No subject

(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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