Plant Parabolic trough capacity (MW)
CCGT Capacity (MW) Ain Beni Mathar,
Morocco
20 452
Hassi r’Mel, Algeria
25 130
Kuraymat, Egypt 20 115
Martin County, Florida, USA
85 Existing 450MW
4.9 Concentrated Photovoltaic (CPV)
CPv uses concentrating optics to focus light onto small, high efficiency cells (see Figure 16 & 17). These high efficiency cells are more expensive than the cells used in normal photovoltaic plants due to the higher efficiency and operating temperatures required. The concept is to reduce the cost of electricity by minimising the amount of expensive photovoltaic material required; the cost of the silicon cells typically comprises more than half of the module cost.
With research cell efficiencies of over 40%, CPv is the most efficient of all the Pv technologies. Efficiencies have been increasing by approximately 1% per annum and are expected to peak between 45% and 50%.
4.9.1 Manufacturers and Examples from Industry
Installed capacity of CPv remains low. only four
companies, Amonix, EnTECH, Guascor Foton and SolFocus, have installed plants of more than 1 MW. Amonix-Guascor Foton, a joint venture, built the largest CPv plant at Parques Solares de navarra, 7.8 MW, in 2008.
[21] A. Fernandez-Garcia, E. Zarza, L. valenzuela, M. Perez (december 2009):
Parabolic-trough solar collectors and their applications;
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VMY-4YNB5Y6-1&_user=8452154&_coverDate=09%2F30%2F2010&_
rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_
searchStrId=1413265686&_rerunOrigin=google&_acct=C000050221&_
version=1&_urlVersion=0&_userid=8452154&md5=dae73bcebffd373c8a 628c8a942157eb (accessed 26/07/2010); renewable and Sustainable Energy reviews, volume 14, Issue 7, September 2010, Pages 1695-1721
Suncore Photovoltaics, a joint venture between Emcore and San’an optoelectronics, is pursuing multiple projects as part of the 280 MW solar energy plan recently announced by the Chinese Government[22].
4.9.2 CPV Advantages and Disadvantages
The principal advantages of CPv are that it requires water for cleaning purposes only, is modular and is more flexible than thermal CSP in terms of site requirements. Like parabolic dishes, CPv systems can be installed at sites with undulating terrain.
Commercialisation of CPv is held back by the availability of concentrator cells. A number of new companies with the capability for epitaxial (single-crystal) growth of multi-junction cells have started competing with the established manufacturers Emcore[23] and Spectrolab. The availability of cells is expected to increase rapidly following the entry of these new suppliers.
Although some standards are available, many key areas are not covered in comparison with conventional Pv. The most critical of the required standards is ‘IEC 61853, Photovoltaic (Pv) module performance testing and energy rating’, which has been in draft for over two years. In the absence of this standard, nameplate energy ratings are debatable and hence some investors have lower confidence in CPv technology than in conventional Pv. In certain situations financing risk may be reduced if CPv is installed alongside a mature technology such as flat plate crystalline Pv in a hybrid installation.
4.10 Linear Fresnel Reflector
Linear Fresnel reflectors differ from parabolic troughs in that the absorber is fixed in space above the slightly curved or flat Fresnel reflector. Several mirrors are fitted into the system, all of which focus their energy on the central line-receiver. In some cases a small parabolic mirror is added to the top of the receiver to further focus the sunlight.
The options for siting and orientation of linear Fresnel plant are similar to those for parabolic trough plant. A flat land area is required, and it is usual to orientate the reflectors in a north-south direction, in order to maximise sunlight captured throughout the day.
Linear Fresnel reflector technology has historically operated at the lowest temperature of the available CSP technologies.
4.10.1 Applications and Examples
Implementation of linear Fresnel plants has been led by Areva Solar (previously Ausra, USA), with the 0.36 MW Liddell plant in Australia commissioned in 2007 and the 5 MW Kimberlina plant commissioned in 2008. Areva Solar (Ausra) technology has been designed for application in utility-scale solar and solar hybrid plants, steam augmentation and industrial processes such as desalination and food processing. The overall concept was to design the technology to be utilised at the MW scale, although
[22] Emcore is the only vertically integrated CPv product provider at present, see:
http://www.euroinvestor.co.uk/news/story.aspx?id=11207570 [23] yourrenewablenews.com; EMCorE enters into multi-year agreement to
supply Solar systems for utility scale power projects in US; http://www.
yourrenewablenews.com/news_item.php?newsId=4085
Figure 16: Illustration of Typical CPV Concentrating Mechanism Figure 17: Example of SolFocus CPV Installation
Primary Mirror
Optical Rod High-Effi ciency
Multi-Junction Solar Cell
buildings for hospitals, factories and schools. These companies may develop and scale up their technologies for applications such as process heat, desalination and power generation in the future.
4.10.2 Reflector and Structure
The mirrors utilised in linear Fresnel technology are
generally manufactured from float glass and have a thickness of around 1-2 mm. This allows the mirror to be sourced from a number of manufacturers worldwide, unlike those of parabolic troughs where precision bent mirrors are required. Fresnel mirrors are relatively cheap to procure at around $9.8 and 3 kg per square metre, which corresponds to approximately one third of the weight of a parabolic trough mirror.
Areva Solar may be withdrawing from the construction of large utility power plants to focus on heat plants for industrial processes or smaller scale generation projects (up to 50 MW) where the permitting process is more straightforward.
The second major player in utility scale linear Fresnel plants is novatec Biosol which is currently constructing the 30 MW Puerto Errado 2 (PE2) project. This follows the commissioning of their 1.4 MW Puerto Errado 1 (PE1) project in Murcia, Spain in 2009.
other companies such as UK based Heliodynamics have developed and implemented facility scale systems for applications where the solar heat is used directly, without conversion to electricity, for air conditioning and cooling in
Figure 18: Kimberlina solar thermal energy plant, installed by AREVA Solar (USA)
4.10.4
Conclusions
In the near term, it appears that linear Fresnel technology is most likely to be implemented in heat, rather than electricity generation applications, where its lower cost can more than outweigh its lower performance compared with the other CSP technologies.
Its use for utility scale power generation is likely to depend on:
•
The commercial success of the Puerto Errado 2 (PE2) project and a small number of other proposed projects.•
Commercial success of small scale applications, economies of serial production, and transfer of technology and production from small scale to larger scale units.•
Technology improvements and cost reductions achieved for other CSP technologies.•
Continuing substantial economic support for CSP power generation.The structures for mounting the mirror systems in linear Fresnel systems are simpler than other CSP technologies allowing a higher volume of automated manufacture. As the mirrors do not need to support the weight of the receiver, the overall weight of the structure can be reduced in comparison to parabolic trough technology. As linear Fresnel systems use mirrors located close together within a few metres of ground level, the wind has a reduced effect on the structure, allowing for a lighter structure to be used. When not in use, the mirrors can turn upside down for further protection from the wind, sand storms or hail.
4.10.3 Receiver and Heat Transfer
Linear Fresnel reflector plants use steam as the heat transfer fluid.
The receiver of the Areva Solar / Ausra system is made from steel tubes with heat absorption coating. Water is vaporised within the receiver tube. The steam is piped directly to the required application, whether it is for electricity generation, steam augmentation or industrial processes. This allows for the elimination of expensive receivers, performance reducing heat exchangers, and the costly transfer fluids that are required by parabolic trough technology. The simplification of components required by the technology means they can be sourced from a variety of manufacturers.
novatec Biosol proposes to use evacuated tubes supplied by Schott on its future projects. These are similar to those used by parabolic troughs, which will enable superheated steam with a temperature of 450ºC to be supplied, compared with a temperature of 270ºC in previous plants.
due to the lightweight nature, the simplicity of the receiver and carrier and the absence of environmentally hazardous heat transfer fluids, the installation of a linear Fresnel solar field is much simpler than that of parabolic troughs. The modular design of the reflector and receiver units and prefabricated components reduce the need for skilled labour, particularly in small scale plants for heat applications.
Fresnel reflectors. An average slope of 3% or less is preferable for parabolic troughs and linear Fresnel reflectors, and 5%
for power towers . Parabolic dishes and CPv, due to their modularity, can be installed on steeper slopes. CSP may require less land area per MWh than Pv, depending on the technologies employed.
A far greater quantity of water is required for parabolic troughs, power towers and linear Fresnel reflectors than for solar Pv plant, due to the need for turbine condenser cooling.
depending on whether dry or wet cooling is employed, a large quantity of water is required and therefore a local water source at an environmentally acceptable and economic price is essential.