Methodology to Design the Capacity of a Microgrid

A methodology was developed to design the number and capacity for each piece of equipment (e.g. gas engines, batteries, thermal storage tanks) in a microgrid with combined heat and power(CHP) system. In the methodology, annual cost is minimized by considering the partial load efficiency of a gas engine and its scale economy, and the optimal number and capacity of each piece of equipment and the annual operational schedule are determined by using the optimal planning method. Based on calculations using this design methodology, the optimal number of gas engines is 1 because efficiency of an engine shows scale economy, considering a turndown(the lowest load factor) constraint of a gas engine. The optimal contract demand for purchasing from or selling power to the utility is 14% of the peak demand. The optimal capacity of a battery required to supply electricity for a limited time during a peak demand period is auxiliary. The thermal storage tank for space cooling and space heating is selected to minimize the use of auxiliary equipment such as a gas absorption chiller.