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SOLAR

ENERGY

Renewable Energy

and the Environment

SOLAR

ENERGY

Renewable Energy

and the Environment

Robert Foster

Majid Ghassemi

Alma Cota

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Library of Congress Cataloging‑in‑Publication Data Solar energy : renewable energy and the environment / Robert Foster … [et al.]. p. cm. -- (Energy and the environment) Includes bibliographical references and index. ISBN 978-1-4200-7566-3 (hardcover : alk. paper)

1. Solar energy. 2. Renewable energy sources--Environmental aspects. I. Foster, Robert, 1962 Apr. 25- II. Title. III. Series. TJ810.S4897 2009 621.47--dc22 2009014967

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• Chapter 1 Introduction to Solar Energy ........................................................................................ The Contributors ..........................................................................................................................xxvii
  • 1.1 The Twenty-First Century’s Perfect Energy Storm ...........................................
  • 1.2 Renewable Energy for Rural Development .......................................................
  • 1.3 Renewable Energy Solutions .............................................................................
  • 1.4 Global Solar Resource .......................................................................................
  • Problems .......................................................................................................................
• Chapter 2 Solar Resource..............................................................................................................
  • 2.1 Introduction .......................................................................................................
  • 2.2 Sun–Earth Geometric Relationship...................................................................
    • 2.2.1 Earth–Sun Distance .............................................................................
    • 2.2.2 Apparent Path of the Sun .....................................................................
    • 2.2.3 Earth and Celestial Coordinate Systems
    • 2.2.4 Position of the Sun with Respect to a Horizontal Surface
    • 2.2.5 Position of the Sun with Respect to a Tilted Surface
  • 2.3 Equation of Time .............................................................................................
  • 2.4 Structure of the Sun
  • 2.5 Electromagnetic Radiation ..............................................................................
  • 2.6 Solar Spectral Distribution
  • 2.7 Solar Constant .................................................................................................
  • 2.8 Extraterrestrial Solar Radiation.......................................................................
  • 2.9 Terrestrial Solar Radiation
  • 2.10 Measurement of Terrestrial Solar Radiation ...................................................
  • 2.11 Terrestrial Insolation on Tilted Collectors
    • 2.11.1 Instantaneous and Hourly Radiation ..................................................
    • 2.11.2 Monthly Average Daily Insolation
  • References
  • Problems
• Chapter 3 Fundamentals of Engineering: Thermodynamics and Heat Transfer
  • 3.1 Introduction
  • 3.2 Conduction Heat Transfer
    • Coordinate 3.3 One-Dimensional Conduction Heat Transfer in a Rectangular
  • 3.4 Thermal Resistance Circuits
  • 3.5 One-Dimensional Conduction Heat Transfer in a Cylindrical Coordinate .....
  • 3.6 Convection Heat Transfer vi Contents
  • 3.7 Radiation Heat Transfer...................................................................................
    • 3.7.1 Surface Property.................................................................................
    • 3.7.2 Blackbody Radiation ..........................................................................
    • 3.7.3 Real Body Radiation
  • 3.8 Introduction to Thermodynamics
    • 3.8.1 The First Law of Thermodynamics....................................................
    • 3.8.2 The Second Law of Thermodynamics
    • 3.8.3 The Third Law of Thermodynamics
  • References
  • Problems
• Chapter 4 Solar Thermal Systems and Applications
  • 4.1 Introduction
  • 4.2 Solar Collectors
    • 4.2.1 Flat-Plate Collectors
      • 4.2.1.1 Flat-Plate Collector Thermal Testing
      • 4.2.1.2 Collector Efficiency Curve
    • 4.2.2 Evacuated-Tube Solar Collectors........................................................
    • 4.2.3 Concentrating Collectors ....................................................................
      • 4.2.3.1 Optic Fundamentals for Solar Concentration .....................
      • 4.2.3.2 Parabolic Concentrators......................................................
    • 4.2.4 Compound Parabolic Concentrators (CPCs) ......................................
    • 4.2.5 Fresnel Lens Concentrators ................................................................
    • 4.2.6 Heliostats ............................................................................................
  • 4.3 Tracking Systems ............................................................................................
  • 4.4 Solar Thermal Systems....................................................................................
    • 4.4.1 Passive and Active Solar Thermal Systems ....................................... - Domestic Use ...................................................................... 4.4.1.1 Solar Thermal Application: Water Heating for - Industrial Use.................................................................... 4.4.1.2 Solar Thermal Application: Water Heating for
    • 4.4.2 Case of Active Solar Drying: Sludge Drying
      • 4.4.2.1 Solar Thermal Application: Solar Distillation..................
      • Desalination...................................................................................... 4.4.3 Case of Passive Direct and Indirect Solar Distillation: Water
    • 4.4.4 Case of Passive Solar Indirect Drying: Food Drying.......................
    • 4.4.5 Case of an Active Solar Chemical Process: Water Detoxification
  • References
• Chapter 5 Photovoltaic Cells
  • 5.1 Introduction Jeannette M. Moore
  • 5.2 Crystal Structure
  • 5.3 Cell Physics
  • 5.4 Energy Bands.................................................................................................
  • 5.5 More about Electrons and Their Energy
  • 5.6 Electrons and Holes
  • 5.7 Direct and Indirect Band-Gap Materials....................................................... Contents vii
  • 5.8 Doping
  • 5.9 Transport........................................................................................................
  • 5.10 Generation and Recombination
  • 5.11 The p–n Junction
  • 5.12 Solar Cell Equations
  • 5.13 Characterization
  • 5.14 Efficiency
    • 5.14.1 Temperature......................................................................................
    • 5.14.2 Light
    • 5.14.3 Type and Purity of Material
    • 5.14.4 Parasitic Resistances
  • 5.15 Current Research
    • 5.15.1 Concentrating Solar Cells
    • 5.15.2 Tandem Cells
    • 5.15.3 Thin Film Technologies
    • 5.15.4 Quantum Dots
  • 5.16 Cell Applications
    • 5.16.1 Utility Power Generation..................................................................
    • 5.16.2 Space Systems
    • 5.16.3 Solar-Powered Products
  • References
  • Problems
• Chapter 6 Photovoltaic Conversion Systems.............................................................................
  • 6.1 Solar Benefits
    • 6.1.1 Energy Alternatives
  • 6.2 Basic Module Electrical Concepts.................................................................
    • 6.2.1 PV Electrical Characteristics
    • 6.2.2 Common PV Terminology
    • 6.2.3 I-V Curves
  • 6.3 PV Arrays
    • 6.3.1 Increasing Voltage
    • 6.3.2 Increasing Current
  • 6.4 PV Array Tilt
  • 6.5 PV Balance of Systems..................................................................................
    • 6.5.1 Energy Storage
    • 6.5.2 Charge Controllers
    • 6.5.3 Inverters and Converters
  • 6.6 PV System Utility
    • 6.6.1 Grounding and Bonding DC and AC Circuits
    • 6.6.2 Net Metering
  • 6.7 PV System Safety
  • 6.8 PV System Testing Rules...............................................................................
  • References
  • Problems
• Chapter 7 Photovoltaic System Sizing and Design
  • 7.1 Introduction
  • 7.2 Solar Resource Sizing Considerations........................................................... viii Contents
  • 7.3 Solar Trajectory
  • 7.4 Solar Energy System Sizing Considerations
  • 7.5 Solar Energy System Sizing
    • 7.5.1 Example of Simple PV DC System Sizing
    • 7.5.2 Sizing Inverters
      • 7.5.2.1 Technical Specifications
      • 7.5.2.2 Load Estimation................................................................
      • 7.5.2.3 Battery Storage Requirement............................................
      • 7.5.2.4 Array Estimation
      • 7.5.2.5 System Summary
  • 7.6 Solar Water Pumping System Sizing
    • 7.6.1 General Method of Sizing a Solar Pump
  • 7.7 Generic Water Pump Sizing Methodology....................................................
  • 7.8 Electrical Codes for PV System Design
  • 7.9 Stand-Alone PV Lighting Design Example...................................................
  • References
  • Problems
• Chapter 8 Photovoltaic (PV) Applications
  • 8.1 Introduction
  • 8.2 Grid-Tied PV
  • 8.3 Japanese PV Development and Applications
    • 8.3.1 Japanese Government’s Approach
    • 8.3.2 Japanese PV Utilities
    • 8.3.3 Japanese Marketing
    • 8.3.4 Japanese PV Electrical Code............................................................
    • 8.3.5 Japanese PV Design
    • 8.3.6 Japanese PV System Guarantees
    • 8.3.7 Japanese PV Development
    • 8.3.8 Japanese PV Module Certification
  • 8.4 Future Japanese Trends
  • 8.5 Stand-Alone PV Applications
    • 8.5.1 PV Solar Home Lighting Systems
    • 8.5.2 PV Battery Charging Stations
      • Corsair, The Johns Hopkins University] [Guest Authors Debora Ley, University of Oxford and H. J.
      • Corsair, The Johns Hopkins University] [Guest Authors Debora Ley, University of Oxford and H. J.
  • 8.6 PV for Schools
  • 8.7 PV for Protected Areas..................................................................................
    • 8.7.1 PV Ice-Making and Refrigeration ....................................................
    • 8.7.2 PV Ice-Making .................................................................................
  • 8.8 PV Water-Pumping ........................................................................................
    • 8.8.1 Hydraulic Workloads........................................................................
    • 8.8.2 Other Considerations ........................................................................
    • 8.8.3 Pressure ............................................................................................
    • 8.8.4 Static Head ....................................................................................... Contents ix
    • 8.8.5 Pumping Requirements ....................................................................
    • 8.8.6 Dynamic Systems .............................................................................
    • 8.8.7 Water Demand
      • 8.8.7.1 Water Resources
    • 8.8.8 Storage of Water versus Storage of Energy in Batteries
    • 8.8.9 Pumping Mechanisms Used for Solar Pumps
      • 8.8.9.1 Centrifugal Pumps
      • 8.8.9.2 Positive Displacement Pumps
      • 8.8.9.3 Surface Pumps versus Submersible Pumps
    • 8.8.10 Types of Motors Used with Solar Pumps
    • 8.8.11 Solar Pump Controllers
      • 8.8.11.1 Additional Features of Pump Controllers
    • 8.8.12 Pump Selection
    • 8.8.13 Installation, Operation, and Maintenance
    • 8.8.14 System Installation
      • 8.8.14.1 Civil Works .......................................................................
      • 8.8.14.2 Piping
      • 8.8.14.3 Surface-Pump Installation
        • Noise 8.8.14.4 Surface Water Pumps: Preventing Cavitation and
      • 8.8.14.5 Installation of Submersible Pumps
  • 8.9 Grounding and Lightning Protection for Solar Water Pumps - Electrical Enclosures 8.9.1 Bond (Interconnect) All Metal Structural Components and
    • 8.9.2 Ground..............................................................................................
    • 8.9.3 Float Switch Cable
    • 8.9.4 Additional Lightning Protection ......................................................
  • 8.10 Solar Tracking for Solar Water Pumps ..........................................................
    • 8.10.1 Passive Trackers ...............................................................................
    • 8.10.2 Active Trackers versus Passive Trackers
  • 8.11 Operation and Maintenance of the Systems
  • 8.12 The PV Array
    • 8.12.1 Pumps and Motors............................................................................
    • 8.12.2 Water Supply Systems
  • 8.13 PV Water-Pumping Results
  • References
• Chapter 9 Economics
  • 9.1 Solar Energy Is Free, but What Does It Cost?............................................... Vaughn Nelson
  • 9.2 Economic Feasibility
    • 9.2.1 PV Costs
  • 9.3 Economic Factors
  • 9.4 Economic Analysis
    • 9.4.1 Simple Payback
    • 9.4.2 Cost of Energy
  • 9.5 Life Cycle Cost
  • 9.6 Present Value and Levelized Costs................................................................
    • 9.6.1 Steps to Determine the LCC x Contents
  • 9.7 Annualized Cost of Energy ...........................................................................
  • 9.8 Externalities ...................................................................................................
    • 9.8.1 Externality Evaluation Methods.......................................................
    • 9.8.2 Societal Perspectives on Solar Energy Utilization
  • 9.9 Solar Irrigation Case Study
    • 9.9.1 Estimating System Costs
    • 9.9.2 Table of Approximate Costs
    • 9.9.3 Comparison of Pumping Alternatives
  • 9.10 Water Pumping Example
  • 9.11 Summary .......................................................................................................
  • References ................................................................................................................
  • Problems ...................................................................................................................
• Chapter 10 Institutional Issues
  • 10.1 Introduction
  • 10.2 Sustainability
  • 10.3 Institutional Considerations
    • 10.3.1 Policy Issues
    • 10.3.2 Capacity Building.............................................................................
    • 10.3.3 Education and Training
    • 10.3.4 Technical Assistance
    • 10.3.5 Local Infrastructure Development
    • 10.3.6 Involving the Community: Sustainability and Inclusion..................
  • 10.4 Stakeholders
    • 10.4.1 Panels versus Fuel or Electric Bills
    • 10.4.2 Community Reduction of Theft Risks
    • 10.4.3 PV and the “Virtuous Circle”...........................................................
  • 10.5 Program Implementation ...............................................................................
    • 10.5.1 Conduct Strategic Planning ..............................................................
    • 10.5.2 Pilot Project Implementation
    • 10.5.3 Create Sustainable Markets
    • 10.5.4 Grassroots Development Approach
    • 10.5.5 Install Appropriate Hardware
    • 10.5.6 Monitoring........................................................................................
  • 10.6 Institutional Models for Solar Energy Dissemination
    • 10.6.1 Cash Sales
    • 10.6.2 Consumer Financing
      • 10.6.2.1 Revolving Credit Fund
      • 10.6.2.2 Local Bank Credit
    • 10.6.3 Leasing
      • 10.6.3.1 Dealer Credit.....................................................................
    • 10.6.4 Subsidies ...........................................................................................
  • 10.7 Management and Ownership .........................................................................
    • 10.7.1 Authorization Arrangement .............................................................
    • 10.7.2 Contracts...........................................................................................
    • 10.7.3 Leases ...............................................................................................
    • 10.7.4 Ownership Transfer (Flip Model)
    • 10.7.5 Associations and Cooperatives.........................................................
  • 10.8 Tariffs and Payment....................................................................................... Contents xi
    • 10.8.1 Free
    • 10.8.2 Nominal (Subsidized)
    • 10.8.3 Fee for Service..................................................................................
    • 10.8.4 Payment
  • 10.9 Other Critical Issues
  • 10.10 Summary
  • Problems
• Chapter 11 Energy Storage
  • 11.1 Introduction
  • 11.2 Batteries in PV Systems
    • 11.2.1 Lead-Antimony Batteries .................................................................
    • 11.2.2 Lead-Calcium Batteries
    • 11.2.3 Captive Electrolyte Batteries
    • 11.2.4 Nickel-Cadmium Batteries ...............................................................
  • 11.3 Lead-Acid Battery Construction ...................................................................
    • 11.3.1 Plate Grids ........................................................................................
      • 11.3.1.1 Positive and Negative Plates .............................................
      • 11.3.1.2 Separators
      • 11.3.1.3 Elements............................................................................
      • 11.3.1.4 Cell Connectors
      • 11.3.1.5 Containers
      • 11.3.1.6 Vent Plugs
  • 11.4 Lead-Acid Battery Operation
    • 11.4.1 Discharge Cycle................................................................................
    • 11.4.2 Charge Cycle
    • 11.4.3 Electrolyte and Specific Gravity
    • 11.4.4 Water
    • 11.4.5 Battery Roundtrip Efficiency
  • 11.5 Lead-Acid Battery Characteristics
    • 11.5.1 Ampere-Hour Storage Capacity
    • 11.5.2 Battery Cycle Life
    • 11.5.3 Battery Connections
  • 11.6 Battery Problem Areas
    • 11.6.1 Overcharging
    • 11.6.2 Undercharging
    • 11.6.3 Short Circuits....................................................................................
    • 11.6.4 Sulfation
    • 11.6.5 Water Loss
    • 11.6.6 Self-Discharge
  • 11.7 Battery Maintenance
    • 11.7.1 Hydrometer Description and Use .....................................................
    • 11.7.2 Temperature Correction ...................................................................
    • 11.7.3 Tropical Climates .............................................................................
  • 11.8 Battery Safety Precautions
    • 11.8.1 Battery Acid
    • 11.8.2 Hydrogen Gas
    • 11.8.3 Battery Enclosures............................................................................
  • 11.9 Determination of Battery Failure .................................................................. xii Contents
    • 11.9.1 Battery Applications and Installation...............................................
    • 11.9.2 Battery Service History ....................................................................
    • 11.9.3 Visual Inspection
    • 11.9.4 Battery Age
    • 11.9.5 Overcharging and Undercharging
    • 11.9.6 Internal Examination........................................................................
    • 11.9.7 Container
    • 11.9.8 Electrolyte
  • 11.10 Battery Selection Criteria
    • 11.10.1 Battery Procurement Considerations................................................
      • 11.10.1.1 Additional Battery Manufacturer Specifications
    • 11.10.2 Additional Battery System Considerations - 11.10.2.1 Small-System Considerations - 11.10.2.2 Large-System Considerations
  • 11.11 Charge Controller Terminology
  • 11.12 Charge Controller Algorithms .......................................................................
    • 11.12.1 Shunt Controller ...............................................................................
    • 11.12.2 Series Controller
  • 11.13 Charge Controller Selection Criteria
    • 11.13.1 Charge Controller Procurement Specifications - Specifications 11.13.1.2 Additional Charge Controller Manufacturer
  • References
  • Problems
• Solar Energy Glossary
  • Batteries
  • Electricity
  • Photovoltaics ............................................................................................................
  • Solar Energy Concepts .............................................................................................
  • Solar Water-Pumping
• Appendix A: World Insolation Data ..........................................................................................
• Appendix B: Friction Loss Factors
• Appendix C: Present Value Factors
• Appendix D: Table of Approximate PV Pumping-System Costs
• Index

xiii

Series Preface

By 2050 the demand for energy could double or even triple as the global population grows and developing countries expand their economies. All life on Earth depends on energy and the cycling of carbon. Energy is essential for economic and social development and also poses an environmen- tal challenge. We must explore all aspects of energy production and consumption, including energy efficiency, clean energy, the global carbon cycle, carbon sources, and sinks and biomass, as well as their relationship to climate and natural resource issues. Knowledge of energy has allowed humans to flourish in numbers unimaginable to our ancestors. The world’s dependence on fossil fuels began approximately 200 years ago. Are we running out of oil? No, but we are certainly running out of the affordable oil that has powered the world economy since the 1950s. We know how to recover fossil fuels and harvest their energy for oper- ating power plants, planes, trains, and automobiles; this leads to modifying the carbon cycle and additional greenhouse gas emissions. The result has been the debate on availability of fossil energy resources; peak oil era and timing for anticipated end of the fossil fuel era; price and environmental impact versus various renewable resources and use; carbon footprint; and emissions and control, including cap and trade and emergence of “green power.” Our current consumption has largely relied on oil for mobile applications and coal, natural gas, and nuclear or water power for stationary applications. In order to address the energy issues in a comprehensive manner, it is vital to consider the complexity of energy. Any energy resource, includ- ing oil, coal, wind, and biomass, is an element of a complex supply chain and must be considered in its entirety as a system from production through consumption. All of the elements of the system are interrelated and interdependent. Oil, for example, requires consideration for interlinking of all of the elements, including exploration, drilling, production, water, transportation, refining, refinery products and byproducts, waste, environmental impact, distribution, consumption/application, and, finally, emissions. Inefficiencies in any part of the system have an impact on the overall system, and disruption in one of these elements causes major interruption in consumption. As we have experienced in the past, interrupted exploration will result in disruption in production, restricted refining and distribution, and consumption shortages. Therefore, any proposed energy solution requires careful evaluation and, as such, may be one of the key barriers to implementing the proposed use of hydrogen as a mobile fuel. Even though an admirable level of effort has gone into improving the efficiency of fuel sources for delivery of energy, we are faced with severe challenges on many fronts. These include population growth, emerging economies, new and expanded usage, and limited natural resources. All energy solutions include some level of risk, including technology snafus, changes in market demand, and economic drivers. This is particularly true when proposing an energy solution involving implemen- tation of untested alternative energy technologies. There are concerns that emissions from fossil fuels will lead to changing climate with possibly disastrous consequences. Over the past five decades, the world’s collective greenhouse gas emis- sions have increased significantly—even as increasing efficiency has resulted in extending energy benefits to more of the population. Many propose that we improve the efficiency of energy use and conserve resources to lessen greenhouse gas emissions and avoid a climate catastrophe. Using fossil fuels more efficiently has not reduced overall greenhouse gas emissions for various reasons, and it is unlikely that such initiatives will have a perceptible effect on atmospheric greenhouse gas content. Although the correlation between energy use and greenhouse gas emissions is debatable, there are effective means to produce energy, even from fossil fuels, while controlling emissions. Emerging technologies and engineered alternatives will also manage the makeup of the atmosphere, but will require significant understanding and careful use of energy.

Series Preface xv

an individual’s career and providing the trained resources needed to interact with financial, govern- mental, and industrial organizations. In all my interactions in this field throughout the years, I have conducted significant searches for integrated textbooks that explain alternative energy resources in a suitable manner that would com- plement a syllabus for a potential course to be taught at the university and provide good reference material for parties getting involved in this field. I have been able to locate a number of books on the subject matter related to energy; energy systems; and resources such as fossil nuclear, renewable energy, and energy conversion, as well as specific books on the subjects of natural resource avail- ability, use, and impact as related to energy and environment. However, books that are correlated and present the various subjects in detail are few and far between. We have therefore started a series in which each text addresses specific technology fields in the renewable energy arena. As a part of this series, there are textbooks on wind, solar, geothermal, biomass, hydro, and other energy forms yet to be developed. Our texts are intended for upper level undergraduate and graduate students and informed readers who have a solid fundamental under- standing of science and mathematics. Individuals and organizations that are involved with design development of the renewable energy field entities and interested in having reference material avail- able to their scientists and engineers, consulting organizations, and reference libraries will also be interested in these texts. Each book presents fundamentals as well as a series of numerical and conceptual problems designed to stimulate creative thinking and problem solving. I wish to express my deep gratitude to my wife, Maryam, who has served as a motivator and intellectual companion and too often has been the victim of this effort. Her support, encouragement, patience, and involvement have been essential to the completion of this series.

Abbas Ghassemi, PhD

xix

Preface

The twenty-first century is rapidly becoming the “perfect energy storm”; modern society is faced with volatile energy prices and growing environmental concerns, as well as energy supply and security issues. Today’s society was founded on hydrocarbon fuel—a finite resource that already is one of the main catalysts for international conflicts, which is likely to intensify in the future. The global energy appetite is enormous, representing over $6 trillion per year, or about 13% of global gross domestic product (GDP). Unfortunately, the vast majority of this energy is not effi- ciently utilized for buildings, vehicles, or industry. This is especially true in the United States, which has about double the per-capita and GDP energy usage rates as compared to the European Union and Japan. The inefficient use of energy strongly exacerbates the global energy crisis. It is time to shed the outdated “burn, baby, burn” hydrocarbon energy thinking with a new energy vision; the time for clean energy solutions is here. Only through energy efficiency and renewable energy technologies can modern civilization extricate itself from the gathering perfect energy storm. The United States is addicted to the consumption of fossil fuels. The country obtains about two- fifths of its energy from petroleum, about one-fourth from coal, and another quarter from natural gas. Two-thirds of oil in the United States is imported; if business continues as usual, by 2020, the country will import three-fourths of its oil. In 2006, the United States spent $384 billion on imported oil. By 2030, carbon fuels will still account for 86% of U.S. energy use with a business-as- usual approach. The United States uses about 100 quadrillion BTUs (29,000 TWh) annually. From this, 39% is energy for buildings, 33% for industry, and 28% for transportation. On average, the country uses 1.4 times more energy than the European Union and Japan in industry, 2.5 times more energy in buildings, and 1.8 times more in transportation. Like the United States, these countries are very much dependent on oil imports. However, in comparison to the United States, Japan uses only 53% energy per capita and 52% energy per GDP, while the European Union uses only 48% and 64%, respectively. The new global energy realities have brought the highest energy prices in history. Sustained price volatility will continue, with large spikes and drops of energy prices tracking global eco- nomic trends. Peak oil is predicted by many within the next decade. The North American energy infrastructure and workforce are aging. China and India are now new global energy customers causing major impacts on primary fuel prices. By 2030, China is projected to import as much oil as the United States does now. Trigger events such as blackouts, hurricanes, floods, and fires further increase volatility due to tight supplies. Food, metal, and transportation prices are rising as a result of increased energy demand. In addition to costs and availability of fossil fuels, a worse panorama results from counting the increase of the millions of tons per year of carbon dioxide emissions—the main gas precursor of the greenhouse effect. Future CO 2 emission increments will be originated mainly in developing coun- tries as population and industry grow. The current CO 2 average concentration in the atmosphere is about 400 parts per million (ppm)—the highest ever experienced by the Earth. Maintaining as much reliance on fossil fuels as today, by 2050, such concentration may exceed 700 or 800 ppm. At higher concentration, the few degrees gained in Earth’s average temperature exert several grave impacts on food safety, water, the ecosystem, and the environment. Currently, only half a Celsius degree increase has been enough for catastrophic natural disasters to occur. To limit sea level rise to only 1 m and species loss to 20% by the end of this century, additional warming must be limited to 1°C. This means stabilizing atmospheric CO 2 at about 450–500 ppm. The United States is the second largest emitter of CO 2 emissions after China. The United States currently emits 23% of