Ben Brading 7 min read

Commercial solar system installation: Step-by-step process and timeline

Installing a commercial solar system is one of the most effective ways to improve sustainability credentials and protect against rising business electricity prices.

However, the process is complex, requires approval from the local grid, and typically takes several months.

This guide provides a clear, step-by-step overview of the commercial solar installation process, along with an indicative timeline to help you understand what to expect at each stage.

What is commercial solar installation?

A commercial solar installation is the process of designing, sourcing, and setting up a solar photovoltaic (PV) system that generates electricity at a business site.

Unlike home systems, commercial setups are usually larger, built to meet higher energy demands, and designed to work with more complex electrical systems already in place.

Commercial solar panel installation process

Commercial solar installation usually takes two to four months. It includes a site survey, design and engineering, DNO approval, installation, and final commissioning.

Below, we explain what is involved at each stage of the installation process:

1. Management assessment of suitability
2. Initial desktop consultation
3. Choose a commercial solar installer
4. Site survey
5. Planning permission
6. DNO approval
7. Solar system design
8. Installation of panels and electronics
9. Commissioning, testing and go-live
10. Handover pack
11. Monitoring, optimisation and maintenance

1. Management assessment of suitability

Before engaging a professional solar installer, the following factors should be considered, as they may affect the suitability of a solar panel installation.

i. Structural considerations

A roof-mounted commercial solar panel installation adds a load of approximately 10–25 kg/m² for 25+ years, so it is essential to ensure your building can safely support this weight.

The following points may suggest that your roof may not be suitable for solar panels:

Roof is near end of life – If a replacement or repairs are planned in the next few years, installing solar panels may be problematic.
Roofing in poor condition – Deteriorating roof structures may not be able to support mounting systems securely.
Timber-frame roofs – Timber-framed roofs, common in older buildings, may have a lower load-bearing capacity.
Asbestos sheet roofs – These often need to be replaced if the roof area is to be used for mounting commercial solar panels.

ii. Ownership and business plans

Commercial solar panels have an expected lifespan of over 25 years. To benefit fully from their installation, your business will need to use the power they produce over their full lifetime. We recommend assessing the following:

Leasehold properties – Consider the remaining length of the lease and any break clauses that could end the lease prematurely.
Business plans – Consider any business plans that will require moving properties or will significantly reduce power consumption.

iii. Planning restrictions

If any of the following apply to your commercial property, expect additional planning consents, restricted design options, and longer lead times for installation:

Listed building – Formal Listed Building Consent (LBC) is usually required.
Conservation area – Permitted development rights may not apply, requiring a planning permission application.

iv. Persistent shading

We recommend reviewing the roof space available for solar panels to identify large areas of persistent shade from adjacent buildings, parapets, and trees.

If shading affects the available area, the expected power output and financial return from the solar installation will be reduced.

v. Demand profile

Assessing how much solar power your business can use each year is important. We recommend reviewing your business energy consumption to ensure that demand during daylight hours supports the business case for installing solar panels.

It is possible to export excess electricity back to the grid; however, the rates received under the Smart Export Guarantee are significantly lower than electricity import prices.

Alternatively, integrating a commercial solar battery can maximise self-consumption, but this requires additional upfront investment.

vi. Financing

Commercial solar panel installations require a significant upfront investment. Review our guide to the cost of commercial solar panel installations to get the latest estimates of upfront costs and available financing options, including:

Capex purchase
Finance or hire purchase
Private wire power purchase agreement.

A cost-free alternative to reducing electricity costs is to use our business electricity comparison service to find a cheaper green business energy tariff.

2. Initial desktop consultation

An initial desktop consultation carried out by a professional solar installer determines whether solar is viable at your property by reviewing:

Recent business electricity bills
Consumption patterns from business energy monitoring software
Half-hourly electricity meter data for energy-intensive properties
The area, pitch, and orientation of the roof space
Site photos
The capacity of your current business electricity connection
A high-level assessment of local grid constraints

A commercial solar installer will present their findings in a solar proposal document that includes:

A recommended system size in kW and number of panels
Recommended commercial solar panel types
Estimated commercial solar installation cost
Projected output, savings, and solar return on investment calculation
Estimated project timeline

We recommend collecting quotations from multiple providers to assess the competitiveness of quotes.

3. Choose a commercial solar installer

To proceed with the installation, you will need to formally appoint a commercial solar installer under contract.

Once appointed, the solar installer will become responsible for the remaining steps of the installation process.

There are many solar installation firms in the UK that offer installations on commercial properties. We recommend considering the following:

Relevant experience – Can they provide case studies of commercial projects similar to your installation?
Aftercare – Do they offer monitoring, long-term support, and system maintenance after installation?
Warranties – Are they clear about who is responsible for workmanship, performance shortfalls, and managing manufacturer warranties?

4. Site survey

The solar installation quote provided at step 2 is provisional and subject to a full site survey.

Solar installation contracts typically allow for changes to costs and timescales, or for termination, if issues are identified during the on site survey.

A site survey usually includes the following:

i. Structural survey

A structural survey will verify the roof’s load capacity, condition, remaining lifespan, and roof membrane manufacturer requirements.

Based on the structural survey, the provider will decide on a mounting approach, typically one of the following:

Ballasted – No penetrations into the roof, instead relying on concrete blocks to hold the system down. This option requires a greater roof load capacity.
Fixed – A lighter system, but it must protect waterproofing and roof warranties.

ii. Electrical survey

An electrical survey confirms whether the building’s existing electrical infrastructure can safely accept and integrate a solar PV system.

The installer reviews the incoming supply (phase, capacity, earthing), main switchgear and distribution boards (spare ways, ratings, fault levels), business electricity meters, and viable cable routes from the roof to the point of connection.

It also checks isolation, protection coordination, fire compartment penetrations, and space for monitoring or export-limiting equipment.

5. Planning permission

In most cases, the installation of commercial solar panels is permitted under Permitted Development Rights and therefore does not require planning permission. However, permission may be required if:

The building is listed or located in a conservation area.
Panels project significantly from the roof.
The installation is ground-mounted.

If consent is likely to be required, your installer will typically adjust the layout to reduce visual impact where possible and either support or coordinate the planning application.

6. DNO approval

Commercial solar panel installations typically require approval from the local Distribution Network Operator (DNO), the company that operates the electricity grid in your area.

This approval, known as a G99 application, is required where the installation exceeds:

Single-phase electricity supply – 3.68 kW (approximately nine standard panels)
Three-phase electricity supply – 11 kW (approximately 27 standard panels)

The DNO approval process is required even if the system is designed to export power back to the grid only occasionally.

Your installer will prepare electrical schematics and submit the G99 application to your local DNO. The standard review process typically takes 8 to 12 weeks for the DNO to approve the installation.

Approval of the commercial solar installation may be conditional on the following:

Export limitations – A requirement to install an export limitation device.
Network reinforcement – Approval may be subject to you covering the cost of local network reinforcement.

If your approval is subject to network reinforcement, this work can take several months before you can proceed with your commercial solar installation.

7. Solar system design

Based on the results of the in-person survey, your installer will prepare a fully engineered, build-ready plan for your installation that includes:

Detailed schematics showing how the system will integrate with the existing electrical infrastructure.
A panel placement plan, including the pitch and orientation of your panels for the mounting system.
Structural calculations demonstrating that the roof can bear the additional weight of the panels.
Component specifications for panels, mountings, and inverters.

You’ll receive a copy of the final design pack for review and approval. Upon approval, your installer will confirm an installation date for your panels.

The installation start date will typically be booked weeks in advance to allow your provider to procure the necessary hardware for your installation.

8. Installation of panels and electronics

The physical installation work required for your solar panels depends on the size and complexity of the system, but typically involves the following activities:

Preparing scaffolding to allow roof access.
Installing the panel mounting system.
Installing the panels onto the mounting system.
Installing a solar inverter.
Wiring the panels and installing isolation switches.
Connecting to the mains electrical distribution board.
Configuring a monitoring system for output tracking and fault detection.

Towards the end of the installation process, a temporary interruption to the electrical supply will be required to connect the panels to the mains distribution board.

9. Commissioning, testing and go-live

Once the installation work is complete, an electrical engineer will test the system for correct operation, protection compliance, and performance.

An Electrical Installation Certificate (EIC) is issued to confirm that the installation work meets UK wiring regulations.

G99 commissioning documentation is prepared by the installer and submitted to the local DNO, providing evidence that the solar installation has been completed in accordance with the approved plans.

Once these commissioning and testing steps have been completed, the system can be energised.

At go-live, we recommend signing up with a business energy supplier that offers a Smart Export Guarantee tariff, allowing you to sell back any unused excess power.

10. Handover pack

Your solar installation provider shall prepare a handover pack for your business, which typically contains:

As-built drawings, datasheets, inverter settings, and protection settings.
Roof warranty confirmations and method statements for the roof interface.
Spares list.
Warranty contacts.
Emergency shutdown procedure.

11. Monitoring, optimisation and maintenance

The best solar providers will offer a facilities team briefing that covers the basic operating procedures around isolators, alarms, and access rules.

The solar monitoring software offered by most providers will track the performance ratio of the panels (compared to theoretical output) to identify any issues.

Read our guide to commercial solar maintenance to find out more about best practice for operating solar panels post-installation.

How long does it take to install commercial solar panels?

The full commercial solar installation process typically takes two to four months, assuming no planning permission or grid reinforcement work is required.

This section outlines the timeline for the most time-intensive steps in the installation process and explains the key factors that affect process speed.

Desktop consultation and initial quotation

Timeline: 1 – 2 weeks.

Assuming your business can provide all the necessary information, most installation providers can produce a budget proposal in approximately one week.

On site survey

Timeline: 1 – 3 weeks.

Once you’ve engaged a solar installer, an on-site survey can typically be scheduled within three weeks. This is usually dependent on the availability of a qualified structural and electrical engineer.

Planning permission (only if required)

Timeline: 8 – 13 weeks.

Eight to 13 weeks is the typical timeframe for receiving a decision in principle from the local authority. However, most installations do not require planning permission under Permitted Development Rights.

DNO application

Timeline: 8 – 12 weeks.

The DNO application is typically the most time-intensive step in a commercial solar installation.

The timeline for a typical, accepted G99 application is 8 to 12 weeks, but this can be significantly affected by:

The workload of your regional grid operator.
How constrained is the grid in your area?
Whether additional studies are required.

Where reinforcement work is required to accept your application, this may add several months to the timeline due to bottlenecks in reinforcement work carried out by DNOs.

Hardware procurement

Timeline: 2 – 6 weeks

The precise model and size of the inverter, along with any export-limiting electrical equipment, can only be confirmed and ordered once the DNO application has been approved.

Once specified, obtaining the equipment can take a few weeks due to the specialised nature of the hardware and global supply chains.

On site installation and electrification

Timeline: 2 – 8 weeks

The number of days required for installation depends on the scale of the solar system and the number of electricians deployed by your installer.

Prior to electrification, the installer must notify the DNO, which adds time to the electrification process, even for smaller installations.

Commercial solar system installation FAQs

Our experts answer common questions about the commercial solar panel installation process.

How much roof space do I need?

A standard commercial solar panel requires approximately 2 square metres (21.5 square feet) of space.

The number of panels required depends on the electricity consumption of your commercial property. On average, a single panel will produce between 1.5 and 2 kWh per day in Britain.

Can I install solar on a leased building?

Yes, but only with the landlord’s written permission. You may need to amend your lease to cover:

Roof access rights.
System ownership and maintenance.
Removal terms at the end of the lease.

Will installation disrupt business operations?

Most of the physical work for a commercial solar installation takes place on the roof, so it is unlikely to disrupt day-to-day operations.

A temporary power outage will be required to connect the system to the mains distribution board, but in larger buildings, this is usually isolated to specific areas.