Where does electricity come from ?
Electricity is not a source of energy. It is a transport mechanism, and way to move energy from one point to another. Along the way, the energy gets converted many times. Each time, there is a little energy lost. Electricity is generated by an energy source - Coal, wind, water power, nuclear reactions, etc. The energy derived from these sources is then converted to electricity by a power plant, or generation source. This may seem to be a trivial distinction, but it is very important in understanding how we use energy.
Let's take one example. A power generation station burns coal. That coal creates heat, which heats water into steam. The steam then turns a turbine which converts the heat into mechanical energy to turn a generator which converts that mechanical motion into electricity. The electricity travels across the distribution grid to your home, through the wires inside your home to your washing machine. Inside the washing machine a motor converts that electricity back into mechanical motion to wash your clothes.
It is also an important note that electricity cannot be stored by our national electric grid. Literally every time you turn that washing machine on, a generating plant - somewhere - starts making a little more electricity to make it run. An amazing thought - but one that is important to many of our discussions of alternative energy. It is the function of operations centers and their computer systems throughout the country to balance this supply and demand.
Not being able to store that electricity makes a significant impact on how we generate it. First impact is, we have just enough generation to meet the demand. It does not make economic sense to build a power plant to create electricity that is not needed! So, if we, as a country, start using a lot more electricity, someone will have to invest in building a power plant to meet that new need. For example, a widespread acceptance of plug-in hybrid cars would use more electricity. Someone will have to build more power plants to meet that need.
A large power plant is only efficient (makes a profit) if it is running at near it's capacity. This is true of Coal and nuclear plants, and somewhat true of hydroelectric (since they still have to be maintained). This gives rise to power companies supplying two kinds of generation capacity. Baseload is the average amount of electricity this country uses 24/7. This is the demand that large scale plants are built to supply. However, there comes a time most every day when our demand exceeds that. It is most often in the late afternoon, early evening. This additional demand is called Peak Load. Power companies maintain many, many, small power generators called "peaking plants". These plants can be quickly brought "on-line" to supply that excess energy. Most of these Peaking plants are run by gas turbines, similar to a jet engine. They supply around 1 - 3 megawatts of power each. Most of these turbines are powered by natural gas. The majority of the natural gas that is used for electricity generation in this country is used to run these "peaking plants".
Since we cannot store the electricity, control is very important. Power companies have to be able to not only increase the supply as demand goes up, but reduce that supply as demand goes down. They do this in real time. As the washing machine example above shows, it is an amazing process. The need for this control has a large impact on our ability to incorporate variable electricity sources such as wind power. We cannot just hook up large electrical supplies to our national grid. They must be controllable. Smart Grid technology is one way the power companies hope to allow better control, and the addition of many small power supplies to our grid - Distributed generation.
But, I digress. Let us first look at what supplies this country with electricity, and then where all that electricity goes.
This country has a total grid connected generation capacity of slightly more than 1,000,000 Megawatts (1,000 gigawatts). Additionally, many companies and factories generate their own power. To that end there are an additional 8,000 megawatts of privately owned generators that are not connected to the grid, and 12,000 megawatts of privately owned generators that are connected to the grid.
Here is a report on installed generation capacity:http://www.eia.doe.gov/cneaf/electricity/epa/epat2p2.html
A note about the above. The generation capacity cited is from the EIA, and called "nameplate capacity". That is the maximum amount the particular generator CAN produce. However, breakdowns, planned maintenance and repairs, and other factors (such as a lack of fuel) reduce the amount of energy that is actually available. This is called Capacity Factor. Various technologies have different capacity factors. In 2008, For Coal that factor is 72%. For nuclear it is 91%. Combined cycle gas plants achieved 42%, while single cycle stood at 10%. All renewables together were at 37%. By my figures, the average across all types of generation plants is currently about 55%. This makes our total actual generation capacity at about 550,000 megawatts, or 4,818,000,000 megawatt-hours per year.
- In the US nearly half of our electricity is generated by Coal fired plants. (49%)
- Nuclear power plants supply about twenty percent of our electricity.
- Natural gas accounts for 21% of our generation - Much of this as a fuel for Peaking Plants.
- Hydroelectric plants comprise six percent of our capacity.
- Renewable energy sources - besides Hydroelectric - comprise 2.5 percent of our capacity.
- Contrary to some beliefs, very little petroleum is used for generating electricity - about 1.9%.
- Much of that petroleum is used in places where Diesel Generator plants are the only reasonable source of power.
In 2008, this country's electric plants generated a total of 4,110,259,000 Megawatt-hours of electricity. And, we used every last watt of it. This represented 86% of our total electrical generation capacity based on my calculation of average capacity factor. Another way of looking at it is we have a 14% safety margin.
Well, where did it all go?
First, some perspective. (EIA Facts and figures: http://www.eia.doe.gov/cneaf/electricity/esr/table5.html)
- There are 123,949,916 residential electricity users in the US. The average residential consumer uses 949 kilowatthours (KWh) of electricity a month. (Your mileage may vary). That electricity costs an average of 10.65 cents per KWh.
- There are 17,377,219 commercial customers who each use an average of 6,408 KWh per month at an average 9.65 cents per KWh.
- Finally, there are 793,767 industrial customers in the US. They each use an average of 107,907 KWh a month at an average cost of 6.39 cents per KWh.
I have decided to just list a few common users of electricity, and what percentage they use. Some of thes figures are from 2008, some from 2007. In no particular order:
- About 215,000,000 megawatt-hours (MWh) of electricity were used for lighting by the residential sector. This was equal to 5% of total U.S. electricity consumption.
- 311,000,000 megawatt-hours were consumed for lighting of commercial buildings. That is 7.5% of the total.
- Residential customers bought 1,379,307 megawatt-hours of electricity - 33%
- Commercial customers bought 1,352,453 megawatt-hours. - another 33%
- Industrial users bought 982,150 megawatt-hours - 23%
- Transportation consumed 7,652 megawatt-hours - .1%
- The rest was produced on site, unaccounted for, or otherwise not bought or sold. - 11%
The EIA Electric Power Summary for 2008. - Good reading!http://www.eia.doe.gov/cneaf/electricity/epa/epa_sum.html
Finally, an Interesting factoid:
Appliances account for 64.7% of electricity consumption in the average American household in 2001. Refrigerators consumed the most electricity (14%), followed by lighting (9%).
Here is a report, a little old, about where electricity goes in your home from the EIA:http://www.eia.doe.gov/emeu/recs/recs2001/enduse2001/enduse2001.html