Quality of ground data for assessment and benchmarking

4th Meeting IEA SHC Task 36 Hamburg 23-25 Oct 2007

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)


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


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


Other procedures

R. Claywell, T. Muneer, M. Asif, 2005. Journal of Solar Energy Engineering

kd-kt scatter envelope

[ 2 , 2 ]d d k d kk k k


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.


Error in time reference

1. Error detection: Kt analysis.



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)).



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.



3. Results:


Error in beam radiation near sunrise and sunset


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)?

Documents

Quality of ground data for assessment and benchmarking