Maximum power sensor for photovoltaic system

• US 6,979,989 B2
• Filed: 10/18/2004
• Issued: 12/27/2005
• Est. Priority Date: 04/17/2002
• Status: Expired due to Fees

• Current Assignee: Heritage Power, LLC
• Original Assignee: Heritage Power, LLC
• Inventors: Grenko, Alysha J., Schripsema, Jason, Johnston, Michael Anthony
• Primary Examiner(s): Vu, Bao Q.
• Application Number:
  US10/967,509
• Publication Number:
  US 20050052172A1
• Time in Patent Office: 435 Days
• Field of Search: 323/906, 323/274, 323/303, 320/101
• US Class Current: 323/303
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 323/906 Solar cell systems

Abstract

A maximum power level sensor and method for reliably providing instantaneous estimates of maximum power level for a photovoltaic system including one or more photovoltaic cells under prevailing conditions of irradiance, array temperature and spectrum of sunlight. The maximum power level sensor produces a reference voltage signal which is proportional to the maximum power level of the photovoltaic system. The maximum power level sensor comprises a reference circuit including at least one reference photovoltaic cell and a thermistor network in parallel with the reference cell. The thermistor network comprises at least one negative temperature coefficient thermistor, at least one resistor in parallel with the thermistor, and at least one resistor in series with the thermistor and the parallel resistor. The thermistor is positioned in or on the photovoltaic array. The reference cell is preferably constructed of materials which are similar to those of the photovoltaic cells in the photovoltaic system.

Claims

1. A PV system including a maximum power level sensor, the system comprising:

a PV array comprising at least one power PV cell;

at least one reference PV cell; and

a thermistor network in parallel with said at least one reference PV cell, said thermistor network comprising at least one negative temperature coefficient thermistor, at least one parallel resistor in parallel with said thermistor, and at least one series resistor in series with said thermistor and said parallel resistor, said thermistor being positioned in or on said PV array.

2. A PV system as recited in claim 1, wherein said thermistor is positioned on a bottom surface of said power PV cell.

3. A PV system as recited in claim 1, further comprising at least one voltage sensor which senses a voltage drop across said thermistor network to provide a reference voltage output.

4. A PV system as recited in claim 1, further comprising a calculator which calculates an estimated maximum power of said PV array.

5. A PV system as recited in claim 1, further comprising a display unit which displays an estimated maximum power of said PV array.

6. A PV system as recited in claim 1, further comprising a power sensor for sensing an actual power level being produced by said PV array.

7. A PV system as recited in claim 4, further comprising a power sensor for sensing an actual power level being produced by said PV array.

8. A PV system as recited in claim 7, further comprising a device for comparing said estimated maximum power of said PV array with said actual power level.

9. A PV system as recited in claim 8, further comprising at least one modem for transmitting data as a result of said comparing said estimated maximum power of said PV array with said actual power level.

10. A PV system as recited in claim 1, further comprising a calculator which calculates an estimated maximum energy of said PV array over time.

11. A PV system as recited in claim 1, further comprising a display unit which displays an estimated maximum energy of said PV array over time.

12. A PV system as recited in claim 1, further comprising an energy sensor for sensing an actual quantity of energy produced by said PV array over time.

13. A PV system as recited in claim 10, further comprising an energy sensor for sensing an actual quantity of energy produced by said PV array over time.

14. A PV system as recited in claim 13, further comprising a device for comparing said estimated maximum energy of said PV array over time with said actual quantity of energy produced by said PV array over time.

15. A PV system as recited in claim 14, further comprising at least one modem for transmitting data as a result of said comparing said estimated maximum energy of said PV array over time with said actual quantity of energy produced by said PV array over time.

16. A PV system as recited in claim 1, wherein all spectral effect elements in said at least one reference PV cell are of substantially identical construction to corresponding elements in said at least one power PV cell.

17. A PV system as recited in claim 1, wherein said at least one reference PV cell is of substantially identical construction to said at least one power PV cell.

18. A PV system as recited in claim 1, further comprising at least one component which varies a PV system voltage so as to continuously be at or near an instantaneous optimum voltage.

19. A PV system as recited in claim 1, further comprising at least one modem for transmitting data sensed by said PV system.

20. A method for estimating the maximum power level of a PV system comprising a PV array comprising at least one power PV cell, the method comprising:

sensing a reference voltage across a thermistor network in parallel with a reference PV cell, said thermistor network comprising at least one negative temperature coefficient thermistor, at least one parallel resistor in parallel with said thermistor, and at least one series resistor in series with said thermistor and said parallel resistor, said thermistor being positioned in or on said PV array, said reference PV cell being subjected to conditions which are substantially similar to conditions to which said at least one power PV cell in said PV array is being subjected.

21. A method as recited in claim 20, further comprising calculating an estimated maximum power of said PV system based on said reference voltage.

22. A method as recited in claim 20, further comprising displaying an estimated maximum power of said PV system based on said reference voltage.

23. A method as recited in claim 20, further comprising estimating a maximum energy output of said PV system over time based on said reference voltage over time.

24. A method as recited in claim 20, further comprising displaying an estimated maximum energy of said PV system over time based on said reference voltage over time.

25. A method as recited in claim 20, wherein said thermistor is positioned on a bottom surface of said power PV cell.

26. A method as recited in claim 20, further comprising sensing an actual power level being produced by said PV system.

27. A method as recited in claim 21, further comprising sensing an actual power level being produced by said PV system.

28. A method as recited in claim 27, further comprising comparing said estimated maximum power of said PV system with said actual power level.

29. A method as recited in claim 28, further comprising transmitting via a modem data as a result of said comparing said estimated maximum power of said PV system with said actual power level of said PV array.

30. A method as recited in claim 20, further comprising transmitting via a modem data sensed by said PV system.

31. A method as recited in claim 20, further comprising sensing an actual quantity of energy produced by said PV system over time.

32. A method as recited in claim 23, further comprising sensing an actual quantity of energy produced by said PV system over time.

33. A method as recited in claim 32, further comprising comparing said estimated maximum energy output of said PV system over time with said actual quantity of energy produced by said PV system over time.