New Build vs Retrofit Solar: Which is Right for Your Warehouse?

New build warehouses offer a unique opportunity to design the building and solar system as an integrated whole. Structural steel sizing, electrical switchgear, cable routes, and inverter locations can all be specified from the outset to accommodate the solar system — eliminating retrofitting compromises and typically reducing installation cost by 10–20%.

Many local planning authorities now condition minimum on-site renewable energy provision in large-format warehouse planning approvals. In the East Midlands, Thames Valley, and South East, conditions requiring minimum 10–20% energy from renewables are common. Planning conditions for BREEAM Excellent certification — required by many logistics REITs and institutional developers — typically mandate solar as part of the energy strategy.

DNO pre-application engagement during the planning stage allows grid connection capacity to be sized correctly. A developer planning a 500,000 sq ft warehouse with 2MW of solar can engage the DNO during the planning period rather than the construction period — potentially avoiding the 6–12 month DNO processing delay that affects many retrofit projects.

Despite the advantages of new build integration, retrofit installations on existing warehouses represent approximately 85% of the UK warehouse solar opportunity by volume. The UK's existing warehouse stock was mostly built without solar — and the combination of rising electricity costs, MEES obligations, corporate net zero commitments, and improving solar economics has made retrofit the primary commercial solar market.

Retrofit solar on most post-2000 warehouse buildings is straightforward. Modern steel portal frame construction with standard purlins and profiled or flat membrane roofing is well-suited to solar. The primary retrofit considerations are structural capacity confirmation, electrical infrastructure adequacy, and DNO connection capacity — all of which are assessed during our free site survey.

Where roof condition is poor — ageing membrane, deteriorated profiled sheet, or asbestos cement — solar retrofit provides an opportunity to combine roof replacement with solar installation. Combined projects benefit from shared mobilisation and access costs, more competitive financing terms (the new roof extends building life, improving security), and the ability to design the new roof surface specifically for solar optimisation.

New build warehouse solar can be financed as part of the overall development cost and included in the development finance facility. This simplifies financing structure but means the solar is being financed at development loan rates (typically 2–4% above base rate) rather than specialist solar finance rates.

For speculative developments where the warehouse will be let on completion, solar specification is increasingly required by institutional investors (REITs, pension funds, infrastructure funds) who have ESG mandates. Buildings without solar may achieve lower rents or face difficulty attracting BREEAM Excellent-requiring occupiers.

Retrofit solar on tenanted buildings involves navigating the landlord-tenant relationship. PPA structures allow tenants to fund solar without landlord capital involvement and without the need for complex lease negotiations. Green lease clauses — increasingly standard in new leases negotiated with major logistics operators — facilitate solar installation by establishing upfront agreement on access, cost recovery, and revenue sharing.