Panel installation and wiring
What Happens at a Solar PV Site Survey?
Before any installer quotes you for solar panels, a reputable company visits your home to check the roof, the electrics and the shading. Understanding what they look for means you can prepare properly and compare quotes intelligently afterwards.
MCS certification and DNO notification are mandatory for all grid-connected solar installs. A site survey is the first step toward an MCS-certificated installation. The installer must notify your Distribution Network Operator before energising the system: G98 for installs up to 16A per phase with no battery export, G99 for larger systems or those with export-capable batteries. A reputable installer will discuss this with you at survey stage, not as an afterthought after the work is done.
1. Roof structure and condition check
The surveyor inspects the roof covering: tiles or slates for breakage, slipping or missing units, ridge tiles, verge details and the guttering for signs of ongoing movement. They also look at what is visible from the loft hatch, checking that the roof timbers are sound and that there are no signs of rot, insect damage or previous poorly repaired leaks.
This matters because fitting panels to a roof that needs repair in the near future is false economy. If a tile lifts or a batten fails after the panels are on, accessing the roof for repair is significantly more disruptive and expensive. A good installer will flag any concerns at survey stage so you can address them beforehand.
For flat roofs, the condition of the membrane or felt covering is the key check, along with whether the substrate can bear the additional loading of a tilted panel frame system.
2. Roof space measurement and orientation assessment
The installer measures usable roof area on each pitch, checking for obstructions: chimneys, party walls, velux or dormer windows, soil vent pipes, satellite dishes and any conservation area restrictions that limit panel placement. The exact azimuth (compass direction) and pitch of each roof section is recorded, usually with a compass and an inclinometer or a surveying app.
From this they calculate how many panels can be fitted in each zone, what the estimated shading profile looks like, and whether a single-string or multi-string inverter setup is the right call. A complex roof with multiple orientations often benefits from a hybrid inverter with multiple maximum power point trackers, one for each string direction.
3. Shading analysis
Shading has a disproportionate effect on solar output: even a small shadow on one panel in a string can significantly reduce output from the whole string. A thorough survey identifies sources of shading: neighbouring rooftops, mature trees, chimney stacks, and the building's own dormers or extensions, then models when during the day and year each shading source affects each part of the roof.
Where significant shading is unavoidable, the installer can recommend panel-level optimisers (such as SolarEdge or Tigo) or microinverters (such as Enphase), which allow each panel to work independently rather than being dragged down by the lowest-performing unit. The cost of optimisers is weighed against the generation they recover.
Some installers use dedicated shading tools at survey stage; others rely on their experience with similar properties in the local area. It is reasonable to ask the surveyor how they assessed the shading impact and what it means for your annual generation estimate.
4. Electrical survey inside the home
The electrical part of the survey covers several things. The surveyor checks your consumer unit (fuse board) for the spare capacity needed to accommodate a solar generation circuit and, if a battery is included, a battery feed. They verify your earthing arrangement, because this affects which type of battery and inverter can be safely installed without additional works.
They also check your main service fuse: older properties with a 60A or 80A fuse may need an upgrade if a large solar-plus-battery system is proposed. This is a DNO matter, not something the installer can simply authorise themselves.
Your metering is another key item. To receive Smart Export Guarantee payments you need a smart meter capable of recording export as well as import. If you do not already have one, your electricity supplier arranges this, and the installer will advise you at survey stage whether to request one before or after installation.
Finally, the surveyor identifies where the inverter and any battery will be located: typically a garage wall, a utility room, a ground-floor cupboard or an internal wall close to the consumer unit. They check that there is adequate ventilation and that the space meets the placement rules under PAS 63100:2024 and BS 7671 Amendment 4 (not in a loft, not in a bedroom, not in an unprotected escape route).
5. System design and DNO pre-check
With the roof and electrical data gathered, the installer produces a preliminary system design: the number and model of panels, the inverter specification, whether optimisers or microinverters are recommended, any battery included, estimated annual generation in kWh, and a projection of bill savings and SEG income.
They also confirm which DNO notification route applies. G98 covers single-phase installs up to 3.68 kW output (16A per phase) without battery export, and the installer self-certifies; this adds no waiting time. G99 covers larger systems and those with battery export capacity, and requires the DNO to approve the application before work begins; timescales vary by network operator but are typically four to ten weeks.
A reputable installer completes the DNO application on your behalf as part of the installation package. If a surveyor does not mention DNO notification at survey stage, that is a gap worth asking about directly before you accept a quote.
Frequently Asked Questions
Is a solar site survey free?
Most reputable installers carry out initial site surveys free of charge as part of the quoting process. Some charge a deposit deducted from the installation cost, or a separate fee for a detailed shading or structural report. Ask upfront what is and is not included before booking the visit.
How long does a solar site survey take?
A thorough residential survey typically takes one to two hours. Larger or more complex properties, those with multiple roof sections, unusual electrical arrangements or significant shading, may take longer. A very short visit that skips the consumer unit inspection or shading assessment is a sign the installer is not doing it properly.
What should I do to prepare for a solar site survey?
Clear access to your consumer unit, your loft hatch if the installer wants to inspect roof timbers from inside, and the proposed inverter and battery location. Have a recent electricity bill to hand so the surveyor can check your annual usage and suggest an appropriate system size. If you have already had a smart meter fitted, note down your supplier's name as this speeds up the SEG registration process.