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Charge Gain per Day
The worksheet below enables you to calculate the average charge that the solar
panel provides to the battery each day for various day lengths and peak solar
irradiance values.
Panel Current at 1000 W/m
Peak Solar Irradiance
Day Length
"Cloud" Factor
Total Gain per Day = (E*F/1000)*0.6*(G*60)*H:
Enter the information into each column and then use the formula to calculate
the total gain for the day. The 0.6 factor includes battery efficiency and the inte-
gration of the solar cosine effect over the day. The total gain per day formula,
therefore, represents the following calculation: (rated panel current) x (peak
solar irradiance/1000) x (battery efficiency and solar cosine effect factor) x (day
length in minutes) x ("cloud" factor).
Line E (Panel Current at 1000 W/m
The charging current provided by the solar panel when solar irradiance
is 1000 Watts per square meter. The panel included with the Davis Solar
Power Kit provides 0.6 Amp at 1000 W/m
Line F (Peak Solar Irradiance)
The solar irradiance at solar noon at the station site, in W/m
Line G (Day Length)
The length of the day, in hours.
Line H ("Cloud" Factor)
A multiplier which you may use to account for cloudiness or other fac-
tors which may limit the sunlight reaching the panel throughout the day.
For example, a factor of 1.0 would represent an extended period with no
clouds. Note that even during cloudy conditions at least 20% of the solar
radiation usually gets through.
The example worksheet below illustrates the calculation.
Panel Current at 1000 W/m
Peak Solar Irradiance
Day Length
"Cloud" Factor
Total Gain per Day = (E*F/1000)*0.6*(G*60)*H:
Charge Budget
F
ACTOR
2
F
ACTOR
2
V
L
ALUE
______ Amps
2
______ W/m
______ hours
______
_______ Amp-min
2
)
2
.
V
L
ALUE
0.6 Amps
2
1000 W/m
10 hours
0.75
INE
E
F
G
H
2
.
INE
E
F
G
H
148.5 Amp-min
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