Review and Outlook on Methods for Product Certification, Energy Yield Measurement, Power Output Determination and Commissioning Test for Large Solar Thermal Installations

Abstract

The market for large solar thermal systems is growing and with it the need to plan, design and simulate these systems precisely. This requires the ability to accurately and meaningfully measure their performance and yields. Hence activities for the development of methods to characterize such plants are on-going. The paper presents three of these methods and compares them with regard to their technical requirements and boundary conditions. The comparison includes the collector models on which they are based, the nature of their results and the use cases for which they are most suitable. It should serve as a decision-making aid for stakeholders in selecting the measurement method best suited to their needs and boundaries. The paper shows that these methods do not contradict, but rather complement each other.

Application of PC Method to Large Collector Arrays

“…The equation used for estimating the collector array power is chosen depending on the collector type and targeted uncertainty level. Three equations are available: Equation A: A simple power performance estimate for non-concentrating collectors: Q̇sec,est = AG • [η0,hem Ghem -a1 (ϑm -ϑa) -a2 (ϑm -ϑa) 2 -a5 (dϑm /dt)] • fsafe (eq. A)…”

“…Q̇sec,est = AG •[η0,b Kb(θL, θT) Gb + η0,b Kd Gd -a1 (ϑm -ϑa) -a2 (ϑm -ϑa) 2 -a5 (dϑm/dt)] • fsafe (eq. B)…”

“…1) σ = standard deviation; value ± 2σ is equal to a 95.45% confidence interval for a normal distribution 2) Contribution to uncertainty of measurand Xi for calculated value Y: (dY/dXi) 2 . u(Xi) 2 /u 2 (Y) 3) for average conditions of eq.…”

“…For the criteria "no shadows" it was required that all data within the hour were without shading. For the criteria "change in collector mean temperature", the difference between maximum and minimum temperature within the hour was used, meaning that the collector mean temperatures was within a band of 5 K. [2] Additionally, only data was used where the operating signal was true for all timestamps. Whereas this did not affect the valid data records for the four subarrays, it proved to be a useful additonal check in the evaluation of other collector arrays, because it occured that data where the collector array was not in operation for the whole hour due to a control failure was mistakenly counted as valid data.…”

“…Performance checks and guarantees for large-scale solar thermal systems are an increasingly important tool to minimize the risk associated with building a solar thermal plant [1]. The development of in situ test methods is currently investigated in numerous research projects [2]. A simple and easy applicable method to check the thermal power output for large collector arrays is the Performance Check (PC) method.…”