# Water cycle: How energy resides

Why falling water holds so little energy per litre

Source page: https://www.materialinsights.org/energy/e_hydro/resides/

What this tab covers The physical form in which the energy is held or carried, where it comes from, the chain of transformations that put it there, and how concentrated it is.

Hydropower taps the gravitational potential energy of water that sunlight has lifted by evaporation and that rain and snow have dropped on high ground. The energy is very dilute: a cubic metre of water falling 100 m holds only about 0.27 kWh.
 Form Gravitational potential energy of raised water (and kinetic energy of flowing rivers) Origin Indirect solar

#### How it got there
 Fusion in the Sun Sunlight Evaporation from oceans, soils and plants (absorbs latent heat) Water vapour rises and condenses into clouds Rain and snow fall on high ground Runoff gathers in rivers and lakes Water falls through turbines back towards the sea

#### How concentrated it is

| Measure | Value | Note |
|---|---|---|
| **Energy in water at 100 m head** | 0.273 kWh per m3 (Wh per litre)^[3](https://web.engr.oregonstate.edu/~webbky/ESE471_files/Section%203%20Pumped%20Hydro.pdf) | Proportional to height: 1.36 at 500 m, 2.73 at 1,000 m. A lithium-ion battery holds about 400 Wh per litre. |
| **Solar energy spent on evaporation (latent heat flux), global mean** | about 85 W/m2^[2](https://doc.rero.ch/record/321020?ln=en) | Climate-model estimate; most is released as heat in the atmosphere when vapour condenses, not left as raised water. |
| **Typical head of hydropower plants (pumped storage)** | 100 to 1,000 m^[3](https://web.engr.oregonstate.edu/~webbky/ESE471_files/Section%203%20Pumped%20Hydro.pdf) | Higher head means less water is needed for the same energy. |

The Sun drives the water cycle. Roughly half of the sunlight absorbed at the Earth's surface goes into evaporating water. When the vapour condenses into clouds, nearly all of that energy is released as heat in the atmosphere; what remains for hydropower is only the potential energy of rain and snow that land on high ground, which gravity returns to the sea through rivers.

That residue is small and spread out. Water at 100 m above a turbine stores just 0.27 kWh per cubic metre, about one fifteen-hundredth of a lithium-ion battery by volume. Hydropower works because rivers concentrate the runoff of whole catchments into one channel and dams stack up hundreds of metres of head, so the flow through a single valley can deliver gigawatts. The same physics makes reservoirs large: storing useful amounts of energy needs vast volumes of water, high head, or both.

#### Sources

1. [The global energy balance from a surface perspective (Wild et al., Climate Dynamics 40, 3107-3134)](https://doc.rero.ch/record/321020?ln=en) Springer / RERO DOC, 2013
2. [ESE 471 Energy Storage Systems, Section 3: Pumped-Hydro Energy Storage](https://web.engr.oregonstate.edu/~webbky/ESE471_files/Section%203%20Pumped%20Hydro.pdf) Oregon State University, 2019

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_hydro/index.md)
- [Overview](https://www.materialinsights.org/energy/e_hydro/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_hydro/correlation/index.md)
- [Abundance](https://www.materialinsights.org/energy/e_hydro/abundance/index.md)
- [Fluctuation in time](https://www.materialinsights.org/energy/e_hydro/time/index.md)
- [Across the Earth](https://www.materialinsights.org/energy/e_hydro/geography/index.md)
- [Impact on nature](https://www.materialinsights.org/energy/e_hydro/nature/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_hydro/links/index.md)