Outback FM60 User Manual

900-0009-01-00 Rev D 97

Applications

Maximum Power Point Tracking

Maximum Power Point Tracking (MPPT) is the technology used by FLEXmax controllers to

optimize the harvest of power from PV arrays.

PV modules do not have a defined operating voltage. Their voltage is defined strictly by the

load connected to them. With no load (disconnected), a module displays “open-circuit” voltage

), and delivers no current. At full load (shorted), a module has no voltage, although it

delivers the maximum “short-circuit” current (I

). In neither case does the module produce

usable wattage.

When partially loaded, a PV module delivers partial current and voltage. These numbers can be

multiplied to see the available wattage. However, the delivery of wattage is not linear. The

current and voltage delivered at a given load will change with the load, along a curve such as

that shown in the drawing to the left in Figure 99. This is known as the V-I curve. The wattage

is different at every point along the curve. (The V-I curve also varies with module type and

manufacturer.) Only one point on the curve represents the delivery of the module’s maximum

(rated) wattage. This is known as the maximum power point , or MPP. The current at this

point, I

, is the highest that can be drawn while still maintaining the highest voltage, V

The FLEXmax controller places a variable load on the PV array and tracks the result to

determine the maximum power point. This process, MPPT, is maintained so that the FLEXmax

can deliver the maximum PV power regardless of any change in conditions. The drawing to the

right in Figure 99 shows the MPP and compares the V-I curve against the available wattage.

Figure 99 Maximum Power Point Tracking

VOLTAGE

CURRENT

-I curve

Available wattage