I don't really know for now what can be profitable to mine, but I see that the miners who have experienced quite a large profit from the mining results they have done last year, including those they mined were Kaspa, Verus, Zano. So I can conclude that what needs to be done is to analyze and research the coins or tokens that we will mine, so that we can also get profit from the increase in value. For reference, you can try looking on these sites :

- Whattomine
- Nicehash

By the way, I don't really understand what you mean by free energy, if it uses solar energy, I don't think it's free either because it still requires maintenance costs and capital to build it. So, what do you mean by free energy?