1 Introduction
Photovoltaics (PVs) is the direct conversion of light into electricity. Typically, this means generation of electricity from sunlight, a renewable energy process without release of pollution or greenhouse gases. PV is one of the renewable energy sources that offers the potential to replace burning of fossil fuels and, therefore, to slow the growing effects of global climate change.
When the author began working in PV at Solarex in 1976, the entire worldwide annual production of PV modules was less than 100 kW. Numerous groups [1, 2] are predicting that more than 100 GW of PV modules will be produced and shipped in 2019. That is a growth in production volume of more than six orders of magnitude across a span of little more than 40 years. PV has gone from a small niche business, providing electricity for remote power applications to a mainstream, electric power producing industry. It has been estimated that PV provided approximately 3% of the world's electricity in 2018. PV and wind have been the two fastest growing sectors in commercial electricity production in the world for a number of years [3].
So why has PV been so successful? Certainly, the fact that PV is a clean, non‐polluting source of electricity is very important. The fact that the prices for PV modules have fallen dramatically from more than $40 per peak watt in the 1970s to around $0.40 per peak watt today [4] has also certainly helped. Today's price level makes PV one of the lowest‐cost sources of electricity in the world. However, none of these would really matter if PV technology, in general and PV modules in particular, were not very reliable and have long service lives. How many products do you know of that have to work outdoors in all kinds of weather and yet are provided with a 25‐year warranty? Since PV is a solid‐state process, there are no moving parts and very little to wear out so PV modules should be able to operate for a long time. Longevity is critical to the value of PV since the investment to install a PV system is made in the beginning and then the income accumulates over years as the electricity is sold. Without reliable PV products, no one would be risking billions of dollars to purchase and install the PV power systems that have made PV the success it is today.
This book is about Photovoltaic Module Reliability. Modules are usually the most reliable component within a PV system, but it is important to continue to study their reliability. Modules are the most expensive and by far the hardest to replace component in the PV system if something goes wrong. Any large‐scale failure of modules could result in dramatic reductions in growth of the PV power industry. This book has been written from a historical prospective to help the reader understand how PV modules were able to achieve 25‐year lifetimes and a well‐deserved reputation for reliability. Knowing how this level of reliability was achieved, can help in understanding how to maintain similar reliability in the future with new generations of products.
This introductory Chapter will provide some background for the in‐depth look into module reliability in subsequent chapters. The first section provides a brief history of PV. The second section discusses some of the different types of materials and devices used for commercial solar cells. The third section covers module packaging, including their purpose; the types of structures used for different modules, and a brief introduction to the types of materials used in today's commercial PV modules. The next section discusses what the author means by the reliability of PV modules as well as introducing several other terms that will be used throughout the book. The final section in this first chapter provides a brief overview of what is contained in each of the subsequent chapters.
1.1 Brief History of PVs
To outsiders, it may seem like PV appeared quickly out of nowhere. In reality, the technology has been under development for a long time. Let's take a brief look at the history of PV.
Edmond Becquerel discovered the PV effect in 1839. So, PV is certainly not a new technology [5].
Albert Einstein published a paper explaining how the PV effect worked in 1905. In 1921, he received the Nobel Prize in Physics for his discovery of how the PV effect works [6]. PV was a lot less controversial than relativity at that time.
In 1954, a group at Bell Laboratories developed the first practical silicon solar cells [7].
The Bell Laboratories development was just in time for PV to provide power for all of the US satellites designed to perform in space for more than a few days. Vanguard 1 launched in March 1958, was powered by PV and continued to transmit data back to earth for six years [8], while purely battery‐powered satellites typically only provided data for a few months. Most US satellites continue to use PV as their primary energy supply. This means that your satellite weather forecasts, long‐distance communications and TV signals have always been powered by PV. Most of us have been taking advantage of PV in this way for decades.
In the 1970s, a terrestrial PV business was developed by two small companies (Solarex Corporation and Sensor Technology) to provide power systems for remote applications. In these remote site applications, PV was cost effective even at a $20–$40/Wp cost for modules. These remote applications included telecommunications, weather stations, navigational aids, water pumping, fence charging, remote vacation homes and cathodic protection.
Partially because of the US energy crises of 1973 and 1979, the US government began an expanded effort in renewable energies. The Flat‐Plate Solar Array (FSA) Project, funded by the US Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the flat‐plate module and array technologies needed to attain widespread terrestrial use of PV [9]. While many important developments came out of this effort, three had particularly important impacts on future PV efforts. The first was the initial efforts to evaluate the potential for PV technologies to undergo significant cost reductions and, therefore, eventually compete with traditional sources of electricity. The second was the proof that PV modules could be assembled into larger‐scale systems that could then power real‐world applications. The third was the Jet Propulsion Laboratory (JPL) Block Buy Program to be discussed in more detail in Chapter 4. This effort led to the use of acceleration stress tests and the establishment of qualification tests for PV modules. This went a long way toward improving the reliability and increasing the service life of PV modules.
The election of Ronald Reagan to the Presidency in 1980 resulted in a huge setback for PV. The national budget for PV was slashed drastically and PV research in the US dropped to a small fraction of what it had been under Jimmy Carter's Administration. As a result, PV progress slowed appreciably and the center of PV development shifted away from the US to Europe and Asia.
In 1994, The Japanese Ministry of Economy, Trade and Industry (METI, formerly called MITI) launched a subsidy program for residential PV systems with an overall goal of installing 4.82 GW of PV by 2010. The program was launched with a subsidy of 50% of the cost of the PV system. The program attracted homeowners not only because of the subsidy, but also because the residential electricity rates in Japan were about 24 Yen/kWh equivalent to about $0.24/kWh at that time, among the highest residential rates in the world. On the other hand, mortgage interest rates in Japan are low (1–2%) and were extendable to cover the costs of residential PV systems. From 1994 until 2003, the Japanese PV market grew steadily by about 30% a year even though the subsidy level was reduced every year. By 2003, the Japanese market was the largest in the world, representing >40% of the world's PV demand.
Germany used a different approach to subsidizing PV systems. Rather than assisting with the initial purchase as was done in Japan, the German program pays a rate or tariff‐based incentive on the electricity actually produced. The PV system owner is paid a specified rate for each kWh produced by the PV system. While such a program had been ongoing in Germany since the late 1990s, a change in the structure of the incentive program that began in 2004, resulted in explosive growth of the German PV market in 2004 and 2005. The feed in tariff rates were established at €45.7 ¢/kWh for ground mounted systems (with a 6.5% annual reduction), at €57.4 ¢/kWh for rooftop residential and at ~€54 ¢/kWh for rooftop commercial (with a 5% annual reduction). In addition to the feed in tariff, preferential loans were made available for PV. This whole program was focused on PV's C02 lowering