While it is well known that the building environment contributes significantly to the global energy demand, further actions should be taken by both governmental bodies as the building industry. Since more policies regarding the energy performance of buildings come into play, the industry must find ways to fulfill these policies.
Due to the abundant ways to do so, it is often difficult for architects, façade- consultants, and engineers to have a good overview of the available technologies which each have their specific benefits. In this article, a new sustainable façade solution will be explained.
But first, it is essential to remember for anyone in the building industry that buildings should be designed for humans, and their wellbeing should be considered in the design process. The transition to a more sustainable building environment should not compromise the indoor climate of the end-user but ideally even be a motive to improve this.
To achieve more sustainable buildings, three issues should be addressed simultaneously; energy production of buildings, reducing its energy demand and the usage of durable materials in the building design. However, with the increase of both glass skin and high-rise buildings, the energy neutrality of premises becomes more challenging to accomplish.
High rise buildings have relatively limited rooftop area for solar panels while the façade area tends to increase to the floor surface. Glass skin buildings then again often have challenging energy physics. However, recently, new technology has entered the market, which tackles all the three described issues while maintaining the focus on the end-user.
– Glass solar panels which simultaneously fulfil the role of sun shading and LED display –
In this case, two glass planes are used as the basis for the board with dots of solar cell material in between. Due to the usage of concentrated photovoltaics (CPV), the direct light of the sun can be focused on solar cell material.
Usually, to magnify the light sufficiently long distances must be covered. However, with the use of a lens on the front of the panel and a mirror in the back, the range and thus panel thickness is massively reduced. In this way, with a self-designed lens shape, the light can be converged with a magnitude of 700 with a panel thickness of just 14 mm. Therefore, only 1/700th of the panel must be covered with solar cell material creating a transparent solar panel with small solar cell dots.
Due to the high solar irradiance and correlating heat energy intensity, traditional silicon solar cell material would not work in this configuration.
(MM Panels) – Close up of the panels
Therefore, a triple junction (III-V) solar cell is used, which usually is only used in aerospace applications. In simple words, the three junctions mean that instead of a single layer with its bandgap width, three coats with each their own effective bandgaps of the light spectrum can be used to convert light into electricity.
The potential of using more layers is most easily shown by the Shockley-Queisser Limit which shows that the maximum efficiency for single-junction cells is 33% while it’s almost 87% for an infinite number of junction cells (Shockley and Queisser, 1961). The triple-junction solar cell material has an efficiency of above 45% from which a solar panel with an efficiency of 30% was realized, which is significantly more than the traditional solar panels on the market.
From this can be seen how these solar panels contribute to the energy production of buildings. The second mentioned issue was related to energy savings. Savings can, among others, be achieved by proper solar heat control. A test office was set up in Amsterdam, The Netherlands, to see the effect on annual energy demand for cooling and heating. It was shown that these panels have an enormous impact on energy demand for both cooling (40% reduction) and heat (24% reduction).
(MM Façade and MM Outside next to each other) –
The first project realized the reason for placing these panels in a second skin type façade are as follows; minimizing dust and dirt accumulation, which can have a significant effect on the panel’s efficiency. Besides, the environmental loads such as wind, hail, or even snow are eliminated due to the closed cavity in which the panels are placed. Last and maybe even most important is that the efficiency of solar panels is always electrical efficiency.
The solar cell material can’t convert the rest of the sun’s energy, and therefore the element heats up. The heat will rise due to natural in the cavity and can be utilized with the use of a heat exchanger. In climates with an excess amount of heat, this could be ventilated outwards, saving on cooling. The potential of produced heat energy for this system has shown to be higher than the electrical potential. Alternatively, instead of glass, ETFE foil could be used as front skin due to its low material weight and high transmissivity.
(Day) – Showing The Elegant Impact Of Glass Solar Panels
The third key point which is often included in new sustainability credentials for buildings such as BREAAM is the use of scarce materials and the recyclability of the materials. The materials used for these panels is glass, copper for the electrical wiring, PMMA for the lenses and triple-V junction material for the solar cell material. Therefore, this panel, in contrast to traditional silicon panels, is fully and easily recyclable.
As mentioned before, buildings should be designed with respect for the end-user. For this group, the indoor climate with respect to daylight regulation and thermal comfort is essential. The panels focus all the direct light of the sun, which is responsible for glare and overheating, on the solar cell material making the use of solar shading devices abundant.
In comparison with these traditional solar shading devices (indoor and outdoor), an improved unobstructed view and increased amount of pleasant daylight entrance are achieved.
The diffuse daylight namely passes through the panel for 70% since its guided along with the solar cell material. Therefore, up to 3 times more, natural sunlight can enter the building, potentially reducing costs of artificial lightning up to 36%, which was also proven by the same test done in Amsterdam.
(Indoor climate) – Effect on the indoor environment
At last, the addition of LED lights within the solar cell panels is a new development within this technology. This increases the attractiveness of the façade, which then can be used throughout the entire day and even when it is heavily clouded or dark outside.
(Night) – Showing the potential of the MEDIA version
Summarized; to make the energy transition of the building environment possible, all technologies together will have to contribute. The strength of this technology lies in the fact that it unlocks an entirely new building surface area which can be utilized.
Having an effect on all three aspects; energy production, energy-saving, and sustainable materials while keeping the end-user in mind might, it could might play a significant impact on the transition.