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I live in Sydney. I have obtained insolation data from the NASA Surface meteorology and Solar Energy web page (you just need to give them an email address to see any data for yourself).
I need help interpreting the results.
Have a look at the 3 blue numbers in the RHS columns. I can't understand why the avg. direct normal radiation value (=4.88) is less than the value of 5.11 for a surface "tilted at the optimum angle". To answer that question we must explain the difference between an "equator pointed tilted surface" and a "surface oriented normal to the solar radiation " (i.e. a direct normal surface). Surely if a surface is normal to the sun then it is continuously tracking it in two axes.
regards
Peter
| Lat -34 Lon 151 |
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual Average |
| 22-year Average | 5.94 | 5.28 | 4.55 | 3.59 | 2.79 | 2.52 | 2.72 | 3.61 | 4.65 | 5.54 | 5.91 | 6.28 | 4.44 |
| Lat -34 Lon 151 |
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual Average |
| 22-year Average | 5.02 | 4.61 | 4.55 | 4.33 | 4.14 | 4.37 | 4.51 | 5.22 | 5.54 | 5.59 | 5.20 | 5.43 | 4.88 |
Parameters for Tilted Solar Panels:
| Lat -34 Lon 151 |
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual Average |
| SSE HRZ | 5.94 | 5.28 | 4.55 | 3.59 | 2.79 | 2.52 | 2.72 | 3.61 | 4.65 | 5.54 | 5.91 | 6.28 | 4.44 |
| K | 0.49 | 0.48 | 0.50 | 0.51 | 0.51 | 0.54 | 0.54 | 0.57 | 0.56 | 0.54 | 0.51 | 0.51 | 0.52 |
| Diffuse | 2.56 | 2.27 | 1.81 | 1.34 | 0.98 | 0.80 | 0.86 | 1.07 | 1.47 | 1.97 | 2.43 | 2.61 | 1.68 |
| Direct | 5.02 | 4.61 | 4.55 | 4.33 | 4.14 | 4.37 | 4.51 | 5.22 | 5.54 | 5.59 | 5.20 | 5.43 | 4.88 |
| Tilt 0 | 5.91 | 5.25 | 4.48 | 3.56 | 2.73 | 2.49 | 2.68 | 3.49 | 4.60 | 5.41 | 5.88 | 6.24 | 4.39 |
| Tilt 19 | 5.76 | 5.32 | 4.83 | 4.18 | 3.50 | 3.41 | 3.58 | 4.32 | 5.18 | 5.63 | 5.79 | 6.02 | 4.79 |
| Tilt 34 | 5.34 | 5.09 | 4.84 | 4.44 | 3.90 | 3.93 | 4.07 | 4.71 | 5.33 | 5.49 | 5.40 | 5.53 | 4.84 |
| Tilt 49 | 4.69 | 4.62 | 4.61 | 4.45 | 4.08 | 4.23 | 4.34 | 4.83 | 5.20 | 5.08 | 4.77 | 4.80 | 4.64 |
| Tilt 90 | 2.35 | 2.56 | 2.94 | 3.36 | 3.44 | 3.78 | 3.79 | 3.84 | 3.55 | 2.84 | 2.41 | 2.32 | 3.10 |
| OPT | 5.91 | 5.34 | 4.86 | 4.47 | 4.09 | 4.29 | 4.38 | 4.83 | 5.33 | 5.63 | 5.90 | 6.24 | 5.11 |
| OPT ANG | 3.00 | 13.0 | 27.0 | 43.0 | 54.0 | 60.0 | 57.0 | 49.0 | 35.0 | 19.0 | 6.00 | 1.00 | 30.6 |
Here are the definitions:
Monthly Averaged Direct Normal Radiation
- 22-year Average
- The monthly average amount of solar radiation incident on a surface oriented normal to the solar radiation for a given month, averaged for that month over the 22-year period (Jul 1983 - Jun 2005). The direct normal radiation is evaluated using the RETScreen method discussed in SSE Methodology.
- Minimum And Maximum Difference From Monthly Averaged Direct Normal Radiation
- The minimum and maximum values for a given month indicate the percent difference between the year that has the least (minimum) or most (maximum) monthly averaged direct normal radiation and the 22-year monthly averaged value.
- Units
- Monthly averaged direct normal radiation in kWh/m2/day
- Minimum and maximum in percent
- Reference
- SSE Methodology
Monthly Averaged Insolation Incident On A Horizontal Surface
- 22-year Average
- The monthly average amount of the total solar radiation incident on a horizontal surface at the surface of the earth for a given month, averaged for that month over the 22-year period (Jul 1983 - Jun 2005). Each monthly averaged value is evaluated as the numerical average of 3-hourly values for the given month.
- Minimum And Maximum Difference From Monthly Averaged Insolation
- The minimum and maximum values for a given month indicate the percent difference between the year that has the least (minimum) or most (maximum) monthly averaged insolation and the 22-year monthly averaged insolation.
- Units
- Monthly averaged insolation incident on horizontal surface in kWh/m2/day
- Minimum and maximum values in percent
- Note
- also referred to as global horizontal radiation
- Reference
- SSE Methodology for detailed discussion of the methodology for deriving surface insolation from satellite observations.
Parameters for Tilted Solar Panels:
Monthly Averaged Radiation Incident On An Equator-Pointed Tilted Surface
- SSE HRZ
- The monthly average amount of the total solar radiation incident on a horizontal surface at the surface of the earth for a given month, averaged for that month over the 22-year period (Jul 1983 - Jun 2005).
- Clearness Index (K)
- The monthly average amount of the total solar radiation incident on a horizontal surface at the surface of the earth divided by the monthly average incoming top-of-atmosphere insolation for a given month, averaged for that month over the 22-year period.
- Diffuse
- The monthly average amount of solar radiation for a given month incident on a horizontal surface at the surface of the earth under all-sky conditions with the direct radiation from the sun's beam blocked by a shadow band or tracking disk, averaged for that month over the 22-year period.
- Direct Normal
- The monthly average amount of direct normal radiation incident on a surface oriented normal to the solar radiation for a given month, averaged for that month over the 22-year period.
- Tilt 0, Latitude-15, Latitude, Latitude+15, 90
- The monthly average amount of the total solar radiation incident on a surface tilted relative to the horizontal and pointed toward the equator for a given month, averaged for that month over the 22-year period (Jul 1983 - Jun 2005). Note that the differences between the Tilt 0 values and the SSE HRZ values are due to approximations in the inputs and time integration inaccuracies when processing the equations and integrating over the "monthly average day" (SSE Methodology). Total solar radiation for each tilt angle was determined using the RETScreen Isotopic Diffuse Method discussed in SSE Methodology.
- OPT
- The monthly average amount of total solar radiation incident on a surface tilted at the optimum angle relative to the horizontal and pointed toward the equator.
- OPT ANG
- The angle relative to the horizontal for which the monthly averaged total solar radiation is a maximum.
- Units
- SSE HRZ, Diffuse, Direct Normal, and OPT in kWh/m2/day
- Tilt angles and OPT ANG in degrees
- K is dimensionless
- Reference
- SSE Methodology
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