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MCS Solar Installation Standard: What Changed in 2025
The Microgeneration Certification Scheme updated its solar PV installation standard (MIS-3002) significantly in 2025. If you are planning an MCS-certified install, or adding to an existing system, here is what changed and what it means for you.
Helpful video reference. eFIXX's "MCS Announces Big Change in Solar Install Standard" covers the key changes from a UK electrical trade perspective, as part of their Electrical News Weekly series. Worth watching for the installer's-eye view of what the new rules actually involve.
Notifiable and certified work
All MCS-certified rooftop solar is notifiable under G98 or G99, and the DNO must be informed before the system is energised. Work on roof-tied DC strings, consumer unit connections, or incoming mains must be carried out by a qualified person. The MCS certificate issued by your installer is evidence of compliance with MIS-3002 and protects your eligibility for SEG payments and 0% VAT.
1. What MIS-3002 is and why it was updated
MIS-3002 is the MCS installation standard for solar PV systems in the UK. It is a technical document that sets out exactly how an MCS-certified installer must design, mount, wire, and commission a rooftop solar system. Any installer holding MCS certification agrees to follow it, and MCS audits check compliance.
The 2025 revision was the most substantial update to the standard in many years, responding to advances in panel technology (larger format panels, bifacial modules), changes in DC circuit protection requirements, and lessons learned from inspection data about where systems commonly fail.
2. The flat roof mounting rule from August 2025
The most talked-about change is the flat roof mounting requirement. From August 2025, any MCS-certified solar installation on a flat roof must use a mounting system that has been certified to MCS 012, a separate MCS standard covering structural loading, ballasting, wind uplift, and compatibility with flat roof membranes.
For homeowners with pitched roofs, this rule does not apply. But if your property has a flat roof section where panels could go, ask your installer specifically which mounting product they plan to use and whether it carries MCS 012 certification.
If your roof is pitched
The new flat roof rule will not apply to a standard pitched tile or slate roof. The updates that do affect all installs are around DC cable routing, commissioning documentation, and string protection. Ask your installer which version of MIS-3002 your system will be commissioned under.
3. DC circuit design and cable routing changes
The 2025 standard tightened several requirements around DC circuit design: how cables are routed through the roof space, protection against reverse-polarity faults, and the positioning of string fuses and disconnects. These changes mainly affect installers' design and paperwork rather than anything a homeowner would see, but they are intended to reduce fire risk from DC arc faults, which have been the cause of a small number of serious incidents in older installations.
4. What you should receive at handover
Under the updated standard, your installer must give you a commissioning checklist, a system design record, and a declaration of conformity at handover. These documents confirm the system meets MIS-3002 and are what you need if you ever make a warranty claim, apply for SEG, or sell your property. If they are not offered without prompting, ask for them before signing off the job.
Frequently Asked Questions
Does the 2025 MCS standard apply to my existing solar system?
No. The updated MIS-3002 standard applies to new installations commissioned after the relevant change dates. Your existing system was installed to the standard in force at the time. If you are adding to or modifying an existing system, however, the new standard applies to the new work.
What is MCS 012 certification for flat roof mounting?
MCS 012 is a separate MCS standard for flat roof and ground mount systems, covering structural loading, ballasting, wind uplift, and waterproofing compatibility. From August 2025, any MCS-certified installation on a flat roof must use a mounting product certified to MCS 012.
Do I need an MCS-certified installer for any solar work?
You need an MCS-certified installer to receive an MCS certificate, which is required for most Smart Export Guarantee registrations and for the installation to qualify for 0% VAT. Grid connection work and DNO notification (G98 or G99) are always required regardless of installer certification. DIY plug-in solar under 800VA does not need MCS certification.