Solar panels can become more efficient and wind turbines can become larger, but solar and wind have hard physical limits. The maximum efficiency of wind turbines is 59.3 percent, something scientists have known for more than one hundred years.66 The achievable power density of a solar farm is up to 50 watts of electricity per square meter. By contrast, the power density of natural gas and nuclear plants ranges from 2,000 to 6,000 watts per square meter.
