photovoltaic solar energy from fundamentals to applications

 In this article we will give a vision of photovoltaic solar energy from its foundations to its applications and  the subsequent development of this kind of energy and I will review its current state in the world and in Spain.

1. First steps and development of photovoltaic solar energy

The discovery of the photovoltaic effect, the basis of operation of solar cells, dates back to the 19th century, when H. Becquerel described it in 1839, although the precise explanation of it was delayed about a century, until the advent of quantum physics early twentieth century [1].

Solar cells were a rare scientific curiosity for a long time. It was necessary to wait until 1954 for the first silicon solar cell to be manufactured, at the hands of scientists DM Chapin, CS Fuller and GL Pearson of Bell Telephone laboratories (USA). After its public presentation, The New York Times, in its issue of April 26, 1954, made the following comment on the invention of the solar cell:  “It can mark the beginning of a new era, allowing the realization of one of the dreams most loved by humanity: the use of unlimited energy from the sun for the uses of civilization ”.

GL Pearson (left), DM Chapin (center) and CS Fuller (right). Right: Fuller’s laboratory notebook, describing the fundamentals of the solar cell manufactured at Bell Laboratories.

A year later, certain industries, driven by the start of the US space program, were commissioned to produce solar cells for space applications. The Hoffman Electronic company was the first to manufacture these devices commercially, although with a very low conversion efficiency, of only 3%.

In 1958, the Vanguard-I satellite was launched into space  , the  first to use solar cells as a source of energy and which would be operational for 8 years. It is shown in the picture:

Vanguard-I satellite, the size of which was similar to that of a soccer ball. The arrows indicate the location of the solar cells that supplied the satellite energy.

In artificial satellites and manned vehicles with which man arrived on the moon in 1969, autonomous, light and reliable electric power batteries were needed and solar cells met all these requirements. Although the electricity obtained with these devices was very expensive (of the order of € 100 / kWh, with prices updated at the present time), the cost represented by the batteries manufactured with the solar cells was very low compared to the rest of the components of the space vehicles.

The technology of the solar cells was impelled enormously thanks to the microelectronic industry, from which it took good part of its manufacturing processes. Thanks to this, in a few years devices with efficiencies of conversion of solar energy into electricity of 15% were obtained. The development in the space field continued during the decade of the 60s and 70s. In 1973 the first American space station, the  Skylab , had installed 20 kW of power in photovoltaic panels. The year 1975 was the first in which space applications were surpassed by terrestrial ones, mainly lighthouses and small experimental production plants.

Since that year, which can be considered as the definitive takeoff of this energy source, its development in the world has gone through three clearly differentiated phases, which are shown in the following graph where the power values ​​of installed solar power plants are detailed in the world, compared to the total installed power coming from all other energy sources. The evolution from 1970 to 2010 is shown and distinguishes three phases, which are detailed in the following paragraph:

Electric power installed in the world in billions of watts (TW; 1 TW = 1,000,000,000,000) depending on the year. The vertical scale is logarithmic. Source:  Massachusetts Institute of Technology

Phase I: 1975-1985. The successive oil crises of the years 1973 (Yom Kippur War) and 1979 (Iran Revolution) made the main industrialized countries aware of the need to seek alternative energy sources to oil, due to the sharp increases in the price of crude (between 1973 and 1979, the price of the barrel multiplied by six). Simultaneously, ecological awareness spread throughout the planet and began to raise the need to limit greenhouse gas emissions to the atmosphere, mainly CO2. For these reasons, in the United States, programs to stimulate fossil fuel-based energies, encouraged by the Carter administration, began. In those years the first experimental solar gardens were installed, of very small size (tens of kW).

Phase II: 1985-1995 . After the successive oil crises, barrel prices were significantly reduced and stabilized at values ​​similar to the pre-crisis moments, which lowered interest and state aid and incentives for renewable energy. During this period, the main R&D activities in photovoltaic devices were carried out by large oil companies, being British Petroleum one of the most representative. However, a good number of research laboratories continued to improve the manufacturing technology of solar cells, overcoming conversion efficiencies year after year.

Phase III: 1995-Present.  The use of renewable energy has been spreading gradually in the world in general and in developed countries in particular. At the beginning of the 21st century, numerous countries, such as Germany, Spain, Italy, the United States and others,  began to strongly encourage  the use of this energy source by paying premiums for the electricity produced. Simultaneously, the manufacturers of photovoltaic panels went from the field of oil companies and electronic industries to being specific manufacturers. Currently the top positions in  the world ranking of manufacturers Asian companies are occupied by solar cells, with China in the lead (Yingli, Hanwha, Trina) and some American companies (Canadian Solar Industries, First Solar).

European manufacturers, who had a very prominent role in the origin and development of photovoltaic technology at the beginning of this century, (Q-cells, Isofoton), have disappeared or have been absorbed by large Asian manufacturers, who have established some Pricing policies with which it is practically impossible to compete.

In recent years, the installed photovoltaic power accumulated worldwide has not stopped growing year after year, as the figure shows. The values ​​shown in the graph are proof that the commitment to this energy source is unstoppable and reaches the entire planet:

Installed photovoltaic power accumulated in the world. Data expressed in Gigawatios (GW; 1 GW = 1,000,000,000 W). Source: Photovoltaic Report 2015 . Fraunhofer Institut ISE

2. Development and stagnation of photovoltaic energy in Spain

In the specific case of our country, since 2007 a firm commitment to this energy was made, through  various decrees  that established premiums for photovoltaic energy producers, but the compensation system established in 2007 was poorly designed, since it did not put limits to installed capacity, which caused the installations boom of 2008 and all the mess and regulatory chaos that came later. The evolution of installed power in Spain is shown in the following graph:

Evolution of photovoltaic solar power installed and accumulated in Spain, expressed in MW (1 MW = 1,000,000 W). The boom of the year 2008 and the brake in new facilities since 2012 are appreciated (22 MW were installed in 2014). Source:  Annual Report 2015 . Spanish Photovoltaic Union.

Since the arrival of the Popular Party to the government in 2011, a whole series of rules have been followed to retroactively cut premiums for renewable energy, which has caused  the ruin of numerous small investors  who bet on this day for this source of energy

Regardless of the current brake, the future of energy will necessarily go through the development of photovoltaic solar energy, especially in a country like ours, which enjoys a privileged geographical position with high levels of irradiation during most of the year in practice The whole territory, which makes it especially attractive in order to reduce the costs of the energy produced.

What are the applications of photovoltaic solar energy today?

Photovoltaic solar systems can be divided into two
large groups:

Isolated grid systems

There are areas where access to the network is impossible or very
expensive, using solar energy for self-consumption.
This option prevents the power line from being taken to the point of consumption, thus avoiding
the high cost that this would entail.

The most common applications are:

• Electrification of homes away from the power grid
• Agricultural and livestock applications (water pumping, irrigation systems,
  greenhouse and farm lighting …)
• Signaling and communications (air and sea navigation, road signs,
  repeaters …)
• Street lighting (streets, monuments, bus stops …)
• Water purification systems

In these applications, to be able to have electricity during the night or in periods of low
sunshine, an accumulation battery is necessary, with the corresponding charge controller.
When alternating current is necessary, an inverter is used.

It is also an ideal solution to improve the quality of life in remote communities through
sustainable solutions. There are already packages for lighting, schools, health centers
with refrigeration systems for vaccines, home systems and pumping systems.

Systems connected to the power grid

The photovoltaic system is connected to the electricity grid and an inverter transforms the direct current
generated by the system into alternating current similar to that of the grid.

Photovoltaic systems are easy to install regardless of whether it is an
existing or newly built building / dwelling and its maintenance is minimal. In addition, they provide
a clear economic profitability since they generate income from the first day and for more than 30
years.

All the energy that the system produces can be sold to the electricity grid providing income,
differentiation and ecological commitment so the user continues to buy the electricity
consumed from the electricity grid at the established price, charging on the other hand the green kilowatts that his system Produces at a higher price.

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[1] The scientific explanation of the photovoltaic effect was made by Albert Einstein in 1905, which is why he won the Nobel Prize in physics in 1921. Why it took so long to get that award is a little known story. I refer the interested reader to  this article  to inquire into the matter.