How to integrate wind into a microgrid
Australia brings to mind the wilds of the Outback, with nearly three million square miles of mostly unsettled and wild country.
Australia brings to mind the wilds of the Outback, with nearly three million square miles of mostly unsettled and wild country. Those remote regions made Australia a great proving ground for some important microgrid technology.
In 1998, the Australian Greenhouse Office awarded a Renewable Energy Showcase grant to install a high-penetration wind energy solution in Denham, the westernmost town in Australia. The costs of buying and delivering diesel fuel to Denham made it essential to find a more economical power source.
This early project provided valuable insights into what it takes to successfully integrate wind into a microgrid. The main issue was — and remains — grid stability. In the Denham installation, the intermittent power output from the wind turbine caused load-hunting issues with the diesel generators. Under fluctuating wind conditions, the diesel generators sometimes struggled to meet the necessary step load requirements to maintain utility-grade power, and on occasion tripped off. The generators also ramped up and down constantly to mitigate the variable wind power instead of operating at their optimum-rated output.
With the knowledge gained from Denham and additional wind-diesel systems across the west coast of Australia and Antarctica, a flywheel and bi-directional inverter system emerged as a solution. With advanced power electronics and controls, this system was able to absorb and inject both real and reactive power into the grid within five milliseconds to counterbalance the output from the wind turbine and any variable network load demands.
In the time since the flywheel inverter system was developed, they have typically been deployed in smaller, more distant grids because of the ability of renewables to offset the high cost of diesel. Today they are becoming more prevalent in larger microgrids in the 10 – 50 mw size. The flywheel solution can be scaled up to these larger installations simply by adding more devices.
In smaller microgrids, where instantaneous, renewable penetration levels are nearing or at 100%, you need to understand the difference between grid stability and energy storage. Wind intermittency means you need to stabilize the grid through voltage and frequency regulation. The need for high cycling of absorbing and injecting both real and reactive power to achieve grid stability makes the flywheel a perfect fit. Battery chemistry limits using flywheel systems for grid stability. Flywheels are better suited for energy storage, discharging and recharging several times per day.
Determining whether a flywheel inverter system makes sense in your microgrid requires modeling the system dynamics to test your grid stability in various scenarios. Based on that modeling, you may discover that a flywheel is the perfect solution for your project.
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