A model for improved solar irradiation measurement at low flux

A model for improved solar irradiation measurement at low flux

► Heat Flux Sensors have high error at low flux. ► A model is developed to compensate for this error in situ. ► It accounts for variations in operation conditions. ► Using the model RMSE decreased from more than 100 (W/m2) to less than 10 (W/m2). ► Calibration is done in situ without the need of lab...

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Bibliographic Details
Published in:Solar energy Vol. 86; no. 3; pp. 837 - 844
Main Authors: Mokhtar, Marwan M., Meyers, Steven A., Rubalcaba, Irene, Chiesa, Matteo, Armstrong, Peter R.
Format: Journal Article
Language:English
Published: Kidlington Elsevier Ltd 01-03-2012
Elsevier
Pergamon Press Inc
Subjects:
Accuracy
Applied sciences
Beam Down
Concentrated solar radiation
Electric power plants
Electrical engineering. Electrical power engineering
Electrical power engineering
Energy
Equipments, installations and applications
Exact sciences and technology
Flux gauge
Flux measurement
Heat Flux Sensor
Measurement
Natural energy
Non classical power plants
Photovoltaic power plants
Radiation
Sensors
Solar energy
Solar radiation
Solar thermal conversion
Solar thermal power plants
Water temperature
Heat Flux Sensor
Beam Down
Concentrated solar radiation
Flux measurement
Flux gauge
Water
Performance evaluation
Thermopile
Solar energy concentrator
Heat flow
Heat flux
Mean square error
Gauge
Learning
Solar power plant
Testing equipment
Heliostat
Solar radiation
Root mean square value
Measurement error
Sun tracking
Measurement sensor
Solar heating
Cooling by water
Irradiation
Measurement accuracy
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Summary:► Heat Flux Sensors have high error at low flux. ► A model is developed to compensate for this error in situ. ► It accounts for variations in operation conditions. ► Using the model RMSE decreased from more than 100 (W/m2) to less than 10 (W/m2). ► Calibration is done in situ without the need of lab equipment. Accurate measurement of solar radiation heat flux is important in characterizing the performance of CSP plants. Thermopile type Heat Flux Sensors (HFSs) are usually used for this purpose. These sensors are typically reasonably accurate at high heat fluxes. However measurement accuracy drops significantly as the measured radiation is below 1kW/m2, this often leads to underestimation of the actual flux. At the Masdar Institute Beam Down Solar Thermal Concentrator (BDSTC), measurement of fluxes ranging from 0kW/m2 to more than 100kW/m2 is required. To improve the accuracy of the sensors in the lower range around 1kW/m2, we have performed a test under ambient (not-concentrated) sunlight. Such low irradiation levels are experienced in characterizing the concentration quality of individual heliostats. It was found during the test that the measurement at this low range is significantly affected by ambient conditions and transients in the HFS cooling water temperature. A Root Mean Square Error (RMSE) of more than 100W/m2 was observed even though we kept the transients in water temperature to a minimum. Hence we devised a model to account for this measurement error at this flux range. Using the proposed model decreased the RMSE to less than 10W/m2. The application of the model on existing heat flux measurement installations is facilitated by the fact that it only employs easily measurable variables. This model was checked by using a test data set and the results were in good agreement with the training data set.
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ISSN:0038-092X
1471-1257
DOI:10.1016/j.solener.2011.12.012