The proposed high-voltage direct current, or DC, technology is tailored for smaller-scale power projects, such as those in rural parts of the state. The direct current technology could cut costs for building inter-village transmission lines by as much as 50 percent compared to the costs of building transmission lines with conventional AC, or alternating current, according to Earle Ausman, president of Polarconsult.

“The purpose of the technology is to reduce the cost of energy in rural Alaska by lowering the cost to connect communities and thus achieve economies of scale necessary to make local renewable energy resources economical to develop,” Ausman said.

Polarconsult and Princeton Power, a company founded by Princeton University scientists and located in the university campus, are developing a less expensive converter to transform electricity between AC current to DC current compared with AC-DC converters now on the market.

The design and testing of sub-assemblies of the prototype are complete and a demonstration module of the converter itself is now being assembled for testing at Princeton Power's lab. Ausman said Princeton Power has built a variety of AC and DC power converters for commercial and military applications using technology similar to that behind the prototype small-scale converter.

Development of a lower-cost converter has important implications for rural Alaska, Ausman said.

“The proposed HVDC system has the potential to reduce the construction cost of power interties in rural Alaska by up to 50 percent. This will make many more interties economically viable, enabling many rural communities to share in the development of local energy projects, such as hydro, geothermal and wind, thus enjoying less costly and more reliable power,” Ausman said.

It has long been known that DC power transmission holds significant technical advantages over AC transmission. The major impediment for DC power transmission in rural Alaska has always been the high cost and excessive capacity of converters that are available.

Alaska Village Electric Cooperative, a rural Alaska utility, estimates costs of an AC overland transmission line at $200,000 per mile. A study of a 191-mile, 70 MW AC line from Bethel to the planned Donlin Creek mine was estimated to be at least $681,000 per mile.

In contrast with an AC system, a DC system with a 100-mile DC transmission line and two 5 MW converters, is estimated to cost $100,000 per mile, Ausman said.

The problem for rural Alaska has been the cost of the AC-DC converter for small projects, but Princeton and Polarconsult have solved this problem, he said.

The two firms are now almost finished with phase one of the project, funded by the Denali Commission for $700,000. “Phase one focuses on demonstrating the technical and economic feasibility of the system, including design and testing of the converter technology” Ausman said.

If funds can be obtained, Polarconsult hopes to accomplish phase two this winter, a $2 million project to design, build and test the converter and transmission hardware, and would include winter testing of low-cost construction techniques for the transmission lines.

Phase three would demonstrate the system with a 25-mile intertie that would connect two lower Yukon River villages, Mountain Village and St. Mary's. Alaska Village Electric Cooperative, which operates utilities in both communities, is working with Polarconsult in development of the technology.

Construction of a conventional AC transmission line connecting the two villages would be about $7 million, making the project cost prohibitive, but the new HVDC system could be built for about $3.5 million, Ausman believes.

For years AVEC and the state's Alaska Energy Authority have looked for cost-effective ways to connect rural villages into regional power grids to allow for construction of larger, more efficient regional power plants.

“By making it less costly to connect villages together, the system can help reduce or eliminate redundant bulk fuel farms and small generating plants in nearby villages,” Ausman said.

Most villages in rural Alaska use diesel fuel in small generators to produce power. This is not very efficient because the power plants are small and each village must store over a year's supply of fuel to provide power.

“Larger, more efficient generators can be located in villages with the best bulk fuel tank farms, or the lowest delivered cost of fuel, to achieve the maximum cost savings for all connected villages,” he said.

Lower-cost transmission lines are also essential if renewable energy projects are to generate significant amounts of power in rural Alaska.

The best locations for wind, hydro or geothermal projects are usually not where a community is located, Ausman said.

If the transmission costs are reduced, regional renewable energy projects built at larger scales could serve several communities. A 1997 study identified 172 potential interties connecting rural villages, but the high costs of building the transmission lines has thwarted the efforts so far.

Joel Groves, manager of the HVDC project for Polarconsult, said the goal of the current project is to have a converter cost about $200,000. The closest competing system for AC/DC conversion costs about $4 million per converter, he said.

In a rural Alaska applications, like that proposed for Mountain Village to St. Mary's, two converters are needed, one at the power plant producing electricity to convert from AC to DC, and then a second converter at the end of the line to convert DC back to AC in the recipient community, Groves said.

One of the key advantages of DC power, however, is that a DC transmission line would be simpler and less expensive to construct than a transmission line built to carry AC current.

Transmission would cost less because only one wire is needed, which means towers can be lighter. The towers and lines can generally be installed with locally available equipment, Groves said. DC power can also be carried with a single cable on land, or under water, and much further without the high “line losses” of electricity that would be the case with AC current.

Submarine cables for the telecommunications industry, for example, use repeaters placed every 60 miles or so that are powered by DC current transmitted through the submarine cable.

Direct-current transmission of electricity has been in use for over 50 years, but mainly with very large-scale projects. “There are many HVDC systems in use. The Pacific Intertie transmits 3,100 Megawatts of power between the Columbia River region in Washington and Oregon and southern California,” Ausman said.

Another example is power transmitted from China's Three Gorges Dam to Shanghai, which similarly is done with an HVDC system. Quebec Hydro also uses high-voltage DC to connect with Canada's Maritime Provinces, as well as the Northeast U.S. power grid.

It is only in recent years that companies have focused on ways to do smaller-scale DC power transmission. ABB, for example, has developed a system it calls “HVDC Lite,” but even this is designed for systems much larger than needed sin rural Alaska, Groves said.

General Electric and Siemens are also active in the field. However, the larger companies have not been interested in very small, niche markets, such as rural Alaska, he said.

However, it might be possible to scale up the small Princeton Power converter for larger applications. The New Jersey company sees no technical reason why this couldn't be done, Groves said.