No subject
Tue Jan 17 15:36:28 EST 2012
(Ghana) for an inclined plane facing north at and angle of 45 deg (not
otimum angle).
The output looks like this:
1 1 7 7 51 46 91 67 74 27.3
1 1 8 8 248 122 365 151 424 27.9
1 1 9 9 393 215 470 235 352 29.4
1 1 10 10 606 236 712 275 545 31.3
1 1 11 11 768 257 879 307 637 32.7
1 1 12 12 764 359 844 401 466 35.1
1 1 13 13 801 339 887 383 528 37.4
1 1 14 14 677 372 733 394 372 38.6
1 1 15 15 533 342 584 361 272 39.3
1 1 16 16 287 247 287 237 73 39.0
We are interested in column 7 which is the radiation incident on the
inclined plane. The help documentation for meteonorm tells you what all the
columns are.
I imported this into excel and added a few formula.
The model is very simplistic. It models the charge in a battery that
receives input from the solar cell and supplies output to the access point.
For each hour the battery stores a net input of solar radiation*area of
cell*cell efficiency*batt efficiency
and has an output of access point power. Units in Wh
Solar radiation in W/m2
Cell area in m2
Cell efficiency is proportion of incident ration converted to electicity,
number in range 0-1
Batt efficiency is proportion of input power stored in battery, number range
0-1
battery charge is in units of Wh
The equations for calculating the charge in the battery are clamped at 0 and
the battery capacity in units of Wh
The spreadsheets for Frankfurt and Accra are at:
http://www.sentinet.demon.co.uk/wireless/frankfurtmodel.xls
http://www.sentinet.demon.co.uk/wireless/accramodel.xls
They use the following assumptions:
Solar cell efficiency 20%
Battery efficiency 66%
The solar cell efficiency of 20% may be way off and perhaps a value of 0.1
might be more realistic.
Conclusion:
It is surprising how big a battery you need and how small a solar pannel. If
we take the model for Accra in Ghana which is a lot sunnier than Frankfurt
then you need a battery reserve of about 5 days worth of power but a solar
pannel of only 0.1 square m.
Frankfurt needs a pannel of 0.2 square m and a battery capacity of 7 days.
A longer run of solar data is needed for a good analysis but this requires
buying a copy of meteonorm which is $390US. It comes with 10 years of
weather data. A more complex model would be good.
Anyone know anyone with a registered copy of this program ?
Lyndon
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