Solar installation day checklist what to check before, during and after

Verify on the MCS installer database that the company's certification is active. Do not rely on the installer's own paperwork — check on the day.

MCS certification for solar PV (MIS 3002) and battery storage (MIS 3012) are separate accreditations. An installer may hold solar certification without battery certification — this is more common than you might expect. Check the scope listed on the MCS database matches the work being done. If the installer does not hold battery MCS certification, check directly with your chosen export provider whether this affects your eligibility for export payments — requirements vary between providers. Make sure you understand and are comfortable with the implications before proceeding.

Confirm whether scaffold or ladders are being used and that it matches what was stated on your quote. Scaffold costs money — if it was quoted and not provided, raise it before work begins.

Compare the panels, inverter and battery being unloaded against your quote and DNO notification. Substitutions happen — sometimes due to supply issues, sometimes not. If anything differs, ask for an explanation before installation begins.

The DNO notification lists the specific equipment notified to the network operator. If different kit is installed, the notification is invalidated — which affects your MCS certificate and SEG eligibility.

Also check the mounting system — rails, hooks and clamps should match the equipment listed on your quote and MCS design certificate. Substituting mounting hardware is as significant as substituting panels or inverter.

Photograph the roof, loft interior and consumer unit before work begins. If a dispute arises later about pre-existing conditions, these are your only evidence.

Screw holes must be pre-drilled before the hook screw goes in. Forcing screws without pre-drilling can split the roof rafter — this may not be visible from above and is best caught by checking the loft after hooks are fitted. A split rafter is a structural issue. Check tiles sit flush after each hook is fitted — a raised tile creates a water ingress route.

On older roofs that undulate, adjustable height hooks should have been identified at survey stage and provided to the installation team. Adjustable hooks compensate for variation in rafter depth and ensure the rail sits level. If the surveyor did not flag an undulating roof and the crew have arrived with standard fixed-height hooks only, raise this before rails go on.

Hooks must also be the correct type for your specific tile profile. Wrong-profile hooks sit proud, lifting the tile and creating a gap.

Where tiles need to be lifted for hooks, they must be notched or flashed to prevent gaps greater than those pre-existing the installation. Gaps created by the installation that were not there before are a weather-tightness failure.

Modules should not be mounted within 400mm of any edge of a domestic roof unless specific measures are taken to resist increased wind uplift, secure ridge tiles, manage rainwater run-off, and prevent snow injury risk.

If you have loft access, check once hooks are in. Look for screws through the breathable membrane and split rafters. Either is a structural issue. A screwed-through membrane is also a condensation and damp risk in the loft space.

Mounting rails must be visibly straight before any panel is fitted. A bowed rail creates uneven loading on the panel frames and is straightforward to correct before panels are on — much harder after.

Look along the row as panels go on. They should be level with their neighbours and in straight lines. Misaligned panels are a sign of a crew rushing — and a useful proxy for care taken with the parts you cannot see.

Panel cables carry live DC voltage any time there is daylight — even when the inverter is off. These cables must be cable-tied to the rail or mounting structure. Loose cables move in wind, chafe against sharp edges, and wear through insulation over time. That is how DC arc faults develop.

RC62:2023 (the Joint Code of Practice for fire safety with PV installations, published by the Fire Protection Association, MCS and Solar Energy UK) identifies DC connectors and loose DC cabling as a leading cause of PV-related fires. Incorrectly assembled or loose DC connectors allow moisture ingress and corrosion, which can lead to arc faults and fire. The RC62 code is free to download from the MCS website and is increasingly used by property insurers when assessing fire claims involving solar systems.

Screws into roof coverings create slow leaks that may not appear for months. The MIS 3002:2025 requirement to maintain weather-tightness applies to all penetrations — including bird mesh fixings. Screwing bird proofing directly into the panel frame is also common on site and will void most panel manufacturer warranties. The correct fixing method is perimeter clips that clamp to the frame without penetrating it.

MC4 connections must be crimped using the correct MC4 crimp tool — not pliers or generic crimping tools. Badly crimped connections are a significant fire risk. The gland (the cable-entry body of the connector) must also be tightened using MC4 spanners to the correct torque — hand-tight is not sufficient and leaves the connector vulnerable to water ingress even if it appears secure externally.

Watch for installers using pliers instead of a dedicated MC4 crimp tool. You can ask the roofer to show you both the MC4 crimp tool and the MC4 spanners before roof work begins — correct tooling takes seconds to verify and is a reliable indicator of the care taken with the parts you cannot easily inspect.

The installer must be able to demonstrate that the installation has not reduced the fire performance of the roof. Ask which fire class the mounting kit is rated to and whether the distance to your nearest boundary requires a specific minimum rating. In-roof systems must use kits certified to the appropriate fire class for the location.

Inverters must not be mounted directly on timber, plasterboard or uPVC. They must be on a heatproof backplate with the minimum clearances specified in the manufacturer's installation manual. Clearances affect both safety and cooling — reduced clearance degrades output and lifespan.

If a backup power (EPS/UPS/island mode) system is being installed, it must have a dedicated earth — separate from the main system earth. It must be commissioned and signed off by a qualified electrician. An incorrectly-earthed EPS can backfeed voltage onto what appears to be a dead circuit during a grid outage — a genuine risk to network engineers working outside your home.

MIS 3012:2025 is specific: when switching to island mode, all line conductors and neutral must be isolated from the grid supply, the protective earth must not be isolated, and a neutral-earth bond relay is required at one point only. This is not a job that can be left to configure later.

On many modern hybrid inverters, the neutral-earth bond relay is built into the inverter and switches automatically on grid loss — check the manufacturer's documentation confirms this is the case for the specific model installed rather than assuming it. If your property has a TT earthing system (common in rural areas), the existing earth electrode may serve as the protective earth for the island-mode system — this must be explicitly confirmed by the installing electrician, not assumed.

BS 7671:2018+A3:2024 Regulation 530.3.201 (in force from 31 July 2024) requires that where a source of supply can appear on either side of a protective device — as is the case with any solar or battery installation — a bidirectional protective device must be used. A standard unidirectional RCBO (the type used for conventional circuits with current flowing in one direction only) is not compliant on a solar or battery circuit.

Ask the installer: "Is the RCBO on this circuit bidirectional?" Bidirectional RCBOs are marked differently from standard ones — the installer should be able to confirm this from the device markings or datasheet. Additionally, BS 7671 Reg 551.7.1 requires that where a generating set (including solar PV) operates in parallel with the grid supply, the RCD providing additional protection shall disconnect all live conductors including the neutral conductor — a single-pole RCBO is not compliant.

Cables through building fabric must be sealed against draughts, pests and moisture. Where cables run across exposed wall surfaces, conduit or trunking is expected. Underground cable runs must be in conduit.

DC isolators must be rated for DC use — not AC isolators repurposed for a DC circuit. As a quick visual check: DC isolators typically have black handles or knobs, and AC isolators red ones. Both the DC array isolator and the AC inverter isolator must be lockable in the open position (BS 7671 Reg 537.2.2.2) — this is a legal requirement.

Some installers use the integral isolation switch built into the inverter to satisfy the DC isolation requirement. Most built-in inverter isolators are not lockable — if they are not, they do not meet BS 7671 Reg 537.2.2.2 and a separate external lockable DC isolator is required.

For larger arrays or longer strings, verify the DC isolator is rated correctly for the array voltage. Standard residential DC isolators are typically rated 450V 16A, but larger residential arrays can produce open-circuit voltages approaching or exceeding 600V DC, which requires a higher-rated device. Your system schematic should show the array open-circuit voltage — use this to check the isolator rating is adequate.

Under BS 7671:2018+A2:2022 Reg 443.4.1, surge protection must be provided where an overvoltage could cause serious harm, interrupt public services, or damage safety systems. For most domestic solar installations the SPD requirement applies and the installer should fit SPDs on the AC side. Under BS 7671 Reg 712.443.101, if SPDs are required on the AC side they must also be fitted on the DC side of the PV installation — using DC-rated SPD devices, not AC ones.

If the installer does not fit SPDs, they must discuss the risks with you and obtain your written refusal — not simply skip them. Ask: "Are SPDs fitted, and if not, can I have confirmation of that in writing?"

BS 7671 Reg 514.15.1 specifies exactly where warning notices must be placed when an installation includes alternative or additional sources of supply. All four of these locations are required:

Each notice must be durably marked and read: "Isolate all electrical supplies before carrying out work" with the locations of all isolation points indicated. If a battery is installed alongside solar PV, PAS 63100:2024 requires a composite battery+solar symbol at the origin so fire services can immediately identify there is battery storage on the premises. Labels must also comply with BS EN IEC/IEEE 82079-1 and MIS 3012:2025 s4.2.1.

Warning labels on DC junction boxes are also required under BS 7671 Reg 712.537.2.2.5.1. All of these must be in place before commissioning.

It is becoming increasingly common for house insurers to require batteries to be installed outside. Although batteries prefer stable temperatures, you may need to install outside to meet your insurer's requirements or fire regulations applicable to your property. Confirm your insurer's requirements before installation — relocating a battery after install is disruptive and expensive.

If the battery is installed outside or in an unheated space, cold-weather performance is a significant consideration. Many batteries de-rate at temperatures below approximately 10°C, and some will stop charging or discharging at or below 0°C. Manufacturer datasheets show a minimum operating temperature but typically do not show the temperatures at which de-rating begins — which is often significantly higher. Check the datasheet carefully. An increasing number of batteries include self-heating technology for cold-climate operation — if external installation is a possibility, confirm whether the specified model has this.

Some manufacturers also specify that batteries must not be exposed to direct sunlight — high ambient temperatures cause performance issues and can affect battery longevity. If the proposed location is south-facing or exposed, raise this with the installer. MIS 3012:2025 has specific requirements for battery location; battery fires in dwellings are covered by PAS 63100:2024.

Minimum clearances between units and to walls are specified in the manufacturer's installation manual. These are both a warranty condition and affect cooling. The wall-mounting method must comply with BS EN 62109-1.

Where arc fault detection is present in the inverter, it shall be enabled. This is a mandatory requirement under MIS 3002:2025 — not an optional feature. Ask the installer to confirm it is enabled before they leave.

Network access credentials (usernames and passwords) must be updated in consultation with the customer — not left as factory defaults or set without your knowledge. Test every login before the crew leave: monitoring portal, battery app, device web interface.

Ask the installer to set your overnight charge window before leaving — particularly if you are already on a cheap overnight tariff. Starting without a schedule means paying peak rate to fill the battery on night one. Also ask them to clear any fault codes logged during commissioning — your system should start with a clean event log.