3. Parabolic Trough Collector Concepts

Figure 25 a) Augustine Mouchout's sun power engine with axis tracking system and truncated concentrator cone. b) John Ericsson's schematic parabolic trough collector with a steam engine and a regulating device (flywheel) for energy storage [41]

b)

Using the solar power as an energy source was not an enigma back in the 19^th century. In fact a group of inventors believed that the sun had the potential to replace coal power. The way of implementation rather meant a technical challenge.

Pioneers of the field like John Ericsson (1803-1889), Augustin Mouchout (1825-1912) and Frank Shuman (1862-1918) shared the notion that one day coal deposits would be lacking easy access at someday. They recognized the need to use another, abundant source of energy. For this reason first concepts were developed for the production of steam by concentrated solar radiation, leading to the construction of the first reflectors, receivers, geometries, tracking systems and plans for new fields of application.

In 1907 Dr. Wilhelm Maier and Adolf Remshardt patented a device for the general use of sun's heat for steam generation in Germany. In 1912 Frank Shuman & Charles Vernon Boys invented the Sun Boiler and set an important milestone in the history of CSP.

A first solar field was deployed in 1913 to generate steam for a low pressure engine to pump water from the Neil River to irrigate a cotton plantation (see Figure 26). The power output at the low pressure steam engine was around 45kW enabling the pumping of around 23 m³ of water per minute. The configuration of the plant was composed of five rows of collectors of each 61 m long and 4 m aperture with a 6 m wide space gap between the rows. In total the operating aperture area of the solar field was around 1200 m². A rough calculation estimates a 41% to 46% peak optical efficiency of those collectors.

b)


a)

Figure 26a) Front sight b) back sight of a collector row at the Solar Engine One power plant in Al Meadi, Egypt 1912 [41]

The solar field's format possessed similarities to current operating plants. It showed the collectors in rows with the pipeline distribution and connections to the main steam pipe. The collector's structure was made out of iron frames with a lead coating which were connected to one another and geared, by means of central rack and cog wheels to the engine at ground level [42]. The boiler (in analogy to the current absorber tubes) was coated with a dull black paint or treated with a chemical process (e.g. the treatment of lead with sulphureted hydrogen) followed by a coating of varnish or enamel to reduce the loss of heat by conduction and convection [42].

At that time terms like automation, efficiency optimization, auxiliary storage tanks and mirror shapes, were already topics with a future vision. Shuman considered also an application of the technology to generate electricity at large scale between the tropics of Cancer and Capricorn (i.e. solar belt), yet limitations were significant. Even though the technology was already proven, the plant operated only for one year (1914) and none of its kind was built in the world until the late 1980s. The First World War led to the dismantling of the plant to supply the metal for Britain's munitions industry. Later the industry, still focused on fossil resources, gave no chance to the still ineffective and expensive solar technology.

2. 
   Category A: Conventional Collectors
   

Parabolic trough collectors within this category follow the same concept defined by their components. They determine the common design and functionality while tracing the sun. Their specific elements and mechanisms are for example

1. 
   Silvered glass reflector facets, about 4 to 5 mm thickness, with a specular reflectance of 93.5% and more than 15 years durability.