<P> The positive impact on the environment globally is less clear . Hans - Werner Sinn, a German economist and chair of the Ifo Institut für Wirtschaftsforschung argues that Germany's renewable energy support reduces world market prices for fossil energy . Thus, countries like China or the US have an incentive to produce more, and the net effect on the climate is zero . This effect is known as the green paradox . </P> <P> One challenge that lies ahead is integrating the electricity generated by decentralized renewable energy into the existing electricity grid structure . The grid was built to suit the centralized energy system of the then four main energy companies, namely, E. ON, EnBW, RWE, and Vattenfall . </P> <P> The need for grid reinforcement from north to south is commonly recognized . In response, the four TSOs proposed 92 expansion projects covering 7300 km of lines, but not all will be required or approved . In 2015 the Federal Network Agency (Bundesnetzagentur) released its report on grid expansion plans covering the next decade . Rapid development of the grid is being driven by the uptake of renewables and the phase - out of nuclear power . </P> <P> But not all experts agree that a substantial build - out of the grid is necessary . Claudia Kemfert believes the large amount of coal - fired generation on the system is part of the problem . Kemfert said "our studies and models show that grid extension does no harm, but it's not strictly necessary...decentralised, intelligent grids with demand management and, in the medium term, storage, would be much more important ." Analysis for Greenpeace Germany in 2016 also suggests that it is inflexible coal and nuclear plants that are clogging the grid and driving up wholesale electricity prices . </P>

A- what is the german renewable energy law