Historically balloonists, and before 1960 that meant gas balloonists, tried to avoid the heating effect of the sun because solar heating caused their balloons to climb too high venting valuable lifting gas. Even today gas balloons such as those used on the successful Trans-Atlantic and Pacific flight have light coloured even silvered tops to reflect the sun’s heat and dark bottoms to trap the reflected heat or the Earth at night. They are in a very real sense anti-solar balloons. 

On the other hand balloons using hot air as their lifting medium have every reason to utilise solar heating.

The world circling balloons which have broken all distance records in the last few years are composite helium gas and hot air balloons called "Roziers" after the first aeronaut, they use some solar heating by day to maintain height with little or no burner heating.

Traditional gas balloon "Jambo" over Africa.
Photo from "The Dangerous Sort " (1)

Trans-Atlantic gas balloon "Double Eagle II"
Photo from "Hot Air Ballooning" (1)

First Round the World Balloon "Breitling Orbiter III" 
With double layer reflective fabric top.


Hot air balloons are fundamentally different. They nearly always fly by day.  They use large quantities of propane gas, about 60-100 litres on an average 2 hour flight - so they need all the free heat they can get! Their burners (air heaters to be more precise) are quite noisy and all hot air balloonists long for the silent, but expensive flight of the gas balloon.


In 1972 British architect Dominic Michaelis designed the first purpose built solar balloon from 6micron Melinex polyester film. You can see the black internal solar collector in the photograph, by Michaelis 

From Hot Air Ballooning (1)


The light weight and relatively large size of these pure solar balloons is due at the feeble heating effect of the sun when compared to the requirements of hot air balloon which regularly operate at between 60 and 100 OC. So to obtain sufficient lift to carry even a single person a huge and/or very light balloon is required. For more on solar warm air balloons 

French Solar Balloon Site

Yahoo Solar Balloon Group

Steve Griffin's Solar Homebuilt Balloon

Solar Montgolfiers for near space missions








In 1981 Julian Nott piloted Michaelis’ 3rd solar balloon across the English Channel. Shown at right, the inner black balloon was 140,000 cu ft (4200 m3) ie the size of an 8-passenger commercial ride balloon, and twice the volume of a normal sport balloon.


My first balloon, "VISION SPLENDID" was a black top Cameron ‘Viva’ 77 (77,000cu ft/ 2100 m2 ) balloon and always had good fuel economy on cool sunny mornings, even when it was quite old and getting porous. Most balloons expire due to porosity rather than structural weakness. In fact it was 467 hrs old - quite elderly for a balloon - when I set the then Australian AX7-10 flight duration record of 6hrs 21min. I have since bettered that record in Solaris, to a record of 8hrs 23min.  

It is obvious to all pilots of dark coloured balloons that they get a free solar heating ‘boost’. However an all black balloon also re-radiates heat toward the darker part of the sky and the cool morning earth, loosing some of it’s valuable heat gain. 

The trick is to trap the sun’s heat without losing it to the sky and ground. One answer is thermal asymmetry.


A 140,000 cu ft pure solar balloon such as Michaelis’s, while admirable in intent, was not very handy for normal recreational flying and a liability in competition. 

I wanted a balloon that could be handled by as few as two people but with reasonable lifting capacity. Therefore 77,000 cu ft was as big as I wanted to go. 

SOLARIS was designed to be asymmetric with regard to solar heating. The black side readily absorbed the sun’s rays and the silver fabric reduced radiant heat loss through the shaded side of the balloon. 

SOL ARIA (right) is identical, another Kavanagh C77, except that the pronounced 'V' at the bottom of the stripes is replaced with a shallower single panel step with the same at the top end resulting in 2 additional panel heights of black at the top.  The red streamers are an aesthetic touch by the ladies in our family but are practical for identification of the balloon at a long distance or when there is haze!

Unfortunately to gain the full effect of the solar assistance, the black side should face the sun whenever heating is required. As balloons normally rotate slowly in flight, this condition cannot be maintained without some means of rotating the balloon. Conventionally this is done by spilling some of the hot air through slits, called ‘rotation vents’, in the side of the balloon. This is not very desirable as heat loss is increased. The alternative would be a solar electric rotator fan, which could even be automated, but I have never had the time to build such a device. None the less, I get good fuel economy under cool sunny conditions, using about half a litre per minute, or about half the ‘normal’ allowance.  As such, it is an excellent long flight balloon.  

These two photographs dramatically illustrate the difference between one side of the "SOLARIS" and the other. (They also irk me because they both show the balloon pointing the wrong way!).

Photos by George Harris


Sol Aria" (Sun Song). Also flying the 'wrong' way! What can I say, people like to photograph the sun reflecting off the silver side. It makes a better photograph! 
Photo by Paul Gibbs


"Solaris" Flying the 'right' way, black to the sun!