Adding panels to a Feed-in Tariff system means increasing the capacity of an installation that is already accredited. Ofgem calls that an extension. The rules are firm. You keep your original tariff on your original capacity. The added capacity earns nothing under FIT.
That does not make it a bad idea. It changes where the money comes from. This article sets out what stays the same, what does not, and what you have to tell your FIT licensee.
Key Points
- Ofgem defines an extension as a modification that increases total installed capacity using the same eligible technology. Adding panels counts. So does replacing panels with more powerful ones.
- Any extension commissioned on or after 15 January 2016 is not eligible for FIT support. Ofgem says this applies to generation payments and to export payments.
- Your original installation keeps its eligibility date, its tariff rate and its eligibility period. Ofgem's supplier guidance says changes to total installed capacity do not affect the tariff rate.
- You must contact your FIT licensee when you increase or reduce your total installed capacity.
- If the extension shares a generation or export meter with the accredited installation, readings are pro rated by capacity. Ofgem's worked example: a 40 kW installation extended by 10 kW, with an unaccredited extension, is paid on 80% of what it generates and exports.
- Meter readings should be taken on the date of the extension.
- Combined capacity of a single technology on a site must not exceed 5 MW. Go over and the whole installation, original plus extension, becomes ineligible.
- Removing a factory set output limit counts as an extension too. Ofgem names de-rating removal and repowering as ways an installation can be extended.
- The extra generation still has value: you use it in the house, and you can be paid for exporting it under the Smart Export Guarantee.
Common Misconceptions
- More panels means a bigger FIT payment. No. The added capacity is not paid under FIT at all.
- Adding panels voids my whole tariff. No. Your original capacity keeps its rate and its term. Only the extra is excluded.
- I will just not mention it. Your statement of FIT terms requires you to tell your licensee about capacity changes. Ofgem can audit installations and can withhold or recoup payments.
- Deemed export means I get paid on the new panels too. Deemed export is worked out from your generation meter reading for the accredited installation. Pro rating is designed to stop the extra capacity being paid.
- There is no point adding panels now. There often is. The gain comes from using more of your own electricity, and from SEG export, not from FIT.
Real-World Advice
We do not have a published case study of a FIT extension. Every project on our work page at the time of writing is a new 2026 installation, not an extension of a FIT era array.
UK-Specific Considerations
Pro rating is the part people miss. If the new panels feed the same generation meter, that meter no longer measures only your accredited installation. Ofgem's answer is to split the readings by capacity. So a bigger array can mean a smaller share of each reading is paid.
A separate installation is a different question. Ofgem says capacity added using a different eligible technology is not an extension; it is treated as a separate installation. That does not help with more solar panels, which are the same technology.
Deemed export can be affected. Deemed export is available where export cannot practically be measured, for installations at or below 30 kW. Ofgem says that if pro rating is available on a shared export meter, export can be measured, so deemed export is not available.
Sharing the export route. Ofgem sets out two options where unaccredited capacity shares a meter with a FIT installation. Opt out of FIT export and take a SEG export tariff across the whole capacity. Or do not claim SEG on the extra, and pro rate the FIT export payments.
Your network operator has a say first. Extra panels usually mean more inverter capacity. The Energy Networks Association sets the threshold at 16 A per phase. That is 3.68 kW on a single phase supply and 11.04 kW on three phase. Below that, G98 applies and the installer notifies the network operator within 28 days of commissioning. Above it, the G99 process applies and the network operator has to be consulted before the work.
Do not switch things on and sort it out later. For a G99 route the application comes first. For a change to an existing G99 connection, the guide says you must notify the network operator before making changes.
What you keep and what you do not
| Original accredited capacity | Capacity you add now | |
|---|---|---|
| FIT generation payment | Yes, at your existing rate | No |
| FIT export payment | Yes, deemed or metered, if you have opted in | No |
| SEG export payment | Only if you opt out of FIT export | Yes, if the export is metered |
| Value from using it at home | Yes | Yes |
| Counts towards the 5 MW site limit | Yes | Yes |
When This Isn't Right For You
- Your roof has no more usable space that faces a sensible direction.
- Your current inverter is already at its limit and replacing it would trigger a full G99 application you do not want.
- You are close to the end of your eligibility period, so the FIT side of the sum is nearly over anyway.
- You use very little electricity in the day and have no battery and no plan to get one.
Before You Spend Money
- Find your accredited capacity on your FIT statement. That number is the line between paid and unpaid.
- Work out what you actually do with the electricity. Extra panels pay through self consumption and export, so your daytime usage matters more than the panel count.
- Ask about metering before you order anything. If the new panels share your generation meter, ask your licensee how they will pro rate, and what that does to your quarterly payments.
- Compare an extension with a separate system. A second array on its own meter and its own export arrangement can be simpler. Ask your installer to price both.
- Get the network operator route confirmed in writing. G98 notification and a G99 application are very different in time and cost.
- Do not assume a SEG tariff. Rates and terms are set by each supplier. Check what is on offer at the time, not what somebody was paid last year.
Frequently Asked Questions
Q: Do extra panels increase my Feed-in Tariff payments?
A: No. Ofgem says an extension commissioned on or after 15 January 2016 is not eligible for FIT support, for generation or for export. Your original capacity keeps its rate.
Q: Will adding panels reduce the payments I already get?
A: It can, if the new panels feed the same meter. Ofgem then requires the readings to be pro rated by capacity, so you are paid on your original share of each reading.
Q: Can I be paid for exporting the extra electricity?
A: Yes, through the Smart Export Guarantee. Ofgem says you must first opt out of FIT export payments, and you can then take a SEG tariff. You do not have to opt out of FIT generation payments.
Q: Do I have to tell anyone?
A: Yes. Ofgem says you must contact your FIT licensee if you extend or reduce your total installed capacity. Your network operator also has to be told, by notification or by application, depending on the size.
Q: What if the extension pushes the system over a network limit?
A: Then the G99 process applies and the network operator must be consulted before the installation goes ahead. Your installer should confirm the route before you commit.
Summary
You can add panels to a FIT system. You keep the tariff you have on the capacity you were accredited for, and you keep it for the rest of your term. The new panels are not paid under FIT, whatever their size. Their value is in the electricity you use yourself and in a SEG export tariff. There are two practical traps. A shared meter means pro rated payments. A larger inverter can move you from a simple notification onto a full network application. Settle both before you order equipment.