Steam, solar, electrical, geothermal, wind… all of these power sources are practical and reliable.

They're practical for us because we have had wood products since the dawn of humanity, but how does a budding intelligent species use any of those without wood or petroleum? Unless I'm wrong, early humanity would not have been capable of using any of those without wood burning first. Maaaybe hydro?

AFAIK, there is no guarantee that fossil fuels will form in a life-bearing planet's geological history. But it's really unlikely not to. On Earth, the initial explosion of photosynthetic life took large amounts of CO2 out of the atmosphere. With nothing initially eating it, layer upon layer of dead biomass was laid down, and buried over geological time. When some alien microbe first figures out how to photosynthesize, it would inherently outcompete every other life-form on the planet, expanding far too fast for anything else to eat it. Even if the input of energy to the planetary ecosystem is something other than light - geothermal heat, perhaps, or some kind of chemical energy, or even radioactive decay - that energy will be stored in biomass, and unless it gets burned, that biomass will become fossil fuels.

The second possibility just doesn't make sense. It may not be something we recognize as plants, but an ecosystem has to have autotrophs of some kind. Something that uses an ambient energy gradient to turn the inorganic materials into more living stuff. And that stuff is inherently a store of energy.

Now, if your question is simply, "what would the chemistry be, if not like ours?" that's a different question, and one that xenobiologists are trying to figure out right now.

Wood is not the only flammable material. And if we assume a carbon-based life form, it would be difficult to imagine them developing in an environment void of plant life.

That makes more sense to me. If fossil fuels or some sort of low level fuel source is almost a requirement when it comes to successful ecosystems as we know it, that makes me feel better about it. I have been thinking a lot about some poor intelligent species stuck in a pre caveman era forever because they simply don't have the necessary resources to advance.

I agree, but even in our own history there was life before trees and I guess that's more of what I'm concerned. Other things are flammable but without substantial things like coal and wood they simply wouldn't really be able to make fires hot enough to be able to forge anything stronger than like...bronze? I guess that's also needing to consider atmospheric content and stuff. Sorry if it feels like I'm arguing with you, I'm absolutely not trying to, I just don't have people that like this sort of thing that are willing to or are knowledgeable enough to talk about it

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There are situations that would seem to make that happen. Evolving underwater, for example. Without fire, it's really hard to imagine a species developing beyond the basic tool use we see in dolphins. Fortunately, it's not likely a species would develop much more than dolphin-level intelligence without fire, either. Brains, especially the complex, wrinkly brains we humans have, are really expensive to build and maintain. That's why so many species invest in claws and teeth instead. Dentin and keratin are pretty cheap. But if you use your brain to figure out how to get more nutrients (especially fats and proteins) from your food by cooking it, then evolution selects for that brain. That's part of how our brains evolved. It's hard to see how a species could leverage high brainpower to increase nutrition from food to that point without fire. Maybe they could do it by fermenting meat, but that would require other advancements that I just don't think are likely.

That's something I actually forgot to consider. Being able to cook food and using tools to break bones and to cook and eat marrow and stuff helped advance us significantly. I've often wondered what species, if any, would become the next super intelligent earthican and it is interesting to think of it soley in terms of ease of nutritional resources. That being said, there aren't a whole lot of candidates. Thanks for the brain food friendo :)