Microgrid system to stabilize grid power in Alaska

Michelle Froese, Senior editor
Windpower Engineering & Development

An innovative microgrid will improve power stability and test scalability and for about 300,000 people in Anchorage, Alaska. The new system will integrate power from a 17-MW wind farm on Fire Island, and work in concert with flywheel and battery storage.

Fire Island is a small island near the top of Cook Inlet in the Municipality of Anchorage, Alaska. While it once served as an Air Force station, the island now sits vacant other than a private FAA aviation airfield and a wind farm.

The 11-turbine, 17.6-MW wind farm, built by Fire Island Wind LLC in 2012 (a subsidiary of island owner Cook Inlet Region Incorporated or CIRI), is the first megawatt-scale project in South-central Alaska. According to Fire Island Wind, the aim of the project was to ease the strain on the natural gas supply in Cook Inlet.

Although the wind farm can generate more than 50,000 MW-hours annually for the utility, Chugach Electric Association, leveraging the project’s full capacity has been a challenge over the years.

“Power usage of this wind farm is relatively low,” says Massimo Danieli, President of ABB’s Grid Automation division. ABB is a power technology company currently working with Chugach Electric on better managing the Alaskan transmission grid. “The wind farm sells roughly 4% of the retail capacity of Chugach Electric, so it is not a large proportion or quota of the overall electricity sold by the utility into the Anchorage area.”

Upon completion of the wind farm, Fire Island Wind entered into a long-term power purchase agreement with Anchorage utility Chugach Electric Association. The 25-year contract provides a flat net price of $97/MW-hour throughout its term.

“A problem for the utility is variability of the load and supply.” Danieli points to the variability of wind along with a number of different energy sources that feed and impact the local transmission system. Anchorage is served by wind energy, hydropower, gas, and fire or thermal capacity. Transportation of fuel is another concern.

“The city has ports, which can mean heavy transportation loads coming from vessels and cranes. This can lead to further pressure on the utility to keep up with power demands,” he says. “To better manage the load and demands, Chugach Electric needs to add regulatory capacity to the transmission grid, which, at only about 500 MW, is not a large grid. ”

There is also talk of expanding the wind farm. CIRI wants to double the number of wind turbines on Fire Island from 11 to 22. It announced a framework deal with utility Golden Valley Electric Association late last summer. So there may be more wind power on the way.

ABB’s PowerStore is a compact and versatile flywheel-based, grid microgrid generator. Its main purpose is to stabilize power systems against fluctuations in frequency and voltage.

For now, Chugach Electric is working with ABB on a “microgrid stabilization” project that will improve power stability, test scalability, and identify a system that enables the integration of more renewables. The project will combine battery and flywheel-based storage.

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“The two devices — the flywheels and lithium-ion batteries — will connect to the grid together with a control system we call PowerStore,” says Danieli. “This system has the important task of master control by monitoring and sharing power capacity across the wind farm, flywheel, and battery. Its goal is to continually maintain grid stability.”

He explains that the flywheel and battery will connect to the grid and act like two generators. “Together, they can take in, sync, and release power to ensure a stable online frequency — in fact, it is very much like a form of load sharing.”

While the two power devices work to share the load, the PowerStore control system continuously monitors the status of the transmission grid. Ultimately, it is in charge of when energy should sync into the flywheel or battery storage. “It also has to ‘decide’ when to release energy, first from the flywheel and secondly from the battery,” says Danieli. “It is constantly assessing and redirecting the power supply or surplus.”

Lithium-ions are the battery of choice here because they are a low-maintenance, high-density battery. One other advantage of lithium-ion cells is that their rate of self-discharge is much lower than that of other rechargeable cells, such as Ni-Cad and NiMH forms.

But why the need for a battery and flywheel? “It is proven that when you have high variability of power generation and a sudden heavy load on the grid, such as when you have strong wind gusts at a wind farm, it is necessary to release that energy quickly to maintain the frequency or stability of the transmission system,” shares Danieli. “Try that over several cycles on a battery used for storage, and you quickly reduce the life of that battery.”

Batteries may work well for storing or generating a constant flow of energy, but they are less than ideal for sudden or abrupt changes, such as those that occur at wind farms. Enter the modern flywheel. It consists of a large rotating mass supported on a stator by magnetic bearings. Furthermore, it typically operates in a vacuum to reduce drag.

Flywheels can bridge the gap between short-term power and long-term energy storage with excellent cyclic and load following characteristics.

“The PowerStore system uses a flywheel for fast release and sync of power, which can go up to one megawatt per second and then back down again. So, these fast variations are managed by a flywheel, where it excels, and the slower variations are dealt with through battery storage.”

Flywheels can bridge the gap between short-term power and long-term energy storage and offer excellent cyclic and load following characteristics. ABB’s Microgrid Plus control system monitors the hybrid storage system to ensure proper load sharing between the two storage mediums (flywheel and battery). It is also equipped for remote service and maintenance, which makes it ideal for use in Alaska.

High-speed software controls the power flow into and out of the flywheel, essentially making it a high inertia, electrical shock absorber that can instantly smooth out power fluctuations.”

The hybrid system prioritizes one over the other, flywheel or battery, depending on the system conditions,” says Danieli. “It rapidly stabilizes voltage, but also improves power quality by absorbing or injecting that power to ensure a smooth network.” PowerStore can stabilize voltage and frequency, hold 18 megawatt-seconds of energy, and shift from full absorption to full injection in one millisecond to stabilize the grid.

What makes ABB’s microgrid system ideal for integration with the Fire Island wind farm is that it is modular and made for extreme weather conditions.

“If tomorrow the size of the wind farm becomes twice what it is today, as may be the case at Fire Island, there will be a PowerStore with twice the capacity. The equipment itself is modular and contains all the connections needed to build on one another or increase in capacity.”

Danieli explains further. “Say you add another 10 or 20 turbines to your wind farm, from a microgrid standpoint, you simply add a small controller for each turbine to the network, and they automatically link up to the network and start co-operating with the other controllers.”

The system is built for efficiency and to minimize installation times. It is also build to endure the Alaskan climate.

“The system is extremely robust and made to last in harsh conditions,” he says. “The lithium-ion batteries, of course, have a degradation period that is in the range of years. But this also depends on the way they are used and maintained.” Danieli says the units are equipped with air conditioning to better sustain the electronic equipment and to evacuate gases and elements that could build up inside the batteries. “There is definitely a bit of art and engineering in making sure the equipment is made and used appropriately.”

A well-devised O&M plan is essential along with system versatility. As more microgrid and energy storage projects develop, the equipment supporting these systems must fit each climate and application.

“One cannot say that this industry is booming yet because I think that most numbers or predictions given on the microgrid market are probably a little optimistic, but we are seeing more and more projects,” he says. “And what’s interesting is that they started in only remote areas, and now projects are developing in other locations where the grid is weak or where there are opportunities to add renewable capacity and storage behind the meter.”

Danieli says regulatory framework in most places still needs to catch up to the advances in microgrid equipment and technology, but the possibility to install these systems is now available to utilities and grid managers. “We’ll see more microgrid systems in the near future, I think, and not just in remote places such as Alaska, but maybe closer to home, providing service to local grids.”

 

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