Solar ROI for Large Industrial Sites (500kW–2MW): Enterprise Analysis
Large-scale industrial solar delivers exceptional returns. A 1MW installation pays back in 2.5-4 years and generates £5-7M in lifetime savings over 25 years. Here is the complete enterprise analysis including G99/G100, IETF grants, AIA phasing strategy, and NPV modelling.
Quick Answer: Large Site Solar ROI
A 1MW solar installation on a large industrial site costs £620,000–£850,000 installed. Annual savings of £210,000–£280,000 at 2026 rates give a payback period of 2.5–4 years. Large sites also unlock IETF grants (up to 50% for eligible energy-intensive industries), G100 grid connection options for complex sites, and Power Purchase Agreements as an alternative to full capital outlay when preferred by the board.
Large Industrial Solar: Complete Cost and ROI Table 2026
Figures based on 2026 installed costs at £620-£700/kWp, 28p/kWh electricity rate, 85% self-consumption, 900 kWh/kWp/year. AIA note: systems over £1M benefit from phasing across tax years.
| Size | Installed Cost | Annual Generation | Annual Savings (28p) | AIA Tax Saving | After-Tax Cost | Payback |
|---|---|---|---|---|---|---|
| 500kW | £315,000–£425,000 | 450,000 kWh | £107,100 | £78,750–£106,250 | £236,250–£318,750 | 2.5–3 yrs |
| 750kW | £472,500–£637,500 | 675,000 kWh | £160,650 | £118,125–£159,375 | £354,375–£478,125 | 2.5–3 yrs |
| 1MW (enterprise) | £620,000–£850,000 | 900,000 kWh | £214,200 | £155,000–£212,500 (*phasing recommended) | £465,000–£637,500 | 2.5–3.5 yrs |
| 1.5MW | £930,000–£1,275,000 | 1,350,000 kWh | £321,300 | £232,500–£318,750 (*phasing required) | £697,500–£956,250 | 2.5–4 yrs |
| 2MW | £1,240,000–£1,700,000 | 1,800,000 kWh | £428,400 | £310,000–£425,000 (*multi-year phasing) | £930,000–£1,275,000 | 2.5–4 yrs |
AIA Note: The £1M annual AIA limit means 1MW+ systems should be phased across tax years for maximum tax efficiency. Annual savings of £50,000-£100,000+ from the first phase can partially fund subsequent phases, improving the overall project IRR.
G99 vs G100: Understanding the Difference for Large Sites
Both G99 and G100 are engineering recommendations for connecting embedded generation to the UK distribution network. For large industrial sites, understanding which applies is critical for project planning.
G99: Standard Large-Scale Connection
G99 applies to most embedded generation projects in the UK. For large industrial solar:
- ✓ Applies to most 500kW-1MW installations
- ✓ Formal DNO application with technical documentation
- ✓ Protection relay scheme required
- ✓ Smart Export Management may be required if export capacity is limited
- ✓ Typical approval timeline: 12-24 weeks at this scale
G100: Enhanced Smart Connection
G100 represents the enhanced smart connection standard, applicable in specific circumstances:
- ● Applied by some DNOs for systems over 1MW connected to lower-voltage networks
- ● Requires additional smart management system with DNO-controlled demand response capability
- ● DNO can remotely reduce export during grid stress events
- ● Higher connection costs but may enable connections where G99 capacity is unavailable
- ● Emerging standard — check with your specific DNO for current policies
DNO Constraints and How to Navigate Them
Large systems in congested grid areas may face export constraints. Here are the primary constraint types and mitigation strategies:
Export Limiting
DNO limits export to grid to protect local network. Mitigation: size system for high self-consumption to minimise the financial impact of export limits.
Voltage Rise Issues
Large solar export can cause voltage rise on local network. Mitigation: reactive power management via inverter settings; consider battery storage to reduce peak export.
Grid Reinforcement Costs
DNO may require you to fund local grid reinforcement. Mitigation: pre-application DNO capacity check; consider accepting export limitation to avoid reinforcement costs.
AIA Phasing Strategy for Large Solar Sites
For systems with total installed cost exceeding £1M, strategic phasing across tax years is essential to maximise the Annual Investment Allowance benefit. Here is how to structure it optimally.
Example: 1.5MW System (£1,100,000 installed cost) — 25% Corp Tax Payer
Without Phasing (Single Year)
With Phasing (Two Tax Years)
On top of the tax saving, phasing provides operational data from Phase 1 to optimise Phase 2 design, and spreads cash flow across two financial years.
IETF Grants for Large Energy-Intensive Manufacturers
The Industrial Energy Transformation Fund (IETF) is the primary grant mechanism for large UK manufacturers pursuing energy efficiency and decarbonisation. For sites consuming over 1GWh/year, IETF can transform the investment case.
IETF Eligibility for Solar
Your site must be in a qualifying energy-intensive sector: glass, ceramics, paper and pulp, chemical, food and drink, metal manufacturing, plastics, or textiles.
IETF grants require minimum eligible costs of £100,000. For large sites with 500kW+ systems, this threshold is easily met.
Applicants must provide a 3-year energy management plan demonstrating how the solar investment fits within a broader decarbonisation strategy.
IETF Financial Impact: 1MW Example
25-Year NPV Modelling: 1MW System at Different Discount Rates
For capital allocation decisions in large organisations, Net Present Value (NPV) analysis provides a more rigorous assessment than simple payback. Here is the NPV modelling for a 1MW system (£730,000 installed cost, after-tax £548,000) across three discount rates.
| Discount Rate | Rationale | Year 5 NPV | Year 10 NPV | Year 25 NPV | IRR |
|---|---|---|---|---|---|
| 6% discount | Low-risk capital allocation, typical for ESG-committed companies | £355,000 | £970,000 | £2,290,000 | 32% |
| 8% discount | Standard corporate hurdle rate for many UK manufacturers | £288,000 | £795,000 | £1,720,000 | 32% |
| 10% discount | Higher hurdle rate for risk-adjusted capital allocation | £224,000 | £593,000 | £1,238,000 | 32% |
Key finding: Across all three discount rates, the 1MW solar investment generates strongly positive NPV by Year 10. The IRR of approximately 32% significantly exceeds typical corporate hurdle rates of 8-12%, making this one of the most attractive capital investments available to large manufacturers. Assumptions: 28p/kWh electricity (with 2% annual escalation), 900 kWh/kWp generation, 0.5% annual system degradation, 25-year panel warranty.
Phased Installation: The Preferred Approach for Large Sites
Most large industrial sites above 500kW benefit from a phased installation approach. Here is why and how to structure it effectively.
Phase 1: 500-700kW
- ✓ Install best-performing roof sections first (south-facing, minimal shading)
- ✓ Establish actual self-consumption baseline
- ✓ Claim AIA on Phase 1 cost in Tax Year 1
- ✓ Begin generating £120,000-£165,000/year savings
Phase 2: Expand to Full Capacity
- ✓ Use Phase 1 data to optimise Phase 2 specifications
- ✓ Add battery storage if self-consumption data supports it
- ✓ Claim AIA on Phase 2 cost in Tax Year 2
- ✓ Phase 1 savings partially fund Phase 2 capex
Optimisation Phase
- ✓ EV charging infrastructure powered by solar
- ✓ Demand-side management to maximise self-consumption
- ✓ Battery storage optimisation and flexibility market revenue
- ✓ Full ISO 50001 and carbon reporting integration
Large Site Case Studies
Three representative examples from our large-scale portfolio.
800kW — National Distribution Centre
40,000m² roof fully utilised. G99 approved in 11 weeks. 200kW EV charging fleet powered by solar. Smart export management to avoid curtailment.
1.2MW — Ambient Food Factory
Phased over 2 years (600kW + 600kW) for AIA optimisation. IETF grant applied to Phase 1. 24-hour operation provided excellent self-consumption.
1.5MW — Steel Fabrication Plant
3-year phasing (500kW/year) for maximum AIA benefit. CBAM exposure reduction a key board-level driver. UK ETS registration supported by solar monitoring data.
Frequently Asked Questions
Does a 1MW solar system need G100? ▼
Not necessarily. G100 is an enhanced G99 application route used for larger or more complex embedded generation projects, typically above 1MW total capacity or where the connection requires enhanced network management. Some DNOs apply G100 thresholds at different capacity points. For a 1MW system, G99 is most commonly the applicable standard. G100 applies when the system has enhanced smart functions or is connected to a higher-voltage network. Your installer will confirm which standard applies based on your specific DNO's current policies.
Can I claim AIA on a £1M+ solar system? ▼
Yes, but strategy matters. The Annual Investment Allowance (AIA) cap is £1,000,000 per year per business. A £1.2M solar system can be spread across two tax years to claim full AIA on both tranches. Phase 1 (e.g., 600kW at £420,000) is installed and claimed in Tax Year 1; Phase 2 (e.g., 600kW at £420,000) is installed and claimed in Tax Year 2. The combined AIA tax saving for a 25% taxpayer is £210,000 — claimed over two years. Careful planning with your tax advisor is essential to maximise this benefit.
Are large industrial sites eligible for IETF grants? ▼
Yes. The Industrial Energy Transformation Fund (IETF) specifically targets large and medium energy-intensive manufacturers. For large sites (typically over 1GWh/year energy consumption), IETF can provide 30-45% of eligible project costs as a capital grant, up to £7.5 million per project. Eligible sectors include glass, ceramics, paper, chemical, food and drink, and metal manufacturing. Applications require a detailed energy assessment and 3-year energy management plan.
What is the typical G99/G100 process for a 500kW+ system? ▼
For 500kW+ systems, the G99 process involves: (1) Pre-application enquiry to the DNO to check available export headroom (2-4 weeks); (2) Formal G99 application with full electrical drawings, protection relay scheme, and equipment schedules (4-8 weeks for DNO assessment at this scale); (3) Technical Acceptance Certificate issued by DNO; (4) Physical installation (4-8 weeks for 1MW+ system); (5) Post-commissioning DNO witness testing and energisation. Total timeline from project start to energisation is typically 16-28 weeks. Starting the G99 process on day one of project inception is essential.
Should a large site phase solar installation? ▼
Yes, for most sites over 500kW, phasing is recommended for three reasons. First, AIA tax optimisation: phasing across tax years allows full AIA on each phase if total cost exceeds £1M. Second, operational learning: Phase 1 data reveals actual self-consumption rates and optimal inverter configurations before committing to full Phase 2 design. Third, cash flow management: phasing spreads capital expenditure and allows Phase 1 savings to partially fund Phase 2 investment. A typical phasing strategy is 500-700kW in Year 1, expanding to full capacity in Year 2-3.
Related Guides and Resources
Factory Solar Panel Costs
Complete 2026 pricing guide including large-scale cost breakdowns.
Three-Phase Integration
Technical guide to large-scale three-phase solar connection.
IETF and Industrial Grants
Full guide to IETF and all other industrial solar grant programmes.
Solar Financing and PPA
PPA and finance options for large industrial solar sites.
Capital Allowances Guide
AIA phasing strategy and tax relief for large solar projects.