By David Jeon
As countries around the world increasingly look to renewable sources to meet their current and future energy requirements, sustainable energy holds particular promise for island nations. Lacking natural resources for energy of their own, islands tend to be heavily dependent on imports of fossil fuels. In fact, Hawaii is the most petroleum-dependent state in the U.S., with oil making up over 80 percent of the state’s energy consumption. Before the 2011 Fukushima accident, Japan increasingly relied on nuclear power to lessen its oil imports (the country has since turned sharply to renewables). Even island nations that discover energy resources, such as the United Kingdom’s North Sea oil and gas fields, may stilldepend on imports to meet demand, and finite fossil fuels do little to meet carbon reduction goals.
Solar and wind hold significant appeal for islands seeking to reduce dependence on fossil fuel imports, especially as most do not possess the sort of water sources that generate hydroelectricity. The decreasing cost of solar and wind makes them accessible, and they do not require the same level of investment as building traditional power plants. Many island governments have also set goals to use entirely renewable energy for power generation, which will require bringing many more solar and wind sources online.
However, islands are also grappling with the limitations of renewables; as intermittent sources, they produce different levels of power depending on the weather. This can lead to grid instability when they are connected to traditional power grids. The U.S. territory of Guam is one such island with this issue – it’s also an example of how real-time energy controls can help ensure grid stability.
Solar Power in Guam
Guam shares many of the typical small island challenges when it comes to energy generation. The small, isolated Western Pacific island of just under 170,000 people is almost entirely dependent on petroleum imports to meet its energy needs.Meanwhile, the island’s government has set a goal for 50 percent of their electricity sales to be from renewables by 2035, and 100 percent by 2045. Like all other utilities, the Guam Power Authority (GPA) faces challenges from operating traditional fossil generation units when large penetration of renewables is present. The government has committed to bringing 120 MW of new solar capacity online by 2022, to help offset the reliance on petroleum; this experience with solar energy serves as an example to island nations with similar energy challenges.
Currently, Guam’s main energy source (aside from imported petroleum) is a 25 MW solar farm that came online in 2015. While this helps Guam add renewable energy, the intermittent nature of solar adds instability to the grid. This is particularly true thanks to Guam’s weather extremes, such as typhoons during the rainy season that can result in the solar farm’s output ranging from 5-25 MW. Volatile power delivery can strain and damage the grid, which was designed to receive steady power from legacy power plants.
GPA must also keep grid frequency in check as solar is added. Grid frequency is typically easy to keep stable when power is supplied from traditional plants - as long as fuel is available, large turbines will provide reliable power and inertia to the grid. For solar, when the sun stops shining, a photovoltaic array simply stops generating electricity, which makes it much more challenging to balance load vs generation. This could destabilize the grid frequency that is crucial for daily society. A variable grid frequency can lead to outages, as well as damage industrial equipment and motors. It also has a peculiar effect on clocks - they lose or gain time. For example, if the daily average frequency is 60.1 Hz, as opposed to the standard 60 Hz, the clocks on Guam will be three minutes fast each day.
Stabilizing the Grid
An energy storage system is one of the easiest ways to compensate for the intermittent nature of solar. When there’s limited access to the sun, power can be retrieved from the batteries, mitigating the issue of intermittent generation by creating a steady supply of solar energy. In the case of Guam, the GPA installed two battery systems: one to mitigate solar fluctuation and the other to support grid frequency.
How should a grid operator manage different sources of power, such as when to draw energy from the batteries and when to charge them? This is where a real-time energy control system comes into the equation.
GPA installed a real-time controller to manage power from the new storage systems. Two separate controllers (one in the capital of Hagåtña and one at the solar farm) help manage grid frequency and stabilize power from the photovoltaic arrays. Following the installation of the control system, GPA’s staff kept the grid frequency between 59.9-60.1 Hz, despite fluctuating power usage and output. The below graph shows the frequency on the upper line, compared with the variation in power output of the frequency-controlled battery at the same time on the lower line.
Real-time energy control software is immediately available and easy to install, which makes it a prime solution for utilities bringing solar arrays online while needing to maintain grid stability. This is especially true of island nations. In Guam alone, the government has enlisted firms to build two more solar farms, which are expected to be operational by 2022. Keeping the electricity supply reliable will be a key priority for power utilities in places like Guam. Their new successes with real-time controls could be a useful example to island grids facing similar challenges.
David Jeon is Head of Engineering and Operations at PXiSE Energy Solutions, a San Diego-based developer of leading grid control technology.
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