Industrial Solar Installation Timeline UK: Week-by-Week From Survey to Switch-On
One of the most common questions from factory managers and operations directors is: "How long will this actually take?" The answer depends on system size, grid connection complexity, and whether planning permission is required — but this timeline gives you a realistic picture of what to expect from a 50kW to 2MW industrial solar installation in the UK.
Total timeline at a glance
straightforward site
typical timeline
complex G100 projects
Phase 1: Survey, assessment and design (Weeks 1–4)
The process begins with a site visit from a qualified installer. This is typically free and covers:
- Structural survey — roof loading capacity, condition, pitch and orientation assessed. Older roofs may need a separate structural engineer's report (add 1–2 weeks).
- Energy consumption analysis — 12 months of half-hourly interval data from your meter (AMR data) is reviewed to model self-consumption accurately.
- Grid connection assessment — the installer checks available DNO capacity at your grid connection point, identifies whether G98, G99 or G100 applies to your system size.
- Shading analysis — roof survey tool (PVsyst or similar) maps any shading from rooflights, plant, neighbouring structures.
- Design and proposal — a specific system design, generation model and financial analysis is produced.
At the end of Phase 1, you should have a specific proposal with panel layout, system specification, estimated generation, financial projections and timeline. If you're comparing multiple installers, ensure all are quoting on the same system size and inverter specification — proposals often differ in ways that make direct comparison difficult.
Phase 2: Contract, planning and applications (Weeks 4–8)
Once you accept a proposal and sign contracts, several parallel processes begin. The speed of this phase has the greatest impact on overall project timeline.
DNO grid application — the critical path
For systems under 50kW, G98 notification is simple and quick. For systems 50kW–1MW (G99), a formal application is submitted to your DNO (Western Power, SP Energy, UK Power Networks, etc.). DNOs take 8–16 weeks to assess available capacity, model network impact and issue connection terms. During this period, they may request additional studies or impose export limitations. This is often the longest single item on the critical path.
Planning permission
Most factory and warehouse solar qualifies as Permitted Development and requires only a prior approval notification to the local planning authority (LPA) — typically a 4-week process. Full planning permission is required for listed buildings, conservation areas, and very large systems that project significantly above rooflines. Full applications add 8–13 weeks. Your installer should confirm PD eligibility before you contract.
Landlord consent (if applicable)
If you're leasing your site, a formal licence to install must be obtained from the landlord. With institutional landlords who have a solar programme, this can take 2–4 weeks. With private landlords, 4–8 weeks is more realistic depending on solicitor speed. Start this in parallel with the DNO application — not after it.
Equipment procurement
Once contracts are signed, the installer orders panels, inverters, mounting systems and switchgear. Standard supply chains are now 6–10 weeks for major equipment. Specialist inverters (string inverters for complex roof configurations, hybrid inverters for battery-ready systems) may have longer lead times. Many installers hold stock for common system sizes, shortening this to 3–4 weeks.
Phase 3: Physical installation (Weeks 14–22 for most systems)
The installation phase itself is often the shortest part of the process, particularly for experienced industrial installers. Actual rooftop time depends on system size:
Physical installation duration by system size
| System size | Panels | Install time | Crew size |
|---|---|---|---|
| 50–100kW | 115–230 | 1–2 weeks | 4–6 people |
| 100–250kW | 230–580 | 2–3 weeks | 6–8 people |
| 250–500kW | 580–1,150 | 3–5 weeks | 8–12 people |
| 500kW–1MW | 1,150–2,300 | 4–8 weeks | 12–20 people |
| 1MW–2MW | 2,300–4,600 | 8–14 weeks | 20–30 people |
The installation sequence for a typical factory system follows a consistent pattern:
- Roof condition survey and preparation — any failed flashings, gutters or fixings addressed before panel installation begins. Existing rooflights checked for load-bearing capacity.
- Mounting rail installation — aluminium rail systems fixed to roof purlins or standing seam clips. For flat roofs, ballasted or mechanically fixed frames installed to structural calculations.
- Panel installation — panels clipped to rails in rows, DC cabling run to combiner boxes.
- Inverter installation — inverters mounted internally (typically in a plant room, switch room or on an external inverter wall). DC cable trays run from roof to inverter room.
- AC connection — AC isolators and protection relays installed. G99 protection relay configured to DNO specification.
- Metering installation — generation meter and export meter installed. Monitoring system commissioned.
- DNO energisation — DNO visit to inspect, witness testing and energise the connection. This final step can take 2–4 weeks to schedule after technical completion.
Phase 4: Commissioning and handover (Weeks 20–28)
Commissioning is more than flipping a switch. For a large industrial system, commissioning involves:
- G99 protection relay testing witnessed by the DNO
- Earth fault loop impedance testing across all DC strings
- Irradiance-corrected IV curve tracing on a representative sample of strings
- Thermal imaging of panel array and connection points
- Monitoring system verification — confirming data match between monitoring platform and generation meter
- MCS certificate issued and registered with the national MCS database
- O&M documentation and manuals handed over
The MCS certificate is required to access the Smart Export Guarantee (SEG) — the payment you receive from your energy supplier for surplus electricity exported to the grid. SEG registration typically takes 2–4 weeks after the MCS certificate is issued.
What causes delays — and how to avoid them
The three most common causes of industrial solar delays are:
1. DNO grid application delays
In areas with constrained grid capacity (South East England, suburban areas of major cities), DNOs are processing record volumes of applications and some are taking 20–24 weeks to issue connection terms. Mitigation: apply early, consider export limitation to speed approval.
2. Structural issues discovered on roof
Older industrial roofs (pre-2000) frequently have unexpected structural issues when loaded. Corroded purlins, failed fixings and sagging asbestos-containing roof sheets can add 4–8 weeks for remediation. Mitigation: commission an independent structural survey before contracting.
3. Planning permission discovered after contracting
Some installers confirm PD eligibility without properly checking conservation area boundaries, listed building status or local development framework restrictions. A planning requirement discovered after contract signature adds 8–13 weeks. Mitigation: request a written PD confirmation from your installer before signing.
G99 vs G100: which grid connection applies to your site?
Understanding which grid connection standard applies saves significant project delays:
G98 — under 50kW
Notification only. No formal application required. DNO must be notified before commissioning. Fastest route.
G99 — 50kW to 1MW
Formal application required. DNO assesses network capacity and issues connection terms. 8–16 weeks typically. Most factory solar projects fall here.
G100 — over 1MW
Full grid connection study required. May require reinforcement works funded by applicant. 6–18 months. Large distribution centres and manufacturing campuses.
For more detail on the full installation process, see our comprehensive guide: Factory Solar Panel Installation Process — Complete UK Guide
Related Reading
Frequently asked questions
How long does industrial solar installation take in the UK?
A typical factory or warehouse solar installation takes 16–28 weeks from initial survey to energisation. The DNO grid application is usually the critical path item for systems over 50kW. For 1MW+ systems requiring G100 connections, allow 28–52 weeks.
What is the DNO grid application process for factory solar?
For systems under 50kW (G98), notification only — works can begin shortly after. For 50kW–1MW (G99), a formal application takes 8–16 weeks. For over 1MW (G100), a full grid connection study is required, typically taking 6–18 months.
Do factories need planning permission for solar panels?
Most factory and warehouse solar qualifies as Permitted Development and doesn't require full planning permission. Exceptions include listed buildings, conservation areas, and installations that significantly project above the roofline. Your installer should confirm PD eligibility in writing before contracting.
What causes delays in industrial solar projects?
The three most common causes are: DNO applications taking longer than expected in constrained grid areas; structural issues discovered on older roofs; and planning permission requirements discovered after contracting. An experienced installer who manages DNO applications proactively is the most effective way to minimise these risks.
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