Install day and the timeline: what actually happens
From accepting a quote to being paid for exports is usually weeks, not days, and most of the elapsed time is other people’s processes rather than work on your roof. The install itself is often one day.
One day on the roof; several weeks of everything else.
Most of the elapsed time between accepting a quote and being paid for exports is other people’s processes — scheduling, scaffolding, network notification, certification, and a SEG application you have to make yourself.
The two things that reliably cause delay are scaffold access and, on larger systems, a G99 application which must be assessed before anything is installed.
The sequence
1. Survey. Ideally a physical one. MIS 3002 requires a specific note where a site was assessed remotely, warning that performance “may be significantly lower or higher” — so if that note is on your paperwork, nobody came. The survey should establish the roof structure, the covering’s condition, shading, cable routes and where the scaffold goes.
2. Network notification or application. This is the branch point:
- At or below 16 A per phase — 3.68 kW single-phase — G98 applies. Install first, notify within 28 days. No wait.
- Above it — G99 applies, and nothing may be installed or commissioned until the operator has assessed the application and told you the outcome. Under the simplified small-generation procedures the response comes within 10 working days, and your planned commissioning date must fall between 10 working days and 3 months from applying.
If your system is above the threshold, this is the item that sets your timeline.
3. Scaffolding. Usually erected a day or two before. On a terrace this is the step to sort early — scaffold may need to stand on a neighbour’s land and there is no statutory right to it.
4. Installation. Typically one day.
5. Commissioning and handover. Testing, settings, and the paperwork.
6. Notification and certification. G98 notification within 28 days; MCS certificate and building regulations compliance certificate usually within a few weeks.
7. Register for a SEG tariff. Yours to do. It does not happen automatically.
What install day looks like
Scaffold and setup. Roof access, tile or slate removal where brackets go.
Mounting. Brackets fixed into rafters, rails across them, panels onto the rails.
DC side. Panels wired in strings, cable routed into the building — typically through the loft to the inverter.
Inverter and AC side. Inverter mounted, usually in the loft or a utility space, then the AC circuit run to the consumer unit. This is when the power goes off, for an hour or two.
Testing and commissioning. Insulation resistance, polarity, earth continuity, inverter settings, and confirmation the system is generating.
Handover. The walkthrough, and the documents.
Before they leave:
Photograph the module and inverter serial numbers, and check the models against the datasheets you were quoted. Note the generation meter reading, photographed and dated — that is your baseline for proving performance later. Confirm monitoring works on your own device, with your own login. Ask to be shown the DC and AC isolators.
All four are trivial while somebody who understands the system is standing in your house, and awkward afterwards.
What delays things
Scaffold access, especially mid-terrace.
A G99 application — by design, since nothing may be installed before assessment.
Roof repairs found at survey. If the covering is near the end of its life the sequencing question arrives: do the roof first.
Structural questions. A roof triggering one of MIS 3002’s five unusual-structure conditions needs a qualified structural engineer — see structural surveys.
Certificates nobody chased. The commonest of all, and entirely avoidable. If nothing has arrived a month after commissioning, chase it while the company is still trading.
The SEG application you did not make. Systems sit exporting for nothing because nobody realised the tariff was a separate arrangement.
After the first year
Compare a full year of metered generation against a modelled figure for your roof. Our dataset is free and published for that purpose, and proving underperformance explains how to read the gap — briefly, a shortfall under about 10% is probably weather and soiling, and 20% or more points at something specific.
Do not judge the system on a winter quarter. Two thirds of annual output arrives between April and September, and the June-to-December ratio runs from about 3.6× on the south coast to 14.9× in Shetland.
Sources
- Engineering Recommendation G98, issue 2 (10 March 2025) Free to download.
- Engineering Recommendation G99, issue 2 (10 March 2025) Free to download.
- Smart Export Guarantee: Guidance for Generators
Contains public sector information licensed under the Open Government Licence v3.0.
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