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a commercial solar system is the difference between a well-performing investment and one that barely moves the needle — or an oversized system that exports most of its generation at low rates.", "image": "https://alliantenergy.co.uk/assets/commercial-solar-DydTBMj7.jpg", "author": { "@type": "Person", "name": "Alliant Energy Team", "url": "https://alliantenergy.co.uk/about" }, "reviewedBy": { "@type": "Person", "name": "MCS Registered Engineer", "jobTitle": "MCS Registered Engineer" }, "publisher": { "@type": "Organization", "name": "Alliant Energy", "url": "https://alliantenergy.co.uk", "logo": { "@type": "ImageObject", "url": "https://alliantenergy.co.uk/logo.png" } }, "datePublished": "2026-01-15", "dateModified": "2026-05-19" }, { "@context": "https://schema.org", "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "Can we install solar on a flat industrial roof?", "acceptedAnswer": { "@type": "Answer", "text": "Yes — flat or low-pitch industrial roofs are among the most common commercial solar installations. Panels are mounted on angled frames using ballasted systems that avoid roof penetrations where possible." } }, { "@type": "Question", "name": "What if our roof faces the wrong direction?", "acceptedAnswer": { "@type": "Answer", "text": "On flat roofs, orientation is less critical — panels can be angled in any direction using the mounting frame. On pitched roofs, east-west orientation loses around 15–20% vs south but is still viable, particularly for larger systems." } }, { "@type": "Question", "name": "How long does a commercial survey take?", "acceptedAnswer": { "@type": "Answer", "text": "Typically 1–3 hours on site for a medium-sized installation. We assess roof condition, structural suitability, panel layout, cable routing and electrical infrastructure. The survey is free and without obligation." } } ] } ] --- [![Alliant Energy — Renewable Energy Solutions](/__l5e/assets-v1/3bd22195-cc6e-43e6-b5ff-5a808ce292d3/alliantenergyltd-2.svg)](/) [Home](/)[About](/about-us) [Services](/services) [Guides](/guides)[Case Studies](/case-study)[![Levelise](/__l5e/assets-v1/59fd362e-361a-47d7-ad1f-65e9beeb5289/levelise-logo.webp)](/guides/levelise-hub-explained) [01282 501589](tel:01282501589)[Get a Quote →](/quote) Spoke guide · Commercial # How to Size a Commercial Solar System for Your Building Correctly sizing a commercial solar system is the difference between a well-performing investment and one that barely moves the needle — or an oversized system that exports most of its generation at low rates. By **Alliant Energy Team**· reviewed by MCS Registered Engineer Last updated 19 May 2026 [Request a Commercial Survey](/quote) [Speak to an Engineer](/request-callback) On this page - [The three inputs](#inputs) - [Consumption profile](#consumption) - [Roof area & capacity](#roof) - [Matching size to use](#matching) - [DNO constraints](#dno) - [Why surveys matter](#survey) - [FAQ](#faq) Ready to act? Free quote in one working day. [Get a Quote →](/quote) Commercial solar sizing starts with three questions: how much electricity you use and when, how much useable roof area you have, and your electricity rate and annual spend. ## The three inputs that determine system size The optimal system size balances these three. It generates enough to make a meaningful impact on your bill, it fits your roof without complex engineering, and it doesn't produce so much surplus that most of it is exported at low rates. ## Understanding your consumption profile A half-hourly data (HHD) download from your energy supplier shows exactly when you use electricity in 30-minute intervals across the year — the single most valuable piece of data for commercial solar design. You're entitled to it free of charge. What you're looking for: how much electricity do you consume between 8am and 6pm on weekdays? That's your solar generation window. If 70% of consumption falls in those hours, a large system makes excellent sense. If 80% is overnight, solar without battery storage will have limited self-consumption. Tip Share your HHD file with us and it dramatically improves the accuracy of the financial projection. ## Roof area and system capacity As a rough guide, 1 kWp of commercial solar requires approximately 5–7 m² of roof area. System size Approx. roof area Annual generation (UK avg) Best suited to 30 kWp ~180–210 m² ~27,000 kWh/yr Small commercial, SME offices, small retail 50 kWp ~300–350 m² ~45,000 kWh/yr Medium commercial, small manufacturing 100 kWp ~600–700 m² ~90,000 kWh/yr Mid-size manufacturing, large retail, logistics 200 kWp ~1,200–1,400 m² ~180,000 kWh/yr Large industrial, distribution depots 500 kWp ~3,000–3,500 m² ~450,000 kWh/yr Very large industrial, agri-commercial ## Matching system size to electricity consumption The general rule: size the system to cover 80–100% of your daytime electricity consumption. Oversizing means exporting at low SEG rates (5–10p/kWh) rather than displacing grid electricity (25–35p/kWh). Undersizing leaves savings on the table — incremental panel cost is low at install time. Example: a manufacturer using 350,000 kWh/year with 250,000 kWh consumed 7am–7pm. A 200kWp system generating ~180,000 kWh covers 72% of daytime consumption — reasonable sizing. 250kWp would approach daytime consumption with minimal oversupply. ### Get a properly sized commercial proposal Free site survey and HHD-based modelling. [Request a Survey](/quote) [Download Brochure](/brochure) ## DNO constraints Your Distribution Network Operator may limit system size. For systems above 50kWp (sometimes lower), a G99 application is required and the DNO assesses whether your existing grid connection can accommodate export capacity. Options if export is constrained: reduce size, add battery to limit export, or apply for a connection upgrade. We handle DNO applications for all commercial installations. ## Why commercial surveys matter Commercial buildings vary enormously in roof condition, structural capacity, aspect, shading, cable routing complexity and electrical infrastructure. Satellite imagery gives a useful first approximation; a proper structural and electrical survey is essential before committing. ## Frequently asked questions ### Can we install solar on a flat industrial roof? Yes — flat or low-pitch industrial roofs are among the most common commercial solar installations. Panels are mounted on angled frames using ballasted systems that avoid roof penetrations where possible. ### What if our roof faces the wrong direction? On flat roofs, orientation is less critical — panels can be angled in any direction using the mounting frame. On pitched roofs, east-west orientation loses around 15–20% vs south but is still viable, particularly for larger systems. ### How long does a commercial survey take? Typically 1–3 hours on site for a medium-sized installation. We assess roof condition, structural suitability, panel layout, cable routing and electrical infrastructure. The survey is free and without obligation. Three ways to get started ## Ready to find out what solar saves you? Get a tailored quote in one working day. No obligation. No hard sell. Speak to a renewable energy engineer — not a salesperson — at a time that suits you. [Get a Quote → ](/quote) [Request a Callback →](/request-callback) [Download Brochure →](/brochure) Accreditations ## Certified, registered, and insured. Every time. MCS certification isn't a box-ticking exercise — it qualifies your system for Smart Export Guarantee payments and government grants. Our installers are also NICEIC-approved and TrustMark-registered, and every install is fully insured. ![Citation ISO Certification: ISO 9001 quality management, ISO 14001 environmental management and ISO 45001 occupational health and safety](/__l5e/assets-v1/180183cd-e6fd-4b0a-984c-83e6a41390d7/accreditations-iso.jpg) ![Alliant Energy — Renewable Energy Solutions](/assets/logo-IFrgP5Dc.png) Renewable energy & energy-saving specialists. MCS-registered solar PV, battery storage, heat pumps and EV charging across the UK. #### Quick Links - [Home](/) - [About Us](/about-us) - [Services](/services) - [Case Studies](/case-study) - [Areas We Cover](/solar-panel-quotes-north-west) - [Contact](/contact) - [Privacy Policy](/privacy) - [Terms & Conditions](/terms) #### Services - [Solar for Homes](/services/solar) - [Commercial Solar](/services/commercial-solar) - [Battery Storage](/services/battery-storage) - [Air Source Heat Pumps](/services/heat-pumps) - [EV Charging](/services/ev-charging) - [Energy Saving Advice](/services/energy-saving-advice) #### Contact - [01282 501589](tel:01282501589) - [info@alliantenergy.co.uk](mailto:info@alliantenergy.co.uk) - Unit 214 Northlight Industries, Pendle Road, Brierfield, Nelson BB9 5FL [Get a Quote](/quote)[Brochure](/brochure) Alliant Energy Ltd is an Introducer Appointed Representative (Financial Services Register No. 1020779) of Phoenix Financial Consultants Limited (Phoenix). Phoenix is a credit broker, not a lender. Phoenix is authorised and regulated by the Financial Conduct Authority (FRN: 539195), and offers finance from its panel of lenders. All finance subject to status and credit checks. © 2026 Alliant Energy Ltd. All rights reserved. [Privacy Policy](/privacy)[Terms & Conditions](/terms) MCS Registered · TrustMark · NICEIC [Chat with AI](/chat) [Call back](/request-callback) [Get a Quote](/quote) [Get a Brochure](/brochure) [Get a Quote](/quote) [Chat with AI](/chat)