Across Spirit Energy's 23-site rollout for B&M Care Homes, internal rate of return ranges from 19 to 30 percent, and payback periods run from three to six years. That spread is not a sign of inconsistent work. It is what happens when the same design team and the same installation standard are applied to buildings that each have a different roof, a different daytime load, and a different grid connection.
It's tempting to assume a portfolio rollout means picking one panel, one inverter, and one mounting system and repeating it 20 times. In practice, that approach ignores the thing that actually determines a system's return: the building itself.
A care home with a large flat roof and high daytime occupancy will generate and use electricity very differently to a smaller site with a steep pitched roof and a weaker local grid connection. Forcing an identical specification onto both would leave savings on the table at one site and overcomplicate the system at the other. Every site in a portfolio still needs its own design, sized to its own roof and its own consumption pattern.
This is why IRR varies site to site even within the same client's portfolio. It's not a flaw in the process. It's evidence that each site was actually assessed on its own merits rather than assigned a generic package.
What should be identical across a portfolio is not the equipment. It's the people and the standard they work to.
Spirit Energy designs and installs in-house across every site in a rollout, without white-labelling the work out to subcontractors who might apply a different standard from one building to the next. The same project management approach runs through site assessment, DNO application, and commissioning at every site, so a client dealing with 20 buildings has one point of accountability rather than 20 separate relationships with different local installers.
This consistency shows up in outcomes that are reliably good, even when they're not identical. A 19 to 30 percent IRR range across a portfolio is a tighter, more dependable band than the outcomes you'd expect from 22 sites each installed by a different local contractor working to their own standard.
Not every site should be installed at once, and not every site should be installed in the order they happen to appear on a spreadsheet.
Sites are usually ranked on three factors: roof suitability and available space, daytime electricity consumption, and how straightforward the DNO connection is likely to be. A site with a large roof, high daytime usage, and a strong local grid connection should generally go first. It delivers savings sooner and gives the programme an early, provable result to point to when justifying the next phase to a board or investment committee.
A realistic multi-site programme runs in phases rather than a single installation. Site assessments happen first across the whole portfolio, so the sequencing decision is based on real data rather than guesswork. Installation then proceeds in batches, typically grouped by region, so installer teams and scaffolding can move efficiently from one site to the next rather than zigzagging across the country.
Across the B&M portfolio, system size and financial performance track together but don't scale in lockstep. Wentworth Lodge's 28.35 kWp installation saves over £4,500 a year with a 6 to 7 year payback. St Leonard's, more than double the size at 70.53 kWp, saves £13,073 a year on a 6 year payback and a 21% IRR. St Luke's, the largest of the three at 132.86 kWp, saves £21,805 a year on the same 6 year payback but a slightly lower 20% IRR.
The pattern is clear: a larger roof means bigger absolute savings, but payback period holds steady across very different system sizes, because it's driven more by daytime consumption patterns than by scale alone.
Multi-site rollouts also open financing options that rarely make sense for a single building. Capex, asset finance, and power purchase agreements can be mixed across a portfolio, buying some sites outright where capital allowances make that attractive, and financing others where cash flow matters more. A finance director evaluating 20 sites has considerably more room to structure the funding around the business's actual balance sheet than one evaluating a single roof.