Super Grid, Smart Grid, Renewable Energy Sources, Distributed Generation and other fashion concepts can be astonishing when they are put together and not clearly harmonized. In fact they only apparently, but not really, imply opposite visions of the future power system.
Distributed Generation (DG) has been associated, at first, with a “small scale” concept of the power system, mainly with a local perspective (“small is beautiful”) and thus calling for advanced network automation necessary to maintain and possibly enhance power quality standards. In general, new automation in the system is generally labelled with the widely inflated term of Smart Grids. On the other hand, the overall scenario of a progressive decarbonisation of the electric energy sector, together with the intrinsic uncertainty and unpredictability of power generation from Renewable Energy Sources (RES), enforces once again the need for strong “large scale” interconnections (“large is necessary”). The small scale concept is then now associated to a large scale concept applied to continental and also inter-continental scenarios, thus introducing the idea of Super Grid. The Super Grid, being just a consequence of the “single bus” (“no network”) ideal target, cannot avoid to be also a Smart Grid, in the sense that it has necessarily to implement all the state-of art functional and technological solutions to face operational uncertainties and to share at best common information.
In other words, the best exploitation of a large set of local distribution networks requires their strong interconnection on the widest possible scale, in order to overcome the fluctuation of small scale power generation from renewables and to share at the best control features, like power reserves. Furthermore, the geopolitical security of the energy sources makes this interconnection strategically needed, in order to diversify possible sources and to assure common reliability levels. Security of supply is indeed one of the three pillars declared by the European Commission, together with sustainability and competitiveness.
The ideal least risk(y) electric system is the one that enables to exploit all possible power/energy sources, of any kind and wherever they are located. Therefore, “small is beautiful” only when it is part of a “necessarily large” interconnected system, capable to harmonize the characteristics of each power system resource, through smart actions coordinated accordingly a unique super grid vision.
From a mere technological point of view, smart local distribution networks, including renewable energy sources, and super grid, implementing smart control paradigms, can easily coexist. On one side, distribution networks can be designed and operated, at some extent, decoupled each from the other and from the superimposed transmission system, but exploiting the advantages of the overall interconnection. On the other side, the super grid infrastructure can rely on the performances of each transmission and distribution subnet, if all of them are well coordinated according to smart grid concept. This is just the main issue: “to get the maximum from both decoupling and coupling”.
Super Grid can be seen as a further layer, mostly in DC, superimposed to the present AC transmission systems, but it has two different scopes:
to enhance the already existing interconnection between present transmission systems, enabling a much more powerful and free exchange of power among national transmission systems without (or at least reducing to a minimum) any technical constraints;
to enable further interconnections on a wider geographical scale, overriding the technological constraints that prevented the traditional transmission systems from being realized in the past and preventing some possible drawback of very large grids.
Technologies to make Super Grid actual and working correctly are becoming available now, based mainly on power electronics (HVDC, FACTS), with associated advanced control and protection systems. Large power corridors across sea and large countries are feasible today, under certain conditions (e.g.: appropriated seabed morphology, possibility of building across the territory overhead UHVDC lines, etc.) and they are environmentally sustainable and progressively economically affordable: the cost of transmission is in general of a lower order of magnitude when compared to the cost of energy production.
However, some further challenges still remain: first of all, the security of a Super Grid spanning over countries around Europe that might not be politically stable. In addition, the way and the cost of making such a Super Grid secure versus possible attacks, which has still to be well defined. In order to fully benefit from Super Grids, a better integration of Planning and Operational Rules of transmission and distribution systems is therefore necessary: the National Grid Codes have to be harmonized and even the operation rules of distribution systems beneath have to be reconsidered. As a consequence, the standardization and regulation bodies will play a fundamental role at this concern.
Just like the World Wide Web (www), commonly known as the "information superhighway", the World Wide Power System (wwps), just accordingly to the “single bus - no network” ideal target, will tend to be a unique interconnected system, requiring also superimposed rules and standards specifically addressed to the Super Grid concept. However the flexibility and security of each transmission and distribution subsystem has to be kept as far as possible, just by means of Smart Grid paradigms: unlike the web, in fact, the physical infrastructure of a power system has huge costs and long life times, as well as it cannot be changed in relatively short times.
Therefore the best balance between the need for merging and harmonization, on one side, and for present assets (physical infrastructure) preservation, on the other side, is really a big challenge. .