CFD applications in Renewable Energy Technology

There are numerous areas within the field of renewable energy where Computational Fluid Dynamics (CFD) is used. The use of CFD simulation  has grown exponentially over the last two decades. Thanks to the improvement in computational speed, CFD  has reduced both prototype test times and costs.  It should be noted cost and time in  wind tunnels testing was exceptionally high.  Another important fact to mention here is that in 1986, R&D investment in the United States alone amounted to $6.25 billion, much of it was devoted to product development.

CFD  itself is prone to both setup and computational errors and therefore wind tunnels should not be consigned to history as yet. CFD has however reduced the number of physical prototype tests substantially before a product is launched. Today thanks to advancement on CAD, Product Lifecyle Management (PLM) and Computer aided Engineering, the design time for launching a product has reduced by several folds. An example form the automotive industry is the development time of  new car models.  It used to to take 35-97 months for a new model to be rolled out whereas now it only requires less than 20 months. The average in the industry is about 27 Months.

Similar scales reduction has been noticed in the product development relevant to renewable energy sector. In this article few areas where  CFD is used in the renewable energy engineering are listed below.

1. Development of Wind Turbine blade

The well designed blade on a wind turbine can last up to 25 years. During its lifetime it has to withstand several stresses that are variable and cyclic. Furthermore the blade also needs to be optimized to maximize the lift force and minimize the drag when pitched for electricity generation.

The profile also changes shape from root to tip to account for to the varying relative wind speed over the blade. CFD in this regards helps to get the best shape. The need of CFD is more pronounced  in the development of shrouded or ducted wind turbines.

2. Optimal Placement of the Turbines

The terrain of the site where a wind farm is to be located has a huge bearing on the output of the turbine. If located on the top of a hill, the output is considerably increased due to acceleration of wind.

Its not just the terrain but also the proximity to other turbines that have a bearing on the output. Ideally each wind turbine should be five hydraulic diameters away from the other to avoid turbulence in the wind shadow. The turbulence can cause unwanted vibration which can be damaging for both the blade and the gearbox in the turbine.

3. Wave Power Device Optimization

Wave power devices are complex to design. The sudden changes in both direction and amplitude of the waves requires the energy harnessing device to be extremely flexible. The higher the degree of flexibility of these devices the more energy can be harnessed, but this movement compromises the structural integrity. Therefore devices have to designed carefully.  CFD helps in providing a virtual wave tank environment where several what if scenarios can be tested. Many devices such as Pelamis or Oyster or the Point absorber have been tested using CFD for the evolution of their design.

4. Solar Water Heater Optimization

CFD not only allows calculation of Fluid flow but it also allows for heat transfer to be accurately estimated. In a Solar water heater both fluid flow and heat transfer phenomenon takes place simultaneously as coolant or water meanders through the absorber pipes. Additionally CFD software such as “Fluent” allows the possibility of estimating incident solar radiation through Solar model in the software.

5. Solar PV systems

It should be remembered Solar PV systems although are solid state electronic devices but their performance is heavily dependent on their  temperature. The cooler the panels are the better they perform. In projects like DESERTEC, there are plans for  massive arrays of solar panels in the Sahara desert. These panels wouldn’t work efficiently unless they are mounted on cooling jacket that wicks the heat away from the panel.  The active cooling system itself runs on portion of the electricity produced by the panel. CFD helps in maximizing the energy gain by  optimizing the design of the cooling system.

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