Here is a breakdown of the cost of renewable energy according to our research, ranked by least to most expensive: 1. Solar, standalone — $32.78 per MWh 2. Geothermal — $36.40 per MWh 3. Wind, onshore — $. The cheapest renewable energy is indeed solar energy. The International Energy Agency's World. Yes! Solar power has recently become the cheapest energy source in history, as mentioned above. And of the wind, solar, and other renewable energy sources in use in 2020, 62% wer. Solar is the cheapest form of energy due to the lower cost of building panels to harvest energy from the sun. Additionally, scientists and engineers are actively researching technology that.