NOVELTY - The system has a power source (PV) e.g. fuel cell, whose a positive terminal is connected to respective terminals of a switch (Sui1) and a resistor (Rui). Another terminal of the switch (Sui1) is connected to another terminal of the resistor. A negative terminal of the power source is connected to a terminal of another switch (Sui2) and to a negative terminal of a capacitor (Cui). The capacitor is charged and discharged during respective time periods.    USE - Apparatus for determining maximum power point of a power source e.g. photovoltaic cell or fuel cell, connected to a merged buck/boost converter in an energy conversion system. Can also be used for a direct-current (DC)-DC up/down converter circuit and/or DC/alternating current inverter circuit.    ADVANTAGE - The apparatus enables obtaining information representative of output current and voltage variations of the power source, so as to determine maximum power point (MPP) of the power source, thus operating photovoltaic cells around the MPP to optimize power generation efficiency of the power source, and reducing the power losses of the power source. The apparatus enables monitoring the voltage and the current on the capacitor at consecutive time samples during specific time period, thus estimating the current variations from the calculation of the voltage derivative while avoiding errors that appear on the current estimation due to temperature and aging effects on the capacitor and eliminating need for an expensive current sensor that leads to additional power losses, and hence enabling efficient power usage from the power source, and improving efficiency and reducing operating cost of the apparatus.    DETAILED DESCRIPTION - The capacitor is charged with current varying from short circuit current to null value current, and voltage (V1) and current values on the capacitor are monitored at consecutive time samples when the switch (Sui1) is in ON state and the switches (Sui2, Sui3) are in OFF state. The capacitor is discharged through the resistor when the switches (Sui1, Sui3) are in OFF state and the switch (Sui2) is in ON state. The direct current does not pass from the power source via the switch (Sui2), so that the capacitor is discharged when the switch (Sui2) is in OFF state.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of an electric circuit comprising a capacitor for obtaining information enabling determination of maximum power point of a power source.    Capacitor (Cui)    Power source (PV)    Resistor (Rui)    Switches (Sui1-Sui3)    Voltage (V1)