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.
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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?
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.
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Mission: Transmission
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”.
[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.
Scarcity of energy is a myth that persists in society, because our fixation remains on fossil fuels. Yet the resource potentials of solar, wind, hydro, geothermal, biomass and ocean energies are abundant far beyond our needs. The winds of the American plains are sufficient to power all the electrical demand of the United States, and solar radiation from just 3% of the world’s deserts could power all global demand. There is no shortage of renewable energy on our planet! While annual growth rates of 20-40% for geothermal, wind and solar are promising, their share of the energy pie remains less than 3%.
Critics state that renewable energies are intermittent—the sun isn’t always shining and the winds don’t always blow—and we need reliable electricity every second. The critical infrastructure that solves this is high-voltage transmission. The interconnected grid acts as the freeway for electricity from generator to user, and it is already built throughout the developed world. Today, bulk transmission can deliver power far beyond political boundaries, with over 100 nations trading electricity for mutual benefit. Interconnected grids enable load levelling, economic exchange of power, system reliability and emergency back-up options. Long-distance transmission allows us to tap remote renewable energy resources, sometimes located in neighbouring nations, and to feed clean electricity throughout the network.
Lifeline for Renewable Power
Without a radically expanded and smarter electrical grid, wind and solar will remain niche power sources.
By David Talbot
“Push through a bulletproof revolving door in a nondescript building in a dreary patch of the former East Berlin and you enter the control center for Vattenfall Europe Transmission, the company that controls northeastern Germany’s electrical grid. A monitor displaying a diagram of that grid takes up most of one wall. A series of smaller screens show the real-time output of regional wind turbines and the output that had been predicted the previous day. Germany is the world’s largest user of wind energy, with enough turbines to produce 22,250 megawatts of electricity. That’s roughly the equivalent of the output from 22 coal plants–enough to meet about 6 percent of Germany’s needs. And because Vattenfall’s service area produces 41 percent of German wind energy, the control room is a critical proving ground for the grid’s ability to handle renewable power.
Like all electrical grids, the one that Vattenfall manages must continually match power production to demand from homes, offices, and factories. The challenge is to maintain a stable power supply while incorporating electricity from a source as erratic as wind. If there’s too little wind-generated power, the company’s engineers might have to start up fossil-fueled power plants on short notice, an inefficient process. If there’s too much, it could overload the system, causing blackouts or forcing plants to shut down.”
Transmission lies
Against the so-called ‘need’ for new long-distance, high-voltage transmission lines
Posted by Guest author (Guest Contributor) at 1:31 PM on 03 Feb 2009
Planning for “peak load” is a transmission lie. Utilities have incentive to overstate “need” when they build for peaks. The higher the peak they build for (with peak occurring only several times annually), the deeper the off-peak valley and the more electricity they can sell on the market when generation is available but not “needed.” Conservation and peak-shaving is against their interest because it lowers peak and lessens the valley of market sales.
“It’s for renewable generation” is a lie. The massive transmission infrastructure expansion proposed is not “for renewables” because transmission may not discriminate by generation type. Federal regulations prohibit discrimination among generators — it’s first come, first ready, first served. There are tens of thousands of megawatts of coal projects, with transmission studies complete or in progress, waiting for interconnection, and whatever generation is ready will be connected. Another side of this lie is when wind advocates support transmission, claiming “it’s for renewables,” and ignore the impacts of transmission on the communities it traverses. Rather than make this convoluted “it’s for renewables” claim, there’s a better way: if renewable energy mandates were directly linked with shut down of fossil generation, and if renewable generators were thoughtfully sited, both the electricity market and transmission infrastructure would be open and available.
“Long distance transmission” is a lie. Transmission is inherently inefficient over long distances. Transmission physics entails high levels of line loss, and the longer the line, the higher the line loss. To avoid this fact of physics, the electric industry has shifted its line loss analysis for new projects to a “system wide” loss, so the numbers look low. But consider actual numbers of megawatts of line loss, and look at “coal plant equivalents” to make up that loss — for every 500-600 MW of line loss, a coal plant or more would have to be built! Line losses are charged in Federal Energy Regulatory Commission rates, but this is not considered directly in the market transactions. Line loss is an afterthought add-on to the customer’s bill after transmission service is provided. Consider too the capital cost of transmission, starting at about $1.5 million per mile for 345kV lines and upward from there
Spreading electricity
A gust of progress
Apr 30th 2009 | CHICAGO
From The Economist print edition
Creating windpower transmission in the Midwest
FRANKLIN ROOSEVELT helped bring electricity beyond America’s cities to its most distant farms. Barack Obama hopes the countryside will return the favour. Much of this challenge rests in the gusty upper Midwest. In recent years Interstates 29 and 80, highways of America’s heartland, have teemed with lorries bringing wind blades to new plants. Efforts to build transmission have moved more slowly. There are 300,000 megawatts of proposed wind projects waiting to connect to the electricity grid, says the American Wind Energy Association. Of these, 70,000 megawatts are in the upper Midwest.
Now action is at last replacing talk. Firms are proposing ambitious transmission lines across the plains. The region’s governors and regulators are mulling ways to help them. The federal government is playing its part. In February the stimulus package allotted $11 billion to modernise the grid. Since then members of Congress have proposed an array of bills to develop transmission. Jeff Bingaman, chairman of the Senate energy committee, intends to start marking up transmission plans next week—though debate over other parts of the energy bill may delay progress.
America’s grid is complex: 3,000 utilities, 500 transmission owners and 164,000 miles (264,000km) of high-voltage transmission lines are stretched across three “interconnections” in the east, west and Texas. If wind is to generate 20% of electricity by 2030, as in one scenario from the Department of Energy, about $60 billion must be spent on new transmission. Just as important, regulations must change.
HVDC is preferred over traditional high-voltage AC lines because less physical hardware is needed, less land area is needed, and the power losses of HVDC are smaller. The power losses on a 3500 km-long HVDC line, including conversion from AC to DC and back, would be about 15%. A further advantage of HVDC systems is that they help stabilize the electricity networks to which they are connected.
High-Temp Superconductors To Connect Power Grids
physburn writes “Somewhere in a triangle between Roswell (UFO) NM, Albuquerque (Left Turn) NM, and Amarillo (Do you know the way?) TX, a 22.5 square mile triangle of High Temperature Superconductor pipeline is to be built. Each leg of the triangle can carry 5GW of electricity. The purpose to load-balance and sell electricity between America’s three power grids. Previously the Eastern Grid, Western Grid and Texan Grid have been separate, preventing cheap electricity being sold from one end of America to the other. The Tres Amiga Superstation, as it is to be called, will finally connect the three grids. The superstation is also designed to link renewable solar and wind power in the grids, and is to use HTS wire from American Superconductor. Some 23 years after its invention, today HTS comes of age. “