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Jan 10, 2013

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.

Recommended Reading


Some images courtesy of Shutterstock.com

Join the Discussion

Showing 1-5 of 5 comments

January 17, 2013

SMA is in the process of piloting an inverter that will operate without batteries when the grid is down…...

January 17, 2013

Natural gas can best supply the base power on any scale.

The main concern for environmentalists worldwide should be to cut the use of coal, especially in
antiquated plants. Here are the top ten coal burners: http://www.treehugger.com/clean-technology/what-are-the-top-10-coal-burning-countries-on-the-planet-whos-1.html

It is possible for the whole world to drastically cut coal burning and benefit the health of all. Coal pollution travels around the world. It is the worst fuel for pollution:http://www.ucsusa.org/clean_energy/coalvswind/c02c.html

Producing and using natural gas is the best solution for base power, in conjunction with solar, wind, geothermal etc. There is plenty of natural gas all around the world, and it can be accessed with new and future technology. In the meantime old coal plants must be replaced with modern ones that can be switched to natural gas fuel when it is available.

Natural gas is the future of energy. It is replacing dirty old coal plants, and dangerous expensive nuclear plants. It will fuel cars, trucks, vans, buses, locomotives, aircraft, ships, tractors, air conditioners, engines of all kinds. It costs far less. It will help keep us out of more useless wars, where we shed our blood and money. It is used to make many products. It lowers CO2 emissions. Over 4,100 natural gas story links on my free blog. An annotated and illustrated bibliography of live links, updated daily. The worldwide picture of natural gas. Read in 66 nations.

January 17, 2013

This article said:
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.

Powering an electric oven with a battery bank sounds crazy to me. Lights, refrigerators, electronics, furnace controls & blower yes...but not ovens or water heaters!

January 18, 2013

This is a great topic to address. And a technical challenge that, if solved on the mass scale, will be a great advance in the practical application of renewable generation's real-world functionality.

Fulfilling the load on a microgrid, especially one as small as one home, is very difficult to manage without an adequate electricity bank which is usually a large and expensive set of chemical batteries as you have pointed out. Another challenge is that the typical grid-tie inverter is designed to handle higher input voltage (typically 300 to 500 volts DC) while the typical battery-based inverter input voltage is 24 VDC or 48 VDC. This is an important matter in that the inverter input voltages determines how many solar panels are wired together in series. So, most grid-tie arrays are wired for high voltage over 300 volts (many panels per string) and most battery backup, with or without grid tie, are wired for 48 volts (few panels per string).

Already having a grid-tie solar system and looking for alternative for adding battery backup to the solar grid-tie system on my home, I talked to my contractor and planted the seed. He made no headway for a couple months but when he had the opportunity to discuss the issue with some SMA engineers (a major inverter manufacturer) and they came up with a system that used just 1 Sunny Island inverter with multiple Sunny Boy inverters and a very small and inexpensive $500 battery bank (4 12 volt car-size deep cycle lead acid batteries and some cables). When the grid goes down for an extended period (and it already has in my locale due to a major transformer fire), I have to throw some breakers to isolate my house from the grid, and the Sunny Island comes on first and creates a microgrid, and 5 minutes later per anti-islanding safety regulations, the Sunny Boys start inverting solar power into house power! It functions very well with the Sunny Island telling the Sunny Boys how much power to output and the Sunny Island deciding how much power to draw from the batteries or put back into them. The communication between the Sunny Island and the Sunny Boys is crucial, otherwise the Boys, normally trying to push power to the huge bank - the grid - will corrupt the quality of the electricity and shut the whole system down.

For those who are very well versed in home battery backup systems, you will have detected that 4 car-size batteries does not provide a lot of storage capacity and you are very correct; it is only about 5 usable KWh. But, this microgrid configuration is designed to minimize the cost of the battery subsystem and when there is no renewable power, it only has sufficient power to manage my essential devices like the refrigerator and freezer and some efficient lighting until the sun rises again. And, if push came to shove as in an extended public grid outage, it would require no more devices other than additional batteries, 48 nameplate volts at a time, to increase the bank capacity.

That's one man's experience. And thanks for bringing up this important and practical topic.

March 26, 2013

This exactly the type of material for which I have been searching, recently here in AU an electricity supplier has been given permission to disconnect single line supply runs in the event of a potential bushfire which they define as a total fire ban day and then comes a report that they wish ban all forms of backup supply including generators except in a medical emergency situation.
Could you let me have any material you supply to back my arguments to the political powers to permit backup battery and generator installations and also to back the concept of distributed base load supply
contact me through irgman@bigpond.com
thanking you in advance\