Upgrading solar panels on a Feed‑in Tariff system what happens to your FIT payments
Old panels degraded or failed? Modern panels can produce significantly more power from the same roof space. You can replace panels on a FIT system — even with higher wattage modules — without losing your Feed-in Tariff. This guide explains the Ofgem rules, how your payments change, and the step-by-step process.
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Book a diagnostic — £75 → How diagnostics workCan you replace panels on a FIT system with higher wattage modules?
Yes. This has been explicitly confirmed by Ofgem — but the rules are often misunderstood by installers and even some FIT licensees. Here is what the regulator actually says.
In December 2021, Ofgem published a formal decision on the treatment of replacement generating equipment under the Feed-in Tariffs scheme. The decision confirmed that replacing some or all of the generating equipment at an accredited FIT installation — including solar panels and inverters — does not affect the accreditation of that installation, provided the installation continues to meet scheme rules.
The current version of Ofgem's FIT Guidance for Generators states that modifications to total installed capacity (TIC) — whether increases or decreases — must be notified to your FIT licensee but do not affect the tariff rate of the accredited installation. The installation remains on the Central FIT Register at its original tariff rate.
Before the December 2021 decision, there was genuine ambiguity. Some FIT licensees took a cautious interpretation and told homeowners that any change to panels would void their FIT. Others were more permissive. The 2021 decision was specifically issued to end this inconsistency. Despite this, some call centre advisors at FIT licensees may still give incorrect advice — always request written confirmation and reference the Ofgem decision if challenged.
How your FIT generation and export payments change
Your tariff rate stays the same. But if you increase the total installed capacity, the proportion of generation that attracts FIT payments changes. Here is exactly how it works.
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.
Step-by-step: how to upgrade panels on a FIT system
Follow this process in order. The most common mistakes happen when homeowners replace panels first and notify later — always notify first.
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. For systems up to 3.68 kW single-phase, G98 notification is sufficient (your installer submits this — it is a notification, not an application). For systems above 3.68 kW, a G99 application is required and the DNO must approve 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.
Common scenarios
The same rules apply in each case, but the practical implications differ. Here are the three situations we see most often.
Panels from 2010–2015 were typically 230–260W. If one or more panels have failed (hot spots, delamination, bypass diode failure), finding identical replacements is often impossible — the models are discontinued. Modern equivalents in the same physical size are 400–450W. Replacing all panels with modern modules means you get a working system again with significantly more capacity from the same roof footprint.
FIT impact: Capacity increases, so generation payments are pro-rated. But since the old panels were degraded or failed, your actual FIT income may increase because the new system produces far more than the degraded old one did.
If your roof is being re-tiled or repaired, panels must come off anyway. This is the ideal time to upgrade — the scaffolding and labour costs are already covered. You avoid the separate cost of a panel removal and reinstallation. Modern panels are also lighter per watt, which is better for aging roof structures.
FIT impact: Same proportional payment rules apply. The cost-effectiveness is strongest here because you are sharing installation costs with the roofing work.
Instead of replacing FIT panels, some homeowners add entirely new panels with a separate inverter. The original FIT system continues untouched on its full tariff rate. The new system generates under the Smart Export Guarantee or is used purely for self-consumption. This avoids any change to FIT payments but requires roof space for additional panels and a second inverter.
FIT impact: None — the original FIT registration is unchanged. The new system is a completely separate installation with its own MCS certificate and DNO registration.
What to watch out for
The rules are clear, but there are practical traps. These are the issues we see cause problems for homeowners.
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.
When upgrading panels makes financial sense
The financial case depends on your original FIT tariff rate, how much your old panels have degraded, your electricity costs, and whether you have battery storage. Here is how to think about it.
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.
Sources and references
This guide is based on the following Ofgem publications and industry sources. All links were verified as of March 2026.
Frequently asked questions
Yes. Ofgem confirmed in December 2021 that replacing generating equipment — including replacing panels with higher capacity modules — does not void your FIT accreditation. You must notify your FIT licensee of the change in total installed capacity. Your generation tariff rate stays the same, but if capacity increases, payments are calculated proportionally against the original registered capacity.
Your tariff rate is unchanged. If your total installed capacity increases, FIT generation payments are applied to a proportion of your metered generation: original capacity divided by new capacity. For example, 4 kWp original upgraded to 6 kWp means FIT is paid on 66.7% (4÷6) of your metered generation. The remaining generation reduces your grid imports or can earn via the Smart Export Guarantee.
Yes, if the total installed capacity changes. Systems up to 3.68 kW single-phase fall under G98 (simple notification). Above 3.68 kW requires a G99 application with DNO approval before the new panels can be energised. Your MCS-certified installer should handle this notification as part of the installation process.
If you are on deemed export (50% of generation assumed as exported), your deemed export payment increases because total generation increases. The proportional factor applies to the FIT-eligible share. Be aware: installing a smart meter permanently moves you to metered export — you cannot return to deemed. With higher capacity and no battery, you may export more than 50% and metered could pay better. With a battery, you may export less than 50% and deemed is more favourable.
Yes. Ofgem's December 2021 decision covers all generating equipment, not just panels. You can replace the inverter with a different brand or model. This is often necessary when upgrading to higher wattage panels, as the new panels may have different voltage and current characteristics. A modern hybrid inverter also enables battery storage if you want to add that later.
Often yes — especially for early FIT adopters (2010–2012) with high tariff rates. Even with pro-rated generation payments, the combination of FIT income, increased self-consumption savings, and potential SEG income on excess export typically justifies the investment. The case is strongest when panels are already degraded or failed, when combined with re-roofing work, or when paired with battery storage to maximise self-consumption.
Related guides
How SEG works, available tariffs, and how excess generation beyond your FIT share can earn under SEG.
Which grid connection standard applies when upgrading your system capacity and what your DNO requires.
Why DNOs set export limits and how higher panel capacity affects export limitation configuration.
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