A practical solution for excess energy management in a diesel-backed microgrid with high renewable penetration

One of the limiting factors in adding high levels of rooftop solar photovoltaic (PV) resources to isolated hybrid microgrids is the ability to maintain the minimum operating point of must-run diesel generators. This research investigates a proposed inexpensive and practical solution to mitigate excess energy from renewables (mainly PVs) while maintaining a diesel-backed grid's acceptable minimum down reserve. It includes the innovative use of a resistive dynamic load bank (DLB) during peak PV periods. A control algorithm was developed to monitor the grid's total generation and control the DLB such that conventional diesel generators are not pushed below a setpoint equal to their minimum reliable operating level defined by the local utility. The setpoint is adjustable to allow for changes in grid conditions over time, such as the addition of more renewable resources or grid upgrades. This DLB system, as a practical and low-cost PV excess energy mitigation solution, has been connected to the grid in coordination with the local utility on the island of Molokai in the Hawaiian Islands. The DLB system addition has enabled the utility to significantly increase the allowed customer-sited PV on the power system without sacrificing grid reliability.