Hydropower
Hydropower (hydroelectric) relies on water to spin turbines and create electricity. It is considered a clean and renewable energy source because it does not directly produce pollutants and because the power source is regenerated. Hydropower provides 35% of the United States renewable energy consumption.
Hydropower dams and the reservoirs they create can have environmental impacts. For example, the migration of fish to their upstream spawning areas can be obstructed by dams. In areas where salmon must travel upstream to spawn, such as along the Columbia River in Washington and Oregon, the dams block their way. This problem can be partially alleviated by using “fish ladders” that help salmon get around the dams. Fish traveling downstream, however, can get killed or injured as water moves through turbines in the dam. Reservoirs and the operation of dams can also affect aquatic habitats due to changes in water temperatures, water depth, chemistry, flow characteristics, and sediment loads, all of which can lead to significant changes in the ecology and physical characteristics of the river both upstream and downstream. As reservoirs fill with water, it may cause natural areas, farms, cities, and archeological sites to be inundated and force populations to relocate.
Small hydropower systems
Large-scale dam hydropower projects are often criticized for impacting wildlife habitat, fish migration, water flow, and quality. However, small run-of-the-river projects are free from many of the environmental problems associated with their large-scale relatives because they use the natural flow of the river and thus produce relatively little change in the stream channel and flow. The dams built for some run-of-the-river projects are very small and impound little water, and many projects do not require a dam at all. Thus, effects such as oxygen depletion, increased temperature, decreased flow, and impeded upstream migration are not problems for many run-of-the-river projects.
Small hydropower projects offer emissions-free power solutions for many remote communities worldwide, such as those in Nepal, India, China, and Peru, as well as for highly industrialized countries like the United States. Small hydropower systems generate between .01 to 30 MW of electricity. Hydropower systems that generate up to 100 kilowatts (kW) of electricity are often called micro hydropower systems (Figure 2). Most of the systems used by home and small business owners would qualify as micro hydropower systems. A 10 kW system generally can provide enough power for a large home, a small resort, or a hobby farm.
Municipal Solid Waste
Municipal solid waste (MSW) is commonly known as garbage and can create electricity by burning it directly or by burning the methane produced as it decays. Waste-to-energy processes are gaining renewed interest as they can solve two problems at once: waste disposal and energy production from a renewable resource. Many environmental impacts are similar