Modelling the economic trade-offs of irrigation pipeline investments for improved energy management

[摘要] The main objective of this research is to develop an integrated non-linear programming modelthat unifies the interrelated linkages between mainline pipe diameter choice and the timing ofirrigation events in conjunction with electricity tariff choice to facilitate better evaluation of theeconomic trade-offs of irrigation pipe investments for improved energy management.The Soil Water Irrigation Planning and Energy Management (SWIP-E) programming model wasdeveloped to address the main objective of the research. The model includes an irrigationmainline design component, soil water budget calculations and an energy accounting componentto model the interaction between irrigation system design, irrigation management and time-of-useelectricity tariff structures. The SWIP-E model was applied in Douglas to evaluate the impact ofdifferent electricity tariff structures and irrigation system designs on the optimal pipe diameter ofan irrigation mainline, electricity costs and profitability.The results showed that Ruraflex is more profitable than Landrate which is a direct result of higherelectricity costs associated with Landrate. The large center pivot resulted in higher net presentvalues than the smaller center pivot and the lower delivery capacities were more profitable thanhigher delivery capacities. More intense management is necessary for delivery capacities lowerthan 12 mm/day to minimise irrigation during peak timeslots. Variable electricity costs are highlydependent on the interaction between kilowatt requirement and irrigation hours. For the largecenter pivot the interaction is dominated by changes in kilowatt whereas the effect of irrigationhours in relation to kilowatts is more important for smaller pivots. Landrate with relatively higherelectricity tariff charges resulted in a change in the optimal pipe diameter at lower deliverycapacities compared to Ruraflex. Optimal pipe diameters will increase for a breakevenpercentage of between 0.6% and 0.66% for Ruraflex and between 0.4% and 0.6% for Landratewhich is much lower than the design norm of 1.5%.The overall conclusion is that the SWIP-E model was successful in modelling the complexinterrelated relationships between irrigation system design, management and electricity tariffchoice that influence the trade-off between main pipeline investment decisions and the resultingoperating costs. Electricity tariff choice has a significant impact on the results which suggest thateconomic principles are important and that it should be included in the design process. Ashortcoming of the model is that the risk of lower irrigation system delivery capacities was notincluded in the model. The conclusion that lower delivery capacities are more profitable shouldtherefore be interpreted with care. The low breakeven friction percentages optimised in thisresearch suggest that the norm of 1.5% friction is too high and a lower norm should beconsidered. Future research should focus on extending the model to include a combination of irrigationsystems and the inclusion of risk to evaluate the risk associated with low irrigation deliverycapacities in combination with load shedding.

[发布机构] University of the Free State