Flat solar thermal panels or evacuated tube?

[russ]

Legionella would be more of a concern on open type systems, IE if you have an open to the atmosphere water storage tank or pumping from a lake or pond. If pumping from an open water source you will also have other organisms to worry about. Legionella is transmitted by air, it does not come from water unless it is a contaminated source, chlorination or better yet treating with ozone will kill it. Ozone is the best disinfectant available it kills all viruses, bacteria, and protozoa. Ozone generators are readily available and simple to install and maintain.

Ozone generators are OK providing they are working though there are different schools of thought about how effective they are.

Like I said, I am not concerned as there is first chlorination and then UV in my system.

[Yianie123.]

I own a 90 tube system

If you live in cool climates go with evacuated tubes I have them on a stand in the yard. *All piping is buried. *I used copper pipe inside of corrugated drain pipe The copper pipe was centered with spacers and filled with spay foam insulation.

[billmckinstry]

I lived in Papua New Guinea for 30 years and we only used standard Solar Hot Water systems ie no heat exchanger as it never freezes.
The Govt passed a Law in the early 1980's banning electric domestic water heaters in coastal regions which means a Solar unit can not have an electric backup element.
This was revised soon after to allow a One Shot Switch which when activated will allow an element to heat the water storage until the thermostat cuts out and then no more power until the switch is re pressed. This means in days of big usage and or a lot of cloud, you can boost the water temperature, once.

The end result is most units had either no electric boost or if installed, it was never used.

We got used to luke warm showers when we had rain for more then one day (seldom happened).

Legionares desease was never an issue and in most cases the water would not reach 70deg c.

We never had any health problems.

The water in the storage tank (180ltr 1 panel or 360 ltr 2 panel) would have changed a few times a day and it was Town supply cold water mains pressure feed.

[russ]

I think evacuated tube (vacuum collectors ) are better but depends on lot of factors. Some will say flat panels has longer and proven history and last longer but vacuum collectors has increased efficiency, so better do some research over net and you can find solution.

Depends - in a cold climate the evacuated tubes can perform better - in a warm sunshiny climate a flat plate

For data http://www.solar-rating.org/default.htm

[Gabriel.H]

evacuated tubes for sure!! u can read this about solar thermal energy :

and there is also a comparasion betewen vaccum tube and flat panels :

Mod note advertising links are not allowed If you want to advertise contact username Jason.

[russ]

evacuated tubes for sure!!

Well - so much for salesmen's blather - this guy has no idea but is busy trying to get suckers lined up. Both types of systems have their disadvantages and disadvantages.

[markbrown178]

I tried Solar Air warming for about 4 decades. The section was effective in producing very hot air. The section would heat-up by 9am, fan convert on (@ 100 degrees) & gradually get warmer. It was not unusual to heat-up beyond the thermometer's restrict of 160 levels, with the fan blowing
(300cfm) regularly.

[MikeSolar]

Howdy, I've been in this business for almost 30 years so i have seen a few things. First, even though Germany has less sun than Canada or the US, 80% of all panels there are flat plate (that ratio is not really changing either) and the reason is simple. When you are heating DHW, 90% of the time the panels will be at 70C or less, 80% of the time 60C or less. At these temps, a flat plate will put out as much heat as a vacuum tube for the same absorber area, on an annual basis.
Second, longevity.....flat panels have been around for decades, in their modern form, can take quite a beating and still work but a vacuum tube, any vacuum tube, has a 5-6% chance of losing it vacuum within 5 years. Simply put, it is under a lot more thermal stress than a flat collector and as they say "somethings gotta give".

I bought and installed 2 container loads of Chinese (Sydney tube) panels before I decided that I would stick to flat panels. I did a survey of my systems about 3 years ago and found that, even in really good running systems, there was an average of 2 tubes in a 60 tube system that had lost vacuum for some reason (systems had been installed from 2000 to 2008). I had researched the best manufacturers in China for a full year before buying the panels. These failure numbers are well known in Germany and in china and it is why there are stalls on many streets selling replacement tubes for $1 or so.

This is not to say that tubes don't have their place and the best place for them is doing high temp work such as a chiller. The secret in this situation is to have a small deltaT across the tube to reduce stress. Be prepared to change tubes out after a few years.

In the real world a flat plate will give you more heat for a longer period than a tube will and with less maintenance. An average flat system for DHW will give perhaps 500kwh of heat/m2 of collector annually. A system sized for heating will be less, perhaps 350-400kwh/m2 for collector area and if you size for winter time, you will overheat in the summer... big time.

My panels are on the wall of my house (90deg) and feed my DHW and floors directly. When they are lower in temp than my storage tank, they feed my ASHP to increase the COP. I have 10m2 (4 Viessmann flat panels).

It is my first post so i won't blabber on any more. Cheers

[Naptown]

I agree with you Mike. Flat plates are the best overall value for hot water and perhaps heating. Yes they are a larger footprint for the same BTU output but the overheating issues etc with evac tubes far outweigh the benefits.
I personally only use them in specific instances. Generally on flat roof urban installs where wind loading is an issue, and commercial installs where there is a constant high load on the array.

[MikeSolar]

I was the importer to Canada for the Schott vacuum collector. They would not import to the the US due to the belief that they would get sued for just about anything if there was an issue and made me promise that I would not sell to the the US. The PV end is a totally different animal, as we know.

These were the most elegant and efficient tube on the market at the time and had a stagnation temp of 300C. This brought on long term problems controlling the temps and pressures and Tyfocor had to come out with a special glycol mix to handle the temps and the as it is a liquid to glass contact, it had to keep the glass clean.

In Europe, Viessmann sold them for a number of years as did a few other companies.

The problem with tubes, and all tubes suffer from this to some extent is when there is no load, the degradation of glycol or glass stress becomes quite a PITA. We all know that the only way SDHW has a payback is when it performs well for a couple of decades and flat panels will do this. Only the rare tube system will do it.

[jee]

Winter

Flat solar hot water panels have been around for close to 100 years, and evacuated tubes for more than 30 years. The flat panels deliver more BTU's per $ than evacuated tubes in clear, moderate conditions, but evacuated tubes perform better in cloudy and/or cold conditions. Doug

flat- and tubescollectors - Winter, Poland -10oC...2012-10-18 14-51-31.jpg

[Peter69_56]

Flat vs Evacuated Tube

flat- and tubescollectors - Winter, Poland -10oC...[ATTACH=CONFIG]2336[/ATTACH]

Flat panels can gather more heat but also lose more heat due to loss from the panel face. Evacuated tubes gather good heat but dont lose as much heat as flat panel.

The end result is overall ET are more efficient in medium to cold climates, and the colder the weather the more efficient they are. Flat panel however do better than ET in hotter climates with a consistent hot daily ambient temperature (closer to the equator).

[russ]

Flat panels can gather more heat but also lose more heat due to loss from the panel face. Evacuated tubes gather good heat but dont lose as much heat as flat panel.

The end result is overall ET are more efficient in medium to cold climates, and the colder the weather the more efficient they are. Flat panel however do better than ET in hotter climates with a consistent hot daily ambient temperature (closer to the equator).

Actually the two types collect similar amounts - just that flat types do better in warmer climates and evacuated tube types in cooler/cloudier locations. In snow covered conditions flat plates win as they typically clear more quickly.

[Peter69_56]

Actually the two types collect similar amounts - just that flat types do better in warmer climates and evacuated tube types in cooler/cloudier locations. In snow covered conditions flat plates win as they typically clear more quickly.

I agree except to say that flat panels will loss more heat over ET due to the ET having a vacuum this provided insulation whereas flat panel does not have a vacuum so loses more heat. This only happens if the ambient temperature is less that the flat panel interior, thus in hot climates flat panel is more efficient, whereas colder climates its not as good, but as you say if there is snow, flat panel clears quickly. You have to look at your climate and get the right one for your area and not just what the salesperson trys to convince you to buy.

Also in Australia I have noticed that many of the flat panels seem to frost over inside after only a few years. Not sure why or which brands are better than others, but I look at many houses in my travels and have noticed this trend. Dont know if its a particular brand or what?

[MikeSolar]

I agree except to say that flat panels will loss more heat over ET due to the ET having a vacuum this provided insulation whereas flat panel does not have a vacuum so loses more heat. This only happens if the ambient temperature is less that the flat panel interior, thus in hot climates flat panel is more efficient, whereas colder climates its not as good, but as you say if there is snow, flat panel clears quickly. You have to look at your climate and get the right one for your area and not just what the salesperson trys to convince you to buy.

Also in Australia I have noticed that many of the flat panels seem to frost over inside after only a few years. Not sure why or which brands are better than others, but I look at many houses in my travels and have noticed this trend. Dont know if its a particular brand or what?

The real differences start with the intended uses for the system. If you need low temp output such as DHW chances are you will get just as much heat output, per m2 gross area, even where I am in Toronto in the winter with a flat panel as a tube (note I didn't say aperture area). You need to get quite cold ambient for the tube to overtake the flat panel and many people add one or two extra tube collectors to get an even better winter performance. The problem with this is it is grossly oversized in the summer and WILL lead to a shorter lifespan and no economy because it sits at stagnation for much of the summer. Tubes need replacing, periodically because nature abhors a vacuum and they have a tendency to lose it. I have changes way more tubes than care to count and it is not, as yet, a long term solution. Add another flat panel, put it on a steep angle and let your system run for 30 years.

There are some brands of glass that look like they have frosting on the inside but it is just the way the surface is textured.