Is there a standard for solar?

rosullivan

I'm beginning the task of researchingthe various solar DHW systems out there. I'm looking for one that will work with my proposed multi-fuelstove with back boiler and with by proposed condensing oil boiler.

Is there any standard(s) in terms of looking at solar? If I was looking at window glass, I'd be looking at u-values. For solar, is it the efficiency that is important? The overall output, regardless of efficiency? What?

sinnerboy

I can't answer the question exactly as you pose it .

however i would not use a panel that was not included here

http://www.sei.ie/index.asp?locID=773&docID=-1

and / or here

http://www.irish-energy.ie/uploadedfiles/RenewableEnergy/REIOBuildingsPackSuppliersList24May05.pdf

Also - you could look here

http://www.arsenal.ac.at/products/products_en_st_en.html

CJhaughey

www.spf.ch has a lot of test reports on various collectors

rosullivan

CJhaughey wrote: »

www.spf.ch has a lot of test reports on various collectors

Thanks Sinnerboy and CJhaughey. I suppose what I mean is whether there is an efficiency rating of some kind that is objective. Something like a u-value that a consumer can use to compare products. I guess from both of your replies that there isn't, but thanks for those links.

MickLimk

rosullivan wrote: »

Thanks Sinnerboy and CJhaughey. I suppose what I mean is whether there is an efficiency rating of some kind that is objective. Something like a u-value that a consumer can use to compare products. I guess from both of your replies that there isn't, but thanks for those links.

What you are looking for does exist but the information that you need isn't presented in any format that's easy for a consumer to interpret.

The reports that CJH linked to have a summary towards the end that give performance/efficiency figures for each panel. One of these figures is a conversion factor (referred to as n0). This is a measure of how efficient the panel is, ignoring the heat losses. It is a basic measurement of how much of the sun's energy the panel is receiving that it can convert into usable form. The closer this figure is to 1.0 the better.

Generally flat plate collectors have a higher n0 figure than tubes but this is where the next figure, loss coefficient (a1), comes into play. This figure gives you an idea how much of the energy received is lost through the structure of the collector. In general, flat plate collectors lose a lot more heat than the evacuated tube ones so flat plates would have a higher a1 figure, therefore lose more of the heat they gain through the structure of the panel.

At first glance, a flat plate system may have a higher efficiency number than a typical evacuated tube system but when the heat losses are taken into account, the actual amount of energy produced may well be the very same. With the lower a1 figures it's said that evacuated tubes perform better in the winter than flat plates as they lose less heat in cold or windy/wet weather.

If you want to see a combined performance figure that takes both the n0 and a1 numbers into account, I'm afraid you'll have to calculate it yourself! Personally I think the SEI should publish these figures in the list of approved products. From the DEAP workbook, the collector performance factor (CPF) is calculated as follows:
CPF = 0.87 - (0.034 (a1/n0)) + (0.0006((a1/n0)^2))

A tube example of this with n0 = 0.561, a1 = 1.61 W/(m2K) gives a CPF of 0.777.

A flat plate example with n0 = 0.761, a1 = 3.94 W/(m2K) gives a CPF of 0.71.

Obviously the closer to 1.0 the better the performance of the collector (in theory!). The literature for every solar system should give the n0 and a1 figures and if it's not there then you should ask the supplier for it. Far from an ideal situation and I really think it's something the SEI should look after...

Cuauhtemoc

Maybe something like this would help.

Have entered the details from www.spf.ch website into a comparison spreadsheet. Has all the tube collectors(that are quality tested EN12975 and Solar keymarked) and a selection of the better flat plate systems(will get them all in but there's a lot more of them than tubes).

If someone( Micklimk??:) ) would like to double check my rusty maths.
I'm not a hundred percent on where the 0.034 and 0.0006 values are arrived at.

Have expressed the cpf as a percentage if that makes any difference.

Hope its some help.

C.

CJhaughey

Thats great work Cuauhtemoc, pity those dolts in the SEI wouldn't pull finger and try and get this kind of information out to the public.
The SEI are about as useful as a chocolate teapot when it comes to actual information rather than vague general statements.

rosullivan

Cuauhtemoc wrote: »

Maybe something like this would help.

Thanks, that is useful. Pity it is left up to helpful boards members to do that chart when the people in the SEI are being paid out of taxpayers money and should be doing it.

Muchos Gracias !!!

MickLimk

Your calculations look fine to me Cuauhtemoc!

I've added a few more panels that are quite widely used across the country. There are some without the solar yield figures as the EN12975 cert is not from SPF but the Fraunhofer Institute (some reckon these guys are better than SPF) which doesn't seem to rate this figure as a reliable performance indicator...

I guess the real comparison a consumer would need to make here is to compare efficiency versus cost. Take an example of the Thermomax MS 20 (81.017%) versus a Navitron SFB 20 (77.737%). There is only a difference of 3.28% in the efficiency numbers here and in my experience the T'max is more expensive. Given these facts, I know I'd go with Navitron and spend the extra money on additional insulation for the pipework or cylinder as this could really make a greater difference to the system performance.

It really does appear that tubes win the battle over plates when using the DEAP calculation though!

Cuauhtemoc

Have updated further.

All the tubes including non spf/en12975/solar keymark rated ones. All rated flat plat ones(theres about 50 more unrated ones which i'll add in when i get a chance.)
Flat Plate sheet1, tubes on sheet 2.

Tubes do seem to have the edge but from April to September when the boiler(if you have one) wouldn't be on, flat plate would be more efficient wouldn't they?
In winter then the boiler would probably do most of the heating. Thoughts?

Enjoy!

C.

heinbloed

The solarkeymark is THE standard for EU solar products. A list of certified collectors-flat panel as well as tubes- is here available: http://www.estif.org/solarkeymark/Links/Internal_links/database/collector-database-updated.htm
Some product data bases are directly available via that link, others are available from the manufacturers,contact their home pages via the list above.
To see what the various test parameters actually mean check this link: http://www.estif.org/solarkeymark/collector-theory.php
As MickLimk said already: efficiency means capital input versus capital output. The cheapest, most efficient collectors are the evacuated tube collectors from SUNSHORE(see list)-as far as I know.
Tubes are more efficient in wintertime compared to flat plate collectors.

MickLimk

heinbloed wrote: »

The solarkeymark is THE standard for EU solar products.

Not 100% sure about that. EN-12975 is the standard that products must meet. The Solar Keymark seems to be more of an optional 'Quality mark' and certainly not THE standard...

heinbloed

The European Norm gives no hint on efficiency, even the worst collector can be tested according to EN 12975, for example a plain garden hose.EN 12975 gives the conditions under wich the testing has to be done, but no classification whilest the solar keymark symbol is only granted to those products that have been tested in acredited (lab-)facilities, guaranteing a min. efficiency of something like 500 Watt per m2 when exposed to 1,000 Watt radiation. For the exact number check the keymark standards, the min. efficiency/performance to be met had been raised (last year?). And will be raised further with newer developments.So the solar keymark symbol granted for a product can be deregistered/withdrawn, The EN might be changed or be scrapped, but without any effect on previously achieved test results.I hope this sheds some light(smiley).

rayh

On the basis that we can achieve around 500kW/m2/yr from Flat Plate and or 600kWh/m2/yr from Evacuated Tubes. What are the typical factors which effect performance relative to storage sizes.
RayH

heinbloed

The performance of the collector is not effected by the storage, this is a different story.A tube collector delivering only 600Watt per m2 is a pretty lousy thing, the better ones make more then 750 watts per m2 when exposed to 1000 W of radiation.
The performance of the collector is higher if fed with cold water, the warmer the input the smaller the gain. But there will still be a gain.

rayh

Solar conversion performance as I understand it varies with transfer temperature - high at low temps and low at high temps. In say a domestic system, water usage is not time related to solar radiation and therefore the system will experience varying temperatures and this range in turn will be related to the volume to collector and hence my query or am I missing something?

heinbloed

The SYSTEM's performance should suit the consumer's demand.No, you aren't missing something there.The collector is only one part of the system, it's performance can be meassured without using a storage tank. Similar to a lightbulb's performance which can be meassured without using a lamp.

sinnerboy

rayh wrote: »

Solar conversion performance as I understand it varies with transfer temperature - high at low temps and low at high temps. In say a domestic system, water usage is not time related to solar radiation and therefore the system will experience varying temperatures and this range in turn will be related to the volume to collector and hence my query or am I missing something?

Don't know if this will help - here goes

DEAP calcs - B1 rated house .
300m2 .
6m2 solar - flat
Data entered - certified values
Aperture area 5.56m2
0 loss efficiency 0.73
Collector loss 3
annual solar radiation 1016 ( from DEAP manual )
Dedicated storage 150 litres ( 1/2 of cylinder )

Qs result 1974 kw/hr/yr

IF - dedicated storage is changed to 300 litres

Qs changes to 2145 kw/hr/yr

I am not a heating engineer but my assessment is that if the dedicated solar storage is smaller - summer DHW may be "lost" - not usable . The energy is discharged ( un wanted ) into the heating system . Towel rails are good for this - it is nice if they are hot even in summer

But if you make the storage area larger to maximise the Qs - you just store more DHW - possibly more than is needed . And you have a larger volume of water for your primary heat source to heat up in winter .

I just know that some of you may rip this to shreds .... Take it easy on me HB , Snyper

rayh

These are very poor performances 1,974kWhr/yr from 6 x 1,200 or 1,000 kWh/m2 depending on where you live oin this country or even the 2,145 figure.
Where are the losses incurred?

sinnerboy

these are the outputs when entered into DEAP software

rayh

Can I recap on this thread;
On the 5th of Aug MickLimk wrote "If you want to see a combined performance figure that takes both the n0 and a1 numbers into account, I'm afraid you'll have to calculate it yourself! Personally I think the SEI should publish these figures in the list of approved products. From the DEAP workbook, the collector performance factor (CPF) is calculated as follows:
CPF = 0.87 - (0.034 (a1/n0)) + (0.0006((a1/n0)^2))

A tube example of this with n0 = 0.561, a1 = 1.61 W/(m2K) gives a CPF of 0.777.

A flat plate example with n0 = 0.761, a1 = 3.94 W/(m2K) gives a CPF of 0.71."

These figure I calculate panel/tube conversion of between 700kWhr/m2 and over 900kWhr/m2 .

According to subsequent DEAP calculations we can only achieve between 330 and 360kWhr/m2.

Is this a correct interpetation as I am getting more confused.

sinnerboy

http://www.sei.ie/uploadedfiles/InfoCentre/BER/DEAP__Version_2.2_Manual_February_2008.pdf

rayh

What am I supposed to see in this which has not already been presented in previous posts?

sinnerboy

that after Collector performance ratio a1/η0 is established - other factors include

Annual solar radiation per m² from Table H2 - orientation and angle
Overshading
Dedicated solar storage volume, Vs, litres
Daily hot water demand, Vd, (litres)

to calculate solar DHW input

Chimpster

sinnerboy wrote: »

that after Collector performance ratio a1/η0 is established - other factors include

Annual solar radiation per m² from Table H2 - orientation and angle
Overshading
Dedicated solar storage volume, Vs, litres
Daily hot water demand, Vd, (litres)

to calculate solar DHW input

Dedicated solar storage volume, Vs, litres.

I am not I fully agree with the concept of dedicated solar volume as its detailed in DEAP. If you have a 300L tank then you should according to DEAP assign 150L as dedicated storage volume. But the warm water rises and is quickly moved to the top of the tank. I would have thought that 300L should be the dedicated storage volume as well.

Any thoughts solar experts?

sinnerboy

Figure H2 page 50 determines that one Chimpster

To address Rayh's apparent frustration with me i should explain I am not a heating engineer and so i will stop trying to assist any further beyond this post . A qualified heating engineer would give a better response - no question

I am an Arch Tech and BER assessor have relied on DEAP for answers posted

There are limitations of course - DEAP calculates assumed DHW consumption based on m2 area . So for an extreme example , a very large house ( say 275m2)with only 2 bathrooms would be treated the same as a very large house with seven bathrooms as far as assumed DHW consumption is concerned . DEAP "punishes" the storage of hot water -i.e. ( assumes a lot of energy is lost in storage ) and factors in related elements such as the provision ( or not ) of heating zones and / or other heating controls .

This is the same for all BER assessors - you must follow the set down procedures in the DEAP manual and rate according to the resulting software output . To clarify - even if a qualified heating engineer can calculate the benefit of a Solar panel installation based on actual DHW consumption and actual storage losses - those calculations would not be relevant to a BER assessment

Rayh - I hope you get your answer

Chimpster

sinnerboy wrote: »

Figure H2 page 50 determines that one Chimpster

Yeah, I have been using this method in my assessments but I'm not sure I agree with it.

sinnerboy

No choice Chimpster . Got to follow the manual .

SEI are pretty good at responding to queries . Ask them and let's know how you get on

rayh

Sorry Sinnerboy if I have appeared to have caused you some displeasure with my questioning on the calculated outputs from Solar heating devices and maybe I should explain.
I have recently installed a Solar heating system (19m2 – 8 Flat Plate x 2.34m2) in my house (156 m2) to provide both DHW and space heating having brought my energy requirements down from over 200kWh/m2/yr to 86kWh/m2/yr though a series of thermal performance upgrades, but more importantly I have brought my CO2 emissions down from 13.7 Tonnes per annum to 2.7 Tonne.
I have installed a 4,250 Litre Buffer tank and included some energy monitoring equipment and therefore my questioning was to try and set down some basis before recording actual outputs which will require a full year before any meaningful conclusions can be arrived at as I too have some concerns about the DEAP basis.

heinbloed

To rayh:Have you monitored already an entire heating season? Or are these values based on pure calculations? 19m2 flatpanel collectors covering a spaceheating demand of 114kWh/m2/a seems to me to be a very optimistic calculation for the Irish climate, but I'm no heating engineer. Thanks.

sinnerboy

rayh wrote: »

Sorry Sinnerboy if I have appeared to have caused you some displeasure with my questioning on the calculated outputs from Solar heating devices and maybe I should explain.
I have recently installed a Solar heating system (19m2 – 8 Flat Plate x 2.34m2) in my house (156 m2) to provide both DHW and space heating having brought my energy requirements down from over 200kWh/m2/yr to 86kWh/m2/yr though a series of thermal performance upgrades, but more importantly I have brought my CO2 emissions down from 13.7 Tonnes per annum to 2.7 Tonne.
I have installed a 4,250 Litre Buffer tank and included some energy monitoring equipment and therefore my questioning was to try and set down some basis before recording actual outputs which will require a full year before any meaningful conclusions can be arrived at as I too have some concerns about the DEAP basis.

That's impresive Rayh - 19m2 panels - 4250 litre tank ? wow ! Bet that's not in the attic
DEAP is concerned with making standardised assumptions about occupancy and enegy usage rates so it won't help answer your case EXCEPT that- it does point towards storage losses , DHW consumption and heating controls all impacting on the actual performance of the solar panels . 200 down to 86 and 13.7 down to 2.7 is quite an indicator in itself .

Try recording DHW consumption in litres - annual . If your monitoring equipment can record water temps and external air temps - this would be good too. MET Eireann can provide weather stats - solar radiation . with a years worth of records like this I am sure a good building services consultant ( not equipment seller ) would be able to answer your queries

Mind sharing the € cost ?

sinnerboy

heinbloed wrote: »

To rayh:Have you monitored already an entire heating season? Or are these values based on pure calculations? 19m2 flatpanel collectors covering a spaceheating demand of 114kWh/m2/a seems to me to be a very optimistic calculation for the Irish climate, but I'm no heating engineer. Thanks.

Hi Heinbloed - I don't think the 114kWh/m2/a improvement is just down to the solar panels - Rayh says he did a series of other measures too - can you tell us more about that Rayh ? Significant insulation upgrade i assume ?

rayh

I will try to cover some of the issues raised;

1. I have 6 data loggers (5 inside and I outside) sampling temperatures at 5 minutes intervals since February 2006 coupled with records of all energy inputs.

2. Insulation upgrade – 400mm Fibre Glass in Attic, Windows and Doors from Single Glazed to U-value 1.4, Full Fill Cavity, 200mm Polyiso in Floors and 75mm centres Underfloor pipe system – Average U-value from 0.79 to 0.26 at an estimated cost €60K.

3. Solar system only commissioned last Tuesday week and will be supported by 12 kW wood pellet with water heating and hence the low CO2.

4. Additional monitoring will include solar radiation, energy from solar and energy to space heating – I do not expect to have this additional monitoring operational for a number of weeks

heinbloed

Thanks,rayh!That's impressive indeed.

Chimpster

sinnerboy wrote: »

No choice Chimpster . Got to follow the manual .

SEI are pretty good at responding to queries . Ask them and let's know how you get on

Thank you for your e-mail.
What you have stated (using half of the cylinder – or up to the bottom of the upper coil) is true for a combined cylinder. As per the DEAP manual “in the case of a combined cylinder (such as arrangement b) in Figure H2), the volume of the dedicated solar storage plus 0.3 times the volume of the remainder of the cylinder;”

If and when the top of the coil is hot due to the boiler rather than the solar coil, the solar coil does not have the ability to heat all of the cylinder. As stated above, some of the remainder of the cylinder is assumed to be part of the dedicated solar storage, but not all of it. Even if the boiler is set using a timer, there is no guarantee that the homeowner will empty the cylinder of “boiler hot water” just before the sun starts to heat the panels.