Repowering an Older Commercial Solar System: Inverters, Panels and FIT Rules
Updated 23 October 2026 · SEO Dons Editorial
When does an older commercial system need repowering?
In 2026 a system commissioned between 2010 and 2019 is between 7 and 16 years old. Energy Saving Trust's guidance for homes says panels should last 25 years or more but that an inverter needs replacing after around 12 years. It adds that most inverters carry warranties of five years as a minimum, which can often be extended by up to 15 years. That is household guidance, but it points the same way for a roof system: the inverter comes up for replacement well before the panels do. How modules age is on the lifespan and degradation page.
The Feed-in Tariff (FIT) closed to new applicants from 1 April 2019, so a system of this age cannot start again with a fresh accreditation. The accreditation it already holds is the one to protect, which is why Ofgem's replacement rules matter before any equipment is ordered.
Replace the inverter, the modules, or both?
| Option | Points to check |
|---|---|
| Inverter only | The new unit's DC input range against the existing strings, a new application to the network operator, monitoring and warranty. Inverter designs are compared on the inverter types page. |
| Replace failed modules | Ofgem allows partial replacement, including with previously accredited equipment. The designer should show the electrical match and the clamp fit. |
| Replace all modules with higher-rated ones | Total installed capacity rises, which is a notifiable change, and roof loading and wind uplift need rechecking (see panel sizes and weights). |
| Add modules | An extension: no FIT payments on added capacity commissioned on or after 15 January 2016, and a new application to the network operator. |
| Add a battery | Connecting storage is a notifiable change for FIT sites. See commercial solar battery storage. |
What do Ofgem's Feed-in Tariff rules say about replacing equipment?
Ofgem's generator guidance says you may repair or replace some or all of the equipment without affecting accreditation, provided the installation keeps meeting the scheme rules. Those rules include that the 5 MW maximum is not exceeded, that the installation keeps generating from the same eligible technology, and that it is not decommissioned or relocated.
Ofgem also allows generating equipment to be replaced with equipment from a previously accredited FIT or Renewables Obligation installation. If all the plant up to the point of grid connection is removed, Ofgem treats the installation as decommissioned and the accreditation as ended, so a full strip-out is not a replacement.
Total installed capacity (TIC) is the term to watch. Ofgem defines it as the maximum capacity at which an installation could be operated for a sustained period without damaging it, usually the total kilowatt capacity of the generating equipment. A change that raises or lowers TIC, including replacing equipment with a larger or smaller TIC, must be notified to the FIT licensee. ROO-FIT generators, with a declared net capacity over 50 kW, must also notify Ofgem; MCS-FIT generators, at 50 kW or less, notify only the licensee.
What happens if you add capacity?
Ofgem says an accredited installation can be modified to increase or decrease capacity as long as the TIC of the installation and any extensions stays within 5 MW. However, no FIT payments are made on electricity from additional capacity unless the extension was commissioned before 15 January 2016. Where meters record both accredited and non-accredited capacity, payments must be prorated.
That wording is about additional capacity, so higher-rated replacement modules that lift TIC raise the same question. Ask the licensee in writing how it treats the increase and how the new capacity will be metered. Export arrangements for FIT sites are covered on the FiT export and SEG page, and the test for whether extra capacity pays is on the payback, ROI and IRR page.
Do you need to tell the network operator?
The connection agreement is a separate matter from FIT accreditation. SSEN, one network operator, says most components of a solar power site have a life span of between 20 and 40 years, after which they may need to be refurbished or replaced, which it calls re-powering. It says that whether a connection conforms to G59, G99 or a combination, you will need to submit a new G99 application.
SSEN adds that new components can have a different impact on fault levels and harmonics, so most if not all components may need to conform to G99. It also says that applying will not automatically affect contracted capacity. Other operators set their own routes, so ask yours before ordering equipment.
What happens to the modules you take off?
GOV.UK lists PV panels as Category 14 of the WEEE rules, so removed modules need a registered carrier, a waste transfer note and an authorised treatment facility. Who pays for collection is covered on the recycling and WEEE page.
What drives the cost of repowering?
This page gives no prices. The factors that move them are:
- Scope: one inverter, several, modules, or the whole system.
- Electrical match: whether new equipment suits the existing strings and cabling, or the DC side needs redesign.
- Roof access: lifting, edge protection and the condition of the roof covering.
- Network operator process: SSEN lists possible charges for a re-powering application, including connection offer expenses where the connection is at 11 kV or above, witnessing of commissioning works, reinforcement works and a transmission impact assessment.
- Downtime: generation lost while the system is off.
- Warranty position: what remains on the kit you keep and what the new kit carries.
- Waste handling: collection and treatment of removed modules.
The commercial PV systems guide shows how these choices fit the wider specification.
What should you do before committing?
- Find the FIT accreditation details: the licensee, whether the system is MCS-FIT or ROO-FIT, and the recorded TIC.
- Ask for the before-and-after TIC for each option in writing.
- Compare the new equipment's datasheet and warranty terms with the old.
- Ask the network operator what application it needs before equipment is ordered.
- Tell the FIT licensee, and Ofgem for a ROO-FIT system, about any change that alters capacity or connects storage.
- File the new commissioning documents with the original handover file.
An enquiry about a specific older system can be sent through this site's form, and the commercial PV systems guide explains what a specification should contain.
Sources
- Energy Saving Trust: Solar panels: costs, savings and benefits explained (household guidance), updated 1 October 2026, checked 22 October 2026.
- Ofgem: Feed-in Tariffs (FIT) generator guidance and FAQs, checked 22 October 2026.
- Ofgem: Key terms explained for Feed-in Tariffs, checked 22 October 2026.
- SSEN: Re-Powering existing Generating Facilities (that operator only), checked 22 October 2026.
- GOV.UK: EEE covered by the WEEE Regulations, updated 12 August 2025, checked 22 October 2026.
Common questions
Will replacing my inverter affect my Feed-in Tariff?
Ofgem says you may repair or replace some or all of the equipment without affecting accreditation, provided the scheme rules still hold. If the replacement changes total installed capacity, tell your FIT licensee, and Ofgem as well for a ROO-FIT system. Ask the licensee how it treats the change before work starts.
Can I fit second-hand panels as replacements?
Ofgem's guidance allows replacement with equipment that has formed part of a previously accredited FIT or Renewables Obligation installation. That sentence does not cover other used equipment, so check with the licensee before buying.
Is it worth adding panels to an old Feed-in Tariff system?
No FIT payments are made on additional capacity commissioned on or after 15 January 2016, so the case rests on bill savings and any export income from the new capacity. The payback, ROI and IRR page explains how to test that.
How long do commercial inverters last?
Energy Saving Trust's household guidance says to replace an inverter after around 12 years. Commercial manufacturers publish their own warranty terms, so read the datasheet for the model on your roof.