Select­ive Timeline of Solar Objects

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Inven­tion of the Gnomon

About four thou­sand years ago, the popu­la­tions inhab­it­ing present-day China began track­ing the chan­ging posi­tion of the Sun relat­ive to the Earth by observing the star through­out the year, using open­ings in what resembled a solar obser­vat­ory. Later, they developed a more precise method by invent­ing the gnomon, a square-sectioned piece of wood or stone planted perpen­dic­u­larly in the ground. As the Sun moved relat­ive to the Earth, they could meas­ure the shadow cast by the rays hitting the gnomon. This method led to the creation of calen­dars that accur­ately dated the equi­noxes and solstices. It also enabled geograph­ical advance­ments by determ­in­ing orient­a­tion and latit­ude for each posi­tion.

In 2002, a stick marked with a gradu­ated scale (2300–1900 BCE) was discovered at the Taosi archae­olo­gical site (Shanxi Province) in a royal tomb, suggest­ing that the gnomon was a symbol of power. Recent simu­la­tions have shown that this stick could have been used to meas­ure the length of shad­ows on specific dates, such as the summer solstice.

The Yang Sui or Burn­ing Mirror

Yang Sui is the name of a concave mirror, also called Jin Shu because it was made of bronze. Confucius, in his descrip­tion of life in China three thou­sand years ago, mentions that every son attached a bronze burn­ing mirror to his belt to light the family fire at the end of a sunny day. The Yang Sui, about eight centi­metres in diameter, was as common then as matches are today.

In 1997, archae­olo­gists discovered a burn­ing mirror in the hand of a three-thou­sand-year-old skel­eton.

Archimedes’ Mirrors

Accord­ing to legend, Archimedes used burn­ing mirrors to set the Roman fleet on fire during the siege of Syra­cuse in 213–212 BCE. Histor­ical evid­ence is far from conclus­ive, and the main proponents of this legend are not very convin­cing. Modern exper­i­ments suggest that a burn­ing mirror would indeed be unlikely to produce a spark and then a fire on a ship. Never­the­less, the fantasy of a weapon using the concen­tra­tion of the sun’s rays has spread over the centur­ies.

In 18^th century France, Count de Buffon succeeded in setting fire to a wooden hut and even melt­ing metal using a mirror composed of 168 silvered glass panes. His exper­i­ment, which he success­fully repro­duced before King Louis XV, earned him the honours of the gazettes of the time, bestow­ing upon him the title of “the new Archimedes.”

The Helio­ther­mo­meter, a Mini­ature Green­house

In 1767, Horace Béné­dicte de Saus­sure, a Genevan phys­i­cist, geolo­gist, and natur­al­ist, created a glass heat trap he called a helio­ther­mo­meter. His box, a verit­able mini­ature green­house, allowed study of the calor­ific effects of the sun’s rays: it gave the same meas­ure­ments at differ­ent alti­tudes in spite of vari­ations in outdoor air temper­at­ures. Saus­sure deduced that if the air at the summits was colder, the reason lay in the func­tion­ing of the atmo­sphere and not a differ­ence in solar radi­ation.

His box served as a proto­type for the solar thermal modules of the 19^th and 20^th centur­ies, capable of provid­ing hot water, heat­ing, and elec­tri­city. In the early 1800s, French math­em­atician Joseph Four­ier used the helio­ther­mo­meter to model global warm­ing. He observed that the atmo­sphere allows sunlight to penet­rate while trap­ping some of its heat: this is the green­house effect.

Augustin Mouchot, pion­eer of Solar Energy

The French inventor has several major innov­a­tions to his credit. He designed a para­bolic solar concen­trator to heat water and produce steam. He built a solar machine using this steam to oper­ate a pump, thus demon­strat­ing the mech­an­ical applic­a­tion of solar energy. Always seek­ing new applic­a­tions, Mouchot arrived in Algeria on 6 March, 1877, to work with the colo­nial army. He imme­di­ately tested an improved solar oven: a trun­cated conical reflector with a cylindrical glass metal pot placed at the centre of the reflector to serve as a boiler. The assembly weighs between thir­teen and eight­een kilos; it can be folded and stored in a 130cm² case. Before witnesses, Mouchot baked a pound of bread in forty-five minutes, nine hundred grams of pota­toes in one hour, a beef stew in three hours, and a roast in less than thirty minutes!

The First Commer­cial Solar Water Heater

In 1882, phys­i­cist Samuel P. Langley used a solar box to heat water during his ascent of Mount Whit­ney, Cali­for­nia, in extremely cold weather. In 1891, inspired by this exper­i­ence, Amer­ican Clar­ence Kemp paten­ted a method combin­ing the expos­ure of metal tanks to the sun with the green­house effect to improve the collec­tion and reten­tion of solar heat. He named his inven­tion Climax, making it the first solar water heater to be proposed for sale.

An “Eternal” Clock

In 1950, the Genevan watch­maker Patek Phil­ippe launched a new clock. Powered by selen­ium solar cells, it combines a conven­tional mech­an­ical clock with a photo­elec­tric motor. The small amount of elec­tri­city produced is sent directly to the motor, which turns a gear to wind the spring. Four hours of light suffice for its oper­a­tion. This inven­tion preceded the first auto­matic move­ment for wrist­watches by several years.

A Small Solar Car

On 31 August, 1955, at the Powerama auto show in Chicago, William G. Cobb, a General Motors employee, presen­ted Sunmobile, the first mini­ature car powered by solar energy. It meas­ures thirty-eight centi­metres in length and incor­por­ates twelve selen­ium photo­elec­tric cells.

The First Solar Radio

In April 1956, the Amer­ican brand Admiral launched the 7L series, the first port­able tran­sistor radios powered by solar energy. Avail­able in four colours, these radios cost $59.95 and oper­ated on batter­ies or with the optional Sun Power Pak for direct power from sunlight or an incan­des­cent bulb. This radio model, equipped with thirty-two silicon solar cells, was one of the first consumer photo­vol­taic products. Despite initial enthu­si­asm, its sales were disap­point­ing due to its high price. Today, the 7L series with solar panels, although rare, still works very well.

The Solar Do-Noth­ing Machine: a Toy

In 1957, at the request of the Amer­ican company Alcoa (Aluminum Company of Amer­ica), design­ers Charles and Ray Eames created a toy: coloured shapes rotated and oscil­lated by motors powered by a small solar panel. Mirrors are used to concen­trate light on the solar cells. The entire assembly is made of aluminium. The Solar Do-Noth­ing Machine aimed to promote Amer­ican ingenu­ity and lead people towards a posit­ive future.

The First Solar-Powered Satel­lite

In 1955, the Naval Research Labor­at­ory considered using solar energy to power satel­lites. The light weight, durab­il­ity, and renew­able nature of photo­vol­taic panels make them partic­u­larly suit­able for space applic­a­tions. This exper­i­ment­a­tion was concret­ised by the launch of the Vanguard 1 satel­lite on 17 March, 1958. Although it was the fourth arti­fi­cial satel­lite launched from Earth, Vanguard 1, equipped with a small solar panel of about one watt, was the first to use solar energy and prove the viab­il­ity of solar power in space. This break­through enabled other Amer­ican satel­lites to oper­ate for years in the hostile envir­on­ment of space, paving the way for future innov­a­tions in the field of renew­able ener­gies.

The First Solar-Powered Airplane

On 4 Novem­ber, 1974, broth­ers Roland A. and Robert J. Boucher flew the first unmanned solar airplane, named Sunrise, over the Mojave Desert in Cali­for­nia. The first flight lasted twenty minutes at an alti­tude of one hundred metres. The airplane had 4,096 solar cells on its wing provid­ing power of 450 W. Its success led to the construc­tion of Sunrise II in 1975, funded by the Defense Advanced Research Projects Agency (Darpa). This new airplane, with a wing­span of 9.75 metres, identical to the first model, was equipped with 4,480 solar cells provid­ing 600 W and a battery system for control. It success­fully completed several flights before being damaged by a sand­storm.

The First Commer­cial Solar Calcu­lator

The first solar calcu­lator to be mass-produced, the Sharp Sunman EL-8026, used thin-film solar cells that had only just been developed. It was an improved version of the EL-8020 model, equipped with batter­ies. Its distinct­ive design featured two Sharp EL-225 solar modules moun­ted on the back, facing away from the screen. The front module, the EL-224, was designed for larger profes­sional infra­struc­tures such as light­houses and off-grid install­a­tions.

The Achieve­ment of the Quiet Achiever

Designed by Australian engin­eer and adven­turer Hans Tholstrup, the Quiet Achiever is a solar car that made history. It success­fully trav­elled a distance of four thou­sand kilo­metres across Australia, from Perth to Sydney, between 19 Decem­ber, 1982, and 7 Janu­ary, 1983. This jour­ney, under­taken by Hans Tholstrup and racing driver Larry Perkins, was a major achieve­ment, prov­ing the solar car’s abil­ity to travel long distances using solar energy.

Solar Cells in Cloth­ing

Wear­able Solar is a research project on the possib­il­it­ies of integ­rat­ing solar cells into textiles. Two models in partic­u­lar were created in 2013: the Wear­able Solar Dress and the Wear­able Solar Coat. Sixty-two flex­ible thin-film solar cells are attached in serial pairs, held by slits in the leather of the dress. This arrange­ment allows the leather to fall freely, redu­cing the mech­an­ical stress on the cells. The leather or wool (coat) proto­types can reveal the solar cells to the sun or fold them away, making them invis­ible. The internal struc­ture of the solar modules, achieved through layer­ing, mimics the layered cells of the human body, natur­ally inter­act­ing with sunlight and trans­form­ing the body into a source of renew­able energy. One hour of full sunlight can thus recharge a smart­phone halfway. Pauline Van Dongen, a Dutch fash­ion creator, Chris­ti­aan Holland, project leader at Geld­er­land Valor­iseert of the Univer­sity of Applied Sciences of Arnhem (HAN), and Gert Jan Jonger­den, a solar energy expert, are behind this project.