The Domestic Solar Job That Is Done But Not Closed
MCS-certified domestic solar jobs finish with the panels on the roof, but the job is not formally closed until six specific documents are in order. Here is what those documents are, where the process typically breaks down, and what a clean commissioning sequence looks like.
The installation crew finishes mid-afternoon. Panels on, inverter running, generation meter confirmed. The customer shakes hands and assumes the job is complete. From an operational standpoint, it is not. Between commissioning sign-off and a balance invoice that can reasonably go out, there is a specific set of documents that must exist - and for a business running 15 or more domestic jobs a month, how quickly those documents are produced determines whether cash arrives this week or two weeks from now.
What Has to Exist Before the Job Can Formally Close
MCS-certified domestic solar work carries a defined set of outputs by commissioning sign-off. Each has a recipient, a deadline, or a dependency on data captured on site.
The Electrical Installation Certificate (EIC) documents the fixed wiring work to BS 7671. It is one of the first items a buyer's solicitor requests when the property sells and is reviewed in every MCS audit. An installation without one is not technically complete.
G98 or G99 notification covers the connection to the distribution network. Systems up to 3.68kW per phase on a single-phase supply fall under G98 - the installer notifies the Distribution Network Operator (DNO) after commissioning, within 28 days, and no prior approval is needed. Anything above that threshold requires a G99 application to be submitted and approved before installation begins, with commissioning confirmation submitted after energisation. Treating a G99 job as G98 is an audit finding - and means the system was energised without the DNO's permission.
MCS Installation Database (MID) registration must be completed within 10 working days of commissioning. The MID entry generates the MCS certificate, and the MCS certificate is what the customer needs to register for Smart Export Guarantee (SEG) payments with their energy supplier. Until it exists, the installation officially did not happen from a compliance standpoint. A slow MID registration delays the customer's export income, and the customer will call the installer to ask why.
The handover pack assembles the above for the homeowner: MCS certificate, EIC, DNO notification or approval evidence, system schematic, component datasheets, warranty terms for panels and inverter, workmanship guarantee documentation, and guidance on applying for SEG. MIS 3002 and the relevant consumer codes - RECC and HIES for domestic work - both require it.
The 10-Day Rule
MID registration must be completed within 10 working days of commissioning. The certificate it generates is what unlocks the customer's Smart Export Guarantee application. A late registration doesn't just affect your compliance record - it delays the customer's income from their system.
Where the Process Breaks Down
The documentation itself is manageable. The problem is that the data it depends on was supposed to be captured on site, and frequently wasn't captured in a format the office can use.
IEC 62446-1 commissioning tests require results recorded per string: open-circuit voltage, short-circuit current, insulation resistance on the DC side, earth continuity, polarity checks. The MID entry needs exact component details, commissioning date, and system size. The EIC references the wiring as actually executed, not as designed. All of this exists at the end of install day - but often only in a site notebook, a phone camera roll, or the engineer's memory.
When the office opens MID registration two or three days after commissioning and finds the test records incomplete, the choice is to call the engineer and try to reconstruct the figures from memory, or book a return visit to the property. A return visit to collect data that should have been captured first time costs £200-400 in unbilled travel and time - and moves the MCS certificate at least another week out.
For an installer completing 15 jobs a month, two or three return visits in any given month is a material cost. More immediately visible, it extends the payment cycle. The balance invoice on a domestic solar job tends to follow the certificate rather than the commissioning date, because customers reasonably feel the job is not done until they have the documents they need to apply for SEG payments. When MID registration takes eight working days and the handover pack is assembled manually from scattered sources on top of that, the balance invoice goes out ten to fourteen days after the panels went up - for work that was capable of billing within 48 hours.
The Upstream Fix
The target for an installer running jobs efficiently is a handover pack out within 48 hours of commissioning, with the balance invoice included. That is achievable, but it requires the data to arrive in the office the same day the engineer leaves the property.
That starts at survey. A G99 application cannot be submitted without the exact inverter and panel specifications, so a survey that leaves kit selection open means the application waits on a design decision. The MIS 3002 performance estimate that must be given to the customer before contract draws from the same survey: roof dimensions and orientation, shading analysis, supply details for the DNO application. If those fields were captured as notes rather than structured data, someone in the office redoes the work before the G99 application can go in.
On install day, commissioning data needs to leave the site in a form the office can use directly. When the engineer works through a digital checklist with required fields - string test results, inverter commissioning, DC labelling, photos of the array, consumer unit before and after - the data is in the system before the engineer starts the drive home. MID registration becomes a matter of transferring information that already exists, not reconstructing it. The certificate follows within a few days, the handover pack follows the certificate, and the balance invoice goes with the pack.
Using a mobile eForms App to capture commissioning evidence on site closes the gap between what was done and what the office can document. Required fields prevent a job being signed off with gaps in the record. Photos attached to the job rather than left in a personal camera roll arrive in the right place at the right time.
Invoice with the Handover Pack
Include the balance invoice in the handover pack. When the pack goes out within 48 hours of commissioning with the MCS certificate attached, the customer has everything they need for their SEG application and the invoice is already in their hands - rather than being sent separately a week later.
The close is the output of the commissioning process, not a separate administrative task. When the commissioning process captures everything it needs on site, the MCS certificate arrives quickly, the handover pack goes out with the invoice, and the job is paid. When it doesn't, the certificate waits, the pack waits, and the invoice waits - for work the customer is already benefiting from.
Sources
- Solar PV commissioning under MCS: from survey to sign-offPayaca · accessed 2026-07-30
- DNO Approval for Solar UK (2026): G98, G99, TimelinesSolarLove · accessed 2026-07-30
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