Skip to main content
Observer Ethical awards Winners 2011

YouGen Blog

Efficiency or cost per watt - which is most important?

Posted by Graham Eastwick on 2 March 2009 at 1:56 pm

The development of thin film photovoltaics (PV) is progressing fast. It's still not as efficient as crystalline silicone solar panels, but I have read of projects using thin film technologies from single roofs up to large “solar farms” with capacities in the region of 40 MW.

Crystalline solar panels can reach efficiencies of up to 20 per cent in production these days (which means it converts 15 per cent of solar radiation into electrical energy). Thin film is currently achieving efficiencies of between 6 and 12 per cent. Is this important or is it simply the cost per watt that matters?

If you have plenty of roof space or land then I would think that the cost per watt is the key factor when deciding how large a solar array to install. Thinking further, thin film technologies are said to perform better under overcast diffuse light so actually it is the cost per watt-hour that is the key factor.

In the UK we have quite a lot of diffuse light on  cloudy days, so perhaps thin film PV is going to be a good technology for the UK market.

I would be interested in your views on this.

About the author: Graham Eastwick is a director of Encraft, and manages renewable energy installations for home owners, community organisations and small businesses across the UK.

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

Like this blog? Keep up to date with our free monthly newsletter


6 comments - read them below or add one


AlternativeComment left on: 4 October 2010 at 12:22 pm

I agree with Graham, that cost per Watt is the most important factor. No use having slightly more efficient panels if they cost 25% more. If you stick to well known makes like Sharp or Sanyo, then you're unlikely to regret it 20 years from now.

report abuse

alan drever

alan dreverComment left on: 4 October 2010 at 11:15 am


I'm planning PV installation on home roof, initially c4kw, then upgrading to 6-7Kw 12 months later (if all's well).

I am wanting to maximise output in interests of emissions reduction & therefore (while aware of other considerations) % efficency is most important factor, especially as in low sunlight level end of the country (Skye - c740Kwp/yr).   Couple of questions:

The highest efficiency array I've found is Sanyo HIT 240HDE4 @ 17.3%.  Do you know of any other currently MCS accredited panel that has higher array efficiency?  It occurs to me that there may well be a Mono-crystalline panel that exceeds this.

Secondly, I have unearthed unsubstantiated information that hybrid panels (while as good in sunlight) operate better than MC or PC in non-sunlight.  If so, then they may well be better choice for Skye.  Is this so?  I am aware that hybrids operate better in warm weather (but uncommon in NW Scotland!).  Also, there may be other advantages of hybrid panels that would justify their higher price over MC.  Aware techology relatively new...

I havent been able to get clarification on above from either CAT (member) or EST.  Renewable Energy Association seem reluctant to respond on these particular points (product commercial interests?) & European Photovoltaic Industry Association has no contact details on website.

Look forward to hearing from you.

Thanks a lot


report abuse


fuelexplorerComment left on: 18 May 2010 at 11:27 pm

The USA has developed black silicon and is reported to be x50 more efficient than existing monocrystaline formats.  It also converts IR light into electricity.  The Yanks are initially going to use it for better X-ray equipment and no doubt DOD uses.  The mass market of PV is currently being ignored.

report abuse

dinesh uberoi

dinesh uberoiComment left on: 27 March 2009 at 7:05 pm

Hi Graham. I would like to know the area required per kw of this sheet and cost per square foot. What would be the life span of the Thin film and the effects of weather on thin film. Could you also suggest the supplier?

report abuse

Graham Eastwick

Graham Eastwick from EncraftComment left on: 12 March 2009 at 12:12 pm

Thin film PV technology has the potential to reduce the installed cost of a PV system when measured per kWp by 25 to 40%. Thin film is just as robust as conventional panels, the solar material is used to make modules, flexible panels or often applied to roofing tiles of integrated into windows.

report abuse

Cathy Debenham

Cathy DebenhamComment left on: 10 March 2009 at 12:36 pm

Hi Graham. The inference here is that the cost per watt - and the cost per watt-hour - will be less with film. Is this the case, and if so, how significant is the saving? Also thin film sounds much easier to damage than solid panels. Is this the case, or does it have the same sort of life expectancy?

report abuse

Leave a comment

You must log in to make a comment. If you haven't already registered, please sign up as a company or an individual, then come back and have your say.