Economic assessment of photovoltaic (PV) water pumping system in drip-irrigated fields

In Iran, pressurized irrigation systems is increasing. One of the requirements of pressurized irrigation systems is to supply energy to pump water. Because of non-renewal, extraction costs and environmental hazards of fossil fuels, solar energy utilization has become inevitable. Solar energy is one of the most important and cleanest forms of new energies which can return the initial cost of solar system to a customer in the long term. One of the reasons for Iran's failure to use a large part of its cultivated land is a large distance from the national electricity network and high electricity costs. In this study, solar and electric pumps were compared economically to pump water in nine gardens under drip irrigation networks including three crops: pistachio, almond, and walnut. The gardens are located in two provinces of Tehran and Hamedan.

The drip irrigation system is applied in these gardens. The gardens were classified into three groups: small (less than 5 hectares), medium (5 to 60 hectares) and large (more than 60 hectares). First of all, pumping station was designed and then investment costs were estimated for all the studied gardens. To design and simulate photovoltaic system, the Lorentz solar pump special design software was used. It is assumed that electricity would supply for these areas in two ways including 1) installation of photovoltaic systems in remote areas without a national electricity grid 2) electricity transmission through the construction of transmission lines and trans-installation. These two conditions were compared by the present value method at two interest rates, 5 and 10%. To convert future costs to present value, real interest rate index is required. Considering the difference between the useful life of equipment for electric pumps and solar pumps, as well as solar panels, the lifetime of the projects was considered unequal in calculating the current value.

The results showed that the utilizing photovoltaic pumping without distances from the electricity distribution network is only economic in 60 ha pistachio garden with an interest rate of 10%. In the walnut garden with medium size, with the same interest rate, despite the slight difference in investment cost, it is not different with electric pumping. In the case of distance from the power distribution network, photovoltaic pumping will be more economical by reducing farm size (less capacity and pressure) and increasing the distance from the power distribution network. Of course, other factors such as temperature, sunshine, radiation intensity and solar angles may also affect photovoltaic pumping during different seasons. The results also showed photovoltaic pumping of irrigation system is economic for small and medium pistachio and walnut gardens, at 0.5 kilometres of the electric distribution network, in the interest rate of 5% and 10%. With increasing distance from the electricity distribution network, only the cost of transferring power lines to electric pumping costs increase and the use of photovoltaic pumping is more justifiable. Changes in the current value of costs for both pumping methods at a rate of 10% relative to the 5% interest rate will lead to cost reductions. In remote areas, which it is difficult to access to electricity distribution and transmission networks, the use of photovoltaic pumping is reasonable and economical. For each area, there is a specific distance from the electric distribution network which photovoltaic pumping is reasonable for drip irrigation.