Solar Thermal Generator
Based On A Fresnel Mirror Array

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A solar thermal generator based on fresnel mirrors can create very efficient, relatively cost-efficient solar harvesting in the right regions.  Here I cover a system supplying utility needs and another aimed at commercial clients.  

The construction of each is different.  Proposed and existing useful locations are also different.

Typical Parabolic Mirror For Solar Thermal Power - iStock Photo

Practically all utility-scale solar thermal arrays throughout the world are based on parabolic mirrors - long "U"-shaped dishes maximally focusing the sun's rays. 

The focal point of the mirrors has a collecting unit, usually a pipe containing water or some similar collecting fluid which can then be fed to power-generating turbines.

The mirrors are relatively difficult to manufacture and require cleaning to maintain output. They require a tracking system to follow the sun as its position changes in the sky throughout the day.

One of the companies I am looking at in this piece started their research approach using such mirrors.

Following photographs courtesy of Chromasun.

Solar Thermal Prototype on Australian National University Building Rooftop - Chromosun

Eight twenty-four metre long parabolic mirrors were installed on the roof the Australian National University in Canberra between 2003 and 2004.  With an initial aim of testing solar thermal production, electrical supply from associated photovoltaic units was to be added later. 

They expected to generate 40kW from the unit, two thirds in solar thermal and the rest from the photovoltaic units.  The solar thermal was planned to run air-conditioning units directly. 

Principal investigators from this trial went on to found Chromasun in California's Silicon Valley in 2008. 

Their design improvement was in changing the space-occupying parabolic mirrors into the fresnal pattern which allow production of a similar collection pattern from a varied angle array of flat mirrors.

Arrangement of faces in a fresnel mirror array - Chromasun

Construction, space saving, replacement and cleaning are all improved with a fresnel mirror collector.  Solar thermal generator costs improve significantly.

Meanwhile in 2006 in Germany Novatec Solar was founded.  Again based on a fresnel mirror array the solar thermal generator is significantly different. 

Much larger mirrors, open to the atmosphere, are used.  They are focused on a collection pipe seven metres above the mirrors.  Steam at 270 degrees C and 55bar pressure is produced to drive steam turbines. 

These are large construction pieces.  They are planned to be located in large desert-type areas as near to the equator as possible to improve solar efficiency.  Places like the western USA, Chile, western central Australia, the Midddle East, South Africa and Namibia are promoted as best sites. 

So far the company has constructed three power stations. 

Breaking ground in March 2008 Puerto Errado 1, or PE1, in the south east of Spain began power production a year later. With sixteen units in two rows, covering 18,000 square metres, producing 1.4MW of power it offered proof of concept.

In the same area a larger installation (PE2) came on line at the end of 2011, after a year's construction.  Covering half a million square metres with just over 300,000 square metres in mirror surface it can supply 30MW power. 

New South Wales in Australia was the site for the next Novatec Solar installation.  Associated with an existing coal-fired power station at Liddell the array covers 18,000 square metres, beginning supply in May 2012.

Meanwhile, the Australian-originated, Silicon-Valley-based Chromasun bases its solar thermal generator on multiple banks of repeated basic units suitable for roof top installation.  Again these units are ideal for high sun-irradiation areas. 

Each unit at 100kg (220lb), measuring 133 iches long, 12 inches high and 48 inches wide is substantial.  The twelve inch depth contains the whole mechanism - much more compact than Novatech Solar's. 

Also all the mirrors, tracking and collecting systems are contained within the unit, giving ideal protection.  They are built to operate at 200 degrees Centigrade (392 degrees Fahrenheit) and 40bar pressure. 

Geared to directly supply heated water, or other carrier, to drive boilers, water heating, space heating and air-conditioning units through heat pumps they benefit from direct use efficiencies.

Solar Thermal Generator Array on Rooftop - Chromasun

For the same area of PE2's array the Chromasun units can produce nine times the amount of power. This is mainly a reflection of the loss that occurs in converting heat into electricity in a power supply approach. 

Chromasun did develop a hybrid system like the original research array in Australia was aimed at. This is covered more in a separate area.  The electricity supply is based on a photovoltaic system rather than heat coversion. 

At present Chromasun is promoting it units more as solar thermal generators. 

The system suits population intensive areas in high sun exposure regions.  Timing of day-time sun energy and the size and weight of the units tends to lend commercial applications an advantage in this company's product. 

For information on a solar thermal generator that would be more helpful to home owners see my other section regarding this.


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