Renewable energy technologies: Making the pathway to energy sector

Although traditional uses of wind, solar, and water power are widespread throughout the world, the mass production of electricity using renewable energy sources has only become more commonplace in recent years

At the beginning of the 21st century, the electric power generation industry worldwide is faced with an urgent need for developing new alternative energy resources to offset global warming, pollution problems associated with fossil fuels, and the increasing vulnerability of dependence on external energy sources. Equally important is the reduction of energy consumption to reasonable levels through continuing research; and by implementing more effective alternative energy resources, including: hydroelectric and nuclear energy, wave and tidal power; as well as non-conventional sustainable energy resources—wind power, solar power, biomass, and geothermal energy.

Although traditional uses of wind, solar, and water power are widespread throughout the world, the mass production of electricity using renewable energy sources has only become more commonplace in recent years—reflecting the major threats of climate change due to pollution, depletion of fossil fuel reserves, and the environmental, social, and political risks of fossil fuels, hydroelectric power, and nuclear energy. Except for nuclear fuels, tidal energy, and geothermal energy, all other terrestrial sources are solar. And, ultimately, both solar power itself and geothermal energy are nuclear in origin.

All renewable energy technologies, however, are not appropriate to all applications or locations. And, as with conventional energy production, there are environmental issues to be considered. But increased use of domestic alternative energy resources would also reduce the need to transport petroleum, thereby reducing chances of oil spill.

This article covers only wind power, solar power, geothermal energy, biomass, and hydrogen fuel—renewable energy technologies not requiring heavy construction work to bring a system on line. (Hydroelectric and nuclear energy; wave power, and tidal power require separate consideration as they do require heavy construction work to install such facilities.)

In the future, the nation’s economy will require adding a balance of alternative energy technologies to meet growing electricity demands and stringent emission regulations. But, before adding alternative energy technology to an existing power generation systems will require thorough evaluation of all the benefits and disadvantages of the available technologies - not just their economic and environmental benefits.

Wind power
One of the most cost-competitive renewables today is wind power technology, having a long-term technical potential that researchers believe to be five times current global consumption—or 40 times current electricity demand. Researchers estimate achieving this potential would require about 13 percent of all land area—or that land area with Class 3 or greater potential, at a height of 80 meters. They assume this on the basis of installing six large wind turbines per square kilometer on land. Offshore wind power resources could increase the estimated potential because the mean wind speeds over water can be about 90 percent greater than on land. And, higher altitude ground-based or airborne turbines could also increase the potential.Today’s turbine technology, wind power is estimated could supply two percent of the country’s electricity. And, according to recent studies, developing wind power on a large scale holds the promise of the most useful and efficient alternative energy source—mitigating the greenhouse effect and global warming.

A variety of constraints, however, limit wind’s potential to deliver electricity, including:

• Environmentally sensitive lands that are excluded from development of any kind,
• Higher development costs on forested land or mountainous terrain, making economic wind generation less feasible,
• Some windy land within urban areas and other areas is already given over to other types of development.

Solar power
Several methods of converting solar energy into electricity include use of solar cells to convert sunlight directly, sunlight hitting solar thermal panels to heat water or air, sunlight hitting a parabolic mirror to heat water (producing steam), or sunlight entering windows for passive solar heating of a building. Today’s commercial solar cells convert about 20 percent of the energy incident sunlight to electrical energy. If outfitted with solar collectors, one percent of the land currently used for crops and pasture could supply the world’s total energy consumption. Solar thermal collectors can capture 70 percent to 80 percent of insolation as usable heat.  In addition passive solar and solar chimneys can heat and cool residences and other buildings. The electricity yield per unit area of a solar collector is 50 times to 100 times that of an average hydro scheme—even though hydropower today uses a similar area.

Other on-going studies include: solar updraft towers and algae farms that researchers estimate could convert 10 percent of incident light into biodiesel energy. Although early applications for photovolatics and solar thermal electric have focused on decentralized, typically remote locations and grid-tied systems, utilities continue to monitor development of the systems for possible larger power generation application.

Biomass energy
Generating electricity from biomass includes decomposition of garbage or other vegetation resources, producing methane that is captured in pipes and later burned to produce electricity, or burning vegetation and wood directly—like fossil fuels, or processed to form alcohols for burning. Advanced anaerobic digester systems offer the ability to produce medium sized power generation (2 MW to 10 MW facilities), provide flexibility and recovery of valuable biodegradable waste while producing power from a renewable energy source.

Current biomass resources include:

• Non-commercial timber (wood and bark residue from logging operations, rotten trees, and salvageable dead trees)—Volume may amount to 40 percent or more of the forest inventory.
• Wood-processing wastes (lumber, plywood, veneer, and paper mills)—Suitable for fuel in the form of sawdust, bark, slabs, sander dust, planer shavings, turnings, and cutoffs
• Agriculture wastes—Massive amounts left over from harvesting that must be disposed of.
• Urban wood wastes (such as wooden pallets) Diversion to biomass-fired power plants.
• Prepared wood fuels Commercial biomass fuels in briquette and pellet forms.

While biomass energy is a well-proven technology, with hundreds of biomass-fired steam and electricity generation stations currently operating in the country, their economics often pose a challenge.

Geothermal energy
Geothermal power has a very large potential, considering all the heat existing inside Earth, even though heat flow from the interior to the surface is only 1/20,000 as great as the energy received from the sun or about two to three times that from tidal power. Although not dependent upon the sun, geothermal power is limited, however, to special locations.

Various geothermal systems include hydrothermal resources, deep-crust heat, hot water reservoirs, and dry-steam reservoirs. At least three factors must be present for geothermal resources to be currently commercial for power production: Heat, conducted laterally or from below; an intercontinental fracture network shallow enough to be economically drilled; and steam water filling the fractured network to heat raise the water’s temperature—and in a few geothermal reservoirs produce dry steam.

Development and operation of a geothermal energy power plant have a positive impact on the environment compared with the development of fossil-fuel energy sources. Modern geothermal power plants operating on hydrothermal resources have extremely low levels of SOx, CO2 , particulate emissions, and reduced greenhouse gases—sulfur emission rates averaging only a few percent of those from fossil-fuel power plants, and no nitrogen (NOx) emission.

The newest generation of geothermal power plants emit only 0.3 lb of carbon per megawatt hour of electricity generated, compared to:

• 282 lb/MWh of carbon for natural gas
• 418 lb/MWh of carbon for No.6 fuel oil
• 497 lb/MWh of carbon for bituminous coal.

Other environmental advantages of geothermal energy include: Requires only a fraction of the land that other energy sources would occupy and can co-exist with other land uses, with little interference or feat of accidents.

Future energy development
Extrapolations from current knowledge to future energy development offer a choice of energy features. Numerous are complex models based scenarios offering ways to analyze diverse strategies, with the hope of finding a road to rapid and sustainable development of humanity. Short term crises are also a concern of energy development.