How do I calculate the right solar PV system size for a UK home?

The standard approach to solar PV sizing for UK homes uses three inputs: annual electricity consumption (from bills or EPC), available roof area, and roof orientation and tilt. A rule of thumb is 1kWp of solar PV generates approximately 850 to 1,100 kWh per year in the UK, depending on location and orientation. For a home using 3,100 kWh per year, a 3.5kWp to 4kWp system will generate roughly 80% to 110% of annual consumption (accounting for self-consumption rates of around 40% to 50% without battery storage). Each 1kWp of standard monocrystalline panels requires approximately 5 to 6 square metres of unshaded roof area. MCS-certified installers use MCS 001 (Product Certification) and the MCS Planning Standards to produce formally compliant sizing calculations.

What is the difference between G98 and G99 for solar PV installations?

G98 and G99 are DNO connection engineering recommendations for generating systems connected to the low voltage (LV) distribution network. G98 applies to systems up to 3.68kW single-phase (or 11.04kW three-phase) — these can be connected and then notified to the DNO within 28 days of commissioning without prior approval. G99 applies to systems larger than these thresholds and requires a formal application to the DNO before installation. The DNO has up to 45 working days to assess a standard G99 application for a residential system, and 90 days for more complex assessments. Failing to apply under G99 before installing an oversized system can result in the DNO requiring the system to be disconnected.

What does BS 7671 Section 712 require for solar PV installations?

BS 7671:2018+A4:2026 Section 712 (Solar photovoltaic (PV) power supply systems) sets out the specific requirements for solar PV electrical installations. Key requirements include isolation on both the AC and DC sides (Regulation 712.537.2); overvoltage protection and surge protective device selection on the DC side (Regulation 712.534); identification and warning notices indicating the presence of a PV system and that DC parts can remain live after isolation (Regulation 712.514); DC cables selected to minimise earth-fault and short-circuit risk, using H1Z2Z2-K cable to BS EN 50618 or equivalent (Regulation 712.521.101); and equipotential bonding of the PV mounting structure where required (Regulation 712.542.101). Note that the former Regulation 712.443 was deleted by A4:2026.

How does battery storage affect the electrical installation requirements?

Battery storage adds complexity to solar PV electrical installations in several areas. Protection coordination: the battery management system (BMS) and inverter-charger must be assessed together to ensure fault current protection operates correctly under both import and export conditions. Energy storage forms part of a prosumer's electrical installation, which BS 7671:2018+A4:2026 addresses in Section 826, and the equipment must comply with its relevant product standard. Export limiting: where a DNO requires export limiting as a condition of G99 approval, the inverter must have an active export limiter with current transformer (CT) monitoring at the grid connection point. Fire safety: battery storage systems must be positioned in accordance with manufacturer requirements and relevant fire safety guidance — lithium-ion batteries should not be installed in habitable rooms without appropriate fire protection.

Do I need MCS accreditation to install solar PV in the UK?

MCS accreditation is not legally required to install solar PV in the UK — Part P and G98/G99 compliance are the statutory requirements. However, MCS accreditation is required for customers to access the Smart Export Guarantee (SEG), which allows them to receive payment for electricity exported to the grid. Without MCS accreditation, the installer cannot certify the installation to MCS standards, and the customer cannot apply to an SEG licensed electricity supplier for export payments. For most residential customers, the ability to earn SEG income is a significant factor in the return on investment calculation, so in practice most reputable solar PV installers hold MCS accreditation.

What are the DNO export limiting requirements for solar PV?

Export limiting (also called active network management or ANM) may be required by the DNO as a condition of G99 approval where the local network does not have sufficient export capacity for the full output of the proposed system. In an export-limited installation, the inverter is fitted with a current transformer at the grid connection point that monitors export and throttles inverter output to stay within the approved export limit (often 3.68kW single-phase or a site-specific limit). Export limiting must be implemented using a DNO-approved method — some DNOs specify particular inverter brands or communication protocols. Export-limited systems must be re-notified to the DNO if the export limit changes, and the limitation must be clearly documented in the G99 agreement.

What orientation and tilt angles give the best solar PV output in the UK?

In the UK, south-facing roofs at a tilt angle of 35 to 40 degrees give the maximum annual output — typically 950 to 1,100 kWh per kWp depending on location (higher in the South West and lower in Scotland). East-west split systems (two arrays facing east and west at around 20 to 30 degrees) can increase self-consumption by spreading generation across the morning and afternoon, typically achieving 80% to 85% of the yield of an equivalent south-facing system. North-facing roofs are generally not viable — output is typically 50% to 60% of a south-facing installation. Shading is the most significant yield reduction factor: even partial shading on one module in a string can significantly reduce whole-string output unless the system uses module-level power electronics (microinverters or DC optimisers).

SOLAR PV GUIDE

Solar PV System Sizing — UK Electrician Guide

A complete guide to sizing solar PV systems for UK homes: kWp calculations, orientation and tilt factors, MCS standards, G98/G99 DNO notification thresholds, BS 7671 Section 712 requirements, and battery storage integration.

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10 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

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What size solar PV system do I need for a UK home?

Match system size to your annual electricity use, roof area and orientation. A typical UK home uses about 3,100 kWh per year and suits a 3.5–4 kWp system, since each 1 kWp generates roughly 850–1,100 kWh annually. Systems up to 3.68 kW single-phase can be notified to the DNO under G98; larger systems need prior G99 approval. Each panel needs around 1.7–2.0 m² of unshaded roof.

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Key Takeaways

1System size in kilowatt-peak (kWp) is determined by the available roof area, the household's annual electricity consumption, and the orientation and tilt of the roof surface. A typical UK 3-bed home uses 3,100 kWh per year and is well served by a 3.5kWp to 4kWp system.
2MCS (Microgeneration Certification Scheme) accreditation is required for solar PV installations where customers wish to access the Smart Export Guarantee (SEG) or claim compliance with MCS standards. Without MCS, the installation cannot be formally certified to the scheme.
3Systems up to 3.68kW single-phase (16A per phase) can be notified to the DNO under the simplified G98 procedure after installation. Larger systems require a G99 application with prior DNO approval — which must be obtained before installation begins.
4BS 7671:2018+A4:2026 Section 712 covers photovoltaic power supply systems and applies to all solar PV electrical installations. Key requirements include DC isolators at the array and inverter, protection against reverse current, and appropriate labelling throughout the installation.
5SAP (Standard Assessment Procedure) calculations are used for new-build solar PV sizing under Building Regulations Part L. For retrofit installations, energy monitoring data or EPC assessments provide the consumption baseline for sizing calculations.
6Battery storage integration requires careful consideration of protection coordination, particularly where export limiting is applied. The PV side is assessed under BS 7671 Section 712, while energy storage falls under the prosumer installation requirements of Section 826, together with the relevant product standards.

01 · Solar PV Guide

Solar PV Sizing Principles for UK Homes

Sizing a solar PV system correctly is the single most important design decision in a domestic solar installation. An undersized system leaves energy potential on the table; an oversized system generates electricity that cannot be consumed or exported within permitted limits. The goal is to match system output to the household's self-consumption pattern and DNO export constraints.

The unit of solar PV capacity is the kilowatt-peak (kWp) — the power output of the array under Standard Test Conditions (STC: 1,000 W/m² irradiance, 25°C cell temperature, 1.5 air mass spectrum). In real UK conditions, the array output is always lower than kWp due to irradiance, temperature, and angle effects.

Annual yield estimate: South-facing, 35° tilt, south England — approximately 950 to 1,100 kWh per kWp per year. Scotland — approximately 750 to 900 kWh per kWp per year.
Typical UK home consumption: 3,100 kWh per year (Ofgem typical domestic consumption values 2024). High-consumption homes (electric heating, EV charging) may use 5,000 to 10,000+ kWh per year.
Self-consumption rate: Without battery storage, typically 25% to 40% of solar generation is self-consumed. With battery storage, this rises to 60% to 80% depending on battery capacity and household demand profile.

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02 · Solar PV Guide

kWp Calculation Methods

MCS-certified solar PV installers use formal design tools — including the MCS Planning Standards methodology and tools such as PVGIS (Photovoltaic Geographic Information System) — to produce accurate yield estimates and system sizing calculations. The following simplified approach is useful for initial assessments; once the capacity is fixed, the covers string layout, inverter sizing, and DC voltage limits.

Step-by-Step Sizing Method

Step 1 — Establish annual consumption: Obtain annual kWh consumption from electricity bills or EPC. Use Ofgem typical values if bills are unavailable (3,100 kWh for medium household).
Step 2 — Calculate target generation: For a self-consumption optimised system, target generation of 100% to 130% of annual consumption (excess is exported via SEG). For a net-zero target, account for EV charging and heat pump loads.
Step 3 — Estimate kWp required: Divide target annual generation (kWh) by estimated specific yield (kWh/kWp/year from PVGIS for the specific location, orientation, and tilt). Round up to the nearest whole module count.
Step 4 — Check roof area: Each 400Wp panel occupies approximately 1.7m² to 2.0m². Multiply panel count by panel area and add 15% for spacing, verge margins, and ridge clearance.
Step 5 — Check G98/G99 threshold: If the resulting kWp exceeds 3.68kW single-phase, a G99 application is required before installation can proceed.

03 · Solar PV Guide

Orientation and Tilt Factors

The orientation (azimuth) and tilt (inclination) of a solar array have a significant effect on annual energy yield. The PVGIS tool, maintained by the European Commission's Joint Research Centre, provides location-specific yield estimates for any combination of tilt and orientation.

Orientation Yield Factors (South England Reference)

Indicative relative annual yield versus an optimal south-facing array. Use PVGIS for the specific site, location and tilt.

Orientation & tilt

Relative yield

South (180°), 35–40° tilt

100%

South-East / South-West (135° / 225°), 35° tilt

~95%

East / West (90° / 270°), 25–30° tilt

~80–85%

Flat roof, ballasted at 10–15° tilt

~87%

North-East / North-West, any tilt

~65–70%

North (0°), any tilt — marginal

~50–60%

Shading: Even partial shading on a single cell in a string can reduce the output of all modules in that string. Always carry out a shading analysis using a solar pathfinder, SunEye tool, or PVGIS shading assessment before finalising the design. Consider microinverters or DC optimisers for shaded installations.

04 · Solar PV Guide

MCS Standards and G98/G99 Notification Thresholds

Two separate certification and notification frameworks apply to residential solar PV installations in the UK: MCS (Microgeneration Certification Scheme) for quality and SEG eligibility, and G98/G99 for DNO connection requirements.

MCS Requirements

MCS 001 — Solar PV product certification standard (modules and inverters must be certified to the relevant IEC standards and registered on MCS)
MCS 005 — Installer certification standard. The installation company must hold MCS 005 certification for solar PV to issue an MCS certificate.
MCS certificate required for Smart Export Guarantee (SEG) application — without it the customer cannot receive SEG export payments.

G98 — notify after install

Single-phase: Up to 3.68 kW (16 A)
Three-phase: Up to 11.04 kW (16 A/phase)
Approval: Notify DNO within 28 days of commissioning

G99 — apply before install

Applies to: Any system above the G98 thresholds
Standard assessment: Up to 45 working days (residential)
Complex sites: Up to 90 working days

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05 · Solar PV Guide

BS 7671 Section 712 — Photovoltaic Systems

Section 712 of BS 7671:2018+A4:2026 sets out the specific additional requirements for photovoltaic power supply systems. These requirements supplement the general requirements of BS 7671 and apply to all solar PV electrical installations, regardless of system size.

Regulation

Requirement

712.537.2

Isolation and switchingMeans of isolation must be provided on both the AC and DC sides. Devices without DC breaking capacity (such as fuse carriers and SPD carriages) that could open a DC circuit must be secured against inadvertent operation, for example by a lockable enclosure or padlocking (Regulation 712.537.2.2.104).

712.534

Overvoltage protection (SPDs)Surge protective devices on the DC side must comply with BS EN 61643-31. SPDs are generally Type 2 with a minimum nominal discharge current of 5 kA; Type 1 SPDs apply where lightning separation distance cannot be maintained per BS EN 62305-3.

712.514

Identification and noticesAn instruction notice indicating the presence of a PV system must be fixed at the origin, the metering position and the consumer unit (712.514.101). Each DC access point needs a warning that live parts can remain energised after isolation (712.514.102), and every inverter must be labelled to isolate both AC and DC before servicing (712.514.103).

712.521.101

DC wiring systemDC cables must be selected and erected to minimise earth-fault and short-circuit risk, using single-core non-metallic-sheathed cable such as H1Z2Z2-K to BS EN 50618, or insulated conductors in individually insulated conduit or trunking. Cables must not be placed directly on the roof surface.

712.533.101

DC overcurrent protectionDC-side overcurrent protective devices must be gPV fuses to BS EN 60269-6 or circuit-breakers to BS EN 60947-2 / BS EN 60898-2 / BS IEC 60898-3, and must be bidirectional with a breaking capacity at least equal to the array short-circuit current.

712.542.101

Equipotential bonding of PV structuresWhere bonding is needed to prevent electrostatic charge accumulation, the metallic support structures and cable management must be bonded; functional bonding conductors must be at least 4 mm² copper equivalent (712.542.3.101).

A4:2026 change: the former Regulation 712.443 was deleted by BS 7671:2018+A4:2026. Always cite the current numbering — DC-side overvoltage and SPD requirements now sit under Regulation 712.534. Outdoor PV enclosures must achieve at least IP44 to BS EN 60529 and IK07 to BS EN 62262 (Regulation 712.512.102).

See the for how non-compliance with Section 712 requirements is typically graded on electrical inspection reports.

06 · Solar PV Guide

Battery Storage Integration

Battery storage is increasingly standard in new solar PV installations, and a growing number of existing systems are being retrofitted with battery storage. Integrating battery storage introduces additional electrical design and safety considerations under BS 7671 and the relevant product standards.

Standards and product compliance

Battery storage forms part of a prosumer's electrical installation, addressed in BS 7671:2018+A4:2026 Section 826. The battery system must comply with its relevant product standard, and the combined inverter-battery system must satisfy the PV requirements of Section 712.

AC-coupled vs DC-coupled

AC-coupled batteries have their own inverter-charger and are simpler to retrofit. DC-coupled batteries connect to the PV inverter's DC bus and are more efficient but need a compatible inverter/battery pairing. Both require G98/G99 assessment as a combined system.

Fire safety and siting

Lithium-ion battery systems should not be installed in habitable rooms without fire separation meeting the manufacturer's requirements. Enclosures should vent thermal runaway to outside where practicable. Manufacturer installation instructions must be followed and taken into account as part of equipment selection and erection under BS 7671.

07 · Solar PV Guide

DNO Connection Requirements and Export Limiting

All solar PV systems in Great Britain must be registered with the relevant DNO under G98 or G99. Some DNOs impose export limiting as a condition of G99 approval where the local network has insufficient export headroom.

Export limit setting: Where a DNO requires export limiting, the approved export limit (in kW or A) is specified in the G99 agreement. The inverter must be configured with the export limiter active, with a current transformer (CT) clamp on the grid supply cable, before commissioning.
Zero export (export prevention): Some DNOs or property types (leasehold, shared supplies) require zero export — the system is configured to prevent any export to the grid. This significantly reduces self-consumption rate and requires careful sizing to avoid wasted generation.
Documentation: The G99 agreement (or G98 notification confirmation) must be retained with the installation documentation and provided to the customer alongside the EIC. Use
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Solar PV System Sizing — Frequently Asked Questions

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Solar PV System Sizing — UK Electrician Guide

What size solar PV system do I need for a UK home?

Key Takeaways

Solar PV Sizing Principles for UK Homes

Get the BS 7671 A4:2026 Cheat Sheet — free

kWp Calculation Methods

Step-by-Step Sizing Method

Orientation and Tilt Factors

Orientation Yield Factors (South England Reference)

MCS Standards and G98/G99 Notification Thresholds

MCS Requirements

G98 — notify after install

G99 — apply before install

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BS 7671 Section 712 — Photovoltaic Systems

Battery Storage Integration

Standards and product compliance

AC-coupled vs DC-coupled

Fire safety and siting

DNO Connection Requirements and Export Limiting

Solar PV System Sizing — Frequently Asked Questions

How do I calculate the right solar PV system size for a UK home?

What is the difference between G98 and G99 for solar PV installations?

What does BS 7671 Section 712 require for solar PV installations?

How does battery storage affect the electrical installation requirements?

Do I need MCS accreditation to install solar PV in the UK?

What are the DNO export limiting requirements for solar PV?

What orientation and tilt angles give the best solar PV output in the UK?

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