Geothermal Power: An underrated alternative source of energy

30 03 2010


For today’s post I am very excited to introduce my friend Peter Buchanan as my first guest writer for ReachFWD.

Peter is currently studying Petroleum Engineering at the University of Alberta and he hopes to study geothermal electricity at grad school. He was explaining the concept to me and it sounded so interesting that I asked him to write a brief explanation for my readers on ReachFWD.

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When we think of alternative sources of energy, renewable resources that can reduce our dependency on fossil fuels to meet our energy needs, often the most vivid pictures that come to mind are wind and solar power. Evidently, this is because the sun and the wind are so ubiquitous in our daily lives. We can feel their energy so it is only natural to notice them. This is probably why geothermal power, another renewable source of energy has been largely overlooked until recently.

Geothermal power comes from energy generated by heat in the earth. The material that makes up our planet gets hotter and hotter as is gets closer and closer to the core of our planet. This energy can be seen on the surface in the form of hot springs, geysers and volcanoes. There is an essentially infinite amount of energy beneath our feet, waiting to be utilized.

(Diagram from www.geo-energy.org/basics.aspx)

Geothermal Energy is not new; the first Geothermal Power Station was build in 1911 in Larderello, Italy[1]. Since then, it has become a common source of energy in places like New Zealand, Iceland, The Phillipines and the Geysers in California. Typically it works like this: Two wells are drilled into a geothermal reservoir (rock hot enough to transfer sufficient energy to water). The geothermal reservoir may contain water or steam in network of pores and fractures that make up the rock or it might be dry. Hot water is extracted from the wells and its energy is used to drive a turbine which generates electrical power. The cooled water is then re-injected down the other well where it reheats and continues in the loop.

While there are various types of geothermal plants, the three most prominent types are: Flash steam, Dry steam and Binary Cycle.

Flash steam plants work when high pressure, high temperature water coming up the producer well are directed in to a large vessel. Because of the large pressure difference the water flashes into steam which is used to power the turbine.

Dry steam plants are used when the wells produce only steam. This can be the case in very high temperature reservoirs. The steam from the reservoir directly turns the turbine and is then condensed into water and re-injected into the ground.

Binary Cycle plants use a working fluid (commonly iso-pentane) with a lower boiling temperature than water to turn the turbine[2]. Hot water from the reservoir heats the fluid in a heat exchanger. The fluid then boils to turn the turbine, while the water is re-injected in a closed loop. Binary Cycle plants allow for lower temperature reservoirs to be used.

(Diagram from: http://www.nevadageothermal.com/s/HowGeoWorks.asp)

If geothermal power is so clean, efficient and abundant, why isn’t it being used for all of our electricity needs across the planet, you ask? Until recently, geothermal power was not viable from and economic or technological point of view in most areas of the world. In places like Iceland, New Zealand and the Philippines where hot reservoir rock can be found close to the surface it was used but in many areas of the world the resource would be too deep to drill for economically if even possible.

(Diagram from: http://www.cangea.ca/what-is-geothermal/)

Fortunately, with today’s advancements in technology such as binary cycle plants and enhanced geothermal systems (EGS; where rock is artificially fractures to allow for more permeability in the rocks and more flow/heat transfer) many new geothermal resources may be unlocked in the near future. Geothermal power is not likely to ever completely replace fossil fuels, however combined with other renewable sources of energy it has the potential to contribute to a much larger percentage of the world’s energy consumption.

Pros of Geothermal Power:

  • Clean and renewable with little or no emissions.
  • Reliable. It doesn’t depend on the weather to produce electricity, so it is always on.
  • Many of the engineering concepts are very similar to Oil & Gas, so we have a head start on the learning curve.
  • Can already compete economically in some regions and the list of regions is growing.

Cons of Geothermal Power:

  • Requires a large initial capital investment (like all power plants) which can take time to recover the costs.
  • Not economical in many regions.
  • Reservoirs can be depleted of heat locally, but will regenerate the heat over time.
  • Not enough awareness!

References:

  1. Larderello Worlds First Geothermal Power Station, Renewable Energy UK,  http://www.reuk.co.uk/Larderello-Worlds-First-Geothermal-Power-Station.htm
  2. How Geothermal Works, Nevada Geothermal Power, http://www.nevadageothermal.com/s/HowGeoWorks.asp
  3. What is Geothermal, Canadian Geothermal Energy Association, http://www.cangea.ca/what-is-geothermal/
  4. Basics, Geothermal Energy Association, http://www.geo-energy.org/basics.aspx
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Seawater rising? Or the riverbeds sinking!

22 09 2009

Climate change has become a big issue in recent decades, and one of the major indicators that many people point to as a worrying potential problem is the rise in sea levels globally. There are island nations buying up land in foreign countries, people moving further inland, worse floods every year from tropical storms and hurricanes – yet perhaps an even more worrying problem is that the land itself is SINKING!

Scientists in the well-known and respected journal “Nature Geoscience” have recently published an article on the impact of human activities on the land drop towards sea level in many deltas worldwide. This closure towards the water, they claim, is far greater than the rise in sea level faced by the same inhabitants. Their abstract, below, will give a quick glimpse into the problem:

Many of the world’s largest deltas are densely populated and heavily farmed. Yet many of their inhabitants are becoming increasingly vulnerable to flooding and conversions of their land to open ocean. The vulnerability is a result of sediment compaction from the removal of oil, gas and water from the delta’s underlying sediments, the trapping of sediment in reservoirs upstream and floodplain engineering in combination with rising global sea level. Here we present an assessment of 33 deltas chosen to represent the world’s deltas. We find that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of 260,000 km2. We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.”

Taken from: http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo629.html

detailed_chao-phraya

Chao Phraya River Basin

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Chao Phraya, (see image above) the river which flows through Bangkok is one of the worst affected – parts of the delta have sunk 15cm (six inches)! Compare this to the global rate of sea level rise due to climate change at only 1.8-3.0mm per year – nearly a tenfold difference!

Scientists estimate that the area of land vulnerable to flooding will increase by about 50% in the next 40 years due to a combination of climate change causing sea levels to rise and land sinking due to human causes.

“This study shows there are a host of human-induced factors that already cause deltas to sink much more rapidly than could be explained by sea level alone.” Journal Geoscience Article

The researchers report that the flow of sediment down to the Chao Phraya delta has been almost entirely blocked, due to  irrigation, damming the river, and directing the main flow through just a few channels. In rivers with no dams or man-made controls, the sediment would pass down the river and add to the height of the land, a process known as aggradation. (see image below) Now, the sediment can’t reach many delta areas. The further extraction of water and gas for irrigation, drinking, and industry further compacts the land.

Aggradation

As reported in the BBC yesterday, “Rivers affected include the Colorado, Nile, Pearl, Rhone and Yangtze. Of the 33 major deltas studied, 24 were found to be sinking. About half a billion people live in these regions…

THE HIGH-RISK LIST
Deltas with “virtually no aggradation (supply of sediment) and/or very high accelerated compaction”
Chao Phraya, Thailand
Colorado, Mexico
Krishna, India
Nile, Egypt
Pearl, China
Po, Italy
Rhone, France
Sao Francisco, Brazil
Tone, Japan
Yangtze, China
Yellow, China

As the ground falls and sea level rises, people become more vulnerable to inundation during storms.
Every year, about 10 million people are being affected by storm surges,” said Irina Overeem, another of the study team from the University of Colorado.

So should we be worrying about the inevitable rise in sea levels? Or more focused on the major impacts we are still having on these sinking river deltas, which around the world are home to almost half a billion human beings?

– Sarah Topps








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