Solar PV and Battery Storage in London Renovations: Specification, Planning, and Returns

Solar photovoltaic (PV) technology has matured to the point where it is a serious specification consideration for a prime London renovation — particularly for properties with south-facing or south-west-facing roof surfaces, and for renovations where improving the EPC rating is a design objective. The combination of solar PV, battery storage, and a heat pump or EV charger creates an energy system that substantially reduces grid energy import and, over a 20–25 year horizon, delivers a genuine financial return.

This guide covers PV system design, battery storage integration, roof suitability assessment, planning considerations for London, the Smart Export Guarantee, and the infrastructure requirements that must be addressed during the renovation.

How Solar PV Works

Photovoltaic panels convert sunlight (not heat — PV panels work in cloudy conditions, though at reduced output) into direct current (DC) electricity. An inverter converts the DC output to alternating current (AC) compatible with the building's electrical system. Excess generation beyond the building's instantaneous consumption can be:

• —Exported to the grid (via the Smart Export Guarantee, with payment per kWh exported)
• —Stored in a battery system for later use (self-consumption maximisation)
• —Used to charge an EV (smart EV charging, coordinated with generation)

Output and yield: PV output is expressed in kilowatt-peak (kWp) — the panel array's output under standard test conditions. In London's climate, a south-facing roof array generates approximately 850–950 kWh per kWp per year (annual yield). A typical prime London terrace house installation of 3–6 kWp generates 2,550–5,700 kWh per year — representing 30–70% of a typical household's annual electricity consumption.

Self-consumption rate: Without battery storage, a household self-consumes (uses directly) approximately 25–40% of solar generation (the rest is exported during periods when the house is unoccupied or consuming less than generation). With battery storage, self-consumption rises to 60–80%.

Roof Suitability

Before specifying a PV system, a roof suitability assessment must consider:

Orientation and pitch: South-facing roofs at 30–40° pitch produce the maximum annual yield. Southeast and southwest orientations produce approximately 85–95% of south-facing output. East and west-facing roofs produce approximately 70–80%. North-facing roofs are generally not viable for PV.

In London's terrace housing stock, the most common configurations are: - *Victorian/Edwardian sloping roofs (30–40° pitch):* Well-suited, but the usable south-facing surface area is often limited (a 6 m wide terrace with a central ridge has two 3 m wide roof slopes — south and north) - *Flat roofs (rear extensions, contemporary upper additions):* Can accommodate panel arrays at an optimised tilt (15–20°) using proprietary tilted mounting frames; east-west facing dual-tilt arrays on flat roofs maximise morning/afternoon generation - *Mansard roofs (steep front slope, shallower rear slope):* The rear slope at lower pitch may be viable; the steep front mansard slope (typically 70°+) is not suitable and would raise significant planning issues if visible from the street

Structural loading: Standard crystalline silicon PV panels weigh 10–15 kg/m². A 6 kWp array of approximately 15 panels occupies 25–30 m² and adds 250–375 kg dead load to the roof structure. For a Victorian terrace with original timber roof structure, the engineer should confirm the rafters and purlins can carry the additional load; strengthening is sometimes required.

Condition: A PV system has a 25–30 year lifespan. If the roof covering (tiles, slates, flat roof membrane) will need replacement within 10 years, replace it before installing PV — removing and reinstalling panels mid-life adds £2,000–£5,000 to the roof replacement cost.

Shading: Trees, chimney stacks, and adjacent buildings that shade the roof surface between 9am and 3pm (the productive generation window) significantly reduce output. A shading analysis (using tools such as SunEye or PVsol modelling software) should be conducted as part of the feasibility assessment.

System Sizing

PV system sizing for a prime London residence is determined by:

• —Available roof area (the binding constraint in most central London properties)
• —Annual electricity consumption (from bills; typical prime London household: 5,000–8,000 kWh/year)
• —EV charging and heat pump loads (if applicable — these substantially increase consumption and therefore the optimal panel array size)

For a typical prime London terrace renovation without EV or heat pump: a 3–4 kWp array (8–10 panels) is the most common feasible specification. For a property with EV and heat pump: 5–6 kWp (13–16 panels) if roof space allows.

Panel technology: Monocrystalline silicon panels dominate the premium residential market — higher efficiency (19–23%), better low-light performance, and a cleaner black appearance than older polycrystalline panels. Premium brands: SunPower (highest efficiency, 22–23%, premium price), LG (recently discontinued residential range, but panels already installed perform well), Panasonic HIT (high efficiency, good temperature coefficient), Jinko Solar and LONGi Solar (high volume, good quality, value pricing).

Inverter: The inverter converts DC to AC and is the most failure-prone component in the system. String inverters (a single inverter for the whole array) are the most economical; microinverters (one per panel) maximise yield from partially shaded or complex arrays and provide panel-level monitoring. SolarEdge and Enphase (microinverters) are the dominant premium residential inverter brands in the UK.

Battery Storage

A home battery stores excess solar generation for use in the evening, overnight, or during grid outages.

Battery technology: Lithium iron phosphate (LiFePO4) batteries are the preferred chemistry for residential storage — safer than NMC (nickel manganese cobalt) chemistry, longer cycle life (3,000–6,000 cycles vs 1,000–2,000 for NMC), and better thermal stability. Leading residential battery brands:

• —Tesla Powerwall 3: 13.5 kWh usable capacity; integrated inverter; strong home automation integration; widely available in the UK
• —Givenergy All-in-One: UK-based manufacturer, 8.2 kWh; good value; popular with MCS installers
• —Sonnen Eco: German, premium, LFP, 5–15 kWh; excellent build quality and software
• —SolarEdge Energy Bank: 9.7 kWh; integrates natively with SolarEdge inverters

Sizing: For a prime London household with 5,000–7,000 kWh/year consumption, a 10–13.5 kWh battery covers approximately one day of average consumption. Sizing to cover overnight demand (typically 3–5 kWh for a household with gas heating) is a common approach; oversizing for EV charging optimisation requires larger capacity (20+ kWh in some cases).

Location: Battery storage systems require a dedicated installation location — typically a utility room, plantroom, garage, or basement. Minimum clearances per manufacturer specification; adequate ventilation (LFP batteries are less sensitive than older chemistries, but temperature-controlled environments extend lifespan). Some systems (Tesla Powerwall) are rated for external installation; most require internal installation.

Planning in Conservation Areas and Listed Buildings

Conservation Areas: Solar panels are Permitted Development (no planning application required) if: - On a roof not visible from a highway - Panels do not protrude more than 200 mm from the roof surface - The system is removed when no longer needed

In practice, for a front-facing roof visible from the street in a Conservation Area, PD rights do not apply — a planning application is required. LPAs in prime London Conservation Areas (RBKC, WCC, Camden) have varying policies, but the general principle is that panels on rear roof slopes, not visible from the street, are generally acceptable; panels on the front elevation are resisted. Rear flat roof installations on extensions are typically acceptable.

Listed Buildings: Installing solar PV on a Listed Building requires Listed Building Consent in addition to any planning permission. LBC for PV on a Listed Building is subject to the heritage test — whether the installation harms the significance of the listed structure. Rear slope or flat roof rear extension installations are more likely to obtain consent than front slope or prominent roof installations.

Smart Export Guarantee (SEG)

The Smart Export Guarantee (SEG) replaced the Feed-in Tariff scheme. Under the SEG, energy suppliers are required to offer export tariffs to small-scale renewable generators (including residential solar PV). Rates vary by supplier and tariff:

• —Standard SEG tariffs: 5–7p/kWh (as of late 2026 — rates change; confirm current rates at point of commissioning)
• —Agile and time-of-use tariffs (Octopus Agile, OVO): export rates can exceed 15–20p/kWh at peak demand times (4–7pm)

The financial case for solar PV and battery in a London renovation is based on self-consumption savings (avoiding buying grid electricity at ~25–30p/kWh) rather than export income. A system that saves 3,000 kWh/year of grid import saves approximately £750–£900/year at current electricity prices. Payback period for a 4 kWp system with 10 kWh battery: typically 8–12 years at current prices.

Installation Requirements

• —All solar PV installations must be by an MCS-certified installer
• —DNO (Distribution Network Operator) notification required for systems above 3.68 kW (G98 notification) or above 16A per phase (G99 application)
• —Building Regulations notification via a Competent Person Scheme (most MCS installers are registered)
• —Consumer Unit (fuse board) may require upgrading to accommodate the additional generation circuit and battery connection