Greenhouses Energy Supply Modeling Using Renewable Energy in Grid-Connected mode

The increasing global population on the one hand and limited water and soil resources on the other hand, contribute to the need for the supply of agricultural products by adopting modern methods. One of the modern methods of farming is the cultivation of products in commercial greenhouses. Despite favorable performance of greenhouses in the agricultural sector, high demand for direct and indirect energy is among the main considerations of developing them because the energy supply of greenhouses has the highest influence on the performance of greenhouses, quality of products, and market price of products. In this study, the energy supply of greenhouses in the case of using renewable resources is done in a grid connection state. Trading energy with main grid is enabled. Decision-makers’ objective is determining the optimal number of renewable resources and energy storage units for the purpose of income maximization.

Basically, the supply of energy for greenhouses or in other terms supply of electric, cooling, and heating loads required by greenhouses is intended to cover lighting, internal temperature, emission of CO2, and relative humidity. Since many greenhouses have proper access to the main grid for the supply of their demanded load, the problem seeks maximum use of renewable energy rather than buying power from the grid for supplying the loads which greenhouses need to its secure revenues. To this, mathematical modeling has used to determine the optimal number of energy sources and storage units that revenues of using renewable energy resources be optimized based on existing limitations. These limitations include balancing generation and consumption of thermal and electrical power in each hour, logical relationship between charging and discharging of batteries, limit of power generation of renewable sources in each hour of the day and the level of capital available for investment.

Based on the collected data, 9 different issues have been defined in terms of the proportion of costs of solar energy and wind energy and the proportion of purchasing and selling price of power. The obtained results suggest that in the case of equality of investment and maintenance costs of solar and wind energies, the use of wind energy rather than solar energy will be justified. The most significant reasons for this is considering proper conditions of wind speed which causes its inclusion in optimal solution of the problem since using solar energy during nightly hours is impossible. In addition, in the case of the equality of above costs, when purchasing and selling price of power cost is the same, the generated energy is completely used in the greenhouse. In the case of increasing the selling price, energy supply to the main grid will be economically justified. Since investment and maintenance costs of wind power are two times and 1.5 times higher than those of solar energy, using wind energy is cost-effective.

The results suggest that in the case of an equal price of selling power to the grid and buying power from it, all of the energy will be consumed in the greenhouse. In the case of an increase in selling price, the supply of energy to the main grid will be economically justified. In addition, the results imply the significant effect of geographic conditions of the region, since sometimes concurrent use of renewable energies is unjustified. Since the lack of supply of energy to greenhouses significantly influences the cultivation of products, considering the cost of lack of energy supply in modeling is one of the contributions of the present study. Another significant aspect of the study is the generalization of modeling from the greenhouse to greenhouse complexes. To do so, using the notion of micro-hub for greenhouses and their management will be useful.