This paper presents a simulation model for assessing the effects of a feed-in tariff and a carbon market with carbon price floor on: the security of supply, emission reduction, and cost of the system. The model is a power capacity expansion model based on system dynamics methodology. The results show that a feed-in tariff is a better policy instrument for reaching emission reduction to a lower cost; however the security of supply is reduced, in particular the gas load factor is reduced considerably during the simulation period. It is necessary to simulate other policies for guarantying the security of supply as a capacity mechanism or a demand side management measure. The model is applied to British electricity market.