Improving Aesthetics and Energy Performance of Photovoltaics for the Building Environment

Abstract

With an estimated global share of greenhouseemissions of 35%, the building sectormust be the target of significant transformation. These next decades represent one of the best opportunities for a giant energy consumer to become an efficient energy prosumer. Of the many technical possibilities available that can help in this objective, building integrated photovoltaic systems is becoming one of the most salient because of their versatility of application and simplicity of operation. However, to achieve their projected market growth, BIPV products must overcome technical, financial, and social barriers.

The interrelationship between these barriers creates requirements that are sometimes in conflict with each other. Research suggests that the most important parameters for the financial viability of a BIPV system (studied in North America) are its electrical performance and its effective lifetime. However, the social acceptance of BIPV systems, among architects and other consumers, increases when photovoltaic modules are provided with a variety of colors, resulting in losses in their electrical output. Furthermore, a BIPV system can present an installation layout in which its modules operate at high values of temperature, which hinders their useful lifetime.

Significant research has been done to tackle these requirements, striving to find a balance in which each, however contradictory, is met. This thesis seeks to add to this body of research through modeling and experimental efforts focused on creating techniques and concepts to improve the aesthetics and thermal behavior of photovoltaic modules.

After an introductory chapter, Chapter 2 presents an overview of the efforts done so far to improve aesthetics and passively cool photovoltaic modules. The challenges and barriers that remain from a technical perspective are outlined, and the base modeling approach deployed to tackle them is introduced. Chapter 3 presents how this model can be complemented by auxiliary algorithms to find ways to provide color directly to c-Si solar cells by using interference optical filters. The chapter also provides insight into ways of stabilizing color and the beneficial impact that a color optical filter has on the operating temperature of a c-Si solar cell.

Chapter 4 expands on the findings of Chapter 3 and discusses that the application of the color optical filter on the front glass of a PV module provides better benefits, particularly in terms of better color saturation and more vivid hues. In addition, it provides guidelines for how colorimetry can be added to the modeling effort to improve the quality of color matching and color stability of a color photovoltaic module based on optical filters. Furthermore it demonstrates that it is possible to achieve colorful designs with relative DC energy losses below 10%.

Chapter 5 argues that optical filters can also be designed to provide thermal control to photovoltaic modules. Furthermore, this thermal control can be achieved by taking advantage of the harmonic reflectance produced by simple designs. It shows that the analysis of a thermal management solution must always consider their benefits related to extended lifetime. A simple optical thermal filter, despite its lossy nature (in terms of electrical output), can still provide a net benefit in terms of energy yield when this benefit is accounted for.

Chapter 6 presents the huge cooling potential provided by phase change material (PCM). This work is entirely experimental and demonstrates that a single type of PCM can be used in different locations, with different installation layouts, to provide substantial temperature reductions and increase the electrical output of photovoltaic modules with great consistency, even during the wintermonths.

Chapter 7 presents the novel concept of a photovoltaic chimney, developed with the purpose of studying the potential use of the thermal energy produced by photovoltaic modules. The concept was analyzed using common modeling approaches to calculate mass flow and heat production, offering quick ways to create sensitivity analysis for earlier stages of design. These initial stages of the model can be used to have insight into the quality (or lack thereof) of the heat produced and its potential use to improve the ventilation of buildings.

Chapter 8 completes this dissertation, highlighting its main conclusions and providing details on potential areas that can drive future research.