With an overwhelming push for “green” renewable energy in the recent years, the American Society of Mechanical Engineers (ASME) Performance Test Codes (PTCs) are being called upon to develop standards for testing solar power facilities. To meet the challenge, ASME formed a committee to develop PTC 52, Performance Test Code on Concentrated Solar Plants.

It was recognized early on by the PTC 52 committee that there is a critical need in the power generation industry to develop a commercial grade test method for the measurement of Total Solar Field Direct Normal Insolation (TSFDNI) that may be used for performance testing. The TSFDNI measurement is important because it is the fuel source (input) for solar power technologies, and is therefore a primary measurement parameter that enters into the solar-to-thermal conversion efficiency calculations.

To meet the recognized need, ASME engaged McHale & Associates, Inc. (McHale) in a research project to investigate a solution to this issue so that the industry may be provided with guidelines that can be included in ASME PTC 52 for the accurate determination of TSFDNI. The product of this effort is a conceptual measurement technique, or method, that utilizes a combination of currently available terrestrial point measurements, aerial photography, and pixel contrast recognition software that allows for a visualization of the entire solar field to provide an accurate determination of TSFDNI by “filling in the gaps” between the point measurements while keeping the number of terrestrial point measurements practical.

This paper will illustrate the conceptual TSFDNI measurement technique and how it can effectively combat the issues associated with performance testing on days when the field may see areas of haze, dust, aerial obstructions with shadows, or cloudiness which are not visible from the ground by the testing personnel or unavoidable by commercial/contractual constraints; thus allowing performance testing to be conducted on partially cloudy days which would allow facilities to be commercially accepted with confidence at an earlier date than if they had to wait for a “clear solar day”. Guidance on the best practices for deployment in a grid style system in combination with an aerial photography pixel analysis method will be presented along with discussion on how the method will result in acceptable predicted error of the TSFDNI measurement through reducing error associated with the spatial components of the field measurements.

This paper will further discuss how this method can be used beyond performance testing by providing the key boundary information for performance models, performance monitoring systems, dispatch models, etc. Ultimately the paper will not only present just how important this measurement technique is for the development of ASME PTC 52, but also to the industry and technology itself, by presenting a way to overcome the current industries short falls in accurately determining TSFDNI.

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