The second most widely-used source of renewable energy (24% of the world’s renewable energy generation capacity), wind power is harnessed by turning a wind turbine’s propeller-like blades around a rotor, which powers a generator and creates electricity. Wind turbines have been used on farms and homesteads for centuries, mostly for things like grinding grain and pumping water.

Lead by China, the United States, Germany, Spain, India, the UK, Italy, France, Brazil, Canada, and Portugal, the world is increasingly adopting wind power to meet its energy needs. And while it certainly deserves its place of prominence, wind turbines have some hidden costs, like high bird fatalities and noise pollution to nearby communities. Some people also consider them to be an eyesore. Still, they’re a step in the right direction and are significantly less problematic than conventional power plants.

With more than 486GW of installed capacity, solar energy is the fastest-growing renewable power source. The most popular technologies are photovoltaic (PV) and concentrating solar power (CSP). Solar panels (PV) work when their photovoltaic cells generate electricity by absorbing sunlight and using its energy to create an electric current.

Concentrating solar power (CSP) plants also harness the power of the sun, but in a very different way: they use specialized mirrors to concentrate its energy and drive traditional steam turbines or engines to create energy. The thermal energy concentrated in CSP plants can then be stored and used to provide electricity whenever it’s needed.

China, the United States, Germany, Japan, Italy, and India lead in PV capacity, while Spain has 42% of global CSP capacity. Solar power is awesome, but it isn’t perfect — photovoltaic cells and the batteries needed to store their energy are made with toxic chemicals and materials. CSV uses hazardous fluids to transfer heat, and if allowed to leak, they can damage the surrounding environment. Solar panels also take up a lot of space, and solar farms are not aesthetically pleasing to most people. Despite these issues, solar is a great technology with a lot of potential!

Two types of energy can be harnessed from the ocean: thermal energy from the sun’s heat and mechanical energy from the motion of tides and waves. Ocean thermal energy uses the ocean's warm surface water to vaporize fluids with a low boiling point (like ammonia). The vapor created spins a turbine attached to a generator to produce electricity. 

Ocean mechanical energy harnesses the ebbs and flows of tides, which are caused by the rotation of the earth and the gravitational influence of the moon. Ocean waves are converted to electricity when they move wave energy converter (WEC) devices, which are attached to generators that can covert this energy into electricity. Several other ocean-based technologies have also shown promise and are in development.

The United States, the UK, Russia, Australia, Sweden, Ireland, Scotland, and the Netherlands lead the world in utilization. However, they can cause coastal erosion, damage the ocean floor, harm marine mammals, create noise pollution, and alter the natural flow of sediment. Still, they are fascinating technologies that deserve more attention as they continue to get refined!

As the simplest and most abundant element in the universe, hydrogen is found in organic compounds and water. It's high in energy but produces comparatively little pollution when burned, and has been used to launch space shuttles since the 1950s. So how does hydrogen energy work?

In some cases, hydrogen fuel cells are used to convert the potential chemical energies of hydrogen and electricity into usable power. In other applications, the cells power the combination of hydrogen and oxygen atoms, generating electricity. Pretty cool, right?

However, hydrogen power by nature is unstable and widespread utilization will remain limited until production costs decrease and durability improves. It's also difficult to store due to the small size of the molecules — and pollutes the air with nitrous oxide when burned. For this reason, many see it as a stopgap measure to help reduce GHG emissions from heavy industries while we work to green up our power supply.

Geothermal energy comes from the earth’s core, and is tapped by drilling wells 1-2 miles deep into the earth to pump steam or hot water to the surface. Once there, the pressure is dropped, causing the water to become steam that then spins a turbine, powers a generator, and produces electricity.

The United States, the Philippines, Indonesia, Mexico, Turkey, and Italy are the top geothermal power producers in the world. But as you may have guessed, drilling holes deep into the earth’s surface is environmentally problematic — with effects like land degradation, possible depletion of local geothermal resources, and the release of greenhouse gases like hydrogen sulfide, carbon dioxide, methane, and ammonia.

Proponents argue that the GHGs released are significantly lower than that of fossil fuels, but it does beg the question — is it really a renewable energy source?

As the most widely-used renewable energy source (18% of the world’s total installed power generation + 54% of the global renewable power generation capacity), we would be remiss not to mention hydropower. The most common method used to harness the power of freshwater is damming up rivers to create massive reservoirs. Then the reservoir water is released, which drives power-generating turbines. China, Brazil, the United States, Canada, and Russia have the biggest hydroelectricity installations in the world.

Of course, this form of hydropower comes at a cost – massive hydroelectric dams damage the environment, disturb aquatic wildlife, and displace nearby populations. Still, humans have been harnessing water for centuries + there are many promising new technologies out there, so we’re hopeful that someday, hydropower will be less damaging to the environment!