Civil Engineering Reference
In-Depth Information
FIGURE 12-16
Duty ratio and peak power of intermittent loads.
The duty ratio is used in determining the contribution of individual load in
the total energy demand. If the load has clean on-off periods as shown in
Figure 12-16(a)
,
then the duty ratio D is defined as D = To/T, where To is
the time the load is on and T is the period of repetition. For irregularly
varying loads shown in (b), the duty ratio is defined as the actual energy
consumed in one period over the peak power times the period, i.e.:
Energy in watt hours consumed in one repetition period
Peak power in watts Repetition period in hours
⋅
D
=
(12-3)
⋅
The peak power consumption and the duty ratio of all loads are compiled,
the product of the two is the actual share of the energy requirement of that
load on the system during one repetition period. If there are distinct intervals
in the period, say between the battery discharge and charge intervals, then
the peak power and the duty ratio of each load are computed over the two
intervals separately. As a simple example of this in a solar power system,
one interval may be from 8
.
. to 6
.
. and the other from 6
.
. to 8
.
.
A
M
P
M
P
M
A
M
The power table is then prepared as shown in
Table 12-2
.
TABLE 12-2
Power and Energy Compilation Table for Energy Balance Analysis
8
.
. to 6
.
. (Interval A)
6
.
. to 8
.
. (Interval B)
A
M
P
M
P
M
A
M
(battery on charge)
(battery on discharge)
Peak
watts
Duty
ratio
Energy per
period Wh
Peak
watts
Duty
ratio
Energy per
period Wh
Load
Load
P
D
E
P
D
E
1
1a
1a
1a
1b
1b
1b
Load
P
D
E
P
D
E
2
2a
2a
2a
2b
2b
2b
..
..
..
..
..
..
..
Load
P
D
E
P
D
E
n
na
na
na
nb
nb
nb
TOTAL
Σ
P
Σ
E
Σ
P
Σ
E
a
a
b
b
Total Battery Discharge Required =
Σ
E
watts-hours
b
