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I was wondering if we changed the way we transmitted electricity from high voltage to high current, wouldn't that make it easier to bury the lines underground thereby mitigating the objection to spoiling the scenery for the new eco-power plants that will be constructed? The Sunrise Powerlink project for San Diego Gas & Electric is having a tough time with this aspect of the project. This is a real shame because I think the Sterling Energy System is the best technology out there. -- Terry B., Paso Robles, California
Terry, Many people believe correctly that burying power lines solves lots of problems like the icing of powerlines and the avoidance of falling tree limbs on windy days that knock down lines. On the other hand, buried power lines make them more susceptable to damage from floods, earthquakes mudslides and can limit how quickly they can be repaired.
But the real limiting factor is that the cost of ditching and burying lines can be more than US $10 per foot. In fact, the state Public Service Commission staff found that burying Louisiana's utility lines to protect them from hurricane-force winds could cost $70 billion — far too much for the state's 2 million electricity customers to pay. Plans to go underground often hit a brick wall nationally, because burying existing overhead power lines costs about 10-15 times more than stringing them from poles.
Washington State's Puget Sound Energy has about 50 percent of the 20,000 miles of power lines underground — about 20 percent for Seattle City Light, mostly in downtown, the University District and about 40 percent of lines in Snohomish County's Public Utility District are underground. PSE may also use other approaches, such as installing more "tree wire," a cable with a coating that makes it more resilient during a storm.
In Florida and North Carolina, statewide initiatives to bury power lines would have prompted a rate increase of 80 to 125 percent, according to a report by the Edison Electric Institute, the utility industry trade group.
All of that said, the national trend in cities is to bury lines when the city's infrastructure is being upgraded. Now that billions from the just-passed Stimulus package will be going into upgrading infrastructure, you will probbaly see smarter grids that are buried, at least in cities.
Scott Sklar of the Washington, DC-based, The Stella Group, Ltd. which is a strategic marketing and policy firm for clean distributed energy users and companies. Sklar was also appointed in April 2007 to the National Advisory Council for Environmental Policy & Technology (NACEPT) of the United States Environmental Protection Agency (EPA) and is Chair of the Steering Committee of the Sustainable Energy Coalition. He also serves on several clean energy national non-profit Boards of Directors.
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Europe has several years of history for underground 500 kv lines. Underground is more expensive but works just fine. A company that does it applied to install Sunrise but was turned it down, as their proposal was not timely. Power lines that size are paid for by the entire customer base in California so monthly cost to the ratepayers is small and distributed over years. Estimates are three times the cost for underground as overhead.
The Stirling Engine is not a proven technology on a large scale. Tracking the sun is not keeping a focus on the Stirling head and unless it's dead center on target the heat will melt the outer edge of the focal bar. The tracking devise for large solar arrays is not cost effective in today's' market.
Unfortunately the private sector is not installing sufficient solar or energy efficiency to show effective savings or generation where the demand is. That creates fuel for the utilities to fetch all the energy they can, based on California laws specifically the RPS (Renewable Portfolio Standard). And indeed that includes moving Sempra's energy from its' power plants in Mexico, Arizona and California into or out of the California market. SDG&E said using the line exclusively for renewables is not practical and I agree. At the same time Sempra, the parent company of SDG&E, will sell their natural gas to the generators all along the line. So far we were able to preserve the Anza Borrego State Park from a blight that would be there long after the line is needed. Now it's time to do in basin solar rooftops and seriously do energy efficiency.
Dan Perkins
I think that poster #1 has it right- power lost as heat due to resistance is I^2*R, so you'll lose a lot of power as heat if you use high current transmission lines.
But I still don't understand why high current is better than high voltage for the purpose of burying them!
Solar Stirling engines are very cost competitive with 31% efficiency. SES, Inc. just finished its 500 MWe Stirling installation just east of San Diego with a contract price of $0.06/kw-hr to SDG & E. They are now building another 300 MWe installation for SDG&E in Imperial county at the same contract price. They are also building 500 MWe installation east of L.A. at $0.06/kw-hr contract price.
Imperial Valley around El Centro is excellent for solar. Our group is considering building in that area for a 24/7 solar-hydrogen power plant (500 MWe). I have been at the intended site in El Centro area and it is excelleint for solar.
Al:
Need to add one more disadvantage to overhead power lines: Fires !
A recent report (20 March) by SDG & E has shown that 17 fires have been caused by lightning strikes of overhead power lines over the past 5 years in So. California. A total of $1.5 billion in homes have been burned.
Warren
The answer for burried cables is ultimately HTSC (high temperature super conductors) but they're not quite there yet, particularly for long haul lines, I think the logest currently installed is about a mile. They are generally based around copper oxides and use about 1% of the volume of material of copper cables (for the same current density) of which only a portion is copper, and for some types of HTSCs the other ingredients are more abundant and cheaper than copper, so when we crack the manufacturing problems HTSCs could end up cheaper.
The real problem with burying transmission lines is heat. When you bury a high capacity line it gets hot. Real hot. The ground acts like a thermal insulator. Oil must be pumped through the protective steel casing to cool the conductors. On high load days an uncooled, buried transmission line can burn through. Very nasty.
This is not usually the case with 15kV distribution lines, although I have seen it happen where cables get kinked or pinched.
FYI, a 36", steel jacketed bore, for 9, 6" conduits will cost up to $750/lineal foot. Cost is a factor.
Let us see: $1.5 billion in homes destroyed divided by the $750/foot cost for steel jacketed buried power lines = 378.9 miles. The lawsuits that SDG & E are facing will more than have paid for their 130 mile Sunrise grid tower link.
One would not use steel jacketed cables anyway due to rust. It is far cheaper to use PVC jacketed Teflon coated power lines under ground at
$280/foot. The constant underground temperature of 55 deg. F certainly would aid any thermal heating of the power lines with proper thermal fins.
For now construction, High Voltage DC seems to be the next generation of technology.
There are two instances steel jackets are used.
1. For distribution voltage of 15kV or less: Steel jacketed conduits are used when cable are placed under highways, canals, or railroads. This is to prevent undermining the overlying structure with weak plastic conduits. In the $750/lf case discussed above, (12) 6" PVC conduits are placed in spacers and slid into the steel jacket. Once in place, the jacket, with the PVC conduits in place, is filled with grout. Grouting provides better heat transfer and strength under crossings. Any type of wire can be placed in the conduits.
2. Underground 250kV or higher transmission cables are place in a schedule 40 steel pipe. Oil is circulated through the pipe to keep the cable cool. Any type of wire can be placed in the conduits.
Burying cable will prevent damage from wind and ice. It will not prevent damage from lightning strikes, water, or solar flare activity.
Lightning regularly penetrates the ground, striking u/g utilities. This is why grounding wires are run along with power cables both above and below the ground.
Water: Properly sheathed cables stand in water for decades without damage. Damage normally occurs when transformers and switchgear get wet. These are placed underground in urban environments regularly. However, doing so increases the risk of flooding a transformer. This usually happens when someone breaks a water main nearby.
Solar activity: The earth's magnetic field PENETRATES the Earth. The cables are in the earth. Need I say more?
I've been designing underground electric utilities for years.
It's better to ask questions and learn.
Where is this 500MWe SES installation east of San Diego? And where is the construction of the 300MWe facility in Imperial County taking place exactly? I think you are confusing proposed projects with actual installations. The CPUC has not even approved these projects. Currently Southern Cal Edison has a contract with SES for a 500MWe system, and with SDG&E for a 300MWe system, but that is all. There is no large scale SES system anywhere.
Also, the SES system might be very efficient (although this data is based on a single dish in the high desert in NM), but you need to factor in the cost of building the transmission line, line loss, and the environmental cost of both projects. There are better ways to get renewable energy without so much destruction to the environment. We are destroying the planet in order to save it.
I realize that there are lawsuits pending in San Diego. Are there any other class action suits against the power companies and what is the status of these suits?
I realize that there are also threats caused by burying the power lines, but maybe these could be worked out. Also consider what is the greatest public health hazard and what should be done about it.
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