Large-Scale Commercial Solar UK: Why 100kW+ Systems Need a Specialist Installer
Commercial solar above 50kW is a fundamentally different proposition from domestic or small business solar. Grid connection applications, structural engineering, planning complexity, and investment-grade financial modelling all require specialist expertise that most residential solar companies simply do not have. This guide explains what makes large commercial solar different — and how to choose the right installer.
EC Eco Energy: UK Commercial Solar Specialists
50kW– 1MW+
System size range
500+installs
Commercial projects completed
MCScertified
Commercial accreditation
G99specialist
DNO connection management
What Makes Large Commercial Solar Different
A 10kW residential solar installation and a 500kW warehouse solar installation both involve panels, inverters, and mounting systems. Beyond that, the similarity ends. Large commercial solar projects involve a chain of engineering, regulatory, legal, and financial processes that residential or small commercial installers encounter rarely, if ever.
The consequences of getting these processes wrong are significant. A poorly prepared G99 application can delay a project by six months or longer. A structural assessment that fails to identify roof loading limits can require costly reinforcement work. A financial model that ignores DNO export limits may overpromise returns. Choosing a specialist commercial installer is not just about quality of installation — it is about managing the entire project lifecycle competently.
G99 Grid Connection: The Process Most Installers Get Wrong
Every commercial solar system above approximately 50kW requires a G99 (formerly G59) application to the local Distribution Network Operator (DNO). The G99 process is a formal engineering assessment that evaluates how the generating unit will interact with the distribution network — covering protection relay settings, export limits, power quality, and the impact on neighbouring properties and network assets.
Different DNOs — UK Power Networks, Northern Powergrid, National Grid Electricity Distribution, SP Energy Networks, Western Power Distribution — have different application processes, different engineering requirements, different timescales, and different thresholds for requiring detailed studies. An installer who has submitted G99 applications to UK Power Networks Eastern region (which covers Essex, Suffolk, and Hertfordshire) may find the process quite different when working with Northern Powergrid in Yorkshire or NGED in the Midlands.
Export Limits and How They Affect System Design
Many commercial solar systems face export limits — a cap on how much electricity the system can export to the grid at any given moment. DNOs impose these limits where the local network lacks the capacity to accept full system output during low-demand periods. Export limits range from zero (export-limited systems where all generation must be consumed on-site or curtailed) to the full system capacity.
A commercial installer who designs a system without considering the likely export limit may specify an oversized system that delivers poor returns after the G99 determination. Specialist installers model multiple scenarios — including conservative export limits — before finalising system size, and recommend battery storage as a tool for managing exported energy and improving self-consumption in constrained grid areas.
Structural Engineering: Not All Roofs Are Equal
Industrial and commercial buildings in the UK span generations of construction standards. A 1980s portal frame warehouse, a 1960s flat-roofed factory, and a modern logistics shed built to current Building Regulations have very different structural characteristics. Before any commercial solar system above 50kW is designed, a structural engineer must assess whether the roof can bear the additional dead load (panel and mounting weight) and wind uplift load.
This assessment may reveal that a roof requires strengthening before solar can be installed — adding cost and time. It may also reveal that a pitched metal roof can accept more capacity than originally estimated, improving the financial case. Structural surveys are a standard part of our commercial solar design process at EC Eco Energy, and the results directly inform system sizing and mounting specification.
Financial Modelling for Investment Decisions
Commercial solar projects above £100,000 are board-level investment decisions that require investment-grade financial analysis. A credible financial model for a large commercial solar project should include: gross and net installation cost (after tax relief), annual generation forecast (modelled against actual consumption data), year-by-year cashflow projections over 25 years, internal rate of return (IRR), net present value (NPV), payback period, sensitivity analysis (energy price scenarios), SEG income projections, and EPC rating impact.
EC Eco Energy provides this analysis as standard for every commercial survey — built on actual metered consumption data from the client's electricity bills, not rule-of-thumb estimates. This level of rigour is what large businesses and their finance directors require before committing capital.
EC Eco Energy: Your UK Large Commercial Solar Partner
EC Eco Energy specialises in commercial solar installations from 50kW to 1MW+ across Essex, East London, Suffolk, Hertfordshire, Milton Keynes, Northampton, and beyond. We manage the entire project lifecycle: structural survey, G99 connection application, planning (where required), MCS-certified installation, DNO commissioning, and ongoing monitoring.
Our team has completed over 500 commercial installations and submitted G99 applications across multiple DNO regions. We work with warehouses, factories, schools, care homes, logistics centres, data centres, and large retail properties — bringing the technical depth and commercial rigour that large-scale solar projects require.
Contact us to arrange a free commercial survey and receive a detailed financial analysis for your building.
Frequently Asked Questions
G98 (formerly G83) covers smaller generating units up to 16A per phase — typically systems below 3.68kW single-phase or 11.04kW three-phase. G99 (formerly G59) applies to larger generating units. In practice, virtually all commercial solar systems above 50kW require a G99 application to the local Distribution Network Operator (DNO). G99 involves a formal engineering assessment by the DNO, takes 45–90 working days, and may result in conditions (export limits, protection settings) that affect system design. Experienced commercial installers manage this process as part of their service.
A G99 connection application typically takes 45–90 working days from submission to determination, depending on the DNO and the complexity of the connection. UK Power Networks (Eastern England), Northern Powergrid (North East and Yorkshire), National Grid Electricity Distribution (Midlands, South West), and SP Energy Networks (Scotland and North West) each have different processes and current backlogs. Well-prepared applications — with accurate technical data, appropriate protection relays specified, and the right single-line diagrams — proceed faster. Specialist commercial solar companies submit dozens of G99 applications per year and understand what each DNO needs.
The Annual Investment Allowance (AIA) provides 100% first-year tax relief on qualifying plant and machinery up to £1 million per year. Commercial solar panels, inverters, battery storage, mounting structures, and associated electrical equipment all qualify. A £500,000 solar installation by a business paying corporation tax at 25% generates a £125,000 tax reduction in year one, reducing the effective net investment to £375,000. Full Expensing provides an equivalent benefit with no upper cap for companies that have used their AIA. These reliefs are available regardless of system size.
The most common commercial solar system sizes in the UK fall into three categories: small commercial (10–50kW) for SMEs with modest roof space; mid-scale commercial (50–250kW) for larger SMEs, schools, care homes, and mid-sized industrial buildings; and large commercial (250kW–1MW+) for warehouses, factories, distribution centres, data centres, and large retail parks. Systems above 1MW — typically for very large logistics parks or multiple-building estates — require additional technical assessment and may involve National Grid rather than DNO connections.
Large commercial solar involves processes that domestic installers rarely encounter: G99 grid connection applications and DNO negotiations, structural engineering assessments of industrial roofs, HV/LV electrical design, commercial contract structures including PPAs and EPC contractor arrangements, planning applications for larger systems, MCS commercial project certification, and financial modelling for board-level investment decisions. A specialist commercial installer has completed dozens or hundreds of these processes and has relationships with DNOs, structural engineers, and planning authorities that accelerate delivery and reduce risk.