Photongrill: Principles and Technology

Our sun is a gigantic fireball. A so-called “yellow dwarf” of average stellar size, our sun emits radiation 625 trillion times the global energy demand (in 2011) as electromagnetic radiation every year. When the weather is fine, about 1000 Watts per square meter reach earth – which is equivalent to the power of a small electric cooking plate.

A Photongrill is focusing the sun’s radiation into one common focal point. Simple optical equipment is sufficient enough to concentrate sunlight onto a smaller surface. Everyone who has once used a magnifying glass to make fire is familiar with this principle. Instead of lenses we use mirrors in our Photongrills to focus sunlight.

Due to the fact that our mirror is shaped like a parabola, every ray that hits the mirror orthogonally gets reflected into the focal point. A frying pan is put onto the focal point where it absorbs a great portion of the sunlight which is transformed into heat.
The pan behaves like everything else that is exposed to direct sunlight – it gets hot – especially when the object is dark – and in the case of a Photongrill the parabolic mirror amplifies this effect several times.

photongrill-principle

There is a legend that in ancient greece, Archimedes defended his hometown Syrakus by setting the enemy roman fleet on fire, only by using several mirrors to concentrate sunlight onto the ships. In the end of the 19th century, french school teacher Augustin Mouchot nearly established solar concentration as the primary energy source for southern regions, but his plans were stopped when a governmental survey classified the technology as uneconomic compared to coal.

Nowadays, several solar thermal power plants located in California and Spain build upon Mouchots idea. Since the 1970s, the solar oven of Odeillo in the french pyrenees serves the purpose of fundamental research in the area of material science due to its focal point’s temperature of over 4000°C (over 7000°F).
Our Photongrill reaches temperatures of about 260°C/500°F which is right above the sweet spot for BBQ.

Being an optic instrument, our parabolic mirror – also called a solar concentrator – has to be aligned orthogonal to the sun’s radiation. For our grill, that means that the mirror has to be adjusted for a few centimeters (an inch) every 10 to 15 minutes to allow the sunrays to hit the focal point. The amount of power is diminished if the sun is covered by clouds; however heat is stored in the pan for several minutes, which makes it possible to continue grilling, until the cloud cover moves on. Contrary to coal grills, there is no need to wait at the beginning of a barbeque, just wait for the grill pan to heat up, which takes less than 5 minutes.

As opposed to other radiation concentration devices, our Photongrill does not use big, heavy, rigid metal parts. We use a mirror foil sealed by a highly transparent safety foil. The foil is high-tech material which is also resistant to hot grease. When inflated, it forms a highly precise parabolic shape. The technology is based on experiments that NASA carried out in the 60s. What was once unachievable at that point in time has now been achieved today: By using heat to thermally deform the plastic’s polymers’ structure, the plastic is able to” remember “and transform into the desired parabolic shape when inflated.

foil-principle

The rack which holds the mirror and the pan in place is made out of a highly robust metal. Therefore, in spite of the mirror’s size of about 1.5 square meters, the PhotonGrill can be folded up and put into a backpack, resulting in a total weight of less than 3 kg, which is less than one bag of charcoal. This is why the Photongrill is also useful for a spontaneous picnic in the park, festivals, camping and outdoor sports.

For any questions, feel free to contact us via our PhotonGrill facebook.