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How do I add more panels to my existing solar PV system?

Posted by Gabby Mallett on 11 September 2015 at 12:45 pm

Q. I would like to have more panels added to my existing system.  What do I need to know?

A. There are a few things to consider, mainly changes to the Feed-in Tariff (FiT) since your last install. 

Firstly the price you get per kWh has decreased substantially.  When you first installed the government was paying you a massive 41.3p per kWh.  This has now reduced to just 12.92p and you would get that amount for the additional panels.  You don’t get to add on at the old rate. A big note of caution; there is a consultation out at present which will not only dramatically reduce the FiTs level, but also remove the possibility of system add-ons to be eligible for FiTs at all.  It’s a consultation, so not definite, but you probably need to get your system extension installed as a priority or wait until you know the outcome of the consultation before proceeding.

The second major change is that the FiT is now only guaranteed for 20 years.  You would have had a 25 year guarantee back in 2010.

Thirdly you will now need to show that you have installed other energy efficiency measures or have a reasonably efficient property to begin with.  You need to have an EPC with a rating of D or better to get the highest FiT rate on offer.  

From a technical perspective you would need to ensure that your roof structure is capable of handling the additional weight of the new panels and that the wiring is capable of handling the additional capacity.  Another consideration is to ensure that the new solar PV panels are compatible with the existing ones.  This last requirement is needed to ensure that your enhanced system performs to its optimum level rather than being limited by lower output panels.

Finally you will need to consider the size of your inverter.  If you want to take your system from 2.75kWp up to 4kWp you may need a new inverter which could add substantially to the cost.  However, there is evidence to say that a smaller inverter, suitable for a 3kWp system, can be used on a 4kWp system without much effect. This is because the inverter has a Maximum Power Point Tracking (mppt). In practise your panels will not be working at full potential all of the time, so will only reach the mppt on rare occasions.  The majority of the time the inverter will not affect performance at all.  Of course your installer should be able to advise you and if he knows that the cost of the extra panels and a new inverter would put you off then he is more likely to tell you what you can get away with.

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4 comments - read them below or add one

NEF Gabby

NEF GabbyComment left on: 15 October 2015 at 4:22 pm

There shouldn't be a problem with getting a new inverter.  Most systems will need one before the end of their useful lives. As long as your post code doesn't change you should still keep the same old rate for the existing part of the system.


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Bill15Comment left on: 15 October 2015 at 12:57 pm

The final paragraph of Gabby's answer states that "you may need a new inverter".

Might a new inverter invalidate the FiT eligibility of the existing installation and thereby jeopardise the original installation with its higher tariff?

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NEF Gabby

NEF GabbyComment left on: 25 September 2015 at 9:49 am

Dear Eszygeeze

please see the Feed in Tariff Guidance for Renewable Installations (version 6) 31st October 2013. This is the most recent version.

point 2.79 on page 20 states that 'where a FIT installation is extended using the same technology type, the extension is assessed as a separate Elibigle Installation. [..] The original installation's eligibility date, tariff, and eligibility period will not be affected.'

There is plenty more detail in the document, but I think you were given incorrect advice previously. You should get your existing FITs exactly as you are getting them now and then any new system at the rates prevailing at the time.

Hope that helps.





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easygeezeComment left on: 18 September 2015 at 12:55 pm

I've had a 3.8 KWh since 2010 I had considered adding another 4 KWh but was told that the whole array would then be down graded to the FiT rates employed at the time of additional installation which seems to be at odds with the above comment "the price you get per kWh has decreased substantially.  When you first installed the government was paying you a massive 41.3p per kWh.  This has now reduced to just 12.92p and you would get that amount for the additional panels. " Can you please clarify, if this is the case how does the FiT payment work ?

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