Yes, the sun is free. Yes, wind is free. But the process of turning sunlight and wind into useable energy on a mass scale is far from free. In fact, compared to the other sources of energy -- fossil fuels, nuclear power, and hydroelectric power, solar and wind power are very expensive.
The basic problem is that sunlight and wind as energy sources are both weak (the more technical term is dilute) and unreliable (the more technical term is intermittent). It takes a lot of resources to collect and concentrate them, and even more resources to make them available on-demand. These are called the diluteness problem and the intermittency problem.
The diluteness problem is that, unlike coal or oil, the sun and the wind don’t deliver concentrated energy -- which means you need a lot of additional materials to produce a unit of energy.
For solar power, such materials can include highly purified silicon, phosphorus, boron, and a dozen other complex compounds like titanium dioxide. All these materials have to be mined, refined and/or manufactured in order to make solar panels. Those industrial processes take a lot of energy.
For wind, needed materials include high-performance compounds for turbine blades and the rare-earth metal neodymium for lightweight, speciality magnets, as well as the steel and concrete necessary to build structures -- thousands of them -- as tall as skyscrapers.
And as big a problem as diluteness is, it’s nothing compared to the intermittency problem. This isn’t exactly a news flash, but the sun doesn’t shine all the time. And the wind doesn’t blow all the time. The only way for solar and wind to be truly useful would be if we could store them so that they would be available when we needed them. You can store oil in a tank. Where do you store solar or wind energy? No such mass-storage system exists. Which is why, in the entire world, there is not one real or proposed independent, free standing solar or wind power plant. All of them require backup. And guess what the go-to back-up is: fossil fuel.
Here’s what solar and wind electricity look like in Germany, which is the world’s leader in “renewables”. The word erratic leaps to mind. Wind is constantly varying, sometimes disappearing completely. And solar produces little in the winter months when Germany most needs energy.