as discussed further below in theory also the composition of the dispatchable portion of supply is likely to change as variable renewables tend to initiate a shift from highfixed cost technologies such as nuclear towards lowfixed costs technologies such as open cycle gas turbines due to the reduction in load factors depending on government policies future fuel costs and carbon pricing the final outcomes are very difficult to predict as operators will compose new leastcost configurations adapted to the new circumstances these are difficult to grasp conceptually very difficult to quantify at the current stage of debate and may not constitute welfarerelevant externalities in the sense that gridlevel or other technical externalities do however they may well constitute the impacts that are currently most acutely felt by electricity producers and may in the long run have the most profound effect on the operations and structure of electricity markets