US20110094503A1

US20110094503A1 - Method and apparatus for solar panel tracking

Info

Publication number: US20110094503A1
Application number: US11/088,767
Authority: US
Inventors: Dale G. Jones; Barbara L. Marcum
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-03-25
Filing date: 2005-03-25
Publication date: 2011-04-28

Abstract

A method for tracking the movement of the sun from East to West across the sky during daylight hours to enable solar photovoltaic (PV) panels or arrays of such panels to capture significantly more solar energy than fixed solar panels. Readily-available sun position data (taken from ephemeris or celestial navigation tables) can be programmed into read-only memory (ROM) chips. Date and time of day information can also be programmed into ROM chips powered by long-life, rechargeable batteries, such as lithium-ion batteries. Using such ROM chip data, a solar panel or an array of solar panels can track the sun position provided that during installation (with the panels aimed longitudinally towards the South), the solar panels are positioned upwards towards the noontime sun position to establish a starting point. This enables the sun tracking system of the present invention to track the sun without requiring a solar sensing device. Sun tracking provides an increase of from about 20% to 50% increased solar energy capture compared with fixed, non-tracking solar panels. Experimental data is also provided to illustrate the effectiveness of the present invention.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from provisional application No. 60/555,694 filed Mar. 24, 2004, which is incorporated herein in its entirety by this reference.

FIELD OF THE INVENTION

The present invention relates to tracking the movement of the sun from East to West across the sky during daylight hours to enable solar photovoltaic (PV) panels, or arrays of such panels to capture significantly more solar energy than fixed solar panels. Readily-available sun position data (taken from ephemeris or celestial navigation tables) can be programmed into read-only memory (ROM) chips. Date and time of day information can also be programmed into ROM chips powered by long-life, rechargeable batteries, such as lithium-ion batteries. Using such ROM chip data, a solar panel or an array of solar panels can track the sun position provided that during installation (with the panels aimed longitudinally towards the South), the solar panels are positioned upwards towards the noontime sun position to establish a starting point. This enables the sun tracking system of the present invention to track the sun without requiring a solar sensing device. Sun tracking provides an increase of from about 20% to 50% increased solar energy capture compared with fixed, non-tracking solar panels. Experimental data is also provided to illustrate the effectiveness of the present invention.

BACKGROUND OF THE INVENTION

Solar photovoltaic (PV) panel systems are becoming increasingly important for residential or commercial energy supply, due to the increasing cost of conventional grid-supplied electricity and the desire to reduce environmental pollution as well as utilize renewable sources of energy. In recent years, improved production and designs have reduced the cost of solar PV panels and related storage battery and electric power inverter equipment. However, large flat “billboard” sized solar panels are both unattractive for residential purposes and also require expensive structural mounting equipment, especially in high wind loading areas. One method to reduce the size of solar panels is to provide sun tracking, because a solar panel that can track the movement of the sun across the daytime sky can capture from about 20% to about 50% increased solar energy compared with a fixed, non-tracking solar panel. Therefore, for the same energy capture, a tracking-type of solar panel can be 20% to 50% smaller and therefore less expensive and more practical compared with a fixed, non-tracking solar panel.
Several types of sun tracking systems are commercially available. One type uses a sun sensor with at least two photocells, one pointed East and the other pointed West. With this system, sun tracking can be accomplished by moving the solar panel to equalize the East and West photocell sensor readings. Another type uses a fluid inside relatively large solar energy collector tubes mounted on the East and West sides of the solar panel. With this system, the working fluid inside the tubes expands as it becomes warmed from solar energy. Sun tracking is accomplished by moving the solar panel to equalize the amount of expansion inside each of the two tubes. In both such systems, a relatively large solar panel is rotated from East (at sunrise) to West (at sunset) with the longitudinal axis of the solar panel facing South at solar noon when the sun is at its highest elevation angle with respect to the horizon. Both such systems suffer the disadvantages of (a) poor sun tracking performance caused by dirt, bird droppings, or other material that might collect on the photocell sensors or the collector tubes, and (b) relatively expensive structural members designed to provide the necessary rotating capability for a relatively large flat solar panel array, generally at least about 4×6 feet in size, but perhaps as much as 12×18 feet in size.
The objective of the present invention is to provide a means of sun tracking to reduce the cost and size of tracking-type solar panel systems, without requiring the use of photocell sensors or collecting tubes, and also to provide sun tracking with a low-profile solar array configuration that would not be aesthetically unpleasing and objectionable for use in residential areas.

BRIEF DESCRIPTION OF THE INVENTION

The present invention does not require the use of any type of solar sensing photocell or thermal collecting tube device to enable a solar panel (or array of solar panels) to track the sun. The present invention makes use of readily-available sun position data (taken from ephemeris or celestial navigation tables). These data are programmed into read-only memory (ROM) chips. Date and time of day information are also programmed into ROM chips powered by long-life, rechargeable batteries, such as lithium-ion batteries, similar to the ROM chips used in personal computers which provide day, date and clock time for computer users. Using such ROM chip data, a solar panel or an array of solar panels can track the sun position provided that during installation (with the panels aimed with the longitudinal axis pointed towards the South), at least one time versus position point is established as a starting point. One such easily-established point is to position the one or more solar panels aimed straight upwards when the sun reaches its highest zenith point at solar noon. The system of the present invention then receives an input signal to establish this initial starting point. The tracking system of the present invention is then energized to become fully operational.
Because of differences in sun position with respect to the horizon at different geographical latitude locations on the earth, it is also desirable to provide a second solar panel position starting point input, which can be used to improve and refine the tracking ability because adjustments programmed within the ROM chip can be set up to account for latitude locations if a second input is provided. For example, another such input signal can be established by aiming the solar panels directly towards the sun at some other known time which is several hours different from solar noon. Once at least two such points are established, the sun tracking system of the present invention enables the solar panels to track the sun with improved accuracy which compensates for different geographic latitude locations.
Another feature of the present invention is to provide a very low-profile solar panel array which lies flat with the surface of almost any type of roof or structure. This eliminates the need to have large “billboard” size solar panels which are aesthetically unpleasing and objectionable for use in most residential areas. The physical appearance of such solar panel arrays would be much more acceptable for use in residential applications, because they would appear to be roof vents, skylights, or louvers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a line drawing showing the arrangement of the experimental system used for testing the present invention which illustrates the configuration of the basic components, in this case being three solar panels. In practice, these solar panels are preferably operated in unison by means of a captive rack and pinion gear arrangement driven by a reversible DC gearmotor, the gearmotor being controlled by inputs provided from the ROM chips and the control circuit;

FIG. 2 is a dimensional drawing showing the arrangement of a typical solar module array of the present invention;

FIG. 3 shows the effect of adjacent solar panel spacing on the amount of solar energy blockage incurred at low sun angles when the sun in low towards the horizon;

FIG. 4 depicts the position of the sun versus time of day, and when used with the explanations in the specification text, enables better understanding of the method used to determine sun position, and hence, the required solar panel tracking angle;

FIG. 5 is a graph showing the decrease in solar energy capture for a typical solar panel when the sun angle deviates away from being perpendicular to the solar panel surface, thus illustrating the importance of tracking the sun to keep the sun angle as close to perpendicular to the solar panel surface as possible as the sun moves across the sky from East to West;

FIG. 6 is a graphical depiction of the improvement in solar energy capture comparing tracking versus fixed solar panels mounted on a flat horizontal roof in San Diego, Calif. for the worst case condition at winter solstice;

FIG. 7 is a graphical depiction of the improvement in solar energy capture comparing tracking versus fixed solar panels mounted on a standard 5/12 roof in San Diego, Calif. for the worst case condition at winter solstice.

RESULTS OF EXPERIMENTAL TESTING

An experimental solar panel system was constructed to test the effectiveness of the present invention. A schematic diagram of the experimental system is shown in FIG. 1, where the components consisted of three (3) rectangular solar panels, 12 a, 12 b and 12 c, each rotating about a longitudinal axis, 13, and supported by a framework, 11. For the purposes of these experiments, the solar panels were manually rotated during data collection. A preferred embodiment of the framework would include a captive rack and pinion gear arrangement driven by a reversible DC gearmotor, so the solar panels could be rotated in unison and kept at the same angle with respect to the sun simply by suitable inputs provided to the gearmotor.
Results of experimental testing are shown in Table 1, where solar panel electrical output was passed through a simulated load consisting of a suitable resistor. The voltage across the resistor was measured and averaged over two independent runs, to enable the power output from the solar panel to be calculated. The power output in watts is the measured voltage squared, divided by the resistance in ohms. The solar panels were aimed with the long axis pointing directly East to allow the effect of changing sun angle to be measured over a short period of time as the solar panels were manually rotated from one angle to the next. These tests were conducted at noon on Oct. 17, 2003 in San Luis Obispo, Calif. with blue sky conditions. The voltages across the resistor were measured and recorded for various sun angles with respect to the solar panel surface. The results were then transposed to calculate the power output from the solar panel assuming a 12 hour day, first with a fixed solar panel and second, assuming that the solar panels were enabled to track the sun. The solar energy capture with sun tracking was about 48% more than provided by the same solar panels in a fixed position to provide maximum solar energy capture at solar noon. The fixed solar panels provided less energy capture at all other times of the day, because fixed panels cannot track the movement of the sun.
Based on these experimental tests, it was obvious that significant improvements in solar energy capture could be obtained with a low profile solar tracking module according to the present invention.

TABLE 1

Solar Panel Tracking Tests

		Tracking
Solar Panel	Fixed Panel	Panel	Measured	Calculated	Fixed	Tracking
Angle	Sun Hours	Sun Hours	Voltage	Watts	Watt-Hours	Watt-Hours

90.00	1.50	12.00	3.22	2.254	3.381	27.048
78.75	1.50	n/a	3.22	2.254	3.381
67.50	1.50	n/a	3.05	2.022	3.033
56.25	1.50	n/a	2.98	1.931	2.896
45.00	1.50	n/a	2.76	1.656	2.484
33.75	1.50	n/a	2.24	1.091	1.636
22.50	1.50	n/a	1.78	0.689	1.033
11.25	1.50	n/a	1.20	0.313	0.470
0.00	0.00	n/a	0.61	0.081	0.000
				Totals	18.314	27.048

Rotate Percent Improvement over Fixed	Baseline	47.7%

Test Date: Oct. 17, 2003 at 12:00 Noon in San Luis Obispo, CA 93401, blue sky conditions
NOTES:
1. Watts = (volts)*(volts)/(ohms) where ohms = 4.6 ohms (5 watt resistor)
2. Solar panel: 2 rows of 12 silicon crystal cells @ 1 × 2 inches each, total 48 sq. in.
3. Panel substrate: FRP with Tefzel over the silicon crystal cells
4. Voltages averaged over two independent runs with stable resistor temperature

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As already shown in FIG. 1, the preferred embodiment for solar panel arrays of the present invention is to arrange long rectangular solar panels in an array like a shutter or a Venetian blind, with the longitudinal axis, 13, of the solar panels, 12 a, 12 b and 12 c, to be aimed directly South, and being enabled to rotate about the longitudinal axis from East to West during daylight hours to thereby track the movement of the sun.
A diagram of such a sun tracking module is shown in FIG. 2, which provides one preferred embodiment of the present invention. As shown in FIG. 2, there are 9 solar panels, 20 a through 20 i, arranged in a modular frame, 21, with outside dimensions of 24 by 48 inches, i.e. 2×4 feet, which fits with most of the roof framing dimensions used in the United States. Each solar panel is approximately 4.3 inches wide by 21.8 inches long, and contains 30 solar PV cells connected in series, each cell about 4.0×0.7 inches in size, with a total of about 84 sq.in. of active cell surface area. This solar module with 9 such rotating solar panels contains about 756 sq. in. of active cell area, and will produce about 14 VDC at about 4.5 amperes, maximum of about 63 watts of electrical power in full sunlight with the solar array pointed directly towards the sun. The active cell area is about 66% of the total area based on the outside dimensions of the modular frame. The full sunlight open circuit voltage for such a solar panel array would be more like 17.8 VDC, but in actual practice, the working voltage for purposes of rating the power output from a solar module is decreased about 20%.
One preferred method for rotating all the sun tracking solar panels in unison is to use a captive rack and pinion gear mechanism, 22 a and 22 b, with pinion gears, 22 b, mounted on each of the axial shafts, 23, connected to each of the parallel-mounted solar panels, 20 a through 20 i, with each axial shaft, 23, securely mounted in a suitable bearing on the solar module framework, 21. The linear rack gear, 22 a, is then preferably supported and “captured” by suitably-flanged roller bearings, which are also mounted on the same solar module framework, 21. East to West sun tracking movement of all the solar panels in unison can then be accomplished using a suitable reversible actuator. For example, a captive-nut type of linear actuator motor could be used, such as the 12 VDC automobile car antenna actuator motor. Other similar types of actuators could be used, such as a reversible DC gearbox motor, 24, with a pinion driving gear that operates both back and forth to move the toothed rack gear, 22 a, over a desired linear distance. The type of actuator itself is not critical, except that it must be capable of both pushing and pulling the linear rack gear, 22 a, so that after sun tracking all day long until evening, then, after sunset in the West, the solar panel array can be returned to the East sunrise position, to be ready for another day of sun tracking at sunrise. As previously stated, the time of day signals needed to enable the control system to know when sunset occurs and when to return the solar panels towards the East to anticipate sunrise on the next day comes from a suitable ROM chip. The ROM chip can be powered from a small long-lifetime battery located inside the control system, or from energy storage batteries that are used for storing the solar energy captured by the solar panel system.
It is preferred that the solar panels are capable of rotating at least about +/−60 degrees from being flat (or pointed straight upwards) with respect to the solar module framework, 21. The pinion gears, 22 b, on each of the solar panel longitudinal axes, 23, are preferably formed as half-circles, to avoid having any portion of the pinion gear itself projecting upwards beyond the plane of the solar panels, and thereby keeping a low profile and also avoiding any sun blockage that would reduce solar energy capture.
The sun tracking solar module of the present invention can be installed on any type of roof, gazebo, greenhouse, patio, open ground, or almost any other type of preferred structure, and not limited to the roof of a residential home or commercial office building. The external physical appearance of the sun tracking solar module of the present invention is similar to a roof vent or louver, and could also be mistaken for some type of skylight. One preferred embodiment, especially for severe winter weather conditions with snow and ice, is to enclose the sun tracking solar module of the present invention inside a flat skylight or dome-shaped transparent or translucent housing designed to minimize the amount of solar energy lost because of sunlight transmission through the housing towards the solar panels. One preferred embodiment is a flat glass covering over the top surface of the module framework, elevated sufficiently to allow free rotation of the solar panels which would be protected inside. The overall height of such a flat glass-covered module for the preferred embodiment of FIG. 2 would be about 5 inches—very acceptable for most residential installations. It should also be noted that such a “skylight” configuration would actually function rather well as a skylight, blocking most of the direct sunlight, but allowing indirect light transmission from the blue sky to pass through the plane of the solar module for interior lighting purposes, as might be desired.
One disadvantage of the preferred linear array of parallel solar panels is that when the sun elevation angle with respect to the horizon is low, each solar panel tends to shade, or block, the adjacent solar panel. This effect for the 4.3 inch wide solar panels mounted on 5.0 inch centers is shown in FIG. 3, where the sun elevation angles corresponding to various amounts of blockage are calculated. For example, if the sun elevation angle is about 20 degrees, there would be a blockage factor of about 50%. The percentage open area between adjacent solar panels in FIG. 3 is about 14%. If the percentage open area is increased, there is less blockage for a given sun elevation angle. For example, if the open area is increased to about 33% (4.3 inch wide solar panels on 6.5 inch centers), the solar blockages versus sun elevation angles change as follows:


	14% Open Area	33% Open Area

0% Blocked	47.6 deg.	0% Blocked	38.5 deg.
	Sun Angle		Sun Angle
25% Blocked	34.9 deg.	25% Blocked	26.6 deg.
	Sun Angle		Sun Angle
50% Blocked	20.8 deg.	50% Blocked	16.7 deg.
	Sun Angle		Sun Angle
75% Blocked	9.0 deg.	75% Blocked	8.4 deg.
	Sun Angle		Sun Angle

Therefore, by suitable selection of percentage open area, the amount of blockage can be adjusted as may be desired.
Calculating Sun Position Vs. Time of Day
The position of the sun as determined from typical locations in the United States can be described in terms of sun azimuth angle (i.e. looking downwards on the horizontal plane and determining the sun position with respect to the four directions of the compass) and the sun elevation angle above the horizon. Since the earth is spherically shaped and revolves on its axis at a constant speed, and since the earth rotates around the sun in a circular orbit, it is possible to exactly predict the position of the sun from any given point on the surface of the earth as a function of the time of day. Sun position data can be obtained from published celestial navigation tables or ephemeris tables. One very convenient source of such data is found on the InterNet. It is posted by the California Institute of Technology Jet Propulsion Laboratory, and is called the JPL Horizons Ephemeris Generator. It can be found on the InterNet at URL: http://ssd.jpl.nasa.gov/cgi-bin/eph
Tables 4 and 5 (below) provide examples of the data for the winter and summer solstices at San Diego, Calif., which were obtained using the JPL Horizons Ephemeris Generator. Note that at San Diego, the sun elevation angle with respect to the horizon at solar noon changes from 33.8 degrees on the winter solstice to 80.7 degrees on the summer solstice. Since the short winter days with lower sun angle represent the worst case conditions for solar energy capture, the calculations which follow are based on the winter solstice data and information.

TABLE 4

Winter Solstice
San Diego, CA

Ephemeris Generator
Ephemeris Settings

Target Body:	Sun (Sol)
Observer Location:	San Diego, CA
Coordinates:	117° 09′21.6′′W, 32° 42′52.9′′N
From:	A.D. 2003-12-20 00:00 UT-8 (PST)
To:	A.D. 2003-12-25 00:00
Step:	1 minute, Rise/Transit/Set only (TVH)
Format:	Calendar Date and Time
Output Quantities:	2, 4
Ref. Frame, RA/Dec Format:	J2000, HMS
Apparent Coordinates Model:	Airloss

HORIZONS Generated Ephemeris

Ephemeris/WWW_USER Mon Mar 22 08:52:42 2004 Pasadena, USA/Horizons

Target body name:	Sun (10)	{source: DE-0406LE-0406}
Center body name:	Earth (399)	{source: DE-0406LE-0406}
Center-site name:	(User Defined Site)

Start time:	A.D. 2003-Dec-20 00:00:00.0000 UT-08:00
Stop time:	A.D. 2003-Dec-25 00:00:00.0000 UT-08:00

Step-size:	1 minutes
Center geodetic:	242.844000, 32.7147, −0.00	{E-lon(deg), Lat(deg), Alt(km)}
Center cylindric:	242.844000, 5371.6412, 3427.38	{E-lon(deg), Dxy(km), Dz(km)}
Center pole/equ:	High-precision EOP model	{East-longitude +}
Center radii:	6378.1 × 6378.1 × 6356.8 km	{Equator, meridian, pole}
Target pole/equ:	IAU_SUN	{East-longitude +}
Target radii:	696000.0 × 696000.0 × 696000.0 k	{Equator, meridian, pole}
Target primary:	Sun	{source: DE-0406LE-0406}
Interfering body:	MOON (Req = 1737.400) km	{source: DE-0406LE-0406}
Deflecting body:	Sun, EARTH	{source: DE-0406LE-0406}
Deflecting GMs:	1.3271E+11, 3.9860E+05 km{circumflex over ( )}3/s{circumflex over ( )}2
Atmos refraction:	NO (AIRLESS)
RA format:	HMS
Time format:	CAL
Time zone:	UT-08:00
RTS-only print:	TVH
RTS elevation:	0. degrees
EOP file:	eop.040319.p040610

EOP coverage:	DATA-BASED 1962-JAN-20 TO 2004-MAR-19. PREDICTS−> 2004-JUN-09
Units conversion:	1 AU = 149597870.691 km, c = 299792.458 km/s, 1 day = 86400.0 s

Date_(ZONE)_HR:MN		R.A._(a-apparent)_DEC Azi_(a-appr)_Elev

2003-Dec-20 06:47	Cr	17	52	33.31	−23	25	50.3	117.7005	−0.6951
2003-Dec-20 11:47	*t	17	53	28.29	−23	26	01.9	180.2259	33.8511
2003-Dec-20 16:47	Cs	17	54	23.26	−23	26	07.9	242.5143	−1.0029
2003-Dec-21 06:47	Cr	17	56	59.75	−23	26	23.7	117.6413	−0.7933
2003-Dec-21 11:47	*t	17	57	54.75	−23	26	29.4	180.0882	33.8437	←	33.8°
2003-Dec-21 16:47	Cs	17	58	49.73	−23	26	29.5	242.4428	−0.9134
2003-Dec-22 06:48	Cr	18	01	26.45	−23	26	28.9	117.7095	−0.7009

TABLE 5

Summer Solstice
San Diego, CA

Ephemeris Generator
Ephemeris Settings

Target Body:	Sun (Sol)
Observer Location:	San Diego, CA
Coordinates:	117° 09′21.6′ ′W, 32° 42′52.9′′N
From:	A.D. 2003-06-20 00:00 UT-8 (PST)
To:	A.D. 2003-06-25 00:00
Step:	1 minute, Rise/Transit/Set only (TVH)
Format:	Calendar Date and Time
Output Quantities:	2, 4
Ref. Frame, RA/Dec Format:	J2000, HMS
Apparent Coordinates Model:	Airloss

HORIZONS Generated Ephemeris

Ephemeris/WWW_USER Mon Mar 22 08:50:47 2004 Pasadena, USA/Horizons

Start time:	A.D. 2003-Jun-20 00:00:00.0000 UT-08:00
Stop time:	A.D. 2003-Jun-25 00:00:00.0000 UT-08:00

Step-size:	1 minutes
Center geodetic:	242.844000, 32.7147,- −0.00	{E-lon(deg), Lat(deg), Alt(km)}
Center cylindric:	242.844000, 5371.6412, 3427.38	{E-lon(deg), Dxy(km), Dz(km)}
Center pole/equ:	High-precision EOP model	{East-longitude +}
Center radii:	6378.1 × 6378.1 × 6356.8 km	{Equator, meridian, pole}
Target pole/equ:	IAU_SUN	{East-longitude +}
Target radii:	696000.0 × 696000.0 × 696000.0 k	{Equator, meridian, pole}
Target primary:	Sun	{source: DE-0406LE-0406}
Interfering body:	MOON (Req = 1737.400) km	{source: DE-0406LE-0406}
Deflecting body:	Sun, EARTH	{source: DE-0406LE-0406}
Deflecting GMs:	1.3271E+11, 3.9860E+05 km{circumflex over ( )}3/g{circumflex over ( )}2
Atmos refraction:	NO (AIRLESS)
RA format:	HMS
Time format:	CAL
Time zone:	UT-08:00
RTS-only print:	TVH
RTS elevation:	0. degrees
EOP file:	eop.040319.p040610

EOP coverage:	DATA-BASED 1962-JAN-20 TO 2004-MAR-19. PREDICTS−> 2004-JUN-09
Units conversion:	1 AU = 149597870.691 km, c = 29979 2.458 km/s, 1 day = 86400.0 s

Date_(ZONE)_HR:MN		R.A._(a-apparent)_DEC Azi_(a-appr)_Elev

2003-Jun-20 04:41	Cr	05	54	43.39	+23	25	58.3	61.1912	−0.8196
2003-Jun-20 11:51	*t	05	55	57.44	+23	26	10.5	181.2062	80.7196
2003-Jun-20 19:00	Cs	05	57	11.27	+23	26	12.9	298.9073	−0.9456
2003-Jun-21 04:42	Cr	05	58	53.16	+23	26	17.5	61.2937	−0.6722
2003-Jun-21 11:51	*t	06	00	07.04	+23	26	22.3	180.8972	80.7237	←	80.7°
2003-Jun-21 19:00	Cs	06	01	20.87	+23	26	17.3	298.8785	−0.9048
2003-Jun-22 04:22	Cr	06	03	02.76	+23	26	11.9	61.2653	−0.7132

The length of the day at various longitude locations along the West Coast of the United States were determined from the same JPL Horizons program. For example, on the shortest day of the year, the winter solstice, the following information was obtained:


Location	Latitude	Sunrise	Sunset	Length of Day

San Diego, CA	32 deg N	06:47	16:47	10 hr 0 min
Eugene, OR	44 deg N	07:48	16:43	8 hr 55 min
Seattle, WA	47 deg N	07:58	16:27	8 hr 09 min
Bellingham, WA	48 deg N	08:03	16:23	8 hr 03 min

It is thus seen that the length of day at winter solstice varies by about 2 hours on December 21 for locations varying from the USA border with Canada on the North and the USA border with Mexico on the South. If an intermediate location were selected as being representative of the entire USA, such as 40 degrees North latitude, then the sunrise prediction on the winter solstice would be about 07:25 hours. This prediction would be 38 minutes behind the actual sunrise time in San Diego, Calif. and 38 minutes before the actual sunrise time in Bellingham, Wash. However, the time of solar noon would be just about the same for all the various locations up and down the West Coast of the United States. The maximum error of 38 minutes occurs only at sunrise and sunset, where there is very little solar energy capture, and decreases as the sun approaches solar noon. The length of day estimate error increasing again as the sun sets, at which time there is very little solar energy capture available.
Careful experiments were conducted to determine the loss of solar energy capture as a function of the angle of the sun with respect to the place of the solar panel. As shown in FIG. 5, the loss in solar energy capture by a solar panel is less than about 11% so long as the angle of the sun to the solar panel is 60 degrees or greater, with 90 degrees being perfect. A maximum error of 38 minutes in solar panel tracking position amounts to an error of 9.5 degrees in solar panel tracking angle, representing a maximum loss of about 2% in solar energy capture, as determined from FIG. 5. This is considered to be an acceptable source of inaccuracy in the preferred solar tracking method of the present invention. Therefore, a simplified solar tracking model can be developed which will function adequately for all locations in the United States, from the Northern border to the Southern border. However, for any given location, adjustments need to be made for the longitudinal location (i.e. time of day) as well as the mounting angle of the sun tracking module, whether on a flat roof, or a roof with a given pitch angle, as will be discussed further below. The key point, however, is that a practical sun tracking system can operate successfully in a variety of geographic locations, without requiring the use of any type of solar sensor, such as a photocell system, or thermal sensor, such as a collector tube system.
The JPL Horizons Ephemeris Generator provides the sun elevation angle at solar noon, as well as the times and sun azimuth angles at both sunrise and sunset. Given this information, it is relatively straightforward to determine the sun position at any time of day. For simplicity, these calculations were performed graphically as shown in FIG. 4.
FIG. 4 shows the winter solstice sun positions versus time of day for San Diego, Calif. The upper unit circle represents the sun azimuth angles versus time of day, looking downwards on the four directions of the compass. From Table 4, at sunrise, 06:47, the sun azimuth angle is 117.7. Subtracting 90 degrees, the sun offset angle from the East-West direction is shown in FIG. 4 as 27.7 degrees at sunrise. From Table 4, we also know the length of the day (10 hours 0 minutes) and the time of sunset as well as the time at solar noon, or mid-day. Since the earth rotates at constant speed, the progression of sun offset angle versus hours in the day are shown marked off in the upper unit circle of FIG. 4. Each hour, the sun offset angle increases by 12.46 degrees (i.e. 62.3 divided by 5). Therefore, the sun offset angle at the 2^ndhour after sunrise is 52.6 degrees.
The lower unit circle in FIG. 4 represents the sun elevation angles versus time of day, with the position of the horizon for the winter solstice day in San Diego marked as shown. Fortunately, the sun traverses a circular arc across the sky, not an elliptical or a parabolic arc. Once the sun elevation angle of 33.8 degrees at solar noon is determined (i.e. from Table 4), then the position of the horizon on the unit circle can be drawn at a distance (corresponding to the sine of the sun elevation angle) below the mid-day position on the unit circle.
The sun azimuth angles for the daylight hours are shown in the upper unit circle. These correspond directly with the sun elevation angles for the daylight hours in the lower unit circle. The connections between these two sun position indicators are shown in dotted lines in FIG. 4. The sun elevation angles for the daylight hours are then determined by measuring the height above the horizon and calculating the arc sin of the measured height (divided by 1 for a unit circle). For example, at the 2^ndhour after sunrise, the height of the sun above the horizon line is measured to be 0.347 vertically upwards to the arc of the unit circle, and the arc sin of 0.347 is 20.3 degrees, which is the sun elevation angle at the 2^ndhour after sunrise. Similar calculations can be made for this particular location and date as shown in Tables 2 and 3.
Table 2 provides a comparison of the mA current capture during the daylight hours for fixed vs. tracking solar panels located on a flat horizontal roof located in San Diego, Calif. on December 21 or the winter solstice. Table 3 provides the same comparison for solar panels located on a standard 5/12 pitch roof in the same location on the same day. A somewhat complex physical model was constructed to enable direct measurement of the sun angle with respect to the plane of the solar panel. This physical model used string to represent the sunlight rays, and the string was set at the given sun elevation angle above a flat horizontal surface. Next, the position of the solar panel array was adjusted to be at the correct angle with respect to the string to represent the correct sun offset angle (sun azimuth angle). For the fixed solar panel, the angle of the string (representing the rays of sunlight) measured perpendicular to the plane of the solar panel was determined. For the easiest situation, Case 1 with the solar panel mounted on a flat horizontal roof, the sun angles to the fixed panel were the same as the sun elevation angles. Then, using FIG. 5 again, the percentage of maximum current output could easily be determined. For the sun tracking module, the best solar panel rotation angle for maximizing the sun angle to panel were decided experimentally, and the results along with the percentage of maximum current output were again recorded. As shown in Table 2 (on the next page), the rotating solar panels capture 62% more mA current than the fixed solar panel for Case 1 on a flat roof in San Diego, Calif. on December 21 or the winter solstice.
Similar experiments and calculations were conducted for Case 2, with the two types of solar panel on a standard 5/12 pitch roof in San Diego, Calif. on December 21 or winter solstice. As shown in Table 3 (on the following page), the rotating solar panels capture 20% more mA current than the fixed solar panel.

TABLE 2

Case 1 Data - Flat Roof
SunTracker Solar Panel Tracking System
Calculation of Improved Performance vs. Fixed Solar Panel
Mar. 22, 2004, DG Jones,

Panel Location:	San Diego, California, USA, 117-deg W, 32-deg N
Worst Case Winter Soltice Day:	Dec 21, 2003
Sun Azimuth Angle:	27.7 deg (offset from 90-deg due East)
Sun Elevation at Mid-Day:	33.9 deg (as measured above horizon plane)
Sunrise Time:	0647 hr
Mid-Day Time:	1147 hr
Sunset Time:	1647 hr
Length of Day:	10.0 hr

Rotating Solar Panels Facing Due South with +/− 60 degree rotate capability

Case 1:	Solar Panels positioned parallel with horizon (straight up)
Case 2:	Solar Panels on standard 5/12 roof, or 22.6 deg tilt above horizontal

NOTES:

Please see unit circle figures which accompany this chart. Below 20 deg sun elevation, partial blockage of rotate panels occurs

Partial Blockage estimated at 25% for +1 and +9 hours and 75% for Sunrise and Sunset

(Theta)

Sin (Theta)

Height (h)

(Alpha)

Case 1 - Panel Flat with Horizon

	Sun	Unit Circle	Above Unit	Sin-1 (h)	Sun Angle	Fixed Panel	Best Panel	Sun Angle	Rotate Panel
	Azimuth	Height	Circle	Sun	to Fixed	% of Max.	Rotation	to Panel	% of Max.
Hour	Offset	Above E-W	Horizon	Elevation	Panel	Current	Angle	with Rotate	Current

Sunrise	27.7	0.465	0.000	0.0	0.0	8.0%	60	41.0	17.0%
“+1”	40.2	0.645	0.182	10.5	10.5	18.0%	60	47.0	57.0%
“+2”	52.6	0.794	0.347	20.3	20.3	30.0%	60	42.0	70.0%
“+3”	65.1	0.907	0.459	27.3	27.3	44.0%	60	38.0	64.0%
“+4”	77.5	0.976	0.526	31.7	31.7	52.0%	50	35.0	58.0%
Mid-Day	90.0	1.000	0.558	33.9	33.9	56.0%	0	33.9	56.0%
“+6”	102.5	0.976	0.526	31.7	31.7	52.0%	50	35.0	58.0%
“+7”	114.9	0.907	0.459	27.3	27.3	44.0%	60	38.0	64.0%
“+8”	127.4	0.794	0.347	20.3	20.3	30.0%	60	42.0	70.0%
“+9”	139.8	0.645	0.182	10.5	10.5	18.0%	60	47.0	57.0%
Sunset	152.3	0.465	0.000	0.0	0.0	8.0%	60	41.0	17.0%
				Daily Totals	35.2%				57.1%

	Percentage Increase over Baseline	Baseline				62.2%

TABLE 3

Case 2 Data -- 5/12 Pitch Roof
SunTracker Solar Panel Tracking System
Calculation of Improved Performance vs. Fixed Solar Panel
Mar. 22, 04, DGJones

Rotating Solar Panels Facing Due South with +/− 60 degree rotate capability

NOTE:

Please see unit circle figures which accompany this chart. Below 20 deg sun elevation, partial blockage of rotat panels occurs.

(Theta)

Sin (Theta)

Height (h)

(Alpha)

Case 2 - Panel on Standard 5/12 Pitch Roof @ 22.6 degrees

	Sun	Unit Circle	Above Unit	Sin-1 (h)	Sun Angle	Fixed Panel	Best Panel	Sun Angle	Rotate Panel
	Azimuth	Height	Circle	Sun	to Fixed	% of Max.	Rotation	to Panel	% of Max.
Hour	Offset	Above E-W	Horizon	Elevation	Panel	Current	Angle	with Rotate	Current

Sunrise	27.7	0.465	0.000	0.0	0.0	8.0%	60	64.0	22.8%
“+1”	40.2	0.645	0.182	10.5	29.0	46.0%	60	75.0	72.8%
“+2”	52.6	0.794	0.347	20.3	43.0	70.0%	45	65.0	92.0%
“+3”	65.1	0.907	0.459	27.3	54.0	82.0%	30	62.0	90.0%
“+4”	77.5	0.976	0.526	31.7	57.0	86.0%	15	60.0	89.0%
Mid-Day	90.0	1.000	0.558	33.9	57.0	86.0%	0	57.0	86.0%
“+6”	102.5	0.976	0.526	31.7	57.0	86.0%	15	60.0	89.0%
“+7”	114.9	0.907	0.459	27.3	54.0	82.0%	30	62.0	90.0%
“+8”	127.4	0.794	0.347	20.3	43.0	70.0%	45	65.0	92.0%
“+9”	139.8	0.645	0.182	10.5	29.0	46.0%	60	75.0	72.8%
Sunset	152.3	0.465	0.000	0.0	0.0	8.0%	60	64.0	22.8%
				Daily Totals		66.2%			79.6%

	Percentage Increase over Baseline		Baseline			20.3%

Looking at both Table 2 and Table 3, it is noteworthy that the best panel rotation angle is quite different for the flat roof compared with the standard 5/12 pitch roof. For example, at +3 hours after sunrise, the flat roof installation would still have the best panel rotation angle at 60 degrees, while for the pitched roof, the best panel rotation angle would be reduced to 30 degrees. Therefore, when installing a sun tracking solar module of the present invention, it would be necessary either to input the roof pitch angle into the programming scheme, or to orient the solar panel array at the best angle towards the sun at some known time after sunrise, and enter the result into the programming scheme. The second method is preferred, because using a straight rod attached perpendicular to the solar panel surface, it is quite easy to adjust the panel rotation angle to minimize the length of the shadow from the rod, and this corresponds to the best panel rotation angle. Also, it is easy to understand that as the roof pitch increases, the effectiveness of the fixed panel increases simply due to increased sun angle, while with the same increased roof pitch, the rotating panel can more easily approach perfectly perpendicular sun angles over a longer number of daylight hours.
The results for Case 1 and Case 2 are compared directly in Table 6, which shows the effects of rotating the sun tracking solar module of the present invention as compared with a fixed solar panel for these two different roof pitch configurations. Both sets of data are for the winter solstice day in San Diego, Calif., with a total of 10 daylight hours. To complete the solar energy capture calculations (watt-hours), it was further assumed that the solar panel output voltage drops to 70% of maximum when the solar panel output current drops below 50%.
As shown in Table 6 (on the next page), the sun tracking solar module collects about 92% more solar energy than the fixed panel on a flat roof (Case 1) and about 25% more on a standard 5/12 pitch roof. These tabulated results are further illustrated in FIG. 6 for the flat roof and FIG. 7 for the pitched roof. It is concluded that regardless the roof pitch angle, the sun tracking solar module of the present invention provides significantly increased solar energy capture compared with a fixed solar panel, whether the number is 25%, 48% or 92%, all of which depend on type of roof; geographic location, day of the year, as well as variable ambient weather conditions.

TABLE 6

Rotate vs. Fixed Solar Performance
Rotate vs. Fixed Solar Panel Performance
Mar. 22, 2004, DGJones

Panel Location:	San Diego, California, USA, 117-deg W, 32-deg. N
Worst Case Winter Soltice Day:	Dec 21, 2003

Please see Case 1 and Case 2 *.xls files for actual data

NOTES:

When current drops below 50% of maximum, it is assumed that voltage drops to 70% of maximum.

Case 2 - Panel on Std 5/12 Pitch Roof

Fixed Solar Panel

Rotating Solar Panel Module

Hours	% Max.	% Max.	% Max.	% Max.	% Max.	% Max.
from	Current	Voltage	Wattage	Wattage	Current	Voltage
Sunrise	mA	V	W	W	mA	V

0	8%	70%	5.6%	16.1%	23%	70%
1	46%	70%	32.2%	73.0%	73%	100%
2	70%	100%	70.0%	92.0%	92%	100%
3	83%	100%	83.0%	90.0%	90%	100%
4	86%	100%	86.0%	89.0%	89%	100%
5	86%	100%	86.0%	86.0%	86%	100%
6	86%	100%	86.0%	89.0%	89%	100%
7	82%	100%	82.0%	90.0%	90%	100%
8	70%	100%	70.0%	92.0%	92%	100%
9	46%	70%	32.2%	73.0%	73%	100%
10	8%	70%	5.6%	16.1%	23%	70%
Totals			63.3%	79.0%

Percentage Increased Power	Baseline	24.8%

Case 1 - Panel on Flat Horizontal Roof

Fixed Solar Panel

Rotating Solar Panel Module

Hours	% Max.	% Max.	% Max.	% Max.	% Max.	% Max.
from	Current	Voltage	Wattage	Wattage	Current	Voltage
Sunrise	mA	V	W	W	mA	V

0	8%	70%	5.6%	11.9%	17.0%	70%
1	18%	70%	12.6%	57.0%	57.0%	100%
2	30%	70%	21.0%	70.0%	70.0%	100%
3	44%	70%	30.8%	64.0%	64.0%	100%
4	52%	100%	52.0%	58.0%	58.0%	100%
5	56%	100%	56.0%	56.0%	56.0%	100%
6	52%	100%	52.0%	58.0%	58.0%	100%
7	44%	70%	30.8%	64.0%	64.0%	100%
8	30%	70%	21.0%	70.0%	70.0%	100%
9	18%	70%	12.6%	57.0%	57.0%	100%
10	8%	70%	5.6%	11.9%	1.70%	70%
Totals			29.4%	56.6%

Percentage Increased Power	Baseline	92.2%

Initial Sun Tracking System Setup

As already described above, the effect of roof pitch angle can be compensated for by orienting the solar panel array at the best angle towards the sun at some known time after sunrise, and entering the result into the tracking system programming scheme.
Readily-available sun position data (taken from ephemeris or celestial navigation tables) can be programmed into read-only memory (ROM) chips. Date and time of day information can also be programmed into ROM chips powered by long-life, rechargeable batteries, such as lithium-ion battery. As with other products such as personal computers, the battery will continue to operate the clock and keep time from the point of manufacture until the sun tracking solar module is installed and put into operation, after which time the battery will be recharged automatically from the solar panel energy capture.
Using such ROM chip data, a solar panel or an array of solar panels can track the sun position provided that during installation (with the panels aimed longitudinally towards the South), at least one sun position versus time of day is entered into the control system. One such easily-established point is to position the solar panels flat with the mounting structure at solar noon. Solar noon is generally about the noon hour, but differs according to the longitude of the physical location, since some locations are close to a standard time zone and other locations are far away from the border of the time zone.
The accuracy of the sun tracking system can be improved if another such point can be established by aiming the solar panels directly towards the sun at some other selected time which is preferably several hours different from solar noon, such as +3 hours after sunrise. Based on two such data points entered into the control system, there is an improved ability to compensate for differences in geographic location. Whether one or two or additional sun position versus time of day starting points are established and entered into the control system, the sun tracking system of the present invention enables the solar panels to track the sun without requiring a solar sensing device. With more than a single starting point, the control system can provide improved sun tracking accuracy.
It should also be noted that on severely cloudy or gray sky overcast days, there is no need for sun tracking because the solar energy capture is primarily due to the overall brightness of the

Claims

1-11. (canceled)

12. A method for tracking the position of the sun during daylight hours, consisting of a programmed control system which drives a suitable reversible electric motor, thereby causing one or more rotating solar panels to track the movement of the sun from East to West, wherein said control system makes use of pre-programmed information including but not limited to the date, a suitable time clock standard, and sun position information which includes at least one starting point input provided after system installation, as well as sun position data such as can be readily obtained from solar ephemeris data.

13. The method for tracking the position of the sun according to claim 12, wherein said tracking system does not utilize any type of solar energy sensing device.

14. The method for tracking the position of the sun according to claim 12, wherein said tracking system makes use of ordinary photocells only for the purpose of detecting sunrise, sunset or sufficiently bad or overcast weather to justify returning said rotating solar panels to the flat position with respect to the solar module framework.

15. The method for tracking the position of the sun according to claim 12, wherein said rotating solar panels are capable of rotating at least about +/−60 degrees from the flat position with respect to the solar module framework.

16. The method for tracking the position of the sun according to claim 12, wherein said tracking system is calibrated by entering at least one and preferably two sun position versus time of day data points into said control system program at different hours of the day, each said sun position defined as the panel rotation angle that maximizes solar energy capture at a particular time of day.

17. The method for tracking the position of the sun according to claim 12, wherein said reversible electric motor is a gearmotor driving a pinion gear which engages a linear rack gear, said linear rack gear being supported and captured by suitable flanged roller bearings which insure proper contact with pinion gears which are mounted on the longitudinal axes of said one or more rotating solar panels.

18. The method for tracking the position of the sun according to claim 12, wherein said rotating solar panels are mounted parallel to one another inside a modular framework.

19. The method of mounting solar panels according to claim 18, wherein said modular framework is low-profile, less than about 6 inches high, and suited for mounting on almost any type of roof or structure, including but not limited to gazebos, patios, greenhouses, garages, residential homes, commercial buildings, shopping centers, sports arenas, open ground, or military installations such as aircraft hangers or ships.

20. The method for tracking the position of the sun according to claim 12, wherein said tracking system is programmed to return said one or more solar panels after sunset from the end of day Westernmost pointing direction to the start of day Easternmost direction, so as to be ready for solar tracking again before sunrise on the next day.

21. The method for tracking the position of the sun according to claim 12, wherein said tracking system is programmed to return said one or more solar panels to the flat or pointed upwards position which is parallel with the modular framework whenever the solar energy capture during daylight hours falls below a predetermined threshold, thereby indicating cloudy or overcast sky conditions.

22. The method for tracking the position of the sun according to claim 12, wherein the control system program is simplified by assuming that all installations are located at the same latitude, for example, in the United States, at about 40 degrees North latitude.