Basics of Energy Flows
Energy flows come from natural processes initially driven by solar energy
A challenge with energy flows is that they are intermittent and not controllable, leading to a need for efficient conversion and storage technologies
Examples of energy flows include solar, wind, hydro, and geothermal
Flows as energy sources
One category of energy sources that humans use are referred to as flows. These flows have energy associated with motion and come from natural processes. Some examples include solar radiation, the movement of tides, wind, or water flowing downstream in a river. The energy from these primary flows can be harnessed for transportation, heating, or electricity generation.
Energy flows are considered renewable, because they are replenished at a higher rate than they are consumed. However, a challenge with energy flows is that they are intermittent and not controllable, so technologies for conversion and storage need to be employed.
The largest flow of energy is sunlight, which in fact provides most of the energy on our planet. The majority of the solar energy on earth goes towards the water cycle and heating our atmosphere to a livable temperature.
An advantage of energy flows is that their kinetic energy can be efficiently converted to electrical energy directly without producing significant amounts of waste heat, making them an attractive choice for electricity generation.
Examples of energy flows
Solar power uses the radiation from the sun in order to create electricity. Solar thermal power plants use the heat from the sun to spin turbines, whereas photovoltaic systems convert the solar energy directly to electricity.
Wind power uses wind currents put into motion by the sun, harnessing their kinetic energy to generate electricity by turning turbines. About 2% of solar energy is converted into kinetic energy in the form of wind.
Hydroelectricity uses the natural flow of water to generate electricity by turning turbines. The water cycle of evaporation, condensation, and downstream flow is driven by the sun.
Geothermal power takes advantage of the heat generated in the earth’s core. Thermal energy from hot spots on the earth’s surface can be used to generate electricity or as a heat source. Geothermal sources are geographically limited, and can be depleted.
All of these energy flows have benefits and challenges associated with them, which will be further outlined in later modules. A unifying consideration is their accessibility and variability in different locations.
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Questions for deeper thinking
What are ways in which flows have been used for energy throughout human history before electricity generation (ex: sailing ships)?
How does geography influence what flows are most readily accessible (such as higher levels of solar irradiation in deserts)?
How will the distribution of flows across the globe influence the capacity for different nations to undergo energy transformations in the next century? For example, how will this process look for nations that are very sunny vs. nations that have a large coast and access to wind?
Sources and further reading
Energy Education: Primary energy flow
Energy Education: Fuel vs flow
Page last updated: November 20, 2022