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This week we are looking at renewable energy sources and why we need them. We’ll explore hydropower, wind, geothermal, and solar power, as well as some of the challenges, and how engineers are working to make their use more widespread.

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CC Kids:
Engineering has given a lot to the world. It's transformed the nature of work, improved sanitation, and helped create vital infrastructure. The bad news is that to power the tools and processes behind those developments, we've relied on non-renewable fuels, the kind that get produced at a much slower rate than we use them.

As the name implies, non-renewables won't be around forever. Resources like oil and natural gas might be gone in just half a century. And using them has been, frankly, pretty terrible for the environment. Eighty-seven percent of the harmful carbon dioxide emitted by humans in the last fifty years has come from burning fuels such as coal, oil, and natural gas, known collectively as fossil fuels. It's been terrible for the atmosphere and oceans, and is changing our climate in dangerous ways.

Whether we like it or not, we're going to have to find new ways to power our world.

[intro music]

Despite their terrible effects on the environment and limited supply, for now non-renewables do a really good job of meeting our energy needs. In 2017, 80% of the power used in the United States was supplied using fossil fuels. And the need for energy doesn't appear to be shrinking any time soon. Another 9% was delivered from nuclear fission, the process of splitting atoms, which releases far less CO2. Unfortunately, fission produces radioactive waste and also relies on non-renewable fuel sources, such as uranium and plutonium.

All of these methods operate on broadly the same principle, essentially operating as a heat engine. A working fluid, often water, is heated by the fuel to expand and do work, turning the blades of a turbine. The turbine is connected to an electrical generator that converts the rotational motion of the blades into electrical power, which is then fed into the grid.

So what about the remaining 11% of power? That came from renewable energy sources, the kind that are generated about as fast as we use them. Some of the major renewable energy sources come from processes that are naturally occurring on earth: wind power, solar power, hydro power, which is based on flowing water, and geothermal power, which uses the heat of the earth deep underground. None of these sources are things we'll run out of. We have a good few billion years of sunlight left, for example. And what's more, renewable energy tends to release fewer harmful by-products, like carbon dioxide, into the environment.

Take hydropower, for example, which converts the kinetic energy from the motion of running water into electrical power. In a fast-flowing river, a run-of-river power plant diverts part of the river's flow, sometimes through a tunnel, to turn the turbines of a generator. That works well in some places, but the problem with this approach is that it's tricky to control the generation of energy to meet demand. You don't want to put lots of power into the grid when it won't get used, and you want to be able to ramp up the supply when the demand suddenly spikes. [2:45]