Comparing Solar System

whelzer

What are the key factors to look for when comapring solar systems from different suppliers? How important is kWh/m2. Other than gross size and obvisousily price, this has been my only measure to date...Any pointers much appreciated.

ccsolar

Hi Whelzer
You should take into account the Aperture area of each system.
I 40 tube solar collector might only have an aperture area of 3-3.5sqm where as another 40 tube system would have an aperture area of 5 sqm.
The bigger aperture area is normally gained by fitting reflectors at the back of the tubes.
The Aperture area is calculated when the collectors are been tested for EN certification.

CC

quentingargan

whelzer wrote: »

What are the key factors to look for when comapring solar systems from different suppliers? How important is kWh/m2. Other than gross size and obvisousily price, this has been my only measure to date...Any pointers much appreciated.

There are three main factors, and these are all comprehensively covered in the EN12075 cert that should be available for all panels;

Zero loss efficiency - the noon efficiency of the panel in harvesting the energy in the sun (usually about 80% for flatplate, and about 56 to 60% for vacuum flasks)

Heat Loss coefficient - the rate at which the panel loses heat to the outside air. This is usually higher for flatplates and much lower for vacuum flasks. This will determine the ability of the system to work during early spring and late autumn

Incidence Angle Modifier - how well the panel works either side of noon. You need to multiply the average of this figure by the zero loss efficiency to get an indication of true efficiency, though that is very approximate.

I use simulation software on the market that can give an indication of how the system will work, given these figures, roof angle, orientation, geographical location etc. You can either use Retscreen, a free utility, or ask companies to run a simulation on the package they are offering.

Another very large element that will affect the performance though, is the quality of installation, insulation and attention to detail. Get references... There are issues like how close the cylinder is to the panel, and of course roof pitch and orientation. But quality of insulation, particularly around the cylinder is also critical in saving you money, both summer and winter.

Lastly, some systems rely on reflectors, and when new, these systems perform extremely well in the EN12975 tests. However, their performance in the field after a couple of years is yet to be proven. I've seen situations in which the back of the tube gathers dirt, and these reflectors are next to useless in year 3 unless you can get up and remove the tubes for cleaning.

deepspeed

quentingargan wrote: »

There are three main factors, and these are all comprehensively covered in the EN12075 cert that should be available for all panels;

Zero loss efficiency - the noon efficiency of the panel in harvesting the energy in the sun (usually about 80% for flatplate, and about 56 to 60% for vacuum flasks)

Heat Loss coefficient - the rate at which the panel loses heat to the outside air. This is usually higher for flatplates and much lower for vacuum flasks. This will determine the ability of the system to work during early spring and late autumn

Incidence Angle Modifier - how well the panel works either side of noon. You need to multiply the average of this figure by the zero loss efficiency to get an indication of true efficiency, though that is very approximate.

I use simulation software on the market that can give an indication of how the system will work, given these figures, roof angle, orientation, geographical location etc. You can either use Retscreen, a free utility, or ask companies to run a simulation on the package they are offering.

Another very large element that will affect the performance though, is the quality of installation, insulation and attention to detail. Get references... There are issues like how close the cylinder is to the panel, and of course roof pitch and orientation. But quality of insulation, particularly around the cylinder is also critical in saving you money, both summer and winter.

Lastly, some systems rely on reflectors, and when new, these systems perform extremely well in the EN12975 tests. However, their performance in the field after a couple of years is yet to be proven. I've seen situations in which the back of the tube gathers dirt, and these reflectors are next to useless in year 3 unless you can get up and remove the tubes for cleaning.

All very good and interesting points. Thanks.

I wanted to ask - does anyone know or have heard of these type of Vacuum Flask type Solar Panels, and are they considered good/bad/indifferent??

Changzhou Blueclean Solar SEI-st-407T ?

Many thanks,

quentingargan

deepspeed wrote: »

I wanted to ask - does anyone know or have heard of these type of Vacuum Flask type Solar Panels, and are they considered good/bad/indifferent??

The company you mention is one of about 2,000 factories in China making vacuum flask systems. The end products are visually indistinguishable, but I visited a few of these factories, and as with so much in China, the manufacturing quality was variable - some excellent with good QC in place, and some that you wouldn't touch with a barge pole.

There is now a plethora of Irish importers bringing panels in from China, often without any factory visit or oversight of any sort - certificates are taken on face value, but with one major Irish brand I have had confirmation from TUV (the certifying body) that their certificate was a forgery.

To make matters worse, many of the panels are so visually identical, that there are panels listed with SEAI that have EN12975 certs, but the importer subsequently is offered a visually identical panel for a lower price from another factory. The end customer would have absolutely no way of verifying the actual manufacturer.

All that said, in general, Chinese vacuum flasks are a very clever concept. They have brought the price of vacuum systems down to below the cost of flatplate, and most of the panels are extremely effective and reliable.

So you have to make a judgement on the ethos and knowledge of your supplier. Ask for a copy of EN12975 certs and compare them. I wouldn't buy panels from somenone who just took a punt and bought in a containerload of panels at a bargain price, regardless of their listing with SEAI.

deepspeed

quentingargan wrote: »

The company you mention is one of about 2,000 factories in China making vacuum flask systems. The end products are visually indistinguishable, but I visited a few of these factories, and as with so much in China, the manufacturing quality was variable - some excellent with good QC in place, and some that you wouldn't touch with a barge pole.

There is now a plethora of Irish importers bringing panels in from China, often without any factory visit or oversight of any sort - certificates are taken on face value, but with one major Irish brand I have had confirmation from TUV (the certifying body) that their certificate was a forgery.

To make matters worse, many of the panels are so visually identical, that there are panels listed with SEAI that have EN12975 certs, but the importer subsequently is offered a visually identical panel for a lower price from another factory. The end customer would have absolutely no way of verifying the actual manufacturer.

All that said, in general, Chinese vacuum flasks are a very clever concept. They have brought the price of vacuum systems down to below the cost of flatplate, and most of the panels are extremely effective and reliable.

So you have to make a judgement on the ethos and knowledge of your supplier. Ask for a copy of EN12975 certs and compare them. I wouldn't buy panels from somenone who just took a punt and bought in a containerload of panels at a bargain price, regardless of their listing with SEAI.

Good stuff - this is great information to have available.

I will see if I can figure out what to do now!

Thanks again

ccsolar

Hi Deepspeed.
On a further note with regards to this company, there vacuum tubes are of very good quality and have EN certification, But this company also make a flat panel which is also of good quality but does not have any EN/solar key mark certification.
The company at no time has tried to sell there flat panel claiming to have certification but you will find that they are still been sold on the Irish market, as Quentin said you will have to make a judgement on your supplier.
Some of the importers are not even aware that they have bought a cheaper copy until it is to late.


Best of luck.

CC

freddyuk

I understood that the SEAI registration allowed the customer to obtain grant funding for the equipment installed. If there is no certification then there is no grant? However as other regulation seems to be a little vague I guess it is a case of the buyer beware.
Also the Solar Keymark should be updated every two years so any company that shows an out of date certificate should be considered suspect. Ask for a copy of the laboratory report backing up the certificate.

On the subject of reflectors I was thinking of using RainX on my new install just to see how effective it may be at keeping them clean. No harm in removing and cleaning the tubes every year to keep them clean and 100%.
Any thoughts?