Much as been written about microgrids recently, suggesting that, more and more, the electric grid's distribution system will become more isolated and self-reliant.

However, less is written about the grid's transmission system—the high-power lines that shuttle power from generation sources to the nation's distribution networks. Not much has changed in the transmission network for decades. However, that may be about to change with a new concept called "supergrids."

Navigant Research, in a new report on supergrids, notes that, "With total demand for electricity growing on a global basis, and concerns over climate change mounting, significant attention is focused on how best to meet electricity needs, while reducing the environmental and economic costs of power production and delivery."

The report goes on to note that much of the conversation centers on decentralized solutions but that a powerful case also exists for transforming the electric power sector in the opposite direction, through a carefully planned network of high-voltage transmission systems that span countries, continents, and eventually the world, enabling the integration of renewable power on a bulk scale.

Such large-scale, coordinated "supergrids" would allow high-volume electricity trade across long distances, and would also facilitate development of renewables where the resource potential is the strongest, rather than where it is most convenient.

The technology behind supergrids is high-voltage direct current (HVDC), rather than the traditional high-voltage alternating current (HVAC). The reason for the appeal of HVDC is that less energy is lost on DC lines as the energy is transmitted over the miles. In addition, there is no need for "reactive compensation" along the lines. The reason is that DC power flows steadily through wires without changing direction many times each second, as is the case with AC.

A recent article in The Economist notes that the potential for HVDC is significant: "Fossils fuels can be carried to power stations far from mines and wells, if necessary, but where wind, solar and hydroelectric power are generated is not negotiable. And even though fossil fuels can be moved, doing so is not desirable. Coal, in particular, is costly to transport. It is better to burn it at the pithead and transport the electricity thus generated instead."

Current growth of HVDC and supergrids is slow, though, and will likely to be that way for at least the next few years. For example, Navigant projects that global supergrid investments are expected to increase from $8.3 billion in 2016 to only $10.2 billion by the end of 2025.

Why not faster growth? According to Navigant's report, "supergrid development is complicated by the need for strong political support, regulatory coordination, and capital mobilization, affecting the pace of development and market growth."

"The HVDC projects we're seeing now tend to be one-off projects, as opposed to carefully-planned networks of projects," said Jessica Lewis, a senior research analyst who worked on the Navigant report. "But, with time and additional investment, they could eventually mesh into a network that functions like a supergrid."

At this point, HVDC and supergrid projects are gaining more headway internationally than domestically. Plans for HVDC projects have been underway in Europe since 2009, and in 2011, plans for the Asia Supergrid project were laid out, with China, Russia, Mongolia, Japan, and South Korea planning a supergrid to connect these nations. The goal of the project is to find a way to shuttle wind energy from Mongolia, coal from southwest China, and hydropower from Russia to urban areas in the five countries, where the need exists.

In the United States, one company, Clean Line Energy Partners, is ready to begin construction on, or is in the final stage of licensing, five transmission projects, four of which are HVDC projects, designed to move wind energy from the Great Plains and Southern Plains to points farther east.

Overall, according to Lewis, supergrids will most likely emerge gradually in a series of projects, and these will likely take decades.