by Nookster » Sat 06 Dec 2008, 17:18:36
While the mass media tells us to replace our incandescent bulbs with compact fluorescent bulbs, they fail to address the bigger issues.
First, compact fluorescent bulbs only save energy when used in locations that are warm enough that you wouldn't otherwise heat them. If you're in a location where it's cold and you're going to be running the heat anyway, there is no efficiency advantage because the waste heat from incandescent bulbs isn't waste in that situation, it's heat that displaces heat that would have had to been created in some other manner.
Second, the amount of energy lost in the electrical transmission system is approximately 17% of that generated and is roughly equal to all of the oil the US imports.
That loss could be reduced to around 2-3% by converting every long distance transmission line 300 kilometers or longer to DC transmission. Most of the loss in AC transmission lines are caused by radiation which also has negative health impacts for those near the lines. DC transmission eliminates radiation, the loss of energy associated with it, and the health issues caused by it.
Copper losses (resistive or IR losses) are also reduced by DC transmission because the skin effect, a condition where the AC magnetic field forces the current to flow only near the surface of the wire, effectively reducing the cross-section of the conductor and increasing resistance, is eliminated in DC transmission allowing the full conductor cross section to be eliminated.
An additional factor is phase shift in the transmission lines changing with load. When lines are heavily loaded, the AC phase relationship at the destination changes and causes current to flow between generating sources without ever going through the load, this energy is lost. DC transmission eliminates the phase issue because the converter equipment takes care of phasing when the DC is converted back into AC.
Converting to DC also increases line capacity through several factors. First, the peak AC voltage is 1.414 times the average RMS voltage, insulators must be designed to withstand this peak voltage. This means, for the same insulators, DC can be run at 1.414x the AC RMS value, this is a 1.414 times improvement in capacity.
Second, because the full cross-section of the conductor can be used, higher currents can be transmitted. Lastly, because sag induced phase shift is no longer an issue, higher currents can be transmitted. The sum of all of these factors approximately doubles the capacity.
DC transmission lines don't suffer the cascading failure mode of AC lines because load does not affect line frequency, and output voltage can be adjusted by the conversion equipment. Thus load shedding to maintain frequency is no longer required.
DC lines are immune to space weather, because low frequency induced voltages don't fry AC transformers at the far end that have a low impedance to those low frequency DC currents. Instead it only slightly adds or subtracts from the DC voltage and that is adjusted for in real time by the conversion electronics.
DC long distance transmission lines make much longer distances practical because of their lower loss. This makes east-west grid ties practical and that in turn would allow us to distribute the regional peak loads, and peak production capacities of renewable sources, across the country.
Although the capital costs of such a conversion nation wide would be high, they would be nothing compared to the 1-2 trillion a year we are spending on imported oil and by enabling greater use of geographical diversity, alternative sources like wind and solar become much more practical.
I'm not saying down with compact fluorescent lights, I use them, but I am saying let's make the big investments where they can make the big difference.
Modernizing the national power grid would make a HUGE difference in our carbon foot print, and while it's initially expensive, the payback is forever. That is, once we make these capital investments, we'll continue getting that energy that was previously lost year after year after year, saving 1-2 trillion a year every year, forever.
