Engerer2-separation-model

Code for the Engerer2 diffuse fraction separation model following the newly parameterised version published in the Journal of Renewable and Sustainable Energy. The model estimates the diffuse horizontal irradiance from inputs of global horizontal irradiance, latitude, longitude and time.

The Engerer Separation Model was first described and validated in the paper: Engerer, N. A. 2015. Minute resolution estimates of the diffuse fraction of global irradiance for southeastern Australia. Solar Energy. 116, 215-237. The paper presents 3 variations of the Engerer separation model: 1, 2 & 3 The Engerer1 is fit to Non-Cloud Enhancement data, the Engerer2 to Cloud Enhancement data and Engerer3 to clear-sky data only.

This original model was trained and tested exclusively on Australian data, and so lacked global scope, despite validating with excellent performance on many comparative studies. This repository illustrates a new performance of the Engerer2 model as per the new paper: Bright, Jamie M. & Engerer, Nicholas A. 2019. Engerer2: Global re-parameterisation, update and validation of an irradiance separation model at different temporal resolutions. Journal of Renewable & Sustainable Energy. 11(2), xxx.

We request that Engerer (2015), Bright & Engerer (2019), as well as this repository be cited if using this code in research.

PREDICTORS

The predictor variables to fit B0-5 are based on: kt = clearness index zen = zenith angle ast = apparent solar time dktc = ktc - kt (ktc is the clear-sky clearness index = ghi,cs/e_exth. k_de = Proportion of kd attributable to cloud enhancement

PARAMETERS

The new parameters are defined in the paper as:

Parameter	Predictor	Orig1-min	New1-min	5-min	10-min	15-min	30-min	1-hr	1-day
C	-	0.042336	0.10562	0.093936	0.079965	0.065972	0.032675	-0.0097539	0.32726
B0	-	-3.7912	-4.1332	-4.5771	-4.8539	-4.7211	-4.8681	-5.3169	-9.4391
B1	K_t	7.5479	8.2578	8.4641	8.4764	8.3294	8.1867	8.5084	17.113
B2	AST	-0.010036	0.010087	0.010012	0.018849	0.0095444	0.015829	0.013241	0.13752
B3	zen	0.003148	0.00088801	0.003975	0.0051497	0.0053493	0.0059922	0.0074356	-0.024099
B4	dKtc	-5.3146	-4.9302	-4.3921	-4.1457	-4.169	-4.0304	-3.0329	6.6257
B5	Kde	1.7073	0.44378	0.39331	0.37466	0.39526	0.47371	0.56403	0.31419

INPUT PARAMETERS

ghi = Global horizontal irradiance [W/m^2]
time = in the matlab datevec format [yyyy, mm, dd, HH, MM, SS] [UTC]
latitudes = either a latitude per measurement or one for all.
longitude = either a longitude per measurement or one for all.
averaging_period = x in minutes. Must be 1, 5, 10, 15, 30, 60 or 1440

OUTPUT PARAMETERS

Kd = diffuse fraction = Edh/ghi [fraction]
Edh = diffuse horizontal irradiance [W/m^2]
Ebn = direct/beam normal irradiance [W/m^2]

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