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Basics of MPPT Solar Charge
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| Basics of
MPPT Solar Charge Controller
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What
is MPPT?
MPPT or
Maximum Power Point Tracking is algorithm that included
in charge controllers used for extracting maximum available
power from PV module under certain conditions. The voltage at
which PV module can produce maximum power is called ‘maximum
power point’ (or peak power voltage). Maximum power varies with
solar radiation, ambient temperature and solar cell temperature.
Typical PV module produces
power with maximum power voltage of around 17 V when measured
at a cell temperature of 25°C, it can drop to around 15
V on a very hot day and it can also rise to 18 V on a very cold
day.
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Figure 1 The I-V curves show maximum power from PV
modules when exposed
to irradiance 1000 W/m2
Source: The parameters are measured by the
IVTracer program by Sandia National Laboratories
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Figure 2 The I-V curves show maximum power from PV
modules when exposed to irradiance 100 W/m2
Source: The parameters are measured by the
IVTracer program by Sandia National Laboratories.
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As the graphs in figure 1 and 2, we see that at the different
solar radiations, PV modules deliver the variations in parameters
as follows:
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(1) Maximum power; Pm
(2) Maximum power voltage; Vpm
(3) Open circuit voltage; Voc
(4) Maximum power current; Ipm
(5) Short circuit current; Isc |
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How MPPT
works?
The major principle of MPPT
is to extract the maximum available power from PV module by
making them operate at the most efficient voltage (maximum power
point). That is to say:
MPPT checks output of PV module, compares it to battery voltage
then fixes what is the best power that PV module can produce
to charge the battery and converts it to the best voltage to
get maximum current into battery. It can also supply power to
a DC load, which is connected directly to the battery.
MPPT is most effective under
these conditions:
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Cold weather, cloudy or hazy days: Normally,
PV module works better at cold temperatures and MPPT is
utilized to extract maximum power available from them. |
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When battery is deeply discharged: MPPT can extract more
current and charge the battery if the state of charge in
the battery is lowers. |
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MPPT solar charge controller
A MPPT solar charge controller is
the charge controller embedded with MPPT algorithm to maximize
the amount of current going into the battery from PV module.
MPPT is DC to DC converter
which operates by taking DC input from PV module, changing it
to AC and converting it back to a different DC voltage and current
to exactly match the PV module to the battery.
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Examples of DC to DC converter
are
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Boost converter is power
converter which DC input voltage is less than DC output
voltage. That means PV input voltage is less than the battery
voltage in system. |
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Buck converter
is power converter which DC input voltage is greater than
DC output voltage. That means PV input voltage is greater
than the battery voltage in system. |
MPPT algorithm can be applied
to both of them depending on system design. Normally, for battery
system voltage is equal or less than 48 V, buck converter is
useful. On the other hand, if battery system voltage is greater
than 48 V, boost converter should be chosen.
MPPT solar charge controllers are useful for off-grid solar power systems such as stand-alone
solar power system, solar home system and solar water pump system,
etc.
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Main
features of MPPT solar charge controller
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In any applications which PV module is energy
source, MPPT solar charge controller is used to correct
for detecting the variations in the current-voltage characteristics
of solar cell and shown by I-V curve. |
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MPPT solar charge controller is necessary for any solar
power systems need to extract maximum power from PV module;
it forces PV module to operate at voltage close to maximum
power point to draw maximum available power. |
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MPPT solar charge controller allows users to use PV module
with a higher voltage output than operating voltage of battery
system.
For example, if PV module has to be placed far away
from charge controller and battery, its wire size must be
very large to reduce voltage drop. With a MPPT solar charge
controller, users can wire PV module for 24 or 48 V (depending
on charge controller and PV modules) and bring power into
12 or 24 V battery system. This means it reduces the wire
size needed while retaining full output of PV module. |
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MPPT solar charge controller reduces complexity of system
while output of system is high efficiency. Additionally,
it can be applied to use with more energy sources. Since
PV output power is used to control DC-DC converter directly. |
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MPPT solar charge controller can be applied to other renewable
energy sources such as small water turbines, wind-power
turbines, etc.
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Figure 3 General configuration
of the MPPT solar charge controller
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SOLAR CHARGE CONTROLLER
WITH MPPT AND
DC LOAD TIMER 10A
- Advance microprocessor control
- Buck regulator wide input range
- Maximum Power Point Tracking (MPPT)
- Solar charge controller with DC load control
- Reverse polarities protection of PV and battery
- Battery overcharge and overdischarge protection
- Temperature compensation (-3 to -7mV/Cell/Celsius)
- Lighting surge protection (TVSS)
- 3-step charging to provide quick and safe charging for battery
- Automatic cooling fan (outside enclosure)
- 7 modes timer control (ON/OFF DC load) selectable
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Table 2 Specifications
of the SOLARCON SPT-series MPPT solar charge controller
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click to enlarge
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