Solar Photovoltaic Cells

Photons to Electricity

Alexander P. Kirk

• Publisher: Academic Press
• Year: 2014
• eBook ISBN: 9780128026038
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

Solar Photovoltaic Cells: Photons to Electricity outlines our need for photovoltaics - a field which is exploding in popularity and importance. This concise book provides a thorough understanding of solar photovoltaic cells including how these devices work, what can be done to optimize the technology, and future trends in the marketplace. This book contains a detailed and logical step-by-step explanation of thermodynamically-consistent solar cell operating physics, a comparison of advanced multi-junction CPV power plants versus combined-cycle thermal power plants in the framework of energy cascading, and a discussion of solar cell semiconductor resource limitations and the scalability of solar electricity as we move forward. Quantitative examples allow the reader to understand the scope of solar PV and the challenges and opportunities of producing clean electricity. - Provides a compact and focused discussion of solar photovoltaics and solar electricity generation. - Helps you understand the limits of solar PV and be able to predict future trends. - Quantitative examples help you grasp the scope of solar PV and the challenges and opportunities of producing electricity from a renewable resource.

Chapter 1

Energy Demand and Solar Electricity

Abstract

The natural connection we humans already have with sunlight in our daily lives is presented in Chapter 1 where we consider how much energy we demand not just to remain alive but also to live life in our increasingly technology-dense societies. From this, the electricity demand in the USA and also globally is examined, and the amount of electricity generated from photovoltaic modules is compared to other electricity generation technologies such as coal-fired power plants and wind turbines.

Keywords

sunlight

energy

electricity demand

solar electricity

1.1. Introduction

This chapter begins with the connection between humans on Earth and the Sun that we depend on, and must adapt to, in order to survive. Then, we quantify how much energy is needed on average to sustain human life. This human energy demand is used as a benchmark when we next investigate electricity generation in the USA followed by global electricity generation. Solar electricity generation is compared with other electricity generation sources such as wind, natural gas, and coal.

1.2. Human-sunlight connection

The remarkable human eye contains photoreceptor cone cells that respond to the visible portion of the solar spectrum from ∼380 nm violet light to ∼740 nm red light with photopic (i.e., bright light) vision peak sensitivity corresponding to ∼555 nm green light [1], as shown in Figure 1.1. The near-ultraviolet light that is not absorbed by atmospheric ozone is used by our skin to synthesize vitamin D.

Fig. 1.1 Peak photopic eye response with respect to AM1.5G photon flux and visible light. Note: the AM1.5G terrestrial solar spectrum (developed by Gueymard) and solar photon flux will be described in Chapter 2.

Meanwhile, oxygenic photosynthetic land plants (via chlorophyll and carotenoid molecules) effectively use visible light from the Sun to produce carbohydrate and perhaps the most benign of all waste products – pure oxygen that we breathe. The overall oxygenic photosynthesis process may be expressed by the chemical reaction given by H₂O + CO₂ → O₂ + CH₂O, where H₂O is water, CO₂ is carbon dioxide, O₂ is oxygen, and CH₂O is used here to represent a generic carbohydrate subunit.

Sunlight-dependent plants provide us plant-dependent humans with the food (carbohydrate) and oxygen that we need to survive and thrive. Plants provide us with clothing (e.g., cotton and linen), shelter for us (e.g., framing material from pine or thatched roofs from straw) and habitat for other animals, shade, furniture, cabinetry, decking and flooring, shipping crates, medicines and homeopathic remedies, paper and cardboard products such as books and boxes, dyes and pigments, perfumes and fragrances, cooking oils, delicious beverages such as tea and coffee, a sink for carbon dioxide, filtration of airborne pollutants, mitigation of soil erosion, coastal storm surge buffering, sound damping, wind breaks, sports fields, and simply enjoyment in our gardens, parks, and nature preserves.

Moreover, the Sun provides warmth, keeps in operation the hydrologic cycle (evaporation of water and precipitation), and in large measure dictates the Earth’s seasonal climate and weather that we must respond and adapt to. Humans even tailor their accessories to enable functionality in sunlight, for example, by using sunglasses and hats or by designing clothing for sunny days such as colorful women’s sundresses. With our natural connection to the Sun and solar radiant energy, it is inherently logical for humans to use sunlight for the purpose of generating clean electricity through the application of solar photovoltaic cells.

1.3. Human energy requirement

Each day, considering an average value, humans require ∼2.33 kWh (kilowatt–hours) of chemical energy to live a healthy life. Typically, instead of the units of kWh, this is expressed (in the USA) on food packaging labels as kcal (kilocalories) where 2.33 kWh is about equal to 2000 kcal [2]. Therefore, each month, on an average, humans require ∼70 kWh of energy. And, in one year, this equates to ∼850 kWh. Stated another way, powering a 100 W light bulb 24 h a day requires about the same energy as the human body each day. With ∼7.1 × 10⁹ humans on the Earth in 2013 [3]; this is nearly equivalent to continually operating a quantity of 7.1 × 10⁹ of the 100 W light bulbs, which results in a yearly energy expenditure of ∼6 × 10¹² kWh or 6 PWh (petawatt–hours). Next, we will compare the demand for (chemical) energy that is required simply to power our bodies and sustain our lives to the demand for electricity that we then use to enrich our lives in technology-dense societies such as the USA.

1.4. Electricity generation in the USA

In 2013, total net generation of electricity (“all sectors”) in the USA was ∼4.06 × 10¹² kWh [4]. At the end of 2013, the population of the USA was ∼3.17 × 10⁸ [5]. If we normalize electricity consumption in the year 2013 by the population, we find that this leads to an equivalent of ∼1.3 × 10⁴ kWh per year of electricity per person to power the USA and run its economy. This means that ∼35 kWh per day per person of electricity was utilized on an average, or ∼15× more energy per day than it takes just to sustain a human body in a state of good health (∼2.33 kWh per day) as we found in the preceding section. Therefore, on the one hand, while we need a sustainable agricultural base just to maintain human life by providing enough food (chemical energy), on the other hand, we see that living in a technology-dense society requires much more energy if we want to power industrial machinery and processes, run air conditioners and heat pumps, operate computers and charge mobile phone batteries, turn on the lights, and so forth.

Most of our electricity comes from thermal power plants that require either the combustion of fossil fuels or fission of radioactive materials. Specifically, the heat from combustion of coal or fission of uranium is used to convert water into steam; the steam is expanded in a steam turbine that in turn is connect...

Table of contents

• Cover
• Title page
• Table of Contents
• Copyright
• Dedication
• Preface
• Introduction
• Chapter 1: Energy Demand and Solar Electricity
• Chapter 2: From Nuclear Fusion to Sunlight
• Chapter 3: Device Operation
• Chapter 4: Energy Cascading
• Chapter 5: Resource Demands and PV Integration
• Chapter 6: Image Gallery
• Note on Technical Content Evolution
• Final Remarks
• Appendix A: List of Symbols
• Appendix B: Abbreviations and Acronyms
• Appendix C: Physical Constants
• Appendix D: Conversion Factors
• Appendix E: Derivation of Absorption Coefficient
• Appendix F: Derivation of Open Circuit Voltage
• Appendix G: Relative Efficiency Ratio
• Appendix H: Recalibrating the Orthodoxy