I have been told by the manufacture the tubes were only guaranteed for 5 years, but after two years I would have to pay half. They finally agreed to send replacements but never have. After seeing the two different types of panels performing side by side, I'm going to go with flat panel now. I think it is important to design and install solar heating systems that are maintainance free.

Thanks, Bob Gagnon





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Pat_35

Cheap Evac Tubes...

Well... the fossil fuel price data shows an average of 15% per year over many years. It went up 100 % a while back... now it is down 8 %. It all works out to why pay for any fossil fuels.

As far as your tubes breaking, it sounds like lower end tubes. We have over 4,250 evac tubes hanging in 17 States. Not one has failed, on their own, since installation in the past 4 years, since we went into business.

There are no overheating issues with a closed loop/pressurized system or drainback with a heat dump for back up.

Also, why do you have 65 degrees tilt? That is the setting for Juneau , Alaska.

You need a max of 15 degrees added to your latitude. That gives you max house floor heat/baseboard and DHW heating from Nov 1st thru March 1st. Minimal in Summer.

At a 40 degree latitude, the Sun only goes down to 63 degrees from zenith for 1 second per year. Why would you go to 65 degrees tilt unless you are up towards the arctic circle?

michael_34

pat

I went on a service call for these solar maxx tubes. This guy has a 75 tube system and was getting no heat. He thought he had air in the system. I got there and looked at the flow meter, no air. Went up to the array and the hot pipe going to the Boiler room was cold. I decided to pull an evacuated tube out and low and behold! There was no connection between the tube and the manifold. The inside guts of the tube slide so far down that it lost it's connection. Very bad design by solmaxx. The customer and I pulled all the tubes off and pulled the guts out and reset the tubes with a good connection. That being said, the customer will have to check those at least once a year. Gravity will just keep pulling them down. The customer has had these for one year now. He says that you can never get a hold anyone. Now that there all reset (tubes) the system is working fine. I just would not want to have a lot of maintenance for a system. Hope that helps. Pat I have seen also Sunda's lose their vacuums . I install both evacuated tubes and flat plates. I prefer flat plates for these reasons. !. warranties are longer 2.They are made here in the states (the ones I use) 3. I have not seen any concrete data proving that evacuated tubes perform better in cloudy cold conditions. 4. I believe flat plates are more durable (my opinion) 5. Tubes do not shade snow. I have seen flat plates systems 25 years old with the glycol change once in that time. I have pictures of Sunda seido tubes with their vacuum gone. I have an old radio from the forties which is a vacuum tube user. They can only hold a vacuum so long. 4 years is nothing in solar heating to say you have not had a tube go bad. I am glad you haven't.
Also about angle of collectors. If you are doing a heating system it is not a bad idea to put your pitch up (last heating system I did I put the collectors at 75*) They way you eliminated some of the summer sun and avoid overheating and still catch a majority of the winter sun.
I have found with solar heating there is always a right way that can be spreadsheeted out.
One other thing I want to say. There is some great minds on the wall. Hear them out and we all we'll learn something. It's not about who's right or wrong, It's about quality.
Michael
There's a good saying from the Upanishads. "When you push to hard for something you get the opposite effect."

scott markle_2

70% and other thoughts


As far as the header and bulb connection it seems to me that the Viessmann duo-tech header with its split spring loaded manifold is miles ahead of all the other header designs. While this manifold design comes at a higher cost, it is going to out last the tubes. I can only imagine the disappointment of fused bulbs and headers when it comes time to replace some failed tubes The Viessmann design eliminates this issue and it has the advantage of counter flow as well. If i was looking at tubes it would be Viessmann or Schott all glass direct flow tubes (no heat pipe).

The 70% chart gets me wondering if all of effort and expense of frost proofing is essential to economically viable systems in temperate climates. Forgetting about the costs adsosoated with seasonal commissioning and decommissioning (this is for the hands on DIY crowd), If 70% of the collection comes in the summer why chase the other 30% a direct tie system could be installed at a much lower cost. Are there flat panels that are rated for direct circulation of potable hot water? I know that water quality would be an issue, but from what I understand there are systems like this in florida that have been going for more than 20 years. Why are we so hung up on the 30% that is so difficult to get.

Pat_35

Thanx

Our tubes are SunMaxx tubes or Viessmann. We do not use solarmax or sunda. But I will try to research any quality and manufacturing issues to make sure our supply line and manufacturer in New York will continue to supply good products. So far so good, but I will look further. We sell Flat Plates also.

Thanx for your input. Go Solar !

Bob Gagnon plumbing and heating

Collector tilt

Pat, I have steep tilt to aim towards the the low winter sun, to harvest the maximum energy in the winter time, and to prevent summertime overheating. I get 100% of my domestic needs from solar and about 20% to 30% of my heating needs. I have an 120 evac tube array and a 4' X 24' flat panel collector and I have never had to dump heat in the summer. You can tell by the attached picture that the steep tilt will always shed snow. I know a lot of people that have 45 degree tilts to their arrays which hold snow and collect little heat during the winter. I know everyone tells you to go with a 45 degree tilt, to collect more energy on average, summer and winter, and this may be the way to go if you only have 30 or 60 tubes, but with the amount of collection I have, and the fact that I use my system for space heating, the steep tilt has worked out very well. We have to think outside the box if we are going to improve solar heating systems, we just con't keep doing things the same way we have for the last 40 years, we should try to improve efficiency. You said I must be using cheap tubes, and while I agree I am not happy with the quality and performance of my tubes, they were very expensive. Suprisingly the manufacturer of my tubes also makes one of the tubes you install, I'm told it is the same tube. I'll e mail that to you privatly, I don't want to badmouth anyone in public.

While we may disagree on many points, I think we can all agree on "Go Solar!" Thanks, Bob Gagnon


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Bob Gagnon plumbing and heating

Michael

Whose flat panel collector are you using??

Thanks, Bob Gagnon

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Unknown

Scott

Is Viessmann using double wall glass tubes or are they trying to make a seal between the metal heat pipe and the glass?

Unknown

Ron

were these thermomax tubes metal to glass or were they double wall glass?

Unknown

Do you ever see

double wall glass tubes fail. Every time I see a pic on here of a bad tube it is one that lost its vac because they are trying to match expansion rates between metal and glass. I dont see where you are going to lose a vac in a double wall tube. Another benefit of the tubes, at least on the ones I sell (SunMaxx)is the wind load rating is almost the weight of the unit itself. Everyone here has an opinion as to what kid of panel they prefer..flat or tube but we need to start to distinguish what type of tubes we are talking about.

hot_rod

glass to glass

tubes are breaking when the two glass tubes bang together during shipping of handeling. Being suspended by just the ends there is potential for the tubes to touch.

I've heard one manufacturer now requires their tubes to be packaged, shipped and handled standing upright. Although it seems a side shock would do the same damage?

The loss of vacuum in the tubes is easy to see, the loss of vacuum in the copper heat pipe tube?? That's where I think the under performers are failing. The intent of the vacuum there is to lower the boiling point. How to check or confirm that tube has the vacuum?

hr

hr

Bob Gagnon plumbing and heating

Double Wall Glass Evac Tube

I had a manufacturers rep break one at a trade show once. He was putting the rubber cap on the bottom end where the glass comes to a point and he pushed a litle too hard on the rubber and you could hear the tube lose it's vacuum.

Thanks, Bob Gagnon

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Unknown

SunMaxx explained

the shipping problem to us and told us if we hold a tube at both ends and shake it back and forth we would break the inner tube but that is not a big problem for me. I drive to New York and pick up my equipment there.
Have you ever seen a double wall tube break after its been installed and securely mounted?

Unknown

The early tubes

were all single wall tubes and tried to hold a seal on the vacuum between the glass and the metal. It seems this is a futile effort to contain a vacuum. We should be trying to stop the spread of misinformation here and get to the truth. Just as it wouldnt be fair to compare the early windmills with constant speed blade assemblies with todays dc inverter units..Two complete different animals.

hot_rod

broken glass

have not personally seen a tube break while on the roof. I did hear from a contractor of tubes breaking in Phoenix, on the roof, possibly from over-heat issues on systems without dump zones. Is that a concern as far as you know? not having a dump on large arrays with no or light loads.

I have seen temperature claimns nearing 700F in stagnant evac tube arrays. That is tough on glycol. And rubber hose solar tubing

I can't seem to find many folks with over 7-10 years of evac tube installation experience.

hr

scott markle_2

Viessmann tubes are single wall with seal between heat pipe and glass as opposed the the double wall test-tube with cork in the top and curved collector inside.

I am also suspicious of the (long term) glass to metal seal, that's why I like the all glass Schott tubes with direct fluid transfer. As far as heat pipe designs are concerned I believe the Viessmann heat pipe to header design is unequaled. When a tube fails after the 10 year warrantee expires at least there will be no issues releasing a failed tube from a seized socket, the spring tensioned split header connection ensures that regardless of thermal stresses, transfer performance will remain excellent from the day it's installed to the day that it needs replacement.

michael_34

pat I missed typed

michael_34

pat I missed typed

I meant Sunmaxx from silicon solar which they are out of New York

michael_34

Heliodynes

Ron Huber_2

Thermomax

Metal to glass

Royboy

have not yet done an evac tube system

and I've gotta say that this thread - and other reports - leave me thinking why would I take the chance, and subject my client to the chance of premature equipment failure, unless I've got a manufacturer that 1) offered a real good warranty and 2) has some reasonable probability of being around to honor that warranty.

compared to flat plates, the odds of collector failure just seem way too high. and any collector failure tends to negate much or all of the economics/energy-savings of a system.

I'd like to be more open minded about these things, cuz they seem apropos for more high-temp applications, but I'd need to hear someone whose been installing tubes for a sustained period and still thinks they are a good way to go.

thanks to Pat for offering the pro-tube message that got this thread perking again. though I'd agree with the opinion that your financial numbers are optimistic to a degree that makes me uncomfortable. I'd much rather have a system overperform my estimate than underperform ...

Roy

Sunrise Energy Services

Pat_35

Time to try new Evac stuff...

Yeah... I really opened a can of flies.

We have been in business for only 4 years and have about 4000 tubes hanging out there with no failures on their own.

There was on Elk attack which took out a large array on the ground, but cant blame that one on overheating.

There aren't many businesses selling Evac tubes more then 5 or 6 years. I do see a major improvement in design but we will see. The numbers crunched were base on tubes operating for a good 15-20 years with no vacuum loss or heat pipe failure at all. If they start failing in year 5 I am moving to a deserted island.

Thanx for your input. The website numbers were based on a savings of $600 per year. And a compounded savings of 14% per year after payback. A yearly maintenance cost of about $50 per year, or about $18,000 in repairs and electricity of 30 years.

Just a basic rundown for folks. If things were only half of that, consumers would still be WAY ahead... but we can not have tube failures that plagued the industry the past few years. Hopefully our SunMaxx tubes continue to produce.

Pat