Pioneering Solar Buildings: A History

Long before rooftop panels became a common sight, architects, engineers and stubborn amateurs were trying to heat buildings with the sun. Their experiments were rarely tidy. Some houses worked brilliantly for a winter and then failed. Some were praised in magazines and never sold. A few ran quietly for half a century. Taken together, they form a kind of laboratory notebook for one of the most important ideas in modern building design: that a building's shape, materials and orientation can do much of the work that fuel and machinery otherwise do.

Wikipedia keeps a list of pioneering solar buildings, running from an MIT experiment in 1939 to German "plus-energy" buildings in the 2000s. A list of names and dates does not explain much on its own. This article tells the story behind the list: what each generation of builders was trying to solve, what their buildings looked like and how they worked, which ideas survived, and what their failures taught. It draws heavily on the work of historians such as Anthony Denzer, whose book "The Solar House: Pioneering Sustainable Design" is a key source for the list, and Ken Butti and John Perlin, authors of "A Golden Thread: 2500 Years of Solar Architecture and Technology."

Two ways to heat with the sun

Every building on the list falls somewhere between two approaches.

Passive solar design uses the building itself. Windows face the winter sun. Heavy materials such as concrete, stone, brick or water absorb heat during the day and release it at night. Overhangs shade the glass in summer, when the sun is high, but let it in during winter, when the sun is low. Insulation and careful sealing keep the collected heat inside. There are few or no moving parts.

Active solar design uses equipment. Collectors, usually flat panels on the roof or wall, absorb sunlight and heat a fluid, either water or air. Pumps or fans move that fluid to a storage tank, a bed of rocks or a chemical store, and then distribute heat through the house when needed. Controls decide when to collect and when to release heat.

Photovoltaics, which turn sunlight directly into electricity, are a third strand that joined the story later, beginning with experimental houses in the 1970s.

In practice, all solar heating involves four tasks: collecting the sun's energy, storing it, distributing it and controlling it. The history of solar buildings is largely the history of how different designers handled those four jobs, and especially the second. Collecting solar heat on a sunny day is relatively easy. Storing it for a cloudy week in January is hard.

Ancient roots

Greece

The idea of designing for the sun is very old. The Greek playwright Aeschylus, writing nearly 2,500 years ago, described a south-facing orientation as a normal feature of civilized houses. In a passage often quoted by historians of solar design, he wrote of primitive peoples who lacked knowledge of "houses turned to face the sun, dwelling like swarming ants in sunless cavities."

The clearest statement comes from Socrates, as recorded by Xenophon in his "Memorabilia" (Book III). Socrates explained that in a house facing south, the winter sun shines into the porticoes, while in summer the sun passes over the roof and provides shade. According to John Perlin's summary, Socrates argued that such a house allows the owner to "find a pleasant retreat in all seasons," making it "at once the most useful and most beautiful."

Greek city planners applied the same principle on a large scale. Olynthus, in northern Greece, has been described by Perlin as the first solar city of ancient Greece, with streets laid out so that every house could face south. Priene, on the southern slope of Mount Mycale in present-day Turkey, is another example of solar planning. Perlin notes that such planning spread to cities as far away as central Bulgaria.

Rome and China

Roman builders refined these ideas. The Wikipedia article on the history of passive solar design notes that Roman bathhouses had large south-facing windows. Other writers on Roman architecture point to south-facing terraces and sunrooms at Hadrian's Villa at Tivoli as evidence of deliberate solar planning.

According to the same Wikipedia history, solar design was largely abandoned in Europe after the fall of Rome, but continued in China, where cosmological traditions associated the south with summer, warmth and health.

Before the 20th century: the first solar air heater

One important precursor came in 1881, when Edward S. Morse patented an air heater consisting of a glazed box on a south-facing wall, with a dark absorbing surface, an air gap, and vents at the top and bottom. Sunlight heated the absorber; warm air rose and flowed into the room through the upper vent, while cooler room air entered through the lower one. Wikipedia's article on the Trombe wall describes Morse's device as working on the same principle as the much more famous wall named after Félix Trombe nearly a century later. Morse's invention was largely ignored for decades.

The 1930s and 1940s: glass houses in the Midwest

George Fred Keck and the House of Tomorrow

The modern story begins, somewhat by accident, at the Century of Progress Exposition in Chicago in 1933 and 1934. The architect George Fred Keck designed a "House of Tomorrow" for the fair's Homes of Tomorrow exhibition. It was a striking 12-sided building wrapped in glass, sometimes described in the press of the time as America's first glass house.

According to the Wikipedia history of passive solar design, Keck noticed that the house was warm on sunny winter days even before its furnace was installed. That observation turned him toward deliberate solar design. After the fair, the developer Robert Bartlett bought the house and moved it by barge and truck to Beverly Shores, Indiana, where it still stands. The National Trust for Historic Preservation has named it a National Treasure.

The Sloan House and the first "solar house"

Keck and his brother William went on to design houses that used large south-facing windows to collect winter sun. The best known is a house in Glenview, Illinois, designed for the developer Howard Sloan and dated to 1939 or 1940 in different sources. According to Wikipedia, the Chicago Tribune called it a "solar house," the first modern use of that term. Sloan built more such houses and publicized them, helping to spark a 1940s "solar house" movement. One account reports that after the first winter, Sloan compared his heating bills with those of a typical house and found a saving of about 20%; a Passive House Plus history similarly credits the Keck brothers with reducing building energy costs by 15% to 20% through double glazing and passive heat gain.

By a second Sloan house in 1942, Keck had added double-pane "Thermopane" windows, ventilating louvers and concrete floors with radiant heating. Yale University's energy history project highlights another Keck design, the 1941 Hugh Duncan House in Flossmoor, Illinois, in which a carefully sized eave controls how sunlight enters the house in different seasons.

Henry P. Glass's house in Northfield, Illinois, completed in 1948, appears on the Wikipedia list as another early Chicago-area solar house.

Frank Lloyd Wright's Solar Hemicycle

Frank Lloyd Wright's contribution was the Herbert and Katherine Jacobs Second House near Madison, Wisconsin, known as the Solar Hemicycle. Wright's first design, in late 1943, was rejected as too expensive (about $12,000) and hard to heat. The revised plan of early 1944, the date usually given on lists of solar buildings, became the house that was built between 1946 and 1948. The Jacobses largely built it themselves, with Katherine helping with the masonry. They moved into the root cellar in July 1948 and into the main house at the end of that August.

The house is a two-story arc, only 17 feet wide. Its curved south wall is glass, about 48 feet wide and 14 feet tall, originally made from quarter-inch panes salvaged from old stores. The north side is partly buried in an earth berm, which shelters the house from cold winds. A circular stone tower about 18 feet across protrudes from the berm, and visitors enter through a tunnel. Wide roof overhangs, about 5 feet on the south side, shade the glass when the summer sun is high, while the low winter sun reaches deep inside to warm the concrete floor slab. A sunken garden in front of the glass sits about 4 feet below floor level.

The Jacobses reported that in deep winter they could turn off the heating in the morning and not restart it until late afternoon. The original underfloor heating did not work properly until a rebuild in the 1980s, when triple-pane glass replaced the original panes. The house was added to the National Register of Historic Places in 1974 and designated a National Historic Landmark in 2003.

The Hemicycle shows the essential features of passive solar design in a single building: south-facing glass, thermal mass in the floor, shading overhangs and earth protection on the cold side.

MIT and the race to store the sun

Cabot's gift and Solar House I

At the same time, a very different approach was developing in Massachusetts. In 1937 the Boston industrialist Godfrey Lowell Cabot, whose fortune came from carbon black used in tires, gave Harvard 100 shares of his company, then worth over $600,000, for solar research. In April 1938 he gave another 100 shares to the Massachusetts Institute of Technology to establish the Godfrey Cabot Fund for Research on Solar Energy Conversion, intended to support research for 50 years. MIT chemical engineering professor Hoyt C. Hottel led the committee overseeing the work.

The result was Solar House I, completed in September 1939. It is generally considered the first U.S. house heated with stored solar energy. It was an active system: glass-covered flat-plate collectors on the roof (MIT Technology Review counts 14 of them) heated water, which was stored in a very large tank. Sources describe the tank as holding about 17,000 to 17,400 gallons and differ on whether it was underground or in the basement. Fans blew air over the tank and into the building. The system kept the house's two rooms at 72 degrees Fahrenheit through the winter. It worked, but it was far too expensive to be practical, and it was torn down in 1941 to make room for war research buildings.

Hottel and his colleagues published a 1942 paper on flat-plate collectors that became a classic reference. Hottel himself remained skeptical about how practical solar heating could be. In a 1985 oral history he said: "We're kidding the public about the sun. It's not worth as much as claimed."

The later MIT houses

MIT went on to build six solar houses between 1939 and 1978, according to MIT Technology Review.

Solar House III's occupants, graduate student Harry Reid, his wife June and their two-year-old son, were profiled in the Saturday Evening Post in 1949. "None of us has had a cold since we moved in," June Reid told the magazine. Historian Anthony Denzer described House IV as "a public relations success, a noteworthy aesthetic effort, an inefficient machine, and an economic tragedy."

The Dover Sun House: chemistry meets architecture

Telkes, Raymond and Peabody

The most famous early solar house was built by a team of three women. Mária Telkes, a Hungarian-born scientist who had joined MIT's solar program in 1939, believed heat could be stored more compactly in chemicals than in water. She worked with the architect Eleanor Raymond, and the project was funded by the Boston philanthropist Amelia Peabody on her estate in Dover, Massachusetts. The Wikipedia list records the Dover Sun House, also called the Peabody House, as completed in 1948.

How it worked

Telkes's idea was phase-change storage. She used Glauber's salt, sodium sulfate decahydrate, which melts at a moderate temperature. A Passive House Plus history describes the salt as liquefying at about 32 degrees Celsius. When the salt melts, it absorbs a large amount of heat without getting much hotter; when it re-solidifies as the house cools, it releases that heat. In principle, a given volume of salt can store far more heat than the same volume of water over a small temperature range.

The house had a tall, south-facing wall of glass-covered collectors and a large attic. Air heated behind the glass was blown by fans through bins holding the salt. The Science History Institute's account puts the quantity at 3,500 gallons of Glauber's salt in metal drums; Passive House Plus gives 28 tonnes. Telkes's design was intended to store heat for up to about ten days. Its long, wedge-shaped plan maximized collector area but raised construction costs.

Success, fame and failure

In its first winter, 1948 to 1949, the house reportedly met 91% of its heating demand. Life magazine ran a story about a house kept warm without a furnace, and the house appeared on the cover of Popular Science in March 1949. Telkes's cousins, the Nemethy family, lived in it, and about 3,000 visitors toured it before tours were stopped.

Then the problems emerged. The salt gradually separated into layers (stratified), which stopped it from re-solidifying properly. It corroded the metal containers until they leaked. Sealant in the double-glazed panels dried out, letting in air and weather. Electricity for the circulation fans cost more than the oil it saved. Andrew Nemethy, who grew up in the house, later recalled: "After week-long strings of cloudy days, indoor temperatures sank to panic levels." By the third winter the family was cold. Electric heaters were added, and in 1954 the solar system was removed and an oil furnace installed.

A key design weakness, according to Passive House Plus, was that the house aimed for 100% solar heating with no backup system. Any shortfall meant a cold house.

Telkes's later career

In 1953, after a review by MIT dean George Harrison that largely sided with Hottel, MIT fired Telkes. Historians Sara Shreve and Daniel Barber have argued that criticism of her reflected sexism and suspicion of a Hungarian immigrant during the anti-communist climate of the time. Telkes continued working at New York University and in industry. She consulted on solar homes near Princeton, New Jersey, including the 1958 Curtiss-Wright "Sun Court" project with Aladar Olgyay listed by Wikipedia; the Science History Institute notes that a Princeton-area Telkes house using Glauber's salt was also plagued by corrosion. She later worked at the University of Delaware on Solar One, discussed below.

Her own view of the skeptics was blunt. "Conservative engineers treat this subject with near derision," she wrote in 1951. "Sunlight will be used as a source of energy sooner or later anyway. Why wait?"

The Southwest and the first solar office building

Arthur T. Brown in Tucson

In Arizona, the architect Arthur T. Brown was developing passive solar ideas suited to a desert climate with cold winter nights and abundant sun. The Wikipedia list includes his Rosenberg House in Tucson (1946) and Rose Elementary School in Tucson (1948). A University of Arizona publication credits the Rosenberg House with an early variation of what became known as a Trombe wall, a solid wall behind glass that absorbs heat by day and releases it at night. Denzer and Polina Novikova-Kinney presented a 2010 paper to the American Solar Energy Society describing Brown as a pioneer of passive solar architecture.

George Löf's houses

The engineer George Löf built a solar-heated house in Boulder, Colorado, in 1945. In 1957 he and the architect James M. Hunter completed a house in the Cherry Hills area of Denver that used rooftop flat-plate collectors to heat air, which was stored in beds of rock or gravel and circulated to heat the house. Air systems avoid the freezing and leaking risks of water, and rock is cheap.

The Denver house became one of the longest-running solar homes. Löf lived there for 53 years, and one account says the heating system operated for about 50 years. He also taught civil engineering at Colorado State University from 1967 to 1987 and founded its Solar Energy Applications Laboratory in 1972. The American Solar Energy Society later documented the house's demolition, titling its account "George Löf House, 1956-2013."

The Bridgers and Paxton Solar Building

In Albuquerque, the engineering firm Bridgers and Paxton, founded in 1951 by Frank Bridgers and Donald Paxton, began serious design work in 1954 on a solar-heated office for itself. The Solar Building, with architects Stanley and Wright, was constructed between March and August 1956. It is often described as the world's first commercial building heated primarily by solar energy, though that claim comes from secondary sources.

The building worked, but it was not as economical as its designers had hoped, mainly because fuel was very cheap at the time. Bridgers and Paxton outgrew it and moved out in 1985. It was added to the National Register of Historic Places on October 10, 1989, when it was only 33 years old, on the grounds that it was "exceptionally significant."

Other 1950s experiments

The 1950s saw a burst of experimental solar houses, many recorded only briefly on the Wikipedia list:

The list shows how international the effort was by the late 1950s, with experiments in Japan, Britain, Canada and North Africa. Harry Thomason went on to build later "Solaris" houses, including one in District Heights, Maryland, featured in Popular Mechanics, and wrote a 1974 Harper's Magazine article titled "Confessions of a solar energy addict."

Wikipedia's history article also mentions Wendell Thomas's "Sunnycave," built in 1958 in the Celo Community in North Carolina: south-facing, earth-bermed on the north and west, with a slot that let cold air drain into a sealed crawl space to be warmed.

The 1960s and 1970s: walls, drums, ponds and panels

Trombe and Michel at Odeillo

The single most influential passive solar idea of the postwar period came from France. Félix Trombe, a French engineer, worked with the architect Jacques Michel on a passive solar house at Odeillo in the French Pyrenees, completed in 1967.

Its key feature, now called the Trombe wall, was a thick concrete wall, about 2 feet thick and painted black, placed behind double glazing on the south side, with an air gap between glass and wall. Sunlight passes through the glass and heats the dark wall. The wall slowly conducts heat inward, reaching the living space hours later, in the evening when it is most needed. Vents at the top and bottom of the wall can also allow warm air from the gap to circulate into the room during the day. According to Wikipedia, solar energy supplied about 70% of the Odeillo house's annual heating needs.

Similar houses followed. Wikipedia describes a house at Montmédy in France (1970) that drew 5,400 of its 7,000 kWh of annual heating need from the sun, and the Kelbaugh House in Princeton, New Jersey (1974), with about 600 square feet of storage wall, which reduced heating costs by 76% and 84% in the winters of 1975 to 1976 and 1976 to 1977.

The Trombe wall's appeal is its simplicity: no pumps, no fans, no fluids, no chemistry. Its drawbacks are that it blocks views and daylight, needs sunny winters to be worthwhile, and can lose heat at night through the glass unless covered with insulation.

Steve Baer's zomes and drum wall

In New Mexico, the inventor Steve Baer, who co-founded the company Zomeworks in 1969 with Barry Hickman and Ed Heinz, built a family home in Corrales in 1971 and 1972. The house was made of eleven "zomes," Baer's name for faceted, polyhedral structures, and was full of passive solar devices, many developed or refined by Steve and his wife Holly Baer. Its best-known feature was a "drum wall": steel drums filled with water, painted dark on the sunny side and stacked behind glass. Water stores more heat per unit of volume than masonry, so a drum wall can store as much heat as a much thicker concrete wall. The house and Baer's work were featured in Life magazine in 1972.

Harold Hay's Skytherm roof ponds

In California, Harold R. Hay developed a system called Skytherm, using water stored in large plastic bags on a flat roof, which also served as the ceiling of the rooms below. Movable insulating panels slid over or away from the water. In winter the panels were opened by day to let the sun heat the water and closed at night to keep the heat in; in summer the process was reversed, letting the water lose heat to the night sky and covering it during the day. Hay's full-scale house in Atascadero, near California Polytechnic State University, was completed in 1973 and tested in 1973 and 1974, including a nine-month evaluation.

Solar One: heat and electricity

In 1973, Karl Wolfgang Böer, who had founded the Institute of Energy Conversion at the University of Delaware in 1972, completed Solar One in Newark, Delaware, with Mária Telkes among the collaborators listed by Wikipedia. It was a two-bedroom house of about 1,300 square feet, built with support from the utility Delmarva Power and Light. Its distinguishing feature was that it combined thin-film photovoltaic cells with thermal collectors, so that it produced both heat and electricity from the sun. Its solar modules had to be built by hand because none were commercially available. The University of Delaware describes it as the first house to directly convert sunlight into both heat and electricity for domestic use. The house still stands, though only its angled roof hints at its history.

The energy crisis and the solar boom

The 1973 oil crisis turned solar buildings from a niche interest into public policy in the United States. The Wikipedia history notes a series of developments: the U.S. Department of Energy was created in 1977, solar energy tax credits were introduced in 1978, and President Jimmy Carter installed solar panels on the White House roof in 1979. Edward Mazria's "The Passive Solar Energy Book," published in 1979, became a widely used guide.

The Wikipedia list from this period includes:

• "Unit One," the Balcomb Residence in Santa Fe, New Mexico (1979), designed by William Lumpkins.
• The first "Zero Energy Design" home in Oklahoma (1979), by Larry Hartweg.
• The Saunders Shrewsbury House in Shrewsbury, Massachusetts (1981), designed by Norman B. Saunders.
• MIT Solar Building V (1978), the last of MIT's solar houses.

From solar houses to energy-efficient houses

Superinsulation

By the late 1970s, a different lesson was becoming clear. Many early solar houses had struggled because they tried to collect and store enormous amounts of heat for buildings that leaked heat badly. North American "superinsulation" projects in the 1970s, such as the Saskatchewan Conservation House in Canada, showed that very heavy insulation and airtight construction could reduce heating needs so much that modest solar gains through windows, along with internal heat from people and appliances, did much of the job.

Passivhaus in Darmstadt

That idea was formalized in Germany. In 1988, a discussion between Bo Adamson of Lund University in Sweden and Wolfgang Feist, then at the Institute for Housing and Environment in Darmstadt, led to what became the Passivhaus standard, developed with research support from the state of Hesse. Four terraced houses in Darmstadt-Kranichstein, built in 1990 and 1991, are widely cited as the first built to the standard. The Wikipedia list records "multiple passive houses" in Darmstadt in 1990 by the architects Bott, Ridder and Westermeyer.

Feist founded the Passivhaus Institut in Darmstadt in 1996. Its core criteria include:

The name "passive house" is somewhat misleading: these buildings use south-facing windows and good orientation, but their main strategy is cutting losses through insulation, airtightness and heat-recovery ventilation. As of January 2025, Wikipedia reports more than 47,400 Passive House units worldwide.

The International Energy Agency's Solar Heating and Cooling Programme also appears on the Wikipedia list for its "Task 13" houses (1989), an international effort on advanced low-energy solar homes.

The plus-energy era

Rolf Disch's Heliotrope

In Freiburg im Breisgau, Germany, the architect Rolf Disch built the Heliotrope in 1994 as his own home. It is a cylindrical house that rotates to follow the sun. In the heating season, its triple-glazed side faces the sun; in warmer months, the house turns its heavily insulated back to the sun. A dual-axis photovoltaic tracking panel on the roof, rated at 6.6 kW according to Wikipedia, turns independently of the building. The house also uses a geothermal heat exchanger, solar thermal balcony railings and vacuum-tube collectors for hot water, along with greywater recycling and a dry composting toilet.

Disch coined the term "PlusEnergy" for buildings that produce more energy than they use, and Wikipedia describes the Freiburg Heliotrope as the first house certified as PlusEnergy. Two other Heliotropes were built: one in Offenburg in 1994 as a showroom for the bathroom fittings company Hansgrohe, and one in Hilpoltstein, Bavaria, in 1995 for a dental laboratory. The Wikipedia article on the building carries warnings about missing citations and promotional tone, so its performance claims, such as producing several times as much energy as it uses, should be treated with caution.

The Solar Settlement and the Sun Ship

Disch then designed the Solar Settlement (Solarsiedlung) at Schlierberg in Freiburg's Vauban district, a development of plus-energy row houses with photovoltaic roofs. Sources give different counts of homes, from about 50 to about 59, and different completion dates. The settlement won a German "House of the Year" award in 2002. At its edge stands the Sun Ship (Sonnenschiff), a large office and retail building. The Wikipedia list dates the Sun Ship to 2006; other sources say it was built in 2004, with its topping-out ceremony in late 2003. It is described as generating several times more energy than it uses.

These projects mark the shift from solar houses as individual experiments to solar neighborhoods as a planning goal.

Solar design beyond the wealthy world

The Druk White Lotus School, Ladakh

One of the most admired solar buildings of the early 2000s is a school in a cold desert. The Druk White Lotus School in Shey, Ladakh, in the Indian Himalaya, was designed by Arup and Arup Associates. Ladakh has a high-altitude, dry climate with cold winters. According to a University of Idaho case study, the classroom buildings are oriented about 30 degrees east of true south as part of the passive heating strategy. Classrooms use Trombe walls for passive heating. The site uses solar-powered water pumping and solar electricity, and ventilated improved pit latrines that save water in a desert setting. The buildings use indigenous materials.

The school won several 2002 World Architecture Awards, including Best Education Building, and later awards including a 2009 Design for Asia Grand Award. Its significance is that it shows passive solar principles, developed for houses in Europe and America, working in a very different climate and culture, with limited budgets and local building skills.

Other entries

The Wikipedia list also includes the 31 Tannery Project in Branchburg, New Jersey (2006), and the former St George's Secondary School in Wallasey, Merseyside, England, designed by Emslie Alexander Morgan (1903 to 1965); the list does not give a year for the Wallasey school.

A timeline at a glance

What the pioneers learned

Storage is the hard part

From MIT's huge water tank to Telkes's salts, Löf's rocks, Baer's drums and Hay's roof ponds, the pioneers spent most of their effort on storing heat. Collecting it was comparatively straightforward. The Dover house shows how a storage system that looks brilliant on paper can fail in practice through chemistry, corrosion and materials science. The Löf house shows that a simple, robust storage medium can run for decades.

Simple systems last

Many of the most complex active systems, including MIT IV and the Dover house, had their solar equipment removed within a few years. Passive buildings such as the Solar Hemicycle, with no moving parts, kept working, if imperfectly. The Löf house's relatively simple air-and-rock system was a notable exception among active designs.

Reduce losses before adding collectors

The superinsulation and Passivhaus movements showed that a building that loses very little heat needs very little solar collection. This reversed the earlier emphasis on large collectors and storage. Today, energy-efficient design typically starts with insulation and airtightness.

Backup matters

The Dover house's attempt at 100% solar heating with no backup left its occupants cold. MIT III's designers, aiming for 90% and achieving 82%, used auxiliary heaters for the remainder. Most successful solar buildings use the sun for a large share of heating, not all of it.

Economics depend on fuel prices

The Bridgers and Paxton building worked technically but was undermined by cheap fuel in the 1950s. MIT's houses were consistently too costly to compete. Interest in solar buildings rose sharply after the 1973 oil crisis and fell when fuel prices dropped. Hottel's patron, Cabot, had insisted that a solar device be judged by the "cost of the product—heat or power—and not the efficiency of producing it." That standard defeated most early systems.

Publicity can outrun performance

Several early houses were celebrated in Life, Popular Science, Popular Mechanics and the Saturday Evening Post before their long-term performance was known. The gap between early praise and later problems, at Dover especially, is a caution against judging any building by its first winter.

Common misconceptions

"Solar buildings began with solar panels." Solar design began with orientation and building form thousands of years ago. Photovoltaic houses appeared only in the 1970s.

"Passive solar means no heating system." Most successful passive buildings still have backup heating. The Dover Sun House's lack of one was a weakness.

"A Passivhaus is a solar house." Passivhaus buildings use solar gain, but their main strategy is minimizing heat loss through insulation, airtightness and heat-recovery ventilation.

"Early solar houses failed because solar does not work." Most worked technically. They failed mainly because of storage problems, high costs compared with cheap fuel, complex equipment or poor materials.

"More glass means more solar heating." Large glass areas without enough thermal mass, shading and insulation can overheat in the day and lose heat rapidly at night.

Practical lessons for anyone building or renovating

The pioneers' experience translates into guidance that remains relevant:

1. Orient the building so that main living spaces and a good share of windows face the winter sun (south in the Northern Hemisphere), as the Greeks and Socrates advised.
2. Size overhangs to shade south-facing glass in summer and admit sun in winter, as Keck did at the Duncan House and Wright did at the Hemicycle.
3. Provide thermal mass in floors or walls where the sun falls, to absorb daytime heat and release it later.
4. Insulate and seal first. As the Passivhaus experience shows, reducing heat loss lowers the amount of solar collection needed.
5. Keep systems simple and maintainable. The MIT and Dover experiences show the risks of complex, experimental equipment.
6. Plan for backup heat rather than aiming for 100% solar heating.
7. Be cautious with glass in hot climates. The Trombe wall literature notes that such systems work best where winters are sunny; elsewhere, shading and ventilation may matter more.

Frequently asked questions

What was the first modern solar house? MIT's Solar House I, completed in 1939, is generally considered the first U.S. house heated with stored solar energy. Keck's Sloan House of about 1940 was the first to be called a "solar house" in the press, according to Wikipedia's history.

Who was Mária Telkes? A Hungarian-born scientist who worked on MIT's solar program, designed the heat-storage system of the 1948 Dover Sun House using Glauber's salt, and later worked on Solar One at the University of Delaware. She was nicknamed the "Sun Queen."

What is a Trombe wall? A thick, dark-colored wall placed behind glass on the sunny side of a building. It absorbs sunlight by day and slowly releases heat into the building at night. It is named after Félix Trombe, who built a well-known example with Jacques Michel at Odeillo, France, in 1967.

What was the first solar-heated office building? The Bridgers and Paxton Solar Building in Albuquerque, completed in 1956, is often described as the first commercial building heated primarily by solar energy.

What was Solar One? A 1973 University of Delaware house in Newark, Delaware, that combined photovoltaic cells and solar thermal collectors to produce both electricity and heat.

What is a plus-energy building? A term coined by architect Rolf Disch for a building that produces more energy than it uses over a year. His Heliotrope in Freiburg (1994) is often cited as the first.

What is the Passivhaus standard? A German-developed building standard, first applied at Darmstadt-Kranichstein in 1990 and 1991, that limits space heating demand to 15 kWh per square meter per year and requires very airtight construction and heat-recovery ventilation.

Why did the Dover Sun House stop working? Its Glauber's salt storage stratified and corroded its containers, its glazing seals failed, its fans were costly to run, and it had no backup heating. The solar system was removed in 1954.

Are any of these buildings still standing? Several are, including the House of Tomorrow in Beverly Shores, Indiana, the Solar Hemicycle near Madison, Wisconsin, and Solar One in Newark, Delaware. George Löf's Denver house was demolished in 2013, and MIT's Solar House I was demolished in 1941.

Sources

• List of pioneering solar buildings - Wikipedia
• History of passive solar building design - Wikipedia
• The Sun Queen and the Skeptic: Building the World's First Solar Houses - Science History Institute, Distillations (2020)
• The first US house to go solar - MIT Technology Review
• 1948: The Dover Sun House - Passive House Plus
• Let It Shine: Solar Design in Ancient Greece - John Perlin, Mother Earth News
• Anthony Denzer, The Solar House: Pioneering Sustainable Design (Rizzoli, 2013)
• Butti and Perlin, A Golden Thread: 2500 Years of Solar Architecture and Technology
• MIT Libraries: MIT Buildings - Solar Houses
• House of Tomorrow (Indiana) - Wikipedia)
• Keck and Keck, Sloan House, Glenview, Illinois - Yale Energy History
• Solar Hemicycle - Wikipedia
• Arthur T. Brown - Architects of Influence, University of Arizona CAPLA
• George Löf House, 1956-2013 - American Solar Energy Society
• George Löf - Wikipedia
• Solar Building (Albuquerque) - Wikipedia
• America's First Solar-Heated Commercial Building - Historic Albuquerque
• Trombe wall - Wikipedia
• Félix Trombe - Wikipedia
• Steve Baer - Wikipedia
• Zome House, Corrales, New Mexico - TU Delft DASH
• Harold R. Hay - Mother Earth News
• UD's Institute of Energy Conversion marks 50 years of solar advances - University of Delaware
• Karl Wolfgang Böer - Wikipedia
• Passive house - Wikipedia
• Heliotrope (building) - Wikipedia)
• Freiburg: Sonnenschiff topping-out ceremony - Solarserver (2003)
• Freiburg plus-energy houses named House of the Year - Solarserver (2002)
• Druk White Lotus School - Wikipedia
• Druk White Lotus School case study - University of Idaho