Skyline Energy guarantee’s clean energy feed to the grid from solar PV and advance battery storage

LOS ANGELES - Nov. 7, 2013 - PRLog -- Introduction and Problem Statement

The increasing integration of distributed renewable energy has increased stress on the power grid. By their very nature, photovoltaic (PV) and wind energy fluctuate dramatically with weather and temperature. This fluctuating power output from these renewable sources cause line regulators, tap changers, and switched capacitors to switch much faster than before. PV and inverter instabilities can also contribute to transients, harmonics, and flicker in the distribution system. For example, if a PV string was generating 100 kW of power and a cloud passed over the array, this power could drop to under 50kW in less than 30 seconds!

The GO system aims to mitigate this disruptive behavior by precisely controlling the output power to the grid. The GO PV system will buffer this power using energy storage. When the system sees one of these power anomalies, it will instantly inject the lost power, keeping the output power to the grid stable and continuous. Since it utilizes energy storage, the system can also be used to create arbitrary power profiles over time by storing and injecting power as needed. This would allow the PV farm to output any generation profile that the grid needs.

System Topology and Operation

The system consists of Lithium Ion cells, a power control unit, PV, and a grid-tied inverter. Under normal operation, the PV will feed directly to the inverter. However, the DC/DC converter will constantly be monitoring the power and managing the storage by either charging it with PV power or injecting power from the storage to the inverter (to bolster the PV). In the morning, while the sun is rising, the PV is used to charge the storage unit when the power is too low to run an inverter. The system then waits to detect if the power is enough to turn on the inverter for normal operation. This system then slowly ramps up the output power, reducing the harmful effect on the grid of an inverter rapidly becoming active. When the inverter is running, the system uses an anomaly identifying algorithm to decide when to inject power. If an increase in power output to the grid is necessary, the storage will inject the correct amount of power. The experimental results of this process can be seen A solid output power (blue line) can be seen even though the PV is being switched on and off (red line). The energy output from the storage unit is shown as a light blue fill.

Operation

Performance of the system

Since this system does all of the power stabilization, storage charging, and power conversions on the DC side, the efficiency extremely high. Both the storage and the PV are designed at the same operating voltage, which leads to even less conversion losses. The system is designed and built in 100kW modules that can then be integrated into a larger system such as multi megawatt level solar farms. The storage has also been designed modularly, so adding storage capacity is extremely simple. Prototypes have shown that the PV can feed both the inverter and charge the storage bank. It has also been proven that the GO system can operate autonomously after installed. Users may interface with the system via a user friendly browser based GUI (Graphic User Interface) capable of monitoring, changing, and recording the system behavior.

Future Considerations

The GO PV system has functionality to achieve a broad range of desired outcomes. Such outcomes include curve smoothing, curve modification, peak leveling, and islanded distribution systems.An example of typical power curve produced by a PV system over a full day; this power is clearly disruptive to the stability of the grid.

The prototyped system can be augmented to include curve smoothing capabilities which would turn the above curve into a simple bell curve. This would be accomplished by charging the storage when excess power is generated and discharging the storage when diminished power is noticed in the PV output. Custom outputs can be achieved by very similar methods. This would consist of the user inputting to the system a desired output power curve, after which the system would adjust its charge and discharge characteristics to meet the curve. This would be beneficial to the user if a typical demand curve is known.Peak leveling could also be implemented by modifying the curve into a flat line so the system would output constant power.

Conclusion

The system described above has been designed and built at Skyline Energy in Riverside, California. Currently, the system is able to monitor and detect anomalies and can successfully inject peak level power when anomalies are detected. It can also create arbitrary power outputs based on the user’s needs such as peak/demand shaving. By default, the system is on autonomous mode to meet AB 2514/CPUC utility company requirments (in which it will keep the PV power smooth), but can be changed to manual mode (in which it will output power at a certain level). The system is being designed as a 100kW module which should be able to integrate easily into larger systems allowing for a broad range of flexibility. Each component is also designed modularly for easy integration into other power electronic projects and systems. Due to its flexibility, modularity, and cost effectiveness, the Skyline Energy GO PV System can greatly increase the stability of PV/energy storage systems while rapidly recouping the initial cost.

Contact us (951)543-7555,  www.skylineenergyusa,com