Photovoltaic powered electrochromic windows. Final report, October 1, 1997--June 30, 1998
With their ability to modulate the amount of sunlight and solar heat entering buildings, electrochromic glazings offer unique opportunities to reduce indoor lighting and cooling costs. The relatively low power needed to effect this control can readily be obtained from small photovoltaic arrays. The goal of this work is to merge these two high tech products by placing the PV inside an electrochromic insulating glass unit (IGU). The internal power source negates the need for external wiring, making the photovoltaic powered electrochromic (PV-EC) window interchangeable with existing windows and opening the possibility for retrofitting this new technology into existing buildings. The development work was carried out in several stages ultimately leading to the fabrication of several prototypes. Solarex provided PY performance data and the PY modules used in the prototypes. The first step toward making PV-EC windows was to determine performance requirements for a completed hybrid and for each of its two components. This analysis revealed that for most applications a PY array taking 2-3% of the vision area, can effectively control an EC window. However, more PY may be required, depending on the application and the degree of control desired. For the initial investigation of the PY-EC product, a programmable power supply was used to simulate a PY module and its interaction with the EC glazing. Subsequent tests, in which the two devices were physically separate but electrically coupled, provided an understanding of the dynamics of their interaction. The information derived from these tests, combined with a definition of performance requirements for PY-EC windows, led to the design and fabrication of several prototypes. One of these assembled prototypes has wireless controls and can be remotely switched to color and bleach. Since the bleaching is done actively, i.e. by applying a reverse voltage, a rapid response is obtained in full sunshine. The exposure of the PY to sunlight is obtained through a clear section of the EC glazing. A wireless EC-PY application was demonstrated in which heat and light through a window were modulated to show the climate control capabilities of this product. The other two prototypes are configured so that the internal PY can be moved either partially or almost completely behind the active EC element. This is done by shifting the position of the PY array inside the IGU magnetically, which results in two effects: (l) When the PY is behind the EC, it provides negative feedback to the coloring voltage, rendering the performance less dependent on EC glazing characteristics than if the PY were totally exposed, and (2) the degree of coloration can be selected, from very dark when the PY is fully exposed to the sun, to very light when the PY is mostly behind the active EC glazing. Initial tests of this prototype confirm the expected behavior, with the test results being in line with calculations of PY-EC performance. In summary, prototype testing to date has confirmed the concept of a stand-alone controllable PY-EC hybrid. Based on these results and other considerations, a preliminary description and specification can be provided for the next phase of large area PY-EC window development.
- Research Organization:
- SAGE Electrochromics, Inc., Piscataway, NJ (United States)
- Sponsoring Organization:
- USDOE Assistant Secretary for Energy Efficiency and Renewable Energy, Washington, DC (United States)
- DOE Contract Number:
- FC36-97GO10251
- OSTI ID:
- 10116647
- Report Number(s):
- DOE/GO/10251-T1; ON: TI99020095; TRN: AHC29913%%6
- Resource Relation:
- Other Information: PBD: 14 Aug 1998
- Country of Publication:
- United States
- Language:
- English
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