Electricity has to be transmitted from large power plants to the consumers via extensive networks. The transmission over long distances creates power losses. The major part of the energy losses comes from Joule effect in transformers and power lines. The energy is lost as heat in the conductors.
Considering the main parts of a typical Transmission & Distribution network, here are the average values of power losses at the different steps*:
- 1-2% – Step-up transformer from generator to Transmission line
- 2-4% – Transmission line
- 1-2% – Step-down transformer from Transmission line to Distribution network
- 4-6% – Distribution network transformers and cables
The overall losses between the power plant and consumers is then in the range between 8 and 15%.
Is it the biggest challenge?
This must not be mixed up with the efficiency of power plants like nuclear, coal-fired or natural gas turbine. These technologies are based on a thermodynamic cycle, which efficiency is in the order of 35%. This means that the combustion of coal, for example, will produce heat, which will be converted into mechanical energy and then into electricity.
The global transformation is summarized on the picture below where “units” represent units of energy.
From the energy assessment, it can be concluded that 100 units saved at home can save 300 units saved at the power plant. This should be a real encouragement to save energy for a greener environment.
Don’t mix up heat and electricity!
However, it is important to note that the units saved at the power plant are units of heat, and not units of electrical energy. Each unit saved at home represents one unit of electrical energy saved at the power plant, in addition to the energy saved along the line. As mentioned earlier, this represent between 8 and 15% of the electrical energy produced.
Otherwise, this energy assessment relates to fuel burning power plants, and not to renewable energy like hydro-electricity or wind turbines. These technologies have a much better efficiency and do not produce heat for the energy conversion. The 100 units saved at home represent much less than 300 units saved at the power plant.
But this is not a good reason for wasting electricity!
*Reference: IEC document “Efficient Electrical Energy Transmission and Distribution” (2007)