If a hydroelectric power station produces 30 TWh per year, but demand including aluminum smelters is only 20 TWh, then there's 10 TWh excess.
This is use-it-or-lose-it. Should they just allow the river to flow and bypass the turbines?
This is use-it-or-lose-it. Should they just allow the river to flow and bypass the turbines?
The (amortized) cost of building out new supply is a major[0] part of the cost of electricity - this is why most big energy producers spend millions of dollars per year on energy efficiency incentives. Haven't you ever wondered why your power company will give you a $50 rebate on an EnergyStar dishwasher? Isn't it counter-intuitive that they would pay you to buy less energy, when they have excess? It's not because they're tree-huggers - it's because decreasing demand growth delays the day when they need to build a new plant to meet demand, which increases the profitability of the current plant enough to make those incentives cost-effective[1].
0: I can't find a good estimate and it varies by fuel type, but I rememeber an environmental engineer at a former job telling me it was about half. Look up "Levelized Cost of Electricity" for more info.
1: If you're not convinced, instead of demanding more details, I urge you to just stop and ask whether the proposition "There is a lot of excess energy production lying around which BTC miners can soak up without impacting everyone else very much" really passes the sniff test.
There's a reason why hydroelectric plants and dams go together.
And they don't need it, because power-generating dams are generally only built in places that provide lots of downstream flow naturally, like the U.S. Pacific Northwest, or in places where a reservoir is already desired for other reasons (typically drinking water, navigation, and/or flood control).
Dams have the capacity to route downstream flow around some turbines to lower their generating capacity. It's not really accurate to think of that routed water as "wasted capacity," because that water would flow naturally even if the dam wasn't there.