The Wikipedia article gives an extremely strained explanation of why TANSTAAFL still holds true in that case by referring to open vs closed systems, but at that

The Wikipedia article gives an extremely strained explanation of why TANSTAAFL still holds true in that case by referring to open vs closed systems, but at that point it's just thermodynamics. In practice, solar energy (whether directly or via evaporation) is "free". I think how most people understand TANSTAAFL is that if it's free, there are always strings attached. This holds true in many situations (owing favors in return, free food being salty so you order more drinks, free trials encouraging vendor lock-in, etc). But it's not true in all situations and stretching the definition so it covers those makes it useless.