*2.1.2. Irradiance*

**•** Capacity to track the MPP for wide ranges of solar radiation and temperature;

The most popular algorithms employed in PV tracking systems [10-18] - Constant Voltage, Perturb and Observe (P&O) and Incremental Conductance (IncCond) – are extensively ex‐ plored by specialized literature, nevertheless, since fast tracking response and accuracy con‐ flict one from other, the mentioned tracking methods cannot satisfy, simultaneously, both of them. In place of the traditional and spread methods, some authors have proposed complex MPPT algorithms, based on fuzzy logic and neural network, in order to accomplish fast tracking response and accuracy in a single system. These proposals, nevertheless, present some disadvantageous: needed for high processing capacity, complexity, cost elevation and,

In this chapter, PV maximum power point tracking systems are analyzed under two distinct points of view: firstly, the influence of the dc-dc converter on the tracking quality is account‐ ed. In this study, the effect of solar radiation, temperature and load variations are consid‐ ered, and the tracking performance of Buck, Boost, Buck-Boost, Cuk, SEPIC and Zeta converters are compared. Secondly, a new tracking algorithm, based on the PV surface tem‐ perature, is introduced. The advantages concerning the proposed method come from the simplicity, low cost, analogue or digital implementation, fast tracking response, accuracy

In order to achieve the main chapter topics, a brief revision of PV generation is highlighted

Photovoltaic modules output power depends on environmental conditions, such as solar ra‐ diation and temperature, resulting in a non-liner and time-variant power source. The em‐ ployment of a PV generator only can be successfully attained if it is correctly characterized.

Photovoltaic cells are the basic building blocks on construction of PV power systems. The amount of power delivered by a PV cell is, typically, restricted to few Watts, due to the sur‐ face area limitation. For raising the generated power, in order to reach hundreds of Watts, PV cells may be grouped in a PV module. Similarly, it is possible to connect a group of PV modules (series, parallel or both) in order to obtain a PV array, whose power range is estab‐ lished from kilo-Watts to mega-Watts [19]. The distinction among PV cell, module and array

**•** Simplicity of implementation;

90 Sustainable Energy - Recent Studies

in some cases, employment of extra sensors.

and no oscillation around the MPP on steady state.

**2.1. Relationship Among PV Cell, Module and Array**

**•** Low cost.

in next section.

**2. Photovoltaic Generation**

is illustrated at Figure 1.

The Sun energy reaches to the Earth through electromagnetic waves, resulting in an irradi‐ ance (or solar radiation) of about 1366 W/m2 on its outer atmosphere. However, due to at‐ mospheric effects – scattering, absorption and reflection -, the incoming irradiance is modified before reaching the Earth's surface [20].

The process of scattering occurs when small particles and gas molecules diffuse the radia‐ tion in random directions, while absorption is defined as a process in which the solar radia‐ tion is retained by atmosphere substances and converted into heat. In addition, part of the total solar radiation is redirected back to the space by reflection and part, termed by direct solar radiation, reaches the Earth's surface unmodified by any of the above atmospheric processes, as depicts Figure 2.

*AM* <sup>=</sup> *<sup>L</sup>*

in mid-latitudes. This value is also adopted as reference at STC.

temperature value adopted for PV modules characterization is *T=*25 °

value comes from a angle of aproximatly 48°

**2.2. I-V and P-V generation curves**

Kyocera KC200GT PV module datasheet.

according to (5) [21], where:

*STC*, *Pmpp*

*V mpp STC*, *I mpp*

(*S*) and surface temperature (*T*);

age) curve may be plotted, in accordance with Figure 5.

are obtained from datasheet and specified on STC (*T STC* and *S STC*);

These parameters are also obtained from datasheet.

*2.1.4. Temperature*

*<sup>L</sup>* <sup>0</sup> <sup>=</sup> <sup>1</sup>

An Optimized Maximum Power Point Tracking Method Based on PV Surface Temperature Measurement

On industry, PV modules are standardized considering an air mass index of AM=1.5. This

the most populed centres across Europe, China, Japan and United States of America, located

The third parameter used to characterize a PV module is its surface temperature. The STC

Under the specified Standard Test Conditions, expressed by (2), PV modules are tested and featured by I-V (current versus voltage) and P-V (power versus voltage) curves, in which the effect of solar radiation and temperature on the PV generated power is evidenced.

Although both, solar radiation and temperature, are strongly coupled, solar radiation pre‐ dominantly influences the PV module output current, while temperature mainly changes the PV module output voltage, as depicts the I-V curve presented at Figure 4, obtained from

One of most important PV module operation point is obtained on the knee of the I-V curve. In this point, named by maximum power point (MPP), the product of the PV output voltage and current results at the maximum available power, for a given solar radiation and temper‐ ature. For emphasizing the maximum power point, an alternative P-V (power versus volt‐

Mathematical expressions for calculating the PV module output voltage *V mpp* and current *I mpp* on MPP are given by (3) and (4), whose product results on the PV output power *P mpp*,

*Vmpp*, *Impp*, *Pmpp* : PV module output voltage, current and power on MPP for any irradiance

*μV* , *μA* : Temperature voltage coefficient (V/◦C) and temperature current coefficient (A/◦C).

*STC* : PV module output voltage, current and power on MPP. These parameters

*S STC* =1000 W/m<sup>2</sup> *T STC* =25 °C *AM STC* =1.5

cos(θ) (1)

http://dx.doi.org/10.5772/51020

93

, proper representing the PV instalitions around

C.

(2)

**Figure 2.** Atmosphere effects on incoming solar radiation.

Since the direct radiation on a clear day, at noon, is typically 1000 W/m2 , this value is adopt‐ ed as reference at STC.

**Figure 3.** Solar radiation path across the Earth's atmosphere.
