THE CONCEPTUAL MODEL AS A BASIS FOR A SIMULATION MODEL OF THE NATURAL GAS SUPPLY CHAIN AIMED AT COST OPTIMIZATION

The functioning of the natural gas system in the Republic of Croatia is based on the laws and regulations of the European Union. Consumers are obliged to sign a contract with suppliers, i.e. energy companies that purchase gas on their behalf under regulated conditions (gas for households) or based on market principles (gas for industry and commercial purposes). Suppliers must predict the amount of gas their consumers will consume and, place their orders accordingly. The gas market in the Republic of Croatia functions on a balancing principle. This means that the total amount of gas injected into the transmission system (quantity ordered by suppliers) must be withdrawn from it. Since it is not possible to accurately predict future gas consumption, differences arise between the ordered (nominated) quantity and the actual amount consumed. This leads to imbalances in the system and the cost of rebalance is paid by the suppliers. The main purpose of this paper is to present the conceptual model as a basis for a developing simulation model to test a potential technical solution that could be used to compensate for prediction errors. Such a solution would be placed at the beginning of the distribution system and it would manage system accumulation. In case of an excess in the transmission system (more nominated than consumed), that surplus would be accumulated in the distribution system. Conversely, if consumption exceeds nomination, when there is a sufficient amount of gas accumulated in the distribution system, the difference would be withdrawn from it. In order to test such a potential solution, a computer simulation of the gas system will be created. This should give the answer as to whether the activation of the balancing energy occurs less frequently and, consequently, reduces the cost to suppliers. However, before designing the simulation model, it was necessary to create a conceptual model that represents the gas system after improvements.