Preface. Last updated 2022-9-5   The first article below explains what microgrids will look like in the future.  But first a brief look at what a microgrid is, as Angwin explains in her book  “Shorting the Grid. The Hidden Fragility of Our Electric Grid”.

Today the grid is mostly a one-way street, with huge power plants pushing power to customers.  A microgrid will have to be “smart” so that people can both buy and consume electricity, pushing it two directions.  So how will you sell power to your neighbors?  Probably not a wind turbine, even in the unlikely event you have enough wind to justify one, they’re expensive, noisy, and break down a lot. Burn wood? No, you would have to build a wood-fired boiler, raise steam, spin a turbine, attach a generator, and connect the whole thing to the grid.  But if you’re a dairy farmer you can buy methane digesters and small diesels attached to the digester using manure as fuel. In reality, if the power goes down a lot, the wealthy, in suburbia, might buy solar panels and batteries for their own home. In India, where Greenpeace tried to supply electricity via solar power and batteries, they were quickly drained, the same is true for most home batteries offered today. The only way you can produce electricity is a noisy and polluting diesel generator, sold to neighbors via jury-rigged and dangerous wires.

This is happening in Beirut. “Power Hungry” Robert Bryce, who runs the “Power Hungry” podcast went to Beirut ask the locals how this worked. They referred to the electricity “brokers” as the “electricity Mafia.” They paid two electricity bills each month: about $35 to the state-owned power company for the little power the provided 6 hours a day, and around $100 a month to their local “mafia” generator. Bryce asked one man why he didn’t just buy his own generator, since he was paying his neighbor a significant amount of money. The answer was that, if he broke away from the local “mafia” generator, he might be killed. At the very least, the wire to his generator would be cut. Bryce reports how a clash between two generator-owners left two people dead and required the Lebanese army to end the violence.”

Pedro Prieto’s work has taken him all over the world and seen “Beiruts” in many places, such as Brazil, the Democratic Republic of Congo, and Cuba to name a few.  Tad Patzek wrote that at 45-50 C people have hours to live, and in the future giant air-conditioned centers will be essential for people to retreat to (if they can get there).

The first article below from Wired magazine, describes Beirut’s diesel generator microgrid in greater detail. It is coming to you some day as  power outages increase when fracked natural gas and imported LNG can’t keep natural gas plants running to balance wind and solar when they happen to be up, and 100% backs them up otherwise.

The second article below explains why renewables are destabilizing the electric grid. Basically, electricity distribution is designed to flow one way from a centralized system to customers. But Distributed Generation (DG) from solar  PV and wind violates this.

Impacts caused by high penetration levels of intermittent renewable DG can be complex and severe and may include voltage increase, voltage fluctuation, interaction with voltage regulation and control equipment, reverse power flows, temporary over-voltage, power quality and protection concerns, and current and voltage unbalance, to name a few.

There are solutions, but they’re expensive, complicated, and add to the already insane challenges of thousands of utilities, power generators, independent system operators, and other entities trying to coordinate the largest machine in the world when cooperation isn’t always in their best interest.

Lebanon in the news:

Bradstock F (2022) Can Lebanon repair its failing energy sector? oilprice.com. Lebanon has been grappling with severe energy shortages over the past year. On average, the Lebanese population gets just one to two hours of electricity per day. Growing political instability threatens to worsen the country’s ongoing energy crisis. Lebanon has continued to face severe energy shortages due to years of poor investment in infrastructure that has led many to rely on polluting diesel generators for their power. Lebanon has faced rolling blackouts for years due to poor infrastructure spending. Now, with such high debt (495% of GDP), the government can no longer afford to run national power plants. Few external powers have been willing to step in to help. In addition, the rise of the militia group Hezbollah is driving others away.

Jo L (2022) Lebanon’s poorest scavenge through trash to survive. AP. In the dark streets of a Beirut now often without electricity, sometimes the only light that shines is from headlamps worn by scavengers, searching through garbage for scrap to sell. Even trash has become a commodity fought over in Lebanon, mired in one of the world’s worst financial crises in modern history. With the ranks of scavengers growing among the desperately poor, some tag trash cans with graffiti to mark their territory and beat those who encroach on it. Meanwhile, even better-off families sell their own recyclables because it can get them U.S. dollars rather than the country’s collapsing currency. The fight for garbage shows the rapid descent of life in Beirut, once known for its entrepreneurial spirit, free-wheeling banking sector and vibrant nightlife. Instead of civil war causing the chaos, the disaster over the past two years was caused by the corruption and mismanagement of the calcified elite that has ruled Lebanon since the end of its 1975-90 conflict. Thugs roaming the streets on motorcycles sometimes target scavengers at the end of day to steal the recyclables they collected.  “They are ready to kill a person for a plastic bag,” Mohammed said. More than half the population has been plunged into poverty. Banks have drastically limited withdrawals and transfers. Hyperinflation has made daily goods either unaffordable or unavailable.

2022 Professor Jan Blomgren: How are we in time?  https://youtu.be/0Oh_w5KrEVc.  There are 5 kinds of large electric power generators, natural gas, coal, oil, nuclear, and hydropower.  These give a stabilizing effect. You can’t keep the grid up with 1,000+ smaller generators. Solar cells have no generators at all. They do not provide stability to the grid like the larger generators.  Big generators also control and regulate electricity so it gets to the right place.  It can’t be done with small generators. They just don’t have the adjustability. They could have more if we built them that way, but even so, could never be as effective.  This means if we shut down large generators and replace them with many smaller ones, the electricity system will be more unstable and inefficient.

Alice Friedemann  www.energyskeptic.com  Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”.  Women in ecology  Podcasts: WGBH, Jore, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity,  Index of best energyskeptic posts

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Rosen KR (2018) Inside the Haywire World of Beirut’s Electricity Brokers. When the grid goes out, gray-market generators power up to keep the Wi-Fi running and laptops charged.Wired

https://www.wired.com/story/beruit-electricity-brokers/

Sometimes the lights do not stay on, even for the power company in Beirut.  Electrical power here does not come without concerted exertion or personal sacrifice. Gas-powered generators and their operators fill the void created by a strained electric grid. Most people in Lebanon, in turn, are often stuck with two bills, and sometimes get creative to keep their personal devices—laptops, cell phones, tablets, smart watches—from going dead. Meanwhile, as citizens scramble to keep their inanimate objects alive, the local authorities are complicit in this patchwork arrangement, taking payments from the gray-market generator operators and perpetuating a nation’s struggle to stay wired.

Lebanon has been a glimmering country ever since the 15-year civil war began in 1975, and the reverberations from that conflict persist. These days there is only one city, Zahle, with electricity 24/7. Computer banks in schools and large air conditioners pumping out chills strain the grid, and daily state-mandated power cuts run from at least three hours to 12 hours or more. Families endure power outages mid-cooking, mid-washing, mid-Netflix binging. Residents rely on mobile phone apps to track the time of day the power will be cut, as it shifts between three-hour windows in the morning and afternoon, rotating throughout the week.

Beirut’s supplementary power needs are effectively under the control of what is known here as the generator mafia: a loose conglomerate of generator owners and landlords who supply a great deal of the country’s power. This group is indirectly responsible for the Wi-Fi, which makes possible any number of WhatsApp conversations—an indispensable lifeline for the country’s refugees, foreign aid workers, and journalists and locals alike.

Electricité du Liban, the Lebanese electricity company, has a meager budget and relies on a patchwork approach—including buying power from neighboring countries and leasing diesel generator barges—to produce power; meanwhile, corruption in local and state politics means that government-allocated funds often do not reach the people or places for which they are intended. The community—or mafia—of generator owners is thus a solution to a widespread problem, and it has grown into a cottage industry, both intractable and necessary.

Sam says he doesn’t buy backup juice for his apartment, which he rented last spring. Somewhere along the electrical wires cast like nets across the city, a bootlegged electrical line running from a generator was spliced in his favor: A single “magic” outlet powers his wireless router during outages. It’s one thing to be kept from doing your laundry, and another thing entirely to be kept from your friends or family. Besides, tracking down the generator owner responsible for this one outlet would be a journey of more than 1,001 nights. In the city of Beirut alone, there are roughly 12,000 generators and their owners. Though it is technically illegal, regulators have a hard time squashing the network, which has grown to cover most of the country. Officials aren’t so much paid off to look the other way; they’re paid because, it is said, they own some of the generators.

In the Mreijeh neighborhood, one of the electricians is known to locals as “the real energy minister.” His wiring, strung between generators and buildings to which they pump power, are so thick that they blot out the sun. In the Bourj al-Barajneh neighborhood, some residents share their power “subscription,” perhaps with magic outlets of their own; the subscription operator and generator owner turns a blind eye. In the district known as Shiah, the “Dons” do not allow any such manipulation—they do, however, have a weakness for European soccer matches and boost power on game nights. And in al-Fanar, it is important that the distributors of this power pay close attention to usage and monitor peak hours, doing their best to keep service operating when the state fails.

“We cover where there is no state,” says Abdel al-Raham, an owner and operator of generators in East Beirut. He began with a small generator, which he used to power his house, around the start of the civil war in 1975. But the generator was loud and noxious, so over time, as a gesture of good faith, he would give his neighbors a lamp connected to his generator. “Just enough for them to light their house and to make up for all the annoying noise,” he says.

But because of his generosity, his wife soon became unable to run the washing machine. He went out and bought a new, bigger generator. Then shop owners nearby needed more power, and his brother came to him and proposed they split profits on the power they could sell to the neighborhood. Self-sufficiency turned into entrepreneurship.

Raham, like other operators, complains about repair costs; under-the-table operating fees—essentially, bribes—to the local municipalities in which they operate; the unpaid bills by some of the country’s Syrian and Egyptian refugees who are using an estimated additional 486 megawatts; and the increasing cost of diesel fuel to run the generators.

But Raham felt a responsibility to his community in which three-quarters of the homes rely on his generators for some portion of their power. In some of those homes, he says, elderly people rely on medical devices 24 hours a day. A lack of electricity would be a threat to their health.

Residents of Lebanon have three basic options: buy a generator subscription, own your own generator, or splurge for what’s known as an uninterruptible power supply.

When you move into an apartment, you will most often connect with the local generator owner who will set up a subscription for 5 amps, 10 amps, 15 amps, or more, depending on your budget and consumption during the scheduled power outages. Residents will also do this with their water providers—one bill and service provider for filtered water, and another bill and service provider for gray water. (Water utilities are likewise a … gray area.) Internet is handled by another ad hoc collection of quasi-legal independent operators, as is trash, which the city is supposed to take care of but often fails to collect. These entities are more than private providers or secret crusaders. They are a necessary convenience to which one is connected through inconvenient terms.

Though they claim they make little money on their ventures, generator owners can net tens of thousands of dollars in monthly revenue. They also undercut one another, vying for customers in any given neighborhood.

Many developing countries suffer from electricity problems, but a World Bank report from 2015 suggested that Lebanon’s problems go beyond technical issues. It would cost the government $5 billion to $6 billion to bring 24-hour power to the country, according to one estimate, and yet the government spends roughly $1.4 billion a year just to cover the cost of fuel.  The report also noted that, on average, Lebanese households spent more than $1,300 a year on electricity in 2016 at a time when gross national income per capita was roughly $9,800.

Haddad pays for 10 amps a month (roughly 2,200 watts, or enough to power an electric kettle and desktop computer concurrently) and also receives a separate bill for the building elevator and hallway lights. It used to be that residents paid $90 for 10 amps, which cost $14 to generate, but Haddad says that today he pays $267 for 5 amps every month—about four times the amount he pays concurrently to Electricité du Liban. Municipalities now regulate the maximum cost the generator owners can charge their clients, though their control over the generator owners is hardly comprehensive. It is a tractor-pull relationship between local officials and generator owners. “The policy by which the municipalities and generator owners are connected is neither legal nor organized,” Antoine K. Gebara, the mayor of an eastern Beirut suburb, told me. “There is no system. … It should not be like this.”

The generator owners stepped in when the government could not provide services, but had to be controlled and regulated (as best as one might regulate a network of entrepreneurial privateers) by the same municipalities that couldn’t effectively supply power. Now, the generator owners turn around and pay the municipalities for the pleasure of dominating a market in which other generator owners might come to set up shop.

“They call us criminals, electricity thieves, robbers with generators. How are we the criminals?” Antanios asks me, his voice a rasp. “Yes, it’s extremely expensive. But that’s the government’s fault.”   He reaches into a drawer and pulls out another sheaf of receipts from the municipality and one signed by a local politician, each one totaling around $1,300. He had paid his commission to the politician—a headache Antanios wishes he could avoid (though perhaps it is better than being under the thumb of Hezbollah factions, who at times questioned me while working on this story as I sought answers about generators and their owners)—along with his taxes to the city government. Such a monthly burden meant his business had to generate substantial cash. He tells me he can sometimes get $32,000 a month in revenue. But he is quick to point out that he works hard for the money. For example, Antanios says, the night before he and his electricians spent six hours trying to identify the cause of a shortage throughout the neighborhood.

Just then the room darkens. A loud popping rips through the room, as though someone were stepping on a floor made of light bulbs. From across the street, emerging from a shantytown, from under an umbrella of corrugated metal, several of Antanios’ workers race to the office. The power from Electricité du Liban had cut in his sector, and now the breakers and generators were turning on, feeding into the lines that were cast out from his office and the nearby generators. But the switchover happens smoothly. An oscillating fan in the office hadn’t come to a stop before the power kicked back on, less than 30 seconds later.

Last year, researchers visited the Hamra neighborhood, a popular tourism and shopping district in Beirut, to study the health effects of generator usage. Fifty-three percent of the 588 buildings there had diesel generators. The study, by the American University of Beirut’s Collaborative for the Study of Inhaled Atmospheric Aerosols, found that throughout the city, the 747 tons of fuel consumed during a typical daily three-hour outage resulted in the production of 11,000 tons of nitrogen oxide annually. The territory of Delhi, India, relies heavily on diesel generators too, but Beirut emissions are more than five times worse per capita than those in the Indian capital.

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IEEE. September 5, 2014. IEEE Report to DOE Quadrennial Energy Review on Priority Issues. IEEE

On the distribution system, high penetration levels of intermittent renewable Distributed Generation (DG) creates a different set of challenges than at transmission system level, given that distribution is generally designed to be operated in a radial fashion with one way flow of power to customers, and DG (including PV and wind technologies) interconnection violates this fundamental assumption. Impacts caused by high penetration levels of intermittent renewable DG can be complex and severe and may include voltage increase, voltage fluctuation, interaction with voltage regulation and control equipment, reverse power flows, temporary overvoltage, power quality and protection concerns, and current and voltage unbalance, among others.

Common impacts of DG in distribution grids are described below; this list is not exhaustive and includes operational and planning aspects50, 51.

• Voltage increase can lead to customer complaints and potentially to customer and utility equipment damage, and service disruption.
• Voltage fluctuation may lead to flicker issues, customer complaints, and undesired interactions with voltage regulation and control equipment.
• Reverse power flow may cause undesirable interactions with voltage control and
• regulation equipment and protection system misoperations.
• Line and equipment loading increase may cause damage to equipment and service disruption may occur.
• Losses increase(under high penetration levels) can reduce system efficiency.
• Power factor decrease below minimum limits set by some utilities in their contractual agreements with transmission organizations, would create economic penalties and losses for utilities.
• Current unbalance and voltage unbalance may lead to system efficiency and protection issues, customer complaints and potentially to equipment damage.
• Interaction with Load Tap Changers (LTC), line voltage regulators (VR), and switched
• capacitor banks due to voltage fluctuations can cause undesired and frequent voltage
• changes, customer complaints, reduce equipment life and increase the need for maintenance
• Temporary Overvoltage (TOV): if accidental islanding occurs and no effective reference to ground is provided then voltages in the island may increase significantly and exceed allowable operating limits. This can damage utility and customer equipment, e.g., arresters may fail, and cause service disruptions.
• Harmonic distortion caused by proliferation of power electronic equipment such as PV inverters.

The aggregate effect from hundreds or thousands of inverters may cause service disruptions, complaints or customer economic losses, particularly for those relying on the utilization of sensitive equipment for critical production processes.

• Voltage sags and swells caused by sudden connection and disconnection of large DG units may cause the tripping of sensitive equipment of end users and service disruptions.
• Interaction with protection systems including increase in fault currents, reach
• modification, sympathetic tripping, miscoordination, etc.
• Voltage and transient stability: voltage and transient stability are well-known phenomena at transmission and sub-transmission system level but until very recently were not a subject of interest for distribution systems. As DG proliferates, such concerns are becoming more common.

The severity of these impacts is a function of multiple variables, particularly of the DG penetration level and real-time monitoring, control and automation of the distribution system. However, generally speaking, it is difficult to define guidelines to determine maximum penetration limits of DG or maximum hosting capacities of distribution grids without conducting detailed studies.

From the utility perspective, high PV penetration and non-utility microgrid implementations shift the legacy, centralized, unidirectional power system to a more  complex, bidirectional power system with new supply and load variables at the grid’s edge. This shift introduces operational issues such as the nature, cost, and impact of interconnections, voltage stability, frequency regulation, and personnel safety, which in turn impact resource planning and investment decisions.

NREL. 2014. Volume 4: Bulk Electric Power Systems: Operations and Transmission Planning. National Renewable Energy Laboratory.

Initial experience with PV indicates that output can vary more rapidly than wind unless aggregated over a large footprint. Further, PV installed at the distribution level (e.g., residential and commercial rooftop systems) can create challenges in management of distribution voltage.

Meier, A. May 2014. Challenges to the integration of renewable resources at high system penetration. California Energy Commission.

3.2 Distribution Level: Local Issues

A significant class of challenges to the integration of renewable resources is associated primarily with distributed siting, and only secondarily with intermittence of output. These site‐specific issues apply equally to renewable and non‐renewable resources, collectively termed distributed generation (DG). However, DG and renewable generation categories overlap to a large extent due to

• technical and environmental feasibility of siting renewables close to loads
• high public interest in owning renewable generation, especially photovoltaics (PV)
• distributed siting as an avenue to meet renewable portfolio standards (RPS), augmenting the contribution from large‐scale installations Motivation exists; therefore, to facilitate the integration of distributed generation, possibly at substantial cost and effort, if this generation is based on renewable resources.

Distributed generation may therefore be clustered, with much higher penetration on individual distribution feeders than the system‐wide average, for any number of reasons outside the utility’s control, including local government initiatives, socio‐economic factors, or neighborhood social dynamics.

The actual effects of distributed generation at high penetration levels are still unknown but are likely to be very location specific, depending on the particular characteristics of individual distribution feeders.

Technical issues associated with high local penetration of distributed generation include

• Clustering: The local effects of distributed generation depend on local, not system‐wide penetration (percent contribution). Local penetration level of distributed generation may be clustered on individual feeders for reasons outside the utility’s control, such as local government initiatives, socio‐economic factors, including neighborhood social dynamics Clustering density is relative to the distribution system’s functional connectivity, not just geographic proximity, and may therefore not be obvious to outside observers.
• Transformer capacity: Locally, the relative impact of DG is measured relative to load – specifically, current. Equipment, especially distribution transformers, may have insufficient capacity to accommodate amounts of distributed generation desired by customers. Financial responsibility for capacity upgrades may need to be negotiated politically.
• Modeling: From the grid perspective, DG is observed in terms of net load. Neither the amount of actual generation nor the unmasked load may be known to the utility or system operator. Without this information, however, it is impossible to construct an accurate model of local load, for purposes of: forecasting future load, including ramp rates, ascertaining system reliability and security in case DG fails Models of load with high local DG penetration will have to account for both generation and load explicitly in order to predict their combined behavior. • Voltage regulation: Areas of concern, explained in more detail in the Background section below, include: maintaining voltage in permissible range, wear on existing voltage regulation equipment, reactive power (VAR) support from DG

Areas of concern and strategic interest, explained in more detail in the Background section below, include: preventing unintentional islanding, application of microgrid concept, variable power quality and reliability Overall, the effect of distributed generation on distribution systems can vary widely between positive and negative, depending on specific circumstances that include

• the layout of distribution circuits
• existing voltage regulation and protection equipment
• the precise location of DG on the circuit

3.2.2 Background: Voltage Regulation Utilities are required to provide voltage at every customer service entrance within permissible range, generally ±5 percent of nominal. For example, a nominal residential service voltage of 120V means that the actual voltage at the service entrance may vary between 114 and 126 V. Due to the relative paucity of instrumentation in the legacy grid, the precise voltage at different points in the distribution system is often unknown, but estimated by engineers as a function of system characteristics and varying load conditions.

Different settings of load tap changer (LTC) or other voltage regulation equipment may be required to maintain voltage in permissible range as DG turns on and off. Potential problems include the following:

• DG drives voltage out of the range of existing equipment’s ability to control
• Due to varying output, DG provokes frequent operation of voltage regulation equipment, causing excessive wear

DG creates conditions where voltage profile status is not transparent to operators

Fundamentally, voltage regulation is a solvable problem, regardless of the level of DG penetration. However, it may not be possible to regulate voltage properly on a given distribution feeder with existing voltage regulation equipment if substantial DG is added. Thus a high level of DG may necessitate upgrading voltage regulation capabilities, possibly at significant cost. Research is needed to determine the best and most cost‐effective ways to provide voltage regulation, where utility distribution system equipment and DG complement each other.

Legacy power distribution systems generally have a radial design, meaning power flows in only one direction: outward from substations toward customers. The “outward” or “downstream” direction of power flow is intuitive on a diagram; on location, it can be defined in terms of the voltage drop (i.e., power flows from higher to lower voltage).

If distributed generation exceeds load in its vicinity at any one moment, power may flow in the opposite direction, or “upstream” on the distribution circuit. To date, interconnection standards are written with the intention to prevent such “upstream” power flow.

The function of circuit protection is to interrupt power flow in case of a fault, i.e. a dangerous electrical contact between wires, ground, trees or animals that results in an abnormal current (fault current). Protective devices include fuses (which simply melt under excessive current), circuit breakers (which are opened by a relay) and reclosers (which are designed to re‐establish contact if the fault has gone away).

The exception is a networked system, where redundant supply is always present. Networks are more complicated to protect and require special circuit breakers called “network protectors” to prevent circulating or reverse power flow. If connected within such a networked system, DG is automatically prevented from backfeeding into the grid. Due to their considerable cost, networked distribution systems are common only in dense urban areas with a high concentration of critical loads, such as downtown Sacramento or San Francisco, and account for a small percentage of distribution feeders in California.

3.2.5 Research Needs Related to Circuit Protection

The presence of distributed generation complicates protection coordination in several ways: • The fault must now be isolated not only from the substation (“upstream”) power source, but also from DG • Until the fault is isolated, DG contributes a fault current that must be modeled and safely managed

Shifting fault current contributions can compromise the safe functioning of other protective devices: it may delay or prevent their actuation (relay desensitization), and it may increase the energy (I2t) that needs to be dissipated by each device.6 Interconnection standards limit permissible fault current contributions (specifically, no more than 10 percent of total for all DG collectively on a given feeder). The complexity of protection coordination and modeling increases dramatically with increasing number of connected DG units, and innovative protection strategies are likely required to enable higher penetration of DG.

Standard utility operating procedures in the United States do not ordinarily permit power islands. The main exception is the restoration of service after an outage, during which islanded portions of the grid are re‐connected in a systematic, sequential process; in this case, each island is controlled by one or larger, utility‐operated generators. Interconnection rules for distributed generation aim to prevent unintentional islanding. To this end, they require that DG shall disconnect in response to disturbances, such as voltage or frequency excursions, that might be precursors to an event that will isolate the distribution circuit with DG from its substation source.

Disconnecting the DG is intended to assure that if the distribution circuit becomes isolated, it will not be energized. This policy is based on several risks entailed by power islands: • Safety of utility crews: If lines are unexpectedly energized by DG, they may pose an electrocution hazard, especially to line workers sent to repair the cause of the interruption. It is important to keep in mind that even though a small DG facility such as a rooftop solar array has limited capacity to provide power, it would still energize the primary distribution line with high voltage through its transformer connection, and is therefore just as potentially lethal as any larger power source. • Power quality: DG may be unable to maintain local voltage and frequency within desired or legally mandated parameters for other customers on its power island, especially without provisions for matching generation to local load. Voltage and frequency departures may cause property damage for which the utility could be held liable, although it would have no control over DG and power quality on the island. • Re‐synchronization: When energized power islands are connected to each other, the frequency and phase of the a.c. cycle must match precisely (i.e., be synchronized), or elsegenerators could be severely damaged. DG may lack the capability to synchronize its output with the grid upon re‐connection of an island.

3.2.7 Research Needs Related to Islanding

In view of the above risks, most experts agree that specifications for the behavior of DG should be sufficiently restrictive to prevent unintentional islanding. Interconnection rules aim to do this by requiring DG to disconnect within a particular time frame in response to a voltage or frequency deviation of particular magnitude, disconnecting more quickly (down to 0.16 seconds, or 10 cycles) in response to a larger deviation. At the same time, however, specifications should not be too conservative to prevent DG from supporting power quality and reliability when it is most needed.

There is no broad consensus among experts at this time about how best to reconcile the competing goals of minimizing the probability of unintentional islanding, while also maximizing the beneficial contribution from DG to distribution circuits.

As for the possibility of permitting DG to intentionally support power islands on portions of the utility distribution system, there is a lack of knowledge and empirical data concerning how power quality might be safely and effectively controlled by different types of DG, and what requirements and procedures would have to be in place to assure the safe creation and re‐connection of islands. Because of these uncertainties, the subject of islanding seems likely to remain somewhat controversial for some time.

Needed: • Modeling of DG behavior at high local penetrations, including o prevention of unintentional islanding o DG control capabilities during intentional islanding • Collaboration across utility and DG industries to facilitate DG performance standardization, reliability and trust. This means that utilities can depend on DG equipment to perform according to expectations during critical times and abnormal conditions on the distribution system, the handling of which is ultimately the utility’s responsibility.

In the long run, intentional islanding capabilities – with appropriate safety and power quality control – may be strategically desirable for reliability goals, security and optimal resource utilization. Such hypothetical power islands are related to but distinct from the concept of microgrids, in that they would be scaled up to the primary distribution system rather than limited to a single customer’s premises. A microgrid is a power island on customer premises, intermittently connected to the distribution system behind a point of common coupling (PCC) that may comprise a diversity of DG resources, energy storage, loads, and control infrastructure. Three key features of a microgrid are • Design around total system energy requirements:

Depending on their importance, time preference or sensitivity to power quality, different loads may be assigned to different primary and/or back‐up generation sources, storage, or uninterruptible power supplies (UPS). A crucial concept is that the expense of providing highly reliable, high‐quality power (i.e., very tightly controlled voltage and frequency) can be focused on those loads where it really matters to the end user (or life of the appliance), at considerable overall economic savings. However, the provision of heterogeneous power quality and reliability (PQR) requires a strategic decision of what service level is desired for each load, as well as the technical capability to discriminate among connected loads and perform appropriate switching operations. • Presentation to the macrogrid as a single controlled entity: At the point of common coupling, the microgrid appears to the utility distribution system simply as a time‐varying load. The complexity and information management involved in coordinating generation, storage and loads is thus contained within the local boundaries of the microgrid.

Note that the concepts of microgrids and power islands differ profoundly in terms of • ownership • legal responsibility (i.e. for safety and power quality) • legality of power transfers (i.e., selling power to loads behind other meters) • regulatory jurisdiction • investment incentives Nevertheless, microgrids and hypothetical power islands on distribution systems involve many of the same fundamental technical issues. In the long run, the increased application of the microgrid concept, possibly at a higher level in distribution systems, may offer a means for integrating renewable DG at high penetration levels, while managing coordination issues and optimizing resource utilization locally. Research Needs: • Empirical performance validation of microgrids • Study of the implications of applying microgrid concepts to higher levels of distribution circuits, including o time‐varying connectivity o heterogeneous power quality and reliability o local coordination of resources and end‐uses to strategically optimize local benefits of distributed renewable generation • Study of interactions among multiple microgrids