Ocean Tidal Power

The following information about ocean tidal power was found at the Department of Energy's Energy Efficiency and Renewable Energy website as part of their Consumer's Guide to Energy Efficiency and Renewable Energy. 

Some of the oldest ocean energy technologies use tidal power. All coastal areas consistently experience two high and two low tides over a period of slightly greater than 24 hours. For those tidal differences to be harnessed into electricity, the difference between high and low tides must be at least five meters, or more than 16 feet. There are only about 40 sites on the Earth with tidal ranges of this magnitude.

Currently, there are no tidal power plants in the United States. However, conditions are good for tidal power generation in both the Pacific Northwest and the Atlantic Northeast regions of the country.

Technologies

Tidal power technologies include the following:

• Barrage or dam

  A barrage or dam is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. Gates and turbines are installed along the dam. When the tides produce an adequate difference in the level of the water on opposite sides of the dam, the gates are opened. The water then flows through the turbines. The turbines turn an electric generator to produce electricity.
   

• Tidal fence

  Tidal fences look like giant turnstiles. They can reach across channels between small islands or across straits between the mainland and an island. The turnstiles spin via tidal currents typical of coastal waters. Some of these currents run at 5–8 knots (5.6–9 miles per hour) and generate as much energy as winds of much higher velocity. Because seawater has a much higher density than air, ocean currents carry significantly more energy than air currents (wind).
   

• Tidal turbine

  Tidal turbines look like wind turbines. They are arrayed underwater in rows, as in some wind farms. The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph). In currents of that speed, a 15-meter (49.2-feet) diameter tidal turbine can generate as much energy as a 60-meter (197-feet) diameter wind turbine. Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).

Environmental and Economic Challenges

Tidal power plants that dam estuaries can impede sea life migration, and silt build-ups behind such facilities can impact local ecosystems. Tidal fences may also disturb sea life migration. Newly developed tidal turbines may prove ultimately to be the least environmentally damaging of the tidal power technologies because they don't block migratory paths.

It doesn't cost much to operate tidal power plants, but their construction costs are high and lengthen payback periods. As a result, the cost per kilowatt-hour of tidal power is not competitive with conventional fossil fuel power.

Photovoltaic

Small Solar Electric Systems

A small solar electric or photovoltaic (PV) system can be a reliable and pollution-free producer of electricity for your home or office. And they're becoming more affordable all the time. Small PV systems also provide a cost-effective power supply in locations where it is expensive or impossible to send electricity through conventional power lines.

Because PV technologies use both direct and scattered sunlight to create electricity, the solar resource across the United States is ample for small solar electric systems. However, the amount of power generated by a solar system at a particular site depends on how much of the sun's energy reaches it. Thus, PV systems, like all solar technologies, function most efficiently in the southwestern United States, which receives the greatest amount of solar energy.

You can also use PV technology to provide outdoor lighting.

The information above on small solar electric systems was found at the Department of Energy's Energy Efficiency and Renewable Energy website as part of their Consumer's Guide to Energy Efficiency and Renewable Energy. 

Pros

Renewable with no CO₂ emissions

Converts diffused and direct sunlight into electricity

 Cons

Very expensive (but prices are slowing dropping)

Requires a large surface area

Biomass

Biomass electrical generation or biopower is second only to hydropower as a renewable energy source.

Most electricity generated using biomass today is by direct combustion using conventional boilers. These boilers burn primarily waste wood products generated by the agriculture and wood-processing industries. When burned, the wood waste produces steam, which is used to spin a turbine. The spinning turbine activates a generator that produces electricity. Many coal-fired power plants also add biomass to their coal-burning process (i.e., co-firing) to reduce the emissions produced by burning the coal.

Biomass can also be gasified prior to combustion. Gases generally burn cleaner and more efficiently than solids, which allows removal of toxic materials. Gasification also makes it possible to use biomass in combined-cycle gas turbines, such as used in the latest natural gas power plants. Using gasification, these natural gas power plants can achieve much higher efficiencies. Small modular biomass gasification systems are well suited for providing isolated communities with electricity.

In addition, the decay of biomass in landfills produces gas (primarily methane) naturally, which can be harvested and burned in a boiler to produce steam for generating electricity.

Where It's Available

Producing electricity from biomass is most cost effective if biomass power or biopower plants are located near biomass feedstocks. Biomass resources are abundant across the eastern half of the United States, and thus, the majority of operating biomass power plants are located there. The future use of dedicated feedstock crops can broaden the resource availability to all regions with agricultural production activity.

The information above on biomass energy was found at the Department of Energy's Energy Efficiency and Renewable Energy website as part of their Consumer's Guide to Energy Efficiency and Renewable Energy. 

Pros

Proven technology
Plentiful sources
Renewable
Not as dependent on fossil fuels

Cons

Burning biomass creates pollution (CO₂ emissions)
Gathering, moving and storing biomass is expensive and uses fossil fuels.

Coal

Pros

Very efficient
Inexpensive

Cons

Large contributor to greenhouse gases
Causes acid rain
Frees radioactive materials (more so that nuclear power plants)
Destroys environment (land, water and air)