Solar panels- tubes or flat panel ?

Builderfromhell · 10-03-2009 10:59am #1

We are installing solar panels (water) on new roof and would like to hear views and opinions on whether to use flat panel or tubular solar panels.

The roof is currently battened and felted ready to receive concrete roof tiles.
There is minimal risk of solar panels being broken by ball playing or falling branches etc.

Thanks, in advance

CJhaughey · 10-03-2009 11:05am

I can only post from my experience with FP collectors, I have found them to be good, easy to clean and efficient.
I would suggest that more important than the type of collector would be the manufacturer.
There are big differences between different tubes and different panels in efficiencies.

FP look cleaner and in your case can be actually mounted in the roof like a velux rather than sitting over the tiles.( I have concrete tiles as well)

gears · 10-03-2009 12:22pm

If it's a tiled roof I know a local company who have a show room with a small roof section made up with an in-roof flat panel and tiles. It may be no where near you but I'll pm the details.

Builderfromhell · 10-03-2009 1:17pm

Thanks guys.

I realise there is a vast differences between manufacturers but for now I'm hoping to get advice on the two main systems.
I understand that sizing panels and installing system correctly can impact greatly on their efficiency.

I am in Limerick.

MickLimk · 10-03-2009 3:06pm

My own personal preference is for tubes whenever possible but flat plates if they're going to be on the front of a house. Why?

In general, I find that you get a better performing system from tubes than plates. Tubes will perform better than plates in cold weather so a properly sized system will prolong the period of the year where the solar system is making a decent contribution to heating the water.

I also find tubes are easier to install than plates but this mostly applies to retrofit. On a new build where scaffolding and a teleporter would be on site, assuming a cooperative builder, the installation should be comparable.

Tubes are also easier to maintain than plates from a damages perspective. A single broken tube (assuming a heat pipe design) won't mean the complete loss of fluid and pressure and the system would continue to function on a slightly reduced efficiency.

The only major advantage that plates have for me is aesthetics. I think they look a lot better than tubes especially when they're properly flashed into a roof like you would a Velux window. This is why I would lean towards plates when the front of the house happens to be south facing.

I suppose plates could also have the advantage of a longer life span of up to 40 years whereas the glass part of the vacuum tube may need replacing after 20-25 years. As mentioned in previous threads the glass of the tube can be replaced for a very small fraction of the total tube cost. One supplier mentioned a figure of €5 per tube but I think it's closer to €10.

Price wise, I'm not sure there's much difference any more when you compare €/m2 of aperature area. Historically, tubes may have been more expensive but given that most of them are manufactured in China now, this has driven the costs down.

I certainly wouldn't be scared away from a product purely due to the fact that it's of Chinese origin as there are many good products out there. Have a look at the EN cert values to compare the efficiency vs. cost and throw this into the equation.

Note that I have made a lot of generalisations here and these are only my opinions before anyone flames me for what I've said!

Builderfromhell · 10-03-2009 4:00pm

Thanks a million Mick.

One last thing. Is there a site or chart that compares the different solar panels based on price and efficiency.
I have links to sites in ireland and the UK that compare boilers etc. and they are very useful.

Thanks again for detailed response. I've learnt something today.

AckwelFoley · 10-03-2009 10:29pm

My advice?

Find out the kw output of either and compare. Make sure the rating is based on Irish weather not european, buecause the company i worked with this did this and the value of the result dropped by 10%

If you are not exactly south facing, tubes can be better at absorbtion.. but all this means little if the output of the tubes are low. Your "yellow brand" solar can have very low output compared to some of the other systems.

Example, ive seen a 60 tube system have a lower output than a 36 tube system, because the former was essentially a jubk system, and ive seen 24 set system with a higher value than the 36!!

Its all about output, believe me.. and to find the best value divide the cost of the system by the kw and it will give you a price per kw - then its easy compare the best value.

Brian

CJhaughey · 10-03-2009 10:55pm

If you searched you will find that this topic has come up before.
The most comprehensive set of tests that I know is at www.solarenergy.ch

MickLimk · 10-03-2009 11:31pm

Builderfromhell wrote: »

Thanks a million Mick.

One last thing. Is there a site or chart that compares the different solar panels based on price and efficiency.
I have links to sites in ireland and the UK that compare boilers etc. and they are very useful.

Thanks again for detailed response. I've learnt something today.

Have never been able to find such a site. It would be useful but think every supplier and manufacturer could dispute such a thing. The only figures that are supposed to be independently tested are those on a product's EN12975 cert. I think that as a minimum the SEI should publish these numbers for each product on their approved product list from these certs but they don't...

PeteHeat · 15-03-2009 1:23am

Hi,

I agree with Mick, if SEI were more consumer friendly it would also help the suppliers and installers when sizing the systems and offering value for money.

The one item in the question that concerns me a little is the potential for damage from falling branches, the real problem being the panels or tubes may be shaded by the branches and foliage in the summer.

Personally I prefer flat plate integrated into the roof as they look better (IMO) and the good quality systems have a much longer life expectancy.

On average tubes are 10% more efficient when new however I believe the only reason for using tubes is when the roof is not south facing and / or the location is beside the sea or at a high elevation (mountains).

It apears panels tend to be favoured over tubes on the Continent where in general they have a lot more experience with solar than we do in Ireland.

quentingargan · 16-03-2009 8:59am

CJhaughey wrote: »

If you searched you will find that this topic has come up before.
The most comprehensive set of tests that I know is at www.solarenergy.ch

The problem with the info on this site is that most people can't easily interpret it. There are three distinct systems - tubes, flasks and flatplates. At a low water temperature, flatplates perform best but as the water heats up, tubes and flasks do better. This is why as Micklmk has mentioned, vacuum tubes extend the season - they work better in cold or windy weather.

However flasks show a misleading low efficiency on these charts because you have to multiply the efficiency figures by something called the Incident Angle Modifier or IAM. This relates to the ability of flasks to passively track the sun, whereas flatplates and tubes are only at their optimum efficiency at noon.

I agree with Mick though - flatplates are more aesthetically appealing, but vacuum flasks and tubes will extend the season. In fact, on hot sunny days flatplates will produce more hot water than you could possibly use, but vacuum tubes will have a somewhat steadier level of production into spring and autumn.

If your house is very well insulated and the central heating is off in spring and autumn, then the vacuum systems will work better for you. Q

Evergreen · 23-03-2009 11:22am

I have been involved in solar panels importation, distribution and installation for quite few years and this is a question that is asked on a large number of occasions. Our company deals in both types of panels so therefore I feel that my opinion is reasonably unbiased. There have been a lot of good points made in the thread so far and one of the most important points has been in relation to panel quality. You can have a poor quality tube collector (for example a heat pipe collector as opposed to a U tube collector) which will have a lower efficiency level than a top quality flat plate panel.

One comment made that in colder weather evacuated tubes operate better than flat plate is factually incorrect. Good evacuated tubes have a general higher efficiency than flat plate regardless of the outdoor temperature. The main things that affect the efficiency of the system are orientation and inclination.

If you have a roof, plint or gable wall facing between SSE and SSW with a possible inclination of between 30° and 55° then you should go with flat plate every time. In such cases the extra expenditure for tubes over the increased efficiency gained from them is not worth the money.

The key to a good system is always quality and the country that the panels are made in has a huge bearing on this. Here is a point that a lot of people are not aware of, to get panels approved by SEI there is no lower efficiency level that solar panels/collectors have to achieve. The panels must be manufactured to a specified EN standard and pass a simple durability test. So beware of the guys selling unapproved solar panels at rock bottom prices. I have seen flat plate panels made in China that just has black paint on the absorber (two weeks of Summer sun and the paint peels off) or crappy evacuated tubes without any CPC reflectors that have been attached tot he roof with galvoband and piped to the cylinder with Qualpex - the fact that the qualpex has not melted says enough about the quality of these systems.

In relation to replacement parts and repairs, it is simple to replace an evacuated tube if it gets damaged when on the roof. However, I have never seen a damaged flat plate panel after it has been installed - they are very sturdy units, I dropped three of them once from 2 meters and did no damage at all to them. Tube collectors are more fragile, so for those with kids kicking balls on the roof there may be some repair work required over the years.

In relation to Tube collectors, you should only consider collectors with stainless steel fluid circuits. Copper circuits tend to be susceptible to internal oxidisation - you can see this in the warranty where most stainless systems offer 10 years while copper systems will only offer 5 years even from the same manufacturer.

One final point, in Austria (the country credited with the introduction of domestic solar panels) all new houses have solar thermal systems installed. Of these approx. 99% of installations are flat plate - compare this to 55% flat plate in Ireland.

Regards,

Jarrath · 23-03-2009 11:35am

I live in Sligo and will hopefully be starting to build in the near future.. I've been looking into the whole renewable energy thing as all new builds have to have some sort of renewable system installed..

Now I remember seeing a chart that showed the top half of Ireland receives the least amount of UV light compared to the rest of the country, so my question is how efficient would a solar panel system be for my area..

I'm looking into wind power but I know you have to have some sort of wind test done before you go down that route, plus I'd have some concerns on how noisy one would be..

Can anyone in my part of the country share their experiences with solar energy or wind energy systems..

Thanks
Jaz

Evergreen · 23-03-2009 11:45am

Hi Jaz,

Follow this link for a radiation map of the british isles http://re.jrc.ec.europa.eu/pvgis/countries/europe/g13y_uk_ie.png you will see that although there is extra radiation in the south, most of the country has a similar level of radiation. There is very little difference between the 1000 and 900 output range from suth tip to north tip.

If you are unsure then just add an extra panel to your system, it is the cheapest part of the system all the rest stays the same (e.g. pipe work, pumping station, controller, tank, etc.

quentingargan · 23-03-2009 7:20pm

Jarrath wrote: »

I live in Sligo and will hopefully be starting to build in the near future.. I've been looking into the whole renewable energy thing as all new builds have to have some sort of renewable system installed..

Now I remember seeing a chart that showed the top half of Ireland receives the least amount of UV light compared to the rest of the country, so my question is how efficient would a solar panel system be for my area..

I'm looking into wind power but I know you have to have some sort of wind test done before you go down that route, plus I'd have some concerns on how noisy one would be..

Can anyone in my part of the country share their experiences with solar energy or wind energy systems..

Thanks
Jaz

Hi Jaz,

I'm commercially involved in both wind and solar, but the origin to both came about because I installed both in my own house about 6 years ago.

Solar water heating is very easy to put in while you are building the house and is probably the cheapest and most cost-effective way of meeting your Part L compliance. It is a lot more expensive to retrofit later.

Wind is something you can easily retrofit later if you don't feel like doing it right now. You could facilitate that by running a length of suitable armoured cable from the area of the fuseboard to the likely site of the turbine, which will cost you about €1.50 per meter and save you a lot of hassle later. There are all sorts of turbines out there - we paid €20K for ours six years ago for a 2.5kw one. There are some very cheap machines on the market at the moment that can be noisy - especially when they are furling in and out of the wind. But turbines can be relatively quiet if their blades are well designed.

If you PM me I can send you info on how to assess your site for wind speed as an attachment.

Solar panels- tubes or flat panel ?

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