SOLAR

Solar energy is the cleanest and most abundant renewable energy source available, and the U.S. has some of the richest solar resources in the world. Modern technology can harness this energy for a variety of uses, including generating electricity, providing light or a comfortable interior environment, and heating water for domestic, commercial, or industrial use.

The U.S. solar market faces both challenges and opportunities; the industry is working to scale up the production of solar technology, and drive down manufacturing and installation costs.


WIND

Most wind energy comes from turbines that can be as tall as a 20-story building and have three 200-foot (60-meter)-long blades. The wind spins the blades, which turn a shaft connected to a generator that produces electricity.

The biggest wind turbines generate enough electricity in a year (about 12 megawatt-hours) to supply about 600 U.S. homes. Wind farms have tens and sometimes hundreds of these turbines lined up together in particularly windy spots. Smaller turbines erected in a backyard can produce enough electricity for a single home or small business.


HYDRO

Harnessing the power of water is the cheapest form of energy, but environmental and other concerns cast doubts on its worth.

A typical hydro plant is a system with three parts: an electric plant where the electricity is produced, a dam that can be opened or closed to control water flow, and a reservoir where water can be stored. The water behind the dam flows through an intake and pushes against blades in a turbine, causing them to turn. The turbine spins a generator to produce electricity. The amount of electricity that can be generated depends on how far the water drops and how much water moves through the system. The electricity can be transported through long-distance electric lines to homes, factories, and businesses.

But damming rivers may destroy or disrupt wildlife and other natural resources. Some fish, like salmon, may be prevented from swimming upstream to spawn. Technologies like fish ladders help salmon go up over dams and enter upstream spawning areas, but the presence of hydroelectric dams changes their migration patterns and hurts fish populations. Hydropower plants can also cause low dissolved oxygen levels in the water, which is harmful to river habitats.

Some researchers believe the strain dams impose on the environment make this method of energy production more trouble than it's worth. A study in the journal BioSciences found that the reservoirs created by dams pollute methane, a greenhouse gas, into the atmosphere as a result of the breakdown of organisms in now stagnant pools of water.

In addition to environmental concerns, dams also pose a strain on the communities around them. The Three Gorges dam on China's Yangtze River displaced an estimated 1.3 million people and flooded thousands of villages.