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Why is solar PV marketed on efficiency, not yield?

Posted by Ian Smith on 14 June 2012 at 11:06 am

I was struck going round Ecobuild in March, not just by the sheer number of exhibitors of PV panels, but by their marketing.  The vast majority were prominently promoting the efficiency of their cells or panels but very few were promoting energy yield at all - and none that I could see for the more diffuse light conditions we see in the UK.

One example even linked high yield to high efficiency but maybe their 'yield' was per square meter not per kilowatt (kW).  Certainly the stand representative could not provide the data to back this up when asked.  If anything, the data generally point to some lower efficiency thin film technologies having higher yields under the sort of light levels we get in UK.

From a purchaser's perspective, two of the key parameters for the economics are low system cost per kW and high yield per kW.  Panel efficiency is a second order consideration as this primarily affects how many kWs one can get on to a particular roof surface. This is often no more important for this purpose, given the relatively modest differences between offerings in the market for mono- & poly- silicon panels, than having a good choice of panel sizes and dimensions to get the best unshaded space fill factor (or a more aesthetically pleasing layout).

So, why is this industry marketing efficiency when it is yield that brings in the money?  Not one salesman I spoke to could answer that question and one even commented that it was a very good question.  

About the author: Ian Smith is a freelance consultant who advises local government, charities and low carbon community groups on renewable energy matters.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

4 comments - read them below or add one

Cathy Debenham

Cathy DebenhamComment left on: 30 November 2012 at 9:39 am

Hi Fran

I'd agree with Ekland Solar's comment below yours. This is a long term investment, and you want the panels to go on performing well for 25+ years. So how well they are manufactured, how good the warranties are and whether the company is going to be around for the long term are all equally important things to consider.

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fran

fran Comment left on: 29 November 2012 at 10:45 pm

Hi Everyone

HELP! HELP! HELP!

I have been looking at Pv panels now for a couple of weeks - reading all the articles - looking at Photon tests, etc I still don't know the best panel for the job!

I have narrowed my choice down to REC 250PE, JINKO JKM250P-60, YINGLI YL250 30b - but they are all similiar in their efficiency % - I cannot workout which give the better yield - if that is the correct way to make your choice!!??

Any comments woud be great.

I should point out that the system to be installed is 6.5kw, south facing and 30' pitch on roof, no shading problems and situated in N Ireland

 

Many thanks

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Ekland Solar

Ekland SolarComment left on: 3 July 2012 at 3:38 pm

There appears to be a lot of mis-selling going on around the efficiency rating of PV modules.  The author is correct to say that the primary benefit of high efficiency is to get more kWp out of a small area. From the point of view of system output and yield a 250w module is a 250w module whatever its efficiency rating. A higher efficiency module will simply be smaller in physical size. 

While quoting efficiency ratings of modules as an indication of performance may be misleading, a standardised 'yield rating' would give no more indication of performance than the existing power output rating at standard test conditions.

The real world yield from any particular panel is affected by the relationship between numerous environmental factors which will vary from day to day and throughout the year. The crux of the matter is how well a module performs (or how well its efficiency holds up) outside of standard test conditions and there is clearly no one easily digestable (or easily marketable) figure for this. 

What manufactures tend to say is, for example, 'our module performs well in low light conditions'.  This will mean that the efficiency of the module will not fall too much as the W/m2 of irradience falls below stc of 1000w/m2. Similarly they may say that their module performs well at high temperature.

These qualitative statments are always going to be a slighlty tricky sell as people tend to like hard figures to back up performance claims.  One place to look for data to back up real world performance is to independant field trials like the Photon Tests.  These trials monitor module yield over the full year recording detailed environmental conditions in tandem.  

Good performance in these trials can provide a degree of substantiation to a manufacturers claims. At Ekland Solar our choice of modules is based on a balanced consideration of build quality, real world performance, price and manufacturer's company profile, warranty and service reputation.  High efficiency modules certainly have their place but high efficiency is not to be mis-sold. Thier use should be weighed up in the context of cost effectivness.

 So why not market on yield? probably because yield is too much affected by real world conditions and cannot be summed up in one easily comparable number.


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Hiltingbury

HiltingburyComment left on: 22 June 2012 at 6:47 pm

You raise an interesting point but I'm not sure how you would express yield. Are you suggesting that the units are something like kW/lumen/m^2 and how would that be aggregated for the whole year?

The more common factor of 'efficiency' was important to me as I have limited south-facing roof space and within the area available I have only managed to fit 3.3kWp. To predict my total output for the year I have used the model below. So far this year this appears to be reasonably accurate although the energy generated over the last 4 weeks has fallen somewhat below par!

http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php#



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