Reliability Evaluation of Grid-Connected Photovoltaic Power Systems

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Photovoltaic systems does not involve greenhouse gas emissions and no fossil fuel consumption. Total capacity of grid connected Photovoltaic system increased from 300mW in 2000 to 21GW in 2010. Annual growth rate increased from 60% in 2004 to 80- 90% in 2011. Features Of Highly Reliable Photovoltaic System are Increase in renewable energy output, Guarantee higher return on investment and Curtail carbon emissions. 

Reliability

Reliability is a measure of overall product health over the expected lifetime of the product. Concerned with probability and frequency of failures. Duration or probability of failures under stated condition. Expressed as probability over a given period of time. Different steps involved in Reliability Evaluvation are

1) Reliability modelling of PV system components

2) Reliability evaluation of PV array

3) Discrete probability distribution of input power

4) Photovoltaic reliability indices

Reliability Evaluation Of Photovoltaic Inverter depends on 

1) Thermal model of IGBT and diode

2) Failure rates of IGBT

3) Failure rates of diode

4) Failure rates of capacitor

5) Inverter reliability

Failure rate of Photovoltaic Inverter is related to Power loss, System power input levels. Temperature depends on Power loss which in turn depends on system input power levels. Reliability of Photovoltaic array is equivalent reliability parameters of PV string. State enumeration for reliability analysis of PV array. Photovoltaic string has two repairable failure modes, Failure at a junction box and Short circuit of PV panel. Both result in outage of whole string. Two modes are characterised by an average failure rate and an average repair rate of Photovoltaic panel.

Discrete Probability Distribution Of Input Power is metered every 1-15 minutes. It produces a chronological intermittent curve with large amount of data points. Input power measurement are aggregated into discrete probability distribution. K mean clustering method is introduced. Photovoltaic reliability indices evaluate system performance, Select best design option at planning stage to reduce cost and increase benefit at operational stage. Two types of indices are energy oriented and time oriented indices.

Major contributions of proposed new analytical methods include, Input/power loss/temperature dependent failure rates for power electronic components, Evaluation of PV arrays considering power output dependent failure rates and Application of clustering technique to the discrete probability distribution.

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