So this is a question that's been in the back of my mind for awhile while seeing celebrations of dams being removed, no worries if you don't want to be the one to answer it.

I think I understand the extent of the damage caused by the implementation of dams, but I guess my impression had been that that damage was done, and there wasn't much of a timeline on fixing it. Like, after eighty years or so, are there fish still trying to get past it?

At the same time, we're struggling (failing?) globally to get away from fossil fuels quickly enough to avoid the worst of climate collapse. It seems like hydro is one of the more reliable green power sources, and is compatible with old grid infrastructure that counts on fairly consistent power so there's less than has to be overhauled in order to just keep using hydro for awhile longer.

So at first glance, it seems like new solar and wind etc production would be better prioritized in replacing oil, coal, natural gas. Prioritizing replacing hydro feels like letting the perfect be the enemy of the good.

I haven't seen that discussion anywhere, so I genuinely expect I'm wrong about that, but I'm wondering why.

There are forms of hydroelectric generation that aren't damaging to the environment. We just need to actually be aware of the consequences and perform an environmental risk assessment. I think this is a requirement for new installations in the US, but I could be wrong.

Creating it from electricity is highly inefficient, so that's why it's made from other fossil fuels (that in theory would have been wasted). If hydrogen was easily compacted and stored long term it would work, but those are the biggest problems it faces, along with having a much lower energy density that fossil fuels. Hard to beat those carbon bonds without going nuclear.

Or you put turbines in your dam and get both, as is common.

There are other types of biomass though. Using waste product from food production or gas from sewage plants is somewhat reasonable.

It is renewable in the sense that given infinite time, you can use it to grow infinite energy (for the nitpickers: assuming an eternal sun).

It is not infinite though and the amount of power you can extract from it is limited but that's true for every renewable sources: you have a limited amount of places where you can put dams, where you can put windmills or even solar panels.

What is important is that it is not power generation that consumes a scarce good (as fossil power does) but that it is increases in power generation that consumes it, in a reversible way.

Poplars and willows are fairly fast growing. Plus there are perennial grass feedstocks

Yes, and, once established, a grove of trees can continue providing biomass for literally centuries. Look up coppicing.

The deforestation of the Amazon is largely driven by a desire for more land to grow biofuels (sugarcane) on.

The byproducts of sugar production (the leaves and stalks) are used to produce ethanol from a biological, renewable source, as opposed to fossil fuels.

Oh, and in the Amazon, said sugarcane farming is often done by slaves.

You either need more farmland to grow what will become biofuels on it, or you have to stop growing food on existing farmland, which means food gets more expensive.

Biomass and hydro* aren't storage for intermittent power (*except pumped hydro). Rather they are natural sources of accumulated solar power that can be tapped on demand. In that sense, so is geothermal.

They aren't forms of energy storage on their own. Just like batteries aren't a source of energy on their own.

You can't turn other forms of energy into solar or wind and store it in those forms. In contrast, hydroelectricity can store energy in pumped storage systems where excess electricity is used to move water to higher elevation (exchanging electricity for potential energy).