Economical study on the most appropriate renewable source to implement in Central Maryland at UMBC

Faculdade de Engenharia da Universidade do Porto

Economical study on the most appropriate

renewable source to implement

Dissertation Conducted under the Master in Electrical

Faculdade de Engenharia da Universidade do Porto

Economical study on the most appropriate

renewable source to implement in Central

Maryland at UMBC

José Miguel Moreira Torres

F

V

Dissertation Conducted under the Master in Electrical and Computer Science

Engineering, Major of Energy

Advisor: Prof. Dr. Marc Zupan

Co-advisor: Prof. Dr. Hélder Leite

14-06-2010

Faculdade de Engenharia da Universidade do Porto

Economical study on the most appropriate

in Central

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Summary

This document presents an economic analysis on the best renewable energy source to implement in Central Maryland and specially in the University of Maryland Baltimore County.

It was created to help the Proficient persons to choose it based on the available data. The document is divided in the following parts

• First it is presented some data about the solar radiation specifications, specially in Central Maryland, to have a general idea of how much is possible to harvest from the Sun. It is also discussed the influence of the inclination and the angle definition.

• Then it is presented the Photovoltaic effect, how can we get energy from the Sun and transform it into electricity. It is explained haw are PV materials, PV cells and the whole module/ solar panel. It is also presented how solar trackers work and an comparison between grid connected and off-grid systems.

• For comparing the two different realities between USA and Europe, it was made an analysis, discussing the different incentives and targets of the two cases and focusing on the Californian and Maryland cases.

• it was made an economic study for the installation of this type of systems in Maryland with the cash flows and payback period

• Finally it is justified why is PV the best energy source, and the conclusions of that study.

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Abstract

The objective is to address both technical and financial aspects of a residential solar system. The impact of these two factors on financial paybacks of a resident is presented. This dissertation is divided to two parts. First, the impact of the technical factors such as geographical location of the solar system, proper panel installation, panel material, and system efficiency on the output electric power are discussed.

Second, the effects of significant financial factors such as utility rebates, federal tax incentives, state tax incentives, maintenance cost and feasible revenues on financial payback of a residential solar system are considered.

Energy production cost and savings for residents of four cities in different states are compared considering both mentioned technical and financial factors. Results indicate how each factor can significantly impact the residential economically. The outcome of this case study can be extended and used for those residents who are interested in the benefits and challenges of installing solar systems.

With existing financial incentives, financial payback of residential PV systems in Central Maryland is 3- 4 years.

“No sensible decision can be made any longer without taking into account not only the world as it is, but the world as it will be…”

Abstract

O objectivo é referenciar tanto a parte técnica, como a financeira de um sistema solar residencial.

È apresentado o impacto desses dois factores no retorno financeiro de um habitante. Esta dissertação está dividida em duas partes. A primeira, retrata o impacto dos factores técnicos tais como localização geográfica do sistema solar, correcta instalação dos painéis, materiais constituintes dos painéis e rendimento do sistema eléctrica são discutidos.

Em segundo lugar, os efeitos dos factores financeiros tais como devoluções da empresa de electricidade, incentivos federaris, incentivos estatais, custos de manutenção e receita exequível do retorno financeiro de um sistema solar residencial também são considerados.

O custo da produção de energia solar e poupanças para os residentes de quatro cidades em diferentes estados são comparadas considerando os factores técnicos e económicos referidos em cima. Os resultados indicam como cada um dos factores pode ter um impacto económico significante para a residência. Os resultados deste estudo podem alargar-se aos residentes que estão interessados nos benefícios e desafios de instalar estes sistemas solares.

Com os actuais incentivos fiscais, o retorno financeiro de um sistema fotovoltaico residencial na zona central de Maryland é de 3-4 anos.

“Nenhuma decisão sensata pode ser tomada sem ter em consideração não so o mundo como ele é, mas como ele poderá ser…”

Acknowledgements

First, I thank my advisor Dr Marc Zupan, for his continuous support in the MS dissertation program. Marc was always there to listen and to give advice. He is responsible for involving me in the exchange program in the first place. He taught me how to ask questions and express my ideas. He showed me different ways to approach a research problem and the need to be persistent to accomplish any goal.

A special thanks goes to my co-advisor, Dr Helder Leite, who is most responsible for helping me complete the writing of this dissertation as well as the challenging research that lies behind it.

Dr. Alex Pavlak taught me how to write academic papers and brought out the good ideas in me, he was always there to meet and talk about my ideas, to proofread and mark up my papers and chapters, and to ask me good questions to help.

I would also like to thank my professors Dr. Robert Fenton, Dr. John MacCarthy and Dr. Bjorn Frogner for the motivation and for the knowledge they gave to me.

Last, but not least, I thank my parents, Miguel Ângelo Torres, and Dorinda Maria Torres, for giving me life in the first place, for educating me with aspects from both arts and sciences, for unconditional support and encouragement to pursue my interests, even when the interests went beyond boundaries of language, field and geography.

Index

Summary ... iii

Abstract ... v

Abstract ... vi

Acknowledgements ... viii

Index ... x

List of Figures ... xii

List de Tables ... xvi

Abbreviations and Symbols ... xvii

Chapter 1 ... 1

1.1 Introduction ... 1

1.2 Motivations and foundations ... 1

1.2.1 The purpose of this Work ... 4

Chapter 2 ... 6

2.1 Solar Radiation ... 6

2.2 The Sun ... 10

2.2.1 Solar radiation Specifications ... 11

2.2.2 Angle definition ... 12

2.2.3 Incident solar radiation in a slant ... 13

Chapter 3 ... 16

3.1 Photovoltaic solar Energy ... 16

3.1.1 The photovoltaic effect ... 16

3.1.2 Photovoltaic materials ... 18

3.1.3 Photovoltaic cells ... 18

3.2 Module/ solar panel ... 21

3.3 Solar trackers ... 22

3.4 Grid connection and Off-Grid connection ... 24

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4.1 Case studies Europe VS United States of America ... 28

4.1.1 The European case ... 28

4.1.2 The US case ... 31

4.1.2.1 The Californian Case ... 32

4.1.3 United states and Maryland´s subsidies and legislation to set up a solar system ... 36

4.1.3 Renewable energy Portfolio Standards ( RPS) ... 37

Chapter 5 ... 42

5.1 Economics of photovoltaic systems in Maryland ... 42

5.1.1 System cost ... 42

5.1.2 System Payback ... 44

Chapter 6 ... 49

6.1 Why is solar PV the best renewable for Central Maryland? ... 49

6.2 Economical study on the best renewable energy source to implement at UMBC ... 50

6.3 Results ... 56

6.3.1 What options are likely to persist after the incentives go away? ... 61

6.4 Recent projects implemented in the United States ... 64

Conclusions and future work ... 66

References ... 67

List of Figures

Figure 1.1 - Total energy supply of the United States, the most part comes from Fossil

fuels, specially from Petroleum ... 2

Figure 1.2 - Types of renewable sources that supply the U.S. in 2008, most part came from Biomass and Hydro-Power. ... 2

Figure 2. 1– Inverse Square law, the lines represent the flux emanating from the source. A greater density of flux lines means a stronger field. ... 6

Figure 2. 2 - The maps show the geographical distribution of the solar radiation incident on the earth's surface each year. Depending on the shape of the sun's apparent path (solar ecliptic), the amount of radiation decreases towards the Polar Regions. ... 7

Figure 2. 3 - Global annual radiation in the United States of America ... 8

Figure 2. 4 - Energy content of the annual solar radiation reaching the earth´s surface ... 10

Figure 2. 5 - The Sun light and its route through atmosphere ... 11

Figure 2. 6 - Angle representation following the solar tecnics ... 12

Figure 2. 7 - Solar Spectrum ... 13

Figure 2. 8 - Global solar radiation for different tilts of the surface for Maryland ... 14

Figure 2. 9 - Sun Path diagram for Baltimore, Maryland ... 15

Figure 3.1 - The solar cell ... 17

Figure 3. 2 - The three generations of solar cells. First-generation are based on expensive silicon wafers. Second generation cells are based on thin films of materials such as amorphous silicon, nanocrystalline silicon, cadmium telluride or copper indium selenide. Thirds generation cells are the research goal, a dramatic increase in efficiency that maintains the cost advantage of second- generation materials ... 20

Figure 3. 3 - Solar panel composition ... 21

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Figure 3.5 - Solar Radiation for winter, differences between a fixed tilted flat plate and

two axis tracker. ... 23

Figure 3.6 - Solar radiation in summer, differences between a fixed tilted flat plate and two axis tracker. ... 23

Figure 3.7 - Off-grid / grid-connected PV Expression in the total industry ... 25

Figure 3.8 – Grid-connected PV growth rate over time ... 26

Figure 4. 1 - EU´s target for 2020 ... 28

Figure 4. 2 - Europe´s renewable targets for 2020 and 2007 performance ... 29

Figure 4.3 - State RPS policies and Non-Binding Renewable Energy Goals ... 31

Figure 4.4 - Electricity Consumption per capita in the United States, California and Maryland. As you can see, California is much more energy efficient that the other in comparison ... 33

Figure 4.5 - Residential Economic Potential of energy efficiency by end use ... 34

Figure 4.6 - Maryland´s Electricity Generation, more than a half cames from Coal ... 35

Figure 4.7 - Maryland Renewable Energy Generation ( 2007) ... 36

Figure 4.8 - Annual RPS Requirements ... 39

Figure 4.9 - Compliance fees for the companies that do not meet the RPS requirements ... 40

Figure 4.10 - 2008 Maryland Compliance RECs by Facility Location ... 40

Figure 4.11 - Tier 1 RECs Retired in Maryland by Fuel Type (2008) ... 40

Figure 4.12 - Compliance REC Market Prices. This Graph was developed by Laurence Berkeley National Laboratory based on data from Evolution Markets ... 41

Figure 4. 1 - EU´s target for 2020 ... 28

Figure 4. 2 - Europe´s renewable targets for 2020 and 2007 performance ... 29

Figure 4.3 - State RPS policies and Non-Binding Renewable Energy Goals ... 31

Figure 4.4 - Electricity Consumption per capita in the United States, California and Maryland. As you can see, California is much more energy efficient that the other in comparison ... 33

Figure 4.5 - Residential Economic Potential of energy efficiency by end use ... 34

Figure 4.6 - Maryland´s Electricity Generation, more than a half cames from Coal ... 35

Figure 4.7 - Maryland Renewable Energy Generation ( 2007) ... 36

Figure 4.8 - Annual RPS Requirements ... 39

Figure 4.9 - Compliance fees for the companies that do not meet the RPS requirements ... 40

Figure 4.11 - Tier 1 RECs Retired in Maryland by Fuel Type (2008) ... 40

Figure 4.12 - Compliance REC Market Prices. This Graph was developed by Laurence Berkeley National Laboratory based on data from Evolution Markets ... 41

Figure 5.1 - PVwatts layout, with chosen parameters ... 45

Figure 6.1 - A schematic of how the different factors contributes to the value and feasability of PV units interact with each other ... 51

Figure 6.2 Projections of oil price till 2020 ... 52

Figure 6.3 - Electricity price prediction for three different cases: High, normal and low economic growth ... 53

Figure 6.4 - Electricity generation by fuel in three cases, 2008 and 2035 ( billion kilowatthours, lable y axis ) ... 54

Figure 6.5 - Typical losses range on a Pv system... 55

Figure 6.6 - Retail price of Pv module ( $/Wp ) ... 56

Figure 6. 7 - Cash Flow for case 1 ( Profit/ Years ) ... 57

Figure 6. 8 - Cash Flow for case 2 ( Profit/ Years ) ... 57

Figure 6. 9 - Cash Flow for case 3 ( Profit/ Years ) ... 58

Figure 6. 10 - Cash Flow for case 4 (Profit/ Years) ... 58

Figure 6.11 - PV profit comparing with oil price for three cases, with a constant electricity price of 8 cents/kwh ... 59

Figure 6.12 - PV profit comparing with the oil price for three cases, with an incresing electricity cost till 10 cents/kwh ... 59

Figure 6.13 - PV profit comparing with oil price, with a constant electricity price and an increase of solar modules efficiency ... 60

Figure 6.14 - PV profit comparing with oil price, with an increasing electricity price till 10 cents/kwh and an increase on solar modules efficiency ... 61

Figure 6. 15 - PV profit comparing with oil price, with a constant electricity price and without federal incentive... 62

Figure 6. 16 - Cash flow for a PV system with energy price constant at 8 cents/kwh without federal incentive... 62

Figure 6. 17 - PV profit comparing with oil price, with a constant electricity price and without any incentive ... 63

Figure 6. 18 - Cash flow for a PV system with energy price constant at 8 cents/kwh without any type of incentive ... 63

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Figure 6. 20 - PV system installed in Vermont State ... 64 Figure 6. 21 - PV system located near Lake Geroge, NY ... 65 Figure 6. 22 - PV system located near Lake George, NY ... 65

List de Tables

Table 2. 1 - Monthly average of the global radiation in U.S. cities Kw/m2 , Data from

NASA[14]. ... 9

Table 2. 2 - Values of the albedo according to each surface ... 12

Table 4.1 - PV technology state-of-the-art and major objectives/milestones for the next 10 years (source EPIA) ... 31

Table 5.1 - Total Capital cost of a solar system with no incentives ... 43

Table 5.2 - Net cost of a solar system which are installed before Jan 1, 2009 ... 43

Table 5.3 - Net cost of a solar system which are installed on Jan 1, 2009 or after. ... 44

Table 5.4 - Fixed tilt PV system Energy production for four US cities ... 45

Table 5.5 - Energy Savings for US cities after 25 years ... 46

Table 5.6 - Capital cost of a residential solar system in 2011 ... 47

Table 5.7 - Final net cost for a residential solar system in 2011 in West Virginia ... 48

Table 5.8 - Final net cost for a residential solar system in 2011 in Maryland ... 48

Table 6. 1 - Utility function of all parameters that influence the best renewable energy choice. ... 49

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Abbreviations and Symbols

A Amperes

AC Alternating current

AZ Arizona

ARRA American Reinvestment and Recovery Act BGE Baltimore Gas and Electric

BOS Balance of system Btu British thermal unit

CA California

CCS Carbon Capture and Storage CdTe Cadmium telluride

CSI Californian solar initiative CIGS Copper Indium Gallium Selenide CPUC Californian Public Utilities commission CuInSe2 Copper-indium-diselenide

DC Direct Current

D.C. District of Columbia DOE Department of Energy DSC dye-sensitized photovoltaics EIA Energy information Agency

EU European Union

FEUP Faculdade de Engenharia da Universidade do Porto FiT Feed in Tariffs

GATS Generation Attribute Tracking System Ga-As gallium arsenide

GW Gigawatt

ITC Investment Tax Credit IOU investor-owned utilities USA United States of America

KW Kilowatt

MW Megawatt

MD Maryland

MSW Municipal Solid Waste

NSRDB National solar Radiation Data Base

NASA National Aeronautics and Space Administration NREL National Renewable Energy Laboratory

NY New York

OPEC Organization of the Petroleum Exporting Countries PBI Performance Based Incentives

PG&E Pacific Gas and Electric Company PEPCO Potomac Electric Power Company

PV Photovoltaic

REC Renewable Energy Certificates REF Renewable Energy Facilities ROI Return on investment

RPS Renewable portfolio standards

Si Silicon

SMECO Southern Maryland Electric Cooperative SREC Strategic Energy Investment Funds UMBC University of Maryland Baltimore county

V Volts

WV West Virginia

Wp Peak watts

List of Symbols

 The solar irradiation

α Degree

$ United States dollar

 Extraterrestrial radiation solar constant

CO2 Carbon dioxide  Ozone   Water  Oxygen γs Sun´s altitude  Price of electricity  Solar efficiency

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 Solar Radiation

 Incentives

Chapter 1

1.1 Introduction

The current trend line in energy consumption and supply are becoming unsustainable – economically, environmentally and socially[1]. If nothing is done, energy-related emissions of CO2 will more than double by 2050[2] and increased oil demand will heighten concerns over the security of supplies. The United States can and must change their current path, but this will take a revolution in the way they face their energy consumption and low-carbon energy technologies will have a crucial role to play. Energy efficiency, many types of renewable energy, carbon capture and storage (CCS), nuclear power and new transport technologies will all require great deployment to reach their greenhouse gas emission goals. Every major country and sector of the economy must be involved and merged together to find a solution. Different geographic locations will require different solutions. The task is also urgent if they want to make sure that investment decisions taken now do not saddle them with suboptimal technologies in the long term.

It is hypothesized that the USA will need incentives to accelerate the development of advanced clean energy technologies and to address the global challenges of energy security, climate change and sustainable development. This challenge was acknowledged by the Ministers from G8 countries, China, India and South Korea, in their meeting in June 2008 in Aomori, Japan.

1.2 Motivations and foundations

Renewable energy consumption increased by about 7% between 2007 and 2008, the inspection of Figure 1.1 shows these renewable amount for 7% of the United States total energy demand, and 9% of total electricity generation in 2008[3].

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Figure 1.1 - Total energy supply of the United S

fuels, specially from Petroleum

Figure 1.2 - Types of renewable sources that supply the U.S. in 2008, most part came from Biomass and Hydro

Source: EIA, Renewable Energy Consumption and Electricity 2008 Statistics, Table 1: U.S. Energy Consumption by Energy Source, 2004

Electricity producers including combined heat and power plants

producing electricity. About 20% of renewable energy used was biomass consumed for industrial applications (principally paper

This kind of energy is also used for transportation fuels (ethanol and biodiesel) and to provide residential and commercial space heating. The largest share of

electricity in 2008 came from biomass (7%), geothermal (5%), and solar (1 over 2007,showing more growth

followed by solar, which increased by 38% in 2008 over 2007 China is the world leader

production due to its recent massive addit Natural Gas

24%

U.S. Energy supply

Renewable Energy Supply

rgy supply of the United States, the most part comes from Fossil fuels, specially from Petroleum

Types of renewable sources that supply the U.S. in 2008, most part came from Biomass and Hydro-Power.

Source: EIA, Renewable Energy Consumption and Electricity 2008 Statistics, Table 1: U.S. Energy Consumption by Energy Source, 2004-2008 (July 2009)

including Electrical utilities, independent power producers, and combined heat and power plants, consumed 51% of total U.S. renewable energy in 2008 for About 20% of renewable energy used was biomass consumed for industrial applications (principally paper-making) by facilities producing only heat and steam. is also used for transportation fuels (ethanol and biodiesel) and to provide residential and commercial space heating. The largest share of the renewable

biomass (53%), followed by hydroelectric energy

(7%), geothermal (5%), and solar (1%)[4]. Wind-generated electricity increased by 51% in 2008 growth than any other renewable energy source. Its growth rate was followed by solar, which increased by 38% in 2008 over 2007[4].

is the world leader in total renewable energy consumption for electricity production due to its recent massive additions to hydroelectric production, followed closely

Renewable energy 7% Nuclear electric power 9% Coal 23% Petroleum 37%

U.S. Energy supply

solar 1% geothermal 5% wind 7% Hydro Power 34% biomass 53%

Renewable Energy Supply

tates, the most part comes from Fossil

Types of renewable sources that supply the U.S. in 2008, most part came

Source: EIA, Renewable Energy Consumption and Electricity 2008 Statistics, Table 1: U.S.

Electrical utilities, independent power producers, and consumed 51% of total U.S. renewable energy in 2008 for About 20% of renewable energy used was biomass consumed for ing only heat and steam. is also used for transportation fuels (ethanol and biodiesel) and to provide the renewable-generated hydroelectric energy (34%), wind generated electricity increased by 51% in 2008 energy source. Its growth rate was

in total renewable energy consumption for electricity ions to hydroelectric production, followed closely

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by the United States, Brazil, and Canada. However, the United States consumes the most non-hydro renewable energy for the production of electricity.On the other hand this country consumes twice as much non-hydro renewable energy for electricity production as Germany and more than three times as much as Spain[5].

The U.S. Energy Information Administration (EIA) [6] projects that renewable-generated electricity will account for 17% of total U.S. electricity generation in 2035, up from 9% in 2008[7]. This growth is driven mainly by the extension of Federal tax credits and the new loan guarantee program in the February 2009 American Recovery and Reinvestment Act (ARRA)[8].

EIA also projects strong growth in the use of the biofuels — ethanol and biodiesel mandated by Federal targets in the Renewable Fuels Standard (RFS).

From a global perspective, EIA projects that renewable energy will be the fastest-growing source of electricity generation through the forecast period to 2030[9]. Much of the increase is expected to be from hydroelectric power and wind power.

In general, most renewable energy power plants have less environmental impact than fossil and nuclear power plants, but society does not use them for several reasons, first Renewable Energy Technologies are capital-intensive, plants are generally more expensive to build and to operate than coal and natural gas plants. Recently, however, some wind-generating plants have proven to be economically feasible in areas with good wind resources, compared with other conventional technologies, when coupled with the renewable electricity Production Tax Credit. Second, renewable resources are often geographically remote, the best renewable resources are often available only in remote areas, so building transmission lines to deliver power to large metropolitan areas is expensive and intermittent. It can be difficult to match intermittent supply with demand.

There are three kinds of policies that may increase the use of renewable energy.

1. Tax credits such as the Renewable Electricity Production Tax Credit, a Federal incentive, has encouraged a quadrupling of wind energy capacity since 2001. EIA projections assume that the tax credits expire as specified in current law. EIA analyses indicate that extending the tax credits would result in additional generation from these resources.

2. Targets, within individual state there are Renewable Portfolio Standards (RPS). These RPS require electricity providers to generate or acquire a percentage of generation from renewable sources[10]. However, many RPS programs have “escape clauses” if renewable generation exceeds a cost threshold. Some States have delayed compliance and others lack enforcement procedures. As a result, some States may not meet their RPS goals. EIA projects that most States should ultimately be able to meet their RPS requirements [11].

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3. Markets, A number of States have built Renewable Energy Certificates/Credits (RECs) into their Renewable Portfolio Standards[10]. This allows electricity providers to sell renewable energy certificates/credits and use their proceeds for renewable projects. Some States have made REC markets mandatory, requiring electricity providers to produce or acquire renewable generation to reduce reliance on fossil fuels to generate electricity.

4. Cost of PV systems, The world economy is driven by cheap power, and Renewables are expensive, so it is mandatory that renewable prices gets lower.

1.2.1 The purpose of this Work

The short term future of fossil fuel is uncertain. Based on present global economic growth rates, fossil fuel energy resources may last a generation or two, at most, before they are exhausted or economical unbearable [12].

In 2007 and 2008, the oil price volatility has been exceptionally high: crude oil price increased from $70 per barrel in July 2007 to nearly $150 in July 2008 (the situation was extremely tense during that summer) and stayed in the range of $90 to $150 during the first half of 2008, while dropping to $40 later on. In early 2009, due to the economic recession and despite several OPEC's production reduction, it was on average at $45.

There are two forces driving change: Clean energy and environmental concerns and peak oil, as a result, the current energy system will come to an end. Ecological and climate concerns are an additional reason for the limited future of fossil fuel use. These concerns may force countries to give up present energy system before physically exhausting the fossil fuel energy resources. Alternative energy policies, especially a deliberate effort to promote the use of renewable energy resources, are inevitable. The sun is the Earth's greatest energy resource, and it is inexhaustible for as long as the solar system exists. Therefore, the future of our energy needs lies in renewable energy resources.

Moving from global point of view this dissertation will focus down on a single university community.

The University of Maryland Baltimore County (UMBC) is an university of 12268 students and 1018 faculty. It is located at 39° 15′ 19.8″ N of Latitude and 76° 42′ 40.52″ W of longitude at the East Coast of the USA in Maryland.

This dissertation focuses on the direct implementation of renewable energy sources for this community.

This work will present the best renewable energy source to implement for Central Maryland.

With so many sources we have in the market, I propose to find out what is the most efficient one and what economical benefit will it give to UMBC

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Chapter two will present an overview about radiation in world and focus on the USA, such as its specifications and on a slant. I also will talk about the sun, and the energy that came to us from it.

The chapter three will focus on the Photovoltaic energy and its effect.

Then it will be explained the photovoltaic composition, starting with the solar cell, then the solar module/ solar panel and solar trackers.

Finally it will be discuss about grid connection or off grid connection, explaining in detail the two types of exploration.

In chapter 4 it will be presented the European case versus the United States case, and then it will be focus on Central Maryland.

Chapter 5 presents the economic study of installing one of these systems in several US cities, always comparing the result with central Maryland.

With this MS dissertation I tried to contribute for the implementation of these renewable energy systems at the UMB, and tried to help choosing the best time for it.

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Chapter 2

2.1 Solar Radiation

Overview

The term for solar radiation striking a surface at a particular time and place is insolation. Insolation is a measure of solar radiation energy received on a given surface area in a given time, it is expressed as a number of watts per square meter ( W/m2 ) and usually presented as an average daily value for each month.

The solar radiation outside the atmosphere changes the intensity by the distance between the sun and earth. In a full year it can vary from 1.47 × 10_{ and 1.52 × 10}_. Due to this, the solar irradiation
_ can vary between 1325 / _{and 1412 / . The} average value is typically defined as the solar constant,
_= 1367 / . [13]

The inverse square law states that radiation energy is reduced in proportion to the inverse square (  ∝ !

"# ) of the distance “r” from the sun as can be seen in Figure 2.1. The

Figure shows a schematic of the radiation being projected from the sun. As the one moves from the radiation source, the energy is reduced by the power of 2. Thus as showing in the figure, moving twice the distance from the sun results in %

& the energy.

Figure 2. 1– Inverse Square law, the lines represent the flux emanating from the source. A greater density of flux lines means a stronger field.

Meanwhile, just a small part of the total amount of solar radiation hits the earth surface. The atmosphere reduces the solar radiation through dispersion that includes reflection, absorption and scattering. Reflection and absorption reduce insolation scattering

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changes it from direct to diffuse. Total irradiation level ( direct plus diffuse ) on earth reaches approximately 1000 W/ _{at midday, in good climacteric conditions ( at normal} incidence ), and at any location. By adding the total amount of solar radiation that insides in the earth surface during one year, we get the annual global irradiation, measured in KWh/ _{. This parameter varies with the region of the globe of interest, as shown in Figure} 2.2[14].

The insolation that strikes the earth’s surface near the poles is reduced because of the high incidence angle. This is the cosine effect[15]. If we tilted a solar collector ( latitude tilt ) the collector would receive almost as much insolation as it would if it were located at the equator. The influence of the tilt will be explained further in the dissertation.

Inspection of Figure 2.2 shows the total radiation specific to geographic locations in the western hemisphere.

Figure 2. 2 - The maps show the geographical distribution of the solar radiation incident on the earth's surface each year. Depending on the shape of the sun's apparent path

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The solar radiation in some southwester regions of the United States may reach 2100 KWh/m2 _{or more per year, while the Eastern side excluding Florida only reaches less than} 1700KWh/m2_.

Table 2.1 and Figure 2.3 shows radiation data specific to cities within the USA as a function of month

Figure 2. 3 - Global annual radiation in the United States of America[16]

This map shows the general trends in the amount of solar radiation received in the United States and its territories. It is a special interpolation of solar radiation values derived from the 1961-1990 National solar Radiation Data Base ( NSRDB ). The dots on the map represent the specific 239 sites of the NSRDB which are presented in table 2.1. Table 2.1 presents schematic city locations as well as the measured monthly data.

Maps of average values are produced by averaging all 30 years of data for each site. Maps of maximum and minimum values are composites of specific months and years for which each site achieved its maximum or minimum amounts of solar radiation.

Though useful for identifying general trends, this map should be used with caution for site-specific resource variations in solar radiation not reflected in the maps can exist, introducing uncertainty into estimates. Also, insolation for tilted surfaces and tracking surfaces would be greater.

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State City Latitude Longitude Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year Avg

(kw/'(_/day) AL Birmingham 33' 34" N 86' 45" W 2.29 3.31 4.04 5.14 5.92 5.98 5.81 5.7 4.8 3.93 2.96 2.25 4.34 AK Anchorage 61' 10" N 150' 1" W 0.21 0.76 1.68 3.12 3.98 4.58 4.25 3.16 1.98 0.98 0.37 0.12 2.09 AR Little Rock 32' 25" N 94' 44" W 2.36 3.39 4.01 5.32 5.71 6.19 6.15 5.85 5.25 4.17 2.95 2.25 4.46 AZ Phoenix 33 ' 26" N 112' 1" W 3.25 4.41 5.17 6.76 7.42 7.7 6.99 6.11 6.02 4.44 3.52 2.75 5.38 CA Los Angeles 34' N 118' W 3.09 4.25 5.09 6.58 7.29 7.62 7.45 6.72 6.11 4.42 3.43 2.72 5.4 CA San Francisco 38' 31" N 121' 30" W 2.35 3.33 4.42 5.95 6.84 7.39 7.55 6.51 5.75 3.92 2.65 2.06 4.89 FL Miami 25' 48" N 80' 16" W 3.72 4.61 5.42 6.4 6.61 6.29 6.26 6.08 5.47 4.84 3.96 3.46 5.26 GA Atlanta 33' 39" N 84' 26" W 2.31 3.37 4.08 5.2 6.02 6.01 5.81 5.59 4.76 3.95 2.98 2.33 4.37 HI Honolulu 21' 20" N 157' 55" W 4.38 5.15 5.99 6.69 7.05 7.48 7.37 7.07 6.51 5.46 4.41 4.01 5.96 IL Chicago 41' 53" N 87' 38" W 1.5 2.45 3.2 4.48 5.56 6.07 5.68 5.27 4.51 3.07 1.69 1.26 3.72 KS Kansas City 39' 12" N 94' 36" W 2.06 2.89 3.62 4.92 5.58 6.17 6.21 5.59 4.9 3.49 2.2 1.75 4.11 KY Louisville 38' 11" N 85' 44" W 1.71 2.65 3.32 4.73 5.38 6.08 5.79 5.35 4.8 3.42 2.1 1.56 3.9 LA New Orleans 29' 37" N 90' 5" W 2.64 3.73 4.67 5.8 6.6 6.15 6.09 5.7 5.13 4.48 3.49 2.68 4.76 MA Boston 42' 22" N 71' 2" W 1.66 2.5 3.51 4.13 5.11 5.47 5.44 5.05 4.12 2.84 1.74 1.4 3.58 MD Annapolis 38' 35" N 76' 21" W 1.96 2.8 3.71 4.55 5.54 6.03 5.77 5.34 4.48 3.4 2.37 1.81 3.98 ME Portland 45' 36" N 122' 36" W 1.38 2.33 3.49 4.57 5.46 6.09 6.64 5.78 4.8 2.79 1.41 1.1 3.82 MI Detroit 42' 25" N 83' 1" W 1.43 2.33 3.19 4.34 5.44 5.98 5.64 4.99 4.25 2.73 1.52 1.14 3.58 MO St.Louis 38' 45" N 90' 23" W 2.02 2.82 3.52 4.97 5.56 6.21 6.05 5.63 4.91 3.55 2.21 1.73 4.09 MN Minneapolis 44' 53" N 93' 13" W 1.6 2.61 3.3 4.55 5.44 5.86 5.77 5.12 4.12 2.9 1.62 1.34 3.68 MS Jackson 42' 16" N 84' 28" W 1.47 2.41 3.22 4.33 5.46 5.93 5.57 4.99 4.3 2.78 1.55 1.17 3.59 MT Billings 45' 48" N 108' 32" W 1.55 2.57 3.52 4.82 5.63 6.45 6.39 5.75 4.67 3.19 1.77 1.3 3.96 MT Great Falls 43' 33" N 96' 42" W 1.3 2.36 3.41 4.84 5.56 6.18 6.44 5.53 4.4 2.9 1.53 1.11 3.79 NV Las Vegas 36' 18" N 115' 16" W 3.02 4.13 5.05 6.57 7.25 7.69 7.37 6.42 6.08 4.26 3.18 2.6 5.3 NY New York 41' N 74' W 1.67 2.37 3.41 3.93 5.11 5.48 5.26 5.01 4.05 2.85 1.82 1.4 3.53 OH Columbus 39' 16" N 85' 54" W 1.64 2.57 3.26 4.63 5.4 6.08 5.73 5.29 4.74 3.29 1.96 1.45 3.83 PA Philadelphia 39' 53" N 75' 15" W 1.85 2.62 3.6 4.33 5.44 5.91 5.64 5.3 4.38 3.23 2.21 1.66 3.84 TN Nashville 36' 7" N 86' 41" W 1.94 2.9 3.54 4.76 5.57 5.9 5.86 5.62 4.63 3.53 2.45 1.82 4.04 TX Houston 29' 59" N 95' 22" W 2.47 3.5 4.4 5.59 6.03 6.45 6.36 6.07 5.46 4.61 3.3 2.44 4.72 UT Salt Lake City 40' 46" N 111" 52" W 2.23 3.15 4.09 5.57 6.26 6.98 6.86 5.98 5.39 3.68 2.29 1.97 4.53 VA Washington 38' 51" N 77' 2" W 1.95 2.8 3.66 4.46 5.42 5.88 5.63 5.22 4.38 3.36 2.34 1.79 3.9 VT Montpelier 44' 16" N 72' 35" W 1.58 2.54 3.5 4.05 5 5.24 5.37 4.92 3.79 2.46 1.52 1.28 3.43 WA Seattle 47' 32" N 122' 18" W 1.14 2.04 3.23 4.26 5.19 5.75 6.27 5.46 4.43 2.5 1.21 0.9 3.53 WV Charleston 38' 22" N 81' 36" W 1.75 2.64 3.34 4.26 5.2 5.67 5.49 5.19 4.26 3.19 2.15 1.62 3.73

Table 2. 1 - Monthly average of the global radiation in U.S. cities Kw/m2 , Data from NASA[14].

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2.2 The Sun

The Sun´s energy comes to us by radiation, and it is the base of all life on the planet Earth. In the sun´s core a fusion process

this process, part of sun´s mass is transformed into energy. So, the Sun is a huge fusion reactor.

Due to the great distance between the sun and the earth, only a small part (approximately two parts per mil

the earth´s surface. That radiation is equal to

Figure 2.4 presents a chart showing the total energy requirement of the earth in comparison to the total sunlight energy rea

Figure 2. 4 - Energy content of the annual solar radiation reaching the earth´s surface

The total quantity of sun´s energy that reaches the earth surface corresponds approximately to ten thousand

0,01% of that energy to meet the world´s energy needs According to the International

reach 21.8TW by the year 2030, up from 13.7TW

planet is 173,000TW, of which 120,000TW strikes the surface. It on Earth. To meet our 2030 demand

emerged lands with 10% efficiency The success of solar power wi do when the sun goes down?'

The Sun´s energy comes to us by radiation, and it is the base of all life on the planet Earth. In the sun´s core a fusion process converts hydrogen atoms into helium atoms. During this process, part of sun´s mass is transformed into energy. So, the Sun is a huge fusion

Due to the great distance between the sun and the earth, only a small part (approximately two parts per million) of the solar radiation produced by the sun impinges on the earth´s surface. That radiation is equal to 1  10! _)/*+,-.

Figure 2.4 presents a chart showing the total energy requirement of the earth in comparison to the total sunlight energy reaching the earth´s surface

Energy content of the annual solar radiation reaching the earth´s surface

The total quantity of sun´s energy that reaches the earth surface corresponds housand times the global demand for energy. So we will just need meet the world´s energy needs.[17]

According to the International Energy Agency (IEA)[18], our total energy

2030, up from 13.7TW today. But the solar radiation shining on this 120,000TW strikes the surface. It is the primary energy source demand would only require the covering of 0.6 per

ncy solar systems.

The success of solar power will depend on the answer to the question: 'What do you World´s energy

requirements

Rest of sunlight energy reaching the earth

The Sun´s energy comes to us by radiation, and it is the base of all life on the planet converts hydrogen atoms into helium atoms. During this process, part of sun´s mass is transformed into energy. So, the Sun is a huge fusion

Due to the great distance between the sun and the earth, only a small part lion) of the solar radiation produced by the sun impinges on

Figure 2.4 presents a chart showing the total energy requirement of the earth in

Energy content of the annual solar radiation reaching the earth´s surface

The total quantity of sun´s energy that reaches the earth surface corresponds energy. So we will just need

nergy demand will the solar radiation shining on this is the primary energy source require the covering of 0.6 per cent of

question: 'What do you Rest of sunlight energy

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2.2.1 Solar radiation Specifications

Radiation is an energy transfer process that requires neither physical medium for its propagation, nor contacts with the radiant body. Solar radiation is the energy emitted by the Sun as electromagnetic waves.

The solar radiation may be observed as global solar radiation corresponding to the total energy emitted by the sun and reaching the Earth. The more common observations consists of measurements of the radiation reaching an horizontal surface, consisting of both radiation from the Sun ( direct solar radiation ) and that reaching the instrument by scattering in the atmosphere and clouds ( diffuse sky radiation ).

When Solar radiation penetrates on the earth´s atmosphere, it suffers various and selective losses. At 150km of altitude the radiation spectrum has almost 100% of its original energy, but when reaches 88 km, it has lost, much of the ultraviolet radiation[19].

The Solar light that hits earth´s surface is composed by a direct fraction and a diffuse fraction. It can be seen on the next Figure 2.5 an illustration of the three types of radiation reaching the earth’s surface

The direct radiation comes from sun´s direction, producing well shaped shadows in every object. Alternatively the diffuse radiation does not have a specific direction. There is also the albedo radiation that originates from the reflection of the incident radiation on the surface. It varies according to the composition of the earth´s surface. The greater albedo is, more solar light reflection results.

Figure 2. 5 - The Sun light and its route through atmosphere

Considering that Central Maryland´s surroundings are green, full of pastures with concrete roads, it can be assumed the value of 0,2 for the albedo.

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Surface Albedo Surface Albedo

Pastures( July, August) 0,25 Asphalt 0,15

Grass 0,18…0,23 Forest 0,05…0,18

Dry Pastures 0,28…0,32 Heather and sand areas 0,1…0,25

Tilled Fields 0,26 Water surface (γs>45º) 0,05

Barren Land 0,17 Water surface (γs>30º) 0,08

Rocks 0,18 Water surface (γs>20º) 0,12

Smooth Concrete 0,3 Water surface (γs>10º) 0,22

Concrete under the effect of erosion

0,2 Fresh snow 0,8…0,9

Plain Cement 0,55 Old snow 0,45…0,7

Table 2. 2 - Values of the albedo according to each surface

2.2.2 Angle definition

To evaluate the radiation data and the energy produced by the solar installations, the exact location of the Sun with respect to the receiver on the earth must be determined. Figure 2.6 presents key geometric features to evaluate sun´s radiation projected to an observer. The exact Sun location can be defined in each place by its altitude and azimuth. By convention in the solar energy field, the south is usually referred as α = 0º. The negative symbol is assigned to the East angles α = -90º and the positive symbol to west angles α = 90º.

Figure 2. 6 - Angle representation following the solar tecnics

The solar light takes the shorter pathway through the atmosphere, when the sun´s position is perpendicular to earth´s surface. If the solar incidence angle is lower, the

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pathway though the atmosphere is longer. In this second position it leads to a higher solar radiation absorption and dispersion. This implies a less irradiance.

In its pathway trough the atmosphere the irradiance is reduced several means by:

• Atmospheric reflection

• Molecular absorption ( ,  ,  ,  )

• Raleigh´s scattering

• Mie´s scattering

Figure 2.7 presents the extraterrestrial radiation, the highest one, then it is reduced by the atmosphere and we have the global radiation that is composed by the direct, diffuse and albedo radiations. As can be seen in the figure, the direct radiation is just a part of the extraterrestrial radiation.

Figure 2. 7 - Solar Spectrum [20]

2.2.3 Incident solar radiation in a slant

The solar radiation is always higher for an area that is perpendicular to the solar radiation, than in a horizontal area with same dimensions. As the azimuth and the solar height changes during the day and the year, the solar incidence angle changes for any fixed surface ( e.g. roofs). The analysis of the annual radiation on an arbitrary fized surface helps to select the most convenient location to set up the system.

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Next figure 2.8 shows the percentage of the solar radiation and relates it with the tilt of the surface and the azimuth.

Figure 2. 8 - Global solar radiation for different tilts of the surface for Maryland [21]

The Solar installation’s orientation results in different levels of irradiation. In Central Maryland the best orientation of an installation is to the south at 39º ( latitude tile ), As can be seen in figure 2.8 [21].

The construction of solar installations in inclined roofs, with orientations different than the optimum results in less energy production due to the radiation reduction.

The utilization of a building´s facade to integrate this solar technologies (inclination angle α _{= 90º ) implies a less energy production, due to the significant insolation reduction. In}

this case,available solar insolation, building architecture and other design aspects have a great role in the final decision of how to construct the building.

A solar collector could be tilted twice per year or fixed to enhance summer or winter production. The summer position gives us a greater portion of the global annual irradiation. Its optimal inclination is 12,6º.

The winter has the least sun, so you want to make the most of it. The tilt should be designed so that the panel points directly at the sun at noon. The optimal angle is 65,1º.

Figure 2.9 shows the reason for this angles being different on summer and winter, as can be seen, we have much more sun during the summer months that we have in the winter.

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Figure 2. 9 - Sun Path diagram for Baltimore, Maryland

So, fixed system used only in the summer, has a small inclination angle. Adjustable PV systems exploit both solar positions to produce more energy.

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Chapter 3

3.1 Photovoltaic solar Energy

Photovoltaic systems are solar energy systems that produce electricity directly from sunlight. Photovoltaic (PV) systems produce clean, reliable energy without consuming fossil fuels whilst producing energy and can be used in a wide variety of applications. Despite Solar PV cost energy to be produced, that´s just a small part of what they can produce. A common application of PV technology is providing power for watches and radios. On a larger scale, many utilities have recently installed large photovoltaic arrays to provide consumers with solar generated electricity, or as backup system for critical, industrial and medical equipment.

A study by National Renewable Energy Laboratory indicates that photovoltaic (PV) modules covering 0.4% of U.S land area could potential supply all of the nation’s electricity assuming intermediate efficiency [22].

3.1.1 The photovoltaic effect

The photovoltaic effect, which is the transformation of solar energy (“photon”) into electricity (“Volt”) was discovered in 1839, by the French physicist A. BECQUEREL.

Its use in industry only began in the 1960’s, mainly for space satellite applications. Since then, other applications have been invented to respond initially to industrial needs, but eventually to the needs of private individuals.

The photovoltaic cells are made of a semiconductor material, usually silicon is the primary phase to which dopping elements are added to create an appropriate material macrostructure to establish the photovoltaic effect, ie, direct conversion of energy from photons into DC electricity.

When a cell is exposed to the sun’s electromagnetic rays, the photons release electrons from the atoms in the crystal, thereby generating electrons (N-charge) and holes (P-charge).

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Figure 3.1 - The solar cell

These charges are kept separate by an electrical field ( the P-N junction ) that forms a “potential barrier”.

Once the P and N charges are isolated, the circuit between the 2 zones (P and N) can be closed, causing the electrons to move and thus create an electric current.

The cell, the smallest element or unit of the photovoltaic system, produces typically 1,5Wp ( peak watts ) electric power, corresponding to a 0, 5 V and 3A. To achieve powers, the cells are connected in series or parallels, forming modules, typically with standard system powers of 50 to 100 Wp.

Today, the photovoltaic systems are used in a wide range of applications such as:

• Medium power applications ( dozens or hundreds of kilowatt )

o Rural electrification: domestic loads supply in remote places, water pump and irrigation.

o Decentralized production connected to the electric grid

• Small power productions ( tenths or units of kilowatts )

o Watches and calculators

o Motor vehicles accessories, for example, supply of refrigeration fans for cars, or battery charge for camping vehicles

o Road signs or parking meters

o Emergency telephones, TV and cell phones transmitters

o Medical fridges in remote places

In many of these applications, the photovoltaic systems are lower cost than other alternative production means, particularly in small power applications, where it is expensive

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to connect to the power grid. Photovoltaic systems were originally developed by the aerospace industry where they offer a significant competitive advantage for powering space satellites.

3.1.2 Photovoltaic materials

The three basic types of solar cells made from silicon are single-crystal,

polycrystalline, and amorphous.

Single-crystal cells are made in long cylinders and sliced into round or hexagonal wafers. While this process is energy-intensive and wasteful of materials, it produces the highest-efficiency cells—as high as 25%[23] in some laboratory tests. Because these high-highest-efficiency cells are more expensive, they are sometimes used in combination with concentrators such as mirrors or lenses. Concentrating systems can boost efficiency to almost 30 percent. Single-crystal accounts for 29% of the global market for PV.[24] Polycrystalline cells are made of molten silicon cast into ingots or drawn into sheets, then sliced into squares. While production costs are lower, the efficiency of the cells is lower too— around 15%. Because the cells are square, they can be packed more closely together. Polycrystalline cells make up 62% of the global PV market.[24] Amorphous silicon (a-Si) is a radically different approach. Silicon is essentially sprayed onto a glass or metal surface in thin films, making the whole module in one step. This approach is by far the least expensive, but it results in very low efficiencies- only about 5% [24].

A number of exotic materials other than silicon are under development, such as gallium arsenide (Ga-As), copper-indium-diselenide (CuInSe2), and cadmium-telluride (CdTe). These materials offer higher efficiencies and other interesting properties, including the ability to manufacture amorphous cells that are sensitive to different parts of the light spectrum. By stacking cells into multiple layers, they can capture more of the available light. Although a-Silicon will forever have efficiencies so low that system costs are dominated by land, installation and maintenance and they are not real contenders.

3.1.3 Photovoltaic cells

Currently solar cells are classified into three generations. The generations indicate the order of which each became fiscally and industrially important. At present there is concurrent research into all three generations.

The first generation made from bulk silicon, technologies are still the most highly represented in commercial production accounting for over 85% of all cells produced.[25]

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These types of cells consist of large-area, high quality and single p-n junction devices and involve high energy and labor inputs.

Single junction silicon devices are approaching the theoretical limiting efficiency of 33% and achieve cost parity with fossil fuel energy generation after a payback period of 5-7 years[26] .They are not likely to achieve lower than US$1/Peak Watt(Wp).

Second generation materials have been developed to address expanding energy requirements and production costs of first generation cells. Also known as thin film technologies, alternative manufacturing techniques such as vapor deposition, electroplating, and use of Ultrasonic Nozzles are advantageous as they reduce high temperature processing significantly.

Some studies states that it is produced at least five time of the energy that is used to produce a solar panel[27].

It is commonly accepted that as manufacturing techniques evolve production costs will be dominated by constituent material requirements, whether this be a silicon substrate, or glass cover.

Second generation technologies have been gaining market share since 2008. Such processes can bring costs down to a little under US$0.50/Wp [28]but because of the defects inherent in the lower quality processing methods, the efficiencies are reduced when compared to first generation cells.

The most successful second generation materials have been cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon and micro amorphous silicon. These materials are applied in a thin film to a supporting substrate such as glass or ceramics reducing material mass and therefore costs.

These technologies do hold promise of higher conversion efficiencies. CIGS, DSC (dye-sensitized photovoltaics ) and CdTe offer significantly cheaper production costs.

Among major manufacturers there is certainly a trend toward second generation technologies, however commercialization of these technologies has proven difficult. In 2007 First Solar produced 200 MW of CdTe solar cells making it the fifth largest producer of solar cells in 2007 and the first ever to reach the top 10 from production of second generation technologies alone. Nanosolar commercialised its CIGS technology in 2007 with a production capacity of 430 MW for 2008 in the USA and Germany. Honda Soltec Co. Ltd also began to commercialize their CIGS base solar panel in 2008.

In 2007, CdTe production represented 4.7% of total market share, thin film silicon 5.2% and CIGS 0.5%[29]. The current record efficiencies for CdTe and CIGS thin film PVs are 16,5%[30] percent and 19.9%[31] respectively.

Third generation technologies aim to enhance poor electrical performance of second generation (thin-film technologies) while maintaining very low production costs. Current

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research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques.

Third generation solar cells can exceed the theoretical solar conversion efficiency limit for a single energy threshold material, due to its nanotechnologie construction.

The threshold was calculated in 1961 by Shockley and Queisser as 31% under 1 sun illumination and 40.8% under maximal concentration of sunlight (46,200 suns, which makes the latter limit more difficult to approach than the former).

There are a few approaches to achieving these high efficiencies[32]:

• Multi-junction photovoltaic cell (multiple energy threshold devices).

• Modifying incident spectrum through up conversion of UV into the conversion band or down conversion of the infrared into the conversion band.

The three generations of solar cells will undoubtedly continue into the fourth generation once all options for third generation solar cells are exhausted.

Figure 3.2 shows efficiency per dollars for commercially available PV units, third generation as can be seen has a great efficiency, but is not yet implemanteted in the market, due to its completely technology.

Figure 3. 2 - The three generations of solar cells. First-generation are based on expensive silicon wafers. Second generation cells are based on thin films of materials such as amorphous silicon, nanocrystalline silicon, cadmium telluride or copper indium selenide.

Thirds generation cells are the research goal, a dramatic increase in efficiency that maintains the cost advantage of second- generation materials [25]

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3.2 Module/ solar panel

A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module. Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module.

Figure 3.3 shows how an individual cell is brought together to create a module. These modules are then connected in series to create an array as shown in the Figure.

Figure 3. 3 - Solar panel composition

Multiple modules can be wired together to form an array. In general, the larger the area of a module or array, the more electricity that will be produced. Photovoltaic modules and arrays produce direct-current (dc) electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination

Today's most common PV devices use a single junction. In a single-junction PV cell, only photons whose energy is equal to or greater than the band gap of the cell material can free an electron for an electric circuit. In other words, the photovoltaic response of

single-22 writing

junction cells is limited to the portion of the sun's spectrum whose energy is above the band gap of the absorbing material, and lower-energy photons are not used

One way to get around this limitation is to use two (or more) different cells, with more than one band gap and more than one junction, to generate a voltage. These are referred to as "multijunction" cells (also called "cascade" or "tandem" cells). Multijunction devices can achieve a higher total conversion efficiency because they can convert more of the energy spectrum of light to electricity.

3.3 Solar trackers

A solar tracker is a system that tracks the sun, in order to have always the best angle to receive the maximum of radiation. Figure 3.5 shows a schematic that explains how it works, there´s an east and west sensor that give an idea of where is the sun, controlling the motor to have the best angle in each period of the day.

Figure 3. 4 - Sun tracker

The solar tracking system achieves greater radiation gains on days with high insulation and large direct radiation component. In summer a tracking system achieves around 50% radiation gains on sunny days and in winter 300% more compared to a horizontal surface.[33]

And as shown on the following Figures 3.5 and 3.6, the two axis trackers can have great gains of radiation with their implementation.

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Figure 3.5 - Solar Radiation for winter, differences between a fixed tilted flat plate and two axis tracker[16].

Figure 3.6 - Solar radiation in summer, differences between a fixed tilted flat plate and two axis tracker[16].

The majority of energy gains when using a tracking system are obtained in the summer, due to the absolute energy yield that is higher than in the winter, and also because the number of cloudy days is much higher in winter.

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There are different types of tracking systems; the most commons are single axis and dual axis tracking. The main difference between these two systems is that with the dual axis system the system always maintains the optimum alignment to the sun.

By the other hand, the single axis tracking system is often preferred, because the dual axis is technically more complicated. This system can either track the sun´s daily path, moving east to west, or annual path, moving north to south. See figures 3.5 and 3.6.

A system that tracks the annual path is relatively easy to implement. To do this, the tilt angle of the array needs to be adjusted at relatively large intervals of time. In some cases this can be done manually.

If the tracking system fails, the PV array may become stuck in a poor-yield position, with the result that the energy yield will be severely reduced until fault is repaired [17].

In the past years the increase of the energy yield provide by this tracking systems does not compensate the increased investment costs of a tracker system. So these technologies have not been widely used.

The single axis tracking systems are more cost-effective, and can be economically viable where there is a good feed in tariffs for solar-generated electricity.

3.4 Grid connection and Off-Grid connection

Installation of grid-connected solar photovoltaic system (PV), has been tripled between 2000 and 2008 [34], but still represents a very small part of overall U.S. electricity generation [34]. Countries such as Germany and Japan are the leaders in solar usage despite a large growth in solar energy in US [34].

The PV industry is changing primarily, not in terms of the technology, but in terms of volume and application focus. The past five years brought significant change in the industry landscape, moving it from megawatts to gigawatts and from unprofitability to higher then lower then higher margins. The industry is recently facing an economical downturn[35]. The market for PV systems is certainly volatile, but the volatility is on the grid-connected side of the market which has experienced stupendous growth since 2004[36].

In the rush for ever-larger installations, the off-grid market has been largely ignored. Recently, rapid change is the order of the day, leaving the industry and its stakeholders struggling to adapt. For example, in the early 2000s a system was considered when it was in the 500kWp to 1MWp range, with the 1MWp system being an upper bound outliner. Multi-megawatt grid-connected systems began to be developed in the mid-2000s, entirely due to the German feed-in tariff ( FIT )[37]. This type of tariffs will be explained in detail on chapter 4. As the FiT incentive model moved through Europe system sizes increased from

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1MWp to plus than 20MWp. Few industry participants thought the trend to multi-megawatt systems would last. Multi-megawatt installations require stable, long-lived, and generous incentives to be viable. With its stable and long-term incentive structure, these large systems have flourished in Europe. But one significant change (such as the threatened retroactive degression to Spain's FiT) would likely decrease the investor´s enthusiasm worldwide because it would add risk to all incentives.

An off-grid solar system, is an autonomous system that operates by itself disconnected from the grid.

So, what are the off-grid solar systems advantages during these heady times of multi-megawatt installations?

First, off-grid solar systems, particularly in remote areas are unlikely to have grid access. Second, they do not require the same sort of incentives as does the grid-connected application because PV is competing with expensive diesel generators. Figure 3.7 shows the size of the of-grid market compared with the entire industry [38].

Figure 3.7 - Off-grid / grid-connected PV Expression in the total industry[38]

The reason for this kind of system being so less expressive in the market is mainly because when going off grid, the storage of energy is a major concern. It will require space for the battery bank. This is not always possible when living in the city and for some might be difficult when living in the suburbs.

In addition to the lack of space for the battery bank, some might experience limited area to place their solar panels.

5%

95%

Off-grid / grid-connected PV Expression

in the total industry

Total off-grid (MWp) Grid connected(MWp)

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For the PV industry, periods of strong growth have been driven by the grid-connected application. Meanwhile, the off-grid market continues to keep its share, even if it is at slower growth rates and a significantly lower share of market.

For the future it is predictable that the market for off-grid products won´t experience boom times similar to the grid-connected application. Affordability remains a barrier for the developing world, and unfortunately, polluting energy sources can be cheaper initially (though potentially more costly as time goes on). There is often a disinclination among populations in rural developing areas of the world to accept solar electric systems as a substitute for utility grid electricity. Solar electricity is seen as different, perceived not as good as the utility-electricity available in urban areas. The perception is that if the solar electric systems are accepted, the opportunity for connection to the utility grid (and have electricity of the same quality as the urban areas) will not be forthcoming. One interesting point is that in many areas of the developing world electricity in urban areas is less reliable than solar home systems, or village power systems in the rural areas. Major funding agencies have come to accept PV power supplies as fully reliable for many social projects in the developing countries. A number of additional agencies have also come into existence, combining an understanding of regional problem solving with novel new approaches to private and public funding.

For industrialized parts of the world, there is demand for vacation homes, campers, telecommunication needs, and others. Though the market for the smaller modules used in these applications is, again, unlikely to boom, it certainly could grow faster with the right product introduction at the right time. Many industries, after all, would enjoy an 8%-11% compound annual growth rate. Figure 3.8 provides application growth rates over time.[38]

Figure 3.8 – Grid-connected PV growth rate over time[39] 0% 10% 20% 30% 40% 50% 60% 1999-2004 2004-2009 2009-2014 Conservative 20092014 -optimistic

Grid-connected PV growth

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Now that the market for grid-connected solar products has driven PV industry demand into the gigawatt range, the subject of off-grid solar products rarely arises at conferences. This is unfortunate because they have also great potential. As stated for the developing world, photovoltaic technology offers the best, cleanest, and perhaps only true chance for electrification due to the lack of an industrial basis and structure. For the industrialized world there is sufficient need for reliable electricity that does not require grid connection. For cities looking to integrate solar in their mix, PV can provide a long-term answer for the need to provide street and freeway lights[40].