Discovering Geothermal Energy
November 21st, 2008 Subscribe To Our Feed
The most focus in the renewable energy industry is placed on solar energy and wind power but there is a lot of potential in geothermal energy. It has already been used to provide power to 1.2 million homes in the United States. It has far greater potential and to both heat and provide electricity to homes and is yet to be properly utilized. That’s about to change.
There is an enormous level of energy trapped beneath the earth’s surface coming from a list of sources: the planet core, decay of naturally occurring substances within the crust and movement of continental plates as they slide against and underneath each other. Volcanoes, hot springs and steam vents represent the easily accessible points to this energy but most geothermal energy is trapped under the earth’s crust and must be accessed by drilling into the resource and harnessing the energy. The thermal energy in the uppermost 6 miles of the earth’s crust contains 50,000 times the energy of all the world’s gas and oil resources.
What Is Geothermal Energy?
Geothermal energy is the heat stored beneath the surface of the earth. In some parts of the world where the earth’s surface is thin or cracked, steam and molten rock can escape. These are usually locations of high seismic activity such as earthquakes and volcanoes. If water finds its way into these cracks, it becomes heated and may come to the surface as geysers, fumaroles, hot springs and mud pots.
Parts of Europe, USA, New Zealand and Japan have high geothermal activity. High grade geothermal energy such as geysers, fumaroles, mud pots and hot, dry rocks is used to generate electricity. Geothermal energy can also be used as a heating source, for example in Iceland hot water is brought to the surface through a bore , then sent through insulated pipes into homes and radiator panels which provide heat. Over 80% of homes in Iceland are heated this way.
While geothermal energy is a renewable resource and the creation of electricity does not pollute the air, the actual process can pose serious environmental problems. Scientists are not sure how the long-term use of this resource could affect our underground water supplies. Some geothermal tourist attractions at Rotorua in New Zealand have already suffered a decline in surface activity due to the draw-off of geothermal fluid from the underground reservoir by domestic and commercial uses.
Geothermal energy can be broken down into 4 main types – Geothermal energy can be broken down into 4 main types – geopressured, hot dry rock, hydrothermal and magma.
Hydrothermal
This is the only type of geothermal energy that is currently producing commercial quantities of electricity and is derived from hot water and steam formed in porous or fractured rock at relatively moderate depths from 100 metres to 5 kilometres.
The hot water and steam come from the intrusion of molten magma into the earth’s crust or the deep circulation and heating of groundwater through faults and fractures.
Electricity is created by bringing hot water to the surface where it is flashed to steam in special vessels by release of pressure. The steam is separated from the liquid and fed into a turbine engine which turns a generator. Spent geothermal water is returned back to the reservoir to help maintain reservoir pressure.
Geopressured
Geopressured energy comes from hot, pressurised waters containing dissolved methane, trapped at depths of three to six kilometres in sedimentary formations. The water temperature ranges from 90°C to 200°C.
Energy in 3 forms can be captured from geopressured sources – thermal energy from the hot water, hydraulic energy from the high pressure, and chemical energy from burning the dissolved methane.
Magma
The prospect of using magma directly has still not been exploited. Found at depths from between 3 and 10 kilometers under the earth’s surface, magma is molten rock reaching temperatures up to 1200°C. Magma is only accessible where volcanic activity or tectonic plate movement occurs.
Hot Dry Rock
Under certain conditions granite at a depth of 3 to 5 kilometers beneath the ground can reach 250°C. Unlike hydrothermal resources, the fractures and faults required to conduct water to the surface are not present, therefore water must be pumped into the rock at high pressure to create an artificial underground reservoir of steam or hot water.
A number of development projects continue into attempting to make use of hot dry rock to create electricity but factors such as cost and questions about resistance of the reservoir to flow, water loss and thermal drawdown remain. As the cost of producing geothermal using hot dry rock technology keeps coming down it will soon be an economically viable option.
The Future Prospect of Geothermal Energy in the US
An exciting new development in the future of geothermal energy in the United States has just been announced by the Department of the Interior who have promised to make 190 million acres of federal land available for geothermal power development. This is good news because the proposed land includes no environmentally sensitive areas such as national parks or designated wilderness areas.
By the year 2015 it is estimated that geothermal powered electricity production in the United States can reach 5,500 MW thanks to this new initiative. It’s a positive move that will promote a form of renewable energy that has been used for years, but perhaps not to its full potential.
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Concentrating Solar Power Plants - The Way of the Future
November 18th, 2008 Subscribe To Our Feed
There are two main types of solar power generation methods used to create electricity on a commercial scale. Photovoltaic panels, which are the large collections of the systems that you see in small scale on house roofs. Using the heat of the sun as thermal solar power are concentrating solar power (CSP) plants.
We will take a look at the way in which concentrating solar power plants create electricity. CSP plants are capable of producing electricity at a higher maximum capacity than a photovoltaic facility of the same size. Technological advancements are making cheaper solar energy, particularly from CSP plants, ever closer to reality.
Commercially, four types of concentrating solar power are in use: parabolic troughs, dish / engine systems, fresnel reflectors and central receiver systems. The technology involved with each is proven and either has been or still is in operation around the world with further developments in solar energy in progress to increase global capacity.
Parabolic troughs use mirrors to direct sunlight onto a fluid-filled receiver positioned in directly in front of each trough. The heat generated from this process heats the fluid to high levels so that super-charged steam is generated. Electricity is then created by means of a conventional steam generator.
A trough-based CSP plant typically consists of rows of mirrored troughs placed parallel to each other along a north-south axis in what is known as a collector field. Optimum heat exposure is maintained thanks to the pivoting nature of the parabolic troughs which track the sun’s movement across the sky. Electricity continues to get generated when the it’s cloudy or after the sun has set thanks to thermal storage. Technological advancements are continuing to prolong this production period in a bid to move to continuous solar electricity production.
Power plants known as Andasol 1, Andasol 2 and Andasol 3 in Spain all use the parabolic trough design, forming a combined 150MW solar power plant. The surface area of the mirrors used to form the energy collection field of Andasol 3 alone is around 500,000m2.
Dish / engine systems are stand-alone units that contain dish-shaped parabolic mirrors that concentrate the sun’s energy onto a receiver mounted above the dish. The receiver takes the energy and converts it into heat which is then converted into mechanical power, similar to a mechanical engine. Each dish / engine unit has a capacity of around 25kW of solar power and it tracks the sun to ensure optimum power.
An example of the dish / engine technology is the Stirling Energy Systems dish called the Suncatcher that will be used in fields of thousands to form a power facility capable of generating over 500MW of electricity
Fresnel reflectors provide a more concentrated focus of solar energy onto centrally placed receivers. This is a simpler system to the parabolic trough system with fewer moving parts and the rows can be positioned closer together. The receiver is stationary and it is shared by multiple mirrors.
An example of a recently commissioned CSP plant using reflector technology is the Kimberlina CSP plant in California developed by Ausra. This power plant is relatively small at only 5MW capacity, but it paves the way for future large-scale developments.
Central receiver systems, known colloquially as power towers, is another way to produce concentrated solar power. These concentrating power systems operate through the use of thousands of mirrors called heliostats that track the sun and reflect the heat energy onto a receiver that sits at the top of a tall tower. The heat that is collected by the receiver then heats molten salt as it flows through which is then used to make steam that operates a conventional steam generator. The molten salt can be stored for great lengths of time which means that this type of solar energy generates electricity continuously around the clock.
An example of a central receiver system in development is the Solar Tres power plant being built in Spain. The Solar Tres power plant will be a 15MW facility and it follows on from the successful demonstration power plant known as Solar Two which was located in the Mojave Desert.
Opponents of solar energy cite cost as a limiting factor, but this is being overcome thanks to advancements in technology. Already, concentrating solar power plants hold a huge advantage over the traditional fossil fuelled counterparts in the lower impact to the environment. In fact, one of the only impacts that concentrating solar power plants have on the environment is land use.
Solar energy continues to grow and with continued support it will eventually become one of the main sources of electricity around the world. Concentrating solar power has proven to be a renewable energy source with still more untapped potential
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