in fundamental understanding, cell processing, and scale‐up of manufacturing (and subsequent drop‐off in product cost). I tend to use the conversion efficiency of solar cells from solar radiation to useful electricity as a criterion for assessing the progress of particular technologies, but with the caveat that high efficiency must be achieved cost‐effectively. Throughout the period in question, I was principally involved at BP Solar and then at NaREC in silicon solar cell design and manufacturing, although along the way I also had responsibilities for thin‐film silicon, cadmium telluride, III‐V cells, and concentrators. I have taken the opportunity to detail progress in these areas, but also to give my own explanation for why they have not been able to displace silicon as the prime solar cell material. The opinions expressed in this book are entirely my own and are not the views of any of my previous employers.
Throughout my career, I had the privilege of working with many able and dedicated people. In particular, I am indebted to Nigel Mason, Stephen Roberts, Daniel Cunningham, Keith Heasman, and Stephen Ransome for their steadfast support and friendship through the years. Following the merger of BP Solar with Solarex in 2000, I was able to connect with a different generation of pioneers, and it was inspiring to be able to share ideas with Steve Shea, John Wohlgemuth, and the late David Carlson. I have also enjoyed interactions with many others through supporting manufacturing in the United Kingdom, Spain, India, Australia, and the United States. There are many other colleagues from my time in BP Solar and NaREC who helped in innumerable ways, and space does not allow me to acknowledge them all by name. I must thank my wife, Margaret, who selflessly supported me throughout my career and without whom this book would not have been written.
1 The Photovoltaics: The Birth of a Technology and Its First Application
1.1 Introduction
‘For more than a generation, solar power was an environmentalist fantasy, an expensive and impractical artefact from the Jimmy Carter era. That was true right up to the moment it wasn’t’ [1]. This quotation neatly encapsulates the theme of this book: how a technology grew from a high‐cost product in a specialist application to a global technology supplying a significant proportion of the world’s electricity against a background of at best scepticism and at worst open hostility. In 2018, 102 GWp of photovoltaic modules were installed globally, leading to a total installed capacity of 509 GWp, while an independent study showed that photovoltaics was the lowest‐cost means of generation of new‐build electricity‐generating capacity, including nuclear and fossil fuel sources [2]. At the end of 2019, photovoltaics provided 3% of the global electricity supply, but the expectation is that this percentage will continue to rise until it is the dominant electricity‐generating technology by 2050, with 60% of global output [3,4]. Figure 1.1 shows the expected growth of all generating technologies to 2050.
This dramatic development of photovoltaic installations has been the work of many inspired individuals. Their stories are told in other places [5–7]. The aim of this book is to describe how the technology changed from small‐area solar cells of 10% efficiency conversion of sunlight to electricity to the mass‐production cells of today, with efficiencies in the range 20–24%, and the route to >30% becoming clear. The present chapter describes how the potential for photovoltaic conversion was first recognised and how it moved into the early stages of commercialisation as a high‐technology product for use in powering space satellites. Later chapters will describe how this space technology became a terrestrial one and the driving forces and technology developments that made it the global force it is today. Furthermore, the options for going beyond the current technology will be reviewed and the route to achieving terawatt global installations discussed.
It should be no surprise that photovoltaics has achieved the advances it has. Since the invention of the semiconductor transistor in 1948, solid‐state electronics has transformed the way in which we live. Computers, mobile phones, the Internet, and so much else would not exist without the underlying semiconductor technology. Photovoltaic solar energy conversion is the application of solid‐state technology to the energy field. Electricity is generated simply by the absorption of sunlight in a semiconducting diode. There are no moving parts. No liquid or gaseous fuels are needed. There are no effluents requiring disposal and no noise is generated. Sunlight is abundant, delivering to the earth’s surface 6000 times humanity’s total energy usage [8]. It is the only renewable resource capable of delivering the world’s energy needs carbon‐free by 2050, and it will remain available for the next 5 billion years. The photovoltaic technology is easily scalable, so that small cells can generate the few milliwatts required for consumer devices such as calculators and watches, while larger ones can be used to assemble modules for deployment at the gigawatt level. It is these advantages which spurred many advocates to continue to promote photovoltaics in the face of significant opposition.
Figure 1.1 Evolution of electricity‐generating technologies to 2050
Source: DNV GL Energy Transition Outlook 2018
1.2 Sunlight and Electricity
1.2.1 The Early Years
While the potency of the sun has been recognised from ancient times, its role has been mainly that of a source of heat and lighting [9]. It was only relatively recently that the connection between sunlight and electricity was established. Through the nineteenth century, there was an important discovery in this regard about once every decade. Probably the first connection between light and electricity was made by Edmond Becquerel in Paris in 1839 [10]. He observed the flow of an electric current when gold or platinum electrodes were immersed into an electrolyte (acidic or alkaline) and exposed to uneven solar radiation. Some ten years later, Alfred Smee in London observed a current in an electrochemical cell on exposure to intense light, which he called a ‘photo‐voltaic’ circuit – linking the Greek word for light phos and the name ‘Volta’, the original inventor of the galvanic cell [11].
The next step was the observation of photoconductivity in a solid material. A British engineer, Willoughby Smith, in search of a high‐resistance metal for use in testing the trans‐Atlantic telegraph cable, was recommended selenium. He purchased some selenium rods of between 5 and 10 cm in length and 1 and 1.5 mm in diameter [12]. These were hermetically sealed in glass cylinders, with leads to the outside. They worked well at night, but in bright daylight they became too conducting. Smith concluded that there was no heating effect and that the change in resistance was purely due to the action of light [13]. This stimulated further research into the properties of selenium. The British scientists William Grylls Adams and Richard Evans Day observed current flowing in their selenium sample when no external voltage was applied and were able to show that ‘a current could be started in the selenium by the action of light alone’ [14]. They had demonstrated for the first time that light caused the flow of electricity in a solid material. They used the term ‘photoelectric’ to describe their device, and Adams believed it could be used as a means of measuring light intensity [15].
The narrative now switches to America, where Charles Fritts made the first working solar module by covering a copper plate with a layer of selenium and applying a semitransparent gold layer as the top electrode [16]. An example is shown in Figure 1.2. Fritts described the module as producing a ‘current that is constant and of considerable force … not only by exposure to sunlight but also to dim diffused light and even to lamplight.’ He supplied samples to the German electricity pioneer Werner von Siemens, who greeted them enthusiastically, announcing Fritts’ module to be ‘scientifically of the most far‐reaching importance’. However, its low efficiency – below 1% – made it of little
