Warehouse Solar ROI: 2 UK Case Studies and a 500kW Payback Model (2026)

Warehouses are the best commercial buildings for solar — large flat roofs, high daytime electricity use, and long-term occupancy. But what do the numbers actually look like? We look at two published UK installations, what their figures do and don't tell you, and a 500kW model with current costs.

Why Do Warehouses Get the Best Solar ROI?

Warehouses consistently outperform other commercial buildings on solar ROI for four reasons:

• Large unobstructed roofs: 1,000-10,000m² of flat, shadow-free space allows optimal panel placement. A 1,000m² roof fits 100-140kW of solar capacity.
• Daytime electricity alignment: Warehouses operate during peak solar hours. Lighting, HVAC, refrigeration, forklifts, and conveyors all draw power when panels generate most.
• High self-consumption: 60-75% of generated electricity is used on-site (vs 30-40% for domestic). Every kWh consumed on-site saves 22p instead of earning 3-15p from export.
• Scale economies: Larger systems cost less per kW. A 500kW system costs £800/kW vs £1,200/kW for a 50kW system.

Case Study 1: Gregory Distribution, Cullompton: 250kWp, Payback Just Over 5 Years

Gregory Distribution put a 250kWp system on the roof of its Cullompton distribution centre in 2014, and most of the output runs its chilled and frozen warehousing. The company projected a payback of just over five years and a 20-year profit of £906,000 (Logistics Manager, 7 February 2014).

What it shows, and what it doesn't: Cold storage draws power around the clock, so nearly all of the output is used on site. But up to £40,000 a year of Gregory's return came from the feed-in tariff, which closed to new applicants in March 2019. A system installed today earns only its bill savings plus export payments, so the 2014 figures overstate today's return; use the 500kW model below for current numbers.

Worked Example: Sizing a 500kW Distribution Centre System

This is an illustrative example, not a named site. Take a distribution centre whose roof could fit 700kW or more. Sizing the system to about 75% of the building's daytime electricity use points to around 500kW instead.

Why smaller can pay better: Self-consumed electricity saves about 22p/kWh (the grid price you avoid), while exported electricity earns only 3-15p/kWh. A system sized to the daytime load sells less at the low export rate, so each panel earns more. The full cost, savings and payback for a 500kW system are in the model below.

Case Study 2: Westbrook Industrial, Warrington: 21kW, Projected 2.5-Year Payback

Westbrook, a warehouse logistics provider in Warrington, installed a 21kW system that generates over 40% of the electricity it needs in a year, with a return on investment projected within two and a half years (CPRE case study). CPRE does not publish the system cost or the savings.

The lesson: You don't need a 5,000m² roof to benefit from warehouse solar. A small system sized below the building's daytime demand uses nearly all of its output on site, at the full avoided grid price. The key factor is daytime electricity demand, not roof size.

How Do These Case Studies Compare?

Both paybacks are the companies' own projections, not audited results, and Gregory's rested partly on a feed-in tariff that new systems no longer get. What they share is a building that uses most of its solar output during the day. For a system installed now, the model below uses current costs and tariffs.

What Does a Typical 500kW Warehouse Solar ROI Look Like?

A 500kW system on a 5,000m² warehouse roof is a common configuration for UK distribution centres. Based on South England irradiance of approximately 950 kWh/kWp, the financial model breaks down as follows:

Assumptions: South England irradiance (~950 kWh/kWp), 70% self-consumption, grid rate 22p/kWh, SEG export rate 15p/kWh. Panel degradation of 0.5%/year not included in simple payback but factored into 25-year total.

What Factors Affect Warehouse Solar ROI?

Four factors determine whether your warehouse solar ROI lands at the high or low end of the range:

• Self-consumption rate (biggest impact): Every kWh consumed on-site saves 22p. Every kWh exported earns 3-15p. A warehouse running 7am-7pm with refrigeration gets 70-80% self-consumption. A warehouse running one shift gets 50-60%.
• System sizing: Oversizing leads to excess export at low rates. Undersizing leaves savings on the table. The optimal system matches 70-80% of peak daytime demand.
• Electricity tariff: Higher grid electricity costs mean higher savings. Warehouses on 25p/kWh tariffs see faster payback than those on 18p/kWh.
• Location: South England generates ~950 kWh/kWp/year. Scotland generates ~800 kWh/kWp/year — roughly 15% less output, extending payback by 6-12 months.

What If You Don't Have the Capital?

If £40,000-£400,000 upfront is not feasible, a Power Purchase Agreement (PPA) lets you get warehouse solar installed at £0 upfront. A third-party investor owns and maintains the system; you buy the electricity at 8-14p/kWh — 30-50% below grid rates.

The trade-off is lower total savings. Over 25 years, buying outright delivers approximately 50-80% more total savings than a PPA because the PPA provider takes a margin. You also miss out on the Annual Investment Allowance tax relief. But if the alternative is no solar at all, a PPA still delivers meaningful bill reduction from day one.

Warehouse Solar ROI FAQs