
Electricity Generation from Renewable Sources
Before beginning our closer look at individual renewable energy sources used for electricity generation, let's frame the discussion with current data about actual electricity generation from these sources. How much electricity do you think we currently generate from renewable energy sources such as wind? solar? biomass? (Hopefully you remember from last lesson!) Based on ads we see on television, you'd think it is a lot, right? Here are some numbers, from the U.S. Energy Information Administration. (Chart generated by course instructor using most recent full-year data.)

Click to here to view the text version
Energy Source | Percentage |
---|---|
Coal | 30.4% |
Nuclear | 19.7% |
Natural Gas | 33.8% |
Hydro | 6.5% |
Wind | 5.6% |
Biomass | 1.5% |
Geothermal | 0.4% |
Solar | 0.9% |
Other | 1.0% |
Hydropower
Hydropower, or hydroelectricity, uses the motion of water to turn a turbine and generate electricity. The water may be in a moving river (run-of-the-river hydro), moving from higher to lower elevations through a specially constructed dam, or in the motion of ocean tides or waves. Hydropower is the most widely used renewable energy source for generating electricity.
The U.S. Geological Survey's (USGS) Water Science for Schools describes a typical hydroelectric plant:
[Referring to picture, Hydroelectric Dam]
The theory is to build a dam on a large river that has a large drop in elevation (there are not many hydroelectric plants in Kansas or Florida). The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to your home and mine. The water continues past the propeller through the tailrace into the river past the dam. By the way, it is not a good idea to be playing in the water right below a dam when water is released!
Reading Assignments
Visit Department of Energy, Energy Explained.
- Under “Renewable Sources", read "Hydropower" and all subpages.
Even though it is an established technology, hydropower is still very much in the news. During a White House forum in Pennsylvania that I attended in 2009, the then U.S. Energy Secretary Steven Chu said, "Hydropower capacity in the United States could double with minimal impact to the environment," clearly dismissing the notion that U.S. hydropower production has peaked. Chu said the industry could add 70,000 MW of capacity by installing more efficient turbines at existing hydroelectric projects or at dams without power components, increasing the use of pumped-storage projects, and encouraging the use of run-of-the-river turbines. "We will be pushing this," Chu said. "We're not talking about a lot of large, new reservoirs. Just work with what we have and it's a massive amount of power." (source Hydroworld):
Shortly thereafter, funding for new hydroelectric projects was announced. Between 2009 and 2011, consumption of electricity generated by hydropower in the USA grew from 2,539 to 3,171 trillion BTUs. (EIA, Total Energy)
Reading Assignment
Read 3-Year DOE Study Assessed Potential Hydropower Upgrades in the US.