SYSTEM FOR DETECTING AND UTILIZING THE MAXIMUM AVAILABLE POWER FROM SOLAR CELLS

• US 3,696,286 A
• Filed: 08/06/1970
• Issued: 10/03/1972
• Est. Priority Date: 08/06/1970
• Status: Expired due to Term

• Current Assignee: Louis A. Ule
• Original Assignee: Louis A. Ule
• Inventors: Ule, Louis A.
• Primary Examiner(s): Pellinen, A. D.
• Application Number:
  US05/061,570
• Time in Patent Office: 789 Days
• Field of Search: 307/48,66 320/15,39,40 325/15
• US Class Current: 320/101
• CPC Class Codes: B64G 1/425 Power storage
• CPC Class Codes: B64G 1/428 Power distribution and management
• CPC Class Codes: B64G 1/443 Photovoltaic cell arrays
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H02J 2310/58 The condition being electrical
• CPC Class Codes: H02J 3/14 by switching loads on to, or off from, network, e.g. progressively balanced loading
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel
• CPC Class Codes: Y10S 136/291 Applications
• CPC Class Codes: Y10S 320/24 Inductor
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

In a power solar cell array consisting of many solar cells connected to deliver useful electrical power, there is imbedded a smaller reference solar array consisting of solar cells connected in series with a Zener diode and load resistor so devised that the voltage that appears across the load resistor is equal to or a constant fraction of the voltage at which the power array, operating at the same temperature and solar exposure as the reference array, delivers maximum electrical power. The voltage difference between the large solar array or the given fraction thereof and the reference solar array is used directly as means to constrain the large array to operate at the voltage of maximum power, typically any excess power being used to charge a storage battery.

Claims

1. A system comprising:

a plurality of first solar cells for providing a source of electrical power with a load voltage, a second means for providing a reference voltage related to the voltage at which the first solar cells should deliver maximum power, a first load coupled to said first solar cells, a second load for storing and making use of excess power from the first solar cells, a third means of comparing the load voltage with the reference voltage, a fourth means responsive to the said third means, for increasing the power to the said second load when said load voltage increases relative to the said reference voltage and for decreasing the power to the said second load when the said load voltage decreases relative to the said reference voltage, said second means comprising;

a plurality of second solar cells which are exposed to the same solar illumination and maintained at the same temperature as said first solar cells, and a Zener diode and a load resistor connected in series across said second solar cells, said load resistor having a value to draw sufficient current to operate the Zener diode at its constant Zener voltage under substantially all load conditions causing said reference voltage to be produced across said load resistor.

2. The system of claim 1 wherein said third means and said fourth means comprises:

a voltage divider circuit for making the ratio of said reference voltage to said maximum power output voltage one-to-one, a differential amplifier to which are coupled the voltages at said one-to-one ratio and which produces a voltage output proportional to the difference between two voltage inputs thereto, a Schmidt trigger which is driven by the output of the differential amplifier and produces positive and negative voltages depending on the sign of the voltage output of said amplifier, a power switching transistor to the base of which said positive and negative Voltages are coupled to switch the transistor to the fully conducting state and to the fully nonconducting state, an inductor coupled between said first solar cells and said power switching transistor so that when said transistor is conducting said inductor is connected across said first solar cells, and a network comprising a diode, an energy storage capacitor, and said second load, said capacitor and second load being connected in parallel and said diode being connected to isolate said capacitor and second load from said first solar cells and to cause power from said first solar cells to flow through to said parallelly connected second load.

3. The system of claim 1 wherein:

said first solar cells are divided into a plurality of independent photovoltaic arrays each made of a plurality of solar cells, each array being subjected to different intensity of solar illumination, said second means producing said reference voltage which is related to the voltage of any one of said arrays which at the time should deliver maximum power, said third means and said fourth means comprises;

a voltage divider for each array for making the ratio of said reference voltage to said respective maximum power voltage one-to-one, a differential amplifier for each array to which are coupled the voltage from a respective one of said dividers and said reference voltage, a Schmidt trigger for each amplifier which trigger is driven by the output of said respective amplifier to produce positive and negative voltages depending on the sign of the voltage output of said respective amplifier, a plurality of transistors each having a base to which is coupled the output of a respective one of said triggers to cause the respective transistor to be conducting and non-conducting depending on the plurality of the voltage input to the base, an inductor coupled between a respective one of said arrays and a respective one of said transistors so that when said one transistor is conducting said inductor is connected across said respective array, a diode coupled to each junction formed by one of said inductors and one of said transistors to conduct current from said respective arrays to said first load, and a capacitor coupled across said first load.

4. A system which scavenges any excess power from a photovoltaic array supplying power to a useful load and a storage battery, said system comprising:

an inductance coupled between said array and said battery, a capacitor coupled in parallel with said battery and in series with said inductor, a transistor having its emitter-collector circuit coupled in parallel with said battery and capacitor and in series with said inductor, and means for sensing when said array is supplying below maximum power to said load and for producing a voltage signal to make said transistor conducting when said array is producing less than maximum power to cause some of the power from said array to be stored in said battery.