Lot Sizing Problem with Fuzzy Capacitated Energy Sources

In this paper, a single-item lot sizing problem is studied with different energy sources having fuzzy capacities. Nowadays, more and more companies invest in renewable energy sources in order to reduce their energy-intensive production costs. However, the energy capacity generated by those sources can be insufficient to cover the whole system production activities. In this case, grid energy should be bought from the market. The aim of our study is to see the impact of the fluctuating capacities of the renewable energy sources on the production planning, in tactical level. When and which quantity to produce and to store, using which energy sources over one year constitutes our problem. The aim is to plan the whole production of the studied industrial case, having an on-site renewable energy generation system, taking into account the demand and energy production fluctuations. In order to express the uncertainty over renewable energy capacities, fuzzy sets are used according to the historical data. As a case study, a 48-week production plan is realized with the existing solar panels of a carpentry factory in Turkey. The behavior of the system is analyzed under different scenarios. Computational results attest the impact of the energy cost and capacity values on the production and storage planning decisions.