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What is a “Biosolar Roof”?
A biosolar roof combines a green roof (vegetation + substrate + drainage over a waterproof roof) with a solar PV installation — in a way that both systems function together. The green roof helps manage water, improve thermal performance, support biodiversity; the solar roof generates clean electricity.
Biosolar roofs must be carefully engineered so the planting substrate, drainage, waterproofing, and PV mounting are all compatible — especially when it comes to waterproofing and ballast loadings.
Green-Roof Based Classifications
(Vegetation & Build-Up Types)
Because the “green roof” part of biosolar systems comes from traditional green-roof typologies, it’s useful to understand those classifications — they influence what kind of biosolar roof is realistic.
Extensive Biosolar Roofs
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Use lightweight, low-maintenance vegetation (e.g. sedum, moss, drought-tolerant groundcover).
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Shallow substrate / build-up; lower structural load than intensive roofs.
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Well suited to many flat roofs, especially where structural load capacity is limited.
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Very common basis for biosolar: green roof + PV share the same lightweight build-up.
Intensive Biosolar Roofs
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Deeper substrate, able to support a wider variety of plants, possibly including perennials, shrubs — potentially even small trees (depending on structure).
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Heavier load, needing stronger structural support — so not always feasible on retrofit or light-duty roofs.
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Can offer a “roof garden” / amenity / biodiverse planting environment + solar, but requires intensive maintenance and stronger roof design.
Biodiverse Biosolar Roofs
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Aims to maximise biodiversity and ecological value (not just a sedum “green carpet”).
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Uses a mix of wildflowers, native plants, and drought-tolerant species.
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Often includes varied substrate depths or micro-topography to support insects, pollinators, and birds.
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With solar panels, design must protect sunlight access, manage water distribution, and keep plants healthy under/around PV arrays.
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Best for: Projects targeting Biodiversity Net Gain (BNG), ecological goals, or climate-resilient landscaping.
Blue/Green Biosolar Roofs
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Combines green roof vegetation + solar PV + water-management / sustainable drainage (SuDS) elements.
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Green roof supports stormwater retention and reduces runoff.
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Overall roof becomes multifunctional (eco + energy + water benefits).
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Works well where developments have stormwater constraints, need urban heat island mitigation, or aim for broader sustainability targets.
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Best for: Sites needing strong drainage performance alongside renewable generation and wider sustainability outcomes.
Alternative & Emerging Forms Related to Biosolar
Beyond traditional green roof + PV combinations, there are hybrid and emerging roof/solar/land-use concepts. Some are well established; others more speculative or context-dependent.
Agrivoltaic (Food + Solar) Roofs
Rooftop systems combining crop cultivation with solar PV.
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More common at ground level; now emerging in urban farming schemes
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Needs deeper substrate plus reliable irrigation for plant growth
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Not widely adopted yet, but interest is rising in research-led schemes
Best for: Specialist projects aiming for food–energy co-production.
Emerging Bio-Solar Technologies
Innovative concepts currently at research or pilot stage.
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Bio-solar electrolysis: biological PV used to support hydrogen production
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Bio-solar purification: biophotovoltaics used for water purification tests
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Not part of mainstream architectural biosolar design yet; future potential
Best for: Early-stage trials and forward-looking research applications.
Why the Green-Roof Type Matters for Biosolar
When specifying a biosolar roof, the underlying green roof type is critical because it affects load capacity (intensive or deep biodiverse roofs are much heavier and not every structure can take them), the maintenance regime (biodiverse or intensive roofs usually need more upkeep like weeding, irrigation, and plant care), the ecological outcome (wildflower/biodiverse systems generally create far more habitat value than a simple sedum carpet), and the water/drainage/SuDS performance (blue-green-solar roofs need very careful drainage and waterproofing design); because of all this, in many UK biosolar projects extensive + PV is the go-to option since it balances a lighter load, lower maintenance, and still achievable biodiversity when it’s designed properly.
A Full Spectrum of Biosolar & Solar-Green Roof Options
What This Means for Architects & Specifiers
Think of “biosolar” not as one single system, but as a spectrum of roof-and-solar combinations; early design coordination is essential because structural load, waterproofing, drainage, maintenance, and ecological ambitions all need to align; for mainstream, robust, low-risk biosolar roofs, Extensive + PV (integrated or overlay mount) is usually the most practical option; if you’re aiming for biodiversity, amenity space, water-management, or ecological targets, consider biodiverse, blue-green, or intensive variants — but only where the structure, maintenance plan, and budget allow; and emerging/speculative options (like building agrivoltaics or bio-solar purification) aren’t standard yet, so treat them as research or future pilot ideas rather than guaranteed delivery.
How Solar Panels Are Mounted on Green Roofs
There are two main mounting approaches used on biosolar roofs. This choice is critical because it determines the structural loads, biodiversity value, detailing and warranties.
A. Integrated Biosolar Mounting Systems
(PV mount and green roof build-up are designed as one system) Integrated systems embed the PV supports within the green roof layers. The substrate and vegetation act as the ballast, eliminating the need for heavy concrete blocks or roof penetrations.
Key Features
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One manufacturer can supply a fully coordinated system
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PV bases sit on protection/drainage layer build-ups
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Green roof substrate provides ballast for the PV mounting
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Predictable detailing, drainage, and long-term performance
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Clearest and strongest warranty responsibility overall
When to use
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New-build projects where details are set from the start
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Jobs needing a single-source warranty and clear ownership
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Where biodiversity goals and PV output must be co-optimised
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When you want consistent, repeatable buildable detailing
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When risk needs lowering and aftercare must be simpler
Design Checks
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Check loads (PV + substrate + water + wind)
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Confirm waterproofing + root barrier layers
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Plan drainage, falls + SuDS (avoid ponding)
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Review wind uplift zones + edge detailing
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Allow safe access for PV + roof maintenance
Examples of Integrated Biosolar Systems
✅ Pros
❌Cons
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Single supplier option — green roof + PV mounting in one package
No roof penetrations — PV sits within the green roof build-up layers
Less extra ballast — substrate often replaces heavy concrete blocks
Tested, predictable system — wind uplift, drainage, loading all coordinated
Easier detailing — consistent layers, clear junctions, proven compatibility
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Less layout flexibility — tilt, spacing and geometry follow manufacturer rules
Matching components needed — roof + PV mount often must be same system brand
Not ideal for existing roofs — usually needs a full integrated build-up from scratch
Higher upfront cost — engineered components and warranties add premium value
Earlier coordination needed — plan from Stage 2/3 for build-up and structure
B. Overlay Biosolar Mounting Systems
(PV frame sits on top of the green roof — independent of the roof brand)Overlay systems use a standalone PV mounting frame designed to rest on or within a green roof without penetrating the waterproofing. They are not tied to a single green-roof manufacturer.
Key features
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Flexible and brand-agnostic mounting approach
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Can be installed on existing green roofs
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Minimal disturbance to vegetation layers
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Often suitable for retrofits or mixed roof zones
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Non-penetrative design helps protect the waterproofing layer
When to use
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Existing green roofs where upgrades are needed
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Mixed-manufacturer projects needing compatibility
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When layout flexibility is a key requirement
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Retrofit schemes or roofs with varied constraints
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Avoid penetrations, protect waterproofing
Design Checks
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Check loads (PV + ballast + water + wind)
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Protect waterproofing (pads/trays + no abrasion)
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Keep drainage clear (outlets + flow paths)
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Allow light/clearance for vegetation growth
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Plan safe access for PV + roof maintenance
Examples of Overlay Biosolar Systems
✅ Pros
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Highly flexible — can be paired with many different green roof systems.
Perfect for retrofits — can be installed onto existing green roofs without removing vegetation.
Layout freedom — more options for tilt angle, spacing and orientation (especially with systems like K2 Vento).
Minimal disruption to planting — some systems (e.g. Over Easy Solar) sit lightly above the vegetation with very low shading.
Simpler phasing — green roof and PV can be delivered separately if needed.
Cost-effective — frame-only systems are often more economical upfront.
❌Cons
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More coordination required — green roof manufacturer + PV mount manufacturer = shared responsibility.
Additional ballast may be needed — especially with tilt-frame systems like K2 Vento.
Mount sits on top of vegetation — can suppress plant growth if not designed with proper clearance and light access.
Less cohesive warranty structure — typically no single-source system warranty.
Greater design responsibility for architects — must ensure compatibility of layers, weights, mats, and vegetation.
Potential for uneven loading — requires careful structural review as ballast is concentrated under mount feet or trays.
What This Means for Architects & Specifiers
A biosolar roof is always a combination of:
Green roof system
Blue-green
(stormwater + cooling)
Biodiverse
(ecology-focused)
Extensive
(lightweight, common)
Solar Mounting Style
Integrated
(best visual finish)
Overlay
(retrofit-friendly)
Blue-green
(stormwater + cooling)
This gives you a wide design palette.
For example:
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Extensive + Integrated (most common, ideal for planning/BREEAM)
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Biodiverse + Integrated (high-value ecological roofs)
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Extensive + Overlay (excellent for retrofits)
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Blue-Green + Integrated (multifunctional stormwater + energy)
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Wildflower + Vertical PV (maximum biodiversity, minimal shading)