Grant / Funding Route
UK Infrastructure Bank debt finance for office solar portfolios
UK Infrastructure Bank: £5m-£100m debt finance, below-market rates. Eligible for larger commercial projects (£5m+).
At a glance
- Funding type
- UK Infrastructure Bank
- Value
- £5m-£100m debt finance, below-market rates
- Eligibility
- Larger commercial projects (£5m+)
The UK Infrastructure Bank (UKIB) is the UK's national investment bank, established in 2021 with £22bn of capital to invest in clean infrastructure and regional economic development. UKIB offers debt finance, equity, and guarantees for projects above £5m total value.
For office solar, UKIB primarily targets portfolio-level investments — typically a multi-building office estate (multi-let landlord with 10+ buildings, public-sector estate, large corporate occupier with multi-site footprint) where the combined investment exceeds £5m. Single-building installations below £5m are generally too small for UKIB direct involvement.
UKIB debt finance typically prices below standard commercial bank rates (currently 1-2 percentage points below comparable senior debt) with terms up to 25 years. For a £20m portfolio solar rollout, that translates to roughly £1-2m of NPV uplift over the financing term compared to standard commercial finance.
UKIB also provides guarantees that enable commercial lenders to extend below-market debt to qualifying projects — a useful route where the customer has an existing banking relationship but the project needs aggressive financing terms.
Application process involves:
We work with specialist project finance advisers on UKIB applications and have supported four successful applications totalling £52m of UKIB debt for office and industrial solar portfolios.
Which office solar projects suit UKIB?
UKIB's minimum deal size of £5m means the fund is relevant for a specific tier of office solar investment:
- Multi-let landlord portfolio rollout: A landlord with 15-20 office assets, each with a 200-500 kWp system, can aggregate a single portfolio facility with UKIB at £5m-£40m. UKIB strongly favours portfolio transactions over single-asset deals.
- Large corporate multi-site: An occupier with 10+ owned offices rolling out solar across their estate in a programmatic MEES 2030 compliance plan, with combined capex over £5m.
- Single large asset (>1 MWp): Very large office parks or data centre campuses where a single site represents a £5m+ investment. Uncommon in pure office — more typical in industrial.
- Public-sector estate programme: Local authority or NHS portfolio combined with Salix PSDS for smaller assets and UKIB for large assets — a hybrid funding stack approach.
UKIB vs commercial project finance: the rate differential
UKIB's pricing mandate requires it to lend at rates that are below what the market would charge for an equivalent credit, but above the risk-free rate (currently ~4.5%). In practice, UKIB senior debt for commercial solar portfolios has priced at 5.5-6.5% in recent transactions — typically 100-175 basis points below comparable senior commercial bank debt (which has priced at 6.5-8% for similar credit profiles).
On a £20m portfolio, the NPV of the interest rate difference over 20 years is approximately £1.8-2.4m — a material reduction in the cost of capital that translates directly to improved portfolio-level IRR.
UKIB also provides longer tenors than commercial markets typically offer for solar assets (15-25 years vs 7-12 years from commercial banks), reducing annual debt service and improving cash-flow-to-debt ratios in the early years when the portfolio is building operational track record.
UKIB application process: what to expect
UKIB is not a quick facility — the appraisal process is thorough. Expect:
- Initial enquiry / project pitch: 2-4 weeks. Submit a structured project summary covering investment size, sector, expected climate and regional economic impact, and financial structure. UKIB's team will advise if the project meets their mandate before proceeding.
- Advisory engagement: 4-8 weeks. UKIB advisers work with the borrower to refine the financial model, structuring approach, and ESG impact metrics (UKIB requires projects to demonstrate alignment with the Green Finance Framework).
- Credit application: Full financial model, third-party technical report, legal due diligence, and credit committee submission. 8-12 weeks.
- Documentation and drawdown: 6-10 weeks from credit approval. UKIB uses standard LMA documentation with project finance-specific amendments.
Total timeline from initial contact to first drawdown: typically 6-10 months. This aligns reasonably with the 6-9 month installation programme for a multi-building portfolio rollout — meaning UKIB financing can be structured to fund buildings as they complete rather than requiring a single upfront commitment.
UKIB green infrastructure: the reporting obligation
UKIB requires borrowers to report annually on the climate and regional economic impact of UKIB-financed assets. For office solar portfolios, this means providing annual generation data (kWh), CO₂ savings (tonnes), and any regional economic contributions (local supply chain employment, regional wage spend). The reporting format is aligned with TCFD recommendations and GHG Protocol Scope 2 methodology. We provide the generation and CO₂ data elements as part of the standard annual O&M report, making UKIB's reporting obligation largely straightforward for our customers.