How Solar PV Works
Solar photovoltaic panels convert sunlight into direct current (DC) electricity. An inverter converts this to alternating current (AC) for use in the home. Any electricity generated that is not immediately consumed can be:
- Stored in a battery for later use
- Exported to the National Grid (generating a payment via the Smart Export Guarantee)
- Used automatically when demand matches generation
Is Your London Roof Suitable?
The ideal solar roof in London is:
- South-facing: A due-south roof maximises output. South-east and south-west are nearly as effective. East and west orientations reduce output by around 20%.
- Pitched: A pitch of 30–40° is optimal. Flat roofs can accommodate panels on mounting frames tilted to the correct angle.
- Unshaded: Shading from trees, chimneys, or neighbouring buildings significantly reduces output. A shading analysis should be carried out before installation.
- Structurally adequate: The roof structure must support the panel weight (typically 10–15kg/m²). This should be confirmed for older properties.
In London, north-facing roofs are generally not viable for solar PV.
Permitted Development for Solar Panels
Solar panels on houses are permitted development in England (no planning permission required) provided:
- The panels do not protrude more than 200mm beyond the plane of the roof
- The panels do not exceed the highest point of the roof
- The installation is not on a building within the grounds of a listed building
- The installation does not face the principal elevation (facing the road) in a Conservation Area
For Conservation Area properties where the roof faces the road, planning permission may be required. Check with the local planning authority.
Listed buildings always require Listed Building Consent for solar panel installation.
Expected Output in London
London's solar resource is moderate by UK standards — broadly similar to central southern England. A typical south-facing 4kWp system in London might generate:
- Annual generation: 3,200–3,600 kWh per year
- Compared with typical household consumption of 3,500–4,000 kWh/year, this covers a significant proportion of annual use
Output varies significantly by month — high in summer (June/July can generate 400–500 kWh from a 4kWp system), very low in December–January.
Battery Storage
A solar battery stores surplus generation for use later in the day or overnight, increasing the proportion of generated electricity that is self-consumed.
- Typical home battery sizes: 5–15 kWh
- A 10kWh battery roughly doubles the self-consumption from a 4kWp system in summer
- Cost: £3,000–£7,000 for a quality lithium-iron-phosphate battery with installation
- Payback period for battery alone (in addition to panels): 10–15 years at current electricity prices
Smart Export Guarantee (SEG)
Since January 2020, electricity suppliers with 150,000+ customers must offer a Smart Export Guarantee tariff, paying for electricity exported to the grid. Rates vary by supplier (typically 4–15p/kWh) and are lower than the import rate, making self-consumption more valuable than export.
Typical Costs and Payback
| System Size | Number of Panels | Approximate Cost | Estimated Annual Saving |
|---|---|---|---|
| 3kWp | 6–8 panels | £5,000–£7,000 | £400–£600 |
| 4kWp | 10–12 panels | £7,000–£9,000 | £550–£800 |
| 6kWp | 14–16 panels | £9,000–£12,000 | £750–£1,100 |
Payback period (without battery): typically 8–12 years. With battery: 12–18 years.
These figures assume significant self-consumption. Properties that are empty during daylight hours (owners at work) will have lower self-consumption and longer payback periods unless a battery is fitted.
Accreditation and Warranties
Use a Microgeneration Certification Scheme (MCS)-certified installer. MCS certification is required for eligibility under the Smart Export Guarantee.
- Panel warranty: typically 25 years (product and performance)
- Inverter warranty: typically 10 years (extendable)
RCB Design & Build
RCB incorporates solar PV assessments into refurbishment and extension projects where appropriate. We coordinate structural checks, Planning or Listed Building Consent where needed, and installation by MCS-certified installers within the main contract or as a specialist package.