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How do I distinguish between two solar PV quotes?

Posted by Cathy Debenham on 19 November 2014 at 10:01 am

Q: I am considering two quotes both similar in price. I live in merseyside and have a south east facing and south west facing roof. There is a chimney on the southwest facing roof and so there are some shading issues.

The first quote is for LG monocrystalline panels, 250watts, with 15.6% efficiency 16 panels in total to make up a 4 kW system to be divided over the two aspects of the roof. They will also use solatech power optimisers . 

The second quote is from IKEA / Hanergy for their thin film  panels,120 watts each, 24 in total to make up a 2.88kwatt system, to be distributed over the two aspects of the roof and two converters. 

The Hanergy people claim that although these panels are only 12.8 % efficient they give better output in shaded and overcast conditions. Also will not degrade as quickly as the monocrystalline ones. They come with a guarantee for 80% output for 20 years. They say that they are better at a lower wattage (120 watts) per panel as each panel reaches their maximum output quicker than a 250 watt monocrystalline one will. They say that even at a lower total wattage of 2.88kwatt their average output over the year will be more than the 4 kW monocrystalline panels will produce and these are designed for overcast conditions. 

A: We put this reader's question to energy expert Chris Jardine of Oxford University Environmental Change Institute and Jojo Solar. His feedback is as follows:

The LG quote seems fairly standard.  I'm not a massive fan of power optimisers, preferring to see shade avoided rather than dealt with in this way, but if the client is keen on capacity, then the optimiser route is the right way to go.

The Hanergy quote seems a bit of a muddle in terms of messages, which is quite tricky to unpack.

  • As a thin film technology, they should give a small performance advantage over the LG over the course of a year, maybe 5% or so.
  • The reason for this advantage is that the Hanergy panels will be better at picking up bluer light in overcast conditions.
  • This is not the same as better performance in low light levels (we have low light levels early in morning and late in afternoon on sunny days as well, but this light is redder (red sky at night etc...).  Hanergy will not offer an advantage under these conditions.
  • So the better performance of Hanergy under some conditions is due to colour, not the overall light level.
  • So Hanergy will NOT help with performance when shaded (light is the same colour, but less of it)

As above I think you will see maybe a 5% advantage per kW for the Hanergy.  You will not see the kind of 35%+increase in performance increase claimed in the last statement. Bit naughty this!

Photo credit: Lori Geig via Compfight cc

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Comments

1 comments - read them below or add one

SunGift Energy

SunGift EnergyComment left on: 24 November 2014 at 8:01 am

I agree with Chris Jardine’s comments, the Hanergy quote does seem somewhat misleading in some points.

We have found on our test array in Exeter that Solar Frontier thin film modules (using the similar CIGS technology as the Hanergy modules) perform on average 12% better than crystalline technologies on East or West facing roofs. However the additional cost of the thin film modules does not always mean that this energy yield advantage is cost effective.

In regard to the guarantee , a good  module these days should come with a linear performance output guarantee of 80% at 25 years, certainly modules from LG and JA Solar do. Hanergys’s offer falls a little short in this respect.

The point that the Hanergy modules will reach their peak output faster is very odd and should be dismissed. As Chris states, the energy yield benefits of some thin film modules is due to their response to a broader part of the spectrum of light received by the module. Thin film manufactures will be producing 250Wp modules and higher just as soon as they can, it is one of the routes to reducing costs!

On the point of shading, the shadow cast by the chimney is best avoided as far as possible. The orientation of the modules will have an effect on the production of the system as the way a shadow moves across a module will impact landscape or portrait modules differently., but maybe this is best saved for a different topic!

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