Patent Application
20130061845
Not applicable.
Not applicable.
The embodiments of the present invention satisfy the needs of having a passive solar tracker that does not depend on refrigerants.
Information relevant to attempts to address these problems can be found in U.S. Pat. Nos. 3,635,015; 4,175,391; 4,476,854, and European Patent 1744006; which patents are not admitted to be prior art with respect to the present invention by its mention in this Background Section. However, it is desirable to have a better device than is disclosed in the references.
In overview, the present invention is a radiant energy driven orientation system comprising an autonomous passive solar tracker having a thermal actuator that is connected through a cable and pulley and drum to a spring. The drum and spring are mounted on a cross beam of the tracker frame. The cable is attached on one end to the actuator push rod. It then threads through the pulley and wraps around the drum. The spring biases the tracker to pivot towards one direction, and the actuator when heated and extended forces the tracker to pivot in the opposite direction. The tracker is oriented so that the spring has a bias to pivot the tracker to the east, and the outward force of the actuator rod against the cable causes the actuator to pivot to the west. One may take advantage of this tracking by attaching a solar collector to the frame of the tracker.
The actuator is enhanced with a shade fin, which fin enables the tracker to follow the sun more closely by amplifying the thermal effects on the actuator of the position errors of the tracker. At any given instant the wax in the actuator is in thermal equilibrium with its environment (its immediate environment is the actuator cylinder). The wax in the actuator is instantaneously heating and expanding, or instantaneously cooling and contracting, in equilibrium with the temperature of the actuator cylinder at that instant. Sometimes the wax is expanding, which forces the rod out, resulting in a force from the actuator that either matches or exceeds that of the spring, causing the tracker either to remain in place or to pivot more westward so that the shadow of the fin is falling onto a portion of the actuator. Sometimes the wax is contracting, resulting in a force from the actuator that is less than that of the spring, causing the tracker to pivot more eastward so that there is no fin shadow on the actuator or so that the fin is reflecting radiant heat onto the actuator. Now, a relatively tall shade fin casts a long shadow onto the actuator cylinder or reflects much sun onto the actuator jacket at even a slight angle from the sun, that is, at even a slight tracker position error (In fact, by simple trigonometry it can be shown that the amount of shadow from the fin onto the actuator cylinder varies linearly with the height of the fin.). By means of this long shadow or long reflecting surface, the fin amplifies the thermal effects on the actuator of a slight tracker position error by increasing or decreasing the changes in temperature of the actuator relative to the changes in temperature of the actuator had there been no fin. In other words, the fin is a mechanical generator of amplified tracking error signals.
Error signal generators and amplifiers are generally circuits, whether analog or digital. See e.g., U.S. Pat. Nos. 3,739,154 and 5,142,518. However, the error signal generator in the present invention is mechanical. Some spacecraft inventions use radiant heat errors to drive the tracking of solar collectors without converting the heat to electronic control signals, but they exclusively use bimetallic elements. U.S. Pat. No. 3,630,020 is a servomechanical invention in which a plurality of bimetallic elements are connected to a crank on an orientation shaft in a manner such that as the elements individually deform under radiant heating, they will actuate the crank and rotate the orientation shaft in a direction corresponding to the direction of movement of the moving heat source. U.S. Pat. No. 3,311,322 is a heat-sensitive device that use bimetallic elements to generate torque as a function of exposure to solar radiation. U.S. Pat. No. 6,062,511 is a heat-sensitive drive mechanism made of a double-acting shape-memory alloy, the drive mechanism being suitable for causing a panel to be displaced relative to a body of the spacecraft as a function of the direction of incidence of the solar radiation on the spacecraft.
The fin is related to the shadow bar or sun shield in your U.S. Pat. Nos. 4,175,391 and 4,476,854. However, '391 and '854 use the fin to create heat differences between two counter-posed cylinders between which flows a low boiling-point liquid such as Freon®. The present invention in contrast uses the fin to exaggerate the response of the wax-filled actuator to the sun.
The present invention utilizes a wax-filled or similar thermal actuator. One type of thermal actuator comprises a straight cylinder containing a substance such as paraffin wax, petroleum jelly, seed oil, or a combination of these. To the substance there is connected a rod, either by immersion or by an intermediate movable close-fitting seal. The majority of systems using thermal actuators rely on convection to trigger the actuator, for example, U.S. Pat. No. 7,143,762. These systems are designed so that the actuator responds to changes in ambient temperature. A few systems using wax-filled thermal actuators rely on conduction to trigger the actuator, but as a supplement to convection. U.S. Pat. No. 4,219,009 for example utilizes a thermal actuator to drive flexible linkages, which vent the plenum inside a solar panel. Though the actuator is in full contact with the solar collector, allowing for conduction, the actuator is fine tuned for convection. Ever fewer systems using thermal actuators rely on radiant heat transfer or direct sunlight to trigger the actuator. U.S. Pat. No. 7,138,960 depends on incident solar radiation to trigger a wax actuator, which deploys a payload on a space vehicle. '009 utilizes convention, conduction and radiant heat transfer.
Outside of the solar arts, wax-filled actuators are used almost exclusively to control thermostats. See, for example, U.S. Pat. Nos. 6,046,666 and 6,742,716. One exception is U.S. Pat. No. 7,138,960, which depends on incident solar radiation to trigger a wax actuator to deploy a payload on a space vehicle.
Except for two counter-examples, within the solar arts wax-filled actuators are used exclusively to open and close vents. It uses a radiant energy-driven expansive fluid-filled actuator to open and close shutters to the solar panel. U.S. Pat. No. 4,219,009 places wax thermal actuators in conductive contact with a solar collector, so that when the collector overheats, the heat will conduct into the actuator, at some point melting the wax and allowing the actuators to act on vent gates through the action of flexible linkages. U.S. Pat. No. 4,809,592 connects a wax-filled actuator to a vent flap inside of a cold frame, so that when the ambient temperature in the cold frame overheats, the wax in the actuator will melt though convention and open the flap to cool the interior of the cold frame. The Window Vent Opener Model 92192 distributed by Harbor Freight Tools is commonly used for that purpose. U.S. Pat. No. 7,143,762 uses a wax-filled actuator in a manner analogous to U.S. Pat. No. 4,809,592.
One counter-example in the solar arts is EP1744006, which uses the wax actuator to passively control a sun shade. Rather than using the wax actuator to open and close a vent, '006 uses the actuator to directly push and pull an attached sun shade. Except for this simple linear motion, patent '006 does not otherwise track the sun.
The other counter-example in the solar arts is U.S. Pat. No. 3,635,015, which is a heat-sensitive device actuated by solar radiation that is suitable for generating torque for angularly positioning solar panels. The invention uses bimetallics to control the thermal environment of a thermal actuator. The thermal actuator rotates solar panels on wings.
The present invention is a solar invention that uses a wax-filled actuator not to open and close a vent, but rather to oppose a spring, for the purpose of tracking the sun. The design operates the actuator with radiant heat, moderated by shadow bars or shade fins as disclosed for example in U.S. Pat. No. 4,476,854.
The actuator is a paraffin filled cylinder that extends a piston when the paraffin melts. Paraffin expands over 10% in volume when it melts. A paraffin actuator can be made to operate a sun tracker. A spring turns the tracker toward the east; the actuator, when heated, turns the tracker west by means of a linkage straining against the spring. The actuator is placed to the west of a vertical reflecting fin aligned parallel to the axis of rotation. Its motion stops or slows to be imperceptible when it has moved far enough to shade itself in the shadow of the fin. It seems to have stopped. That is deceiving since the motion of the sun persists and the tracker again receives heat and creeps on.
The actuator is blind and only feels its way by warmth. During cold or dim weather it falls behind progress during warm or bright weather. The blind actuator is helped to follow the sun closely by having a tall shade fin which casts a long shadow or reflects much sun even at a slight angle. If the weather becomes cloudy the spring causes the tracker to return to the east as paraffin cools and freezes and the piston retracts.
The actuator is blind, but forceful. It can be helped to feel its way to the correct position by a guide that assists in determining which way to move. Freon gravity trackers are accurate and reliable, but neither versatile nor compact. A small gravity tracker can ride along with a tracker powered by an actuator. The gravity tracker notices whether the blind actuator has felt its way ahead or behind where it should be and tips the shade fin accordingly to guide the actuator to more perfect tracking.
We have observed a paraffin tracker operating among Freon gravity trackers in our yard. The paraffin tracker works well on sunny days. It stays with the others. Clouds cause it to lose the sun and not quickly recover on the sun's reappearance. If, instead of cooling and returning to the east in a matter of an hour, this took 4 hours, the tracker would be more effective. The tracker can be fitted so that it warms quickly in the sun, but cools slowly when the sun is absent. An insulated water jacket about the actuator is connected to a solar collector placed at the base of a shadow fin parallel with the axis of rotation. The solar collector can be longer than the actuators body and thus a tracking device can be made that finds the sun quickly when the sun appears and loses interest in the sun slowly. The sun sensor for a tracker is best long and thin in the direction of the axis. In this orientation a long shade fin can take away or return a large area of sun with a small change of orientation.
When the actuator must be parallel with its sun sensor the piston moves parallel as well. Its motion must be converted by a linkage, cable or twist bar to turn the tracker.
An actuator fed heat by a separate collector can be mounted perpendicular to the axis and operate a simple crank to turn the tracker. This is an advantage.
Each paraffin has a different range of melting temperatures. A carefully refined paraffin is solid below this temperature and a liquid above. None have exact melting points, the ranges are several degrees. Poorly refined paraffin melts the blend of its several components. Vaseline, a mix of paraffins, is partly melted at body temperature, but not completely melted until it is above 120° F.
The extension of the actuator piston is a function of the actuator temperature. The Paraffin is unlike ice. It takes heat to melt ice, but no temperatures higher than 32° F. To melt paraffin in an actuator you add heat and raise temperatures. Different paraffins melt through different temperature ranges. This makes it difficult to closely track the sun. Sometimes you need more sun on the actuator to reach a given temperature than at others.
A proper paraffin for a tracker is one that melts in the sunlight and freezes in the shade in all seasons. A suitable actuator and paraffin for extreme climates like North Dakota, with very hot days in summer and very cold days in winter, will likely employ a high temperature paraffin (melts above 130° F.), a selective surface on the actuator and a clear tube about it.
For a certain design example, we know that extending the piston to point the tracker exactly at an 11:06 sun the temperature must be 124.5° F. While, to point at a 15:31 sun it must be 139.6° F. Position and temperature are locked together, but time of day has leeway. If it is bright and warm we get to the position early. If it is dim or cold, we get there late. A tall shadow fin makes a tracker more accurate than a short one. The sun moves 1° every four minutes. A shadow at the base of a 12″ tall shade fin is 0.21″ wide if the tracker is off 1° (late or early by four minutes). If the fin were 6″ tall it would only cast a 0.1″ shadow when off by 1° while a 24″ shade fin cast a wide 0.42″ wide shadow. Two trackers of the same design, but different shade fin heights would have the same pattern of sun and shade each moment as the day's weather changed. The tracker with the tall shade fin would follow the sun with half the error of the other. The actuator with the taller fin is always closer to a target in the ratio as the height of its fin.
The push of an actuator can cause the turn of a tracker if pushing pulls a cable that travels about a wheel, then over or under a fixed drum. Another way for pushing to cause turning is a twisted bar through a slot as the devices to loft toy helicopters. The twisted bar requires a spring to push back against the actuator, but has an advantage over the cable. With the right pitch to the twisted bar, wind could not disturb the position of the tracker.
The actuator or its heat collector should see the sky. A tracker must be able to find the sun whenever it appears. A shadow fin blocks the view of half the sky, but normally the half the sun has passed through and cannot appear in until the next morning. A spring or the balance of weight tirelessly, if slowly, returns the tracker for the next day. As mentioned earlier, during intermittent sun, a slow return is an advantage. The actuator, expecting to drive farther west might correctly argue, “wait, there will be more sun”. While the spring tells it, “time to go east, time to go home and be ready for tomorrow's sunrise”. The position of the tracker is the outcome of the battle of the two forces.
The fin may be formed as a partial paraboloid. Should the tracker fall behind the sun, the paraboloid concentrates the errant sunlight onto the actuator to hurry the melting of more paraffin and a return to better focus.
These and other features, aspects and advantages of the embodiments of the device and/or methods will become better understood with reference to the following description, appended claim and accompanying drawings where:
The preferred embodiment and best mode present invention comprises a radiant energy driven orientation system comprising, as shown in
The frame 27 may also comprise a flat mounting surface for solar panels. The pivoting of the frame 27 is limited to .+−.55.degree. from vertical. The axis of the frame 27 is inclined to horizontal to direct the frame 27 toward the path of the sun.
To render the device operable, the frame 27 is oriented so that it is pivotable about a generally north/south axis, and where said actuator 28 is located at the west end of the frame 27 so that movement of the sun from east to west during the day heats the actuator 28 and causes it to extend its actuator rod 30 and tilt the frame 27 eastward to follow the sun, the spring 42 forcing the device at nightfall to pivot eastwards in preparation for the morning sunrise.
To optimize the performance, the axis of the frame 27 is inclined to horizontal to direct the frame 27 toward the path of the sun. Because clouds cause these trackers to lose the sun and not quickly recover on the sun's appearance, the actuator 28 may also be covered with an insulated water jacket to make it warm quickly but cool slowly.
It is also possible to engineer a reverse tracker. Here the actuator 28 is placed on the east end cross beam 24 and the reflective fin 32 is situated to the actuators 28 west. The spring 42 biases the tracker to pivot west, so that the tracker spends the night at rest pointing east. In the morning the tracker quickly pivots west to the east as the sun warms the actuator. The spring 42 forces the slowly cooling actuator 28 to travel west as the progress of the sun's shadow allows the actuator 28 to cool. Notice that it is more difficult to have something cool as a day warms than to have it warm.
As shown in
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The advantages of the embodiments of the invention include but are not limited to providing a solar tracker that has the utility of being both passive and autonomous, and not using refrigerants. Every advantageous feature does not need to be incorporated into every embodiment of the apparatus and/or methods.
In response to an increase in absolute temperature, paraffin wax undergoes volumetric expansion of approximately 15%. Most of this occurs during the solid to liquid phase change, although some expansion also occurs within the solid and liquid phases. This effect is used in thermostats, linear actuators (of relatively short stroke), valves and other devices. To further increase the usefulness and adaptability of this process, a device consisting of a cable doubled over a pulley mounted to the piston is used. This modification achieves several things:
Although these versions of the invention have been described in considerable detail, other versions are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the versions contained therein.
