

The U.S. electricity transport and distribution system have grown into a complex network containing according to the EIA "the U.S. power grid is made up of over 7,300 power plants, nearly 160,000 miles of high-voltage power lines, and millions of miles of low-voltage power lines and distribution transformers, connecting 145 million customers throughout the country".
We tend not to transport electricity over great distances. There are problems with electricity losses over distance, but, more importantly, the connections from one part of the country to another are not there. We can send electrons (which is, after all how you are accessing this material) across the country but we cannot send lots of electricity. The capacity to carry enough of the electrons does not exist. Thus, if California was experiencing an electricity shortage, we in Pennsylvania could not increase our output to help. Thus instead of a national network, we have Regional
This inability to transport electricity also means that industries that are electricity intensive tend to be close to cheap sources of electricity such as hydroelectric sites. (Las Vegas baby!) Adding intermittent renewable energy (such as wind and solar) into this mix is a challenge.
The Flow of Electricity


Somewhere in your house, there is a circuit box containing a number of circuit breakers. I can remember when fuse boxes were the standard. These contained huge fuses that would simply blow if the electrical current overwhelmed the circuit. Perhaps you've had this exact experience when running a hair dryer or space heater in an older house, sending you to the basement to find the box. Hence, the advantage of breakers over fuses - simply switch a breaker back on after it shuts down, but for a fuse, you'd better hope you have a backup waiting, or it's wet hair for you!
Breaker boxes are where all the electricity used in your home enters the house and is distributed to the electricity-hungry devices, such as electric dryers, electric ovens, electric heated hot tubs, and to all those lights, computers, fans, video game consoles, TVs, etc. The question is; How does the electricity make its way into your home?
Now, if you go outside and look around, odds are you will be able to find the meter, which conveniently keeps track of all the juice you use, and then the transformer, a drum-shaped piece of equipment sitting atop a pole somewhere close to your house. This has the important job of stepping down the voltage entering your home from several 1,000 volts to 240 volts. Volts is a measure of the "pressure" behind the electric current, and most home appliances use 110 V, but those dryers, hot tubs, etc. will need to have more electrons than the rest of your appliances, so a higher voltage is needed to "push" those extra electrons along.

In the images above, the electricity meter measures how much electricity you use, so the company can bill you for all those lovely electrons (Kwh). Poles follow the roads, carrying electricity to each of our dwellings. On those nights when you're forced to sit in the dark, odds are that the problem is at the transformer (right image). Lightning, falling tree branches, overzealous squirrels, and drunk drivers all take a toll on these poles and wires, and when they get disrupted, we go back to the age of the candle.
About High Voltage Power Lines

Up atop the mountain, the high voltage lines carry electricity over the mountains, rivers, and highways. Unfortunately, we have not been building new lines and are running out of carrying capacity for electricity. (Recall the blackouts?) For those of you who like Yoga: Ohm's law states:
V=IR (VOLTAGE = Current x Resistance)
P = VI (power = voltage x current).
A bit of magic mathematical manipulation and P=I2R
(don't worry about memorizing the equations here)
The losses we obtain by flowing electricity through wires (which causes them to heat up) is proportional to the current squared and the resistance of the wires. This is why we use high voltage lines, to keep the current low. For the math impaired, doubling the current results in quadrupling the losses, doubling the resistance only doubles the losses. Thus, we use very high voltages, 155,000 to 765,000 V, to do the long-distance trip at about 300 miles range.
These substations have switches and transformers to regulate the flow of electricity. Larger ones are close to the utility where the electricity is generated. In Lesson 2 we cover the wonderful world of electricity generation.
Note that our demand for electricity tends to increase as the population grows, and as we use more and more electronics. This puts an ever-increasing strain on the generation capacity and distribution network.
Renewable Intermittence
One of the items that we will come back to is the challenge of supplying electricity with the challenge of intermittency of renewable energy (specifically solar and wind). The following figure shows data for Spain for September/October. Notice the variability in the electricity generated by wind and solar (concentrated solar thermal in this case). Solar will have the obvious peak in the day with some overlap into the evening (solar thermal plants) but will also depend on the sunny days. The wind is also variable with some days having poor solar and poor wind (this would be a bad day in Germany because of their reliance on both wind and solar). Thus, we need to have the ability to generate much more electricity on those days and the electric grid has to cope with the variable renewable supply that adds extra stress. More on this later.

So as we are discussing electricity demand it is important to recall that the answer that is always right in aiding the reduction of pollution is conservation (not the only answer, however). Surprisingly, your local utility organization is happy to help you conserve electricity. Given the very large capital cost required to build a large utility, the more we can conserve, the longer that new utility construction can be delayed. Thus, assistance with weatherization can be obtained in some areas courtesy of the local utility. In the UK, it is common to have 2 prices for electricity: a peak demand price and an off-peak demand price. Similar to many service industries, if they lower the prices for certain times, more people will use those time slots. Hence, dishwashers, clothes washing and drying–appliances often have timers to turn them on when the electricity is cheaper (after 10:00 PM). Now the utilities can run the cheaper sources at a higher capacity, longer. We are moving in a similar direction and beyond with the adoption of smart grid technologies and smart meters that know when the electricity is used, not just the amount (so variable pricing is possible).