Technology

CSP Today speaks to Dr. Eckhard Lüpfert, one of the founders of engineering and consulting firm, CSP Services GmbH, to learn more about cutting edge tools and strategies that can aid developers in site selection, optimal solar field layout, and collector design to ensure CSP plants deliver maximum yield.

Interview by Rikki Stancich

CSP Today: Where can CSP project developers avoid incurring unnecessary high costs?

Dr. Lüpfert: Examples include design and assembly issues of concentrator structures; correct specifications for key components; and high accuracy DNI measurements for performance evaluation.

For many years such expert contributions have contributed to significant performance improvements and risk reduction, and have thus prevented expensive corrective measures at later project stages.

CSP Today: What are some of the common cost drivers in CSP project development?

Dr. Lüpfert: Timing; licencing - all the administrative preparation; and technology risk.

CSP Services contribution is not to improve the timing or speed the bureaucratic process, but rather to assist on the technical side. We contribute our experience in the qualification of materials to reduce the components risk that is priced in by contractors. We provide knowledge, experience, robust data, accurate DNI measuring and qualified components.

CSP Today: How does CSP Service's deflectometric measurement system optimise parabolic trough shape at the design phase?

Dr Lüpfert: CSP Services' measurement systems QFoto and QDec include in particular vision surveying (photogrammetric and deflectometric) technology, with developments based in and licensed from DLR (German Aerospace Center), and with an application for quality monitoring and inspection during manufacturing of shaped mirror panels and collector support structure geometry.

Photogrammetry (QFoto) is used for in-line measurement of steel structure assembly accuracy. Deflectometry (QDec) is used for mirror shape measurements on single mirrors (mirror panels). The system is now also available for in-line analysis of whole modules (QDec-M, for troughs, heliostats, dishes) in the fabrication environment.

The measurement data give immediate feedback into the production process for optimisation purposes. They include up-to-date standardized evaluation criteria and quality specs specific to the CSP technology, such as standard focus deviation FDx and intercept factor calculation.

Production process monitoring and quality assessment achieves optimised production results, reduced quality issues, and reliable output quality. Our measurement experience has been used in several key projects to optimise solar collector perfomance.

CSP Today: Who has used deflectometric measurement in the CSP sector? By how much has it contributed to increased collector efficiency?

Dr Lüpfert: It is quite commonly used – in several industries it is already the standard, for example in the mirror industry, where it is used for quality control.

For the solar field, it is used during collector development in order to optimise the parabolic trough shape. It is used during the development of new collector products to measure the performance, or rather, the gap between the performance achieved and the benchmark expectation.

It is also used for quality control. Once the product has been designed, tested and manufactured, it is used to ensure that the performance standard is being met. A good contractor will undertake continuous quality control in order to maintain product performance at design level.

CSP Today: Would you say that the upper limit on performance has been reached for concentrated solar power collectors?

Dr Lüpfert: The limits have not yet been reached. There is room for improvement – albeit not much.

CSP Today: In your view, what is the maximum optical performance that collectors will achieve?

Dr Lüpfert: We would be in the low 80’s for optical efficiency. It also depends on its definition details.

Over the last ten years there has been an improvement in collector efficiency of around 10% in part due to the work we have conducted here, but mainly due to the consequential improvements made by industry in mirror coatings, collector shapes, support structures and so on. 

CSP Today: To what extent is there a correlation between the quality of measuring and the performance of mirrors – is some of the 10% improvement attributable to improvements in measuring technologies?

Dr Lüpfert: Yes, there is certainly a correlation between the quality of the measuring tools and the achieved efficiency and quality of the collector production. The measurement methods are continuously being improved on, from cost efficiency, speed of measuring, and usability from a practical application in the field.

CSP Today: Why is the MDI system for solar resource assessment considered to be a superior option for irradiation measurements? How does it differ from existing models and is there room for improvement?

Dr. Lüpfert: MDI is a meteorological station with specific measurement of the DNI, and also the most used meteorological parameters (ambient temperature, humidity, wind, pressure, precipitation) especially designed for remote sites, where most solar resource assessments are performed. The MDI advantages are the low maintenance and high reliability of this remote meteorological station.

It is equipped with a rotating shadowband irradiometer (RSI), which is what sets it apart from other models. Although pyrheliometers primarily yield higher accuracy, their response decreases on average, nearly one percent per day if not cleaned daily. They are thus not suitable for remote sites.

In our system, which is designed specifically for CSP applications, the accuracy of our sensors and reliability of the overall system, i.e. no data failure is noteworthy. 

In project development and consulting, poor data quality at the project preparation and start-up phase is a recurring issue. The quality of data of other systems is low due to poor quality and poor maintenance of the equipment – this is a key advantage we have over our competitors.

Scientifically thorough calibration, including special correction algorithms, yield irradiance data measured with an RSI close to (and, under several circumstances, even better than) pyrheliometer measurements. Investigations on further data improvement are ongoing.

Additional continuous monitoring of the daily data by experts and the proven design of the station ensure high quality data for CSP site analysis in order to detect possible errors early on, and to reduce data gaps to a minimum.

CSP Today: How do CSP Services' MHP systems help operators to achieve optimal plant yield?

Dr. Lüpfert: MHP is a meteorological station with high-precision tracking pyrheliometer equipment and temperature corrected pyranometer according to highest international standards. The system provides most accurate instantaneous solar direct beam irradiance values, and also the most used meteorological parameters (ambient temperature, humidity, wind, pressure, precipitation).

It is used in high precision monitoring for CSP plant sites, in particular for continuously maintained operating sites and monitoring of CSP plants. Design and equipment of the MHP station yields measures to check the data quality and advises when maintenance is required.

With the highly accurate irradiance data, plant yield can be controlled continuously, and plant operators can take the measures for improvement. 

CSP Today:  As a consultant, are you seeing any recurrent challenges that operators run up against, from pre-feasibility through to construction?

Dr. Lüpfert: Realisation of the construction works is often dominated by time and money constraints. In addition, in such new technology fields, the construction and operation phases typically suffer from lack of experience, professionalism and elaborate standards of the solar field technology.

Companies that have been involved in other kinds of power plants or process installations still do not have sufficient experience in working with CSP technologies. On the flip side, developers of CSP that have developed their own technologies to hook onto power plants often lack experience in the power plant side.

As such, risk of failure is a challenge that they are running up against. Many of the players have this problem, given the newness of the technology. This happens in many constellations – in financing for example – the lack of experience with the technology in the field affects every player.

This will likely lead to consolidation as time goes on. The key to success is experience and professionalism.

Appropriate specifications for components, quality, and project monitoring are needed to reduce risks of delay and negligence in the construction and start-up phase of the plants. Experienced consultants will effectively support that phase by feeding existing experience back into the projects.

CSP Today: When are we likely to see component standardisation?

Dr. Lüpfert: Standardisation is on-going, but is still at the early stages in some fields given the lack of wider field experience.

Standards will contribute to consolidation, without blocking innovation – it will provide an instruction manual for players to avoid repeating mistakes.

Heat transfer pipes, turbines, and transformers were all standardised in previous power plants. The new components that are undergoing standardisation include mirrors, receivers and support structures.

CSP Today: In the longer-term, which reflector is likely to be dominant: glass, aluminium of polymer reflectors?

Dr. Lüpfert: At this stage, glass is likely to be the winner, but polymer and aluminum have yet to reveal all of their secrets. So far, however, glass has proven to be the most durable over the long-term.

To respond to this article, please write to the editor:

Rikki Stancich: rstancich@csptoday.com

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