We propose an effective hybrid method, the CSGM, to forecast electricity consumption in NSW. Based on the inherent characteristics of GM(1,1), a series of suitable concepts, which
include data selection, an abnormality analysis, a feasibility test, and optimized algorithms, were used to improve forecasting accuracy. A case study shows that CSGM performs better than the classic GM(1,1), the GM(1,1) optimized using IA and the ARIMA model. Finally, we analyzed the forecasting errors based on statistical theory, which showed that the ARIMA electricity consumption forecasting model yielded a significant result with a small average error but with a high error at certain time-points; thus, ARIMA is not a suitable consumption forecasting model of electricity consumption in NSW.