This document discusses the importance of assessing the quality of ground-based solar radiation data used for model development, benchmarking, and assessment. It outlines several existing quality control procedures from organizations like BSRN, ARM, and NREL that check for physically realistic values and consistency between radiation components. Common errors found in some databases are also described, such as errors in the recorded time reference affecting clearness index calculations and erroneous beam radiation near sunrise/sunset. The document raises questions about whether Task 36 should propose a general quality control procedure and which criteria should be included in a solar radiation data guide.

1. Quality of ground data for Assessment and
Benchmarking
L. Ramírez, J. Polo, L.F.Zarzalejo, L. Martín, A. Navarro
CIEMAT (Energy department – Solar Platform of Almería)
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

2. Objective
 Model development, benchmarking exercises, assessment of
models could be strongly affected by the quality of the solar
radiation ground data.
 As a consequence, quality checking of ground data use to be a
first step prior to model development or assessment, etc..
 Excepting the case of BSRN, ARM, WRC etc, many times ground
databases with unknown quality criteria are used.
 What quality criteria are then available? Are there consensus?
Are them complete enough?
 Any guide on how to use solar radiation data should include
a chapter for data quality
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

3. Background on Quality Procedures
BSRN
 Measurements with physical sense (Solar Constant, I0, .)
 Extremely rare values (Idiffuse > 700 Wm-2)
 Crossing components (Iglobal=Ibeamcosθ+Idiffuse±50 Wm-2)
NREL SERI_QC for Atmospheric Radiation Measurement (ARM) Program
 Physical sense (Max & Min values for Kn,Kt,Kd
 Crossing components (Kt=Kn+Kd ± 0.03)
 Other one, two or three-component tests
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

4. Other procedures
R. Claywell, T. Muneer, M. Asif, 2005. Journal of Solar Energy
Engineering
kd-kt scatter envelope
kd ∈[< kd > −2σ k , < kd > +2σ k ]
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

5. Frequent errors found in some databases
 Error in time reference registered. This error affects to the
clearness index estimation.
 Error in beam measurements close to sunset/sunrises.
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

6. Error in time reference
1. Error detection: Kt analysis.
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

7. Error in time reference
2. Proposed correction:
THEORY
1. Depending on the time frequency, data interpolation in
intervals lower than 10 minutes.
2. Centering data around midday.
3. Trying different displacements: (±1 hour)
4. Kt analysis: (from wsr+1 to wss-1)=> n iterations.
5. In each iteration, Maxi(Kt) of the whole day is selected.
6. True displacement = position (i), where min(Maxi(Kt)).
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

8. Error in time reference
2. Proposed correction:
PRACTICCE:
 Start : centered position: green points (hourly);
yellow (interpolated)
 Kt matrix analyzed (red big square)
 Position selected: position (i), where min(Maxi(Kt)).
hourly data selected: blue points.
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

9. Error in time reference
3. Results:
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

10. Error in beam radiation near sunrise and
sunset
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

11. Conclusion
 Should Task 36 propose a general procedure for quality of
ground measurements?
 In that case, which criteria should be included?
 Should this procedure be included in a guide of solar
radiation data (MESoR)?
4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007