Solar PV and Green Roofs: Innovations, challenges and industry trends

Flat roofs present a unique opportunity for integrating sustainable technologies, such as solar panels and green roof solutions. Over the last few years, there has been a huge increase in interest in how we can better utilise these spaces, both in new constructions and retrofitting projects, and deliver benefits such as renewable energy production and improved biodiversity.

So, what are the benefits of installing solar panels on flat roofs, as well as green roof systems, and how can these two technologies be combined for maximum environmental and financial benefits?

Luke Rootham, Solar PV and Green Roof Product Manager, offers a deeper dive into the technical innovations, benefits, and challenges of solar PV, green roofs, and biosolar, and shares his visionary outlook on the future of renewable energy and green infrastructure in the UK.

What are the benefits of adding solar panels to flat roofs?

The key benefit of adding solar panels to flat roofs is the generation of clean energy, which lowers energy bills for the occupants of the property; this is the main driver behind the adoption of solar panels. Unlike other roofing features, solar panels do not provide direct benefits to the roofing membrane itself; their value lies in energy production and cost savings.

In new builds, the inclusion of solar panels is often driven by legislative and planning requirements, making it a mandatory feature. However, in the retrofit market, more clients are becoming aware of the financial advantages, particularly the reduced payback period.

Previously, payback periods were typically between 8 to 12 years. Now, due to the rise in energy costs, this has shortened to around 4 to 6 years, making solar panels an increasingly attractive option.

While factors like system maintenance and additional components like batteries can influence the payback period, the overall trend shows that more people are recognising solar panels as a viable and effective solution for reducing energy costs.

What are the benefits of installing green roof systems?

Green roof systems offer three core benefits. First, they extend the life of the roofing membrane. By covering the membrane, green roofs protect it from harmful UV rays, which are one of the main causes of membrane degradation. This protection helps to prolong the roof's lifespan.

Second, green roofs improve drainage. They incorporate drainage boards and the growing medium itself—essentially the soil—enhances the roof's ability to manage water runoff, reducing the risk of flooding and water damage.

Finally, green roofs provide biodiversity benefits. They create habitats for wildlife, contributing to improved air quality and supporting local flora and fauna. This makes green roofs beneficial for the building as well as the environment and surrounding ecosystem.

How do you integrate green roof systems with solar PV installations? What are the benefits of this combination?

Integrating green roof systems with solar PV installations involves using the green roof as ballast for the panels. Instead of traditional ballast blocks, a denser, thinner substrate is used to secure the solar panels. Taller frames elevate the panels, ensuring plants below receive enough light. A shade-tolerant seeding mix supports plant growth under the panels, creating a biosolar system.

On hot days, the green roof helps mitigate the urban heat island effect by lowering the ambient temperature around the panels. This cooler environment can improve the efficiency and performance of the solar PV system, although the exact increase in performance can vary.

This integrated approach supports sustainability by combining energy generation with biodiversity benefits.

How has the market for solar PV evolved in recent years, and what trends are you seeing?

One of the most notable changes is the strong backing we are seeing from the government, particularly from figures like Ed Miliband – the current Secretary of State for Energy Security and Net Zero – who has a history of promoting solar energy through initiatives like the feed-in tariff. This political backing is very positive for the industry, with upcoming programmes like the Warm Homes Plan expected to further drive demand.

Another major trend is the increasing prevalence of battery storage. In the past, the focus was primarily on selling excess energy back to the grid as a way to generate income. However, the current shift is towards more efficient energy usage, with a growing emphasis on storing and using energy locally. This shift has led to a rise in battery storage installations, as seen in the latest MCS (Microgeneration Certification Scheme) figures, which show a dramatic increase in the adoption of storage solutions.

While the MCS data primarily covers installations of 50 kilowatts or below, focusing on the domestic market, it still provides valuable insights into the overall trends. The growing adoption of battery storage and supportive government policies indicate a robust upward trajectory for the solar PV market, with both new builds and retrofits benefiting from these advancements.

What role do you see solar PV playing in the broader context of renewable energy adoption in the UK?

One of the key areas where it can make a huge impact is in the retrofit market. There is a vast amount of existing building stock that needs to be decarbonised, and solar PV offers a practical solution.

With the Labour government potentially easing restrictions on ground-mounted systems and supporting solar farms, the expansion of solar PV is likely to accelerate. Upcoming regulations requiring commercial buildings to achieve an EPC rating of C further underscore the importance of solar PV in helping businesses meet these targets.

Wind energy will also play a major role in the UK's renewable energy landscape, but the recent project at the Port of Liverpool, set to be the largest roof-mounted solar project ever undertaken in the UK, highlights the significant potential of utilising available rooftop space for solar PV. This project demonstrates the scale and impact that solar PV can have.

With its ability to be integrated into both new builds and retrofits, solar PV is essential for the country's energy future.

What advice would you give to property owners considering retrofitting their buildings with sustainable technologies like green roofs and solar PV?

The first and most crucial step is to thoroughly assess the existing structure. It's essential to evaluate whether the building can support the added weight and installation requirements of these systems.

We recommend starting with a detailed survey of the roof structure conducted by a competent professional. This ensures that the chosen solutions are suitable for the specific conditions of the building. Our team offers a no-cost survey for retrofitting projects to help identify the most appropriate approach.

Once the structural assessment is complete, we can recommend the best solutions based on the project’s needs. Whether it’s a lightweight thin-film system, a biodiverse biosolar setup, or a fixed versus balanced installation, we have the flexibility to adapt to different requirements. We also accommodate various factors such as desired kilowatt peak, panel specifications, or preferences for European-made products and longer guarantees.

Ultimately, the key is to provide a tailored solution that addresses the unique needs of each property, following a process similar to our approach with roofing projects. This ensures that the retrofit is both effective and sustainable.

Where do you see the future of solar PV and green roof systems heading in the next five to ten years?

Over the next five to ten years, solar PV and green roof systems will undergo significant evolution, driven by technological advancements, safety improvements, and community-focused design.

Green roofs will see more ambitious and multifunctional designs. I would love to see ‘healing’ green roofs, which feature plants with health benefits, such as those that promote natural healing or improve air quality. For instance, hospitals might have green roofs designed to support patient well-being through therapeutic plants.

Future green roofs will be customised to better serve local communities, moving beyond generic designs to spaces designed with the specific needs and wants of a community in mind. The future of green roofs will emphasise sustainability that goes beyond environmental metrics. These spaces will improve the quality of life for users, offering practical benefits and enriching daily lives.

If you’re interested in learning more about Axter’s green roof and solar PV products and services, please contact us.