Maximum power point

FIG. 60. Current-voltage characteristics of a solar cell made at 65 MHz and 42 mW/cm-, The dashed line indicates the maximum-power point. 

Figure L Cell (lower left), cell energetics at maximum power point (upper left), and output characteristics (right) for an n-type WS2-based photoelectrochemical cell, The electrolyte is 12 M LiBr and Eredox = +0,64 V vs, SCE for current density multiply current shown times 32 cm 2...

Figure 2. Cell (lower left), cell energetics at maximum power point (upper left), and output...

Figure 5. Output characteristics and photocurrent density at maximum power point against time (inset) for an intrinsic a-Si H photoanode-based cell. (Reproduced from Ref. 5.)...

When cells are delivering power to electrical loads under real-world conditions, the intensity of solar radiation often varies over time. Many systems use a maximum power point circuit that automatically varies the load seen by the cell in such a way that it is always operating around the maximum power point and so delivering maximum power to the load. 

Here AVmax = Vsave(max) represents the difference in voltages at the semiconductor electrode and metal electrode at the maximum power conversion point. For example, in their experiment using a p-type InP photocathode, Heller and Vadimsky [120] obtained a current 23.5 mA/cm at maximum power point. A voltage of 0.1 IV vs SCE was applied in the case of InP electrode and -0.33V vs SCE in the case of platinum electrode, to obtain this current. Thus, the maximum saved voltage AVmax= 0.11( 0.33) V= 0.43V. Therefore, Psaved=0.43 V X 23.5 mA/cm = lO.lmW/cm. As they used a solar illumination of 84.7 mW/cm, the efficiency is 11.9%. 

Muhida R, Park M, Dakkak M, Matsuura K, Tsuyoshi A, Michira M (2003) A maximum power point tracking for photovoltaic-SPE system using a maximum current controller. Sol Energy Mater Sol Cells 75 697-706... 

Fig. 9.7 Current-voltage characteristic of a photoanode showing maximum power point (Pmax)- The fill factor is given by the product Vp X Ip divided by the product of Voc and Isc-...

The cell delivers maximum power when operating at a point on the characteristic where the product FV is maximum. This is shown graphically in Fig. 17.2, where the position of the maximum power point represents the largest area of the rectangle shown. 

The power rating of a battery specifies whether or not it is capable of sustaining a large current drain without undue polarization. As more and more current is drawn from a cell, the power initially rises it reaches a maximum and then drops as the cell voltage falls away due to polarization effects (Fig. 2.21). The maximum power point is best determined experi-... 

In order to get an estimate of the solar-to-electrical conversion efficiency on layered compounds, sample D has been measured in sunlight. The result, obtained at 92.5mW/cm2 insolation is shown in Fig. 8. The maximum power point is at 0.33V and 10.7mA/cm2, with a resulting solar conversion efficiency of 3.7%. As is evident from Fig. 7, some samples show better overall performance than sample D. The best of these, sample G, the surface of which was accidentally damaged before being measured in the sun, had a maximum power output which exceeded that of sample D by a factor of 1.4 bringing the estimated solar conversion efficiency to 5.2%. 

The point on the j/V characteristic where the product of voltage Vmpp and current jQ,mpp has a maximum value is called the maximum power point... 

For solar cells, the fill factor FF determines the position of the maximum power point in the 4th I/V quadrant of the illuminated diode and is therefore a quality sign of the photodiode. Besides the increased efficiency, the FF of a photodiode is also important when evaluating the proper function of the diode. High FF values are expected only for diodes with a strict selection principle for the separation of positive and negative carriers. There are several loss mechanisms for photodiodes that can reduce the FF in a photodiode ... 

The principal method of characterizing solar-cell performance is the measurement of conversion efficiency while the cell is exposed to 1 sun illumination (—100 mW cm-2). The conversion efficiency is determined by measuring the current - voltage characteristic (see Fig- 8), locating the maximum power point (Pm = JmVm), and also measuring the solar insolation... 

We have used a simplified approach to check whether the superposition principle is approximately valid. We apply Eq. (5.1) directly to the experimental results obtained with the solar cells. We choose three values of the voltage, V = V0c, V = Vp (Vp is the voltage at the maximum power point) and V = 0.25 Foe- We read Id and /sc for each voltage from Fig. 5.18. We do this for each composition. We then plot 81 = Id — Isc versus composition. We also plot I(V) read from Fig. 5.18. The difference of 81 from I(V) is a measure of the deviation from the superposition principle. For open circuit... 

Photoelectrochemical cells for solar photon conversion are usually designed to produce either electric power or solar fuels this book focuses on the latter. Power-producing solar cells are designed to be operated at their maximum-power point to produce electric power at the energy conversion efficiency... 

Figure 1.8 Cell schematics for a regenerative solar cell based on (a) an n-type photoelectrode (b) ap-type photoelectrode. The top diagrams show the cell reactions under illumination, the middle diagrams the electronic energy levels and band bending, and the bottom diagrams the cell current-voltage (I-U) characteristics with the photoelectrode and counter electrode (CE) currents shown in the same quadrant. The maximum power point is located at the point on the current-voltage curve at which the rectangle of maximum area may be inscribed in this quadrant. The photovoltage V, the electron and hole quasi-Fermi levels E and fip and the solution Fermi level f o.R, the open-circuit potential Ugc of the photoelectrode and the standard redox potential 17 ° of the 0,R redox couple are also shown.

From Fig. 7 the calculation of the power conversion efficiency rj can be derived only the fourth quadrant of the I-V curve represents deliverable power from the device. One point on the curve, denoted as maximum power point (MPP), corresponds to the maximum of the product of photocurrent and voltage and therefore power. The ratio between Vmpp mpp (or the maximum power) and Vqc he is called the fill factor (FF), and therefore the power output is written in the form Pmax = oc fsc FF- Division of the output power by the incident light power res ults in the power conversion efficiency rj ... 

The authors also investigated the probability of polaron pair dissociation and bimolecular recombination. At short circuit and at the maximum power point the losses were clearly dominated by polaron pair dissociation probabilities of roughly 60 and 50%, respectively [59]. In contrast, Gommans et al. claimed bimolecular recombination to be the dominant factor for free charge carrier losses [154]. Using their numerical model, Koster et al. were also able... 

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