Installation and Operation Manual
8
consumption during the day will decrease net battery charge current, which decreases battery voltage. Operating a
large inverter or application of other heavy loads can produce substantial drops in output voltage leading to significant
increases in output current. Additionally, anything that can be done to lower PV array temperature will also lead to
increased charge current by increasing PV power production. Installing modules in a breezy location for example will
cool the PV array due to increased air circulation.
HOW MPPT WORKS
A PV module is a
constant current
type device. As shown on a typical PV module voltage vs. current curve,
current remains relatively constant over a wide range of voltage. A typical single 75 watt module is specified to deliver
4.45 amps @ 17 volts @ 25
°
C. Conventional PV controllers essentially connect the PV array directly to the battery
when battery voltage is low. When a pair of 75 watt modules are connected directly to a battery charging at 24 volts, the
modules still provide approximately the same current. But, because output voltage is now at 24 volts rather than 34
volts (2x17V), they only delivers 106 watts to the battery. This wastes 44 watts of available power.
Solar Boost 3048’s patented MPPT technology operates in a very different fashion. Under these conditions Solar
Boost 3048 calculates the maximum power voltage (V
MP
) at which the PV module delivers maximum power, in this
case 17 volts. It then operates the PV module pair at 2x17 volts which extracts maximum power from the modules.
Solar Boost 3048 continually recalculates the maximum power voltage as operating conditions change. Input power
from the peak power tracking controller, in this case 150 watts, feeds a switching type power converter which reduces
the 34 volt input to battery voltage at the output. The full 150 watts which is now being delivered at 24 volts would
produce a current of 6.25 amps. A charge current increase of 1.8 amps or 40% is achieved by converting the 44 watts
that would have been wasted into useable charge current. Note that this example assumes 100% efficiency to illustrate
the principal of operation. In actual operation, boost will be somewhat less as some available power is lost in wiring,
connections, and in Solar Boost 3048.
TYPICAL CURRENT BOOST PERFORMANCE
As described above current boost performance for a particular installation varies with PV array temperature and
battery voltage. Two of the other primary factors which affect boost performance include system wiring and PV module
design. The effect wiring has on performance is that power wasted heating undersized wiring is unavailable for
charging. This is discussed further in the Battery And PV Wiring section. The effect PV module design has on
performance is that modules with a maximum power voltage (V
MP
) of 17 volts or higher will tend to produce more
boost, whereas PV modules with V
MP
less than 17 volts will tend to produce less boost. Additionally, more PV modules
will tend to produce more boost, whereas fewer PV modules will tend to produce less boost.
For a 24 volt system using eight 75 watt PV modules with peak power specifications of 4.45 amps @ 17 volts @
25
°
C, representative boost performance under a variety of operating conditions is shown in Table 2. Your current boost
performance will vary due to a variety of factors. What you can be sure of is that Solar Boost 3048 will automatically
deliver the highest charge current possible for a given installation and operating conditions.
TYPICAL 24V CURRENT BOOST PERFORMANCE
EIGHT 75 WATT PV MODULES
BATTERY CONDITION
AND VOLTAGE
AMBIENT
CONDITIONS
PV INPUT
CURRENT
OUTPUT CHARGE
CURRENT
PERCENT
INCREASE
FULLY DISCHARGED
21.8V
35
°
F
EARLY MORNING
8.8 AMPS
12.1 AMPS
38%
HIGHLY CHARGED
27.6V
45
°
F
CLOUDY, BREEZY
7.9 AMPS
9.3 AMPS
18%
HIGHLY DISCHARGED
23.6V
65
°
F
CLEAR, STILL AIR
16.7 AMPS
18.4 AMPS
10%
HIGHLY CHARGED
27.6V
75
°
F
CLEAR, STILL AIR
18.5 AMPS
18.5 AMPS
0%
TABLE 2
