Carbon Footprint question?

Question

Stanwell is the most northerly major power station in Queensland. If it provides one MW of electrical power at 220V to consumers in Cairns (approx 1400 km away) what is an estimate of the additional power that is dissipated in the supply grid? Also, what is the carbon footprint of this loss in one year?

Answer 1

Need a lot more detailed info to estimate transmission losses.

Also need more info to estimate carbon footprint, such as type of plant.

.

Answer 2

After making a bunch of assumptions, I'd put the upper limit of the power lost at about 3000kW.  That's about 0.3% of the total power delivered and is much lower than typical for a transmission line which can be as high as 10% due to much high power being delivered.

To answer your question though:  3000 kW in power losses over a year translates to about 26,280,000 kg of CO2.  The earth's atmosphere weighs 201 billion times more than that (it weighs 5.3*10^18 kgs).  

The loses for a high voltage transmission line are due to both Corona discharge (Corona Loss) and Joule Heating due to resistance (current squared times the resistance).  There is also radiation loss, but I'll assume they are negligiable at 50Hz for 4 Amps on the Transmission Line.

Here are some givens and assumptions:

1) Given that Stanwell is a coal fired plant capable of 1.4MW and uses 275kV transmission line voltage

( http://stanwellenergy.com/frame.asp?Cont... )

2) Given that 1kWh from a coal fired plant represents about 1kg of CO2 (http://www.eia.doe.gov/cneaf/electricity...

3) Assume there is one 3-phase circuit in the transmission line made of #6AWG Aluminum (Al is 30% lighter than Cu which lends itself to fewer towers, but has a 60% higher resistivity – it's slightly cheaper too)

4) Given that #6 AWG wire has a cross section of approximately 12 square mm

5) Given that the resistivity of Al is 2.65*10^-8 Ohm-m.  Combined with the given in line 4 above, the resitance of one line of the 3-phase transmission line is about 3091 Ohms and the total resistance of the three phase bundle is about 1000 Ohms  {2.65E-8 Ohm-m * 1400km / (12 (mm^2)) = 3091}.

6) Given that Corona Loss is approximately 1-2kW/km for a 500kV 3-phase bundle.  The total corona loss over the entire line will be less than 2800 kW since 275kV is less than 500kV and corona loss decreases with decreasing voltage.  Corona Loss is independent of load.  You'd still have this loss even with no current flowing in the transmission line.

( http://www.aset.ab.ca/pdfs/techarts/arti... )

7) Assume there is only 70% load and the power delivered to the transmission line is only 1MW (not 1.4MW).  At 250,000V the current flowing in the 3 phase bundle is 1MW/275kV = 3.6A or about 4A.

8) A current of 4A into 1000 Ohms gives a power loss to Joule Heating of 4^2*1000 = 16kW which is much smaller than the Corona Loss.

In the future, there may be even better power savings with transmission lines.  For example, in NY there has just been a new success (April 2008) with the worlds first High Temperature Superconducting cable. It runs on the Long Island Power Authority's Holbrook Transmission Right of Way.

It provides 574MegaWatts of power to about 300,000 homes. It's a 2000 foot long cable cooled with liquid nitrogen in a closed loop system. A small fraction of the power is used to cool and pump the nitrogen alongside the cable and back.  The voltage is 138,000V.

HTS cables conduct electricity with virtually no electrical losses, meaning more of the power generated at power plants gets to customers. Conventional power grids typically lose seven to 10 percent of power due to the inherent electrical resistance experienced with copper wires. The higher electrical efficiency of HTS cables provides a means to reduce carbon emissions while meeting the growing demand for electric power in the digital age.

The physical phenomenon is pretty neat. Usually loss is from interactions of electrons with atoms in the periodic structure of the metal. In the superconducting state, electrons pair up and essentially are guided through the lattice between atoms. There are no interactions. The resistance to electrical current is basically zero.  The voltage can be lower and result in lower corona losses.