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Solar & Alternative Energy

Patent review: New developments in solar energy technologies

3 June 2008, SPIE Newsroom. DOI: 10.1117/2.2200806.0002

Meeting the energy needs of a hungry planet is not going to get easier on its own. As the rapidly growing concern over the negative consequences of increased efforts in ethanol production from food stocks shows, complex problems tend to require complex solutions. Without a major upheaval in the corn-to-ethanol paradigm, it seems unlikely that biofuels will offer much of a long-term, large-scale solution. Sharp increases in demand are unlikely to be met by a limited-supply commodity, concerns linger over a negative carbon balance of biofuel programs, and they exhibit a low energy balance.

On the other hand, the abundant supply of solar energy, if properly harnessed, is capable of supplying all of the world's energy needs while using only a fraction of the Earth's available land. For a variety of reasons, solar energy currently provides only a minute part of the world's energy. However, systems that convert sunlight to energy face a different set of daunting problems, led by high installation costs and followed by concerns over low efficiency.

Unlike biofuels, solar energy technologies have the potential to improve efficiencies and implement large scale production in the relative near term. This paper reviews granted patents and published patent applications of the past year showing improvements in some critical aspects of solar technologies. To be sure, this should not be considered a comprehensive review. Patent activity in solar technology remains extremely busy. The patents identified below represent only a small, but interesting number of the total portfolio of activity on the topic of heliostat technology, the ability to track the motion of the sun, both during the day and during its seasonal changes of position. The technology offers high returns of efficiency for both active and passive systems. Extinction of solar intensity caused by the passage of light through thicker blankets of atmosphere and low angles in the sky is a primary need for tracking technology.

Solar Thermal Aircraft

For stationary solar units, tracking the sun is a two-dimension effort. In an airplane, however, a more complex system is needed. US 7 270 295 describes a solar thermal system concentrating solar energy and running a heat engine. Photo-diodes ensure the concentrators adequately track the sun as the airplane is flown.

Abstract: A solar thermal-powered aircraft powered by heat energy from the sun. A heat engine, such as a Stirling engine, is carried by the aircraft body for producing power for a propulsion mechanism, such as a propeller. The heat engine has a thermal battery in thermal contact with it so that heat is supplied from the thermal battery. A solar concentrator, such as reflective parabolic trough, is movably connected to an optically transparent section of the aircraft body for receiving and concentrating solar energy from within the aircraft. Concentrated solar energy is collected by a heat collection and transport conduit, and heat transported to the thermal battery. A solar tracker includes a heliostat for determining optimal alignment with the sun, and a drive motor actuating the solar concentrator into optimal alignment with the sun based on a determination by the heliostat.

Solar concentrator array with grouped adjustable elements

This invention described in US 7 192 146 seeks to improve the efficiency of solar concentrating devices by providing interconnectivity to the solar array.

Abstract: A tracking heliostat array comprises a plurality of optical elements. The tracking heliostat array further comprises a frame separated from the optical elements. Each of the optical elements has an orientation with respect to the frame. The tracking heliostat array further comprises a plurality of supports coupled to at least one of the optical elements. The tracking heliostat array further comprises a turnbuckle coupled to at least one of the supports and to the frame. Rotation of the turnbuckle causes the corresponding support to be displaced relative to the frame. The orientation of the optical element relative to the frame is adjustable. The tracking heliostat array further comprises a traveling actuator configured to rotate at least one of the turnbuckles. The tracking heliostat array further comprises a positioning mechanism supporting the traveling actuator. The positioning mechanism is configured to move the traveling actuator from a first selected turnbuckle to a second selected turnbuckle.

Solar Collection Apparatus and Methods Using Accelerometers and Magnetic Sensors

The invention described in US 2008/0011288 A1 uses one of the more active systems seen in recent patent activity to maintain an optimized orientation between sun, mirror and collector. Not surprisingly, a two-axis approach is taken.

Abstract: A mirror or other reflecting surface is used for collecting and reflecting incident solar radiation. The mirror is supported for independent motion about a pair of axes. An accelerometer generates signals representative of an amount and direction of motion of the mirror about each of the axes. Motors or other drive mechanisms independently drive the mirror about each of the axes. A tracking device provides information about the current position of the Sun. A control is connected to the accelerometer, the motors and the tracking device for maintaining a predetermined optimum orientation of the mirror as the Sun moves across the sky. Position sensors that sense the position of the mirror relative to the earth's magnetic field may also be employed.

Solar tracking device with springs

This invention (US 2007/0012311 A1) tracks using a much lower technology approach to the sun's changing position in the sky. Two tanks are capable of being filling and drained. The tanks are on opposite sides of a fulcrum. As one tank is filled or drained, the imbalance across the system causes changes in the orientation of the solar collectors. Spring allows smooth tracking based upon the changing weight balance.

Abstract: A solar tracking device is disclosed. In particular, a solar tracking device for overcoming the disadvantages of conventional solar energy system utilizing motors and to lower electricity consumption and decrease cost is provided. The device includes a solar module or solar collector supported by two springs under both ends, and two water tanks on both ends, wherein the solar module or solar collector, similar to a heliostat, is adapted to slowly revolve in response to the imbalanced water tanks filled with different amount of water.

Solar heat engine system

The invention publication US 2007/0062195 A1 describes a much more complex system. In this high-temperature system, solar tracking, parabolic mirrors and one or more concentrator lenses focus energy into an intense beam in this heat engine.

Abstract: The invention includes a solar collector subsystem and a heat engine. The solar collector system uses heliostat mirrors, a parabolic mirror, and a convex concentrator lens or compound parabolic concentrator to gather a large amount of solar energy into a very intense beam. The beam is used to vaporize an injected droplet of working fluid, whereby multiple opposed pistons responsive to the vapor formed reciprocate to produce electric energy by means of linear electric generators. The heat engine includes a chamber having three orthogonal sets of opposed pistons, wherein each piston is independently axially reciprocable and coupled to a linear electric generator. One piston is provided with an axially located window that admits the concentrated solar beam from the solar collector subsystem into the chamber of the heat engine. Another piston is provided with an injector that selectably injects a water drop into the center of the chamber where it can be vaporized by impingement of the concentrated solar beam.

The varied approaches in these inventions and publications are a mere glimpse of the technological advancements seeking to improve the feasibility of solar-energy technologies. Others may be of similar use. Fresnel lenses and novel designs for solar concentrators likewise show promise. The critical factor here seems to lie in moving along a number of paths. Complex systems are not always required, nor would simple systems be cost-effective everywhere. Many solutions have the ability to move solar technologies forward.

James Johnson is a USPTO-registered attorney who performs detailed, exacting research and high-level analyses for tasks of critical importance to business success: invalidity investigations, patent landscapes, freedom to operate reviews, licensing opportunities, and portfolio evaluations. After practicing law for most of his career, he pursued a master's degree in physics, concentrating on numerical and computational methods, turbulent systems and mechanical engineering.

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