Sonntag, 8. November 2015

Intercontinental Energy Grid

The Vision of China State Grid

The energy production in the future will be based on wind an solar power. Even in a carbon-rich power production country, like China, there is no doubt about this long-term development.
At the Dii conference 2015 in Dubai, I learned in the presentation given by Han Jun, Senior Vice President, State Grid Company of China, that a global energy grid can solve the problem of intermittent power production.
State Grid China, the vision of a global electricity balance

  Is a global grid possible

The idea, to have a global grid is simple, but the physical hurdles are hard to overcome. The best solution would be, we take a high-temperature superconductor and span the globe with this type of grid. The only remaining problem is, we don't have the technology, and although "high-temperature superconductor" (Working at -130°C not high in everyday experience) have been discovered 1986 by Georg Bednorz and K. Alex Müller at the IBM laboratory. Till today it was not possible to construct a power line on the base of this very brittle material.

Knowing this, the only path, in reality, is the use of high voltage direct current connections. And it has been shown by Chinese engineering, that the power connection between the three gorges dam and the 2,600 km distant city of Shanghai works to transport 7.2 GW of electricity.

Knowing this, we can try to calculate the necessary equipment to transport the power of wind and solar energy around the globe by conventional technology. 

How much power?

The first question concerns the amount of power that has to be delivered to far apart regions and continents. Today, a conventional power fleet of 5300 GW produces electricity where the consumers live. In a renewable future, this will still be true in some part for solar and wind, but it might be necessary to transmit 10% over very far distances. This would require a power line, able to transport about 600 GW and with a length of 10,000 km. 

These assumptions are very rough, but it is helpful to start with a plausible range, additional demands are then simple multiplications of the result. If we assume that the power line has a voltage of one million Volts, the current through this line is 600,000 Ampere and we don't want to lose more than 20% of the energy within the line. 

With these assumptions, the resistance of the line has to be in the range of R=U/I = 200kV/600kA = 0,3 Ohm. Knowing this, we can lookup in the table of material properties the necessary material demand. Only cooper and aluminum seem to be sufficient, aluminum is much cheaper, so we take aluminum. The electrical resistance of aluminum is 28.2 nΩ·m. The diameter of the 10,000,000 m wire has therefor 1 m², quite thick, but able to transport a significant amount of our global electricity demand on an intercontinental distance.
Sources of electricity in the year 2050, estimated by China State Grid.

How expensive is that cable?

To get an idea of the price, we have to know the raw material price of aluminum. At the moment, aluminum sells for 2000 $/t, with limited deviations from that value. Our power line needs 27.000.000 tons of aluminum because the density is 2700kg/m³. The price tag is 14 G$, not that bad if we consider the impact on the global power supply.
A real cable will be at last ten times as expensive as this first assumption because we have to include an isolation, that can keep one million Volt, but even a price of 140 Billion $ is small compared to the equipment, that is necessary to produce the power.

To produce 600 GW of power, even the cheapest wind power converter at the best suitable places around the arctic circle would cost 600 Billion $.

Impact of a global Grid

A global grid would be a tremendous step to a reliable energy supply. We can compare the solution with the alternative path of large-scale storage. The necessary storage for 600 GW over 10 hours needs a capacity of 6000 GWh. This could be done by ultra-cheap Lithium Batteries with a price tag of 300$/kWh or 1,800 Billion $ for the required amount. Using the Hydraulic Rock Storage HRS technology, the price could be reduced to 600 G$.

A global grid would use the oceans to wire the continents. The ocean floors are a relatively safe place to wire the world, as we already know from the internet fiber optic cables. Another advantage is the international law, the floor of the ocean is not under the same dispute as for the land surface and it seems much easier to get a permit to roll out the cables there.

When a country like China takes the lead to interconnect the continents with electric cables, this would change the way, we think about the local generation of power. But keep in mind, today, our energy supply system is intercontinental over the ocean, the supertankers distribute comparable amounts of energy over the ocean. 

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