Renewable energy sources (solar, wind, hydro, geothermal, and marine energy) are grouped together in the online En-ROADS simulator, although wind, solar, geothermal, and hydro are modeled individually. Renewable energy sources are powered by means that are not exhausted by continued energy production. The sun, for example, will keep shining regardless of whether a solar panel captures some of its energy. Energy generation from renewables is assumed to produce zero greenhouse gas emissions.
Currently, wind and solar energy individually are not a large part of the global energy supply, although they are growing rapidly. According to the IEA, in 2018, wind energy was 4.8% of global electricity production, and solar energy was 2.1%. Geothermal and marine energy made up only about 0.5%.
The largest source of renewable energy is currently hydro (16.2% in 2018). Hydro is not expected to grow substantially, given the limitations in locating suitable places for new hydropower development.
Bioenergy and nuclear energy are separated out in En-ROADS, although some classify them as renewable energy. They have unique characteristics from wind, solar, and hydro. Biomass releases carbon when it is burned, although this can be offset by the replanting or regrowth of other biomass. However, this regrowth takes a long time and is not guaranteed. Nuclear is separated out because of the significant role it plays in the energy mix and because it is often its own topic of conversation separate from renewables.