# Ocean currents: Fluctuation in time

The steadiest flow in the ocean

Source page: https://www.materialinsights.org/energy/e_currents/time/

What this tab covers How availability changes over seconds, days, seasons, years and longer, how predictable it is, and what that means for the plants that use it.

Ocean currents are the steadiest of the marine energy flows: they do not reverse like tides or stop like wind, so a turbine in a strong current could run most of the time.

#### Variation by time scale

| Time scale | What happens | How large |
|---|---|---|
| **Hours to days** | Continuous, one-directional flow with no daily or tidal reversal.^[4](https://www.energy.gov/sites/prod/files/2021/02/f82/78773_3.pdf) | Described as offering 'steady, reliable power' to the US south-eastern states. |
| **Year (operation)** | High expected utilisation compared with other marine resources.^[4](https://www.energy.gov/sites/prod/files/2021/02/f82/78773_3.pdf) | Assumed capacity factor 70%, against 30% for wave and tidal devices. |
| **Decades (response to extraction)** | Large arrays could shift a current's path.^[4](https://www.energy.gov/sites/prod/files/2021/02/f82/78773_3.pdf) | The Gulf Stream would likely shift its course around turbine arrays; climatic implications not yet understood. |

#### How predictable it is

Boundary currents such as the Gulf Stream are persistent features that flow all year, which makes their output much more predictable than wind or waves. Their exact position meanders over days to months, so a fixed turbine may see the fast core move towards or away from it.

#### Capacity factors and utilisation

| Plant or measure | Value |
|---|---|
| **Ocean current turbines, US national resource assessment assumption** | 70%^[4](https://www.energy.gov/sites/prod/files/2021/02/f82/78773_3.pdf) |

The appeal of ocean currents is constancy: unlike wind, waves or tides, the flow keeps going in the same direction day and night. National assessments therefore assume ocean current turbines could reach capacity factors around 70%, far above most renewables. The uncertainties are at longer time scales: meanders of the current's core, and how the current would respond if large amounts of energy were removed.

Because the flow is continuous, a current turbine would need far less storage or backup per unit of energy than wind or solar, which is the main reason the resource attracts research despite its remote, deep-water locations.

#### Sources

1. [Marine Energy in the United States: An Overview of Opportunities (Kilcher, Fogarty and Lawson, NREL/TP-5700-78773)](https://www.energy.gov/sites/prod/files/2021/02/f82/78773_3.pdf) National Renewable Energy Laboratory / US DOE, 2021

## Other sections

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