Microgrids: Providing safe harbor in a storm
As Hurricane-cum-Superstorm Sandy approached the Eastern Seaboard, millions of Americans living in New York and New Jersey spent the days before the storm stocking up on bread, water, batteries, and other critical supplies; many others sought safety by fleeing the area, seeking refuge with friends and relatives beyond the storm’s path.
The impacts of Sandy are now familiar to many: the electricity grid went down, leaving upwards of 8.5 million people without power. Yet, there were a handful of literal bright spots in the darkness. One man in New Jersey powered his home with his Toyota Prius hybrid and inverter-based power balancing controls, which ensured that the power from his car was at the right voltage and frequency for his house. At the Brevoort Tower in New York City, the story was much the same: the building kept its lights on—and its heat and hot water—with a natural gas combined heat and power generation system, inverter controls, and most importantly, an automatic transfer switch (aka smart switch) that allowed the building to seamlessly disconnect from and reconnect to the grid. In other words, both the New Jersey homeowner and the Brevoort became microgrids.
But in New Jersey, which ranks second only to California in total installed solar capacity, scores of residential and business customers with rooftop solar PV sat in the dark, even after Sandy’s clouds parted and the sunshine returned. Why? Based on its lower cost and simpler setup, most customers had installed grid-tied solar, and in accordance with current regulatory codes nationwide, such systems are required to have a control feature that automatically disables the inverter—the device that converts power generated by the PV panels into usable electricity for home appliances—in the event that the grid goes down.
The control device is intended to prevent unintentional islanding, a scenario where a device—such as rooftop solar PV panels—continues to feed electricity into the local grid, even when that grid should be without power. Preventing unintentional islanding is important for a number of reasons, foremost among them the safety of utility electricians working to repair faults in the grid and restore power to customers.
But it doesn’t have to be that way. Imagine a scenario in which the grid goes down but customers with solar PV keep their lights on. It’s entirely possible with the use of a smart switch, much like that used by the Brevoort Tower, in order to achieve intentional islanding. When the grid goes down, the solar PV system switches from grid-tied to an independent mode, allowing it to continue generating electricity without feeding the local grid and endangering utility workers.
Such flexible solar PV systems would typically work in conjunction with a bank of batteries to power critical loads in your home, such as the refrigerator and oven.
However, two hurdles stand in the way of greater adoption of this more flexible system, which offers a kind of safe harbor in a storm when the normally reliable grid goes down: 1) heightened cost, and 2) rigorous permitting which serves as a disincentive.
Grid-tied systems with the flexibility to become grid-independent are more complex, typically involving the addition of batteries for energy storage plus rewiring the home to establish a subpanel that carries the circuits for the house’s critical loads. This more complex system comes with a cost.
Consider, for example, the systems offered by the company Wholesale Solar. WS offers a traditional grid-tied solar PV system (2,000W capable of up to 271 kWh per month) for a little over $4,000. Meanwhile, they offer a grid-tied solar PV system, which switches to backup battery power in the event of a grid outage and uses the solar PV to charge the batteries in an "off-grid mode" (1,500W capable of up to 204 kWh per month) for close to $6,000, plus the cost of batteries, which adds at least another $2,000, depending on the size of the battery bank, double the hardware cost. Finally, if you’re a customer who already has traditional grid-tied solar PV installed on your home, WS offers a “conversion” kit that starts at around $7,000.
But in the wake of Sandy, Hurricane Irene, the derecho summer storm of 2012, and other threats to the grid, customers are increasingly reaching the conclusion that such added costs and complexity may be worth it. Plus, compared to diesel, propane, or natural gas stand-by generators—which can be similarly expensive, have associated fuel costs, and are both loud and dirty—the safe harbor offered by clean, quiet solar is looking more and more attractive.
For certain, the flexibility to take harbor in a hybrid system—one that includes solar PV, energy storage or generation, and smart switch technology that enables intentional islanding—is an exciting opportunity. But it’s not a case in favor of abandoning the grid entirely. This technology can and should provide value and resilience to utilities and their customers alike.
While utilities may fear that their customers will find intentional islands a paradise from which they never return, the reality is that most homeowners and businesses don’t want an intentional island, but rather a harbor where they can receive power from their utility when it is available and affordable, and the flexibility to temporarily leave the grid and generate power of their own when practical. With more hybrid systems installed in homes, businesses, neighborhoods, and campuses, microgrids can become our safe harbor for the next storm.
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