The document discusses renewable energy sources used in the UK, including wind, solar, hydroelectric, geothermal, and biofuels. It provides data on the percentage contribution of each renewable source to UK electricity generation in 2017, led by wind at 28%. Case studies of Iceland, Costa Rica, and Brazil show high reliance on renewable energy sources due to natural conditions like strong winds, abundant rainfall and hydroelectric potential, and biofuel feedstock availability. Each country still faces challenges to further develop renewable energy.