Upgrading existing solar - what about the feed-in tariff?

Hive mind, I need your wisdom. I have a 3.5kw solar array which the previous owner put in c.2011, so I have the benefit of the big FIT. Is it possible for me to add new panels without messing up the feed-in tariff? Would they need to run through a separate inverter or something? Or could I replace/upgrade the whole array?

I have a good deal at the moment as I get about 50p/unit for 50% of the units generated, but the panels are not really kicking out more than 2.9kw at very best and I would like to look at a battery and a bigger array at some point.

Hey Jason. Cool that you inherited a FIT installation from the previous owner!

Re: the extension question

  • Since Jan 2016, extensions to accredited FIT installations are not eligible to receive FIT payments.
  • Adding an extension shouldn’t disqualify the existing FIT installation, but you’ll have to make sure the electricity generated by the extension is metered separately from the electricity generated by the FIT installation.
  • For further information check out p.23-24 of this Ofgem doc.

Re: batteries

  • The regulations around FIT & batteries were drafted by Ofgem in Dec 2017. They should be finalised soon.
  • The 4 key principles communicated so far are:
  1. Co-located storage does not change generators’ obligations to comply with the FIT scheme requirements.
  2. Generators will only receive support for eligible renewable electricity generated by an accredited FIT installation.
  3. Installing storage will not alter the TIC of the FIT installation.
  4. The schemes’ eligibility requirements are not changed by the type of storage technology.
  • For further information, check out this Ofgem doc.


You’ll need to confirm with your DNO that they will allow any addition in the first place. There seems to be some variability across different DNO’s in this regard. Understandably they’ll not want to see the different phases becoming too unbalanced.

It is likely that any such addition will need to be via a G59/ 3 certified inverter.

You may not need an additional meter, I believe that your FIT payment can be pro-rata’d.



Hi Jason

Since moving in, have you cleaned the solar panels? That may help to improve you 2.9kw return. It’s rather expensive to get them professionally cleaned, but I bought myself an extending brush that attached to the hosepipe. Once, maybe twice a years is as good as it gets for me. One American on YouTube suggested cleaning them every 6 weeks, but he did have easy access to his roof.

My challenge is how to stop a pair of pigeons nesting under the panels each year!