Ocean energy: what is it, and how can extract

If less than one tenth of 1% of all the solar energy trapped oceans were converted into electrical energy, you could meet the energy needs of 20 times the total energy consumed by the United States every day. But how? What technology is used to extract energy from water?

The U.S. national laboratory for renewable energy is estimated that the energy talassotermica (under the name of Ocean Thermal Energy Conversion) could be one of the cheapest renewable sources and extended to exploit.

The principle of energy talassotermica, to date still little known and widespread, is based on the temperature difference between the water in the surface and that in depth but requires a temperature difference of at least 20 degrees so that the system can work. The operation is based on a cycle of temperature changes that allow to evaporate a liquid (in the closed loop is often used as ammonia while in the open water itself) and thus create an increase in pressure allowing the turbine to rotate and produce energy. The advantage resulting in the use of the open-loop derived from the evaporation of sea that separates the salt and produces usable water for domestic, agricultural or commercial. And the benefit is available 24 hours a day, 365 days a year unlike other energy sources such as sun or wind.

The first prototype was created in 1881 and since then numerous studies have been conducted, especially at the turn of the years 70 and 90, in order to optimize the efficiency of a very low yield (between 1 and 3%), but already economically interesting due to the intrinsic characteristics of this renewable source. Despite early difficulties, according to the latest research you should be able to reach an efficiency equal to 6-7% of the plants.

All experiments have been performed so far with small-size systems as the biggest problem encountered so far resides in the losses and the pressure generated by the tube that exchanges the hot / cold water up to 800-1000 meters deep. The plant expansion will not be so simple and test engineers from the National Indian Ocean Technology Instituite of the current outlook at the time of production does not exceed the 5-10MW.

Confirmation of this is the new project to be delivered in 2011 on the island of Diego Garcia, located in the Indian Ocean, which will provide 8 MW of electricity and 5 million liters of drinking water per day.

The enlarged image of the production model is necessary to address other issues such as the management of algae that could clog the heat exchangers and the durability of the materials, subject to great stress from the salt water and subject to possible corrosion. That's why we are experimenting with new technologies to optimize the performance of the materials: the U.S. Department of Energy (DOE) has granted research funds to develop new fiberglass pipes more resistant to great difficulties in the marine environment: they are not to be underestimated either storms in the open ocean that could damage the platforms seriously compromising the operation.

Other applications American raised the hypothesis of OTEC technologies combine with the HDD (horizontal directional drilling) and turbines hydrocarbon to increase efficiency: also the liquid used for the generation of pressure to the turbines could be revised giving life to mixed systems with the use of propane R-290, an excellent fluid at low temperatures as it passes from liquid to gas and vice versa very simply. Other patents filed in this direction would use the production of a solar energy system installed on the platform to provide a boost accelerator was to propane gas.

The challenge of bringing the technology on a large scale has been collected by the founder dell'OCEES, Krock, who is following for a large corporation making an OTEC plant in Indonesia with a capacity of 100MW expected to generate even hydrogen. The cost of the structure is currently estimated at 750 million to 800 million dollars with a time of commissioning of about 2-4 years. The cost, according to recent studies, would generate power at a cost of 17 cents versus 25 cents per KWh current applied to residential sales from energy produced by oil.

Size matters even more when you compare the new costs to previous estimates for construction of small plants that, to produce 5 MW, would require 80 to 100 million dollars of investment. E 'therefore of fundamental importance to be able to get on a large scale to exploit economies arising therefrom: for example, the costs of installation and the pipes are not proportional to the sizing of the system and would result in a much lower cost for the production of electric energy .

The OTEC plants not only produce energy: Applications of controlling the flow of hot and cold water are varied and benefits of streamlining of the plants would fall positively on the armature. As seen it is possible to create, through the process of pressure generation, drinking water can be used for both domestic use and for commercial use. Not to mention that the city of Toronto came to the village to use the water of Ontario to cool buildings. Fishing from the bottom of the lake you will benefit from a much lower temperature that will save you up to speed tens of MW of electricity.

The principle can then be used for air conditioning systems allowing an annual savings of $ 200,000 to $ 400,000 according to estimates by the U.S. Department of Energy. The production process also generates waste plankton and microorganisms that could be reused on aquaculture. Last but perhaps most important is that the process generates clean energy that can be used for the extraction of hydrogen by electrolysis.

Why then this technology has remained still so unknown? It 'convenient to produce energy from the sea?

The power plants are cheaper in which fossil fuel is burned and gas that allows an efficiency of around 50%. Clearly, the fossil fuel plants contribute to the warming of the planet and the consequences glocable (disastrous) on the ecosystem can not be quantified in advance.

The enegia nuclear power is seen as a clean energy instead when you forget which is removed in the form of leakage or waste about 50% of the fuel used: leakage can occur in rivers, seas or nell'atmostera. In addition to possible nuclear disasters in fact you have to consider the costs associated with decommissioning, deliberately hidden charges or those that lead to an effective cost much higher.

It may seem within reasonable therefore to compare the costs of a "clean" energy such as nuclear technology with OTEC, expressed in euro kilowatts.

The current cost of a central "atom" are provided by Finland, where the plant is under construction (with considerable delay, the expected delivery in 2009 with the latest EPR (European Pressurized Reactor).

Areva and Siemens have planned a 1600MW plant at an initial cost of about $ 3 billion, now risen to 10 billion. The initial estimate of EUR 2,383 per KW will be largely obsolete, even though they were introduced to the new reactors Westinghouse AP-1000 AP-600 derived from their predecessors with a development cost of about € 900 per kW. A basic cost more prudent than 1100 euro per kW can be taken as the standard production theory: the real costs of the new central Finnish open a window on the actual very important convenience due to a tripling of spending exchanged in the realization.

How much does an OTEC plant instead? From the numerous and various provisions of various American and Indian experts, a 200 MW plant would theoretically generate 240 million liters per day, with an overall benefit to the system which leads to a cost / performance of 1400 Euros per kW.

The first conclusion is that a platform OTEC can justify a budget about twice a nuclear center, including the same yield per installed capacity (1100 € / kW) and the value of desalination (1400 € / kW) which leads to a performance total of about 2500euro/kW.

Ragionando over a period of 25 years and including maintenance costs and operation is necessary to apply to an OTEC plant a multiple of 1.75, which leads to a net total of benefits to 2400 € / kW, more than double the cost of a plant nuclear power.

The costs are relevant in the cycle OTEC open but they are an integral part of the operation and power generation, which implies that there will be significant extra costs. Maintaining a Reverse Osmosis system for 25 years may justify a budget of 3 times the cost of nuclear power.

A further conclusion emerged in studies performed by the OTEC is that if water desalination can be doubled you can get up to a sustainable benefit by investing 5 times the cost of a nuclear power plant.

Although it is not a proven technology in the long term shows a glimpse of his own theoretical convenience. Why, then, is not made a serious test? The obstacles are considerable but not insurmountable: first there is the legal status of the platforms positioned in the open ocean. The costs also remain uncertain about large systems, but some American studies argue that it is theoretically possible to arrive at costs close to 7 cents per kWh with the latest experiments.

So what is the real reason of the lack of investment? The risk derived by the high capital intensity and a lack of investment guarantee in the evolution of time. Other renewable energies, although they have still many problems also in terms of environmental impact (such as disposal of old solar panels) require smaller investments and have a lower risk rate. In a crisis situation involving all the international context it is confirmed that it is necessary to show as soon as possible dell'OTEC new successes to funders or the current experiments at the Hawaii and other tropical islands will remain so.

The search for clean energy future really close the door, along with the great decline of the oil lobby and the nuclear industry.

26/01/2011

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Translated via software

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Source:

Italian version of ReteIngegneri.it