# Appendix B: Excel Structure for DISC Model of Direct Normal Irradiance (DNI) from Global Horizontal Irradiance (GHI)

Tables B.1 and B.2 show the structure and functions for implementing the DISC (direct insolation simulation code) model in Excel®. Note the cell references rely on the exact structure of rows and columns shown. User values are entered in shaded cells.

TABLE B.1

User Location Input Parameters

 Row Column A Label/Vali 1 2 3 4 USER 5 INPUTS 6 Latitude 7 User Value (+N, – S) 8 Longitude 9 User Value (+E, – W) 10 Time Zone 11 User Value (-W, +E) 12 Stn. Pressure 13 User Value mB 14 Pstn/P0 15 = A13/1013.250

TABLE B.2

Functions to Be Entered in Row 2, from Columns G to W

 Column Label (Row 1) Value or Function (Rows 2-8761) B Month 1 to 12 C Day 1 to 28, 30, or 31 D DOY 1 to 365 E Hr 1 to 23 F Obs. Hour 1 to 8760 G ETR = 1370*(1.00011+0.034221*COS(H2)+0.00128*SIN(H2)+0.000719 *COS(2*H2) +0.000077*(SIN(2*H2))) H Day Angle = 6.283185*(D2-1)/365 I DEC = (0.006918-0.399912*C0S(H2)+0.070257*SIN(H2)-0.006758 *COS(2*H2) +0.000907*SIN(2*H2)-0.002697 *COS(3*H2)+0.00148 *SIN(3*H2))*(180/3.14159) J EQT = (0.000075+0.001868*C0S(H2)-0.032077*SIN(H2)-0.014615 *COS(2*H2)-0.040849*SIN(2*H2))*(229.18) K Hour Angle = 15*( E2-12.5+ J2/60 +((\$A\$9-\$A\$11*15)*4)/60) L Zenith Ang = ACOS(COS(I2/(180/3.14159))*COS(\$A\$7/(180/3.14159)) *COS(K2/(180/3.14159))+SIN(I2/(180/3.14159)) *SIN(\$A\$7/(180/3.14159))) *(180/3.14159) M Air Mass = IF(L2<89,\$A\$15*(1/(COS(L2/(180/3.14159)) +0.15/(93.885-L2)A1.253)),0) N Global Horizontal USER VALUE O Diffuse (optional) USER VALUE P Direct (Optional) USER VALUE Q Kt = IF(L2<80,N2/(COS(L2/(180/3.14159))*G2),0) R DISC Coeff. A = IF(Q2>0,IF(Q2>0.6, -5.743+21.77*Q2-27.49*Q2A2+11.56 *Q2A3, IF(Q2<0.6,0.512-1.56*Q2+2.286*Q2A2-2.222*Q2A3)),0) S DISC Coeff. B = IF(Q2>0,IF(Q2>0.6, 41.4-118.5*Q2+66.05*Q2A2+31.9 *Q2A3, IF(Q2<0.6,0.37+0.962*Q2,0)),0) T DISC Coeff. C = IF(Q2>0,IF(Q2>0.6, -47.01+184.2*Q2-222*Q2A2+73.81 *Q2A3, IF(Q2<0.6,-0.28+0.932*Q2-2.048*Q2A2,0)),0) U DKn = IF(Q2>0,(R2+S2*EXP(T2*M2))*\$A\$15,0) V Knc = IF(Q2>0,(0.886-0.122*M2+0.0121*(M2)A2-0.000653 *(M2)A3+0.000014*(M2)A4),0) W Model DNI = IF(Q2>0,G2*(V2-U2),0)

Note: Columns B to F may use either specific, noncontinuous values or be filled as serially complete to the extent needed. Column N is the required user value for global horizontal total hemispherical irradiance.

Updated: August 22, 2015 — 5:01 am