Upgrading solar panels on a Feed‑in Tariff system what happens to your FIT payments

Your generation tariff rate (the pence per kWh you locked in when your system was first registered) does not change. However, if your new total installed capacity is higher than your original registered capacity, your FIT generation payment is applied to a proportional share of your metered generation.

The formula is straightforward: FIT payment = metered generation × (original capacity ÷ new capacity) × tariff rate.

If you are on deemed export (no export meter — 50% of generation assumed as exported), the same proportional logic applies: your deemed export is calculated on the FIT-eligible share of generation. However, the additional generation above the FIT share can be exported under the Smart Export Guarantee (SEG) separately.

If you are on metered export, your actual export reading is used. The FIT export tariff applies to the proportional share of your metered export.

Email or write to your FIT licensee (the energy company that pays your FIT — check your latest FIT statement). Explain that you intend to replace your solar panels with higher capacity modules. Ask them to confirm in writing that your FIT accreditation will be maintained and how your generation payments will be adjusted. Keep all correspondence. If they claim the FIT will be lost, reference Ofgem's December 2021 decision on replacement generating equipment and request escalation.

The installer must be MCS-certified. They will assess your roof structure, existing wiring, and inverter compatibility. Modern panels produce higher voltage per panel — your existing string configuration and inverter DC input ratings may need adjustment. The installer should provide a clear specification showing old and new total installed capacity.

If your original inverter cannot handle the new panel configuration (higher string voltage, higher total wattage), it will need replacing. This is permitted under FIT rules — Ofgem's decision covers replacement of all generating equipment including inverters. A new inverter may also unlock features like battery compatibility, better MPPT tracking, and remote monitoring. Factor this into your budget.

If the total installed capacity changes, your Distribution Network Operator must be notified. G98 covers systems up to 16 A per phase, which is 3.68 kW on a single-phase supply and 11.04 kW on three-phase. That limit is on the total inverter output, not the panel capacity, and notification is sufficient (your installer submits it: a notification, not an application). Anything bigger is always G99, even with export limited: a 5 kW inverter limited to 3.68 kW is still G99, never G98. Under G99 the installer usually needs the DNO's approval before the new panels are energised. Your installer should handle this, but always ask for the reference number.

The installer removes the old panels and installs the new ones. A new electrical installation certificate (BS 7671) must be issued. If the inverter was replaced, the new inverter must be commissioned and export limitation configured if required by your DNO. The installer should take a generation meter reading before and after the swap to clearly mark the changeover point for FIT billing purposes.

After installation, notify your FIT licensee of the new total installed capacity. They must update the Central FIT Register. Your generation payments will then be calculated on the new proportional basis. Request written confirmation of the updated registration and retain a copy of the MCS certificate, electrical installation certificate, and DNO notification reference.

If you are on deemed export (50% assumed), installing a smart meter permanently moves you to metered export. You cannot go back to deemed. This is relevant because with higher capacity panels, your self-consumption percentage may be lower — meaning you might export more than 50% and benefit from deemed. Conversely, if you have a battery, you might export less than 50% and metered export would pay you less. Think carefully before combining a panel upgrade with a smart meter installation.

Some FIT licensee customer service teams may still tell you that changing panels voids your FIT. This is incorrect per Ofgem's December 2021 decision. If you encounter resistance, ask them to put their position in writing and reference the Ofgem decision. If necessary, escalate to the Energy Ombudsman. Never proceed with installation without written confirmation from your FIT licensee that your accreditation will be maintained.

Work on FIT-accredited installations should be carried out by an MCS-certified installer. Non-MCS installation could be used by a FIT licensee as grounds to question your accreditation. The MCS certificate is also required for DNO notification and for any future warranty claim on the new panels or inverter.

The replacement panels must not have been previously used at another FIT or Renewables Obligation accredited installation. Second-hand panels from a decommissioned FIT system cannot be used to replace panels at a different FIT installation. New panels — or panels that were never part of a registered scheme — are fine.

Systems registered between 2010 and 2012 locked in generation tariffs of 30–45p/kWh (index-linked, so even higher now). Even with pro-rated payments after a capacity increase, the FIT income per kWh remains far higher than current electricity savings. A 4 kWp system on 43p/kWh generation tariff upgraded to 6 kWp still earns 43p on two-thirds of every kWh generated — that is a substantial income stream that no new installation can match.

Every kWh you generate and use yourself avoids buying from the grid at 24–30p/kWh. Higher capacity panels produce more energy, increasing the amount available for self-consumption — especially if you have a battery to store midday surplus. This self-consumption saving applies to all generation, not just the FIT-eligible proportion.

Solar panels degrade at roughly 0.5–0.7% per year. A 15-year-old system may be producing 7–10% less than when new. But degradation is not the only issue — older panels suffer from hot spots, micro-cracks, PID (potential induced degradation), and failed bypass diodes. A system that was originally 4 kWp may only produce 3.2 kWp in practice. Replacing these degraded panels with new 5 kWp capacity actually increases your FIT-eligible generation because the proportional factor (4 ÷ 5 = 80%) applied to significantly higher output can exceed what the degraded old panels were earning.