Supergrid Covering Europe, Africa, and Asia

Because Asia, Africa, and Europe are connected by land, it is very important that we pick a common voltage for the supergrid. As of today, no standard voltage has been agreed. Logically, the standard voltage should be selected to minimize the cost of the supergrid. This figure:

appears in several of my papers. The less costly is a metal per unit conductivity, the lower is the optimum voltage as well. These three curves show that 400kV to 600kV sodium-based conductors achieve the lowest cost for any conductor + insulator option. I have assumed for the plot above that we are comparing pipes with equal outside diameter, so that waste heat shedding is equal for the copper, aluminum, and sodium bus pipe conductors, and the conduit cost is also identical. At 10 GW and 1% resistive loss per 1000 km, a solid sodium conductor would be a circular cylinder 25.4 cm in diameter. As seen in the figure below, copper and aluminum pipes with equal conductivity are hollow pipes:

Sodium is scary to most everyone, so let me defend it here. Past mistakes were made by using long sodium-filled cables, directly inside an extruded plastic pipe. Let's face it: that's stupid. If sodium were used inside an extruded tube of copper or steel, it would be safer, but not as safe as what I propose: The sodium should be contained in strong metal shells. Inside these steel or Invar shells (in addition to the sodium) is a compressible bladder that compensates for the volume change upon melting (as in my patent applications). 

<above modified on 12/23/2013>

I believe that long distance underground power transmission is the "missing piece of the puzzle" on making non-dispatchable and/or remote non-fossil fueled energy generation practical. None of the current technologies are capable of transmitting the power levels that need to be moved around North America or Europe to implement the supergrid. At present, the highest energy carrying capacity in a single line is 7.2 GW (one of the two recent 800kV HVDC projects in China). My conversations with ABB indicate that they think this can be stretched to perhaps 9 GW/line maximum for an overhead 800kV DC line, which is not nearly enough capacity to serve central Europe with offshore wind from the North Sea (as proposed by Friends of the Supergrid, or Airtricity) or by solar power from Northern Africa (as proposed by the DESERTEC consortium, http://www.desertec.org/) according to the number of transmission lines shown on these organizations' websites. Furthermore, constructing multiple overhead 9 GW lines into Central Europe is not politically feasible. By contrast, US DOE's National Renewable Energy Laboratory's EWITS wind integration proposal is at least honest in proposing seven large 800kV DC lines fom the Great Plains to the Eastern Seaboard to move Midwestern wind energy to the East coast. Even EWITS does not enable sufficient sharing of resources throughout the Eastern US to even out wind energy availability over the entire Eastern US, as is necessary to reduce variability of wind energy enough to allow it to become reliable enough in aggregate to supply most of the region's electricity.

Both FOSG and DESERTEC show plans that imply much higher power transfer levels in the trunk lines than 9 GW. What is needed to implement the schemes sketched out by both DESERTEC and FOSG is an underground HVDC line capable of carrying at least 30 GW per line, which is feasible for passively cooled elpipes. Tying Africa in strongly, as we all realize is desirable, can either be done with several 30-GW lines or a single 100 GW HVDC loop, in principle. (Actively cooled elpipes can go to > 200 GW with great economics of transmission, in principle; active rather than passive cooling would also allow elpipes to be buried deeply, as is desirable for security or in crossing rivers for example.)

During the question and answer session at the launch of FOSG (http://www.friendsofthesupergrid.eu/videos.aspx?videoID=14) Eddie O'Connor glossed over the intermittency problem, in the same way that Atlantic Wind Power LLC is doing on our side of the Atlantic. Yes, I agree that multiple wind farms spread the risk of being becalmed, therefore increasing aggregate reliability of wind power from the whole area, but one still needs balancing resources way beyond the hydro capacity of Norway and Scotland to implement the grand scheme proposed by FOSG (which I support). Though rare, the energy output even from a large, regionally aggregated area containing multiple wind farms will occasionally be as low as 10% of the average output. Is it acceptable to shut down Europe for a day?

I believe the low cost method to develop the needed balancing capacity is to extend the supergrid to tie in Siberian hydropower and various African resources, especially pumped storage based on sea water at Danakil, as discussed in my white paper on Africa, co-authored with noted energy blogger Harry Valentine (the Danakil concept came from Harry).

Underground HVDC transmission via elpipes: role in the supergrid:

My polymer-insulated elpipe technology isn't "sexy" like HTS (high temperature superconductors), but it will be easier to make reliable, and the production of the elpipes will generate more jobs than would an HTS electric pipeline with equal capacity. Unlike HTS, elpipes are inter-operable with HVDC technology at 500-800kV, and so fit into a future HVDC supergrid that has all types of HVDC transmission technologies (overhead, cables, gas insulated lines "GIL," and elpipes) operating at a common voltage; at present HTS cannot operate above 200kV DC. My technology represents an alternative to GIL (sulfur hexafluoride gas insulated lines), which have a different set of problems compared to elpipes. I do certainly admit that GIL is the main practical alternative to elpipes for underground HVDC connections carrying >5 GW. (At present the maximum capacity of cables is ~1.1 GW/cable pair).