I’d like to thank my Arkansas friend, Luis, for asking this great question.
The shortest answer seems to be it gets used, stored or wasted. The part that is wasted goes into heat and “sink” loads. There are several ways electric power gets wasted and a limited number of ways it can be stored (today).
Storage: There are few resources here– batteries (a very small %) and some higher capacity solutions like pumping water back above dams.
Electric generation also produces heat which is best used locally as in a “distributed generation” system where the heat can go a short distance to a bakery, school, university, hospital or buildings in a city. All of downtown Milwaukee used to be heated by the excess steam created by on coal to coke conversion plant through a network underground pipes. This resource lowered business costs so much that it created many vacant buildings when the system was shut down. In terms of electric power management, our bigger problem is creating too much heat, or wasting power.
Waste: First, take a look at this chart: http://blog.opower.com/wp-content/uploads/2013/08/LLNL_Flow-Chart_20121.png
38 quads (large units of energy) of the 95 quads of energy used in the U.S. goes to electricity generation. From this, 12 quads of power are sent through transmission lines to residents, commercial buildings and industrial uses.
This initial inefficiency, or loss, is huge in terms of planet resources/emissions. Every kilowatt-hour of power you save through diligence (energy efficiency and conservation) saves (38-12 = 26) or more than 2 kilowatts MORE of comparable energy that was avoided. So when you save a kilowatt-hour, you save the earth 3.
700 kWh, the WI monthly average, is a lot of energy. Our masonry wood stove heats our whole house on 2-3 cords of wood per year. Our fairly efficient refrigerator uses about 1 kWh/day. The power from coal power plant used to run the frig is responsible for more CO2 emissions each year than our wood heater is.
As more than 70% of our electric power is inefficiently generated by coal and natural gas in the Midwest, one can quickly see why Energy Efficiency (EE) is such an effective means of reducing carbon emissions. Combine the fact that EE works 24-7 and renewable energy power is highly variable,.., and one can see why utility PR pictures wind turbines instead of super high efficiency air conditioners. REMOTE Renewable Energy (RRE) poses much less sales competition than EE and can be used to “justify” utility capital investments like regional high voltage transmission expansion– very profitable prizes for utilities that we pay for.
Remote renewables are not cost/environment effective enough to be a primary investment focus. Local renewable installations have several more benefits and they are great tools for learning about energy management– problem solving that is comprehensive and much more productive than solutions at a distance.
To the core of your question as it pertaining to transmission:
Most power generators “see” and adjust to demand. For example, the turbines in a hydro electric dam actually allow water to flow through more quickly when demand is low (flow is also restricted to not waste the potential). The same is true with coal/steam generation but less efficiently. Wind turbines do not respond efficiently to varying demand. PV or solar responds almost perfectly. If you have an off-grid solar array and no batteries, the PV array will only generate what is demanded by your house. The array will send 90+% of the excess to the grid if connected. So, some adjustment to demand occurs depending on the generation type. The excess that remains in the centralized power system is dissipated through heat and load “sinks”.
Heat: Copper and aluminum wire in transmission lines, transformers, voltage and phase stabilizers create heat. The heat produced can increase for several reasons– one being when supply significantly exceeds demand.
Transmission loss over longer distances is in the 6-20% range. There’s a lot of wire over 150 miles to heat-up when supply is greater than demand. I read that a 1.25″ diameter aluminum strand conductor (wire) at 345 kV heats the air around it to about 180F under average air temperatures. I bet that can get much higher when the system heats up. When wires get hot, they “droop” considerably– one reason the towers have to be so high. Hot wires are also less efficient than cool wires. If you’ve been to a substation, there are usually fans cooling some transformers and when the system gets hot, more fans turn on. If transmission cables are buried, the heat builds-up and the air has to be exhausted/cooled = less efficiency.
Heat Sinks: (We learned about this attending the American Transmission Company’s FERC-required publicly accessible planning meetings. I suggest that anyone interested in energy planning attend the meetings in their state across the U.S. The meetings are usually on the web too.)
In WI, when supply exceeds demand, large industrial users actually get paid to turn on their equipment. This is currently cheaper than other ways to rid the excess power. The factory “sinks” do not necessarily produce proportional extra product,.. some basically “spin” and heat-up.
There are creative ways to use excess power in a smaller system or locally. For example, a “smart” grid in a small town would detect when supply exceeds demand and know that its a good time to pump water into the town’s water tank, run the saw mill, and pre-cool buildings that use lots of AC.
If you have a solar array, such “smarts” become obvious. Do the wash, dishes and vacuum the house when the sun shines. Pre-cool the house in the am so you can shut off the AC during peak demand after the sun goes down. This is called, “energy management” and it avoids a lot of gird power being generated.
Rewards in thinking about waste:
Practicing conservation and energy efficiency is better driven as an “aesthetic” choice than it is a moral obligation. Why? Energy “is;” it is “live-ness” or “perception” in human terms. When one personally interacts with energy it connects one to “elegance” — the greater awareness of the beauty the world down to molecular thermo-dynamics. There is no greater or more pervasive connection point to a greater awareness of our matter-energy world than our electric outlets. In other words, doing good is more rewarding and fun than not doing bad.
Newton showed us how to see one big system or machine. So, when we look for “where excess power goes,” we don’t have to look far. What we can see around us is our earth’s atmosphere becoming the default, “storage” system as we struggle to find an aesthetic powerful enough to teach us to experience energy. I think Newton would probably observe that its far easier to slow down our requirements of a very inefficient machine than it is to make a much-much better machine.
The “renewal” we “need” the most is in our awareness– not in more and bigger machines.
Or more simply: “Waste not; want not,” and, “Less is more.”