ABSTRACT One of the main concerns facing those of us who work on the future of the built environment is how our architecture can responsibly and productively contribute to our energy needs. The increasing efficiency of buildings and their capacity to generate electricity has raised problems of their occupants’ literacy of this new infrastructural role.
In this project we explore the potential of interactive energy harvesting using paper-like materials to draw attention to buildings-as-generators. This self-powered installation harnesses the most basic architectural trope of inside/ outside to speculate on the future of electrical generation in the built environment.
STATEMENT OF PROBLEM Within the built environment we predominantly encounter either environmental, explicit methods of electrical generation, in the form of photo-voltaic or wind turbine generation, or incidental methods, harnessing wasted energy from the electromagnetic radiation around cell towers, ambient vibrations and similar.
What we are proposing here is to use both the very fabric of the built environment itself and the behavior of the people who use it. This raises two crucial avenues for exploration: the first is the possibilities of materials used in the construction of the built environment, either currently in use or possible alternatives for future construction that would better facilitate such electrical generation; and the second is harnessing the behaviors of those people who use the built environment, whether that means understanding and capitalizing on prevailing interactions, or proposing a change in behavior to enhance the generation of electricity.
SOLUTION In this particular exploration we have proposed a system which encourages a playful interaction with the problem of interior/ exterior such that the act of greeting someone through a pane of glass can be parried into a competition to generate electricity locally, feeding respective banks of LEDs demarcating the individual generating the most electricity.
OPERATION The operation of the Paper Generators relies on the movement of the two conductive sheets relative to each other and the electric field source, i.e., PTFE. As the relative positions of the sheets change, the distribution of the induced charges, the electric field, and the total capacitance between the sheets change, resulting in an electric potential difference between the conductors (Figure 1c). Hence, the mechanical movements of the sheets and the field source are converted into electrical potential energy that can do work.
It is important to emphasize that although the fundamental principles of operation are relatively simple, a broad variety of movements and gestures can be used to generate power by designing structures that are highly optimized for specific gestures. Different materials for electrodes and electret can also be used.
TECHNICAL Energy harvesting devices typically employ a magnetic or electric field source, such as a small battery, a permanent magnet, or a permanent electret. In our application, the field source is the semi-permanent charge on the surface of a thin and flexible sheet of PTFE (polytetrafluoroethylene), commonly known by its brand name – Teflon. When the sheet is rubbed with ordinary newspaper, opposite-polarity charges P and T accumulate on the surfaces of the paper and PTFE due to the triboelectric effect (Figure 1a). Because PTFE has a lower electron affinity than paper, charge T is negative. This charge on the PTFE sheet can then act as an electric field source. When the PTFE sheet is brought near conductive objects, e.g., sheets of aluminum (Figure 1b), the charge on the PTFE attracts free charges of opposite polarity σ1 and σ2 that are available in the conductors. These charges accumulate on the surface of the conductors, as shown in Figure 1b.
MEASUREMENTS Figure 2a shows the short circuit current of three taps, figure 2b shows the open circuit voltage during two taps.
FUTURE Possible future scenarios necessitate recognizing likely sites for explicit interactive or behavioral electrical generation in the built environment as well as any changes to the fabric of the built environment or the behavior of those using it which might be necessary to enhance such generation as much as possible. Then there is the question of the use of such electricity, whether it should be used, so to speak, in real time, or whether it should be stored in capacitors for maximum discharge resulting in a more profound effect.
Both methods have a certain pedagogical value - a necessary step if behavioral changes are in order. Any number of mechanical motions in the built environment could be augmented with such technology, feasibly altering the way we interact with doors, handles, drawers and so forth in the home or office. Everyday movements in the city could be dramatically reinvented if it were necessary to maintain contact with a surface, such as a wall, or if increased frequency of contact - i.e. walking - resulted in a more effective generation of electricity.
One imagines that if it were possible to generate electricity for one’s own devices through such motions it would result in a distinctly different urban scene.
REFERENCES Karagozler, M. E., Poupyrev, I., Fedder, G. K. and Suzuki, Y.,
Paper Generators: Harvesting Energy from Touching, Rubbing and Sliding. In Proc. of UIST’13, ACM