I’ve been using satelite data from Nasa to estimate the output of our solar panels. This website gives you more data than you can possibly use ! For my purposes the ‘data tables for a particular location’ (under Meterology and Solar Energy) are what I wanted. In particular the table of Average monthly insolation on tilted panel.
For our location (51.7N-1.7E) this gives this table:-
| Lat 51.583 Lon 1.71 |
Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Annual Average |
| SSE HRZ | 0.82 | 1.46 | 2.45 | 3.72 | 4.71 | 4.97 | 4.98 | 4.34 | 2.93 | 1.79 | 0.99 | 0.62 | 2.82 |
| K | 0.35 | 0.37 | 0.39 | 0.42 | 0.44 | 0.43 | 0.45 | 0.46 | 0.41 | 0.38 | 0.36 | 0.32 | 0.40 |
| Diffuse | 0.55 | 0.87 | 1.47 | 2.10 | 2.56 | 2.76 | 2.65 | 2.26 | 1.60 | 1.00 | 0.63 | 0.43 | 1.58 |
| Direct | 1.22 | 1.88 | 2.33 | 3.13 | 3.78 | 3.78 | 4.03 | 3.85 | 2.89 | 2.25 | 1.43 | 0.93 | 2.63 |
| Tilt 0 | 0.80 | 1.44 | 2.42 | 3.70 | 4.73 | 4.99 | 5.00 | 4.31 | 2.88 | 1.75 | 0.95 | 0.62 | 2.81 |
| Tilt 36 | 1.29 | 2.07 | 2.94 | 4.00 | 4.67 | 4.75 | 4.84 | 4.54 | 3.40 | 2.42 | 1.49 | 1.02 | 3.13 |
| Tilt 51 | 1.39 | 2.17 | 2.93 | 3.83 | 4.30 | 4.31 | 4.42 | 4.29 | 3.36 | 2.51 | 1.60 | 1.11 | 3.02 |
| Tilt 66 | 1.43 | 2.17 | 2.79 | 3.49 | 3.78 | 3.79 | 3.90 | 3.85 | 3.16 | 2.48 | 1.63 | 1.14 | 2.80 |
| Tilt 90 | 1.33 | 1.93 | 2.32 | 2.69 | 2.79 | 2.70 | 2.80 | 2.88 | 2.55 | 2.17 | 1.49 | 1.07 | 2.23 |
| OPT | 1.43 | 2.18 | 2.95 | 4.02 | 4.85 | 5.05 | 5.09 | 4.59 | 3.41 | 2.52 | 1.63 | 1.14 | 3.24 |
| OPT ANG | 65.0 | 57.0 | 43.0 | 29.0 | 16.0 | 11.0 | 13.0 | 25.0 | 39.0 | 54.0 | 63.0 | 67.0 | 40.0 |