Solar energy has two histories that people usually tell at the same time without realizing it. One is solar thermal — using the sun’s heat, by concentrating it or absorbing it, to do useful mechanical or heating work. That history goes back to Greek and Roman house orientation. The other is solar photovoltaic — using the sun’s light to produce electric current directly in a semiconductor. That history starts in 1839 with Becquerel and gets commercially useful in 1954 at Bell Labs. This page tells both stories as one continuous arc, from ancient sunlit porticoes through today’s grid-scale utility modules — with a few notes from a working lender who watches long-useful-life equipment get financed every day.
Two histories, one fuel
Most stories about the history of solar energy blend two different technologies. Solar thermal means using the sun’s heat — by orienting a building to catch it, by absorbing it in a dark surface, or by concentrating it with a mirror or a lens to heat a working fluid. Solar photovoltaic, or PV, means using the sun’s light to produce electricity directly. The photovoltaic effect happens inside a semiconductor, where incoming photons free electrons and those electrons flow as direct current. The two technologies share sunlight as a fuel and nothing else. They have separate timelines, separate pioneers, and, until the 21st century, separate markets.
A working history of solar energy is the interleaving of those two threads. Until roughly 1950, almost every practical solar device was thermal. The 1954 Bell Labs breakthrough inverted that balance, and the growth industry of the last seventy years has been PV. Both threads matter, and the story below walks through them in order.
Ancient foundations
Passive solar design — orienting buildings to admit winter sun and shade summer sun — is old enough to predate the written record. Ancient Greek and Roman houses were often sited and arranged to catch low winter light through south-facing porticoes and to shade the same spaces from high summer sun with overhangs. Roman bathhouses used thin sheet-glass glazing on south-facing windows to trap solar heat for the warm-water rooms. The knowledge was practical and unmathematical — architects knew it worked because buildings that did it were warmer in winter and cooler in summer — but it is recognizably the same engineering idea that modern passive-solar homes use.
The most colorful ancient solar story is the claim that Archimedes set fire to a Roman fleet besieging Syracuse in 212 BC using bronze shields arranged as concentrating mirrors. Historians have spent decades arguing about whether the feat as described is physically plausible. The story illustrates a real principle — concentrated sunlight can deliver enough heat to ignite wood — but it should be treated as legend, not established history. The real lineage of concentrating solar power starts in the 19th century with engineers who could measure what they built.
The 19th-century pioneers
The key 19th-century year is 1839, when the 19-year-old French physicist Edmond Becquerel, working in his father’s laboratory, observed that an electrolytic cell made of two metal electrodes in an electricity-conducting solution produced more current when it was exposed to light. Becquerel had no theory of how that worked — the electron would not be identified for another fifty-eight years — but he had correctly observed the photovoltaic effect. The Britannica entry on the solar cell treats that observation as the origin of the entire photovoltaic lineage.
The solar-thermal side of the 19th century is associated with three inventors. Auguste Mouchout, a French mathematics instructor worried about Europe’s dependence on coal, built the first machine that converted solar heat into mechanical power. He demonstrated a solar-powered steam engine at the 1878 Paris Exposition that could also drive a refrigeration cycle. Around the same time, the Englishman William Grylls Adams, working with his apprentice Richard Day, designed an array of 17-by-10-inch flat silver mirrors that reflected sunlight onto a central boiler — the basic geometry we now call a solar power tower. Adams’s book A Substitute for Fuel in Tropical Countries argued, correctly as it turned out, that the idea would be most useful in sunny places without cheap coal. The Swedish-American engineer John Ericsson built parabolic-trough solar concentrators in the 1870s and 1880s, refining the geometry still used in some utility-scale thermal plants today.
The first photovoltaic device came in 1883, when the American inventor Charles Fritts coated a plate of selenium with a thin, nearly transparent layer of gold and found that the sandwich produced a current when illuminated. Fritts’s cell was about 1 to 2 percent efficient — enough to demonstrate the principle but not enough to displace a kerosene lamp. It would take the invention of the transistor and seventy years of semiconductor physics before a solar cell efficient enough to be useful in the field showed up.
Early 20th-century solar thermal
The early decades of the 20th century were mostly a story of solar thermal refinement. Henry E. Willsie, working in California in the first decade of the 1900s, built the first solar thermal system that could store heat well enough to produce power after sundown: he collected solar-heated water in insulated tanks and used the stored heat to drive a steam engine into the night. Frank Shuman, working with engineer Charles Vernon Boys, built a large parabolic-trough solar steam plant at Maadi, south of Cairo, that began pumping Nile water in 1913. Shuman’s plant ran productively for several years before cheap oil and the outbreak of the First World War shut down the solar-thermal-in-the-desert business model for several decades.
This is the era in which solar thermal proved, at utility scale, that it could do useful work — and in which fossil fuel became abundant and cheap enough that nobody was going to finance the alternative for most of the 20th century. Solar work continued in research labs, but the commercial industry effectively went dormant until the 1970s.
Bell Labs, 1954
On April 25, 1954, at Bell Telephone Laboratories in Murray Hill, New Jersey, three researchers — Daryl Chapin, Calvin Fuller, and Gerald Pearson — unveiled a silicon semiconductor solar cell with an energy-conversion efficiency of about 6 percent. That efficiency was an order-of-magnitude improvement over any earlier photovoltaic cell, and it was the first one efficient enough to be practically useful outside a laboratory. The American Physical Society treats the announcement as the birth of the modern photovoltaic industry.
Bell’s motivation was specific: the telephone company needed a reliable power source for remote rural telephone amplifier repeaters that did not require battery swaps. In 1955, Bell ran a field trial of silicon-powered repeaters in Americus, Georgia. Western Electric began licensing the technology commercially the same year — early industrial applications included PV-powered dollar-bill changers and devices that read computer punch tape. None of those applications became major markets, and for most of the 1950s and 1960s, silicon cells were too expensive to compete with coal-fired grid electricity almost anywhere on Earth. But the physics had been proven, and the cost curve had started.
Vanguard 1 and the space age
The first market where Bell Labs’ silicon cells were unambiguously the right technology was outer space. On March 17, 1958, the U.S. Navy launched Vanguard 1, a 3.2-pound aluminum sphere six inches across, into Earth orbit. Vanguard 1 carried two radio transmitters. One ran on a conventional mercury battery; the other ran on six small silicon solar cells mounted on the satellite’s body. The mercury-battery transmitter stopped working within weeks. The solar-powered transmitter ran for more than six years. According to NASA’s NSSDCA master catalog for the spacecraft, Vanguard 1 was the first satellite to use solar electric power, and it remains the oldest artificial object still in orbit.
The Vanguard mission settled a practical argument: solar cells in space paid for themselves, because any other power source for a satellite eventually ran out. For the next fifteen years, space power applications essentially paid for the silicon-cell industry. NASA’s requirement for reliable, long-lived cells pushed manufacturing tolerances and efficiency upward while unit costs remained high. The industry that eventually delivered rooftop and utility-scale modules to Earth customers was, for most of its first two decades, a space industry.
The oil shock, SERI, and NREL
The 1973 Arab oil embargo and the associated price shock were the proximate political causes of the U.S. government’s first serious investment in renewable energy research. Congress passed the Solar Energy Research, Development and Demonstration Act of 1974, which chartered the Solar Energy Research Institute (SERI) to coordinate federal solar R&D. SERI opened in Golden, Colorado on July 5, 1977, with photovoltaic researcher Paul Rappaport as its first director.
The Carter administration made SERI highly visible — Jimmy Carter put photovoltaic panels on the White House roof in 1979 — and President Carter’s public appearances at SERI on Sun Day in 1978 anchored solar politically as a national priority. Federal solar funding fluctuated significantly across subsequent administrations. In 1991, under President George H.W. Bush, SERI was elevated to national-laboratory status and renamed the National Renewable Energy Laboratory (NREL). NREL has been the Department of Energy’s primary research laboratory for solar, wind, biomass, hydrogen, and related renewable technologies ever since.
The modern utility-scale industry
The market transformation most Americans have lived through — solar panels becoming cheap enough to put on grocery-store roofs and open-desert power plants — is a 21st-century phenomenon. Two things changed at once in the late 2000s and 2010s. Global photovoltaic manufacturing capacity grew rapidly, led especially by Chinese module producers who scaled crystalline-silicon manufacturing to levels that the original 1980s U.S. industry could not have imagined. At the same time, U.S. and European tax credits, research funding, and state-level renewable-portfolio standards pushed deployment sideways into the utility grid and onto commercial rooftops. The DOE’s Solar Energy Technologies Office documents the cost and deployment trajectory in detail; the headline is that utility-scale PV, which was uncompetitive with natural-gas generation in most U.S. markets in 2010, became cost-competitive in many markets before the end of the decade.
Utility-scale solar projects now routinely deploy in single-project sizes measured in hundreds of megawatts. Commercial rooftop PV is common enough that most mid-sized American businesses have at least evaluated it. The technology that Bell Labs’ engineers demonstrated in 1954 at single-digit efficiencies on hand-built wafers is now, in crystalline-silicon form, routinely manufactured at efficiencies above 20 percent and module prices a tiny fraction of their 1970s levels. None of that is a forecast — it is the shape of the industry that has already happened.
Interactive timeline
A chronological pass through the milestones covered above. Use the filter buttons to narrow by era; reset with All eras. The full list is always readable without JavaScript.
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c. 500 BC–100 ADPre-industrial
Ancient Greek and Roman builders orient houses to admit winter sun and use overhangs to shade summer sun. Roman bathhouses add sheet-glass windows to trap solar heat in warm-water rooms — the earliest documented passive-solar engineering. -
c. 212 BCPre-industrial
Legend holds that Archimedes used bronze shields as concentrating mirrors to set fire to Roman ships at the siege of Syracuse. Historians treat the story as plausible physics but unverified history; we list it here as legend. -
183919th century
French physicist Edmond Becquerel observes the photovoltaic effect while experimenting with an electrolytic cell. Current produced by the cell increases when it is exposed to light — the founding observation of the entire photovoltaic lineage. -
1865–187819th century
Auguste Mouchout builds the first machine that converts solar heat into mechanical power, and demonstrates a solar-powered steam-and-refrigeration engine at the 1878 Paris Exposition — the first public exhibition of working solar thermal at industrial scale. -
1870s–1880s19th century
William Grylls Adams and apprentice Richard Day design an array of flat silver mirrors that reflects sunlight onto a central boiler — the geometry now known as a solar power tower — and publish A Substitute for Fuel in Tropical Countries. John Ericsson refines parabolic-trough concentrators in parallel. -
188319th century
The American inventor Charles Fritts builds the first working solar cell by coating selenium with a thin gold layer. Efficiency is 1 to 2 percent — enough to prove the principle, not enough to power practical equipment. -
c. 1900–1913Early 20th
Henry E. Willsie builds the first solar thermal system with insulated heat storage, producing power after sundown. Frank Shuman builds a large parabolic-trough solar steam plant at Maadi, Egypt, that pumps Nile water starting in 1913. -
April 25, 1954Space age
At Bell Telephone Laboratories in Murray Hill, NJ, Daryl Chapin, Calvin Fuller, and Gerald Pearson announce a silicon solar cell with an efficiency of about 6 percent — the American Physical Society’s “first practical” photovoltaic cell. -
1955Space age
Bell runs the first field trial of silicon-powered rural telephone repeaters in Americus, Georgia. Western Electric begins licensing silicon-cell technology commercially the same year. -
March 17, 1958Space age
The U.S. Navy launches Vanguard 1 with six small silicon solar cells powering one of its two radio transmitters. The solar-powered transmitter runs for more than six years; the satellite remains the oldest artificial object still in orbit. -
1974Oil shock
Congress passes the Solar Energy Research, Development and Demonstration Act in the aftermath of the 1973 oil embargo — the first federal statute making solar R&D a national priority. -
July 5, 1977Oil shock
The Solar Energy Research Institute (SERI) opens in Golden, Colorado, with photovoltaic researcher Paul Rappaport as director. In 1979, President Carter installs solar panels on the White House roof. -
September 1991Oil shock
Under President George H.W. Bush, SERI is elevated to national-laboratory status and renamed the National Renewable Energy Laboratory (NREL) — still the DOE’s primary research lab for solar and related renewables. -
2010sModern
Global crystalline-silicon manufacturing capacity (led by Chinese module producers) expands sharply and module prices fall dramatically over the decade. Utility-scale solar becomes cost-competitive with natural gas in many U.S. markets by the end of the decade. -
2020sModern
Utility-scale projects routinely deploy at hundred-megawatt scale. Commercial rooftop PV becomes a common financing category for mid-sized American businesses. Module efficiencies above 20 percent are standard; research cells approach the theoretical limit for single-junction silicon.
A lender’s view
I spend most of my working hours at Crest Capital structuring financing for long-lived productive equipment. Watching the history of solar energy play out, three patterns feel familiar to me from nearly two decades of underwriting capital equipment in other categories.
In my experience, the categories of equipment that are hardest to underwrite are the ones whose physical useful life runs fifteen to twenty-five years while the customer’s financing term is five to seven. Medical imaging suites, heavy construction fleets, and commercial presses all sit in that band, and solar modules sit there too. A lender’s job in that case is not to match the lease term to the equipment life — that would make the payments unaffordable — but to structure the deal so the productive cash flows during the first third of the equipment’s life cover the full obligation. That is a different underwriting posture than financing, say, a delivery van, whose useful life and financing term are roughly the same. The long-life category has always been the interesting one, and solar is the latest version of a problem lenders have been solving in imaging and heavy equipment for decades.
I have watched generational turnover rewrite the financing conversation in almost every category I cover. CNC moved from three-axis to five-axis and changed the capacity of a single shop. Medical imaging moved from film to digital and changed what counts as a current-generation asset. Commercial printing moved from offset to digital and shortened useful-life expectations across the category. Solar has done the same thing several times — from Bell Labs’ 1954 silicon wafer to today’s crystalline-silicon modules, thin-film, and bifacial designs, each generation has rewritten the efficiency and cost assumptions a lender would use to evaluate the equipment. The posture that stays stable across generations: finance the generation that is currently bankable, not the generation the trade press is excited about. By the time a generation shows up in a lender’s deal pipeline, the technology risk has usually been priced out.
Solar demand has been partly policy-dependent for its entire modern history. SERI existed because of the 1974 act. Carter-era deployment rode tax credits. The 2010s utility-scale expansion ran on a mix of federal tax credits and state renewable-portfolio standards. That is a real feature of the category — not a flaw. Almost every long-life capital-equipment category a lender covers has some kind of policy-dependent tailwind or headwind; Section 179 and bonus depreciation are policy-dependent, too, and they shape almost every equipment-finance deal I write. What I listen for, underwriting a solar shop, is whether the shop understands the incentive that currently supports its market and has thought about what the deal looks like if the incentive changes. Shops that can answer that question cleanly are the ones we can underwrite with confidence.
Frequently asked questions
What is the difference between solar thermal and solar photovoltaic energy?
Solar thermal uses the sun’s heat — typically by concentrating sunlight with mirrors or lenses to boil a working fluid or drive a steam engine. Solar photovoltaic (PV) uses the sun’s light — specifically, the photovoltaic effect, in which photons free electrons in a semiconductor material to produce a direct electric current. Most of the history of solar energy up through about 1950 was thermal. Most of the industry that exists today is photovoltaic. They are different technologies that happen to share a fuel source.
Who discovered the photovoltaic effect?
The French physicist Edmond Becquerel observed the photovoltaic effect in 1839 while experimenting with an electrolytic cell made up of metal electrodes in a conducting solution. He noticed that the current the cell produced increased when the cell was exposed to light. The effect was real, but nobody at the time knew how to turn it into a practical device — it would take more than a century of work on semiconductor physics before a commercially meaningful solar cell existed.
When was the first solar cell built?
The American inventor Charles Fritts built the first working solar cell in 1883 by coating selenium with a thin, nearly transparent layer of gold. Fritts’s selenium cell converted about 1 to 2 percent of the sunlight falling on it into electricity — enough to demonstrate the principle but not enough to power practical equipment. The modern era began in 1954 when Daryl Chapin, Calvin Fuller, and Gerald Pearson at Bell Telephone Laboratories announced a silicon solar cell with an efficiency of about 6 percent, which the American Physical Society treats as the “first practical” photovoltaic cell.
Why did Bell Labs’ 1954 silicon solar cell matter?
Bell Labs’ silicon cell was the first photovoltaic device efficient enough and stable enough to be useful outside a laboratory, even though it remained too expensive for most ordinary terrestrial power applications. Earlier cells (including Fritts’s 1883 selenium cell) had shown the photovoltaic principle, but their conversion efficiency was low and the materials degraded. Bell’s silicon cell cleared the bar to power specialized equipment whose owners valued reliability over price — most famously the Vanguard 1 satellite, launched in 1958, which became the first spacecraft to use solar electric power and remains the oldest artificial object still in orbit.
How did U.S. solar research become a national program?
The Solar Energy Research, Development and Demonstration Act of 1974, passed in the aftermath of the 1973 oil shock, directed the federal government to treat solar as a national R&D priority. Congress chartered the Solar Energy Research Institute (SERI) in that legislation, and the institute opened in Golden, Colorado in 1977 during the Carter administration. In 1991, under President George H.W. Bush, SERI was elevated to national-laboratory status and renamed the National Renewable Energy Laboratory (NREL), which has since been the U.S. Department of Energy’s primary research lab for solar, wind, biomass, and related renewables.
What changed about solar in the 2010s?
Two things changed simultaneously in the 2010s: manufacturing scale and policy support. Global photovoltaic manufacturing capacity grew sharply — driven especially by Chinese module producers — and module prices fell dramatically over the decade. On the policy side, the U.S. and many other countries extended tax credits and research funding that had been episodic for decades. The combined effect was that utility-scale solar, which had not been cost-competitive with natural gas in most U.S. markets in 2010, became cost-competitive in many markets by the end of the decade. The U.S. Department of Energy’s Solar Energy Technologies Office documents the timeline of these cost and deployment changes.
Selected sources
- U.S. Department of Energy — Solar Achievements Timeline The DOE Solar Energy Technologies Office’s chronological record of U.S. solar-industry milestones from 1955 to the present — the source this page relies on for the Bell Labs commercialization era and the 21st-century utility-scale deployment trajectory.
- National Renewable Energy Laboratory — Laboratory History NREL’s own account of its founding as the Solar Energy Research Institute under the Solar Energy Research, Development and Demonstration Act of 1974, the 1977 SERI opening with Paul Rappaport as director, Carter-era Sun Day and White House rooftop solar, and the 1991 elevation to national-laboratory status and renaming under President George H.W. Bush.
- American Physical Society — First Practical Silicon Solar Cell APS’s “This Month in Physics History” entry on the April 25, 1954 Bell Labs announcement, the Chapin / Fuller / Pearson collaboration, the roughly 6-percent conversion efficiency, and the 1955 Americus, Georgia field trial.
- U.S. Naval Research Laboratory — NRL Celebrates 60 Years in Space With Vanguard NRL’s anniversary account of the Vanguard 1 satellite, which NRL designed and built: the March 17, 1958 launch, the satellite’s two radio transmitters (one mercury-battery, one powered by six silicon solar cells), the contrast in operational lifetimes between the two power sources, and the 1964 loss of signal.
- Encyclopaedia Britannica — Solar cell Britannica’s entry on the photovoltaic cell, covering Becquerel’s 1839 photovoltaic observation, the 19th-century selenium and gold-on-selenium devices (including Fritts’s 1883 cell), and the semiconductor physics underneath the 1954 Bell Labs breakthrough.
- U.S. Energy Information Administration — Solar Thermal Timeline The EIA’s solar-thermal timeline, covering the 19th- and early-20th-century concentrating-solar pioneers (Mouchout, Adams, Ericsson, Willsie, Shuman) whose work anchors the solar-thermal half of this page’s story.
- U.S. Energy Information Administration — Photovoltaic Timeline The EIA’s photovoltaic-timeline reference covering the 20th-century PV chronology — useful as an EIA cross-check for the Bell Labs commercialization era, Western Electric licensing, Vanguard, and late-20th-century policy milestones covered on this page.