In practice, however, there are additional costs and benefits associated with the use of DG technologies over and above the financial costs and revenues. In particular, the potential environmental benefit of distributed generation systems is one of the main drivers of the current enthusiasm for DG. DG can play a role in helping environmental obligations be met in two key ways. Firstly, CHP applications (associated with DG technologies such as fuel cells, gas turbines and microturbines) allow for emissions savings and optimal energy consumption for firms or communities where there is a simultaneous demand for heat and electricity. Secondly, most renewable energy technologies (with the exception of large hydro stations) are decentralised because of their nature. Various studies attempt to capture such externalities (social costs and benefits) associated with DG energy systems.