Communal rooftop array sized to building-attributable share. 90 kWp PV with PPA agreement — operator owns array, tenants get 15% discount on grid rates through smart sub-meter. Scheme's annualised EPC: B+ across all flats.
The brief
A 280-unit Build-to-Rent block in East London (Royal Docks redevelopment area), operator-owned and operator-let. The block is HRB-status (Higher-Risk Building, exceeds 18 m) so falls within the Building Safety Regulator pathway. FHS-compliant PV required under the building-attributable-share calculation rather than the per-plot 40% rule (which doesn't straightforwardly apply to vertically-stacked dwellings). Operator wanted a financial model that earned a return on the array while passing meaningful savings to tenants, recognising that BTR tenants' energy bills are increasingly a material rent-pricing factor.
PV sizing calculation
Building-attributable ground floor area methodology: total roof area × proportional contribution to dwelling floor area = required PV. For the 280-unit block (total dwelling floor area 14,200 m², ground floor footprint 760 m²) the FHS-equivalent PV requirement was 304 m² of panel area. 90 kWp installed on the available 308 m² of roof — comfortably satisfies the building-attributable calculation. Roof space optimisation included siting plant room equipment (MVHR units, lift overruns) carefully to maximise contiguous PV area.
System specification
210 × LONGi Hi-MO 5 425W panels in 6 strings, 4 × SolarEdge SE25K commercial inverters in the rooftop plantroom, communal monitoring via SolarEdge Designer. AC-side connection to the building's communal landlord supply through a 100A 3-phase board. Building energy management system (Siemens Desigo CC) integrates PV generation data with the building's ASHP system (centralised 4 × 80 kW Mitsubishi CAHV heat pumps serving a building-wide LTHW heat network) and the basement car park's 24 × 7 kW EV chargers.
PPA structure and tenant economics
Operator owns the array. Tenants pay for solar electricity through smart sub-meters at a 15% discount to the prevailing grid retail rate (currently ~22p/kWh × 0.85 = ~18.7p/kWh). Sun-aware EV charging in the basement diverts surplus PV to chargers during the working day. Average annual tenant saving from the discounted electricity: ~£85/yr per flat. Operator PPA economics: array cost £156,000 installed; annual revenue £15,500 (at 83 MWh × 18.7p); payback ~10 years; net 15-year IRR ~7.5%.
EPC compliance approach
Annualised EPC across all 280 flats: average 84 (band B+). Required additional fabric performance to achieve band B given the lower per-flat PV contribution vs a low-rise scheme — delivered through tighter window U-values (1.0 W/m²K throughout vs FHS 1.4 minimum) and triple glazing on north-facing flats. Communal ASHP scheme efficient at ~340% COP across the year. Building-wide MVHR system provides controlled ventilation at the air permeability target.
Tenant feedback and operator outcomes
Tenant satisfaction with the energy package: top 10% of operator's 12-scheme portfolio (resident survey, 6-month follow-up). PV-discounted electricity rate cited as a "decision factor" by ~25% of new tenants in initial leasing rounds. Operator-side: scheme listed in their 2026 ESG report as the flagship low-carbon delivery; data shared with three peer BTR operators considering similar PPA structures on 2027 schemes.
