The history of using solar energy

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The History of Using Solar Energy
Loránd Szabó
Department of Electrical Machines and Drives
Technical University of Cluj-Napoca
Cluj-Napoca, Romania
e-mail: Lorand.Szabo@emd.utcluj.ro
Abstract—The energy received on Earth from the Sun is
plentiful and totally renewable. Basically, the sun enabled life on
our planet, and our life cannot be imagined without it. The sun is
directly or indirectly at the origin for nearly all the energy
resources on Earth, as fossil fuels (coal, natural gas and oil),
hydro (global water circulation is due to the sun), wind, waves,
biomass, etc. The sunlight was used as an energy resource
already by ancient civilizations. Since than a lot of innovative
technologies and advancements were performed in this field. The
paper presents the main milestones of the developments
performed in this important field of energy conversion.
Keywords—solar energy; science history.
I. INTRODUCTION
The energy requirement of the mankind is continuously
growing. It is forecasted that by the middle of our century the
global energy demand will at least double. This huge energy
necessity and the actual environmental challenges will be
possible to be covered by the increasing electrical energy
conversion from renewables, among them solar energy [1].
The annual solar energy potential of the Earth is
23,000 TWy. 1,600 TWy should be the world energy
consumption for 100 years (computed with the yearly
consumption in 2009), as it is illustrated in Fig. 1. For
comparison, the Earth's total finite energy resources (coal,
uranium, petroleum and natural gas) are of 1,655 TWy and the
most optimist estimations of the energy that can be converted
yearly from non-solar renewable resources (wind, ocean,
biomass, hydro and geothermal) is only 94 TWy [2].
Fig. 1 The solar potential vs. energy consumption
Almost all the energy forms used in electrical power
generation are of solar origin. Oil, coal, natural gas and woods
were originally produced by means of photosynthesis. Wind
and waves are due to temperature differences [3], [4], [5].
Throughout the history, each new applied energy form
contributed to the development of the society [6].
The use of the very clean solar energy is not a new
discovery of the scientist of our days. It was used in diverse
scopes since a lot of centuries. Therefore, the history of solar
energy conversion is long, various and exciting.
The paper will deal with the most important and interesting
milestones of the developments performed in this field of
energy conversion.
II. ANCIENT AGES
The sun has a vital role in the life on Earth. This was
recognized and celebrated by all the cultures already in the
ancient ages. Peoples of those days admired the Sun, and even
frequently personified and worshipped it as a deity [7].
Egyptian pharaoh Akhenaten IV (1353 BC - 1336 BC),
husband of the more famous Nefertiti queen, forced religious
reforms concerning monotheistic state religion instead of
traditional polytheism religious conviction of the ancient
Egyptians. He deified himself as a god, who alone could
worship Aten, the single god accepted that time. Aten was the
sun disk in the Egyptian mythology, and originally an aspect of
the god Ra, the Egyptians' sun god. The contact with Aten was
possible through the sunrays, as shown in Fig. 2 [8].
Fig. 2 Pharaoh Akhenaten IV in the sunrays being in contact with Aten
This work was supported by the Romanian Executive Agency for Higher
Education, Research, Development and Innovation Funding (UEFISCDI) via
SWTOMP ERANet-LAC project no. 21/2017.
978-1-5090-6565-3/17/$31.00 ©2017 IEEE
The 7th International Conference on Modern Power Systems (MPS 2017)

In several scripts of the ancient Egypt is stated that Great
Pyramid, the last remaining construction from the list of the
Seven Wonders of the Ancient World, was built as a stairway
to the sun [3].
Almost all of the ancient cultures around the world had
their god of Sun, which represented the power and force of the
star of our solar system. Some of these gods were: Amaterasu
in Japan, in Greece Helios and later Apollo (this last was also
sun deity in Rome), Surya the Hindu sun god, etc. [9].
Given the immense abundance and usefulness of the solar
energy, it slowly moved from the metaphysical approach to
more practical applications [7], [10].
The first such applications were connected to architecture.
6000 years ago, the Neolithic Chinese people had their sole
opening of their homes facing south to catch wintertime the
low sun rays for assisting the warm of the houses. Suspended
thatched roof was used to keep away the high summer sun
from the houses. This technology was used thousands of years
later also by the ancient Egyptians and Greeks [7]. Aristotle
(384 BC-322 BC) was teaching how to use of the winter sun
for heating, and how to keep the house in shade during
summertime. This approach was the pioneer of present passive
heating and cooling techniques [11].
The proper house orientation was taken from the Greeks by
the famous Roman architect Vitruvius (80 BC - 15 BC),
author of De architectura, one of the basic books in the field.
The technology was further developed by applying large
transparent single pane windows (fenestra in Latin) of mica,
translucent marble or clear glass. These windows were acting
like solar heat traps, admitting the sunlight and keeping the
accumulated heat inside [11], [12].
Since prehistory, the sun was used to dry and preserve food
[3]. Food processing was a crucial avocation of mankind. The
ancient Egyptians used specific dehydration technology to dry
grains, formerly storing them in seal silos. This technology
enabled them to keep the stored grain for several years.
Fig. 3 Ancient Egyptians drying meat [13]
Salting was vital in food preparation and conservation, too.
The sun was used to evaporate sea water to obtain salt [3]. The
saltwater was collected in solar ponds, and after the water was
evaporated the salt remained at their disposal. This very simple
technology is still used around the world (see Fig. 4).
Fig. 4 Salt pans in Marakkanam (Tamil Nadu, India)
Ancient people early recognized that the concentrated
waves of the sun can be used for lighting fire. Already in the 7th
century BC magnifying glasses were used to focus the sunrays.
Upon a more advanced approach in the 3rd century BC the
ancient Greeks and Romans used mirrors to concentrate the
sunbeam for lighting torches [14].
One of the most controversy stories of the ancient history is
related to this kind of solar energy use. Upon this, the Greek
scientist Archimedes of Syracuse (287 BC - 212 BC) lit
Roman enemy wooden ships by concentrating sunrays. The
"burning mirror" was probably an angled hexagonal giant
mirror, or a system of mirrors, focusing the so-called "heat
ray", or "death ray" by Archimedes on the approaching ships
(see Fig. 5).
Fig. 5 Archimedes lighting Roman warships
III. MIDDLE AGES
The early middle ages (5th÷10th century), the so-called
"dark ages" was the period in Europe following the collapse of
the Western Roman Empire. It was the epoch of intellectual
and economic darkness, when superstition and illiteracy ruled.
Scholars were few, and reason and logic was marginalized by
bigot belief and religion. This time period was not suitable for
technology progress [15].
The Europe of the 12th÷14th century became more open for
technical advancements. But these were either based on
long-established techniques originating from Roman and
Byzantine cultures, or adapted from Eastern civilizations, as
the Islamic world, China or India. At that time, frequently the
revolutionary aspect did not lay in the act of invention itself,
but in its technological refinement and application to local
conditions. During this period, European people continued to

satisfy their energy needs almost exclusively with renewable
energy [16].
During the Renaissance (literally "rebirth") era (14th÷17th
century) in the medieval Europe the number of new inventions
and innovations was radically increased. This period can be
considered as the bridge between the dark middle ages and
modern history.
Leonardo da Vinci (1452–1519), the "Renaissance Man",
was an Italian polymath and the most well-known inventor of
that age. Beside his famous paintings, like the Mona Lisa and
the Last Supper, he had forward showing contributions in a
large diversity of science fields, as engineering, chemistry,
mathematics, physics, etc. [17]. Seemly he was already at that
time aware about environmental issues, since he worried about
the destruction of the earth's huge forests. Hence he performed
several studies concerning the use of the solar energy for
heating purposes.
He investigated the geometry of the reflections of parallel
sunrays on a curved metal plate (see Fig. 6). He obtained a
geometric relationship which was independent from the curve
of the plate. It is believed that Leonardo da Vinci proposed the
first industrial application of a concave mirror solar
concentrator to be used for a water heater. He also proposed a
technology to weld copper using concentrated solar radiation,
and technical solutions to heat bathing installations or to
operate textile machines.
Fig. 6 Drawing of Leonardo da Vinci concerning sunray concentration
The Age of Discovery, also named as the Age of
Exploration, (15th÷18th century) was characterized by broad
overseas exploration. The emerging colonialism and
mercantilism resulted in an empowered and rich Europe.
Technical innovations had again the necessary background of
interest and financial support.
After the decline of the Roman Empire, the use of
transparent glass almost disappeared since these years. The rich
citizens living in this age wanted to enjoy tropical fruits also at
home. South-facing glass covered greenhouses were built to
trap the solar heat, necessary for the growth of exotic plants in
Europe, having colder climate. In some cases, a greenhouse
was attached to the south-side of houses, from where the hot air
was conveying into the interior of the building [11].
The architecture of that age used also more common
approaches to fructify the thermal energy of the sun. Carefully
designed passive systems applied insulation, south-facing
glass, and massive floors and walls, naturally assisting heating,
cooling and lighting. In more advanced active solar heating and
cooling systems, liquids or air were circulated through pipes or
channels to move the heat to where it was necessary [3].
Several innovations were proposed for the collection,
storage and control of energy converted from the sun, mainly
due to reawake of the glass awareness to trap solar heat.
In 1767, the Swiss polymath Horace-Bénédict de Saussure
(1740-1799) built his so-called "hot box" plate collector,
known as the world's first solar energy collector. It was a
rectangular box made of wood, insulated with black cork and
covered by glass. Inside the box was a smaller similar
glass-covered box, as shown in Fig. 7. When the box was
placed in the sunlight, the water from the inner box could boil.
The hot box became the prototype for solar thermal collectors
used also in our ages [18].
Hot space Inner wooden
box
Outer wooden
box Insulation
Glass
Sunlight
Fig. 7 Saussure's hot box [18]
In the next decades Saussure's invention was further
improved. Significant contributions in this filed had John
Frederick William Herschel (1792-1871) and Samuel Pierpont
Langley (1834-1906) [19].
IV. FROM INDUSTRIAL REVOLUTION AGE UP TO NOW
During the Industrial Revolution (began in Britain in the
18th century) the agrarian and handicraft based economy was
changed by industry and machine manufacturing.
The technological feature characterized the Industrial
Revolution, beside socioeconomic and cultural ones. The
technological advances due to the increasing application of
science to industry were connected to [20]:
– enlarged use of iron and steel;
– new energy sources, including both fuels (coal,
electricity, petroleum) and motive power (steam and
internal combustion engine);
– radically improved productivity due to the invention of
new machines

– important advancements in transportation and
communication (steam locomotive and ship, automobile,
airplane, telegraph, radio, etc.).
In this age, also numerous, solar energy related industrial
achievements and innovations were reported. Here only some
specific ones can be mentioned.
The sun collector of W. Adams was more efficient than all
the previously constructed variants. The oven made by him had
8 symmetrically placed silvered glass mirrors forming an
octagonal reflector, as shown in Fig. 8. The sunlight was
concentrated by the mirrors into a glass covered wooden box,
in which the pot with the food to be boiled was placed.
Mirror
Glass
Pot
Fig. 8 Adam's solar oven [18]
The box had to be rotated by hand to align with sunrays. As
it was related, the temperature in the box could exceed 200°C.
This was the first mass-produced solar oven, very popular both
in India and the United States of America [18], [19].
In this age, sunray concentrators were developed for solar
furnaces, capable of melting iron, copper and other metals.
They were made of polished-iron, glass lenses or mirrors [3].
The record holder at that time in this field was the
Frenchman Antoine Lavoisier (1743-1794), the greatest
chemist of the 18th century and an accomplished polymath. He
could attain in his furnace 1750°C. The furnace used two
lenses of 1.32 and 0.2 m diameter, made from curved sheets of
glass, having their internal space filled by vinegar, as shown in
Fig. 9 [3]. This world record was not beaten for more than a
hundred years. Lavoisier was also concerned about the
environmental issues connected to burning fuels; therefore, he
intended this way to clearly generate the heat needed for his
experiments.
Fig. 9 The solar furnace built by Antoine Lavoisier [21]
During the 19th century the technology evolved to a level
where it became possible to directly convert the solar energy
into other forms, mainly in low-pressure steam, needed in the
very wide-spread steam engines.
The French mathematics professor and inventor August
Monchot (1825-1911) pioneered this field by developing
diverse sunray powered devices, as ovens, stills, pumps and
ultimately the first solar steam engines. The greatest such
engine, given in Fig. 10, was made of a silver-coated metal
plate of 5.4 m diameter, having a total collecting area of
18.6 m2. Its moving parts were of 1400 kg [3].
Fig. 10 Monchot's largest sun machine [22]
Monchot's researches were catalyzed by his conviction that
there are no sufficient resources needed by the extremely
growing industry, and only solar energy conversion can solve
this crisis.
The developments of Monchot were continued by his
assistant, Abel Pifre (1852-1928). His solar collectors were
parabolic reflectors made of very small mirrors. They shape
was slightly similar to Mouchot's truncated cones given in
Fig. 10 [3]. His best-known solar steam engine was constructed
in 1882. He used a concave 3.5 m diameter mirror having in its
focus a cylindrical steam boiler. The generated steam actuated
a small vertical engine of about 300 W, which was driving a
printing press (see in Fig. 11).
Fig. 11 The sun-powered printing press of Abel Pifre [23]

John Ericsson (1803-1889), a Swedish-American inventor
was also devoted to the development of useful power from
solar energy. In 1873 he invented a displacer type (so-called
Stirling) engine (shown in Fig. 12), which was working upon
the sunrays collected by a parabolic reflector. By this engine he
demonstrated that power can be produced by solar energy
alone, without the intervention of steam.
Fig. 12 The solar Stirling machine of John Ericsson [24]
The development of the sun collectors continued also at the
beginning of the 20th century. The most significant milestones
are given below.
In 1901 A.G. Eneas installed a 10 m diameter focusing
collector, which powered a water pump in California. The
device comprised of a great umbrella-like structure having
inside it 1788 mirrors. The water inside the boiler placed in the
the collector was heated, and the produced steam acted a
conventional compound engine and centrifugal pump [3].
In 1912 Frank Shuman (1862-1918), an American solar
energy pioneer, built the world's first solar thermal power
station for a pumping plant in Meadi, Egypt (see it in Fig. 13).
The system was using several 62 m long cylindrical-parabolic
shaped cylinders to focus sunlight onto an absorbing tube. The
cylinders covered totally more than 1200 m2 area. The solar
engine was able to develop 37÷45 kW power continuously for
a 5 hours period [3]. It enabled the pumping of more than
20,000 L water per minute from the Nile to the adjacent
agricultural fields.
Fig. 13 The world's first solar thermal power station [22]
During the last 50 years, a lot of sunray focusing collector
variants were designed and constructed. Two primary solar
technologies were used: with the central and distributed
receivers. Central receiver systems are based on heliostats
(two-axis tracking mirrors) to focus the sunlight onto a single
tower-mounted receiver. Distributed receiver technology
applies diverse approaches, as parabolic dishes or troughs,
Fresnel lenses, etc. [3].
The world's first commercial concentrating solar power
plant, the Planta Solar 10, was set up in 2004 near Seville,
Spain. The sunlight is reflected by 624 large movable mirrors
(so-called heliostats) to the top of a 115 m high tower, where a
solar receiver, a steam turbine and a generator can produce
11 MW of electrical power (enough for 5500 homes).
The world's largest such power plant was opened on
February 13, 2014 in Ivanpah Dry Lake (California, USA). The
Ivanpah Solar Electric Generating System's nominal power is
377 MW (enough to power 140,000 homes). Here over
300,000 software-controlled mirrors are tracking the sun in two
dimensions, and reflect the sunlight to the boilers placed atop
of three 140 m tall towers, as it can be seen in Fig. 14.
Fig. 14 The power plant in Ivanpah Dry Lake
Another, now very widespread application area of sun
concentration is the water and house heating. These became
extensively used in the 1940s when they began to replace
heating systems mainly based on coal burn boilers [3].
But this warming approach is rather older. The first such
water heaters were practically black painted tanks filled with
water. Their major disadvantage was that it took a long time to
be warmed up, and they rapidly cooled down when the sun was
not shining, since they were not insulated or did not have other
heat retention system [25].
The first commercial product which overcame these
disadvantages was the Climax Solar Water Heater, marketed
beginning 1891 by his inventor, Clarence Kemp (see Fig. 15).
They became very popular at that time on the West Cost of the
USA. Further improvements were made at the beginning of the
20th century by incorporating sun exposed pipes and remote
insulated storage tanks in which the warm water entered. All
these enabled people to enjoy hot water all the day and night
[22].

Fig. 15 Commercial for the Climax Solar Water Heater
V. THE HISTORY OF PHOTOVOLTAICS
Probably the most significant breakthrough in the use of
solar energy was the discovery of the photovoltaic effect. The
photovoltaic cells (often called also solar cells) can convert the
sunlight directly into electricity based on the operating
principles relying on the photovoltaic effect [26], [27].
The "photovoltaic" term comes from the Greek "phos"
meaning light, and from "volt", the unit of electro-motive force.
The photovoltaic effect was discovered by the French
physicist Alexandre-Edmond Becquerel (1820-1891). In 1839,
at the age of 19, experimenting in his father's laboratory, he
built the world's first photovoltaic cell. In his experiment, he
placed silver chloride in an acidic solution. While illuminating
it, he observed voltage on the connected platinum electrodes.
His discovery was reported in his "Mémoire sur les effets
électriques produits sous l'influence des rayons solaires" [28].
Fig. 16 Alexandre-Edmond Becquerel
A.E. Becquerel also had pioneering works in the field of
photography. He discovered in 1840 the photosensitive
properties of the silver halides, which allowed the development
of daguerreotypes and other similar photographic materials. In
1848 he could produce color photographs.
Willoughby Smith (1828-1891), an English electrical
engineer, first observed and reported in 1873 the light
sensitivity of selenium: exposed to sunlight its conductivity
increased.
Fig. 17 Selenium bars used in the experiments of Willoughby Smith
Two British scientists, William Grylls Adams (1836-1915)
and his student Richard Evans Day proved that light shone on
selenium bars produces a flow of electricity.
An American inventor Charles Fritts (1850-1903) is
recognized as the creator of the first working photovoltaic cell.
In 1883 he sandwiched selenium between an iron plate and a
semi-transparent gold top layer. Although these devices had
very low efficiency (under 1%), they were the starting point of
one of the nowadays most dynamically developing areas of
engineering [29].
Charles Fritts was also the pioneer of using solar panels.
He connected several selenium modules, and placed the test
array on a New York rooftop in the mid 1880s. He was very
optimistic concerning the end of the steam engines and the
related pollutions [11]. But the practical widespread
applications of the photovoltaic devices had to wait until the
1950s.
Few people know that Albert Einstein (1879-1955), the
famous theoretical physicist, was awarded the Nobel Prize in
Physics in 1922 "for his services to Theoretical Physics, and
especially for his discovery of the law of the photoelectric
effect", and not for his new theories of general and special
relativity, as that time those were considered still somewhat
controversial.
An American engineer, Russell Shoemaker Ohl
(1898-1987) patented the modern junction semiconductor solar
cell in 1946. He is also the discoverer of the P-N barrier (the
so-called "P–N junction").
In 1954, while experimenting the newly-discovered silicon
transistors, three American scientists working for the Bell
Laboratories, Daryl Chapin (1906-1995), Calvin Fuller
(1902-1994) and Gerald Pearson (1905-1987) developed a
solar cell that could convert enough solar energy into electricity
to run any usual electrical equipment. They proposed a diffused
silicon P-N junction based cell having 6% efficiency. The New
York Times eulogized the discovery "as the beginning of a new
era, leading eventually to the realization of one of mankind's
most cherished dreams – the harnessing of the almost limitless
energy of the sun for the uses of civilization" [11].
The conversion efficiency of solar cells begun to slowly
increase up to 11% in 1958, and 14% in 1960, but they price
was prohibitively high (about 1000 USD/W) [3].

Researchers discovered in the 1960s also other photovoltaic
materials, such as gallium arsenide (GaAs). These could
operate at higher temperatures than silicon, but were still
expensive [3].
Due to high costs and low efficiency, at the beginnings of
the photovoltaic era solar cells were used only in toys and other
minor applications. Their first important applications were in
space exploration. Vanguard I, launched by the USA in 1958,
was the world's first solar-powered satellite. The 165 mm
diameter and 1.47 kg aluminum sphere spacecraft had 6 solar
cells of 100 cm2 total surface, which produced only a few tens
of mW, and was supplying one of its two transmitters (see
Fig. 18).
Solar panel
Fig. 18 Full-scale Vanguard I satellite model
Since then, large solar arrays resembling wings, are a
typical feature of the satellites. In practice the solar cells were
adequate for this application, since their small efficiency and
high costs were balanced by their high power-to-weight ratio, a
very important issue in aerospace industry.
The success of the solar cell in aerospace photovoltaics
radically changed the general vision on their applications also
on Earth. First those remote terrestrial applications were
targeted, where there was no possibility for connection to a
public electricity grid. Hence, solar cells were used for
supplying offshore navigation horns and lights, microwave
repeaters and other telecommunication devices. Step by step
beginning with the mid 1980s photovoltaics become the prime
electrical energy source for remote applications [22].
A significant breakthrough in the field in the 1970s was
catalyzed by the very rapidly growing semiconductor industry.
As the technology evolved, the price of solar cells fell together
with the price of the integrated circuits (see Fig. 19).
1977 1981 1985 1990 1995 2000 2005 2010 2015
10
20
30
40
50
60
70
80
Fig. 19 Price history of crystalline silicon solar cells [30]
Meanwhile, due to the intensive research efforts round the
world the efficiency of the solar cells slowly increased, as it
can be seen in Fig. 20 [31]. It must be mentioned, that the
efficiencies from Fig. 20 are research paper reported values,
and not of commercially available solar cells.
Fig. 20 Efficiency history of solar cells (research data) [31]

As it can be seen, the most promising technologies, as
efficiency is concerned, are the multi-junction cells. Most
photovoltaic cells use only the visual light spectrum to generate
electricity. The unused photons of ultraviolet and infrared light
do not have enough energy to dislodge the electrons in the P-N
junction, and are absorbed as heat. In multi-junction cells each
layer is specifically doped to take advantage of a certain
wavelength, hence these can covert a wider spectrum of the
solar energy [32]. This is the secret of their higher efficiency.
The multi-junction cells are made of various layers of
different semiconductor materials. Practically, they consist of
some single-junction cells stacked upon each other. They can
be fabricated either by mechanical stacking of independently
grown layers, or each semiconductor layer can be
monolithically grown on top of the other, as one single piece.
Although nowadays the multi-junction solar cells have the
highest theoretical efficiency as compared to other photovoltaic
technologies, yet their price is excessively high (around 150
times more than that of silicon solar cells).
VI. CONCLUSIONS
The Sun is not only the center of our Solar System, but also
the greatest energy source in it. The Earth receives more energy
from the Sun in an hour than the entire world energy uses for a
year.
The humans are using this free and clear energy source
since thousands of years. Basically, there are three solar
technologies having a very long history: passive solar, solar
thermal and concentrated solar. All of them are intensively
used also nowadays. In the last decades, a new technology was
developed, the photovoltaics, which enables electricity direct
conversion from solar to electrical energy. The permanent
innovations in this field resulted in increase of efficiency, and
size and cost reduction, making it more prevalent throughout
all the human society.
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