The Call, Column 51 – Go With the Flow: Energy from the Wind and Water

31 07 2016

(July 17, 2016)

The Urban Farmer

Go With the Flow: Energy from the Wind and Water

Think back to the last time you walked outside on a blustery day, feeling the great force as the wind gusted around you; or the last time you swam at the beach, being bounced around forcefully by the motion of the waves and currents; or even (if you were lucky enough to live somewhere where the water wasn’t toxic), dropping a little toy boat into a stream as a child, chasing after it as the flowing water quickly took it away. These are all examples of fluid motion, where the energy present in the flow of air and water makes itself obvious, by moving something (or someone) that would otherwise be standing still.

For our first true installment of this exciting series on renewable energy, I want to talk about a category of energy technologies that are similar both because they harness energy from the motion of fluids in the environment, and because they use the same technology to do so: wind power, hydropower, and ocean energy.

As always, let’s start with a little background. Air and water are what chemists call “fluids”, materials whose molecules move freely when a force is applied to them, which (if you remember back to high school chemistry) are primarily gases and liquids. On Earth, the forces that move air and water around come mostly from the sun’s energy. For example, when the sun heats the air or water in one area more than that in an adjacent area, the pressure and temperature of the fluid is different in the two areas and it flows to try to equalize itself, creating ocean currents and wind. And when the wind blows over the surface of the water, it transfers some of its energy to the water, creating waves. And when the sun’s energy causes the water to evaporate upwards against gravity, and it rains down, accumulates at a higher point than it started, it ends up flowing downward (towards the Earth) as a river or stream.

All of these are examples of the sunlight turning into some sort of “hidden” energy (that’s totally not a scientific term, but in it are included “potential”, “thermal”, and “internal” types of energy) in stationary air or water, which then gets turned into the more visible “kinetic” energy of moving air or water. And from this fluid flow, either in the air, or freshwater streams and rivers, or the ocean, we have technologies which can extract massive amounts of energy with little disruption to the ecosystem, and essentially no negative effect on the environment! How cool is that?

For the most part, these technologies utilize a mechanical device, called a “turbine”, to harness energy from the flow of air or water. To understand a turbine, first think about a ceiling fan. When you turn it on, it pulls electricity from the electric grid which runs through the wires in a motor, produces rotational motion that spins its blades and forces air to flow downward. Well, a turbine has the exact opposite operation, using basically the same technology!
A turbine, which consists of blades much like a ceiling fan’s, connected to the shaft of a generator, is placed in an area where there is large volumes of fluid flow – above the tree-line where the wind is strongest, in a river or stream where the water all moves in one direction, or in specific locations in the ocean where tide and wave motion are the most pronounced. As the air or water rushes through and past the blades, it causes them to spin, which rotates the shaft of the generator and creates electricity!

As I mentioned above, the three types of energy technologies in this category are ocean power, (freshwater) hydroelectric power, and wind power. Let’s discuss each one briefly below.

Hydroelectric power is probably the most pervasive alternative energy at the present time. At its most basic, energy can be extracted from flowing freshwater by placing a turbine in the stream or river and allowing its rotation to generate electricity – a turbine – or even other forms of mechanical energy – like old-country water wheels. Modern hydroelectricity generally includes a dam built in a larger river, which raises the height of the water on one side (and therefore, the rate of energy capture), and allows it to flow through turbines in its course to the other side.

Modern hydroelectric power technology has been under serious development for decades and currently produces around 3% of the total electricity in the United States, making it the largest single source of renewable energy we use as a country (I know, we have a long way to go). It is used prominently in many other areas of the world. It is hugely beneficial because of its scalability – hydroelectric generators can be installed both in the biggest rivers (for city-scale generation) and the littlest brooks (for home-scale). In addition, it is available anywhere that has a flowing body of water.

“Ocean power” is much less developed at this point in time. It takes two major forms – tidal power and wave energy.

Tidal power is actually driven by the rotational energy of the Earth and the moon, via the gravitational force between them (rather than the sunlight); in practice, the energy is extracted from the overall, vertical motion of the ocean, which rises and falls daily with the tides. There are various tidal generator technologies under development, including tried-and-true turbines, along with others than take advantage of tidal motion.

Wave energy, on the other hand, takes advantage of the overall horizontal motion of the waves and underlying ocean currents; this motion, like most of the others discussed here, is the indirect result of solar energy. This is primarily captured using turbines. But, like tidal power, there have been developments in other, more novel configurations that take advantage of different aspects of the wave and current motion to generate electricity.

Finally wind energy is one of the most endearing, useful, promising sources of renewable energy presently available, and therefore happens to be one of my favorites.

Wind turbines harness the energy present in moving air by much the same mechanism as hydroelectric and ocean power. Wind flows through and past the blades of the turbine – either the familiar looking three-bladed ones, or less-familiar vertical axis, bladeless, and Savonius ones – which spins the shaft of the generator, and generates electricity.

Wind energy is being developed as you read this. The first off-shore wind farm in the country is nearing completely off the coast of our own Block Island – something I am very proud of, as a native Rhode Islander. Both off-shore and on-land wind energy are up-and-coming major energy sources, and should be encouraged at every turn.

The science is in: climate change is happening, and it’s the result of human activity. The biggest challenge of the next few decades is to completely wean ourselves off of fossil fuels, replacing the current energy economy with an even better one, based on renewable energy sources. It is up to those of us who recognize the truth of climate change (I can’t believe that I still have to make that distinction in 2016), who understand the seriousness of this challenge, and who see the promise that exists in renewable energy technologies, to champion their quick and wide-scale development. Whether it’s adding more hydroelectric capacity to the Blackstone River, or funding research for better wave and tidal energy generators, or constructing small-scale wind turbines at our homes and businesses, I call on my fellow urban farmers and environmentalists to usher us into the energy future.

My column appears every other Sunday in The Woonsocket Call (also in areas where The Pawtucket Times is available). The above article is the property of The Woonsocket Call and The Pawtucket Times, and is reprinted here with permission from these publications. These are excellent newspapers, covering important local news topics with voices out of our own communities, and skillfully addressing statewide and national news. Click these links to subscribe to The Woonsocket Call or to The Pawtucket Times. To subscribe to the online editions, click here for The Call and here for The Times. They can also be found on Twitter, @WoonsocketCall and @Pawtuckettimes.




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