how
the
batteries
are
charged
and
what
element
(batteries
or
diesel
generator)
have
priority
to
supply
energy
when
the
load
exceeds
the
energy
generated
from
renewable
sources[2]
.
There
are
also
many
conditions[5]
like
Diesel
generators
operating
near
their
optimal
point
(70
80%),
necessity
to
maximize
the
power
coming
from
solar
panel,
etc.
That
is
why;
the
power
control
strategy
plays
an
important
role
in
the
optimum
design
and
efficient
utilization
of
hybrid
energy
systems.
The
power
available
and
the
overall
lifetime
of
system
components
are
highly
affected
by
power
control
strategy
[6].
·
The
problem
in
PV/Diesel
hybrid
systems
becomes
complicated
through
uncertain
renewable
energy
supplies
and
load
demand,
non
linear
characteristics
of
some
components,
and
the
fact
that
optimum
operation
strategies
and
optimum
sizing
of
hybrid
system
components
are
interdependent
[7],
[1].
·
In
the
PV/diesel
hybrid
systems,
fluctuating
PV
power
causes
frequency
deviations
when
large
PV
power
is
penetrated
in
the
isolated
utility:
usually,
the
battery
is
mainly
used
to
smooth
the
PV
power
fluctuations
by
following
moving
point
average
law[8].
The
system
frequency
regulation
and
voltage
control
always
depends
on
the
diesel
generator.
Hence,
these
types
of
conventional
methods
cannot
control
PV
power
corresponding
to
power
system
condition
and
insolation
variations.
·
There
is
also
noticed
problem
of
high
voltage
distortion
with
unbalanced
and/or
nonlinear
loads.
All
these
difficulties
are
resumed
as
the
cost
effective,
the
reliable
design
and
the
appropriate
operation
problems.
As
indicated
in
[7],
resolve
them
is
very
important.
Thus
the
issue
is
to
find
the
optimal
techno
economic
PV/Diesel
hybrid
system.
3.
Different
optimization
problems
Due
to
the
fact
that
PV/battery/diesel
hybrid
configuration
has
advantages
of
flexibility,
system
load
can
be
met
in
the
optimal
way;
diesel
efficiency
can
be
maximized;
diesel
maintenance
can
be
minimized;
and
a
reduction
in
the
capacities
of
diesel
and
battery
(while
matching
the
peak
loads)
can
occur.
The
optimal
Power
Management
System
[6],
the
minimal
cost
of
the
system,
minimal
unmet
loads,
minimal
fuel
emission[12,16],
the
optimal
configuration
that
meets
the
autonomy
constraint
(no
loss
of
load)
and
the
minimization
of
the
battery
storage
[10]are
the
optimizations
problems
commonly
encountered
in
the
literature.
For
example,
it
is
well
known
that
batteries
are
used
to
meet
the
transient
load
and
to
avoid
power
fluctuations,
so
how
to
minimize
them?
Studied
by
Shaadid
[11]
in
the
case
of
at
Dhahran,
Saudi
Arabia;
while
focalize
herself
on
minimizing
also
the
operation/contribution
of
diesel
system,
he
suggests
that
for
optimum
use
of
battery
storage
and
for
optimum
operation
of
diesel
system,
battery
storage
of
1218
h
days
can
be
used
for
design
purposes.
Two
parameters
were
used
to
characterize
the
role
of
the
engine
generator:
denoted
SDM
and
SAR,
they
are,
respectively,
the
battery
charge
threshold
at
which
it
is
started
up,
and
the
storage
capacity
threshold
at
which
it
is
stopped,
both
expressed
as
a
percentage
of
the
nominal
battery
storage
capacity
of
the
PV/diesel
hybrid
system
studied
by
[3]
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