ESOS Phase 4 — What Factories Must Do by December 2027
The Energy Savings Opportunity Scheme (ESOS) is a mandatory energy assessment scheme for large UK organisations. It requires qualifying businesses to conduct comprehensive energy audits of their buildings, transport and industrial processes, identify economically viable energy savings opportunities, and notify the Environment Agency of compliance. Phase 4 of the scheme covers the reference period from 6 December 2022 to 5 December 2026, with the compliance notification deadline of 5 December 2027.
Does Your Organisation Qualify for ESOS?
You must comply with ESOS Phase 4 if your organisation (or the corporate group it belongs to) meets any of these thresholds: 250 or more employees, or an annual turnover exceeding £44 million AND a balance sheet total exceeding £38 million. Sole traders, partnerships and public bodies are generally exempt, though public bodies have equivalent obligations under SECR. Penalties for non-compliance include civil penalties of up to £50,000 plus continuing daily penalties — enforced by the Environment Agency.
ESOS Phase 4 introduced important changes compared to earlier phases. The regulations now explicitly require organisations not only to identify but also to act on energy saving recommendations within specified timeframes. This action requirement — rather than a simple audit-and-notify approach — means that ESOS Phase 4 compliance now requires demonstrable implementation of energy efficiency measures. Solar installation is one of the highest-value, most clearly evidenced actions a manufacturing business can take.
| ESOS Phase 4 Requirement | Deadline | How Solar Helps |
|---|---|---|
| Conduct energy audit covering 90%+ of organisational energy | Before Dec 2027 | Solar site assessment contributes to audit evidence; consumption data required for sizing |
| Identify energy saving opportunities | Before Dec 2027 | Solar is typically the largest single saving identified in manufacturing audits |
| Implement a proportion of identified measures | Ongoing / before Dec 2027 | Installed solar directly satisfies implementation requirement with documented annual savings |
| Appoint an ESOS Lead Assessor | Before Dec 2027 | Lead Assessor can incorporate solar generation data into energy performance assessment |
| Notify the Environment Agency | 5 December 2027 | Solar installation strengthens notification with evidence of action taken |
How Solar Satisfies ESOS Energy Reduction Obligations
Solar photovoltaic generation is the most powerful single energy saving measure available to most UK factories. An on-site solar installation directly reduces the quantity of electricity purchased from the grid — making it a straightforward, quantifiable energy saving that maps precisely to ESOS audit metrics and performance reporting.
A 500kW rooftop solar installation at a typical UK manufacturing factory generates approximately 475,000 kWh per year. If the factory's ESOS baseline electricity consumption is 3,500,000 kWh/year, this represents a 13.6% reduction in purchased electricity from generation alone. Over a 25-year period, the cumulative energy saving exceeds 11,000 MWh — sufficient to satisfy the ESOS energy reduction obligation many times over and provide continuous audit evidence.
ESOS Evidence Documentation for Solar
To use a solar installation as ESOS evidence, ensure your system includes a data logger or monitoring platform that records generation data at half-hourly intervals. Monitoring platforms from inverter manufacturers (SolarEdge, Solis, Fronius, Huawei FusionSolar) all provide this. Your ESOS Lead Assessor will need: annual generation data (kWh), self-consumption vs export split, estimated CO2e reduction, and commissioning certificate. Export the generation data in CSV format and retain for ESOS notification purposes.
UK CBAM — What It Is and Which Industries Are Caught
The UK Carbon Border Adjustment Mechanism (UK CBAM) was announced in the 2024 Autumn Statement and takes effect from 1 January 2027. It places a carbon cost on imports of specified goods from countries where the carbon price is lower than the UK Emissions Trading Scheme (UK ETS) price. The mechanism is designed to prevent "carbon leakage" — the shifting of carbon-intensive production to lower-regulation jurisdictions to avoid UK carbon costs.
UK CBAM Covered Sectors from January 2027
- Aluminium (primary and secondary)
- Cement (clinker, Portland cement, aluminous cement)
- Ceramics (specific products)
- Fertilisers (ammonia, nitric acid, urea)
- Glass (flat glass, glass containers)
- Hydrogen (electrolytic)
- Iron and steel (hot and cold rolled, tubes, pipes)
- Electricity (imported)
Note: The UK CBAM applies to imports into the UK of goods in these sectors. UK producers of these goods are already subject to UK ETS carbon costs; CBAM ensures imported equivalents face the same carbon price.
The UK ETS carbon price, which CBAM tracks, was approximately £35–45 per tonne CO2e through 2025 and is forecast to rise to £50–80/tonne by 2030 as the UK ETS cap tightens in line with net zero commitments. For importers of covered goods, the CBAM charge is calculated as: (tonnes of embedded carbon) x (UK ETS price minus carbon price paid in country of origin). If the country of origin has no carbon pricing, the full UK ETS price applies.
How Factory Solar Reduces CBAM Liability
For UK manufacturers that produce goods covered by the UK CBAM — primarily steel, aluminium, cement and ceramics producers — reducing the electricity consumed from the grid directly reduces the embedded carbon in their products. This operates through the carbon intensity of electricity: every kWh of solar generation displacing grid electricity with a carbon intensity of approximately 170g CO2/kWh (UK grid average, 2025) reduces the embedded carbon of the manufactured product.
CBAM Carbon Saving Calculation: Steel Components Example
A UK steel section manufacturer installs 800kW of rooftop solar, generating 760,000 kWh/year. Of this, 640,000 kWh is self-consumed (displacing grid electricity).
- Carbon displaced: 640,000 kWh x 170g CO2/kWh = 108.8 tonnes CO2e/year
- UK ETS carbon value at £50/tonne: £5,440/year in CBAM liability reduction
- UK ETS carbon value at £80/tonne (2030 forecast): £8,704/year
- Over 25 years (at rising ETS prices): cumulative CBAM liability reduction of approximately £180,000–£240,000
This is in addition to the primary electricity cost saving of approximately £185,000/year. The CBAM benefit is a secondary financial gain on top of the core electricity saving.
For UK manufacturers exporting products to the EU — and thus facing EU CBAM charges at the EU border — the mechanism operates in reverse: lower embedded carbon in UK-produced goods reduces the EU CBAM charge applied by the EU importer. This improves the price competitiveness of UK exports against third-country alternatives with higher embedded carbon. UK steel and aluminium producers investing in on-site renewable energy are directly improving their EU export competitiveness through lower embedded carbon.
EPC Band C — the 2027 Lease Deadline for Commercial Properties
The government's Minimum Energy Efficiency Standards (MEES) for commercial properties are tightening in 2027. From April 2027, commercial properties in England and Wales being let under a new or renewed lease must achieve a minimum EPC rating of Band C (score of 55 or above on the Standard Assessment Procedure scale). From April 2030, this requirement extends to all existing leases — meaning any commercial property with a live lease must be Band C or above, regardless of when the lease was first signed.
The consequences of failing to meet Band C are material:
Building Becomes Unlettable
High RiskFrom April 2027 (new leases) and April 2030 (all leases), a commercial property that cannot demonstrate EPC Band C cannot be legally let. Landlords with industrial units below Band C face either capital investment to upgrade or loss of rental income.
Reduced Asset Value
Moderate RiskCommercial property valuers are already discounting buildings with poor EPC ratings in anticipation of the MEES requirement. RICS guidance published in 2024 requires valuers to reflect MEES compliance risk in commercial property valuations. Industrial buildings with EPC D or E ratings that have not been upgraded are trading at a measurable discount to comparable Band C+ buildings.
Civil Penalties
Moderate RiskLandlords who let commercial properties in breach of MEES can face civil penalties of up to £150,000 per property. Local authorities are the enforcement body. Compliance is checked at the point of lease grant or renewal.
Solar panels are one of the most effective interventions for improving a commercial building's EPC rating. A large industrial unit currently rated EPC Band D (score 30–54) can typically achieve Band C through rooftop solar installation alone, without requiring additional insulation, HVAC upgrades or glazing improvements. The EPC assessment model attributes credit for on-site renewable generation that reduces the notional energy demand of the building. A solar installer experienced in commercial EPC assessments can model the projected post-installation EPC rating before committing to the project.
Business Rates and Solar — the 2026 Revaluation Explained
Business rates — the commercial property tax administered by local councils — are assessed by the Valuation Office Agency (VOA) based on the rateable value of the property. A common concern among factory owners considering solar is whether installing panels will increase their rateable value and therefore their business rates liability.
The position as of the 2023 VOA revaluation (which took effect 1 April 2023, based on April 2021 values) and the expected 2026 revaluation is as follows:
Solar Panels and Business Rates Relief (England)
In England, solar panels installed on business premises are exempt from business rates under a mandatory exemption for plant and machinery used to generate electricity for on-site consumption. This exemption was put on a permanent statutory footing in the Non-Domestic Rating Act 2023. Panels must be used primarily for on-site electricity generation and consumption (not primarily for export) to qualify. This means the business rates position for a typical factory solar installation is neutral — no additional rates liability arises from the solar installation itself.
Position in Scotland and Wales
Scotland and Wales have devolved business rates systems. In Scotland, the position broadly mirrors England under the Rating (Valuation) Act guidance, with plant and machinery exemptions applying to generating equipment. In Wales, guidance from the Welsh Government confirms that solar panels used for on-site generation are not separately rateable. However, if the solar installation substantially changes the character of the property (for example, a large ground-mounted array on factory land), local assessors may reassess. Always seek VOA or assessor guidance before installation if you are in Wales or Scotland.
ISO 50001 and Solar — a Natural Fit
ISO 50001 is the international standard for energy management systems (EnMS). It provides a framework for organisations to establish energy policies, set measurable energy performance objectives, and continuously improve energy use. For UK manufacturers, ISO 50001 is increasingly relevant for three reasons: it provides automatic ESOS exemption, it satisfies OEM supply chain sustainability requirements, and it underpins credible net zero reporting.
Solar installation is the single most impactful energy performance improvement measure available to most manufacturing sites. Within an ISO 50001 framework, solar contributes to:
Energy Performance Indicators (EnPIs)
ISO 50001 requires the organisation to establish energy performance indicators — measurable metrics that track energy consumption relative to output. Solar generation directly reduces the energy intensity (kWh per unit produced) of the facility. Monitoring platforms provide the automated generation and consumption data required for EnPI tracking without manual data collection.
Energy Baseline and Targets
ISO 50001 requires an energy baseline against which improvements are measured. Solar installation creates a clear, measurable improvement from the pre-installation baseline. Generation monitoring data provides auditable evidence of energy performance improvement year on year, satisfying the standard's continuous improvement requirement.
ESOS Automatic Exemption
Organisations holding a valid ISO 50001 certification covering all organisational energy use are automatically deemed compliant with ESOS — the separate energy audit, Lead Assessor appointment and notification requirements are all covered by the certification. For multi-site manufacturers, this can represent a significant saving in professional fees and management time compared to standalone ESOS compliance.
Certification Evidence
ISO 50001 certifiers (typically UKAS-accredited bodies such as BSI, SGS or Bureau Veritas) conduct regular surveillance audits. Solar generation data provides clear, independently verifiable evidence of energy performance improvement — making surveillance audits straightforward and reducing certification risk.
Building a Compliance Roadmap: Solar as the Centrepiece
For a typical UK manufacturing business facing ESOS Phase 4, UK CBAM, MEES Band C and ISO 50001 requirements simultaneously, the following roadmap places solar at the strategic centre of a coherent compliance programme. The critical insight is that solar installation generates compliance benefits across all four frameworks simultaneously — making it a uniquely efficient use of capital.
Months 1–2: Baseline Energy Audit and ESOS Assessment
Commission an ESOS Lead Assessor to conduct a Phase 4 energy audit. This provides the consumption baseline data required for solar system sizing and for ESOS notification. Simultaneously, collect 12 months of half-hourly consumption data (available from your electricity supplier or smart meter) for solar design purposes. Estimated cost: £5,000–£15,000 depending on organisational complexity.
Months 2–4: Solar Design, Tender and Contract
Commission a detailed solar design using the consumption data from step 1. Obtain a minimum of three tenders from MCS-certified commercial solar installers. Evaluate on system size, equipment specification, monitoring capability, warranty terms, structural engineering assessment and installation programme. Sign contract and confirm grid connection application with DNO (Distribution Network Operator) — allow 3–6 months for grid connection approval on systems above 50kW.
Months 4–8: Installation and Commissioning
Solar installation for a 300–800kW factory system typically takes 3–6 weeks for roof work and 1–2 further weeks for electrical commissioning and DNO connection. Ensure MCS certification is issued on completion — required for ESOS evidence and for SEG export registration. Commission monitoring platform and set up automated energy reporting dashboards for ESOS, ISO 50001 and carbon reporting.
Months 8–12: ISO 50001 Implementation and ESOS Notification
With solar generating and monitoring operational, commission ISO 50001 gap analysis and implementation programme. The solar system's generation and consumption data provides the foundation for ISO 50001 energy performance indicators and baseline documentation. ESOS Lead Assessor completes notification to the Environment Agency, referencing the solar installation as the primary implemented energy saving measure. Well before the December 2027 deadline, the organisation will have satisfied ESOS, improved its EPC rating toward Band C, and established the energy management framework for ongoing compliance.
Frequently Asked Questions
Does my factory need to comply with ESOS Phase 4?
Which UK industries are caught by CBAM from 2027?
What is the EPC Band C deadline for commercial properties?
How does ISO 50001 relate to ESOS compliance?
Can solar panels alone make my factory ESOS compliant?
Trusted Solar Installers Across the UK
We work with a network of MCS-certified regional installers. If you need a recommendation outside our coverage area, these are the firms we trust:
- EC Eco Energy — UK-wide commercial solar & renewables installer
- Midland Solar — Commercial & industrial solar — West Midlands
- ALPS Electrical — MCS-certified solar installer — North East England
- Carbon Legacy — Solar & green energy solutions — East Midlands
- YEERS — Solar panels & heat pumps — Yorkshire