SOLAR ELECTRICAL APPLICATION-

1876 - PHOTOELECTRIC DREAMS

William Grylls Adams, who, with his student, Richard Evans Day, discovered in 1876 that a solid material - selenium - produced electricity when exposed to light. Today, we refer to electricity produced directly from light as the photovoltaic effect.

When William Grylls Adams and his student, Richard Evans Day, discovered that an electrical current could be started in selenium solely by exposing it to light, they felt confident that they had discovered something completely new. Werner von Siemens, a contemporary whose reputation in the field of electricity ranked him alongside Thomas Edison, called the discovery "scientifically of the most far-reaching importance." This pioneering work portended quantum mechanics long before most chemists and physicist had accepted the reality of atoms. Although selenium solar cells failed to convert enough sunlight to power electrical equipment, they proved that a solid material could change light into electricity without heat or without moving parts.

1953 - THE DREAM BECOMES REAL

Gerald Pearson, Daryl Chapin, and Calvin Fuller (left-to-right), the principle discoverers of the silicon solar cell, the first material to directly convert enough sunlight into electricity to run electrical devices, measure electrical energy produced by one of their first cells under a lamp. (with permission from ATT Bell Labs)

In spring 1953, while researching silicon for its possible applications in electronics, Gerald Pearson, an empirical physicist at Bell Laboratories, inadvertently made a solar cell that was far more efficient than solar cells made from selenium. Two other Bell scientists - Daryl Chapin and Calvin Fuller - refined Pearson's discovery came up with the first solar cell capable of converting enough of the sun's energy into power to run everyday electrical equipment. Reporting the Bell discovery, The New York Times praised it as "the beginning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.

1956 Searching for Applications

During the first years after the discovery of the silicon solar cell, its prohibitive cost kept it out of the electrical power market. Desperate to find commercial outlets for solar cells, novelty items such as toys and radios run by solar cells were manufactured and sold as this advertisement illustrates.

Although technical progress of silicon solar cells continued at breakneck speed - doubling their efficiency in eighteen months - commercial success eluded the Bell solar cell. A one-watt cell cost almost $300 per watt in 1956 while a commercial power plant cost 50 cents a watt to build at that time. The only demand for silicon solar cells came from radio and toy manufacturers to power miniature ships in wading pools, propellers of model DC-4's, and beach radios. With solar cells running only playthings, Daryl Chapin could not help but wonder, "What to do with our new baby?"

Late 1950s - Saved by the Space Race

The late Dr. Hans Ziegler, the chief advocate for powering satellites with silicon solar cells

While efforts to commercialize the silicon solar cell faltered, the Army and Air Force saw the device as the ideal power source for a top-secret project - earth-orbiting satellites. But when the Navy was awarded the task of launching America's first satellite, it rejected solar cells as an untried technology and decided to use chemical batteries as the power source for its Vanguard satellite. The late Dr. Hans Ziegler, probably the world's foremost expert in satellite instrumentation in the late 1950s, strongly differed with the Navy. He argued that conventional batteries would run out of power in days, silencing millions of dollar worth of electronic equipment. In contrast, solar cells could power a satellite for years. Through an unrelenting crusade led by Dr. Ziegler to get the Navy to change its mind, the Navy finally relented and as a compromise, put a dual power system of chemical batteries and silicon solar cells on the Vanguard. Just as Ziegler predicted, the batteries failed after a week or so, but the silicon solar cells kept the Vanguard communicating with Earth for years. 

Early 1960s - Bringing Solar Cells Down to Earth

Hoffman Electronics, the leading manufacturer of silicon solar cells in the 1950s and 1960s, showed a variety of space satellites powered by the sun in a company brochure.

Despite solar cells' success in powering both American and Soviet satellites during the 1950s and early 1960s, many at NASA doubted the technology's ability to power its more ambitious space ventures. The agency viewed solar cells as merely a stopgap measure until nuclear power systems became available. But solar engineers proved the skeptics wrong. They met the increasing power demands by designing ever larger and more powerful solar cell arrays. Nuclear energy, in contrast, never powered more than a handful of satellites. Hence, since the late 1960s, solar cells have become the accepted power source for the world's satellites. The increasing demand for solar cells in space opened an increasing and relatively large business for those manufacturing solar cells. Even more significantly, our past, present and future application of space would have been impossible if not for solar cells. The telecommunication revolution would never have gotten off the ground if not for solar powered satellites. Unbeknown to most, solar energy has played a crucial role in society's technological progress over the past forty years.

Early 1970s - The First Mass Earth Market

Solar cells power navigation warning lights and horns on most off-shore gas and oil rigs throughout the world

While the use of solar cells in space flourished during the 1960s and early 1970s, down on Earth electricity from the sun seemed as distant as ever. Cost was never a factor for space cells. Manufacturers worried more about size, efficiency and durability: the cost of the launch, and the continuing operation of equipment once in space far outweighed the price of power in space applications. But on Earth, the primary criteria is price per kilowatt hour. Solar-cell technology proved too expensive for terrestrial use until the early 1970s when Dr. Elliot Berman, with financial help from Exxon Corporation, designed a significantly less costly solar cell by using a poorer grade of silicon and packaging the cells with cheaper materials. Bringing the price down from $100 a watt to $20 per watt, solar cells could now compete in situations where people needed electricity distant from power lines. Off-shore oil rigs, for example, required warning lights and horns to prevent ships from running into them but had no power other than toxic, cumbersome, short-lived batteries. Compared to their installation, maintenance and replacement, solar modules proved a bargain. Many gas and oil fields on land but far away from power lines needed small amounts of electricity to combat corrosion in well heads and piping. Once again, electricity from the sun saved the day. Major purchases of solar modules by the gas and oil industry gave the fledgling terrestrial solar cell industry the needed capital to persevere.

1970s - Captain Lomer's Saga

Solar cells power the lights of almost every lighthouse run by the U.S. Coast Guard

It cost the Coast Guard more money to install, maintain and replace the non rechargeable batteries that powered its buoys than the buoys themselves. A brave Coast Guard officer, then Lieutenant Commander Lloyd Lomer, who had training in optics and physics, believed that their replacement by solar modules could save taxpayers millions of dollars and do the job better. But his commander refused to listen. Exasperated by such stonewalling, Lomer finally appealed to higher authorities and got the nod to solarize the Coast Guard's navigational aids. President Ronald Reagan commended Lomer for "saving a substantial amount of the taxpayer's money through your initiative and managerial effectiveness as project manager for the conversion of aids to navigation from battery to solar photovoltaic power." Thanks to Lomer's persistence, not only does the U.S. Coast Guard rely almost entirely on solar power for all of its buoys and light houses but so do all the other Coast Guards throughout the world.

1974 - Working on the Railroad

The first solar-powered crossing depicted in this picture began operating at Rex, Georgia in 1974 for the Southern Railway (now the Norfolk/Southern)

When the Southern Railway put in solar modules to power warning lights at a railroad crossing near Rex, Georgia, the railroad had so little confidence that the cells would work that they also connected the lights to a utility line for back up. But that winter, ice build up on the wires caused them to fall, and the only electricity in Rex, Georgia came from the solar array. Around the same time, novel telecommunication systems such as microwave repeaters had made telephone and power poles that followed the tracks obsolete. and many railroad lines wanted to remove these poles to save on maintenance. To avoid train accidents, the railroads still needed a few watts here and there to power signaling and shunting equipment along their lines. Word spread about the Southern's success with solar, leading many lines in the United States and throughout the world to choose the sun to run on site their track safety devices rather than waste huge sums to bring in distant centrally-generated electricity.

Late 1970s - Long Distance for Everyone

One of Telecom Australia's (now Telstra) many solar-powered microwave repeaters, whose installation began in the late 1970s, to provide Australians living in remote areas with same high-quality telecommunication service as those living in larger cities such as Sydney and Melbourne had.

In the early 1970s, the Australian government mandated Telecom Australia, the quasi-public agency in charge of the nation's telecommunications, to provide every citizen, no matter how remotely situated, with the same high-quality telephone and television service that those living in urban areas took for granted. To accomplish the mandate, Telecom Australia searched for an reliable stand-alone power source to run rural telephones and microwave repeater stations. Generators and wind machines did not pass muster. Fortunately, solar cells had come down in price to put them in the running as well. Putting them through a vigorous testing program, Telecom Australia came up with a module design that would only need periodic servicing checks despite the harsh conditions of the Australian outback. Thirteen solar-powered repeaters went up in 1978, each situated twenty-five miles apart. They worked so well that Telecom Australia put up seventy more - the longest network consisting of forty three repeaters spanning fifteen hundred miles. The Australian experience helped make, by 1985, solar modules the power system of choice for remote telecommunications.

1970s - Father Verspieren Preaches the Solar Gospel

The "perfect marriage" of sun and water, made possible by solar cells, made the sun a friend, rather than an enemy, in the drought-stricken sub-Sahara, by providing, instead of denying, precious water for people and livestock.

Dominique Campana, a graduate student in Paris in the 1970s, came up with the idea of applying solar cells to pump water. French physicist Jean Roger translated her concept into a working prototype on the island of Corsica. People from all over the world concerned about supplying healthy water to those where no power existed came to see the solar-run pump. Among the visitors was Father Verspieren - a French priest whom the Malian government put in charge to tap the deep aquifers that run underneath the sands of Mali to save the country then suffering from the worst drought of the twentieth century. After viewing the Corsican installation, Verspieren saw the sun as the solution, not the problem. Starting in the late 1970s, Verspieren initiated a solar water pumping program that has become the template for success in the developing world. Fewer than ten pumps powered by solar cells existed in the world when Father Verspieren installed his first in Mali. Now, tens of thousands power pumps on every continent. As one expert stated, "Thank you, Father Verspieren that today we have lots of solar pumps everywhere and for showing the international community that solar cells are an excellent power source for the people of Africa and the rest of the developing world.

1980s - Electrifying the Unelectrified

A common sight in French Polynesia: solar modules on thatched roofs

From the 1960s through the 1980s, experts planned to power rural parts of the developing world - where the majority live - according to the Western model: build centralized generating plants and by networks of wires transmit the electricity to consumers. But constructing such networks has proven too costly, leaving billions of rural people without electricity. These people have had to rely on costly and inadequate ad hoc solutions to light their homes and power their appliances such as kerosene lamps, automobile batteries and generators. In many cases, solar cells have provided to those living far away from electrical lines the means to obtain higher quality lighting and more reliable power. Since 1983, half of the households in the outlying islands of Tahiti have relied on solar-generated power. More rural Kenyans use electricity from the sun than that offered by the national utility. At least one hundred thousand families in Mexico, Central America and the West Indies run their lights, television sets, and radios with solar electricity. These successes has led the World Energy Council, the international organization of utilities, to recognize, "Solar cells for use at individual houses are a very important development that warrants particular attention as they are ideal for low-power rural applications.

1980s - Solarizing the Electrified

Solar electric modules cover the rooftops of this apartment complex in Bremen, Germany

When governments of developing countries began to fund solar energy programs in the mid-1970s and early 1980s, they favored large-scale, centralized solar-cell plants. Since engineers can tailor solar electric modules to any particular electrical need at the site of use, many came to realize that solar cells could allow each building to become its own electrical power plant by placing them on the roof. This would eliminate much of the capital costs inherent in constructing a centralized power plant such as buying land, putting up transmission lines, laying foundations and support structures and so on. Swiss engineer Marcus Real proved the economic advantages of the micro approach by selling 333 rooftop solar systems to homeowners in Zurich, Switzerland. After the success at Zurich, no one talks about centralized solar-cell plants anymore. Instead, governments are developing financial incentives to encourage homeowners to place modules on their rooftops. Architects and builders can use solar-cell material to build with, becoming facades, roofing, walls and windows. This eliminates a lot of duplication and extra work. For such reasons, Architectural Record lauds this approach as "a cost-effective energy option that architects should routinely consider.

1990s - Better Cells, Cheaper Cells

Tubular octagons of crystalline silicon shaped in a die eliminate much of the expense of producing solar cells.

As the price of solar cells has dropped over the years, they have become the least expensive power source for small-scale electrical demands located away from utility lines. Solar cells have also proven a cheaper source of electricity whenever people have to excavate to lay utility lines underground. Solar cells have therefore saved taxpayers millions in powering emergency call boxes along highways. When a new bus shelter goes up, cities have discovered that it costs less to install solar cells to keep it lit at night than to dig up pavement for the placement of power lines. For the same reason, many municipalities or the highway departments choose solar cells to run street lamps or warning lights. However, solar electricity still costs more to generate than power from existing overhead utility lines. Many believe that current production methods - growing silicon into cylinders or casting them as ingots and then cutting them into very small pieces - cost too much to ever bring down the price to compete with centrally-generated electricity. To dramatically bring down their price, solar cell companies have invested a lot of money to somehow either grow the silicon into a shape that eliminates most of the slicing or merely deposit solar cell material onto an inexpensive but rigid support structure such as ceramic, glass, plastic, or steel.

The Silent Revolution Continues...

With its wing covered entirely by solar cells, the Pathfinder has flown higher than any other aircraft except for the famous spy plane, the Blackbird.

The solar-cell industry has grown dramatically over the last twenty years, increasing output 200 fold in this time period. Today, those needing power in remote areas no longer regard solar cells as an alternative source of energy but consider them the most effective solution. Institutions like the World Bank now believe that solar cells "have an important and growing part to play in providing electrical services to the developing world." In less developed countries, where over half of the population must travel over two hours just to make a phone call, the United Nations today sees solar cells offering these people "for the first time a real practical possibility of reliable telecommunications for general use. Opportunities for solar cells in the developed world continue to grow as well. Solar cells produce electricity than highly polluting diesel generators. The National Parks Service and Defense Department have begun to replace their generators with solar cells. No longer on the highways or roads do portable generators power portable signs warning motorists of lane closures or other important news. Solar cells have replaced them. As the increasing demand for electricity starts to clog the world's power lines, like traffic jams on our freeways, solar cells strategically built on or into homes and buildings can provide the much needed electricity without further burdening the old electrical routes. Or at times, like on a hot August afternoon, when the electrical highways have emptied, mini-electrical plants consisting of solar modules can refill transmission lines to prevent brownouts and blackouts. The skyrocketing price of oil and natural gas and their dwindling supplies as world demand continues to grow will force the world to use more and more electricity generated by the sun. The change from fossil fuels to solar cells will also help clean up our polluted skies and keep a lid on global warming. As Science magazine wrote more than twenty years ago, "If there is a dream solar technology, it is solar cells, a space-age electronic marvel at once the most sophisticated solar technology and the simplest, most environmentally benign source of electricity yet conceived.

SOLAR THERMAL APP HISTORY-

SOLAR HOT WATER HEATING

A cross-section of a hot box. Eighteenth- and nineteenth-century scientists used the hot box to test how much sunheat glass-covered enclosures could trap.

Horace de Saussure, a noted Swiss naturalist, observed in the 1760s, "It is a known fact, and a fact that has probably been known for a long time, that a room, a carriage, or any other place is hotter when the rays of the sun pass through glass. To determine the effectiveness of trapping heat with glass covers, de Saussure built a rectangular box out of half-inch pine, insulated the inside, and had the top covered with glass, and had two smaller boxes placed inside. When exposed to the sun, the bottom box heated to 228 degrees F (109 degrees C) or 16 degrees F (9 degrees C) above the boiling point of water. de Saussure was unsure of how the sun heated the glass boxes. Today we can better explain what happened. Sunshine penetrated the glass covers. The black inner lining absorbed the sunlight and converted it into heat. Though clear glass allows the rays of the sun to easily enter through it, it prevents heat from doing the same. As the glass trapped the solar heat in the box, it heated up. Its inventor realized that someday the hot box might have important practical applications, as "it is quite small, inexpensive and easy to make." Indeed, the hot box has become the prototype for the solar collectors that have provided sun-heated water to millions since 1892.

Early Heating Efforts

The first solar water heaters were bare metal tanks painted black containing water and tilted to face the sun.

In the nineteenth century, no easy way existed to heat water. People generally used a cook stove for this purpose. Wood had to be chopped or heavy hods of coal lifted, then the fuel had to be kindled and the fire periodically stocked. In cities, the wealthier heated their water with gas manufactured from coal. Still, the fuel didn't burn clean and the heater had to be lit each time someone wanted to heat water. If someone forgot to extinguish the flame, the tank would blow up. To add to the problem of heating water, in many areas, wood or coal or coal-gas cost a lot and many times could not be easily obtained. To circumvent these problems, many handy farmers or prospectors or other outdoors men devised a much safer, easier, and cheaper way to heat water - placing into the sun a metal water tank painted black to absorb as much solar energy as possible. These were the first solar water heaters on record. The downside was that even on clear, hot days it usually took from morning to early afternoon for the water to get hot. And as soon as the sun went down, the tanks rapidly lost their heat because they had no protection from the night air.

1891 - World's First Solar Solution

Advertisement for the Climax Solar-Water Heater, the world's first commercial solar water heater, patented in 1891.

The shortcomings of the bare tank solar water heaters came to the attention of Clarence Kemp, who sold, in Baltimore, Maryland, the latest home heating equipment. In 1891, Kemp patented a way to combine the old practice of exposing metal tanks to the sun with the scientific principle of the hot box, thereby increasing the tanks' capability to collect and retain solar heat. He called his new solar water heater the Climax - the world's first commercial solar water heater. Kemp originally marketed his invention to eastern gentlemen whose wives had gone off with their maids to summer at some resort, leaving their husbands to fend for themselves. The solar water heater, Kemp advertised, would simplify housekeeping duties for this class of men already burdened by their wives and domestic staffs absence and unaccustomed to such work as lighting the gas furnace or stove to heat water.

1896 - Sunshine States Use Advantage

The home of Walter van Rossem, overlooking the Pasadena Rose Bowl. In 1896, the van Rossem home had a Climax Solar Water Heater placed on the roof.

In California and other such temperate states, having greater amounts of sunshine throughout the year and higher fuel costs (than in places like Maryland) made it essential for residents to take their solar assets seriously and not waste them. The Climax sold well in such areas. Sixteen hundred had gone up in homes throughout Southern California by 1900, including the one installed for Walter van Rossem's mother in Pasadena where three years earlier a third of the households in this California city heated their water with the sun.

Early 1900s - New Invention Revolutionizes Business

This Pomona Valley, California family had switched in 1911 from the Climax tanks in a glass-covered box system to a solar panel for their hot water needs.

Cutaway drawing shows how the Pomona Valley installation worked. The sun-heated water flowing through pipes attached to metal backing inside a glass-covered box. The heated water, lighter than the incoming cold water, naturally and immediately rose through the pipes to an insulated storage tank where the sun-heated water was kept warm for use both day and night. Notice, too, the connection of the furnace to the storage tank, guaranteeing hot water even after several rainy days.

From the turn of the century to 1911, more than a dozen inventors filed patents that improved upon the Climax. But none changed the fact that the heating unit and the storage unit were one and the same and both laid exposed to the weather and the cold night air. Hence, water heated by the sun the night before never stayed hot enough to do the wash the next morning or to heat the bath. In 1909, William J. Bailey patented a solar water heater that revolutionized the business. He separated the solar water heater into two parts: a heating element exposed to the sun and an insulated storage unit tucked away in the house so families could have sun heated water day and night and early the next morning. The heating element consisted of pipes attached to a black-painted metal sheet placed in a glass-covered box. Because the water to be heated passed through narrow pipes rather than sat in a large tank, Bailey reduced the volume of water exposed to the sun at any single moment and therefore, the water heated up faster. Providing hotter water for longer periods put Bailey's solar hot water heater, called the Day and Night, at a great advantage over the competition. Soon the Climax went out of business. From 1909, when Bailey started up his business, through 1918, his company had sold more than 4,000 Day and Night Solar Hot Water Heaters.

1920s to 1940s - Nation's Use of Solar in Flux

Workman installing solar water heater on the roof of the laundry room in a Florida subdivision going up in the 1930s. Like most housing in Florida, every house in this tract used solar energy to heat its water.

Because people had to rely on expensive imported coal or wood for fuel, many found solar a cheaper alternative. The huge discoveries of natural gas in the Los Angeles basin during the 1920s and 1930s killed the local solar water heater industry. Rather than lose money from the energy changes in the Southland, Bailey took the innovations he had made in solar and applied them to develop the thermostatically-controlled gas water. His Day and Night Gas Water Heater made him his second fortune. He also sold the patent rights of the Day and Night Solar Water Heater to a Florida firm. A building boom in Florida during the 1920s had tripled, but just as in California before the great oil strikes, people had to pay a pretty penny to heat water. The high cost of energy combined with the tropical climate and the great growth in housing stock created a big business for those selling solar water heaters. By 1941, more than half the population heated its water with the sun! Declining electric rates after World War II, in tandem with an aggressive campaign by Florida Power and Light to increase electrical consumption by offering electric water heaters at bargain prices, brought Florida's once flourishing solar water heater industry to a screeching halt.

1960s and 70s - Japanese Embrace the Sun

Cylindrically shaped metal water tanks, placed in glass-covered boxes, covered the roofs of almost four million Japanese homes by 1969.

Unlike America during the post World War II years, the Japanese lacked cheap and abundant energy to supply hot water on demand. Rice farmers in particular yearned for a hot bath after working long hours in the hot humid patties. But to heat water, they had to burn rice straw, which they could have otherwise used to feed their cattle or fertilize the earth. So when a Japanese company began marketing a simple solar water heater consisting of a basin with its top covered by glass, more than 100,000 were in use by the 1960s. People living in the towns and cities bought either a plastic solar water heater that resembled an inflated air mattress with a clear plastic canopy or a more expensive but longer lasting model that resembled the old Climax Solar Water Heaters - cylindrically shaped metal water tanks placed in a glass-covered box. Close to 4,000,000 of these solar water heaters sat on roof tops by 1969.

The advent of huge oil tankers in the 1960s allowed the Japanese access to new oil fields in the Middle East, supplying them with cheap, abundant fuel. As had happened in California and Florida, the solar water heater industry collapsed. But not for long. The Oil Embargo of 1973 and the subsequent dramatic increase in the price of petroleum revived the local solar water heater industry. Annual sales of greater than 100,000 units continued to hold steady from 1973 until the second oil shock of 1979. Sales then jumped to almost half a million that year and leaped to nearly a million the following year. By this time, the Japanese favored solar water heaters closely resembling the type introduced to California in 1909 by William J. Bailey with the heating and storage units separated. As the price of oil began to stabilize in 1985 and then drop sharply in subsequent years, so did the sales of solar water heaters; still the Japanese purchase around 250,000 each year. Today, more than 10,000,000 Japanese households heat their water with the sun.

1970s - Australia Hops Aboard

Solahart, the leading Australian manufacturer of solar water heaters, chose in the 1970s an integral collector-tank configuration for easy installation on pitched roofs commonly found in Australia. The new design also saved money by eliminating extensive piping and the need for a heavy storage tank in the attic.

From the 1950s to the early 1970s, a few thousand Australians relied on the sun to heat their water. The numbers grew phenomenally as a consequence of two huge spikes in oil prices in 1973 and 1979. Interestingly, purchasing of solar water heaters during these heady years varied from state to state. While 40 to 50% of those living in Australia's Northern Territory heated their water with the sun, the percentage dropped to around 15% in Western Australia and sunk to below 5% in the more populated eastern states. The sharp difference had more to do with the cost of electricity than the amount of sun available. People in the Northern Territory and Western Australia bought electricity generated by imported and increasingly costly petroleum while those in the eastern states of New South Wales, Queensland and Victoria had their electricity produced by locally mined and very cheap coal. In the late 1980s, the Australian solar water heater market began to stagnate. Pipelines bringing newly discovered natural gas to previously fuel-short regions such as the Northern Territory and Western Australia has braked any growth in these once fertile markets for solar water heaters. Exports now account for more than 50% of the sales made by Solahart, Australia's leading manufacturer of solar water heaters.

Israel Heats Up

Levi Yissar, who brought solar water heating to Israel, stands next to his prototype. It closely resembled the type introduced in California in the first decade of the twentieth century with heating and storage separated. The headline in the this 1953 issue of Israel's principle newspaper, Maariv, reads, "Heating Water by the Sun Begins."

Unlike the United States and much of Europe, Israel, like Japan, found itself without sufficient fuel supplies in the early 1950s. The power situation became so bleak in the early days of the Jewish State that the government had to forbid heating water between 10 p.m. and 6 p.m. Despite mandatory domestic rationing of electricity, power shortages worsened, causing pumping stations to fail and threatening factory closures. A special committee impaneled by the government could only suggest the purchase of more centralized generators to overcome the problem. This conclusion raised the ire of Israeli engineer, Levi Yissar, who complained, "How about an already existing energy source which our country has plenty of - the sun. Surely we need to change from electrical energy to solar energy, at least to heat our water." Yissar put his money where his mouth was, becoming Israel's first manufacturer of solar water heaters. By 1967 about one in twenty households heated their water with the sun. But cheap oil coming from Iran in the late 1960s as well from oil fields captured during the Six Day War drastically reduced the price of electricity and the number of people purchasing solar water heaters.

With the government of Israel mandating the use of the sun for heating water, solar waters have become a common sight on Israeli rooftops.

Israeli success in the Yom Kippur War brought on the infamous oil boycott of 1973. The Israelis responded by mass purchasing of solar water heaters. By 1983, 60% of the population heated their water with the sun. When the price of oil dropped in the mid 1980s, the Israeli government did not want people backsliding in their energy habits as has happened in the rest of the world. It therefore required its inhabitants to heat their water with the sun. Today, more than 90% of Israeli households own solar water heaters.

Pool Owners Get in the Swim

Two swimmers enjoy pool water heated by the Climax Solar Water Heater.

Solar swimming pool water heaters rank as the most successful yet least heralded commercial solar application. The use of solar energy for pool heating and the equipment and need of pool owners make a perfect match. The storage unit for the solar heated water already exists - the swimming pool. The pump needed to push water through the solar collector also must be bought irrespective of the technology used to heat the water. The pool owner merely has to purchase the solar collectors. Since those using the pool only want the temperature of the pool to reach no greater than 80 or so degrees F (27 degrees C), the solar collector does not require a costly glass cover or expensive metal sheeting and piping. In fact, in the 1970s, American Freeman Ford developed low-cost plastic to act as the solar collector. Exposed to the sun, water would pass through narrow ducts in the plastic and heat up sufficiently to warm the pool. Of course, the outdoor swimming season harmoniously coincides with the maximum output of the solar collectors. Even with other forms of energy selling very cheaply, the pool owner buying a solar unit starts to save money very quickly. In the United States alone, solar swimming pool heaters have produced the energy output equivalent to running ten nuclear power plants.

What are Photovoltaic (PV) Panels?

Photovoltaic Panels are are used to transform sunlight energy into electrical energy.  ”PV panel” is the common name for a photovoltaic panel.  Literally translated photovoltaic means "light-electricity".

Photovoltaic means "light-electricity".  It is formed from photo- which means light and -voltaic which means electrical current or electricity.

PV panels are made up of smaller sections called solar cells.  Solar cells, like batteries, each have a rated value of voltage (V or volts) and amperage (A or amps).  The total power in wattage (W or watts) delivered is the voltage times the amperage.

Volts x Amps = Watts or

V x A = W

Batteries can be arranged in parallel or in series depending on the requirements of the device we want to power.

Batteries in Parallel

In parallel the amperage is additive and the voltage is constant.  If we have batteries that are 1.5 V each and 1.8 A each then:

A_total = A₁ + A₂

A_total = 1.8 A + 1.8 A = 3.6 A and

Power = 1.5 V x 3.6 A = 5.4 Watts

Batteries in Series

In series the voltage is additive and the amperage is constant.

V_total = V₁ + V₂

V_total = 1.5 V + 1.5 V = 3.00 V and

Power = 3.00 V x 1.8 A = 5.40 Watts

How many of these batteries will you need and how will you have to arrange them if you want to power a 6 volt radio?

Solar Cells or Panels in Parallel

In parallel the amperage is additive and the voltage is constant.  If we have cells that are 0.5 V each and 0.1 A each then:

A_total = A₁ + A₂

A_total = 0.1 A + 0.1 A = 0.2 A and

Power = 0.5 V x 0.2 A = 0.1 Watts

Solar Cells or Panels in Series 

In series the voltage is additive and the amperage is constant.

V_total = V₁ + V₂

V_total = 0.5 V + 0.5 V = 1.0 V and

Power = 1.0 V x 0.1 A = 0.1 Watts

Solar cells are connected and arranged into a single panel.  Some standard panel sizes are 12 volt and 24 volt.

How many of these cells will you need and how will you have to connect them to make a 12 volt solar panel?

If you have 2 panels that are rated at 12 volts each how many of them will you need and how will you have to connect them if you want a 24 volt system?

The terms "Solar Panel" and "Photovoltaic Panel" describe two different devices.  We use the terms as follows:

A Solar Panel collects and utilizes heat energy from the sun.

A Photovoltaic Panel transforms light energy into electrical energy.

CONCEPT--

 What is Solar Energy?

The Law of Conservation of Energy:

• Energy can only change from one form to another.
• Energy can not be created or destroyed.

Solar Energy is the energy from the Sun.  The Sun is a big ball of heat and light resulting from nuclear fusion at its core.  The nuclear reaction releases energy that travels outward to the surface of the Sun.  Along the way to the surface the energy transforms so that by the time it is released it is primarily light energy.  Sunlight.  The two major types of solar energy that make it to Earth are heat and light.

Solar energy is often called "alternative energy" to fossil fuel energy sources such as oil and coal.

One example of our use of solar heat energy is for water heating systems.  A solar panel is used to collect heat.  The heat is transferred to pipes inside the solar panel and water is heated as it passes through the pipes.  The hot water, heated by the Sun, can then be used for showers, cleaning, or heating your home.

We also use solar thermal energy through passive solar designs.  Windows or skylights in your home can be designed to face the Sun so that they let heat into the house, keeping you warmer in the winter.

The light energy from the Sun can be transformed into electrical energy and used immediately or stored in batteries. Photovoltaic (PV) panels are the devices that convert light energy into electrical energy.

Energy changes from one Form to Another.

Let's look at a solar powered vehicle that runs on electricity directly from solar energy as a simple example in the transformation of energy from one form to another.

• Sunlight hits the PV panel and the panel transforms the light energy into electrical energy.
• The electrical energy (electricity) passes through the wire circuit to the motor.
• The motor transforms the electrical energy into mechanical energy to turn the drive shaft which turns the wheels.
• The wheels rotate on the ground to move the vehicle transforming mechanical energy into vehicle motion (kinetic energy).

Solar Vehicle Ideal Energy Chain:  

Light Energy >> Electrical Energy >> Mechanical Energy >> Kinetic Energy

Energy transformation is not perfect.....

The above case is ideal because not all systems are perfect and in reality there will be losses of energy from our system.

In a simplified view of this case some losses will be from:

• friction of electrons passing through the wires;  this is released as heat energy.
• friction of the drive shaft or wheels on the ground;  this is released as either heat or sound energy.

Even with these losses the law of conservation of energy still holds.  The amount of energy into a system will always equal the amount of energy out of a system.

SUN THE FATHER OF SOLAR ENERGY-

How energy we can consume from sun?

The sun is a star.  It is the largest object in our solar system and one of the larger stars in our galaxy.  The source of energy in the Sun is at its core where hydrogen is converted to helium in a thermonuclear reaction.  This energy travels from the core to the surface of the Sun and is released into space primarily as light.  The energy that comes to the Earth is in 2 main forms, heat and light.

Every hour, enough sunlight energy reaches the Earth to meet the world’s energy demand for a whole year.

--- U.S. Department of Energy ---

The amount of energy from the Sun that reaches the Earth annually is 4 x 10¹⁸ Joules.***

4 x 10¹⁸ Joules/ Year ÷ 365 Days/ Year = 1 x 10¹⁶ Joules/ Day

1 x 10¹⁶ Joules/ Day ÷ 24 Hours/ Day = 4 x 10¹⁴ Joules/ Hour

The amount of energy consumed annually by the world's population is about 3 x 10¹⁴ Joules.

Speed of Light Energy from the Sun to Earth.

The earth is the third planet from the sun at a distance of about 93,000,000 (93 million) miles.  If you could pitch a fast baseball to the sun at 100 miles per hour (mph) it would take the ball over 100 years to get there.  On the other hand, it only takes light energy 8½ minutes to reach the earth from the surface of the sun, traveling at the speed of light of course.

Pitching a Baseball at 100 mph to the Sun***

93,000,000 miles ÷ 100 miles/ hour

= 930,000 hours to reach the Sun.;

930,000 hours ÷ 24 hours/ day

= 38,750 days to reach the Sun;

38,750 days ÷ 365 days per year= 106.16 years to reach the Sun

Light Energy traveling to Earth***

The speed of light is equal to about 11,000,000 (11 million) miles/ minute. 

93,000,000 miles ÷ 11,000,000 miles/ minute

= 8.45 minutes for light  to travel from the Sun to Earth.

HISTORY OF SOLAR ENERGY

Solar energy has been used by humans for thousands of years.  For example, ancient cultures used energy from the sun to keep warm by starting fires with it.  They also kept their homes warm through passive solar energy designs.  Buildings were designed so that walls and floors collected solar heat during the day that was released at night to keep them warm.  If you have ever stood in the sun to get warm then you too have utilized solar thermal energy.

The discovery of photovoltaics happened in 1839 when the French physicist Edmond Becquerel first showed photovoltaic activity.  

Edmond had found that electrical current in certain materials could be increased when exposed to light.  66 years later, in 1905, we gained an understanding of Edmonds' work when the famous physicist Albert Einstein clearly described thephotoelectric effect, the principle on which photovoltaics are based.  In 1921 Einstein received the Nobel Prize for his theories on the photoelectric effect.

Solar cells of practical use have been available since the mid 1950’s when AT&T Labs first developed 6% efficient silicon solar cells.  By 1960 Hoffman Electronics increased commercial solar cell efficiencies to as much as 14% and today researchers have developed cells with more than 20% efficiencies.  20% efficient means that out of the total energy that hits the surface of a solar cell, about 20% is converted into usable electricity.

The first long-term practical application of PV cells was in satellite systems.  In 1958 the Vanguard I, was launched into space.  It was the first orbiting vehicle to be powered by solar energy.  Photovoltaic silicon solar cells provided the electrical power to the satellite until 1964 when the system was shut down.  The solar power system was so successful that PV’s have been a part of world-wide satellite space programs ever since.  The sun provides endless nonpolluting energy to the satellite power systems and demand for solar cells has risen as a result of the telecommunications revolution and need for satellites.

The energy crisis and oil embargos of the 1970’s made many nations aware of their dependency on controlled non-renewable energy sources and this fueled exploration of alternative energy sources.  This included further research into renewable sources such as solar power, wind power and geothermal power.

An economic breakthrough occurred in the 1970's when Dr. Elliot Berman was able to design a less expensive solar cell bringing the price down from $100 per watt to $20 per watt.  This huge cost savings opened up a large number of applications that were not considered before because of high costs.  These applications included railroads, lighthouses, off-shore oil rigs, buoys, and remote homes.  For some countries and many applications, solar energy is now considered a primary energy source, not an alternative.