Mirror Manufacturing for Solar Concentrator

Selection of Reflective Mirror

In almost all of the STSs plane mirrors are used. The reason is that the cost of manufacturing curved mirrors is enormous which results in an increased amount of capital required to install the plant.

Despite the higher cost, curved mirrors were selected for this project due to following reasons

1.      Through literature survey we came to know that in terms of “Levelized Cost of Electricity” (LCOE) reduction, a design improvement that results in 1% performance improvement is equivalent to a design improvement that reduces solar field cost by about 2.3% i.e. the leverage of performance vs. cost on LCOE is better by a factor of about 2.3x

The exact improvement in efficiency due to this decision is unknown at this stage & it is possible that this improvement might not be able to balance out the increase in capital cost. Any and all results will be reported at the end of the project including the impact of this decision.

2.      There is another factor that inspired us to use curved mirrors. As the distance from the solar tower increases, the effect of scattering from dust particles becomes more and more pronounced. Thus the advantage of using a converging beam of light become more evident as this kind of reflected beam will be able to transfer a considerably more amount energy to the solar tower even after scattering.

3.      As the beam is converging therefore the area of the “wave front” formed at the receiver will be of small size. This enables us to design a receiver of smaller size which will reduce cost.

4.     Higher concentration of light due to converging beam will result in increased temperature which will result in increased efficiency of the system.

5.     Very high precision tracking is usually not feasible. The decreased wave front area of the reflected beam gives us an increased margin of tolerable error in our tracking.

1.1      Concave Mirror

The concave mirror at first seemed to be the ideal choice but a closer inspection resulted in numerous flaws.

1.      If we compare a  concave mirror and a plane mirror (square in shape) that take up the same amount of volume then the concave mirror only collects 78.5% (pi/4) of the incident beam while the plane mirror collects 100%.

2.      Concave mirrors if fitted in rectangular/square frames will be unable to sustain high dynamic or static loads.

3.     Specialized circular frames for concave mirrors will cost more & will still be unsuitable for opposing high speed winds.

4.      The market cost of customized concave mirrors is very high.

1.2     Toroidal Mirror

Toroidal mirrors fulfilled all our requirements. They sat well with rectangular frames. Their ability to converge the beam of light was satisfactory. Unfortunately toroidal mirrors of our required specifications are unavailable in our vicinity.

1.3      Cylindrical mirror

With the unavailability of toroidal mirrors the next best option was cylindrical mirrors. They are able to converge beam only in one dimension. Concave mirrors converge light on a point whereas cylindrical mirrors converge light on an axis/line.

The curved surface of the cylindrical mirror will be in such a way that the axis of the cylinder will be parallel to the height of the frame.