Blue Sky Solar Boost 2000 - Manual (Page 6)

RV Power Products - Solar Boost 2000
5
Because output power is constant while MPPT is operating, anything that leads to lower battery voltage will
produce an increase in Output Charge Current. While a discharged battery is one way to produce lower output voltage,
and therefore higher output current, other normal conditions may produce lower voltage as well. Any 12 volt power
consumption during the day will decrease net battery charge current, which decreases battery voltage. Operating a
large inverter to make coffee or run a microwave oven will produce substantial drops in output voltage leading to an
increase in output current. Additionally, anything that can be done to lower PV array temperature will also lead to an
increase in charge current by increasing PV power production. Locating the PV array in a breezy location for example
will cool the PV array due to increased air circulation.
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
panel design. The effect wiring has on performance is that power wasted heating undersized wiring becomes
unavailable for charging. The effect PV panel design has on performance is that panels with a maximum power voltage
(V
MP
) of 17 volts or greater will tend to produce more boost, whereas PV panels with V
MP
less than 17 volts will tend to
produce less boost. Additionally, more PV panels will tend to produce more boost, whereas fewer PV panels will tend to
produce less boost.
For a system using four 75 watt PV panels 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 1. Your current boost
performance will vary due to a variety of factors. What you can be sure of is that Solar Boost 2000 will automatically
deliver the highest charge current possible for a given installation and set of operating conditions.
TYPICAL CURRENT BOOST PERFORMANCE
FOUR 75 WATT PV PANELS
BATTERY CONDITION
AND VOLTAGE
AMBIENT
CONDITIONS
PV INPUT
CURRENT
OUTPUT CHARGE
CURRENT
PERCENT
INCREASE
FULLY DISCHARGED
10.9V
35 °F
EARLY MORNING
8.8 AMPS 12.1 AMPS 38%
HIGHLY CHARGED
13.8V
45 °F
CLOUDY, BREEZY
7.9 AMPS 9.3 AMPS 18%
HIGHLY DISCHARGED
11.8V
65 °F
CLEAR, STILL AIR
16.7 AMPS 18.4 AMPS 10%
HIGHLY CHARGED
13.8V
75 °F
CLEAR, STILL AIR
18.5 AMPS 18.5 AMPS 0%
TABLE 1
HOW MPPT AND CURRENT BOOST WORKS
A PV panel is a constant current type device. As shown on a typical PV panel voltage vs. current curve, current
remains relatively constant over a wide range of voltage. A typical 75 watt panel is specified to deliver 4.45 amps @ 17
volts @ 25
°C. Traditional PV controllers essentially connect the PV array directly to the battery when battery voltage is
low. When this 75 watt panel is connected directly to a battery charging at 12 volts, the PV panel still provides
approximately the same current. But, because PV output voltage is now held at 12 volts by the battery rather than 17
volts, it only delivers 53 watts to the battery. This wastes 22 watts of available power.
Solar Boost 2000’s patent pending MPPT technology operates in a very different fashion. Under these
conditions Solar Boost 2000 calculates the maximum power voltage (V
MP
) at which the PV panel delivers its maximum
available power, in this case 17 volts. It then operates the PV panel at 17 volts which extracts maximum power from the
PV panel. Solar Boost 2000 continually recalculates the maximum power voltage as operating conditions change. This
is referred to as Maximum Power Point Tracking (MPPT). Input power from the MPPT controller, in this case 75 watts,
feeds a switching type power converter which reduces the 17 volt input to battery voltage at the output. The full 75 watts