Perspectives for the Sake of Photovoltaic Pumping Development in the South

The utilisation of photovoltaic conversion of solar energy to power water pumps is today an emerging technology, characterised by gradually declining costs and increasing acquitance with the technology. Since the first installations in the end of the seventies, solar water pumping systems for providing domestic, livestock and irrigation water supplies in remote areas have gained enormously in acceptance, reliability and performance and nowadays belong most significant applications of photovoltaic energy. This can be mainly attributed to the fact that it is not economically viable to connect such remote locations to national electric grids. It is now estimated that over 12000 PV pump units made up of different configurations have been supplied worldwide. The present work suggests how an optimal operation of a direct photovoltaic pumping system based on an induction motor can be achieved. The optimisation problem consists in maximising the daily pumped water quantity via the minimisation of a non-linear criterion for any operating point. This has led to an optimum ‘ v-f ’ relationship useful in controlling the motor. The voltage source inverter feeding the motor was controlled via one of the following three PWM strategies called : the ‘sinusoidal PWM strategy’; the ‘Harmonic Elimination Technic’ or the ‘Harmonic Minimisation Technic’. The chosen optimisation criterion fixes the maximisation of the motor efficiency or the power factor, since these two objective functions provides similar results. The extracted electric power is controlled by the inverter frequency instead of MPPT, which leads to a less expensive and non complex implementation. Thus the advantages described in are acquired mean while overriding their inconvenient. The obtained simulation results show that an increase of all the system performances such as the daily pumped quantity, the motor power factor and the pump efficiency are reached by the proposed approach when either the ‘sinusoidal PWM strategy’ or the ‘Harmonic Minimisation Technic’ is used. To illustrate the economic performance brought by the proposed approach, the irrigated area by this solar pumping system is calculated under sahara climate conditions for two crops. The pumped volume collected in the ten typical years and the irrigated area show well promising results.