Buying solar per plot across a whole site is usually cheaper per kWp than one-off retail installation. Published figures put build-stage in-roof PV at around £1,200/kWp (Spirit Energy), against an MCS retrofit average of £1,565–£1,686/kWp. This page covers what drives the per-plot price, what a developer package should include, and how price certainty is agreed.
What drives per-plot cost
Three factors dominate: the panel and inverter purchase price, which falls with volume; site labour, which depends on how well the roofing and solar work are sequenced; and the design and SAP modelling cost, which is spread across the number of plots of each house type.
What a package should include
Panels, inverter, in-roof mounting, isolators, cabling, monitoring, commissioning, the MCS certificate, network operator notification, the installer’s workmanship warranty (check the term and whether it is insurance-backed) and the buyer handover documents. Ask whether the SAP modelling is included or priced separately.
What is often priced separately
Battery storage, the heat pump system, mechanical ventilation, EV chargers and building control fees are usually separate line items. Compare quotes on a like-for-like scope.
Off-site pre-fit vs on-site install
Some panelised roof systems allow the in-roof mounting to be fitted off-site and delivered to plot, which can reduce weather exposure and site labour. On-site installation during the roofing stage remains the norm on most sites.
Agreeing price certainty
Agree whether the per-plot price is fixed for a set period or index-linked on longer programmes, which index applies, and any cap on increases. Put it in the contract before start on site.