Is MCS Needed for Commercial Solar? The 50 kW Rule Explained
Updated 11 November 2026 · SEO Dons Editorial
Planning an array above 50 kW? Go to the quote form; we reply by email.
What does MCS certify, and where does it stop?
MCS says its certification "covers installations of small-scale renewables in both domestic and commercial settings up to a certain size - 50kW for electrical technologies". A hypothetical 35 kW array on an office roof can sit inside that scope. A 120 kW array on a warehouse cannot, however good the installer, because there is no MCS certificate to issue for it.
MIS 3002 is the MCS standard behind solar PV work. The MCS standards library describes it as outlining "the requirements for the design and installation of solar PV systems", and lists two versions, both dated 18 March 2026: MIS 3002 version 6.0 for the current installer scheme and MIS 3002:2025 version 2.0 for the redeveloped installer scheme.
MCS is also clear about its legal status: "it is not a legal requirement for a system to be MCS certified". A certificate needs the installation to be commissioned by an MCS certified installer, to use MCS certified products, and to have a commissioning date after 15 July 2009. It records the technology, the installer and confirmation that the system complies with MCS standards.
Why do some pages say the Smart Export Guarantee needs MCS?
MCS's own Smart Export Guarantee (SEG) page lists two eligibility points side by side: solar panels of "5MW or less", and "Your system was installed by an MCS certified installer using certified products." Read together they imply MCS reaches 5 MW. It does not.
The government's SEG page is wider: you "need to show that your installation and installer are certified through the microgeneration certification scheme (MCS) or a scheme accredited as equivalent". The Welsh Government's grid connection note shows what a power purchaser may ask for: "a Microgeneration Certification Scheme (MCS) certificate associated with the installation, or proof the installation and installer are accredited in accordance with EN 45011 or EN ISO/IEC 17065:2012". Ofgem puts the SEG ceiling at "a total installed capacity up to 5MW".
| Array size | MCS certificate | Evidence for an SEG licensee |
|---|---|---|
| Up to 50 kW | Available, with an MCS certified installer and certified products | The MCS certificate |
| Over 50 kW, up to 5 MW | Not available, as MCS certification stops at 50 kW | "MCS or a scheme accredited as equivalent", for example proof of accreditation to EN ISO/IEC 17065 |
| Over 5 MW | Not available | Outside the SEG capacity limit |
Ask each licensee what evidence it accepts before an installer is chosen. The SEG guide for business covers meters, tariffs and the export MPAN.
What applies instead above 50 kW?
The absence of an MCS certificate removes one proof of quality, not the rules. The pieces that carry the load are:
- The wiring standard. The IET says the transition period for BS 7671:2018+A2:2022 ended on 15 October 2026 and that Amendment 4 is "now the current edition". A specification still naming the older edition needs updating.
- The grid code. The Energy Networks Association says a generator above 3.68 kW per phase comes under EREC G99, and that "compliance is the responsibility of the customer". MCS notes that G99 Type A covers 0.8 kW to less than 1 MW, so Type A spans commercial arrays well above 50 kW.
- A code of practice. The IET Code of Practice for Grid-connected Solar Photovoltaic Systems covers design, specification, installation, commissioning, operation and maintenance "from small domestic systems to large scale PV farms".
- Competence. Under CDM 2015 a commercial client appoints contractors and designers "while making sure they have the skills, knowledge, experience and organisational capability". The installer vetting checklist turns that into twelve checks.
- Handover and warranties. MCS gives smaller systems a handover pack with "product details and workmanship warranty". On a larger array, write the handover pack, test records and warranty documents into the contract; see commissioning commercial solar PV and commercial solar warranties.
Module certification is a separate question, covered in solar panel certifications.
How do you check MCS status for a system up to 50 kW?
- Check the installer. MCS encourages use of its Find an Installer search, and says "it's worth checking as you get a quote, before you sign your contract, and before the installation starts".
- Ask when the certificate will arrive. MCS's pages give different windows: 10 working days of completion on its solar page, within 14 days on its certificate queries page, and 30 days for installers on the redeveloped scheme. Put the date in the contract.
- Read what it records. The certificate should show the technology and model, the installation company and certification details, and confirmation of compliance with MCS standards.
- Match it to the product. MCS describes the certificate as proof the installation was designed, installed and commissioned "using only MCS certified products by an MCS certified installer".
- Verify with MCS if needed. Its helpdesk can confirm whether a certificate exists if given the technology type and full address, and it asks for proof that you "reside at the installation address". That process is written around households, so a business should ask MCS what it accepts for commercial premises.
The commercial PV installations guide shows where certification checks fall in a project, and you can send an enquiry through the quote form to put the same brief to several bidders.
Sources
- MCS, checked 22 October 2026: Becoming certified; MCS certificate queries; Installer MID guidance; Solar panels; Smart Export Guarantee; Notifying DNOs; Standards and tools library.
- GOV.UK, checked 22 October 2026: Smart Export Guarantee (SEG).
- Ofgem, SEG guidance for generators; Welsh Government, connecting site generation to the grid, both checked 22 October 2026.
- Energy Networks Association, connecting generation, checked 22 October 2026.
- IET, checked 22 October 2026: BS 7671 amendments; Code of Practice, 2nd edition.
- Health and Safety Executive, commercial clients under CDM 2015, checked 22 October 2026.
Common questions
Is MIS 3002 a law or a standard?
It is an MCS standard for the design and installation of solar PV systems. MCS itself says it is not a legal requirement for a system to be MCS certified, so MIS 3002 binds MCS certified installers rather than the market as a whole.
What if an installer says a larger system will be "MCS compliant"?
Ask which certificate will be issued and by whom. MCS says its certification covers electrical technologies up to 50 kW. For export payments, the government asks for MCS or a scheme accredited as equivalent, so request the scheme's name and accreditation in writing.
Does an MCS system skip the network operator?
No. MCS says the relevant network operator must be notified of electricity-generating installations "in all instances", including solar PV. Above 3.68 kW per phase that means G99, and MCS says its installers complete the Type A form for higher-capacity installations.
Should a business cap an array at 50 kW to keep MCS?
Size follows load, roof and the network connection. An MCS certificate is one route to evidence quality and SEG eligibility, but the government also accepts schemes accredited as equivalent, so the certificate should not drive the size on its own.
Can an existing array be MCS certified retrospectively?
Only if it met the rules when it was commissioned. MCS lists three requirements for a certificate: commissioning by an MCS certified installer, MCS certified products and a commissioning date after 15 July 2009, so a system fitted outside the scheme, or one above 50 kW, has no MCS certificate to apply for. Where an MCS certified installer did the work but never issued the certificate, MCS says it cannot help raise a new one and that the original installer is the first contact; MCS itself supplies a copy or an amendment only where that installer is no longer MCS certified or no longer trading.
Sources:
- MCS certificate queries, MCS, checked 10 November 2026.
- Becoming certified, MCS, checked 10 November 2026.