Photovoltaic energy system with preemptive ramp rate control

1. A photovoltaic energy system comprising:

a photovoltaic field configured to convert solar energy into electrical energy provided as an electric power output of the photovoltaic energy system, wherein the photovoltaic field has a long side and a short side;

one or more cloud detectors configured to detect a cloud approaching the photovoltaic field, wherein a greater number of the cloud detectors are located along the long side of the photovoltaic field and a lesser number of the cloud detectors are located along the short side of the photovoltaic field such that cloud movement perpendicular to the long side of the photovoltaic field is more precisely detected relative to cloud movement perpendicular to the short side of the photovoltaic field; and

a controller configured to use input from the one or more cloud detectors to predict a disturbance in the electric power output of the photovoltaic energy system, determine a time at which the disturbance is expected to occur, and determine an amount by which the electric power output is expected to decrease as a result of the disturbance;

wherein the controller is configured to preemptively adjust the electric power output of the photovoltaic energy system before the disturbance occurs in accordance with a predetermined ramp rate.

2. The photovoltaic energy system of claim 1 , wherein the controller is configured to:

use the input from the one or more cloud detectors to determine a velocity of the cloud approaching the photovoltaic field;

use the velocity of the cloud to determine the time at which the disturbance is expected to occur.

3. The photovoltaic energy system of claim 1 , wherein the controller is configured to determine the time at which the disturbance is expected to occur by predicting at least one of a start time, an end time, and a duration of the disturbance.

4. The photovoltaic energy system of claim 1 , wherein the controller is configured to:

use the input from the one or more cloud detectors to determine one or more cloud attributes comprising at least one of a size, a position, and a direction of the cloud approaching the photovoltaic field; and

use the one or more cloud attributes to determine the amount by which the electric power output is expected to decrease as a result of the disturbance.

5. The photovoltaic energy system of claim 1 , wherein the controller is configured to determine a time at which to begin preemptively adjusting the electric power output by:

determining an amount of time needed to ramp down the electric power output by the amount which the electric power output is expected to decrease as a result of the disturbance without violating the predetermined ramp rate; and

determining a time at which to start ramping down the electric power by subtracting the amount of time needed to ramp down the electric power output from the time at which the disturbance is expected to occur.

6. The photovoltaic energy system of claim 1 , wherein a greater number of the cloud detectors are located along a West side of the photovoltaic field and a lesser number of the cloud detectors are located along an East side of the photovoltaic field.

7. A photovoltaic energy system comprising:

a photovoltaic field configured to convert solar energy into electrical energy provided as an electric power output of the photovoltaic energy system, wherein the photovoltaic field has a long side and a short side;

one or more cloud detectors configured to detect a cloud approaching the photovoltaic field, wherein a greater number of the cloud detectors are located along the long side of the photovoltaic field and a lesser number of the cloud detectors are located along the short side of the photovoltaic field such that cloud movement perpendicular to the long side of the photovoltaic field is more precisely detected relative to cloud movement perpendicular to the short side of the photovoltaic field; and

a controller configured to use input from the one or more cloud detectors to predict a decrease in the electric power output of the photovoltaic energy system and determine a time at which to begin preemptively ramping down the electric power output of the photovoltaic energy system before the decrease in the electric power output occurs;

wherein the controller is configured to adjust the electric power output of the photovoltaic energy system by beginning to ramp down the electric power output at the determined time.

8. The photovoltaic energy system of claim 7 , wherein the controller is configured to use the predicted decrease in the electric power output in combination with a predetermined ramp rate to determine a minimum amount of time required to decrease the electric power output by an amount of the predicted decrease without exceeding the predetermined ramp rate.

9. The photovoltaic energy system of claim 7 , wherein a greater number of the cloud detectors are located along a West side of the photovoltaic field and a lesser number of the cloud detectors are located along an East side of the photovoltaic field.

10. The photovoltaic energy system of claim 7 , wherein the controller is configured to monitor the electric power output of the photovoltaic energy system and calculate a rate of change of the electric power output, the rate of change defining an actual ramp rate of the photovoltaic energy system.

11. The photovoltaic energy system of claim 10 , wherein the controller is configured to compare the actual ramp rate to a predetermined ramp rate and use feedback control to adjust the electric power output of the photovoltaic energy system in response to the actual ramp rate exceeding the predetermined ramp rate.

12. The photovoltaic energy system of claim 11 , wherein the controller is configured to adjust the electric power output such that the actual ramp rate does not exceed the predetermined ramp rate.

13. A renewable energy system comprising:

a renewable energy field that converts a renewable energy source into electrical energy, wherein the renewable energy field has a long side and a short side;

one or more sensors configured to detect a change in an environmental condition that will affect an electric power output of the renewable energy field, wherein a greater number of the sensors are located along the long side of the renewable energy field and a lesser number of the sensors are located along the short side of the renewable energy field such that the change in the environmental condition along the long side of the renewable energy field is more precisely detected relative to the change in the environmental condition along the short side of the renewable energy field; and

a controller configured to use input from the one or more sensors to predict a decrease in the electric power output of the renewable energy system and determine a time at which to begin preemptively ramping down the electric power output of the renewable energy system before the decrease in the electric power output occurs;

wherein the controller is configured to adjust the electric power output of the renewable energy system by beginning to ramp down the electric power output at the determined time.

14. The renewable energy system of claim 13 , wherein the renewable energy field comprises at least one of a photovoltaic field, a wind turbine field, a hydroelectric field, a tidal energy field, and a geothermal energy field.

15. The renewable energy system of claim 13 , wherein the controller is configured to use the input from the one or more sensors to predict a change in the environmental condition within the renewable energy field before the change in the environmental condition occurs within the renewable energy field.

16. The renewable energy system of claim 13 , wherein the controller is configured to use the input from the one or more sensors to determine a time at which an environmental disturbance is expected to occur and an amount by which the electric power output is expected to decrease as a result of the environmental disturbance.

17. The renewable energy system of claim 16 , wherein the controller is configured to use the amount by which the electric power output is expected to decrease in combination with a predetermined ramp rate to determine a minimum amount of time required to decrease the electric power output without exceeding the predetermined ramp rate.

18. The renewable energy system of claim 13 , wherein a greater number of the sensors are located along a West side of the renewable energy field and a lesser number of the sensors are located along an East side of the renewable energy field.

19. The renewable energy system of claim 13 , wherein the controller is configured to monitor the electric power output of the renewable energy system and calculate a rate of change of the electric power output, the rate of change defining an actual ramp rate of the renewable energy system.

20. The renewable energy system of claim 19 , wherein the controller is configured to compare the actual ramp rate to a predetermined ramp rate and use feedback control to adjust the electric power output of the renewable energy system in response to the actual ramp rate exceeding the predetermined ramp rate.