The Paperwork Behind a Cornwall Solar Install: MCS, G98 and Your SEG Application

The three documents that matter

A solar installation generates a handover pack that can run to thirty pages, most of which you will never open. Three documents in it do real work, and you should be able to name all three before the scaffolding comes down: the MCS certificate, the DNO notification, and the electrical installation certificate. Everything else — datasheets, warranty cards, the inverter manual — is reference material.

This matters in Cornwall more than most places, because a high proportion of systems here are fitted specifically to earn from export, and the export payment is the one thing that depends entirely on a piece of paper.

The MCS certificate

The MCS certificate records that your system was designed and installed by a certified company to the scheme's standards. It carries a certificate number, your address, the installed capacity and the estimated annual generation.

Its practical importance is simple: a system has to be MCS certified to be eligible for the Smart Export Guarantee, which is the mechanism that pays you for electricity you export. Without it, the panels still work and still cut your import bill, but no supplier is obliged to buy your surplus. The certificate is issued after commissioning, and it is normally registered on the MCS database within a few days.

Two things to check on it. First, that the capacity matches what you paid for — a 4.4 kWp system certified at 3.8 kWp is somebody's typing error and it will follow you into the SEG application. Second, that the installer is certified for solar PV: MCS certification is granted per technology, so you can verify the company on the public register at mcscertified.com and see exactly which technologies it covers.

G98, G99 and telling the DNO

Your system is a generator connected to the public network, so the distribution network operator has to know about it. In Cornwall that is National Grid Electricity Distribution (South West). Which route your installation takes depends on its size:

• Up to 16 A per phase — 3.68 kW — the installation is notified under G98 after commissioning, within 28 days. This covers a lot of standard domestic arrays.
• Above that, a G99 application has to be made and approved before the system is energised. Approval is not instant, and it is the single most common reason a quoted install date slips.

If your installer cannot tell you which route applies to your design, the design is not finished. An inverter can also be limited in software to keep an installation inside the G98 threshold — a legitimate approach, but one you should be told about, because it caps what the system can export on its best afternoon.

The electrical certificate

The solar array is electrical work, so it produces an Electrical Installation Certificate under BS 7671, and the work is notifiable under Part P of the Building Regulations. The certificate names the person who designed, constructed and inspected the installation, and it is the document a surveyor or a conveyancer will ask for when you sell. Keep it with the MCS certificate rather than in the inverter box in the loft.

Applying for the Smart Export Guarantee

The SEG is an obligation on larger electricity suppliers to offer a tariff that pays for exported electricity. You apply to a supplier — not necessarily the one that sells you electricity — and you will be asked for:

• your MCS certificate number;
• proof of a meter capable of half-hourly export readings, in practice a working smart meter;
• the system's capacity and commissioning date.

Rates differ sharply between suppliers and change more often than people expect, so it is worth comparing rather than defaulting to your own supplier. Our guide to Smart Export Guarantee rates covers what is currently on offer.

If a document never arrives

Chase it immediately, not in the spring when you get round to the SEG. An MCS certificate is issued by the installer against their certification; if that company stops trading before issuing it, you are in a far weaker position, and it is one of the reasons the consumer-code route matters. Ask, at the point of quotation, how long after commissioning the certificate is issued and who to contact if it does not appear.

If you are weighing up quotes in Cornwall now, our page on solar panel installers Cornwall sets out the five things worth checking before you sign — the registers to search, who applies to the DNO, and who actually does the work. For what a system costs here, see solar panel costs in Cornwall.