The Regional Grid Concept
BackgroundIn the case of Japan, its land stretches from north to south. Climates and industries are therefore different
from region to region, and appropriate renewable energy generation methods and energy demand
characteristics are also different. This suggests creating different electricity grids which are distinctivefrom region to region so as to optimize their performance, thus leading to a basis to achieve reduced
carbon emission.

PurposeFor discussions to deduce better ideas, this article proposes a "Regional Grid" concept promotingelectricity grids which are distinctive from region to region.

Conceptualization
The Change
The power flow in a power system has been basically unidirectional, that is, electrical power is generated
at remote and large-scale power plants then transmitted through transmission lines to demand sites andfinally distributed to customers via distribution systems. Today, a large number of photovoltaic (PV)power generation systems are interconnected to various layers of the power transmission anddistribution systems, and wind power generation systems and battery energy storage systems includingelectric vehicles (EVs) to be interconnected are increasing. They are called distributed energy resources(DERs). In this regard, the role of the power transmission and distribution systems is not only transmitting
and distributing electrical energy but also exchanging it among producers and consumers.

Regional Grid Concept
The figure below illustrates the "Regional Grid" concept that we are proposing.

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As mentioned earlier, climates, industries, appropriate renewable energy generation methods and energy
demand characteristics are different from region to region. This suggests creating a distinctive electricity
grid for each region so as to optimize its performance, thus leading to a basis to achieve reduced carbon
emission. In the figure, three examples of regional grids are shown. Large cities are highly populated
during the day time and often face the ocean with industrial areas. Suburbs with a large number ofhouses whose owners commute to a large city are highly populated during the night time, and thosehouses may be equipped with roof-top PV power generation systems. Villages which are lightly
populated may have enough spaces and incentives for renewable energy production utilizing the power
not only of PV and wind but also of biomass and other resources. Each region forms a regional grid for
optimizing power generation and consumption. This model may fit to growing calls for the age of local
autonomy today. Regional grids can never be energy-independent considering their different
characteristics, and therefore they must be interconnected via transmission lines to exchange electricalenergy. Large-scale power plants such as off-shore wind farms and traditional hydro and thermal
generator stations are also interconnected to the transmission systems, and regional grids and largescale power plants are coordinated to exchange electrical power at a higher level to achieve reduced
carbon emission.

Prospective Topics
The Regional Grid Concept proposed above gives us a framework for investigating optimized design andoperation of power grids. Prospective topics to be discussed are listed below.

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To create a design methodology of a regional grid for a designated region is an important topic. By
definition, the optimized form of a regional grid for a designated region must be unique. However, itis also true that we can classify cities, suburbs, villages and so on into some categories. If design
patterns for those categories are established, we can efficiently design a regional grid. Carbonemission, initial costs and running costs may be minimized in the design process.
After designing a regional grid for a certain region, to create an operation methodology for that
regional grid is an important topic. We may use the categorization strategy in the same way as thedesign stage. If operation patterns for those categories are established, we can efficiently operate aregional grid. Carbon emission and running costs may be minimized in the operation process.
At the highest level, different regional grids and large-scale power plants are interconnected througha transmission network, and electrical energy is exchanged. This highest-level exchange must becoordinated and optimized to minimize carbon emission, initial costs especially for transmission
lines and large-scale power plants, and running costs. An operation methodology is required to beestablished for this highest-level energy exchange.
Resilience of the power grid is also an important topic especially for countries like Japan which often
suffer from disasters. To enhance resilience of a regional grid, we have to change its design andoperation. This means that we have to incorporate resilience, in addition to carbon emission, initialcosts and running costs, in the process of the design and operation optimization.
At this moment, we do not have an optimization methodology which is able to consider all small
electrical loads such as your computer or tablet in front of you to read this article and small PV power
generation systems such as the one on top of the roof of your house in order to obtain a total optimized
solution of the entire power grid. Therefore, we have to divide the large and complicated power system
into layers and apply an optimization method to each layer. The Regional Grid Concept is one way toassume layers to help us create optimized design and operation methodologies. In view of this point,
another way to structure power grids should be proposed and discussed, since the ultimate goal is toachieve reduced carbon emission.

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