1540-7977/17©2017IEEE64 ieee power & energy magazine may/june 2017

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Achieving Resilience at the Distribution Level

IncreasIng power system resIlIence at the dIstrIbutIon level is crucial due to the negative social impact of blackouts, as the undesired consequences get worse the longer the system restoration takes. statistical records demonstrate that system recovery times after high-impact, low- probability events (e.g., earthquakes, tsunamis, and floods) are often faster for generation and trans-mission segments than for the distribution system. during the 2010 chilean earth-quake (8.8 mw on the richter scale), for example, the distribution system in the most affected area (almost 1.1 million customers) was not totally back in service until two weeks after the first major seismic event. In contrast, the transmission system rapidly recovered, with most of the bulk system buses re-energized by the end of the first day and the remainder during the second day. additional installed generation capacity and repairing minor damage to most of the affected genera-tion plants allowed for the recovery of most of the supply within a few days. only 6.1% of the installed generation capacity required major repairs (which took up to six months to complete).

unfortunately, in chile, high-impact, low-probability power system events present a latent risk of human catastrophe, particularly in disadvantaged commu-nities. system resilience is essential. In this context, microgrids, which are subsets of distribution systems (e.g., equipped smart technologies), offer the capability to maintain energy supplies under emergency conditions, serving critical infrastruc-ture like hospitals, street lighting, communication antennas, and other assets.

By Guillermo Jiménez-Estévez, Alejandro Navarro-Espinosa, Rodrigo Palma-Behnke, Luigi Lanuzza, and Nicolás Velázquez

Digital Object Identifier 10.1109/MPE.2017.2662328Date of publication: 19 April 2017

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Learning from Isolated Community Microgrids

In this article, we describe three isolated microgrid proj-ects (huatacondo, chile; ollagüe, chile; and puertecitos, mexico) developed in the last few years with the support of the university of chile. the huatacondo project was funded by a mining company. In ollagüe, a power producer was the main provider. puertecitos was mainly funded by the mexican government and the Inter american develop-ment bank. In these three projects, both r&d support from

the universities and laboratories involved and engagement with the local community were key factors to ensure the long-term sustainability of the projects. From a technical perspective and with operational statis-tical data, the cost structure of such schemes is better understood as well as the contribution of microgrids to the resilience of larger distribution systems.

these lessons were considered in the design of two larger projects that we present here: an emergency microgrid for the city of arica, chile (200,000 inhabitants), and a resilient smart grid introduced in the town of diego de almagro, chile (16,000 inhabitants), after a devastating flood required a new city plan. throughout the article, we highlight the relevance of social aspects and community engagement to achieve sustainable and resilient distribution systems.

©istockphoto.com/violetkalpa

66 ieee power & energy magazine may/june 2017

Challenges at Distribution Systemsdistribution systems face many challenges due to the intro-duction of new agents (e.g., distributed energy resources), enablers (e.g., remote monitoring), and requirements (e.g., better reliability standards, new pricing alternatives, and energy decarbonization). this new framework increases the need for new attributes and technical solutions at the dis-tribution level. one of these attributes is system resilience, which is the capability of the system to react, resist, and recover under low-probability, high-consequence events, such as earthquakes and floods. compared with the other segments of the electricity supply chain, recovery times at the distribution system are longer than those for transmis-sion and generation.

after the chilean earthquake of 2010, the chilean cen-tral Interconnected system, which provides electricity to over 93% of the population, suffered an immediate loss of 4,522 mw (the peak demand of the system was 6,145 mw). a total of 693 mw of existing power plants (6.1% of the installed generating capacity) was forced out of service for repairs. sufficient energy supply remained to serve load but operated with an n-0 security condition in several places. most of the main grid level was recovered within a few hours

of the event. two electrical islands operated, with the central part of the country separated from the south due to damage at some substations and isolated problems in transmission structures. two days later, the two islands were intercon-nected. In contrast, there was major damage at the distri-bution level. although repairs were made, it took weeks to recover supply at the end user level. For instance, coastal networks were completely destroyed due to the resulting tsu-nami after the earthquake.

this experience clearly shows that major changes are required at the distribution system level, and technological and social tools should be used to increase the capability of distribution systems to react/resist/recover under high-impact events. In this context, lessons from microgrids and community participation are key tools in providing a resilient feature for smart grids (i.e., resilient smart grids). there have been several experiences of microgrid development for remote locations that identify the resilience characteristic as a major challenge, as shown in Figure 1.

Resilience in Microgridsmicrogrids are planned and operated to account for expected system states (i.e., the amount of charging in the battery stor-

age system) and to deal with uncontrollable disturbances (i.e., intermittency in the renewable energy sources and load changes). If an unexpected system distur-bance occurs, the microgrid reacts to maintain grid reli-ability by keeping voltage magnitude and frequency at predisturbance conditions (these variables provide a measure of security and adequacy). once the dis-turbance is cleared, man-aging the resources returns to standard procedures.

high-impact, low-prob-ability events could even-tually collapse a particular microgrid. a microgrid could potentially have the capability to recover qu -ickly and prioritize which load to connect (i.e., critical loads) if full recovery is not possible due to infra-structure damage. thus, the resilience framework can be applied to microgrids, with a resilient microgrid able to figure 1. Isolated microgrid challenges.

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lism

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✔✔ withstand technical, social, economic, and/or natural hazards without losing its functionality

✔✔ keep a minimum level of supply to assure the supply of crucial load and facilitate the potential recovery if it is impossible to keep full functionality

✔✔ recover its operating conditions back to normal levels, the same as before the disturbance.

In brief, a resilient microgrid maintains its functionalities as best as possible before, during, and after a disturbance.

the three isolated microgrids are described next. spe-cial attention is given to operation features and reaction to unex-pected disturbances.

Huatacondothis microgrid is located in the small isolated village of huatacondo in the atacama desert, chile. the village’s electric network is isolated from the interconnected system, and power was provided for only 10 h per day by a diesel generator. a renewable-based micro grid that takes advantage of the distributed renewable resources in the area to provide 24-h service was devel-oped in 2010. since the village experienced problems with its water supply system, a water man-agement solution was also included in the electric system. additionally, a demand-side option to compen-sate for generation fluctuations due to the renewable sources was considered. Figure 2(a) summa-rizes the microgrid, composed of photovoltaic (pV) panels, a wind turbine, diesel generators, a battery bank, a water supply system, and a demand-side management mecha-nism (loads).

the huatacondo microgrid has been under operation since 2010, supplying continuous power to the community. this available ene rgy has facilitated the development of productive projects, such as the con-struction of cabins for tourism. In addition, new organizational struc-tures were created at the commu-nity level for the management and operation of the microgrid over the long term.

Figure 2(b) shows the operation of the huatacondo microgrid on

a typical day, which begins with the distributed generator system (genset) working (black line) and finalizing the bat-tery charge (blue line). then the demand is supplied by the battery, discharging until approximately 20% of capacity remains. when the sun rises, the pV plant begins to oper-ate (red line), supplying demand and using its surplus to charge the battery (blue line). the genset operates at night to supply peak demand hours and complete charg-ing the battery. even if there are high power supply varia-tions from the pVs (between 13 and 18 h), the difference is

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figure 2. The Huatacondo microgrid: (a) a diagram and (b) daily operation.

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immediately covered by the battery, allowing for the sys-tem’s continuous operation. there have been high-impact events during the operational life of the huatacondo micro -grid that demonstrate the capability of this technologi-cal solution.

2012 Venidaduring the summer months (January and February), there is a climatic phenomenon known as “altiplano winter,” which is a rainy season originating in the bolivian altiplano. some years, this rain produces large inflows in the andes streams, such as the one that flows near huatacondo. In 2012, a large water inflow caused a mud avalanche (venida) that blocked the route that connects huatacondo with other locations, so the fuel supply was cut for approximately three months. careful microgrid operation based on local resources (the sun) and stocked fuel allowed for continued operation when the route was blocked, significantly reducing the loca-tion’s fuel dependency.

2014 Iquique earthquakeon 1 april 2014, there was an earthquake that mea-sured 8.2 on the richter scale with an epicenter approxi-mately 95 km (59 mi) northwest of Iquique. that quake produced a complete blackout of the northern intercon-nected system: 17 h after the event there were approxi-ma tely 38,000 consumers without power. huatacondo did not experience any type of power interruption during the earthquake.

2014 Stormon 23 may 2014, there was an unexpected storm in the north of chile with high-speed winds and sleet. as a result of the storm, a wind turbine fell down, making the power supply from that component unavailable. however, microgrid oper-ation was not interrupted due to support from the batteries and the diesel genset.

Ollagüethis microgrid was developed in the small town of ollagüe, antofagasta region, chile, a village along the antofagasta-bolivia railway. the town is at an altitude of 3,700 m above mean sea level with a marginal desert climate. there is a large temperature variation between day and night (changes of up to 22 °c), with the absolute minimum temperature reaching −20 °c during the winter season. ollagüe was not connected to the national grid but just to a system powered

by a 250-kw diesel genset, which didn’t supply electricity from 1 a.m. to 8 a.m.

a microgrid was developed with the following objec-tives: supply energy to the town for 24 h/day, seven days/week; minimize fuel consumption of the existing diesel generator; test advanced renewable generation and storage  systems in a harsh environment (the great tem-perature fluctuation between day and night and extreme solar radiation in a rarefied atmosphere); and develop technical solutions for a fast-growing market of microgrid developments. this project was developed by enel green power with the cooperation of the energy center, uni-versidad de chile. the characteristics of the microgrid are as follows:

✔✔ solar pV: 200 kwp (thin film modules)✔✔ storage: 200 kw, 752 kwh (sodium nickel chloride)✔✔ wind turbine: 30 kw✔✔ diesel generator: 410 kVa✔✔ separate dish stirling engines: two, providing warm water to the local school.

there have not been many high-impact events since the ollagüe microgrid began operating in april 2015. there was an event that tested the black start capability of this microgrid. on 3 november 2015, there was a fault in the medium-voltage line that joins the pV and wind power plant with the rest of the system, which caused a complete black-out of the microgrid. Figure 3(b) shows the daily operation of the microgrid during that day, with the fault occurring at approximately 13:00 h. the microgrid was completely recovered 1 h later.

Puertecitospuertecitos is a small village located in baja california, mexico. like the previous two cases, it is an isolated loca-tion dependent on a diesel genset with limited power supply. In this case, there is a clear opportunity to promote tour-ism activities if a continuous power supply is guaranteed. the autonomous university of baja california led this proj-ect that began operation in January 2016. the puertecitos microgrid diagram is shown in Figure 4. the puertecitos microgrid comprises the following:

✔✔ storage: 100 kw, 522 kwh✔✔ solar pV: 55 kw✔✔ wind turbine: 5 kw✔✔ diesel generator: 75 kVa.

one of the most important challenges of this microgrid is related to the large temperature variation. during the

Distribution systems face many challenges due to the introduction of new agents, enablers, and requirements.

may/june 2017 ieee power & energy magazine 69

summer months, the temperature can be greater than 40 ºc, causing consumers to use air-conditioning equipment that makes the summer seasonal demand more than six times greater than winter. thus, the dimensioning of the resource mix was a critical task. this installed capacity in the puer-tecitos microgrid makes it a highly flexible system able to provide power supply for different scenarios. Figure 5 shows the seasonal variation of demand behavior in the puertecitos microgrid, with (a) a low demand scenario and (b) the sum-mer peak season.

Lessons and Methodological ApproachFrom our experiences with these microgrids, different les-sons about the resilience capabilities of distribution systems are summarized below.

✔✔ the engagement of the local community in the de-sign, operation, and maintenance of a microgrid al-lows a for a cost-effective provision of a power supply with resilient characteristics and with high social acceptance rates. thus, new business models and pric-ing schemes can be developed for users in a distri-bution system.

✔✔ dependency on a single energy source can be avoid-ed when microgrids are adequately designed; the incorporation of local distributed energy resources offers the opportunity to endure disturbances when a resource is not available. For instance, in the hua-tacondo case, when the wind turbine was offline because of a huge storm, the microgrid did not lose its functionality.

✔✔ microgrids incorporate security characteristics that facil-itate a quick and robust response to specific disturbances such as black start capability, load control, and voltage/frequency control features that allow the system to re-main within the operational standards without risk for

the local community. this was observed on the ollagüe microgrid when a major fault occurred, and the system quickly returned to operation.

✔✔ extreme environmental conditions, as is the case of puertecitos and ollague (involving both daily and sea-sonal temperature variations of up to 20 ºc), converge in technical solutions with high flexibility.

✔✔ demand response and active community participa-tion are also significant characteristics of isolated mi-crogrids that contribute to the resilience of the whole system. In the huatacondo case, during the “venida,” community members also reduced their energy con-sumption so the stocked fuel and the local energy re-sources were enough to cover electricity consumption.

✔✔ all the resilience features identified at the microgrid level, from the economic point of view, are related to capital expenditures. this means that there is little

Genset410 kVA

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figure 4. A diagram of the Puertecitos microgrid.

70 ieee power & energy magazine may/june 2017

difference in operating costs between systems with smart capabilities and without them. consequently, traditional business models at the distribution level are compatible with resilience targets specified by public policies that cover capital expenditures.

✔✔ the experience from pilot projects based on isolated microgrids can be converted into a learning platform (public good) for future resilient distribution systems.

Figure 6 depicts a methodological proposal that, in its first stage, includes the assessment of four main aspects:

✔✔ local conditions: environmental aspects such as tem-perature and humidity must be considered. It is also important to identify major disturbances that the loca-tion may be exposed to, such as earthquakes, tsunamis, and floods.

✔✔ energy resource availability: the identification of lo-cal energy resources such as wind, solar radiation, and water inflows.

✔✔ stakeholder participation: isolated microgrids require the active participation of local communities. In this context, the involvement of local stakeholders is cru-cial (such as representatives of local communities, in-stitutions, and the private sector).

✔✔ network infrastructure: this aspect is particularly impor-tant for a microgrid embedded in distribution systems. the resources and the smart grid system to be deployed for the microgrid should also consider the interactions (and impacts) on the existing network infrastructure during normal operation (i.e., a non- isolated microgrid).

Further considerations during system design and devel-opment include the following:

✔✔ operational capabilities: features such as black start, load control, and islanding operation are defined in response to the project’s local conditions.

✔✔ role of stakeholders: it is important to define how to articulate the different responsibilities and roles of the stakeholders. today, community plays a more active role, so this definition includes consumers, network operators, and government institutions.

✔✔ business model: a proper definition of how to inte-grate the cost associated with the smart grid solutions into the tariff model, considering that this feature is related to capital expenditures.

Upcoming Projectsthe framework discussed in the previous section is being employed to propose and design two new projects: an emer-gency microgrid in the arica city distribution system and a new distribution system in diego de almagro, a city that was severely damaged by a flood in 2015.

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figure 6. A methodological approach.

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Arica—Emergency Microgridthe project in arica (a city located in the very north of chile) consists of an emergency microgrid based on solar energy. the microgrid’s objectives are to improve public safety and raise awareness of the possible uses of solar energy in emer-gency situations.

the technical proposal is based on a solar-powered microgrid that uses components such as pV modules, diesel engines, and battery energy storage systems. the microgrid is designed to be able to provide power supply to meeting points, shelters, and care centers located in the south zone of arica. there is the possibility to sell surplus energy through a net-billing scheme or use it for electromobility (charging electric bikes).

the proposed project is in the first stage out of ten, cover-ing part of the city. Figure 7(a) shows the map of the whole city and the risk area (in blue), which is identified as a high-impact zone under a tsunami scenario. In Figure 7(b), the specific infrastructure to be covered by the microgrid is shown in more detail. technical and financial information of this initial stage is provided below in table 1. Incorpo-rating this technical solution in addition to an electromobil-ity application promotes the image of the city as safe and sustainable. the value of this classification as a cobenefit is difficult to monetize.

the project proposal includes collaborating with com-munity institutions to guarantee the sustainability of the emergency microgrid. the involvement of the arica com-munity, especially those who live in the risk zones, is fun-damental to the robust development and long-term sustain-ability of the microgrid.

Diego de Almagroalthough policy makers and researchers are increasingly interested in the application of resilience concepts to power systems, an analysis of this at the distribution level is just beginning. the modeling of the distribution system is very important because load recovery can be slower than the recovery of generation and transmission facilities. therefore, it is insufficient to measure system recovery only by consid-ering the availability of generation and bulk capacity. this was the case in diego de almagro (a small town located in northern chile with approximately 18,500 inhabitants) after a march 2015 flood. this town was almost destroyed due to the unprecedented high level and flow of the salado river; it experienced around 50 mm of rain in three days, which is approximately four times the area’s average yearly rainfall.

the main supply points were not affected, but most of the population was without power for several days due to problems with the distribution infrastructure, causing additional distress in a community already suffering devastation. to increase the resilience of electric service to diego de almagro, the govern-ment funded a project to investigate different alternatives of large-scale residential pV generation and develop a prototype.

(a) (b)

figure 7. (a) The Arica city emergency map and (b) tsunami flood areas (blue area), meeting points (green points), and escape routes (black). This area was selected for the first stage.

table 1. The Arica emergency microgrid project.

Initial investment (phase one of ten)

1 MUSD

Installed capacity 205 kW

Critical load to be supplied 45 kW (peak load) for 24 h

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the idea behind the incorporation of residential genera-tion is to have local supply available in the event of a disas-ter, which is possible only if energy storage is available. the idea of having one battery for each house with pV panels is too expensive, especially in a poor community, so some kind of community arrangement must be put in place. hence, the prototype will be implemented on a small street, where each house will be equipped with a pV panel, and a battery stor-age system will be shared by all the houses. the interaction, control, and communication among the devices will be made through an energy management system. the battery storage system will have the double objective of avoiding technical problems in the network (e.g., voltage rise and thermal prob-lems) and supplying critical loads when main grid supply is lost, and this will be achieved economically by using both thermal and battery storage.

thermal storage (i.e., water heaters) will be used to store heat from day to night, which is useful in this geographical area where the thermal oscillation between day and night is considerable (a 13–15 °c difference on average). part of the peak generation can be used to heat the water, therefore minimizing the possibility of reverse power flows. the bat-tery storage is used to store electricity for emergency pur-poses. so in the event of supply loss due to a natural disas-ter, the community can supply electricity for essential loads

like lighting, communication, and refrigeration. community engagement is crucial to optimally select critical loads from an economic, technical, and social perspective. For exam-ple, the choice of where to locate the battery must take into account possible voltage problems (technical perspective), the size and cost of the battery (economic perspective), and the loads that should be protected (social/community per-spective). In conclusion, the prototype will allow the large penetration of residential pV panels within standard volt-age and thermal limits but, more importantly, will help to increase the resilience of the community.

Transition to Microgrid-Based Resilient Distribution Systemsbased on the experience and outcome from these microgrid projects, Figure 8 shows a conceptual approach for the transi-tion process to achieve a resilient distribution system through the implementation of microgrids. this process can be accomplished by following two parallel tracks: single agent and multiple agent.

In the first track, the implementation of single-agent microgrids, the operation and management of urban micro -grids, are developed by only one agent. generation assets might be shared by different owners [i.e., distributed gen-eration (dg) solutions], but usually it will be a single owner

Transition to Microgrid-Based ResilientDistribution Systems

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• Ownership: – Generation: Multiple – Grid: DS Operator – Enablers: DS Operator and Aggregators

• DNO Role: Operation• Boundary: One or More PCC• Economic Viability: Not Viable to Date• Existing Subset of the Distribution Network• Examples: Feeder-Based Microgrid

Single-Agent Microgrids

• Ownership: – Generation: Single/Multiple* – Grid: Single – Enablers: Single• DNO Role: Coordination

• Boundary: PCC

• Economic Viability: According to the Owner Business Model

• Additional Subset of the Distribution Network

• Examples: Community Based Microgrid, Campus Microgrid.

*: Community, Private, or Public Institution.

figure 8. The proposed tracks to incorporate resilience by means of microgrid implementation.

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for the entire solution. In this case, the role of the distribu-tion system operator is to coordinate the integration of these microgrids by a control platform where the boundary and responsibilities are clearly identified at the point of common coupling. the economic viability of this solution is defined by the owner’s business model. this doesn’t imply a major change in the tariffs because all investments are the respon-sibility of the owner. nevertheless, a high penetration of this solution will impact the distribution system operator’s business because of a lower infrastructure requirements. examples of these type of applications are community-based microgrids and campus microgrids.

In the second track, in the multiple-agent microgrid scheme, the ownership of different microgrid assets is not unique. In fact, some dg assets (e.g., residential pV panels) could be owned by private homeowners and/or small busi-nesses, and others could be owned by a local authority and/or an entire community. while the dg facilities can have several owners, the distribution system operator is the only owner of the network infrastructure used by the microgrid. It is important to note that additional devices installed to enable microgrid operation, such as batteries, on-load tap changers, control and communication infrastructure, can be owned by different actors.

the multiple-agent microgrid is implemented in a subset of the existing distribution system infrastructure (i.e., using the existing network as a starting point), and therefore the distribu-tion system operator is responsible for managing the resources (e.g., dg units, and battery systems). here, it is important to note that the quality of supply inside the microgrid must sat-isfy all distribution system regulatory requirements. In this framework, the microgrid can be integrated through one or more points of common coupling.

From a business perspective, microgrids are usually not economically viable in chile. In fact, chile does not subsidize the installation of residential pVs; power injections into the system are accounted through a net billing scheme. consider-ing current energy prices, residential pVs are not profitable as the capital recovery time can be approximately ten years. hence, the implementation of a microgrid in chile usually requires financial help from third parties such as private com-panies (i.e., mining companies in towns close to their extrac-tive operations) or from government subsidies.

the resilience of microgrid systems during low-fre-quency, high-impact events can help justify subsidies. the size of the subsidy will depend on the level of self-supply that the policy maker wishes to achieve. a system designed to supply only critical loads when the main grid connection is lost requires less investment than a system designed to supply normal community consumption.

Summarycommunities benefit from more robust distribution systems that can endure technical, social, economic, and environ-

mental disturbances without losing functionality and can quickly be restored to normal operating conditions. this characteristic may be achieved through the implementa-tion of smart grids solutions such as microgrids. lessons learned from the isolated microgrids discussed here contrib-ute to the development of a design methodology for larger smart grid solutions at the distribution level, as shown by two major projects to be developed in chile. the experi-ence and learning outcomes from these projects have led to the production of two transition schemes for the integration of microgrids at the distribution level that can provide a starting point for distribution planners, policy makers, and other stakeholders.

Acknowledgmentsthis work has been partially funded by joint conicyt-chile/rcuK-uK project: disaster management and resil-ience in electric power systems (newton-picarte/mr/n026721/1) by conIcyt/Fondap/15110019 and ayllu solar project.

For Further ReadingJ. c. araneda, h. rudnick, s. mocarquer, and p. miquel, “lessons from the 2010 chilean earthquake and its im-pact on electricity supply,” in Proc. Int. Conf. Power Sys-tem Technology (POWERCON), China, 2010, pp. 1–7.

m. panteli and p. mancarella, “the grid: stronger, big-ger, smarter?,” IEEE Power Energy Mag., vol. 13, no. 3, pp. 58–66, 2015.

m. panteli and p. mancarella, “modeling and evaluat-ing the resilience of critical electrical power infrastructure to extreme weather events,” IEEE Syst. J., no. 99, pp. 1–10, Feb. 2015.

g. Jiménez-estévez, r. palma-behnke, d. ortiz-Villalba, o. núñez, and c. silva, “It takes a village,” IEEE Power En-ergy Mag., vol. 12, no. 4, pp. 60–69, July/aug. 2014.

K. ubilla, g. Jiménez-estévez, r. hernández, l. reyes-chamorro, c. hernández, b. severino, and r. palma-behnke, “smart microgrids as a solution for rural electrifi-cation: ensuring long-term sustainability through cadastre and business models,” IEEE Trans. Sustain. Energy, vol. 5, no. 4, pp. 1310–1318, oct. 2014.

BiographiesGuillermo Jiménez-Estévez is with the universidad de chile, chile.

Alejandro Navarro-Espinosa is with the universidad de chile and systep, chile.

Rodrigo Palma-Behnke is with the universidad de chile and serc, chile.

Luigi Lanuzza is with enel green power, Italy.Nicolás Velázquez is with universidad autonoma de

baja california, mexico. p&e

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