Renewable Revolution

Power tower solar has been under a cloud — in the U.S., anyway — after 321 birds or bats were killed in the first 6 months of operation by flying through solar flux above the Ivanpah Concentrated Solar Power (CSP) plant, the Google-funded colossus in California’s Mojave desert.

Opponents  then greatly exaggerated the numbers, making it a challenge for California regulators to maintain a level-headed approach to permitting future power tower projects.

Standby is the high risk position for birds.

fossils 34 times wind.

Buildings, power lines and cats are estimated to comprise approximately 82 percent of the mortality, vehicles 8 percent, pesticides 7 percent, communication towers 0.5 percent, and wind turbines 0.003 percent.

The optimum heliostat size — if in fact one exists — will be better understood as the power tower industry continues to deploy and operate more systems. Power tower industry is forced at least by market and commercial constrains to design and produce optimum (cost-effective) heliostats, in the near, medium term to significantly reduce capital cost of CSP becoming more and more competitive in the energy market, CR technologies have the potential of leading Solar Power through effective cost reduction to competitiveness.

Starting with initial heliostat efforts in the early 1970s up to today, there has been a general tendency to increase the heliostat size from about 12 m2 to approximately 150-200 m2, with several counter-examples of much smaller heliostats, primarily in the past several years. So that, currently, there is no consensus among CR-CSP developers regarding the optimum size of a heliostat.

The tendency to favor larger heliostats during this period has apparently been based more in local experiences while building and testing the first prototypes than in a holistic analysis of the problem, leaving aside the benefits of mass production, lean manufacturing processes in terms of quality control and cost reduction both demanded by CR technologies in part on the assumed advantages of “economies of scale”.

An expected benefit with larger heliostats was that the fixed cost of some components that are needed per each unit of heliostat could be spread over a larger area, thus reducing the specific cost per unit area.

Other factors may have played a role in this general trend, such as availability of commercial drive units potentially offering high performance and low cost, or relaxing design criteria to achieve lower costs by increasing the reflector area to the maximum allowable for a given drive unit. In efforts to reduce the cost of the drive, a number of customized drive products have been developed by companies such as Sener [Lata2010], Flender Siemens [Siemens2008, Teufel2008, Kunert2009], Winsmith [Kolb2007, Winsmith2003] and Cone Drive [ConeDrive2013].

For smaller heliostats, the cost of the control and communication system also becomes an important cost driver favoring larger heliostats.

Table 3: Advantages and drawbacks appearing when heliostat size is varying.

Heliostat Increasing size

PROs
   
Increasing Benefit from the economics of enlargement

Reducing the number of heliostat leads to reducing the cost by:

taking as much advantage as possible from expensive high-tech components mainly high precision tracking systems,

Lowering the specific operation and maintenance costs   


CONs               

Increase of torques from wind loads, resulting in higher specific weight and higher specific drive power. Thus the level of demand in the technical specifications of the heliostat’s tracking system increases with the size.

On-site heliostat assembly is difficult (facilities not well-equipped, not easily automated and time consuming processes are involved such as canting);

Canting accuracy becomes critical for a large heliostat. (For large heliostat fields where last row of heliostats could be placed at several kilometers from the solar tower, to be able to concentrate, large area heliostat need to keep their theoretical curvature).

Land use might be worse with large heliostats and the long distance heliostats provide worse optical efficiency.

Strong limitations when applying mass productions and lean manufacturing processes

There are now 226,852 heliostats in operation (Table 5) with a total mirror surface of about 3.3 millions of square meters. The figures for the heliostats to be implemented in the plants (and/or facilities) under construction are very similar: about 238,000 heliostats with a total surface of about 2 million square meters.

The total number of heliostats by adding the plants under development and planned to the operational and under construction plants, amounts to 835,838 heliostat units with a total mirror surface of about 17 million square meters.

Renewable energy=                                =Fossil Fuelers

Solar thermal power plant use solar arrays to heat water that produces steam that runs turbines to produce electricity.