The countdown is on for Solar Solutions International Düsseldorf , happening November 27–28, 2024 , and we can’t wait to see you there! Over Easy Solar, alongside our partner Sempergreen , is excited to present the VPV-Unit . Designed for green and flat roofs, the VPV-Unit offers a unique combination of lightweight construction ( 11 kg/sqm ) and ballast-free installation. Its vertical design is perfect for green roof integration, providing clean energy without overshadowing plant growth or restricting access to rooftop areas. Sempergreen , a global leader in sustainable green roof solutions, shares our commitment to building greener, smarter cities. Together, we’re driving innovation in biosolar technology, combining renewable energy with green infrastructure to address climate challenges and promote urban biodiversity. Come see the VPV-Unit in action at Booth C17 – Hall 14 and learn how our innovative systems are transforming urban energy and sustainability. Want to join us? Find your free entry pass here , and find additional event information here .

In 2022, Løren School in Oslo became the site of Over Easy Solar’s first green roof pilot project, integrating the Vertical Photovoltaic (VPV) Unit from Over Easy Solar with a sedum roof. Following the success of this initial phase, the second phase was installed during the summer of 2023, marking the first full-scale installation of Over Easy Solar’s technology. Today, the project has a total capacity of 46 kWp, covering an area of about 500 m² of the school’s roof. Supported by Oslo's "Smart Oslo" Innovation Program Both phases of the Løren School project were made possible with support from Oslo Municipality's “Smart Oslo” initiative. This innovation program is designed to give startups in Oslo the opportunity to pilot their technologies with municipal utilities. For the municipality, it represented a chance to demonstrate the combined potential of green roofs and solar energy. The Løren School project not only showcases the potential of vertical solar panels but also highlights how Oslo Municipality through the Smart Oslo initiative promotes innovation, providing startups with real-world use cases to test and refine their products. This support mechanism is now a vital part of Oslo’s thriving startup ecosystem. Pictures of the first pilot on Løren School from 2022 and the full installation from 2023 (swipe for more pictures). A Model for Future Sustainable Buildings The solar panels were retrofitted on an existing green roof installed by Bergknapp in 2018. The results from the Løren School pilot have been very positive. Andreas A. Nilsen from Oslobygg KF , shares his insights: “We saw very good results from the first pilot in 2022 with regards to energy yield, and the green roof quality was even better under the panels than on the openly exposed sedum roof.” - Andreas A. Nilsen, Oslobygg KF The project has since become a model for similar installations in many different countries. Over Easy Solar is now rolling out its technology to municipalities and building owners across Europe, in close collaboration with the renown green roof innovator and distributor Sempergreen . The Løren School project serves as an example of how integrating solar technology with urban green spaces can create energy-efficient and environmentally resilient buildings.

Together with the Swiss company PlanPRO , a VPV installation was mounted in Beinwil am See, Switzerland, in January 2024. This project demonstrates how we are addressing the challenges of weight and complexity often associated with solar installations on green and flat rooftops. Streamlined Biosolar Installations with Reduced Ballast Requirements The essence of Over Easy Solar's approach lies in its ability to minimize the reliance on heavy ballasting , a common obstacle in traditional solar projects. By deploying vertical solar panels, the company has ingeniously negated wind lift and uniformly distributed transversal and horizontal forces throughout the installation. This method not only simplifies the installation process but also broadens the scope for solar energy applications on structures previously considered unsuitable due to weight constraints. "Our vertical solar panels effectively negate wind lift and, by integrating the installation as a cohesive structure, it evenly distributes transversal and horizontal forces across the installation," said Trygve Mongstad, CEO and Founder of Over Easy Solar. This technical insight emphasizes the practical and efficient nature of Over Easy Solar's system, reflecting the company's commitment to advancing solar technology. A Testimonial to Simplicity: Vertical Solar Panels for Green Roofs The project in Beinwil am See stands as a testament to the system's user-friendly design and effectiveness. PlanPro, a local company, executed the installation of a 10 kWp system atop an existing sedum rooftop with remarkable efficiency. The process showcased not only the ease of retrofitting the system on a green roof but also the satisfaction of the stakeholders involved. “We were impressed at how easy and fast this product can be retrofitted on an existing green rooftop,” remarked Sven Meuschke, Project Manager at PlanPRO in Switzerland. This statement encapsulates the project's success and Over Easy Solar's ability to deliver solutions that meet the practical demands of installation professionals and end-users alike.

Most flat roof solar installations are ballasted . It means, the solar installer will put ballast stones below the solar panels to keep the solar installation in place, and not be lifted off the roof in case of extreme winds.  In most cases, Over Easy Solar’s VPV unit eliminates the need for ballast.    What exactly is ballast?   Ballast for a solar installation is “something heavy” that gives additional weight to the installation, to counteract for lift and push forces generated by wind. In most cases, concrete blocks or stones are used, mainly because such stones are easily available, easy to stack on a pallet, and relatively easy to handle for the installers on the rooftop.    How much ballast is necessary for a flat roof solar installation?  Depending on the type of installation, the building geometry, and the wind zone, the necessary amount of ballast varies a lot. The need for ballast is especially high on small installations (like a private house or garage), on tall buildings and in areas where you have strong winds. It also depends highly on which mounting system is used – south-facing solar panels elevated at a distance from the rooftop, for example, gives high wind loads and high need for ballast. In the best cases, conventional installations may need only 5-10 kg of ballast on the outer rows of panels in an installation. The worst cases may need over 100 kg of ballast for every panel in the installation. For a private house, we could be talking about several tons of ballast added to one small rooftop. For a higher and larger commercial rooftop in a windy area, we are talking about tens of tons.    Why should you care about ballast for a solar installation?  For the owner of the solar installation, ballast seems not to be a very big problem. It only lays there, right? But there are some important things you should keep in mind:    What is the load bearing capacity of the roof? Not only is the structural strength important, but also the strength of the roofing membrane and the underlying insulation. Both can take damage from a heavy installation, especially if the weight is concentrated on a small surface area.    What is the maintenance need of your roof? If you think it is likely that there will be some maintenance work on the roof in the next 30 years, which demands that you remove the solar panels, ballast may be a challenge as it complicates the work on the roof (imagine finding the ballast plan for a solar installation in 15 years from now!).    For the installer, ballast is not desired because it introduces more work and logistics with the installation. A wind-exposed solar installation will therefore be more expensive, and installers may be reluctant to take on such projects. Sadly, some installers will also forget the ballast or even manipulate the calculations or the mounting system itself, sometimes resulting in accidents during strong wind events.   How much ballast is needed for Over Easy Solar’s VPV unit?  In 2023, we published the results of our wind certification . After thorough testing both in digital models and in a physical wind tunnel, we have now proven that our technology is ballast free  for most flat roof buildings. Meaning, you can save money on ballast in your solar system and save your roof the strain of a heavy installation.   As for other installations, a calculation for each project is needed. Our PV engineers will help you plan your installation step by step, customizing it to the needs of your roof.

Why you should install your solar panels facing east-west instead of south, and the different types of East-West orientation. As solar energy continues to grow in importance, it is becoming increasingly valuable to orient your solar panels not to the south, but to the east and west. Read on to learn why, and to discover that there are different types of east-west installations—this is where the real difference lies! In recent years, energy prices across Europe have risen significantly, leaving many households and businesses struggling with higher bills. Throughout the EU, energy prices have surged by 30-40% compared to pre-crisis levels. Additionally, the summer months have seen an increase in negative electricity prices during midday due to an oversupply of solar energy flooding the grid. These trends pose a challenge for traditional south-facing solar installations, which are designed to maximize energy capture during midday—precisely when energy prices can drop the most. To truly harness the benefits of solar power, it’s time to consider an east-west-facing solar setup. Here are three reasons why this orientation can optimize your solar energy production and value. Better Self-Consumption and Reduced Storage Needs With East-West Solar While south-facing solar panels are great for capturing sunlight during midday, this is also when energy prices tend to plummet due to oversupply. An east-west-facing installation is designed to capture sunlight during the morning and evening peaks when energy demand—and prices—are highest. This configuration ensures your solar panels generate electricity when it is most valuable, potentially offsetting the highest energy costs and maximizing your savings. Moreover, vertical panels used in east-west orientations offer a distinct advantage by reducing the need for battery storage. A study by HTWK Leipzig, titled "Integration of Vertical Solar Power Plants into a Future German Energy System,"  highlights the benefits of bifacial solar modules in lowering battery storage requirements. Sophia Reker, who led the study, explains: "Bifacial solar modules can use solar energy from both sides. Installed in an east-west orientation, most electricity is generated in the morning and evening. This reduces the need for electricity storage and minimizes the land required for electricity generation." By capturing energy during these critical periods, homeowners and businesses can maintain a more consistent energy supply without the additional costs and complexities of large-scale battery storage systems. Three Different Types of East-West Solar Installations There are three main ways to orient your solar panels east-west: A 10-degree tilt  using a standard flat-roof solar mounting solution in an east-west configuration Mounting on east- and west-facing surfaces  of a tilted roof Using vertical bifacial solar panels  in an east-west configuration Which option provides the most valuable production profile? Let’s look at the numbers. Below, you can see the production profiles for these three configurations, compared to a south-facing panel inclined at 15 degrees. Clearly, the 10-degree east-west configuration makes little difference. The 45-degree tilt provides a flatter profile but still peaks in midday, when energy is least valuable. However, the vertical configuration makes the most significant difference.     A Future-Proof Solution for Solar Energy As the energy landscape evolves, it’s essential to invest in solar systems that align with current and future trends. With negative energy prices becoming more common during summer midday peaks , the economics of solar orientation are changing. South-facing installations risk reduced capture rates during times of overproduction, while east-west-facing systems provide a more resilient solution. It’s important to understand the varying energy production profiles based on different panel inclinations. Vertical solar panels, by generating most of their power during the most valuable hours, improve self-consumption and contribute to a balanced, sustainable energy ecosystem. Vertical Solar Fits Into the Picture Vertical solar panels are particularly well-suited to east-west configurations. They capture sunlight from both sides, optimizing energy generation during high-demand periods — especially in the morning and evening when electricity prices are higher. This setup reduces reliance on battery storage and prevents overproduction during midday when prices are lower. The financial benefits of vertical panels are also significant. With high bifaciality and optimized energy capture, vertical panels are projected to deliver over 50% higher returns per installed kWp over the next decade than traditional solar systems. As energy markets continue to evolve, investing in vertical bifacial panels for east-west installations is a smart move for those looking to maximize both energy production and long-term savings. For more information, visit our website and discover how our solar solutions can improve your energy efficiency. Sources: House of Commons Library Greenmatch Energy Prices Europe EU Energy Price Increase PV Magazine Over Easy Solar

We are happy to announce that Over Easy Solar is partnering with Sempergreen, Europe’s leading provider of green roofing systems and materials. This collaboration marks an important step in our mission to enable solar energy and biodiversity on roofs by combining innovative solar technologies with Sempergreen's world-renowned green roof systems. Sempergreen will be a distributor of Over Easy Solar’s VPV Unit  for green solar roofs, making it available for the entire European continent. Sempergreen: Pioneers in Green Roofing and Sustainable Solutions With more than 25 years of experience, Sempergreen is a leader in converting urban landscapes and rooftops into green spaces. With a strong global presence, supported by sedum and plant nurseries on five continents, they specialize in innovative solutions such as vertical gardens and green roofs. Sempergreen’s dedication to sustainability drives their ongoing efforts to improve urban biodiversity, reduce heat islands, and manage rainwater, ensuring that cities become more resilient and environmentally friendly. As the Founder and Chairman of the Board, Corné van Garderen, explains: “At Sempergreen, our mission has always been to bring nature back into urban environments, creating healthier, more sustainable cities. Partnering with Over Easy Solar allows us to take this mission to the next level by seamlessly integrating renewable energy with our green roof systems.”  - Corne van Garderen, Sempergreen Bringing Green Roof Solutions with Solar to Market By partnering with Sempergreen, Over Easy Solar is excited to push towards solar integration on green roofs, also called “biosolar” solutions. Our solution is specifically designed to harmonize with green roofs. The vertical PV units avoid conflicts between plants and solar panels, and users enjoy seamless access to their green roofs without compromising energy production. Additionally, the VPV system eliminates the need for intrusive fasteners or heavy ballast, and with only 11kg per sqm of added weight to the green roof, it’s the most lightweight solution on the market. The freestanding system also reduces the risk of leaks and wear, and the plug-and-play installation technique simplifies the planning, installation, and commissioning processes by up to 90%. As the Founder and CEO of Over Easy Solar explains, “This partnership will contribute to a more sustainable future by maximizing the potential of urban roofs. Together, Over Easy Solar and Sempergreen provide the materials for future-proof and double sustainability roofs that fits both existing and new buildings.” – Trygve Mongstad, Over Easy Solar If you are interested to know more about our solutions, send us a message through our contact form , or get in touch with Sempergreen  for a complete offer. For more information, reach out to: Sempergreen Over Easy Solar

When it comes to building energy efficiency, the roof plays a crucial role. A popular strategy to enhance this efficiency is the use of cool roofs —roofs designed to reflect more sunlight and absorb less heat than standard roofs. But what happens when you add solar panels to the mix? And how can vertical solar panels optimize your building's energy performance? Let’s dive into these questions.  What are cool roofs and why are they important?   Cool roofs reduce the need for building cooling and reduce the urban heat island effect . They are designed with materials that reflect more of the sun's rays and release the absorbed heat more quickly, keeping buildings cooler and reducing the need for air conditioning. Cool roofs are especially important for buildings with a high cooling need, like data centers and cold storage warehouses. A cool roof can be made of highly reflective or white roofing membranes, different types of paint, a sheet covering, or highly reflective tiles or shingles. These materials work by increasing the roof's albedo—a measure of how much of the light that hits a surface is reflected without being absorbed. The higher the albedo, the cooler the roof remains, which translates to lower cooling costs and a reduced environmental footprint. With the different options available, a building renovation project can easily include a cool roof retrofit. The impact of traditional solar panels on cool roofs   While cool roofs are excellent for reducing heat absorption, their benefits can be compromised when traditional solar panels are installed on top. Conventional solar panels are typically mounted at a nearly horizontal angle and cover large portions of the roof. This can turn your reflective cool roof into a black, heat-absorbing surface, essentially nullifying the cooling effect. Solar panel temperatures can easily reach up to 70 degrees C during hot summer days!  When a cool roof is covered with traditional solar panels, the roof loses its reflective properties, as the dark-colored panels absorb sunlight and increase the surface temperature. This not only undermines the purpose of having a cool roof but also potentially increases the heat load on your building, negating some of the energy savings provided by the solar panels.  Vertical solar panels are better for cool roofs   This is where vertical solar panels come into play. Unlike traditional horizontal panels, vertical panels don’t cover the roof, so the roof itself is not heated in the same way as with conventional solar panels. The high albedo of the cool roof is also a huge advantage for the energy production of the vertical solar! Let’s explain these benefits more in depth: 1. Maintain the cool roof function with vertical solar panels : By keeping the main surface of the roof uncovered, vertical panels allow the cool roof to maintain its reflective properties, ensuring that the roof continues to reduce heat absorption and keeps the building cooler. 2. Lower solar panel temperature : Vertical solar panels have a more efficient heat exchange with the air since they radiate heat from both sides, which contributes to a lower solar panel temperature. This has been confirmed by researchers from TNO in The Netherlands, and Over Easy Solar’s own measurements shows that temperature of vertical solar panels normally stay at only 10-15 degrees C higher than ambient temperatures during sunny summer days, about 10 degrees lower than for conventional solar mounting. This maintains the cooling effect of the roof and keeps the efficiency of the solar panels high. 3. Higher energy output : Vertical panels capture reflected light from the roof. This is why the increased reflection from the cool roof can significantly boost the energy output of the panels. In fact, simulations and measurements conducted by Over Easy Solar suggest that a high-albedo white roof can enhance the energy yield of vertical solar panels by up to 40% compared to a black bitumen roof! Maximizing energy efficiency of buildings with cool roofs and vertical solar panels   By combining cool roofs with vertical solar panels, building owners can maximize their energy efficiency, maintain lower building temperatures, and even boost the performance of their solar installations. This innovative approach not only helps in reducing energy costs but also contributes to a more sustainable and environmentally friendly building design. If you're considering solar panels for your building, vertical installations on cool roofs could be the perfect solution to optimize both your energy production and your building's thermal performance.

In May 2024, our partner Solenergi FUSen  mounted the biggest Over Easy Solar installation so far – a 248.4 kWp solar installation on the rooftop of the Norwegian National Football Stadium – Ullevaal Stadion . This installation is now the largest rooftop vertical bifacial solar installation in the world. It was installed on an existing bitumen rooftop – the mechanical installation was done in a matter of few days.  Solar Installation at Ullevaal Stadium Sets World Record This unique installation entails 1242 vertical solar units of 200 Wp, positioned to harness the full potential of the sun’s rays. This installation is estimated to generate an impressive 219 000 kWh per year clean energy.   Vertical Solar Panel Benefits Showcased at Ullevaal Stadium Analysis from Over Easy Solar’s pilot projects demonstrates that vertical solar panels can achieve more than 20-30% higher specific yield than traditional flat roof solutions. The solar panels are in this installation oriented in a general south-north orientation (20 degrees east of south), providing a energy distribution with higher energy yield in winter months. Vertical solar panels also yield increased performance during winter due to less snow coverage and increased production from the high albedo of snow.   Other key benefits that are appreciated by the customer is the low weight of the installation and the easy access to the rooftop for inspection and local repairs of the roofing membrane.   We’re proud to present this as the largest vertical rooftop project in the world to date, but we are also certain that the record will not last long.

A Significant Step Towards Green Energy The green roof solar installation in Kassel, Germany, came to life thanks to Over Easy’s easy mounting solution. Our system has a fantastic capacity of 19.8 kWp and is set to produce about 18,500 kWh of clean energy every year. Community involvement was crucial to this project’s success. With professional support from SoLocal Energy, local firefighters generously volunteered their time and expertise, playing a significant role in developing this solar energy system. Their combined efforts show how valuable teamwork and professional knowledge are in making projects like this happen. At Over Easy Solar, we aim to empower communities, and this partnership is proof of that. It’s more than just a business venture; it’s based on shared principles of solidarity, inclusion, and sustainability. Drone Shots Captured by SoLocal Energy (Kassel, DE) A Global Imperative: Prioritizing Renewable Energy Germany has made impressive progress in switching to renewable energy sources. In 2023, over 50% of the country’s electricity came from renewables. However, there’s still a reliance on fossil fuels. It’s crucial for Germany and all nations to prioritize renewable energy as the main source of electricity. Embracing clean energy is vital to reduce the risks of global warming and the related health hazards. Non-renewable sources like coal and natural gas have severe environmental and public health impacts. A Harvard study estimated coal’s annual life cycle cost and health effects at a staggering $74.6 billion, highlighting the urgent need for a global shift to renewables. Addressing climate change and environmental concerns requires global collaboration. Governments, businesses, and civil society must work together to overcome barriers to adopting renewable energy. By investing in infrastructure, implementing supportive policies, and fostering innovation, we can reduce carbon footprints, create economic opportunities, and improve public health outcomes. The switch to renewable energy is essential for our practical needs: it protects the environment, ensures energy security, and promotes long-term economic stability. Photo of the installation in Stadt Kassel, Germany

We at Over Easy Solar are proud to announce the successful installation of our vertical bifacial solar panels in Austria, marking a significant milestone for our company. This project took place on the green roof of "Amann die Dachmarke" in Vorarlberg, a prominent Austrian roofing company renowned for its expertise in a variety of roofing products and innovative green roofing solutions. Amann die Dachmarke, led by CEO Marius Amann, has been an exceptional partner in this project. With their extensive knowledge and commitment to green roofing, they provided the perfect platform for showcasing our technology. This installation, with a capacity of nearly 7 kWp, is projected to generate around 7,000 kWh of clean energy annually. As Marius Amann expressed, “We are happy to showcase this innovative product on our green roof and educate people on the symbiosis of green roofs and solar.” This collaboration not only highlights the innovation in green energy solutions but also serves as an educational tool, demonstrating the mutual benefits of integrating solar panels with green roofs. Our vertical bifacial solar panels provide partial shading to the green roof, which can lower temperatures by up to 10 degrees compared to non-shaded areas. In return, the green roof offers a cooling effect, helping the solar panels maintain their optimal operating temperatures even on hot days. This symbiotic relationship enhances the efficiency and longevity of both systems. The feedback from the installer company has been incredibly positive. They noted, “The installation was self-explanatory, we didn't even need the installation manual to install it. It was also very quick and comfortable to work with.” Such comments reinforce our commitment to delivering user-friendly solar solutions that are not only effective but also easy to mount. According to the Austrian Green Market Report, every tenth roof in Austria is built as a green roof, highlighting the immense potential for combining green roofs with solar panels to produce sustainable energy. As we expand our presence in Austria, we look forward to contributing significantly to the country's green energy landscape. Our installation in Vorarlberg represents a significant step towards a greener future. We are excited to continue demonstrating how innovative technology and ecological roofing solutions can work together to create a sustainable energy ecosystem.

This article will explain why vertical bifacial solar panels produce higher value energy compared to conventional solar panels, helping understand why investing in this technology is beneficial and can be more future-proof than investing in conventional flat roof solar solutions. Understanding Capture Rates and Capture Prices for Solar Capture rates refer to the proportion of the average power price that a power production technology achieve compared to average prices in the market. Capture prices are the actual prices at which this electricity is sold in the markets. For solar energy producers, these metrics are critical as they determine the financial return on their investments. The Importance of Capture Rates for Solar Energy Dynamic pricing of energy is becoming increasingly important for solar installation owners. Many electricity customers in Scandinavia, Germany, and other countries are already experiencing dynamic pricing. This trend is expected to grow, enabling customers to actively participate in the power market. Solar power often saturates the market during midday, causing prices to drop significantly. In contrast, power prices usually peak during the morning and evening when demand is highest, and solar output is lower. In 2024, we now start seeing the real effects of this trend with a lot of zero or negative midday prices. The price typically peaks from 7-9 in the morning and from 18-21 in the evening, while staying low or zero in the hours 11-15, as can be seen in the data illustration below. The Higher Capture Rates of Vertical Bifacial Solar Panels A 2023 study by the German management consulting firm Enervis showed a significant difference in future capture rates between conventional and vertical bifacial solar panels (see full report). By 2030, capture rates for conventional solar panels are expected to average at 53%, decreasing to 31% by 2040. Vertical bifacial solar panels, however, are projected to maintain a capture rate of 73% in 2030 and 52% in 2040. This represents roughly 40% higher capture rates in 2030 and 60% higher in 2040 compared to conventional panels. Recent Data for Capture Rates for Solar Energy Recent data highlights the growing importance of vertical bifacial solar panels. In May 2024, capture rates for conventional solar panels were as low as 50% in the German power market, according to independent LinkedIn posts by Thomas Rosentopf from Enervis and the energy expert Julien Jomeaux. Other vertical solar specialists are talking about an improvement in VPV increased capture rates from 5% in previous years to 15% for 2023 in the German power market, demonstrating the enhanced efficiency of vertical bifacial panels. "May 2024 was the first month ever we saw solar capture rates below 50% in Germany" Thomas Rosentopf, Enervis Over Easy Solar’s own calculations, based on data from solar installations in Oslo and the NO1 price zone in Norway for May 2024, show a capture rate of 76% for conventional solar and 89% for VPV (vertical photovoltaics). This represents a 17% improvement, and these data align well with the projections proposed by Enervis in the earlier mentioned report. The graphics below illustrate the power price variations in the Norwegian market in May 2024, alongside real measurements from a conventional flat roof solar installation and a vertical PV solar installation close to Oslo. You can clearly understand why VPV delivers higher value, producing in the hours of higher power price in the morning and in the afternoon. Maximizing Solar Energy Value with Vertical Photovoltaics The higher capture rates of vertical bifacial solar panels mean that energy is delivered at times of higher power prices, generating more value per produced kWh. Additionally, the value of self-consumption versus exports further enhances the financial returns. Over the next decade, VPV units are expected to offer over 50% higher returns per installed kWp compared to conventional solar panels, making investment in VPV a much better business case in the long run. Investment in VPV Gives Better Financial Returns in the Long Run Investing in Over Easy Solar’s VPV Units with vertical bifacial solar panels is a sound decision that promises higher value energy production and substantial financial returns in the long run. As dynamic pricing becomes more prevalent, vertical bifacial panels will be crucial for maximizing solar energy investments, and it will provide value to the power grids and our cities by producing energy outside of peak solar hours. For more information on our solar solutions, contact Over Easy Solar and learn how you can benefit from our technology.

Modern urban buildings must take maximum advantage of all spaces, including rooftops. In many cities, there are regulations that require green roofs, and often architects and planners believe that it rules out solar energy. But the good news is that you can make green roof and solar a great combination! Types of green roof There are different types of green roofs, and many ways to build them up. Generally, a layered structure consisting of a root barrier, a drainage system, a substrate (soil) and plants build up the green roof. Most green roofs are so-called extensive green roofs, planted with sedum plants. Extensive means that they are optimized for large area coverage, low weight and low maintenance needs. Sedum plants are succulent plants that can hold a lot of moisture and therefore resist long periods of little rain and the strong sun and heat that rooftops are exposed to. The sedum plants typically grow 5-15 cm over the rooftop, depending on the season, the substrate thickness, climate and maintenance. Extensive green roofs are designed to be light-weight, and typically weigh 50-150 kg/m2 when soaked in rainwater. Extensive green roofs are good for combination with solar panels. The other main type of green roof is intensive green roofs, which offers thicker soil substrate and more biodiversity. The weight is high (150-800 kg/m2), and therefore put high demands on the building structure. Plants include bushes, weeds, grasses and sometimes even trees, and the typical plant height is in the range of 30-60 cm. Intensive green roofs are difficult to combine with solar panels. Read also: Why are green roofs so important? Checklist for combination roofs To combine green roofs with solar energy, you need to plan well. There are many examples of installations that don’t work very well. We here want to propose a set of design principles and guidelines for planning a good combination. Know your type of green roof To plan a working solar installation on a green roof it is important to know the type of green roof to ensure that you select a suitable solar solution. The substrate thickness, plant height and maintenance needs are crucial to know. Plan for the right roof load While green roofs in themselves add substantial weight to the roof, adding a solar installation may end up with doubling the roof load. For existing buildings, this is important to know in order not to compromise the safety of the building, and new buildings may need to be reinforced with respect to original plans, adding cost and consuming more concrete and other materials in the construction process. Ensure low conflict between plants and solar panels It is important to plan for a solution where the green roof and the solar panels will not be “fighting against each other”. Solar panels may alter sunlight, evaporation and water flow on the roof, and might create unexpected negative consequences. It is important not to completely cover the green roof with solar panels. A conventional east-west solar installation may provide a lot of kWp in theory, but the fact is that plants will end up covering the solar panels to a smaller or larger degree. In general, a green roof solar installation will have less power (kWp) than a completely covering flat roof solar installation. We recommend planning with 50-70% of a the power of a conventional solar installation for flat roofs, otherwise it will be a suboptimal solution both for the green roof and the solar panels. Optimize for easy maintenance Although extensive green roofs require very little maintenance, they need more than traditional dead materials. You must make sure that the green roof is accessible through the lifetime of the building. If planned wrong, as we will see below, the combination of green roof and solar may also generate a much higher need for maintenance than what each solution separately would have. Types of solar installations for green roofs A solar installation consists of solar panels, a mounting system, cabling and an inverter. The type of solar panels and mounting system is extremely important to make a good combination roof. There are three main ways used to build a solar installation on a green roof. Conventional solar panels and conventional flat roof mounting structures For flat roofs without green, regular solar panels that measure about 1 by 2 m in size are mounted into a mounting system in an east-west configuration. The solar panels will cover nearly the entire roof, except for some walkpaths in between the panels for most mounting systems. While this is an efficient and well-established way to build a solar installation, it is not a good idea for combination with a green roof. Why? Because the large solar panels will cover the green roof almost completely. Below the panels there will be a humid and dark environment, which favors the growth of plants that can grow fast to reach the light above the solar panels. These plants will shade for the solar installation and generates a massive maintenance need to remove them continuously through the growth season. The large solar panels will also make the maintenance very difficult, as maintenance personnel will need to lean over the large solar panels without putting much weight on them to remove the weeds in between. This combination is therefore not recommended. Conventional solar panels with a specialized mounting structure There are several providers of specialized structures for usage of conventional solar panels on green roofs, for example the well-established solutions from Bauder and Zinco. These solutions provide an elevated mounting of the solar panels at an angle of 15-30 degrees, with ample space between, for plants to grow and maintenance personnel to move. The elevated and sparse installation of solar panels make them highly exposed to winds and winds can generate substantial lift forces on the structure. Therefore, they need high ballast and may add up to 100 kg or more per square meter of rooftop. When planning such an installation it is crucial that the building is designed for such loads, and, for retrofitting of existing buildings with green roofs, it might not be a viable solution. The roof is relatively easily available for maintenance. However, since the tilted panels will concentrate rainwater on the lower end of the panel, there will often be accumulation of plant growth at the lower end of the panel. Good planners of such installations know this, and intentionally divide the thickness of the green roof substrate on the roof, so the lower end of the solar panel has thinner substrate, in order to avoid growth of tall plants that shade the solar panels on the lower edge. In the end, these installations are well-established in the market, but the installation may be complex, the weight might be high, and therefore it is not always a possible solution. Specialized vertical bifacial solar panels in a specialized mounting structure To address the challenges that arise when using conventional solar panels (weight, maintenance, etc), you might consider a third way to install solar panels on green roofs. An example of this is the system offered by Over Easy Solar. Use of vertical solar panels in combination with green roofs were first tested in Switzerland in 2015, and it offers a solution that may give the best of both worlds. The vertical solar panels do not cover the green roof, so all of the plants get access to rainwater, light and evaporation. Small vertical solar panels mounted at a suitable distance over the rooftop require little or no ballast, making it a very light-weight and easy system to mount. The VPV solution from Over Easy Solar normally only adds 11 kg/m2 to the rooftop. However, you still need to know which type of green roof is under, and for intensive green roofs this is not a recommended solution since tall plants will overgrow the solar panels. In sum, you need to use a specialized system for green roofs. Over Easy Solar's solution with the VPV Unit is a good option, and there are also other alternatives that makes a high-quality and low-maintenance green roof solar installation possible.