Solar panels on windows, façades, and roofs

Solar energy on buildings

Generating energy from sunlight is essential for reducing CO2 emissions. But it takes a lot of space to install solar panels on land. What if you could use existing space in the built environment? We’re developing opportunities for innovative solar panels in façades, roofs and in windows.

Solar panels on façades

There is a total of some 2,200 square kilometres of façade area in the Netherlands, of which 660 square kilometres are suitable for solar energy generation. Altogether, a capacity of 58 gigawatt peak can be installed on it. To put that in perspective, in 2022 the capacity of all solar power installations in the Netherlands was 18.8 gigawatt peak. Huge opportunities therefore for solar power generation, which we want to exploit. That is why we are working on a revolutionary product for the market, together with construction companies and manufacturers.

Over the last few years, in the Dutch Solar Design project, we’ve been working with partners to develop technology that makes this possible. In doing so, we pay attention to aesthetics and sustainability. For example, unimaginative façades of old blocks of flats can be transformed into attractive walls that generate energy. Within the foreseeable future, we want solar panels that generate energy to cost the same as the most common materials used in construction. This is how we’ll accelerate the creation of energy-neutral houses and other buildings.

The new generation of solar panels is so flexible that you have endless possibilities in terms of size, shape, and colour pattern. Situations where solar panels have been installed on façades include:

  • an image formed by aesthetic solar panels of matt glass on a concrete house along the track, at Naarden-Bussum railway station (see image)
  • aesthetic solar panels on the façade of the Royal BAM Group head office, where a brick pattern was chosen that blends in seamlessly with the façade itself
  • solar panels mounted in old air intakes, on the façade of Shell Technology Centre on the IJ in Amsterdam.
  • Solar panels as ivy on a facade in Eindhoven.

The variety of sizes, shapes, colours, and transparency of solar panels we’re working on may reduce the yield per panel. But on the plus side, many more surfaces in the built environment are suddenly able to generate solar energy. This can significantly boost the total amount of energy generated.

Brief explanation of the importance of new technology for solar cells on façade at BAM’s head office.

Solar panels on roofs

The Netherlands has some 800 square kilometres of roofs free for solar panels, half of which are commercial properties or agricultural roofs. But not all roofs are suitable. Also, the weight of standard solar panels is often too high for the load-bearing capacity of the roof, or the panels are not desirable from an aesthetic point of view. Therefore, we are working on solutions for lighter, more beautiful, cheaper and simpler constructions.

We do those innovations together with companies. For example, by developing an approach that ensures solar cells can be incorporated flexibly and affordably into surfaces and objects. From solar roofs and facades to on cars. We have built a research pilot line for this purpose. This is a model for a new generation of factories that will produce flexible semi-finished products with solar power.

Variations in shape, size, and colour are also important for the wider acceptance of solar panels. And to ensure that using solar power doesn’t undermine an architect’s creative freedom. Moreover, these innovative solutions create new market combinations and business activities. There are opportunities for construction companies, suppliers, machine manufacturers, and installation engineers.

An important aspect of solar panels is fire safety. Together with various parties, we examine existing solar panels and systems and develop new products. These include solutions to minimise the risk of arcs or new technology that prevents hotspots caused by shade.

We also provide expertise on solar modules and systems in relation to power electronics for various parties. We do this with our state-of-the-art test facilities for measuring, analysing and characterising these modules.

Solar panels in windows

If you can incorporate solar panels into windows, it opens up a world of possibilities. However, you have to make sure the window remains transparent and that’s a challenge. The right balance is important here. We found the solution in solar windows: a slightly tinted window pane that generates a lot of solar energy but also lets sunlight through (see image).

For solar windows, we use thin-film solar cells, produced mainly from the material perovskite. The goal is to create glass that lets in at least 20% of sunlight, while converting at least 10% into solar power. In this way, the windows can help make buildings energy-neutral, for example.

We’ve created a working prototype glass window that generates solar energy. Together with companies in the construction and glass industries, we’re developing this further so that it can be marketed. The prototype is 10 by 10 centimetres, with 5% efficiency. If we remove 50% of the material, 40% of the yield remains. Within 2 years, we want to improve the 5% efficiency rate to 10%, without compromising on aesthetics or transparency.

Ramen gevels daken1-TNO_Solar BEAT_EDV7530

Converting solar energy into heat

It’s common practice to convert the solar energy generated through roofs, windows, and façades into electricity. But another possibility is to use solar collectors that convert sunlight into heat. In time, solar energy could provide about a quarter of the heat needed in the Netherlands. However, seasonal storage is needed to store heat generated during summer in heat batteries for use in winter.

We work together with market parties on innovations in photovoltaic-thermal systems (PV-T systems). To make them better and more affordable, among other things. PV-T systems on roofs, combined with a heat pump, can make part of the built environment energy-neutral.

Solar heat can provide 10% of total heat demand in the built environment, utilities, agriculture, and industry. We’ve done research on the use of solar energy as a heat source. You can read about the problem areas and specific recommendations for making the best use of solar heat in an exploratory study (in Dutch) (pdf).

Previous research (pdf)shows that PV-T modules should harmonise optically with a building in terms of colour pattern and size. Making the built environment energy-neutral will then become a good market opportunity for PV-T. We’ve demonstrated this in aesthetic façades with solar modules and with a heat-absorbing paint on façade elements.

We’ve designed 3 PV-T systems together with Eindhoven University of Technology and a large number of companies. We did this work at our SolarBEAT research site. The systems were then built and tested in simulations in a lab environment. We use the results to calculate the business case for PV-T systems.


TNO develops innovations and technologies for a more sustainable society. If you work at a company that is interested in collaborating with us on innovations, please contact us.

If you are a consumer with questions about solar panels, please contact organisations that give advice on this topic such as Vereniging Eigen Huis, Consumentenbond, and Milieu Centraal. Also read the frequently asked questions about solar panels on our website.