Ocean Thermal Energy Conversion (OTEC)

The oceans harness within themselves two types of energy: thermal energy and mechanical energy. The mechanical is derived from gravity which moves the tides and waves. The thermal comes from the sun which alters the temperature of the ocean water. 

Like solar panels in your calculator the surface of the ocean absorbs solar radiation. The solar panels on the calculator create electricity while the oceans surface create thermal energy. If only a small portion of this thermal energy could be harnessed, it could power the whole world.

In fact, there is so much thermal energy absorbed each day by the oceans it would equal the thermal output of 250 billion barrels of crude oil.

There are three ways the OTEC method can produce electricity.

Closed-Cycle: This system relies on low-boiling point fluids such as ammonia. The warm ocean water is used to heat up and boil the ammonia, which will turn a turbine. The turbine then produces electricity.

Open-Cycle: This system relies on a low-pressure environment to actually boil the ocean water and create steam. When warm ocean water moves into a low-pressure environment it will boil. The steam is almost pure water as the salts and other impurities are left behind. The steam then recirculates to deeper and colder areas of the ocean and condenses back to water. Just like the ammonia gas, the steam will turn a turbine.

Hybrid System: This system simply combines both Closed and Open Cycle systems.

For more info on OTEC visit The National Renewable Energy Laboratory HERE

Renewable Energy

Renewable Energy: an energy source that can be replaced at a rate either equal to that of human consumption or faster.

It is important to keep in mind that "renewable" is a relative term. It applies to human endeavors. Technically, energy does not "renew" itself. It just is. Going back to the first law of thermodynamics we see that energy can neither be created nor destroyed.
Renewable energy sources come from on-going natural processes on earth or in the solar system. When thinking about renewable energy we also tend to think of a low-pollution energy source. Therefore, due to the polluting nature of nuclear energy, it is not included.

If we try to get at what the originating sources of renewable energy are we will find that there are currently only two sources: the sun and gravity. Gravity technically only stores energy and it is the most difficult to understand when talking about it in terms of renewable energy. The work we get from gravity is due to "gravitational potential energy." More on that later.

Let's examine the sources of renewable energy:
Main Originating Sources:
Sun - gives us thermal and solar energy
Gravity - gravitational potential energy, gravitational binding energy

Sub-categories and sources:
Solar Power - sun
Wind Power - sun, gravity
Hydropower - gravity
Biomass - sun
Geothermal - radioactive decay, gravity
*Note: Geothermal is argued as not renewable by some.

As you can see, except for geothermal, the originating sources have a monopoly on renewable energy categories. The easier of the two to explain is energy supplied by the sun as gravity is still a bit of a mystery. For more information on Solar renewable energy visit The National Renewable Energy Laboratory HERE

Absolute Zero And Thermal Energy

Absolute Zero: The coldest theoretical temperature but also unachievable according to the third law of thermodynamics.

Absolute zero is a temperature. To understand how cold absolute zero is let's start with the temperature at which water freezes, which is 32 degrees Fahrenheit (0 Celsius). The coldest temperature ever recorded in Alaska was -80 Fahrenheit and the coldest temperature ever recorded on earth was -129 Fahrenheit in 1983 in the Antarctic. Absolute zero is -459.67 Fahrenheit. Humans have been able to come within a billionth of one degree Kelvin to absolute zero!

The coldest natural temperatures reached are in outerspace with the depths of space reaching just -454 Fahrenheit. Humans can do much better, reaching just a few hundred billionths of a degree above absolute zero (Kelvin scale). On the Kelvin scale absolute zero is 0 Kelvin.

What happens at this temperature?
Scientists predict what theoretically will happen at this temperature because it can't ever be achieved. The third law of thermodynamics forbids that humans should ever be able to reach that temperature. As we mentined before, thermal energy is the kinetic energy of the oscillation, vibration, and random activity of atoms and their constituent particles. As an object gets colder, its atoms and molecules begin to move slower and slower. Before we move on it is important to note that the way something is made colder is by heat (thermal energy) being removed, not "coldness" being introduced into the object.

Theoretically, at absolute zero all motion of the atom and its constinuent parts would cease. All thermal energy that could be, would be extracted from the atom. This presents an interesing perspective on time. If all motion would ceases then time would effectively cease also. If there is no time then how could you have space? (cue freaky twilight zone music)

HEAT TRANSFER

Thermal energy and heat are often confused. Rightly so because they are physically the same thing. The confusion comes from the usage of the term. Heat is always the thermal energy of some system. Using the word heat can help physicists to make a distinction relative to the system they are talking about.

Heat: Term used to describe the transfer of thermal energy between two thermodynamic systems at different temperatures.  

Caveat: Although physicists and scientists do use this term - there is a colloquial quality to it. For students - talk to your physics teachers!

 

Take a small piece of ice out of your fridge and hold it in your hand. The thermal energy content of your hand is higher then the thermal energy content of the ice cube.

The atoms that comprise your hand are moving more rapidly then the atoms that make up the ice cube. Therefore, there will be a transfer of thermal energy from your hand to the ice cube. While this thermal energy is in transfer, it is called heat. This will cause the atoms in the ice cube to speed up while the atoms in your hand slow down.

The increase in speed of the ice cube atoms changes the state of water from solid to liquid. This transfer of thermal energy will continue until an equilibrium is reached between your hand, the ice (now water), and the air in the room.

Let's return to our overview from the homepage. If we put our hand into the box with the three systems (not touching the iron pieces), our hand becomes system D. We could then say that the heat from system B is warming our hand. So we have made an accurate statement. But let's say we preparing a college paper after we conducted our experiment and our hand is no longer in the box - then we would want to say: "There was a transfer of thermal energy from system B (iron) to system D (hand). The heat from system C increased the temperature of system A by convection". Someone reading your paper may then ask "where did system C get that heat (thermal energy)"? In a way we are saying that there was thermal energy at that time flowing through system C derived from a different system that is relevant to the discussion.

 

The physics of thermal energy:

Energy: The capacity of a system to do work.

Matter: Composed of atoms and molecules. Always has mass.

Thermodynamic System: Term describing a defined quantity of matter and energy that is relative to another system. Utilizing thermodynamic systems is about practical applications. There is diminishing returns in applying thermodynamics to matter and energy at microscopic levels, although there is the study of quantum thermodynamics.

Selected thermodynamic systems.

Fig.1

• A: Air inside room
• B: Human Being
• C: Computer
• D: Monitor
• E: Desk

Our selection of the systems is relative to the relationships we wish to analyze. Here we are analyzing a few thermodynamic systems inside a room. But if we wish we can zoom out.

If we zoom out we can select a different set of systems for analysis.

Fig.2

• A: Air outside.
• B: House
• C: Land
• D: Lake
• E: Trees/plants

Our selection of systems has changed. Now all the systems in the room of Fig.1 become part of one system - the house.

Thermodynamic System Relationships

Now that we have described our thermodynamic systems, we can discuss the physics of thermal energy within these systems.

Atoms and molecules

Atoms and molecules make up systems. In Fig.1 the human being is (in a dry physical sense), just a jumble of molecules and atoms. All these molecules and atoms are in motion. This motion is the culmination of the constant little movements, wiggles, jiggles, and vibrations of those atoms and molecules that make up this human. In describing the capacity of all this atomic and molecular movement to do work, physicists refer to it as thermal energy. Remember, energy is defined as the capacity to do work.

These constant wiggles, jiggles, and vibrations are called translational, rotational, and vibrational movements.

If we move further down the scale, thermal energy is the culmination of the kinetic energy of the movement of the constituent parts of an atom (electrons,protons, and neutrons).

Atoms and moleclues have movement because the constituent parts have movement. When this kinetic energy is transfered to another atom it's called the transfer of thermal energy. When the transfer happens in objects such as from a stove to a pan, it does so over the trillions upon trillions of atoms in those objects.

Why do electrons, protons, and neutrons move?
Well, now we are getting down closer to the mysteries of our universe. Except for the electron, which is a fundamental particle, the proton and neutron are made up of smaller particles called quarks. Quarks have electrical charges. Electrically charged particles produce an electromagnetic force and this force creates interaction with other electrically charged particles. These interactions, along with other fundamental particle movements such as "spin" combine to produce these movements, vibrations, and general active nature of atoms. For a discussion on how temperature affects atoms check out  Absolute Zero

Why do these all these particles have electrical charges anyway?
That information is classified. Just kidding. It's just how things are, the way the universe came together after the big bang. Basically, within just a fraction of a second one force known as the "superforce" split into the four fundamental forces of our universe.:

• Gravitational Force
• Electromagnetic Force
• Strong Force
• Weak Force

Why did the universe come together in this precise manner at the moment of the big bang?. Time to do some research on the big bang theory! It's very deep stuff and many people make a career out of trying to find the answer! If you have any more questions after that it's all just philosophy!

What is thermal energy ?

The ultimate source of thermal energy available to mankind is the sun, the huge thermo-nuclear furnace that supplies the earth with the heat and light that are essential to life. The nuclear fusion in the sun increases the sun's thermal energy. Once the thermal energy leaves the sun (in the form of radiation) it is called heat. Heat is thermal energy in transfer. Thermal energy is part of the overall internal energy of a system. Read about the physics of thermal energy

  

At a more basic level, thermal energy comes from the movement of atoms and molecules in matter. It is a form of kinetic energy produced from the random movements of those molecules. Thermal energy of a system can be increased or decreased.
           

 

When you put your hand over a hot stove you can feel the heat. You are feeling thermal energy in transfer, otherwise known as heat. The atoms and molecules in the metal of the burner are moving very rapidly because the electrical energy from the wall outlet has increased the thermal energy in the burner. We all know what happens when we rub our hands together. Our mechanical energy increases the thermal energy content of the atoms in our hands and skin. We then feel the consequence of this - heat. Laws of Thermodynamics

 

On the left you can see 3 hypothetical thermodynamic systems. I've labeled system C as air for simplicity and the other systems could be anything really. We'll pretend they are solid objects though, two pieces of round iron. One is cold, one is hot. The air we'll make a temperature the same as system A. Instantaneously we put all three into a sealed box. Technically the the box now becomes System D but for simplicity we will leave it out.
 

By convection and radiation the fast moving atoms of system B impact the movement of the atoms of the air. So the transfer of thermal energy begins. As the air "heats up" the faster moving air atoms and molecules now start hitting the thermodynamic boundary of system B and transfering that energy (thermal energy). All this will occur spontaneously until an equilibrium temperature is reached among all 3 systems. What is the lowest that the equilibrium temperature can be? Can it reach Absolute Zero?