Solar for offices with a weekday daytime load

An office has one of the cleanest load shapes for solar in commercial property. Occupancy builds from about eight, lighting, small power, ventilation and comfort cooling run through the day, and demand falls away in the early evening. Generation does very nearly the same thing.

The summer alignment is better still. Air conditioning load peaks on bright warm afternoons, which is precisely when an array produces most, so the most expensive hours of the year to import are the hours the roof is working hardest.

Then the weekend arrives and the building empties. Two days in seven, generation meets a base load of servers, security, standby plant and comms, and the rest exports. Exported units earn a small fraction of the rate you avoid by consuming them, so those two days are worth far less than the other five. That single fact drives most office sizing decisions.

Because of the weekend, the temptation to fill an office roof should be resisted unless there is a plan for the surplus. An array sized close to the weekday daytime base load will self consume very well. One sized to the full roof will spill a significant share into a low value export.

There are three sensible ways to use more roof. A battery charged at the weekend and discharged into Monday morning, which needs modelling against half hourly data rather than assuming. Electric vehicle charging in the car park, which adds daytime load directly and is often the single best pairing an office can make. Or hybrid and flexible working patterns, which counter intuitively can flatten the weekly profile if the building runs its plant regardless of headcount.

Heat pumps change the picture too, moving heating from gas to electricity and lifting consumption, though the new demand lands in winter when the array contributes least. Both should be assessed together, along with whether the incoming supply has capacity for both.

Office roofs are the most congested in commercial property. Air handling units, chillers, condensers, lift overruns, plant enclosures, smoke ventilation, window cleaning anchor and cradle systems, edge exclusion zones and maintenance walkways all occupy the deck.

It is common for the genuinely usable area to be around half of the plan area, sometimes less on a heavily serviced building. Shading is a second problem, because plant, parapets, lift overruns and neighbouring buildings all cast shadows across a flat roof at low sun angles, and a well designed layout uses inverter and optimiser arrangements to limit the effect rather than pretending it does not exist.

This is why an outline traced honestly around the clear space produces a far more useful estimate than a gross roof measurement. Flat roofs also carry a lower usable fraction than pitched ones because rows must be spaced to avoid shading each other, which the assessment accounts for automatically.

In a multi let office, the landlord owns the roof and the structure, tenants hold their own supply contracts, and the landlord supply covers common parts, lifts, plant and central services. Generation has to be directed somewhere, and that choice is a commercial and legal decision before it is a technical one.

The straightforward route is landlord owned generation supplying landlord services and common parts only. It needs no tenant agreement, the metering is simple, and the benefit reaches tenants indirectly through a lower service charge. The limitation is that common parts consumption caps the array size.

Supplying tenants directly is possible but must be designed in, not retrofitted. It requires a metering arrangement that allocates generation, a supply agreement with each tenant, and lease provisions that permit it. The third route is a tenant funded array under a landlord licence, which suits a single let building with a long term. Whichever applies, settle it before design, because it determines the metering topology and physical rework afterwards is expensive.

On site renewable generation is a recognised input to the EPC calculation for non domestic buildings, so an array generally improves a rating. How much depends on the building's overall performance, its size relative to the array, and where it sits on the banding, and no honest assessment will promise a specific band uplift before the calculation is run.

Minimum energy efficiency standards for commercial property have been tightening over time, which makes the rating a lettability and asset value question rather than a compliance footnote. BREEAM and similar assessment methods award credits for on site renewable generation, which matters for refurbishment schemes targeting a rating.

Occupier due diligence has moved as well. Corporate tenants with their own carbon commitments now ask about on site generation, charge point provision and metered energy data during agent conversations, and a building that can answer concretely competes better. NRG Solar assesses and matches. We produce indicative figures from your own roof outline and spend, then introduce one vetted installer working in your area. We do not install, and the service is free to you.