PARIS, Feb. 27 (UPI) -- The International Energy Agency said expanding the use of renewable energy resources like wind and solar requires transforming the system to be cost effective.
IEA published a 238-page book Wednesday that said technologies like wind power and solar photovoltaics are "crucial" to a future energy mix, though there are "unique" questions remaining in terms of cost and reliability.
"Electricity generation from both technologies is constrained by the varying availability of wind and sunshine," the IEA said. "This can make it challenging to maintain the necessary balance of electricity supply and consumption at all times."
IEA adds that as renewable energy systems become more prevalent, the grid needs to adapt and transform. This could require the costly decision to shut down older power plants.
The report finds, however, that large shares of renewable energy can be integrated into the power system if the right flexibility options are in place.
IEA Executive Director Maria van der Hoeven said in a statement that integrating more renewable resources into the grid requires transforming the power system in general.
"Integration is not simply about adding wind and solar on top of 'business as usual'," she said. "We need to transform the system as a whole to do this cost-effectively."