Panasonic BP-5917C40 Technical Handbook page 41

SOLAR CELL DESIGN - CONTINUED
12.2 Solar Cell Power Supply System Design Guide
(1) Direct Connection to Load
This configuration is suitable for applications such as
warehouse ventilation systems in which equipment is
driven only when the sun is shining. When selecting a
solar cell, it is necessary to consider the power
consumption of the device to be driven and the weather
conditions in the place where the system will be
installed. Generally speaking, the power output of the
solar cells must be approximately 2 to 3 times as high as
(1) First, the load conditions of the equipment to be driven must be determined and I
consumption per day, calculated
Equipment operating voltage
Equipment current consumption
Equipment operating time
(2) Next, the solar cell operating current, I
2) Calculation of operating current: I
I (Ah/day)
R
I (A)=
P
K x K x T
1 2 S
(3) Next, the storage capacity, C, of the storage
battery is calculated
3) Calculation of storage battery capacity: C
I (Ah/day) x D(day)
R
C(Ah)=
(4) Last, the operating voltage, VP, of the solar cell is calculated.
V = storage battery charging voltage + additional voltage required due to diode for preventing reverse
P
flow + additional voltage required due to output cable + additional voltage required due to temperature
12.3. Calculation Example
Lighting System (DC or Direct Current)
•
In the following example, a solar cell and a storage battery are selected to power a 12V, 20W lamp which will be
illuminated 2 hour per day.
1. Basic System Configuration
Solar cell
Panasonic
V (V)
L
I A)
L (
T h/day
is calculated.
P
P
(h/day)
K
3
(VL + ) (0.3~0.5)
(0.1~0.5)
Diode to prevent reverse
Solar Cells Handbook, Page 40
the power consumption of the equipment. Consult your
Panasonic representative for details.
(2) Paired with Storage Battery
This configuration is mainly used for power supply
systems employing solar cells. Refer to the Design
Guide below when selecting solar cells and storage
batteries to match the load presented by the equipment
to be driven.
Design Guide
1) Calculation of average current consumption
per day
* K : The deterioration value based on temperature
1
change, surface area of the solar battery which may
become dirty after many years, and which may
cause the solar battery output to deteriorate.
* K : The deterioration value of the battery charge and
2
discharge efficiency.
* T : Solar cell average rated output generation time per
S
day.
* D: The number of non-illumination backup days. This is
the number of days that in order to run the equipment
the storage battery must backup the solar cell because
the sun is not shining.
*K : Safety factor for self-discharge by the storage battery,
3
etc. (approx. 0.8)
Charge / discharge
control circuit
flow Storage
battery
, the average current
R
1 (Ah/day)=I (A) x T(h/day)
L
R
Load
Lamp
illumination: 20W
2h/day
August 1998