• Energy Research

The supply rate goal for new and renewable energy has been set to 20% by 2030 through the expansion of biogas production. The goal to reduce CO2 and greenhouse gas emissions by 37% below the business-as-usual (BAU) level of 851 million by 2030 was set by the Korean Government. However, biogas from corresponding treatment facilities is not used for the purpose of energy production, but is incinerated to raise the temperature of digesters. This study aimed to conduct a simulation of a solid oxide fuel cell (SOFC) hybrid plant using actual biogas operation data, analyzing annual performance. The 2450 kW SOFC system was set to its maximum capacity, with the available amount of biogas and the heat of the exhaust gas used to heat the anaerobic digester, but the amount of digester heat decreased in summer because of high air temperature. Up to 55% of total power usage could be produced via biogas, and a 45% reduction in CO2 was achieved.

In the Republic of Korea, efficient biogas-fuelled power systems are needed to use the excess biogas that is currently burned due to a lack of suitable power technology. We examined the performance of a biogas-fuelled micro-gas turbine (MGT) system and a bottoming organic Rankine cycle (ORC). The MGT provides robust operation with low-grade biogas, and the exhaust can be used for heating the biodigester. Similarly, the bottoming ORC generates additional power output with the exhaust gas. We selected a 1000-kW MGT for four co-digestion plants with 28,000-m3 capacity. A 150-kW ORC system was selected for the MGT exhaust gas. We analysed the effects of the system size, methane concentration, and ORC operating conditions. Based on the system performance, we analysed the annual performance of the MGT with a combined heat and power (CHP) system, bottoming ORC, or both a bottoming ORC and CHP system. The annual net power outputs for each system were 7.4, 8.5, and 9.0 MWh per year, respectively.

A mathematical model of hourly solar radiation with weather variability is proposed based on the simple sky model. The model uses a superposition of trigonometric functions with short and long periods. We investigate the effects of the model variables on the clearness (kD) and the probability of persistence (POPD) indices and also evaluate the proposed model for all of the kD-POPD weather classes. A simple solar organic Rankine cycle (SORC) system with thermal storage is simulated using the actual weather conditions, and then, the results are compared with the simulation results using the proposed model and the simple sky model. The simulation results show that the proposed model provides more accurate system operation characteristics than the simple sky model.