Renewable Energy Sources Today: A Review The emergence of modern-day developed economies depended heavily on the availability of cheap and abundant energy, but the planet's oil reserves, which supplies over 35% of the world's energy needs, are projected to be depleted within a hundred years (Balat 19). As this resource is depleted, demand will increase and drive prices to unheard of levels, thereby threatening the stability of economies in some of the most powerful nations the world. To avoid a catastrophic meltdown of what is now a global economic engine; governments worldwide have begun to invest in developing and promoting the use of renewable forms of energy. Although reducing fossil fuel use to lower green house gas emissions is a more laudable goal, it seems likely that economic incentives will be the primary driving force behind renewable energy development and implementation. This article reviews the various types of renewable energy in use today that will likely help reduce our dependence on fossil fuels.

Solar Energy

Sources of solar energy can be divided into direct or indirect. Direct solar energy converts photons produced by the sun directly into either electricity or heat. The primary indirect forms of solar energy (energy carriers) are created by the power of the sun and include biomass, wind, ocean currents, and hydropower.

Direct Solar Energy

Passive Solar Heating

Passive solar heating captures the energy contained in direct sunlight to heat water, cook food, dry clothing or agricultural products, heat the interiors of buildings, provide air-conditioning, power desalination and water purification projects, and generate electricity. Given that building structures consume 35.3% of energy worldwide (Chan, Riffat, and Zhu 781), the development and use of passive solar technology will become critical to relieving our dependence on fossil fuels.

Photovoltaic Cells

Photovoltaic cells are able to directly convert solar photons into electricity, because the photons are have enough energy to free electrons on one side of a light-absorbing material, thereby creating...

A single cell doesn't produce a significant amount of power, but when linked together in arrays they produce enough to energy to support the needs of whole households and neighborhoods. The primary limitation is the cost, which is typically more than five times higher than hydropower, geothermal, or wind (Balat 20). Concerns about cost, reliability, and performance explains why photovoltaic cells produced only 1.8 GWh (Balat 25) of the 3,157,000 GWh of all electricity produced by renewable energy sources in 2004 (Balat 19). In spite of the high cost, the annual growth rate in photovoltaic use between 2000 and 2004 was an unprecedented 60% (Balat 25).
Solar Energy Carriers

Hydropower

Solar energy drives weather patterns, which in turn carries precipitation to higher elevations. Solar energy is thereby stored in the form of mountain snow packs and watersheds, which can be harvested by hydroelectric power plants positioned on a river or at the base of a reservoir. Because of the low cost and reliability of hydropower, close to 89% of all electricity produced by renewable energy sources comes from hydroelectric power plants (Balat 21). The annual growth of hydroelectric power is low compared to wind and photovoltaic cells, averaging between 1-2% annually. Market saturation in developed countries, environmental concerns, and population displacement contribute to the slow growth of hydroelectric plants worldwide.

Wind Power

Wind turbines are second only to hydropower in terms of cost and reliability and represent one of the fastest growing renewable energy sectors. In 2004 alone, over 6000 wind turbines, with an average capacity of 1.25 MW, were put into use worldwide (Balat 23). On a global scale though, wind turbines contribute only 0.5% of all electricity consumed (Balat 21). Given the annual growth rate in wind turbine capacity, which was close to 29% between 1994 and 2004, the contribution from wind energy should…