Construction:
The Helios is simply a solar machine with frame made of steel angle and square tube supporting 54 mirrors measuring 30cm x 30cm each (4.86 square meters) at an angle 60degrees from horizontal, which reflect the sun’s rays to a focal point 1 meter off the ground 4.5 meters away.
Reflecting horizontally is necessary because the larger the collection area, the further the focal point must be (reflecting upwards soon results in a focal point too difficult to access). The Helios delivers roughly 3 kilowatts and is remarkable in the concentration it can reach (155 intensities of the sun) while using simple materials and techniques.
The array of mirrors on the right rests on two wheels which are pivoted around the central strut, oriented such that the machine can rotate easily.
The end with the oven has no wheels and is supported by the main beams which run the length of the array.
The oven is mounted on a wheeled trolley which lets it be moved forward and back over the course of the day because as the sun approaches its zenith, the focal point moves further away. This phenomenon is called focal drift. The range of the drift is around 70cm and is accommodated by the trolley/track system.
For each pair of mirrors rows there is a control wheel near the oven attached to the mirrors by a cable. By turning the wheels the user is able to control the inclination of the mirrors to attain focus.
A bump of the hip is all that is required to rotate the array around the central pivot, following the sun from east to west. Tracking the sun with the Helios consists of 4 simple movements and takes roughly 10 seconds of work every 7 minutes.
The labor required to keep a Helios focused is easily trainable and can be managed quite well.
The key to the Helios technology is the fact that a 30cm x 30cm, 3mm thick mirror can be bent to create a parabola-like shape which yields a 10 cm diameter focal point 4.5 meters away, a concentration of 10:1.
To keep the mirror in this parabolic shape the ‘Spider’ has been developed (see picture below). The Spider is a structure that has 8 legs extending from a central support which is glued to the back of a 30cm by 30cm mirror. At the end of each leg there is a screw or bolt. With the leverage that is achieved by being fixed to the mirror at the center, the bolts at the end of the spider legs can push the mirror outwards at the edges while being held firm at the center, creating a parabola like shape. The mirrors are calibrated by a simple trial and error process taking roughly 2 per mirror to complete. This focusing process does not need to be done more often than every 6 months.
The list of materials and tools needed to construct a Helios can be found here. The process for building the Spiders is summarized in this document, and the full process is explained here.
We have also developed a nearly universal construction guide that, without words, takes you step by step through the process. The universal Spider Construction Guide can be downloaded by clicking here.
Versatile Applications:
The Helios offers high amounts of solar heat with very versatile uses.
We have designed ovens, roasters, water purifiers, crop dehydrators and wood distillation units to work with the heat energy provided by the Helios.
The roaster (seen above) and ovens are constructed with tin, rivets, small pieces of structural steel, and a 5 centimeter layer of fiber glass insulation (various alternatives exist to fiberglass).
The oven is 0.5m³ and cube-like, reaching 300° C in 15 minutes.
The roaster is a hand turned cylinder, 0.5m3 that rotates in order to stir the produce. They weight is about 15 kilos each.
The roaster can roast 8 kilos of coffee, peanuts or cocoa beans in one hour. The ovens and roasters are built with a 30cm x 30cm ceramic glass window at the focal point, which allows the light to enter the application where it strikes a light bed and is converted into thermal radiation and hot air (alternatives to the ceramic glass window exist, though they are not as efficient).
Our water purification unit consists of a glass-fronted boiler, which receives the solar radiation, exposing the water to UV light, which helps to pasteurize it.
Water is flowed in at the bottom, and is left long enough to rise to 100degC, at which point it exits the boiler at the top. The ingenious element of the device is the heat exchanger which, once the system is up and running, recaptures 80% of the heat from the hot outflow water and steam. This purifier can UV pasteurize and boil around 70L/hr while providing approximately 4 liters of distilled water per hour.
The wood carbonizer is simply an airtight steel box with a release valve on the top. Around 5 kg of wood is placed inside and heated as much as possible, causing the water and gases contained within it to evaporate and be expelled through the release valve.
The gases released contain methane, among others, and can be captured or can be burned, resulting in a 20cm jet of flame which lasts for 2 hours. Once the process is finished, what remains is high quality charcoal, which can be used for artistic purposes or can be burned during the night or indoors, without releasing large amounts of smoke. Typically, around two-third of the energy is lost in the process (RWEDP)
The same kiln that is used to carbonize wood can be used as a small kiln for pottery and ceramics. The focal point of the Helios array reaches approximately 950degC and if it is efficiently harnessed can serve to bake a great variety of pottery and ceramics.
The crop dehydrator is a device that works by heating air at the base of a 60cm x 60cm x 120cm chamber which is filled with racks of fruits and vegetables. The hot air rises and escapes the top of the tower after having sucked some of the moisture out of the fruits and vegetables. Passive solar dehydrators exist, though they take more time and are exposed to pests. The great quantity of heat energy that is used to heat the air powers a strong convection current which carries away moisture very quickly.
Construction guides and user manuals for the various applications for the Helios array might be found here one day.