Photovoltaic Windows: Theories, Devices and Applications

Abstract

Current photovoltaic (PV) industrial chain mainly serves the conventional utility-scale PV power stations. Rigid and opaque silicon-based PV modules domain the market so far. As distributed PV capacities expand, PV modules tend to be integrated with existing infrastructures (mostly, buildings). To adapt with the building environment, innovative design is required from the cell level to the system level. This dissertation specially deals with the window-integrated photovoltaics. Two types of PV windows, those with opaque PV shading elements and those with semi-transparent PV (STPV) glazing, are mainly explored in terms of concerned performances. A mathematical model of solar irradiance and a geometrical model of a reference office are built in Chapter 2. One-axis PV blinds and the total input power are modeled and analyzed in regard to annual power generation and glare protection. An optimal sun-tracking angle has been found to achieve both maximum power generation and non-glare daylighting. Optimal design of cell layout is also proposed to avoid shading from window frames. Compared with conventional quasi-perpendicular sun tracking, the proposed sun-tracking methods improve the annual energy generation by 12.00% and the annual average efficiency by 8.52%. In Chapter 3, PV shading elements with extra degree of freedoms (DOFs) have been modeled and analyzed in a similar way as in Chapter 2. Two-DOF PV shading elements have been proved to be the same as one-axis PV blinds in respect to optimal sun-tracking positions. PV shading elements with three-DOF sun-tracking abilities are demonstrated capable to meet all the requirements, i.e. gaining the maximum power generation, protecting from glare, and avoiding shadows from the window frame. A corresponding variable-pivot three DOF (VP-3-DOF) sun-tracking algorithm is given in the form of an analytical solution. Following aforementioned two chapters, the overall energy performance of the reference office with one-axis PV blinds is analyzed over an entire year in Chapter 4. Simulations show that using the optimal shade-free tracking method, the net energy consumption of the building, considering PV production, artificial lighting, heating and cooling, is reduced by 10.49%, compared to the perpendicular tracking method. In Chapter 5, PV windows are applied to the skylight in Dutch greenhouses. Unlike vertically-mounted PV windows mentioned above, the greenhouse PV panels are installed on a pitched roof to regulate the sunlight for plants, instead of humankind. PV layouts in high and low densities are evaluated under four special sun-tracking positions with regard to power generation and interior irradiance. Simulation results provide guidelines to balance the PV power generation and food production in greenhouses. In Chapter 6, semi-transparent thin-film amorphous silicon solar cells are designed and fabricated for PV windows. Using an optical model, GenPro4, we provide with a simulation method to optimize the configuration of such solar cells. According to the optimized results, we fabricate the single-junction amorphous silicon solar cell, showing an average transmittance of 20.04% with the conversion efficiency of 6.94%. Additionally attached to a polymer dispersed liquid crystal (PDLC) film, which can switch from opaque to transparent state in a second by applying an alternating-current (AC) voltage, the transmittance of the PV window can be further controlled. The prototype of a house model, containing the STPV-PDLC system, has been built to demonstrate the feasibility of such a combination. Besides building applications, PV windows can be further applied to any occasion that requires light transmittance and power supply, such as electric vehicles, aircrafts, billboards, and even mobile phones. Applications of PV windows could be beyond imagination.