A Biosolar installation brings together two powerful technologies — solar PV and living green roofs — into one multifunctional system. It’s not just about putting panels on a green roof. When done properly, biosolar design supports biodiversity, improves stormwater management, enhances thermal insulation, and generates renewable energy — all while keeping the roof compliant, resilient, and safe.
At PV Plus, we specialise in the solar side of biosolar. We work alongside experienced roofing contractors who install the substrate and vegetation. We then supply and install the solar PV system, including the mounting structure, panels, and inverters — so each trade does what they do best.
How Biosolar PV Systems Work
Biosolar systems combine:
- A green or biodiverse roof with substrate and vegetation
- A solar PV system, typically mounted either within or above the green roof layer
The integration process depends on the system type. With Bauder and Optigreen systems, anchor boards sit below the substrate and the mounting frame clicks into place before vegetation is added. The substrate itself provides the ballast. Alternatively, non-ballasted systems like OverEasy Solar sit on top of an existing green roof, using vertical panels and a self-stabilising frame that requires minimal additional load.
Ballast calculations are typically provided by the solar mounting manufacturer (e.g. Bauder or Optigreen), and it’s the responsibility of the roofing contractor to ensure these specifications are followed. Getting this right is critical to safety, wind uplift resistance, and long-term system stability.
Access and shading are both major design considerations — addressed jointly during planning and system layout.
Planning Your Biosolar Installation
Structural Considerations
Not all roofs can support heavy green roof photovoltaics — especially when fully saturated with water. It’s essential to:
- Confirm structural load capacity early with a structural engineer
- Consider both static and dynamic loads, including saturated substrate and ballast weight
- Identify potential point loading from panel supports and ensure distributed weight
- Factor in wind uplift risks, especially for exposed or high-rise sites
In some cases, non-ballasted systems like OverEasy are ideal for retrofit or lightweight roofs, as they remove the need for heavy substrate-mounted anchors.
Plant Selection Criteria
There’s a major difference between quick-fit sedum blankets and a well-designed biodiverse green roof:
- Sedum blankets are often limited to 5–10 species, selected for survival rather than ecological value. They’re usually grown in coir or matting and laid over minimal substrate, offering very low habitat benefit.
- Biodiverse planting supports pollinators, birds, soil health, and climate adaptation. These roofs typically use deeper substrate (100–150mm), naturalistic planting, and avoid invasive or overly competitive species.
According to the GRO Green Roof Code and BS 8616, truly biodiverse roofs:
- Use a wide range of native or naturalised species (e.g. birdsfoot trefoil, wild thyme, yarrow, self-heal)
- Avoid plastic-based mats or rolls, relying on plug plants or seed mixes
- Support insects, invertebrates, and nesting birds — creating urban ecology corridors
From 2024, Biodiversity Net Gain (BNG) is a legal requirement under the Environment Act 2021 for most developments in England. Green roofs with high ecological value can directly contribute to meeting those requirements.
Green roofs should be multifunctional, not just decorative or compliance-led. The best biosolar systems deliver energy, biodiversity, stormwater control, and insulation — all working together in a single, resilient rooftop.
Technical Specifications and Performance
Power Output by System Type
| System Type | Panel Type | Output | Mounting | Best Use Case |
|---|---|---|---|---|
| Bauder BioSOLAR / Optigreen | Standard 400–500W panel | High | Ballasted below substrate | New builds or roofs with high load tolerance |
| OverEasy Solar | Vertical ~200W per 2.4m² frame | Lower | Non-ballasted on top | Lightweight roofs, retrofits |
While OverEasy generates less energy per m², it’s ideal for roofs where weight or retrofit limitations rule out heavier systems.
System Configuration
We install:
- String inverter systems (e.g. Solis) for simple arrays
- Optimised systems (e.g. SolarEdge) for shaded roofs or complex layouts, ensuring panel-level monitoring and higher yield. Optimisers are especially useful where vegetation may eventually grow near modules.
Maintenance Requirements
Maintaining a biosolar roof isn’t as simple as treating it like a typical solar PV system or a standalone green roof — both systems need ongoing care, and they need to work together seamlessly. That’s why we take an integrated approach:
- The roofing contractor is responsible for vegetation maintenance, drainage checks, and ensuring the substrate layer remains healthy and well-distributed. This includes weeding, checking for waterlogging or compaction, and keeping outlets clear.
- PV Plus handles all aspects of the solar side — from electrical testing and inverter servicing to system monitoring and performance checks. We’re trained to work on green roofs without damaging the planting.
Key considerations for maintaining biosolar systems:
- The system design must allow for safe, walkable access to the panels for servicing, without crushing the vegetation or disturbing the drainage.
- Remote monitoring (particularly with SolarEdge) makes it easier to spot and resolve issues early — often before they affect output or safety. This is especially useful on larger or less frequently accessed roofs.
- We recommend scheduling seasonal maintenance visits, ideally in spring and autumn. These should include:
- Electrical testing (DC string checks, inverter readings, etc.)
- Visual inspections of wiring and connections
- Trimming back any vegetation that could shade panels or grow into cabling
- Confirming ballast and fixings remain secure and free of obstructions
Keeping both the green and solar elements in good condition ensures the system performs at its best — for biodiversity, carbon savings, and long-term energy generation.
Regulatory and Certification Requirements
Compliant biosolar systems must follow:
- GRO Fire Guidance (2023): fire breaks of 500mm–1m, no flammable substrate, <20% organic matter if no irrigation
- RC62: specific guidance on fire separation, cable containment, and rooftop safety
- MCS 3002: updated solar PV installation standard (2025)
- CDM Regulations: Fire safety is a shared duty — Principal Designer, Main Contractor, and Building Owner all have responsibility
Environmental and Economic Benefits
Biosolar roofs pack a lot of value into a single rooftop — combining green infrastructure with clean energy generation. The benefits span across air quality, energy efficiency, biodiversity, and bottom-line savings.
Environmental advantages include:
- Cleaner air: Vegetation helps filter pollutants and fine dust particles from the air, contributing to healthier urban environments.
- Reduced urban heat island effect: Green roofs absorb less heat than bare rooftops, helping to cool surrounding areas — especially important in densely built-up city centres.
- Boosted biodiversity: With the right substrate and planting, biosolar systems can support pollinators, invertebrates, and even bird species, making them valuable ecological stepping stones across urban landscapes.
- Rainwater attenuation: Green roofs slow the flow of rainwater into drainage systems, reducing flood risk and supporting sustainable urban drainage strategies.
- Thermal insulation: The green roof layer adds a natural thermal barrier. In summer, it helps keep buildings cooler; in winter, it reduces heat loss — which can translate into real energy savings on HVAC systems.
- On-site renewable energy generation: The PV element offsets electricity use from the grid, helping buildings lower both their carbon footprint and operational costs.
From a financial and compliance perspective:
- Solar generation qualifies for the Smart Export Guarantee (SEG), allowing building owners to earn money for surplus electricity exported back to the grid.
- Capital allowances may be available for the PV installation under the Annual Investment Allowance or other schemes, making biosolar a more attractive investment.
- Biosolar systems can strengthen planning applications, particularly where local authorities require green infrastructure, biodiversity net gain, or Net Zero-ready buildings. They’re often a persuasive addition when meeting BREEAM or ESG targets.
- Green roof lifespan is extended: The PV panels provide partial shading, reducing UV exposure and slowing the rate of substrate drying, which can help the green roof layer remain healthier for longer with less frequent irrigation.
In short, biosolar isn’t just about saving energy — it’s about building smarter, more resilient roofs that deliver value across sustainability, compliance, and lifecycle performance.
Choosing the Right Biosolar System
Key selection factors include:
- Structural loading — OverEasy suits lightweight or existing roofs
- Energy goals — Bauder and Optigreen allow full-sized panels for maximum output
- Installation timeline — some systems are quicker to deploy than others
Regardless of the system, team coordination is critical. Roofer, solar installer, and supplier must collaborate closely from design to delivery.
Future-Proofing Your Investment
Biosolar systems are future-ready when designed with flexibility:
- OverEasy is modular, so more frames can be added later
- Smart systems allow for future battery or EV integration
- Climate resilience: living roofs adapt to rain and heat extremes, helping buildings cope with climate change
Project Spotlight: Mottingham Lane, London
We recently completed a biosolar install at Mottingham Lane, London. This involved 109x Solarwatt 430W panels using the Bauder BioSOLAR system. Working alongside the green roof contractor, we delivered a compliant, high-performing PV system that sits perfectly within the planted roof.
Frequently Asked Questions (FAQ)
With ballasted systems like Bauder and Optigreen, the frame is integrated below the planting layer and doesn’t disturb the roots. OverEasy frames sit above the substrate without penetrating the roof build-up.
Biodiverse mixes with wildflowers, sedum, and native grasses perform best. They attract pollinators, increase stormwater absorption, and thrive long-term.
Slightly less. The trade-off is worthwhile for biodiversity, insulation, and planning benefits. System choice matters — standard panels generate more than vertical ones.
Loads must account for wet substrate, PV frames, ballast, and access zones. Structural engineers should assess early in the design stage.
Maintenance must be shared: PV Plus manages the electrical checks, while the roofing contractor handles vegetation care and drainage. Good access is designed in from the start.
Interested in a biosolar solution for your next project? We’re happy to advise on system selection, design integration, and full PV delivery to ensure a safe, compliant, and high-performance install.
