Dynamic solar panels

Optimizing the net energy demand of the building with dynamic shading

Using a dynamic photovoltaic system for adaptive shading can improve building energy performance by controlling solar heat gains and daylighting while simultaneously generating electricity on site. This paper first presents an integrated simulation framework to couple PV electricity generation with building energy savings through adaptive shading. A high-resolution light and PV model calculates the PV electricity yield taking into account partial shading between modules. The remaining solar irradiance entering the window is used in a thermal capacity-resistance building model. A simulation of all possible dynamic configurations is performed for each time phase, from which the most energy efficient configuration is chosen. We then use this framework to determine the optimal orientation of the PV panels to maximize electricity generation while minimizing the heating, lighting, and cooling demand of the building.

An existing adaptive solar façade was used as a case study for the evaluation. Our results report a net energy saving of 20–80% compared to an equivalent static solar shading system depending on the efficiency of the heating and cooling system. In some cases the adaptive solar façade can almost offset the entire energy demand of the office space behind it. Controlling the PV generation on the façade, simultaneously with the energy demand of the building, opens up new methods of building management as the façade can control both electricity generation and consumption.

There is currently a shift in the building industry towards adaptive and dynamic building envelopes that can utilize changing weather conditions throughout the day and year. Adaptive control of solar insolation results in reductions in heating/cooling loads, improvements in daylight distribution, and on-site electricity generation (when equipped with photovoltaic modules).
The Adaptive Solar Façade (ASF), suitable for both new and existing buildings, produces electricity and regulates the generation of light and heat. The lightweight photovoltaic system thus reduces or eliminates the use of fossil fuels for electricity.

Current efforts to improve building envelopes focus primarily on reducing energy demand through static measures such as insulation, selective glazing, and shading. The resulting envelopes are limited in their ability to adapt to weather conditions or occupant needs, leaving enormous potential for energy savings, on-site energy generation, and improved occupant comfort.

In this work, we report a dynamic building envelope that uses lightweight modules based on a hybrid hard/soft material actuator to actively modulate solar radiation for local energy generation, passive heating, shading, and daylight penetration. We describe two envelope prototypes and demonstrate autonomous solar monitoring under real-world weather conditions. The dynamic PV envelope achieves up to 50% increase in electricity gains compared to a static PV envelope. We evaluate energy savings potentials for three locations, six construction periods, and two types of building use. The envelope is most effective in temperate and arid climates, where, for the cases analyzed, it can provide up to 115% of the net energy demand of an office room.

It is an adaptable solar facade system. The facade is composed of a series of movable solar panels mounted on a system of steel cables, each of which is individually controlled and moved vertically and horizontally by a robotic joint. 

Intelligent mobile solar panels, capable of saving much more energy and at the same time producing it with the right amount of light or shade, depending on the weather and internal use: described in the journal Nature Energy, they were developed by the group at the ETH Zurich led by Arno Schluter.
Building envelope optimization plays a substantial role in reducing global energy consumption and achieving energy and climate goals. A dynamic PV building envelope has now been shown to improve the energy self-sufficiency of the building while adapting to changing weather conditions and occupant needs.

Simulated savings potential

The façade not only generates electricity, but can also regulate how much light and heat enters the building envelope, thereby regulating the indoor climate. An adaptive learning algorithm controls the movement of the panels so that the savings achieved in heating and cooling the interior spaces reduce net energy demand. At the same time, the algorithm also takes into account how the current building uses and adjusts the climate accordingly.
To determine the extent to which a room’s energy consumption could theoretically be reduced, the researchers simulated different scenarios using prototype data. They calculated the energy-saving potential of building envelopes with movable façades in Cairo, Zurich, and Helsinki. They performed simulations for both office and residential spaces.

The greatest potential in temperate zones

The results show that energy savings tend to be higher in offices than in living spaces, in warm climates than in cold ones, and especially in temperate zones such as Central Europe. Arno Schluter summarizes the results: “The more variable the environmental conditions, the greater the advantages of the adaptive façade.”

The best energy balance is found in simulations of office spaces in a temperate zone (in this case Zurich) in buildings constructed according to the latest standards. In this scenario, where both internal heating and cooling are required throughout the year, the adaptive façade generated 115 percent of the energy required for a comfortable environment.
An equally positive result comes from the simulation of an office space in a house in Cairo built before 1920, which required much more shading and cooling. In this case, the façade produced 114 percent of the total annual energy requirement. In other words, the study highlights the energy saving potential for both new and old buildings, but the façade must always be considered in conjunction with the interior space and its use.

“We want to solve the trade-off between user comfort and energy efficiency in buildings,” says Arno Schlüter. “Theoretically, the most energy-efficient space would have no windows. We are therefore happy to demonstrate how an intelligent interface between the inside and outside of a building can provide optimal user comfort and also generate excess energy.”

Professor Schlüter's group will soon be able to measure the impact of the adaptive solar façade on a physical building: the system is part of the futuristic “HiLo” unit currently under construction on the highest platform of the NEST research building in Dübendorf.

The modules are movable thanks to a new device, the soft robotic actuator, which comes from a new and promising field of robotics, soft robotics. It is made of flexible materials that assume multiple shapes when the pressure in special chambers changes. Such actuators are normally used mainly for prosthetic and biomimetic robots; we are exploring and developing them for future energy and climate systems in buildings.

Operating principle and characterization of a two-axis hybrid pneumatic actuator, soft/hard material a, A hybrid actuator consists of a three-chamber pneumatic actuator made of soft material and an external universal joint made of stainless steel. The roll and pitch directions are shown for the side view of the actuator. b, c, Vertical sections of the finite element model of the soft actuator when one of the three chambers is inflated. The dotted lines in the top view insets indicate the positions of the vertical sections.

The color scale bar indicates the maximum von Mises stress in the material in megapascals. d, Adjustable stiffness effect: Displacement from the external torque characteristics for different internal actuator parameters—chamber pressures, pc. As the pressure in all three chambers increases, the actuator stiffness increases. The maximum stiffening factor is 2,5 times at 1,6 bar with this actuator design and material selection. e, Adjustable damping effect: Damping also increases with an increase in the common pressure in the three chambers.

The dominant time constant (Td) of the response decreases with high common pressure in the chambers. f, Roll-pitch plane showing the principal actuation axes and the angular range of the actuator. The four diamond shapes indicate the roll angles achieved when the three chambers are sequentially inflated and deflated, with two being inflated simultaneously, at four maximum pressures (0,5 bar, 1 bar, 1,5 bar, and 2 bar). The pressures in chambers 1 to 3 are indicated as triplets (e.g., (2,0, 2,0, 0,0) bar) indicating which chambers are inflated. g, Motion repeatability for 50 consecutive inflation-deflation cycles of 1 chamber.

Arno Schluter describes the system: the modules are movable thanks to a new device, the soft robotic actuator, which comes from a new and promising field of robotics, soft robotics. It is made of flexible materials that take on multiple shapes when the pressure in the special chambers changes. Such actuators s normally used mainly for prosthetic and biomimetic robots; we are exploring and developing them for future energy and climate systems in buildings.

Our soft actuator is manufactured using a specially developed hollow casting process and the chamber is then filled with air. Valves control the airflow by pumping or releasing air to deform the actuator and thus move the solar element selectively. With soft actuators, we can control each adaptive solar facade module individually and rotate it on two axes, alone or in groups. This allows the modules to track the movement of the sun and generate energy, use or limit solar energy, create privacy or open views. An intelligent and adaptive controller allows the facade to adapt to changing weather conditions and the habits and wishes of the user.

Other useful information

HiLo Research Building

HiLo is a research and innovation platform for NEST. This modular building is a flagship project of the Swiss Federal Laboratories for Materials Science and Technology (Empa) and the Swiss Federal Institute of Aquatic Science and Technology (Eawag). It provides a platform for researchers and industry partners to test new building and energy technologies under real-world conditions. NEST comprises the central building core onto which different modules or building units can be anchored.

“HiLo” is short for “High Performance, Low Energy“. Numerous sensors, temperature-regulating floors and ceilings, and the adaptive solar facade are designed to ensure that the building produces more energy than it consumes overall. The digitally optimized lightweight construction saves on building materials and therefore also on grey energy. Construction work on the project began in July at the NEST research platform in Dübendorf. ETH professors Philippe Block and Arno Schlüter are implementing the project in collaboration with numerous industry partners.

Sources:
https://www.nature.com/articles/s41560-019-0424-0
https://systems.arch.ethz.ch/research/active-and-adaptive-components/asf-adaptive-solar-facade.html
https://ethz.ch/en/news-and-events/eth-news/news/2015/06/soft-robotics-for-adaptive-building-facades.html

References:
Arno Schluter
Professor of Architecture & Sustainable Building Technologies (SuAT), ETH Zurich

Svetozarevic B, Begle M, Jayathissa P, Caranovic S, Shepherd RF, Nagy Z, Hischier I, Hofer J & Schlueter A: Dynamic photovoltaic building envelopes for adaptive energy and comfort management. Nature Energy 4, pages 671–682, 2019.
Two: 10.1038/s41560-019-0424-0