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martes, 19 de febrero de 2013

Parabolic dish, not necessary with a Stirling engine. The Clique Solar case

Jorge Alcauza -
15 February, 2013

Parabolic dishes are, in the Concentrated Solar Power sector, generally associated with the purpose of generating electricity and, by default, with a Stirling engine.
In these cases, it’s often compared to PV systems, which are, most of the times, cheaper, simpler and easier to install, and furthermore, more easily bankable, what has made this technology not to be deployed as expected.
But when it comes to produce heat or steam, the parabolic dish technology has a lot to say in this market.
This technology offers a high concentrating ratio for a single unit that can be easily placed almost anywhere -over the ground, a rooftop, in your house’s backyard- and its assembling is generally easy, depending on the size.
It’s often made with widely-available low-cost materials, mostly steel and glass, what makes it suitable to be manufactured and installed anywhere in the world. It’s highly scalable and moreover, unlike other technologies, it can be placed on sloped terrains and hills.
With a proper receiver and Heat Transfer Fluid (HTF) it’s extraordinarily easy to produce heat just with the free fuel that the sun gives us every day.

Clique Solar, an India based company, offers two commercially available parabolic dishes, the ARUN 100 and the ARUN 160, basically the same but with different sizes.  These models are based on the Fresnel concept to create a paraboloid with small slightly curved mirrors.

We have talked to Clique Solar’s team to know more about the research and development of this technology and, surprisingly, they started the ARUN project back in the late nineties when, as they said, “the concept of solar energy in India was largely unheard of. So the first challenge was the limited awareness about the industry and limited research practices in the country. Internet in India had just made its entry, so knowledge-sharing was also a limitation. This also meant that we hardly had people specialized in this domain; so in a way we were shaping the entire domain”.
They had to face some challenges, starting by making solar energy relevant to industry and companies, not as easy as it may seems, not to mention funding limitations, although fortunately, “somehow we never had to wait for the next step. So it never proved to be a roadblock”.
The team focused in making “a solar concentrating system that not only is effective and efficient in terms of technology but also scores high in terms of utility to the end user – i.e. Industry”. This way, engineering concepts, constraints and requirements were re-visited innumerable times until the final design.
Besides the common challenge of capturing solar energy efficiently, as it occurs in the whole solar sector, Clique Solar has taken into account the availability of space. “Our vision was and is to make solar energy viable for companies on a standalone basiswhich means that not only the cost and efficiency should favor them but should work in space constraints as well. This is because land is not a luxury for companies and factories”.
The dishes, as we can see in the pictures, are not exactly ‘parabolic dishes’ since it has been applied the Fresnel concept to design the reflector, what makes them look like ‘flat dishes’. “The idea of making it work in a limited space is what helped us to freeze on a Fresnel paraboloid arrangement, (…) the efficiency and more important accuracy increases substantially when each plate is independent to capture their share of radiance. This is also helpful in reducing maintenance cost”.-

For now, the company does not intend to develop models for electricity production and is focused on the concentrated solar thermal segment.
Regarding their future plans, company said, “Awareness is the biggest challenge for this industry. It is proving such a huge impediment that demand is still lying latent. This latency needs to be converted into active demand by creating awareness and by keeping focus on sales. Thus we plan to create reference installations in different industries across the country in the near future”.
The ARUN dishes can use water/steam or oil as HTF and are suitable to produce pressurized hot water (up to 250 ºC) or steam (up to 25 bar), and in some cases, a pressurized water storage tank is used for thermal energy storage. India’s Ministry of New and Renewable Energy and Indian Institute of Technology Bombay have supported this development.
As it’s stated in Clique Solar’s website, these models are being used in some industries, such as dairies, automobile manufacturing or chemical industries, where process heat or steam is needed, and also for cooling systems for buildings making use of an absorption refrigerator. A set of case studies can be found at the company’s website.

Fuente: http://www.blogger.com/blogger.g?blogID=831753605691375960#editor/target=post;postID=5827162003515211725

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