HVDC transmission for renewable energy
One limitation of renewable sources of energy is that they are often best captured in places far from where energy is used: remote bays with large tides, desert areas with bright and constant sun, and windswept ridges. In these cases, losses associated with transmitting the power over standard alternating current (AC) power lines can lead to very significant losses.
This is where high voltage direct current (HVDC) transmission lines come in. Originally developed in the 1930s, HVDC technology is only really suited to long-range transmission. This is because of the static inverters that must be used to convert the energy to DC for transmission. These are expensive devices, both in terms of capital cost and energy losses. With contemporary HVDC technology, energy losses can be kept to about 3% per 1000km. This makes the connection of remote generating centres much more feasible.
HVDC has another advantage: it can be used as a link between AC systems that are out of sync with each other. This could be different national grids running on different frequencies; it could be different grids on the same frequency with different timing; finally, it could be the multiple unsynchronized AC currents produced by something like a field of wind turbines.
Building national and international HVDC backbones is probably necessary to achieve the full potential of renewable energy. Because of their ability to stem losses, they can play a vital role in load balancing. With truly comprehensive systems, wind power from the west coast of Vancouver Island could compensate when the sun in Arizona isn’t shining. Likewise, offshore turbines in Scotland could complement solar panels in Italy and hydroelectric dams in Norway. With some storage capacity and a sufficient diversity of sources, renewables could provide all the electricity we use - including quantities sufficient for electric vehicles, which could be charged at times when demand for other things is low.
With further technological improvements, the cost of static inverters can probably be reduced. So too, perhaps, the per-kilometre energy losses. All told, investing in research on such renewable-facilitating technologies seems a lot more sensible than gambling on the eventual existence of ‘clean’ coal.
January 7th, 2008 at 11:45 am
At what range does it become more energy efficient to use HVDC?
Also, at what range does it make more sense to use electricity to produce hydrogen and then ship that? Does it make a difference if the energy source is located offshore?
January 8th, 2008 at 1:02 am
The phenomenon which makes AC transmission inefficient is particularly interesting. I can find wikipedia articles on inductance, and on AC transmission loses, but no proper discussion of how inductance operates in an AC circuit.
January 9th, 2008 at 4:12 pm
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April 29th, 2008 at 9:46 am
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Apr 28th 2008
From Economist.com
Harvesting the breeze is trickier than it sounds
Transmission is expensive and often an afterthought, at least for consumers. Even within windy areas the generators are often scattered across wide expanses, which makes gathering it and bringing it to market difficult. Rob Gramlich of the American Wind Energy Association calls transmission the industry’s “biggest long-term barrier”.
June 25th, 2008 at 7:58 am
[...] will be the relative efficiency of differently sized facilities, the rate at which low-loss high voltage direct current (HVDC) transmission emerges, and the rate at which financing options for small facilities [...]
June 27th, 2008 at 12:24 pm
[P]eople do not necessarily live where the wind blows. Indeed, they often avoid living in such places. Solving these problems, though, is a task not for the mechanical engineers who build the turbines but for the electrical engineers who link them to places where power is wanted. That means electricity grids are about to become bigger and smarter.
Bigger means transcontinental, at least for people like Vinod Khosla. His analogy is America’s interstate highway system, built after the second world war. The new grids would use direct, rather than alternating, current. AC was adopted as standard over a century ago, when the electrical world was rather different. But DC is better suited to transporting power over long distances. Less power is lost, even on land. And DC cables can also be laid on the seabed (the presence of all that water would dissipate an AC current very quickly). In the right geographical circumstances that eliminates both the difficulty of obtaining wayleaves to cross private land and the not-in-my-backyard objections that power lines are ugly. Indeed, there is already a plan to use underwater cables to ship wind power from Maine to Boston in this way.
July 19th, 2008 at 7:52 am
[...] capture and storage necessary. Then, there are those who assert that with more efficiency and a better grid, we can move to a renewable-dominated grid within the next few [...]