EGEE 102
Energy Conservation for Environmental Protection

Entropy and Quality of Energy


Let’s look at an example of how temperature differences are used to generate power. Power plants convert chemical energy into electrical power. Here is a video overviewing the operation of a geothermal energy system, a classic thermal power generation plant.

Click for Transcript of Energy 101: Geothermal Energy

You may have relaxed in a natural hot springs pool.

Or seen the old faithful geyser blasting hot water into the air in yellowstone national park. But have you ever thought of where all that heat comes from?

Well, it comes from deep beneath the surface of the earth -- and it's called geothermal energy...

And we can use it to generate clean renewable electricity. Ok, here's how geothermal works.

Heat from the earth's crust warms water that has seeped into underground reservoirs. When water becomes hot enough it can break through the earth's surface as steam or hot water. This usually happens where the earth's crust or 'plates' meet and shift.

In the past, taking advantage of geothermal energy was limited to areas where hot water flowed near the surface. But, as geothermal technologies advance, we can leverage even more of these natural renewable energy sources. Engineers have developed a few different ways to produce power from geothermal wells drilled into the ground.

Have a look at this. It's a dry steam geothermal power plant and it's the most common type of geothermal technology used today... Underground steam flows directly to a turbine to drive a generator that produces electricity. Pretty straightforward.

Another geothermal technology is called a flash steam power plant. A pump pushes hot fluid into a tank at the surface, where it cools. As it cools the fluid quickly turns into vapor-- or "flash" vaporizes. The vapor then drives a turbine -- and powers a generator.

A binary cycle plant works differently.

It uses two types of fluid. Hot fluid from underground heats a second fluid, called a heat transfer fluid, in a giant heat exchanger. The second fluid has a much lower boiling point than the first fluid and so it 'flashes' into vapor at a lower temperature. When the second fluid flashes... It spins a turbine that drives a generator.

The environmental benefits of this clean, round-the-clock renewable energy source are substantial: low emissions, small physical footprint, and minimal environmental impact. The few byproducts that can come up are often re-injected underground.

Geothermal energy can also help recycle wastewater. In california, wastewater from the city of santa rosa is injected into the ground to generate more geothermal energy.

Some plants do produce solid waste, but that solid waste may contain minerals that we can remove and sell... Which lowers the cost of this energy source.

The u.s. geological survey estimates that untapped geothermal resources in the united states, if developed, could supply the equivalent of 10% of today's energy needs. In fact, electricity generated by geothermal energy already provides about 60% of the power along the northern california coast...

From the golden gate bridge to the oregon state line.

Geothermal energy... ...helping to push america toward energy independence, and a clean, renewable way to meet our growing energy demands...

Below are two temperature scales. The scale labeled "HOT," shows the range of temperatures for the combustion of gases in a power plant. The scale, "COLD," shows the range of temperatures at which gases are exhausted from the power plant.

Scales showing combustion temperatures ranging from 350 to 1,000 degres C and exhaust gases ranging from 100 to 300 degrees C.
Power Plant Temperatures: red indicates power plant combustion temperatures and blue indicates exhausted gas temperatures.

Instructions: Look carefully at the efficiency numbers in the body of the table. How do the Hot and Cold temperatures' effect on the efficiency.

Power Plant Efficiency
8 15 26 34 41 47 51 55
16 22 32 40 46 51 55 59
24 30 39 46 51 56 60 63
32 37 45 52 57 61 64 67
40 45 52 57 62 65 68 71

Answer the following questions based on the information in the Power Plant Efficiency table above.