How to Upgrade Your FIT Solar PV System in 2025: Batteries, Inverter Replacements & MCS Servicing
- hannahharvey2
- Jul 29
- 3 min read
If your solar PV array was installed under the UK Feed‑in Tariff (FIT) scheme, you’re already earning two valuable payments:
Generation tariff – paid for every kWh your panels produce.
Export tariff – paid for energy you send back to the grid (usually deemed at 50% of generation on systems ≤ 30 kW).
Although the FIT closed to new applicants in 2019, more than 850,000 UK homes still benefit from it.
Many are now exploring battery storage, inverter upgrades, and routine servicing to squeeze more value from their PV — without losing their precious FIT income.
This guide explains what you can and can’t change in 2025, and how a battery can shorten your payback period.
Can I add battery to FIT solar PV??
Key Benefits
Boost self-consumption – Store surplus solar during the day and use it in the evening, reducing reliance on expensive grid energy.
Time-of-Use (TOU) arbitrage – Charge your battery overnight using off-peak tariffs (from ~7.9p/kWh) and use it during peak times (>29p/kWh).
Backup during outages – Many batteries offer limited off-grid capability.
Future-proof for EVs & heat pumps – Store more energy as your home’s electricity demand grows.
Example Battery Payback (3.68 kW FIT + 10 kWh battery)
Item | Value |
Battery & install cost | £6,000 (e.g. GivEnergy 9.5 kWh AC) |
Annual savings (1,600 kWh @ 29p) | £464 |
TOU arbitrage gain (700 kWh @ 21p) | £147 |
Total yearly benefit | ≈ £610 |
Simple payback | ~9.8 years |
Battery life: ~12–15 years. FIT income remains unaffected.
Battery Setups for FIT Solar - Protect the Income
Configuration | Allowed? | Notes |
AC-coupled (after generation meter) | Yes | Safest. Battery is outside FIT circuit. May charge from grid, but must not export it. |
DC-coupled (before generation meter) | Risky - not the safe option | May under-record generation or interfere with deemed exports. |
Hybrid inverter (like-for-like) | Yes | Fine as long as capacity doesn’t increase and metering stays accurate. |
Always notify your FIT licensee of any changes.
SEG vs FIT: 2025 Export Payment Comparison
Scheme | Export Type | Typical Rate (July 2025) | Notes |
FIT Export | Deemed (50%) | 5.24p/kWh (fixed) | No metering required. |
SEG – Octopus Outgoing | Metered | 15p/kWh flat | |
SEG – British Gas | Metered | 15.1p/kWh | |
Best promotional SEG deals | Metered | Up to 27p/kWh | Changes often. Use export meter. |
Switching to SEG forfeits your FIT export payment permanently — we would not advise doing this.
Solar Inverter Replacements & Capacity Changes
Like-for-like inverter swaps are allowed (e.g., replacing a failed inverter).
Hybrid inverter upgrades are fine if the PV capacity doesn't increase.
Adding panels usually voids your FIT — unless done as a separate system (e.g. SEG only).
Can I Extend My FIT Installation?
Yes — in some cases!
If your system was installed before 15 January 2016, you can work with an MCS-accredited installer like Limitless Energy to repower your system.
What is Repowering?
Repowering means replacing older generating equipment with newer, more efficient models, which may:
Improve performance
Slightly increase system capacity (kW)
According to OFGEM FIT Guidance (Chapter 3, section 3.10):
You must notify and get approval from your FIT licensee prior to any changes.
Any additional capacity added after the upgrade is ineligible for FIT payments.
What Does This Mean in Practice?
If your original system was 3.5 kW and is repowered to 4.0 kW:
Your FIT payments apply only to 3.5 kW of capacity.
The extra 0.5 kW can still generate energy for self-use or SEG export.
Your FIT tariff may be pro-rated if capacity boundaries are adjusted.
Repowering lets you keep earning on your legacy FIT setup while modernising and improving your home’s solar performance.
MCS Recommends: Service Every 10 Years
The Microgeneration Certification Scheme (MCS) recommends a professional solar service every 10 years.
What’s Included:
Full panel inspection (mounts, wiring, shading)
Inverter performance check and firmware update
Generation meter test/calibration
DC/AC isolator and RCD test
Output benchmark against PV GIS estimates
Servicing helps maintain safety, maximise output, and ensure your system stays compliant and insurable.
Key Takeaways
AC-coupled batteries can slash bills without affecting FIT.
Payback on batteries now under 10 years — faster with TOU savings.
Inverter swaps are fine if like-for-like.
Repowering is possible on pre-2016 systems (extra capacity won’t get FIT but still adds value).
Book your 10-year MCS service to keep everything running smoothly.
You can find out more from OFGEM in their most recent guidance for generators which is published here:
Contact Us to book a service or for a battery quote
Tel: 01792 361638
Email: info@limitless-energy.org
Based in Swansea — installing and servicing in Swansea, Neath Port Talbot, Brecon, Bridgend, Cardiff and Carmarthenshire.
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