Designing solar into a scheme from the start

The gap between designing solar in and retrofitting it later is not a small premium. A retrofit means a structural appraisal of a completed building, a cable route improvised through finished space, plant space that was allocated to something else, and switchgear with no spare way.

Four decisions at design stage remove nearly all of that. Structural allowance for the additional array and mounting load. A riser and cable route from roof level to the intake position. Plant space with ventilation for inverters. Switchgear specified with a spare way and adequate fault level headroom.

None of them costs much when the model is still open. All of them are expensive after practical completion, and some are effectively unfixable without disproportionate work. Even where no array is installed on day one, building the enabling infrastructure keeps the option alive at negligible cost.

Commercial new build gives an unusual advantage: the roof is new, its condition is known, and its remaining life matches the twenty five year design life of an array. That alignment is exactly what makes retrofit projects on existing stock so awkward.

What varies is the roof form. Industrial and logistics units offer large simple decks with plenty of area. Offices are congested with air handling, chillers and lift overruns, and the usable share of the plan area is often around half. Residential led mixed use schemes have small roof plates fought over by plant, terraces and lift motor rooms.

Rooflight strategy, sprinkler zones, edge protection and maintenance access should all be coordinated with the array layout while the drawings are live. Coordinating them afterwards means moving whichever one was designed second.

Local plan policies commonly require a proportion of regulated energy to come from on site renewables, and the energy statement submitted with an application has to demonstrate it. An array is usually the cheapest and most predictable way to satisfy that requirement, which is why it appears in so many schemes.

Under the building regulations energy efficiency requirements, on site generation contributes to the comparison against the notional building, so it forms part of the compliance strategy rather than sitting outside it. Minimum energy efficiency standards for commercial property have been tightening over time, which also makes a better performing asset easier to let and easier to hold.

BREEAM and similar assessment methods award credits for on site renewable generation and for the energy performance it supports. Where a scheme is targeting a rating, the array is often doing several jobs at once and should be valued accordingly.

The common objection is that the tenant is unknown, so the load is unknown, so the array cannot be sized. That is a reason to phase, not a reason to omit.

The usual approach is to design the infrastructure for the maximum the roof and structure could ever support, install a base array or none at all, and let the occupier extend once the load is understood. A building that arrives solar ready, with structure, route, plant space and switchgear in place, is far more attractive to an occupier with their own carbon commitments than one that arrives with a promise.

There is a letting argument too. Occupiers increasingly ask about energy performance, on site generation and charge point provision during agent conversations, and a scheme that can answer those questions concretely competes better.

We are not a contractor and we do not tender for the works. We assess what a scheme could support, produce indicative generation and performance figures from the roof plan and expected loads, and match the project with a vetted installer in the network when the time comes to build.

Used early, that gives the design team a realistic capacity figure to write into the energy statement rather than an optimistic one that has to be defended later. Used at handover, it gives the occupier or investor an independent view of what the roof will actually do.

The service is free, and installers pay us only where work proceeds. That is what allows us to tell a developer when a roof will not deliver what a planning consultant has assumed.