where applicable the alternative fuels to gasbased generation such as diesel fuel oil or coal are mainly stored on the site of ccgts the period of load duration depends on a number of factors including the ability to restock backup fuels generator characteristics the type of gas supply contract either firm or interruptible and expectations about the variability of electricity prices as these determine the installation of backup facilities berr however when information on this indicator remains disaggregated the overall picture for the national energy system may be less clear