Ventre, Gerard; Wilson, William
Data Analysis; Photovoltaics
Satellite Supervisory Control and Data Acquisition (SCADA) of a Photovoltaic (PV)/diesel hybrid system was tested using NASA's Advanced Communication Technology Satellite (ACTS) and Ultra Small Aperture Terminal (USAT) ground stations. The setup consisted of a custom-designed PV/diesel hybrid system, located at the Florida Solar Energy Center (FSEC), which was controlled and monitored at a remote hub via Ka-band satellite link connecting two USATs in a SCADA arrangement. The robustness of the communications link was tested for remote monitoring of the health and performance of a PV/diesel hybrid system, and for investigating load control and battery charging strategies to maximize battery capacity and lifetime, and minimize loss of critical load probability.
Baseline hardware performance test results demonstrated that continuous two-second data transfers can be accomplished under clear sky conditions with a failure rate of less than 1%. The delay introduced by the satellite (1/4 second) was transparent to synchronization of the satellite modem as well as to the PV/diesel hybrid and the control computer. End-to-end communications link recovery times were less than 36 seconds for loss of power and less than one second for loss of link. The system recovered by resuming operation without any manual intervention, which is important since the 4-decibel margin is not sufficient to prevent loss of the satellite link during moderate to heavy rain. The overall failure rate for two second data transfers during the 100+ hours of the SCADA experiment was 9%. This increased rate was attributed to precipitation along the USAT to ACTS slant path and to satellite tracking problems. Hybrid operations during loss of communications link continued seamlessly, but real-time monitoring was interrupted. For this sub-tropical region, the estimated amount of time that the signal fade due to precipitation will exceed the system margin is about 10%. These results suggest that data rates of 4800 bits per second and a link margin of 4 decibels with a 1/4-Watt transmitter are sufficient for end-to-end operation in this SCADA application.
The next phase of this project is a SCADA/training experiment. In preparation for this, the USAT ground stations have been upgraded with two one-Watt transmitters to increase system margin, and audio/video equipment has been added at both ends of the communications link. Baseline testing of the software and hardware is nearing completion. Delivery of the SCADA/training program is planned for May 2000.
This paper will present results obtained during both the SCADA and SCADA/Training experiments. Lessons learned associated with implementation of these tasks will also be discussed.
Data Analysis; Photovoltaics
Florida Solar Energy Center and Emrich, Carol, "Supervisory Control And Data Acquisition Experiment Using The Advanced Communications Technology Satellite - Lessons Learned" (1999). FSEC Energy Research Center®. 666.