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SunCone Solar Energy Thermal Concentration System


Made of an aluminized film (e.g. nylon or Mylar) with a transparent film over the end facing the sun, the SunCone, by Barnabus Energy, maintains its shape through air pressure. The system is expected to be less expensive and labor-intensive than standard parabolic dish or trough design and require less precise placement.

Contents

About

Official Website

Overview

from http://www.barnabusenergy.com/en/projects/suncone.asp

Focusing solar energy to high intensity can provide high temperatures at the target (focal point) in order to drive high-efficiency heat engines. Parabolic trough reflectors have been used effectively in this role. Parabolic dish mirrors can achieve even higher temperatures.

The problem with parabolic dish mirrors is that considerable precision is required in their construction and maintenance. The mirror facets are fairly expensive to manufacture. Each facet (approximately one square meter) must be mounted on a very rigid structure and must be precisely aligned to keep the sun's image on the target. About once a week, each mirror must be re-aligned. For a 100 square meter dish (1 m 2 per facet), 100 mirrors must be realigned. Realignment can be done by electronically-controlled actuators, but that requires two motors per mirror facet in addition to sophisticated electronics, thus adding to the expense of the solar collector.

Another problem with parabolic dish reflectors is that they have been known to start fires in grass when accidentally pointed in the wrong direction. They can also cause damage to human eyes if the mirror points in a direction that causes sunlight reflection toward a person or if the person looks at the target (focal point).
A new system called “Suncone��? provides an inexpensive method of producing high-temperature solar energy collection using plastic films. Figure 1 shows an artist's conception of the Suncone solar collector. Like the parabolic dish, it must be pointed toward the sun but requires less precision than a parabolic dish or parabolic trough. Air pressure within the enclosure maintains rigid configuration.

Disadvantage

from http://www.barnabusenergy.com/en/projects/suncone.asp

The problem with this design is that the entire cone is supported by its narrow end. Thus, wind could easily blow the cone to the side. If guy wires are used, they tend to crumple the narrow part of the cone.

Patent

U.S. Patent 4,267,824 describes an inflatable solar concentrator that consists of a flexible material inflated to the shape of a cone with a transparent end covering. Internal air pressure maintains the shape.

Advantages

from http://www.barnabusenergy.com/en/projects/suncone.asp

  • Less expensive than other solar concentrators.
  • Lighter weight.
  • Produces high temperatures, similar to parabolic dish collectors.
  • Does not require a boom to support a target at the focal point.
  • Requires less precision in sun orientation than solar dishes or troughs.
  • Less likely to be damaged by large hailstones.
  • Higher efficiency than parabolic trough collectors.
  • Inexpensive to replace plastic films if damaged.
  • Unlikely to start fires on the ground, in contrast to parabolic dish mirrors.
  • Brightly-lit target areas are shielded from human eyes.
Suncone, with regular cones and conical metal reflectors, can achieve about 2,000° C. But operating at 600° C, its solar collection efficiency is about 90%, depending on the geometry.
The cones in Suncone do not have to be precisely constructed. Minor flaws are insignificant. Computer simulations were run with SUNCONE in which numerous perturbations of up to a half-centimeter were applied to the cone surface randomly. The energy reaching the target rod was still above 90% of what a perfect cone would provide. The mirror facets on a parabolic mirror must be precise.

Prototype

The prototype is approximately 2 meters long with a 1.5-meter radius at the wide end.

  • Barnabus Energy Announces SunCone Achieves Critical Milestone - Barnabus Energy, Inc. is pleased to announce that its principal contractor on the Suncone project, HYTEC, Inc. of Los Alamos, NM, has achieved a significant milestone in its first phase of work: The construction of the first full-scale prototype, and commencement of engineering analysis. (MarketWire; Feb. 27, 2006)

Product Details

from http://www.barnabusenergy.com/en/projects/suncone.asp

In Suncone, the cones consist of thin aluminized Mylar, Nylon or other film. Instead of having air pressure inside the cone to maintain its shape, air pressure is applied inside a cylindrical enclosure. The conical shape of the interior cones is maintained by tension on the film, since air pressure is pushing upward on the end of the unit. The pressure inside and outside each cone is the same. Air pressure maintains the cylindrical shape of the enclosure, which also consists of a strong plastic. The transparent films that cover the ends of the cones are made of clear plastic, such as Tefzel, which has a transparency of 96%, a tensile strength of over 30,000 psi, is UV resistant, and can tolerate weather for decades. Since Tefzel is rather expensive, other suitable films may be used.
Figure 2 shows a cross-sectional schematic of one embodiment of Suncone. The insides of the cones are aluminized for high reflectivity. The outsides of the cones are coated by flat black, which radiates heat well. Computer simulations show that the cone material remains cool, since the inside reflective layer allows little solar energy to enter the plastic, but the outside black layer radiates the heat away. The enclosure should be clear so that it allows the radiant energy to pass through or should be black plastic or coated with flat black so that it absorbs the radiant heat from the cones and radiates the heat away on the outside. Since the surface of the enclosure is parallel to the sun's rays, it does not get hot from direct sunshine.
The sun's rays are concentrated on the target rod, which may have channels inside for the flow of water or other working fluid. The target rod should have a cylindrical glass tube around it to reduce convective heat loss, and the glass tube should be evacuated. Since the rod will get quite hot, it is surrounded by a metal reflector. The plastic cone is attached to the metal reflector with an insulating connector. The metal reflector and the target rod are attached to the base, which is shown as a solid circular cylinder, but it may be any suitable assembly of metal beams. The structure does not have to be as robust at that of a parabolic dish, since it does not have to be as rigid and since it does not have to support a long metal boom that holds a heavy target at the end. In Suncone, the heat absorption is located adjacent to the base. (Some important details of the construction are not shown in these figures).
Figure 3 shows a top-view schematic of Suncone with seven cones. Note the spaces between the cones that appears to be wasted area for solar energy collection. The cones could be extended so that the total area is used, but the upper end would not be circular, which would not hurt the performance but would make construction more expensive.
The evacuated glass tubes that surround the target rod not only improve efficiency by reducing heat loss, but they also prevent hot convective air currents from flowing from the target rods to the plastic films.
Figures 2 and 3 show schematics of assemblies that have only a few cones. If the cones are 2 meters (6.56 feet) long with a radius of 1.5 meters at the upper end, it would require 7 cones to provide a total of 50m2 of solar collection. This would be similar to the arrangement of Figure 3 with a central cone surrounded by 6 other cones. Of course, more cones can be added.
For photovoltaic applications, the rods could be larger in diameter and coated with photovoltaic films. The metal reflector might also be covered with photovoltaic films and would be conical in shape. The concentration of light would provide higher energy collection per unit area of photovoltaic material.
It should be noted that the target rods are completely shielded from ground observers, so that eye damage to passersby is impossible. If Suncone is accidentally pointed toward the ground, it will not be pointed toward the sun, so that it cannot start a grass fire. A parabolic reflector, on the other hand, can intercept sunlight even when it is not pointed directly toward the sun, and the reflected light can ignite fires on the ground. Suncone units could be mounted in parking lots above cars to generate electricity for nearby buildings without concern for the safety of people or property below them. They could also be mounted on tops of buildings. Engineers would be reluctant to place parabolic reflectors in these locations.
For high wind conditions, cables or cords extending from the base to the top can be reeled in to draw the top downward while the air pressure is reduced. The plastic film portion of the unit would be withdrawn into a sturdy cylinder surrounding the lower part of the enclosure to shield against the wind. Even if the plastic materials are destroyed, they are inexpensive to replace.

Alternative Designs

from http://www.barnabusenergy.com/en/projects/suncone.asp

The design illustrated in Figure 5 would encase each cone with a cylindrical plastic film enclosure. Air pressure would be supplied to each enclosure, which would ensure that the cone is tight and circular. The enclosure would sustain the force produced by the air pressure on the clear window, thus eliminating large stress on the narrow end of the cone.
Each of these units, incorporating the enclosure, cone, transparent window, and base sheet could be manufactured in a factory and assembled onto the base in the field. After each unit is installed, it would be attached to adjacent units by adhesive or Velcro. An additional enclosure film could be wrapped around the entire assembly. External and internal tether cords or cables (guy wires) will maintain structural stability.
Figure 6 is an embodiment of the Suncone in which the sunrays are reflected into a hohlraum cavity, in which the target rod is placed. The interior walls of the hohlraum chamber are coated with a light-absorbing layer. It absorbs solar energy and becomes hot. The cooling fluid that flows through the target rod can also flow through channels in the hohlraum chamber wall to be heated. Alternatively, the fluid can flow through pipes (not shown) that are welded to the outside of the hohlraum chamber. A hohlraum chamber tends to trap radiant heat. Some of the radiation from the wall on one side is radiated to the opposite wall or to the target rod. Likewise, much radiation from the target rod flows to the chamber walls. Insulation (not shown) on the outside of the chamber prevents loss of heat.
The advantage of this embodiment is that it is quite insensitive to the accuracy of a tracking mechanism that points the device toward the sun. In this design, the cone is divided into two reflective film cone frustums in order to more closely match an exponential generatrix for the collector shape. A circumferential rigid ring holds the reflective cone frustums in place. The top of the upper cone frustum is held in place by air pressure on the transparent cover (not shown, but like that in Figure 2). The bottom of the lower cone frustum is connected to the metal reflector, whose shape is defined by an exponential generatrix. Reflected sunlight passes through a glass window, which has the purpose of reducing convective heat losses. The cavity can be evacuated for further reduction in heat losses.

Cost

from http://www.barnabusenergy.com/en/projects/suncone.asp

Hydro-Tech quoted the price for their aluminized Mylar, with a reflectivity of 0.95, at 20 cents per square foot. The material cost for the cones in the above example of a 50-m2collector would be under $100. Transparent windows would cost $500. The enclosure and other plastic materials would cost $800. Total cost for plastic materials is $1,400.
The metal reflectors can be thin polished aluminum. In mass production, they can be pressed into shape, so that the cost for seven of them would be $400. The table below provides an estimate to the cost of a completed Suncone unit with 50 square meter solar collecting area.

Table 1 - COST FOR A 50-SQUARE METER SUNCONE UNIT
Plastic materials $1,400
Stainless steel target rods and piping 700
Base structural materials 600
Metal reflectors 400
Hohlraum chambers 400
Pivot and foundation support 1,500
Miscellaneous hardware 800
Assembly (mass production) 1,100

- - - -

Total $6,900


This would provide an efficient solar collecting system with a cost of $139 per square meter of collection area. This does not include the cost of a sun-tracking system. Presently, trough collectors (which are not as efficient as Suncone collectors) are running at about $250 per square meter, and dish collectors are about $400 per square meter.

In the News

  • Inflatable SunCone boosts efficiency and lowers price - Made of an aluminized film (e.g. nylon or Mylar) with a transparent film over the end facing the sun, the SunCone, by Barnabus Energy, maintains its shape through air pressure. (Renewable Energy Access; Mar. 9, 2006)
  • Open Energy Corporation Announces SunCone Achieves Critical Milestone - Open Energy Corporation is pleased to announce that its principal contractor on the Suncone project, HYTEC, Inc. of Los Alamos, NM, has achieved a significant milestone in its first phase of work: The construction of the first full-scale prototype, and commencement of engineering analysis. (MarketWire; Feb. 27, 2006)

Contact

Open Energy Corporation (Name changed from Barnabus Energy)
514 Via de la Valle
Suite 200
Solana Beach, CA 92075
P: 858 794 8800
F: 858 794 8811


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