Solar PV Assessment and Design Under PAS2035

Solar photovoltaic (PV) systems represent a valuable renewable energy component within whole-building retrofit projects. However, integrating solar PV under the PAS2035 framework requires careful assessment and design to ensure performance, safety and regulatory compliance.

Understanding PAS2035 Requirements for Solar PV

PAS2035:2019 establishes principles for whole-building retrofit coordination. When solar PV forms part of a retrofit project, it must be assessed and designed within this holistic framework rather than as an isolated installation.

Key considerations include:

• How PV integration affects building fabric performance and thermal characteristics
• Interaction with other retrofit measures, particularly insulation and ventilation upgrades
• Electrical system capacity and distribution implications
• Structural adequacy for mounting systems and additional loads
• Alignment with the building's overall energy strategy and performance targets

Initial Assessment Phase

Begin with a comprehensive site survey that goes beyond standard PV assessments. Document:

• Roof condition and structural integrity: Existing defects must be remedied before PV installation to avoid future access complications
• Orientation and shading analysis: Include seasonal variations and consider future vegetation growth
• Electrical infrastructure: Current distribution board capacity, earthing arrangements and any planned upgrades
• Building services coordination: Identify existing equipment requiring roof access or that may conflict with PV placement
• Planning and conservation constraints: Verify local authority requirements, particularly for listed buildings or conservation areas

System Design Considerations

Technical Specification

Design specifications must account for UK climate conditions and retrofit context:

• Typical residential systems range from 3–6 kWp; larger installations require detailed grid impact assessments
• Inverter sizing should accommodate potential future battery storage, even if not installed initially
• Module selection should consider degradation rates, temperature coefficients and warranty longevity (25+ years typical)
• Cable routing and protection within retrofitted buildings requires careful planning around existing services

Integration with Building Fabric

Solar PV installation presents opportunities to address wider retrofit issues:

• Roof access allows simultaneous inspection and remediation of roof voids, ventilation paths and insulation
• Electrical upgrades required for PV can support concurrent electrification of heating systems
• Structural improvements needed for PV mounting may align with other load-bearing requirements

Quality Assurance and Compliance

Ensure all design and installation work meets relevant standards:

• BS 7909:2021 covers PV system design and installation
• BS 7671:2018+A2 governs electrical installation requirements
• Building Regulations Part P: Electrical safety and Part L (energy efficiency) requirements apply
• DNO notification: Contact the Distribution Network Operator for systems exceeding 3.68 kWp; larger installations may require formal application
• MCS certification: For government incentive schemes, systems must be installed by MCS-certified installers

Design Documentation

Maintain comprehensive records aligned with PAS2035 retrofit coordination principles:

• Single-line electrical diagrams showing integration with building systems
• Structural calculations confirming roof load capacity
• Shading analysis and performance predictions
• Detailed installation specifications and method statements
• Maintenance and operation guidance for building occupants
• Links to other retrofit measures and their interdependencies

Performance Prediction and Monitoring

Design should include realistic performance estimates:

• Use industry-standard software (PVSYST, PVsyst or equivalent) incorporating local irradiance data
• Apply conservative factors for soiling, temperature losses and inverter efficiency
• Account for actual usage patterns and grid export potential
• Plan for post-installation monitoring to verify performance against predictions

Common Integration Challenges

Address these frequently encountered issues during design:

1. Roof condition: Schedule concurrent roof repairs; poor condition adds cost and complexity
2. Electrical capacity: Existing distribution boards may require upgrading; plan this work early
3. Planning restrictions: Conservation area designations or listed building status may limit system size or placement options
4. Grid constraints: Some network areas have capacity limitations; engage DNO early for larger systems
5. Storage integration: Design with future battery storage capability even if not immediately implemented

Client Communication and Expectations

Clear documentation supports informed decision-making:

• Provide realistic estimates of annual generation based on location and building characteristics
• Explain financial implications, including installation costs, expected payback periods and government incentives
• Clarify maintenance requirements and performance monitoring arrangements
• Document how PV integration supports broader retrofit objectives and building decarbonisation

Solar PV assessment and design within PAS2035 retrofit coordination requires integration thinking that extends beyond conventional solar installation practices. By addressing solar PV as part of a coordinated whole-building strategy, retrofit coordinators can optimise both technical performance and client outcomes whilst ensuring compliance with current standards and regulations.