Saturday, November 01, 2008
HVDC or high-voltage, direct current electric power transmission systems contrast with the more common alternating current systems as a means for the bulk transmission of electrical power.....Depending on voltage level and construction details, losses are quoted as about 3% per 1000 km. High-voltage direct current transmission allows efficient use of energy sources remote from load centers....Long undersea cables have a high capacitance. While this has minimal effect for DC transmission, the current required to charge and discharge the capacitance of the cable causes additional I2R power losses when the cable is carrying AC.....The disadvantages of HVDC are in conversion, switching and control. The required static inverters are expensive and have limited overload capacity. At smaller transmission distances the losses in the static inverters may be bigger than in an AC transmission line
Just as the national grid put together in the 1930s allowed major efficiencies in electricity distribution & increased supply & lower cost without a comparable increase in generating capacity the formation of an international grid, based on HVDC would do the same for the world.
Bearing in mind that so much of the cost is on the transformers it is quite surprising that most of the systems currently in use are about 100 km but looking at the list it is clear why - with the exceptions of a few in Scandinavia, links between France & its neighbours & a 1700km link between Mozambique & South Africa they are virtually all within a single country. By comparison if there were a line running round the world in the northern hemisphere, which would be about 25,000 km 3% losses would still mean that 70% of the power would reach the other side of the world. Compare this with the fact that within Scotland we lose 8% of our power to transmission losses while the pumped storage we already use returns only 75%.
The unit cost of the electric power, transmitted by d.c, shows only small increases when increasing transmission distance: for every additional 1000 km the increase is of the order of 0.15 to 0.26 kWh for transmission of 10 GW and 2.5 GW respectively.
How to get there from here: I suggest the setting up of an International Electricity Transmission Organisation like the International Civil Aviation Organisation a body authorised by the UN but controlled by professionals which "codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport." Such a body would monitor common standards, negotiate usual charges for transmission of power, act as moderator in disputes & negotiation & monitor that what was said to be being put into the grid actually was. Clearly the fact that there are so few international lines, while air travel works efficiently, means that not having such a moderator is a problem.
The world's longest current cable is 1700 km across Zaire - which is 300 more than from Glasgow to Moscow so it is clear that such a grid is technically feasible. More famously the 3 Gorges dam's power is transferred from upland China 890 km to Guandong province which is beside & nearly as economically free as Hong Kong (& growing at about 20%)
Trade between nations in almost all goods is considered a good thing & relatively free trade has made us all wealthier. I have not been able to find prices of baseload electricity listed by nation but since price is determined by the point at which demand & supply meet & I have previously listed how much supply varies per unit of GNP (the UK needing 2.5 times more GNP per unit power than China) & assume price varies at least proportionately.
It may be argued that we would thus become dependent on Chinese or Russian electricity to produce our goods - but then of course we already are it is just that it is cheaper to produce them in China. If our homegrown electricity is grossly overpriced, which it is, not trading the stuff would not change but merely conceal the fact.
2 bonuses such a grid would produce:
Firstly there are many places where hydro power can be produced in great quantity (as with the Congo mentioned above which has 15 times as much water as flows through the Aswan dam) but where there is no economic demand. Northern Canada is full of lakes & run off from the Rockies & I am sure has capacity for many times what the Hoover dam produces, but very few locals to use it. The electricity produced by hydro is a multiple of the amount of water by the distance it falls & need have no close relationship to the cost of building it. We are regularly told that in Scotland we are set to be the "Saudi Arabia of Marine Power" from the Murray Firth & our northern coast. I have my doubts but if there is anything to it we should certainly make it easier to export the stuff. I have also seen "environmentalists" holding up long distance transmission as the reason we will not need nuclear to stop the lights going out.
Secondly, a bonus which is not just an expansion of the advantage of having a national grid is that in east/west transmission crosses time zones. The US, for example, has 4 time zones so that when demand is still at a peak at 10pm in one it is close to minimum at 2am across the country. This is of enormous use where the production is by nuclear reactors since they in particular produce constantly at a flat rate (coal is more efficient at a flat rate too though not so much so). Thus we could see Chinese coal power, produced at their midnight keeping the lights on in Europe & European nuclear returning the favour after our midnight.
If there were an international, minute by minute, spot market for electricity, probably hovering around 2.5p per kWh, all those with access to it would be much better off.
UPDATE Michael in comments has given this link http://www.terrawatts.com/ which contains a whole lot of articles on on various forms of international grid (ignore that they have a picture of Gore the rest of it is pretty good).
It is a global energy network and, like the internet, it will change our culture, society and how we do business. More importantly, it will alter how we use, transform and exchange energy.
Enough solar energy falls on the surface of the earth every 40 minutes to meet 100 percent of the entire world's energy needs for a full year.
There is no energy supply problem, there is an energy distribution problem -- and the emerging solution is a new world wide web of electricity.
For more information, see http://www.terrawatts.com
And yes one benefit of such a grid is solar power isn't limited by nightime.
I have also written on solar power satellites & on space industry - I would not be surprised if room temperature superconducters will turn out to be one of the materials that can be produced comparatively easily in a zero G environment.
Whether earth based solar, nuclear, space solar, or something left field like fusion is best doesn't matter so long as people are allowed to do something.