Solar balloon
Encyclopedia
A solar balloon is a balloon
that gains buoyancy
when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a hot air balloon
. Current usage of solar balloons is predominately in the toy market, although it has been proposed that they be used in the investigation of planet Mars
, and some solar balloons are large enough for human flight. A vent at the top can be opened to release hot air for descent and deflation.
Raising the air temperature inside the envelope makes it less dense than the surrounding (ambient) air. The balloon floats because of the buoyant force exerted on it. This force is the same force that acts on objects when they are in water and is described by Archimedes' principle. The amount of lift (or buoyancy
) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the envelope and the temperature of the air outside the envelope.
The lift generated by 100,000 ft³ (2831.7 m³) of dry air heated to various temperatures may be calculated as follows:
The density of air
at 20 °C, 68 °F is about 1.2 kg/m³. The total lift for a balloon of 100,000 ft³ heated to (99 °C, 210 °F) would be 1595 lb, 723.5 kg. In reality, the air contained in the envelope is not all the same temperature, as the accompanying thermal image shows, and so these calculations are based on averages.
For typical atmospheric conditions (20 °C, 68 °F), a hot air balloon heated to (99 °C, 210 °F) requires about 3.91 m³ of envelope volume to lift 1 kilogram (62.5 ft³/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above sea level, and humidity of the surrounding air. On a warm day, a balloon cannot lift as much as on a cool day, because the temperature required for launch will exceed the maximum sustainable for the envelope fabric. Also, in the lower atmosphere, the lift provided by a hot air balloon decreases about 3% for each 1,000 meters (1% per 1,000 ft) of altitude gained.
is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance
in watts per square meter (W/m2). Direct insolation
is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant
minus the atmospheric losses due to absorption
and scattering
. While the solar constant varies with the Earth-Sun distance
and solar cycle
s, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle
), cloud cover
, moisture
content, and other impurities.
Over the course of a year the average solar radiation arriving at the top of the Earth's atmosphere is roughly 1,366 watt
s per square meter
(see solar constant
). The radiant power is distributed across the entire electromagnetic spectrum
, although most of the power is in the visible light portion of the spectrum. The Sun's rays are attenuated
as they pass though the atmosphere
, thus reducing the insolation at the Earth's surface to approximately 1,000 watts per square meter for a surface perpendicular to the Sun's rays at sea level on a clear day.
A black body
absorbs all the radiation that hits it. Real world objects are gray objects, with their absorption being equal to their emissivity
. Black plastic might have an emissivity of around 0.95, meaning 95 percent of all radiation that hits it will be absorbed, and the remaining 5 percent reflected.
, the sunlight received by this sphere can be imagined as the cross-section of a cylinder with the same radius as this sphere, see diagram. The area of this circle can be calculated via:
For example, a solar balloon in the shape of sphere, with a radius of 5 meters, with an envelope of black plastic, and with the direct insolation being 1000 watts, receives energy that can be calculated by first calculating the area of its great circle:
Then multiplying this with the emissivity of the plastic and the direct insolation of the sun:
78.54 * 0.95 * 1000 = 74,613 Watts
At sea level
and at 15°C according to ISA (International Standard Atmosphere), air has a density of approximately 1.22521 kg/m3. The density of air
decreases with higher temperatures, at the rate of around 20 grams per kilogram per 5°C. Roughly 1 kilojoules of energy is needed to heat 1 kilogram of dry air (see heat capacity
). So, to increase the temperature of 1 m3 of air (at sea level and at 15°C) 5°C requires roughly 5°C * 1 kilojoules * 1.225 kilograms = 6.125 kilojoules. By doing so, you've reduced the mass of 1 m3 of air by roughly 24 grams. On a clear day with a black body surface of 1 m2 perpendicular to the sun, this should take a little over 6 seconds.
, a British architect and the inventor of many solar utilities and projects, invented and built the first solar balloon, with an clear external surface and dark, heat-catching internal walls.
across the English Channel. Records compiled for the FAI show that on 6th February 1978 Iranian Frederick Eshoo also made a solar flight in a balloon called Sunstat. This used a standard balloon design, but used clear plastic on one side, allowing the sun's radiation to reflect off the inner surface, heating the inside air.
Today, the Brisbane Hot Air Ballooning company in Australia flies a solar balloon.
, helium or hydrogen, would be precious. The flight was a success, approaching 46000ft. The savings do not only concern the lifting gas in itself. The ORA Balloon alleviates the need for the transportation, in and out, of the heavy gas canisters.
Manned flights carry special risks. Unexpected clouds pose a serious risk, akin to regular hot air ballooning without reserve fuel. Solar balloons can descend rapidly when cooling occurs, making ballast very important.
Balloon (aircraft)
A balloon is a type of aircraft that remains aloft due to its buoyancy. A balloon travels by moving with the wind. It is distinct from an airship, which is a buoyant aircraft that can be propelled through the air in a controlled manner....
that gains buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...
. Current usage of solar balloons is predominately in the toy market, although it has been proposed that they be used in the investigation of planet Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, and some solar balloons are large enough for human flight. A vent at the top can be opened to release hot air for descent and deflation.
Generating lift
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
) provided by a hot air balloon depends primarily upon the difference between the temperature of the air inside the envelope and the temperature of the air outside the envelope.
The lift generated by 100,000 ft³ (2831.7 m³) of dry air heated to various temperatures may be calculated as follows:
| air temperature | air density | air mass | lift generated |
|---|---|---|---|
| 68 °F, 20 °C | 1.2041 kg/m³ | 7517 lbs, 3409.7 kg | 0 lbs, 0 kg |
| 210 °F, 99 °C | 0.9486 kg/m³ | 5922 lbs, 2686.2 kg | 1595 lbs, 723.5 kg |
| 250 °F, 120 °C | 0.8978 kg/m³ | 5606 lbs, 2542.4 kg | 1912 lbs, 867.3 kg |
The density of air
Density of air
The density of air, ρ , is the mass per unit volume of Earth's atmosphere, and is a useful value in aeronautics and other sciences. Air density decreases with increasing altitude, as does air pressure. It also changes with variances in temperature or humidity...
at 20 °C, 68 °F is about 1.2 kg/m³. The total lift for a balloon of 100,000 ft³ heated to (99 °C, 210 °F) would be 1595 lb, 723.5 kg. In reality, the air contained in the envelope is not all the same temperature, as the accompanying thermal image shows, and so these calculations are based on averages.
For typical atmospheric conditions (20 °C, 68 °F), a hot air balloon heated to (99 °C, 210 °F) requires about 3.91 m³ of envelope volume to lift 1 kilogram (62.5 ft³/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above sea level, and humidity of the surrounding air. On a warm day, a balloon cannot lift as much as on a cool day, because the temperature required for launch will exceed the maximum sustainable for the envelope fabric. Also, in the lower atmosphere, the lift provided by a hot air balloon decreases about 3% for each 1,000 meters (1% per 1,000 ft) of altitude gained.
Solar radiation
InsolationInsolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...
is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance
Irradiance
Irradiance is the power of electromagnetic radiation per unit area incident on a surface. Radiant emittance or radiant exitance is the power per unit area radiated by a surface. The SI units for all of these quantities are watts per square meter , while the cgs units are ergs per square centimeter...
in watts per square meter (W/m2). Direct insolation
Direct insolation
Direct insolation is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation . Direct insolation is equal to the solar constant minus the atmospheric losses due to absorption and scattering...
is the solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation (the solar radiation that is scattered or reflected by atmospheric components in the sky). Direct insolation is equal to the solar constant
Solar constant
The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit...
minus the atmospheric losses due to absorption
Absorption (electromagnetic radiation)
In physics, absorption of electromagnetic radiation is the way by which the energy of a photon is taken up by matter, typically the electrons of an atom. Thus, the electromagnetic energy is transformed to other forms of energy for example, to heat. The absorption of light during wave propagation is...
and scattering
Light scattering
Light scattering is a form of scattering in which light is the form of propagating energy which is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media...
. While the solar constant varies with the Earth-Sun distance
Earth's orbit
In astronomy, the Earth's orbit is the motion of the Earth around the Sun, at an average distance of about 150 million kilometers, every 365.256363 mean solar days .A solar day is on average 24 hours; it takes 365.256363 of these to orbit the sun once in the sense of returning...
and solar cycle
Solar cycle
The solar cycle, or the solar magnetic activity cycle, is a periodic change in the amount of irradiation from the Sun that is experienced on Earth. It has a period of about 11 years, and is one component of solar variation, the other being aperiodic fluctuations. Solar variation causes changes in...
s, the losses depend on the time of day (length of light's path through the atmosphere depending on the Solar elevation angle
Solar elevation angle
The solar elevation angle is the elevation angle of the sun. That is, the angle between the directionof the geometric center of the sun's apparent disk and the horizon...
), cloud cover
Cloud cover
Cloud cover refers to the fraction of the sky obscured by clouds when observed from a particular location...
, moisture
Moisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
content, and other impurities.
Over the course of a year the average solar radiation arriving at the top of the Earth's atmosphere is roughly 1,366 watt
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s per square meter
Square metre
The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...
(see solar constant
Solar constant
The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit...
). The radiant power is distributed across the entire electromagnetic spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
, although most of the power is in the visible light portion of the spectrum. The Sun's rays are attenuated
Attenuation
In physics, attenuation is the gradual loss in intensity of any kind of flux through a medium. For instance, sunlight is attenuated by dark glasses, X-rays are attenuated by lead, and light and sound are attenuated by water.In electrical engineering and telecommunications, attenuation affects the...
as they pass though the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
, thus reducing the insolation at the Earth's surface to approximately 1,000 watts per square meter for a surface perpendicular to the Sun's rays at sea level on a clear day.
A black body
Black body
A black body is an idealized physical body that absorbs all incident electromagnetic radiation. Because of this perfect absorptivity at all wavelengths, a black body is also the best possible emitter of thermal radiation, which it radiates incandescently in a characteristic, continuous spectrum...
absorbs all the radiation that hits it. Real world objects are gray objects, with their absorption being equal to their emissivity
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
. Black plastic might have an emissivity of around 0.95, meaning 95 percent of all radiation that hits it will be absorbed, and the remaining 5 percent reflected.
Calculating energy received
If the balloon is imagined as a sphereSphere
A sphere is a perfectly round geometrical object in three-dimensional space, such as the shape of a round ball. Like a circle in two dimensions, a perfect sphere is completely symmetrical around its center, with all points on the surface lying the same distance r from the center point...
, the sunlight received by this sphere can be imagined as the cross-section of a cylinder with the same radius as this sphere, see diagram. The area of this circle can be calculated via:
For example, a solar balloon in the shape of sphere, with a radius of 5 meters, with an envelope of black plastic, and with the direct insolation being 1000 watts, receives energy that can be calculated by first calculating the area of its great circle:
Then multiplying this with the emissivity of the plastic and the direct insolation of the sun:
78.54 * 0.95 * 1000 = 74,613 Watts
At sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...
and at 15°C according to ISA (International Standard Atmosphere), air has a density of approximately 1.22521 kg/m3. The density of air
Density of air
The density of air, ρ , is the mass per unit volume of Earth's atmosphere, and is a useful value in aeronautics and other sciences. Air density decreases with increasing altitude, as does air pressure. It also changes with variances in temperature or humidity...
decreases with higher temperatures, at the rate of around 20 grams per kilogram per 5°C. Roughly 1 kilojoules of energy is needed to heat 1 kilogram of dry air (see heat capacity
Heat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...
). So, to increase the temperature of 1 m3 of air (at sea level and at 15°C) 5°C requires roughly 5°C * 1 kilojoules * 1.225 kilograms = 6.125 kilojoules. By doing so, you've reduced the mass of 1 m3 of air by roughly 24 grams. On a clear day with a black body surface of 1 m2 perpendicular to the sun, this should take a little over 6 seconds.
Equilibrium
The system is in equilibrium when the energy lost from the balloon through convection, radiation and conduction, equals the energy received through radiation from the sun.History
In 1972, Dominic MichaelisDominic Michaelis
Dominic Michaelis is an English architect and inventor.-Biography:Born in 1938 in England, Michaelis studied architecture and engineering at Cambridge. His thesis, written in 1964 was about a solar house and a floating solar village. He continued at Cornell studying for an M.Sc...
, a British architect and the inventor of many solar utilities and projects, invented and built the first solar balloon, with an clear external surface and dark, heat-catching internal walls.
Manned flight
The first human carrying pure solar balloon flight was made on the 1st May 1973 by Tracy Barnes in his balloon 'Barnes Solar Firefly Tetrahedron'. This balloon was made from a spiral tube of fabric that was formed into a tetrahedron. Dominic Michaelis is recorded as having owned the first pure solar balloon in Europe. This balloon was flown by Julian NottJulian Nott (balloonist)
Julian Nott is a British balloonist who now lives in Santa Barbara, CA, USA. He is known for his achievements in record-setting exploits. Nott has set 79 World ballooning Records and 96 British aviation records. He is currently actively involved in developing balloons for flights at Solar System...
across the English Channel. Records compiled for the FAI show that on 6th February 1978 Iranian Frederick Eshoo also made a solar flight in a balloon called Sunstat. This used a standard balloon design, but used clear plastic on one side, allowing the sun's radiation to reflect off the inner surface, heating the inside air.
Today, the Brisbane Hot Air Ballooning company in Australia flies a solar balloon.
First antarctic solar weather balloon flight
The first 100% solar weather probe, named Ballon ORA, was launched from the French Antarctic Dumont d'Urville station in January 2011, by a joint team of students, scientists and engineers. The idea was to assess the feasibility of using solar balloons as probes in remote area, where saving the use of lifting gasLifting gas
Because of the Archimedes' principle, a lifting gas is required for aerostats to create buoyancy. Its density is lower than that of air . Only certain lighter than air gases are suitable as lifting gases.- Hot Air :...
, helium or hydrogen, would be precious. The flight was a success, approaching 46000ft. The savings do not only concern the lifting gas in itself. The ORA Balloon alleviates the need for the transportation, in and out, of the heavy gas canisters.
Use in outer space
California Institute of Technology's Jet Propulsion Laboratory has conducted a study on the use of solar balloons on several planets and moons in the solar system, concluding they are a viable option for Mars, Jupiter and Saturn.Safety
Managing persons are responsible for damages that might occur to themselves, other persons, or property. Released or tethered solar ballon can injure other aircraft, persons, and property. Planning and airspace permissions may be required by local or national airspace authorities.Manned flights carry special risks. Unexpected clouds pose a serious risk, akin to regular hot air ballooning without reserve fuel. Solar balloons can descend rapidly when cooling occurs, making ballast very important.