**8. Performance and reliability**

Researchers and scientists had developed and proposed various methods for evaluation of performance of a photovoltaic system. A brief review of these methods is presented here.

Li et al. (2005) investigated the operational performance and efficiency characteristic of a small PV system installed at the City University of Hong Kong and the amount of solar irradiance data falling on the PV panel was determined using the luminous efficacy approach. Yu et al. (2004) developed a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and

Itoh et al. conducted electrical output performances of 'democratic module photovoltaic system' consisting of amorphous-, multicrystalline- and crystalline-silicon-based solar cells that reveal significant differences, mainly with respect to seasonal variation and found that the annual output energy generated by amorphous-Si-based solar cell is about 5% higher than that of crystalline-Si-based arrays (Itoh et al., 2001). Wu et al. proposed a new technique of maximum power point controller, through which the proposed hybrid PV system could adopt amorphous Si solar cell together with crystalline Si solar cell to realize a PV system

Mainz et al. demonstrated that rapid thermal sulphurisation of sputtered Cu/In precursor layers is suitable for industrial production of thin film photovoltaic modules. Yoosuf et al. (2005) investigated the effect of sulfurization temperature and time on the growth, structural, electrical and photoelectrical properties of b-In2S3 films. Nishiokaa et al. (2006) evaluated the temperature dependences of the electrical characteristics of InGaP/InGaAs/Ge triple junction solar cells under concentration and found that for these solar cells, conversion efficiency decreased with increasing temperature, and increased with increasing concentration ratio owing to an increase in open-circuit voltage (Nishiokaa et al., 2006). Phani et al. (2001) described the titania solar cells that converts sunlight directly into electricity through a process similar to photosynthesis and has performance advantages over other solar cells, which include the ability to perform well in low light and shade, and

Some commercial manufacturers use self-organised nanostructured glass surfaces to improve system efficiencies b yaround 10%. More carefully constructed silicon nanostructure that mimic the eyes of species of moth promise further improvements but are currently too expensive to implement (Bagnall and Boreland, 2008). However, nanoembossing and nano-imprinting technologies are rapidly developing and it is now possible to envisage regular commercial use of nanostructured broad-band antireflective surfaces

The most promising application fields for the energy conversion domain will be mainly focused on solar energy (mostly PV). Hence to improve the conversion efficiency, structures from nanotechnology products that absorb more sunlight are emphasized: devices such as

Researchers and scientists had developed and proposed various methods for evaluation of performance of a photovoltaic system. A brief review of these methods is presented here.

Li et al. (2005) investigated the operational performance and efficiency characteristic of a small PV system installed at the City University of Hong Kong and the amount of solar irradiance data falling on the PV panel was determined using the luminous efficacy approach. Yu et al. (2004) developed a novel two-mode maximum power point tracking (MPPT) control algorithm combining the modified constant voltage control and

to perform consistently well over a wide range of temperatures and low cost.

within the near future, enhancing system efficiencies by more than10%(Fig.15).

nanotubes, quantum dots (QDs), and "hot carrier" solar cells.

**8. Performance and reliability** 

**6. Hybrid photovoltaic cell** 

**7. Some other solar cells** 

with higher ratio of performance to cost (Wu et al., 2005).

incremental conductance method (IncCond) method to improve the efficiency of the 3 kWPV power generation system at different insolation conditions that provides excellent performance at less than 30% insolation intensity, covering the whole insolation area without additional hardware circuitry. Huang et al. (2006) proposed a PV system design, called "near-maximum power-point-operation" (nMPPO) that can maintain the performance very close to PV system with MPPT (maximum-power-point tracking) but eliminate the hardware of the MPPT and the long term performance simulation shows that the overall nMPPO efficiency is higher than 93%. Jaber et al. (2003) developed a computer-simulation model of the behavior of a photovoltaic (PV) gas-turbine hybrid system, with a compressed-air store, to evaluate its performance as well as to predict the total energy-conversion efficiency and found that hybrid plant produces approximately 140% more power per unit of fuel consumed compared with corresponding conventional gas turbine plants and lower rates of pollutant emissions to the atmosphere per kWh of electricity generated. Stoppato (2008) presented the results of a life cycle assessment (LCA) of the electric generation by means of photovoltaic panels. Wiemken et al. (2001) studied effects of combined power generation by monitoring data from 100 PV systems that reveals a considerable decrease in power fluctuations compared to an individual system and the energy spectrum of combined power generation showed that produced energy is generated in a range below65%of the overall installedpower. Keogh et al. (2004) presented a new tester (commonly used for measuring solar cells and modules) design that is simple, low cost, and reduces transient errors by use of a constant voltage cell-bias circuit and it extracts a family of I–V curves over a decade range of light intensity, which provides comprehensive information on cell performance.

Fig. 15. SEM micrographofasilicon'moth-eye'antireflective surface (Bagnall and Boreland 2008).

Photovoltaic Systems and Applications 41

 

0 1 ( ) *ref T Tref*

Here *To* is the maximum temperature at which the efficiency of the PV cells decreases to zero. For a crystalline Si cell this temperature is about 270° C (Kumar and Rosen, 2011). A

*ref* are suggested for silicon based PV technologies.

The increasing efficiency, lowering cost and minimal pollution are the boons of the

The PV system is composed of a number of individual PV modules that can be connected either in series (to increase the dc output voltage up to the desired value) to form a string. Then, multiple strings are connected in parallel to increase the output current. The possibility of using multiple strings ensures the PV system modularity, which is one of the most important features of the PV technology. The arrangement of the PV modules in strings also allows for using different solutions for the dc/ac conversion. Available solutions include the centralised inverter, collecting the dc output from the whole array of PV modules, string inverters (with one inverter for each string) or module-integrated inverters (with a mono inverter for each PV module). The centralised inverter is a solution most suitable for PV systems with rated power indicatively above 20kW, connected to the supply system through a three-phase inverter. The other solutions are typical of residential installations, where the power is usually not higher than 5–10kW and the inverters are mono-phase. The adoption of module-integrated inverters requires the installation of a relatively high number of inverters, each one with its protections, directly on the field, paying attention to the fact that the inverters have to withstand different climatic conditions. Yet, the adoption of module-integrated inverters allows for individual and independent control of the mono inverters, with possibility of minimising the losses due to different

manufacturer, and on the Tref, and can be written as (Agarwal and Garg, 1994):

**PV cell type Temperature coefficient a,** 

Mono c-Si 0.003-0.005 Multi c-Si 0.004

a-Si 0.0011-0.0026 PV/Thermal 0.00375-0.0063

Table 1. Temperature coefficients for various PV Technologies.

photovoltaic systems that have led to a wide range of their application.

where

coefficient

range of values of

**11. Applications** 

aThe reference temperature for each case is 25° C.

**11.1 Building integrated photovoltaic systems** 

1( )

*ref* is the efficiency of the photovoltaic cell at temperature Tref. The temperature

*ref* is mainly determined by the cell material, which usually is provided by the

*c ref ref c ref T T* (1)

(2)

*ref* **, (** *<sup>o</sup>* <sup>1</sup> *<sup>C</sup>* **)** 
