**6. Hybrid photovoltaic cell**

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