Lesson 6 of 7

Hydropower & Other Renewables

7 min read

Not every renewable behaves like solar or wind. Hydropower, in particular, breaks almost every pattern set by the last four lessons — and understanding why is as instructive as the technology itself.

Hydropower: the dispatchable renewable

A hydro plant uses falling or flowing water to spin a turbine connected directly to a conventional synchronous generator — mechanically, it has far more in common with a traditional thermal power plant than with solar or wind. That matters enormously: unlike solar and wind, a reservoir-based hydro plant can typically be dispatched on demand and can ramp output up or down quickly, making it one of the few genuinely dispatchable, low-carbon generation sources available today.

Reservoir (storage) hydro: Water is held behind a dam and released as needed — effectively a form of energy storage in its own right, and often used specifically to balance variable solar and wind output.
Run-of-river hydro: Generates from the natural flow of a river with little to no storage — output follows seasonal river flow rather than operator choice, behaving more like a variable resource than reservoir hydro.
Pumped storage hydro: Covered in the previous lesson as storage, but worth remembering it's built on the same turbine technology as conventional hydro.

Why hydro still has rotating mass — and why that matters

Because a hydro plant spins a conventional synchronous generator directly connected to the grid, it contributes real physical inertia and natural reactive power support — exactly the properties solar and wind (via inverters) don't inherently provide. This is a major reason grids with substantial hydro capacity often find high renewable penetration easier to manage than grids relying purely on solar and wind.

Geothermal and biomass, briefly

Geothermal: Uses heat from the earth to produce steam that drives a conventional turbine-generator — geographically limited to regions with accessible geothermal resources, but where available, it's dispatchable and available around the clock, unlike solar or wind.
Biomass: Burns organic material (wood pellets, agricultural waste, biogas) to drive a conventional steam turbine — dispatchable like a fossil plant, with its renewable status resting on the fuel being replenished rather than on the generation technology itself.

The common thread across this lesson

Geothermal, biomass and hydro all share one property that sets them apart from solar and wind: they spin a conventional generator whenever their fuel or resource is available, on a schedule the operator can largely control. That's precisely why grid planners often describe them as "dispatchable renewables" — and why a grid with a healthy mix of these alongside solar and wind faces a meaningfully easier integration problem than one relying on variable sources alone.

Key takeaways

Hydropower uses conventional synchronous generators, making it dispatchable and inertia-providing unlike solar or wind.
Reservoir hydro can be dispatched on demand; run-of-river hydro follows natural river flow instead.
Geothermal and biomass are also dispatchable renewables, geographically or fuel-supply limited respectively.
A generation mix that includes dispatchable renewables alongside variable solar/wind is generally easier to balance.