Efficiency can decrease slightly over time, one of the main reasons being dust and insect carcasses on the blades which alters the aerodynamic profile and essentially reduces the lift to drag ratio of the airfoil. Analysis of 3128 wind turbines older than 10 years in Denmark showed that half of the turbines had no decrease, while the other half saw a production decrease of 1.2% per year.[19] Ice accretion on turbine blades has also been found to greatly reduce the efficiency of wind turbines, which is a common challenge in cold climates where in-cloud icing and freezing rain events occur.[20] Vertical turbine designs have much lower efficiency than standard horizontal designs.[21]
I ask Gore about the lessons he takes from Georgetown. “I think it’s important to pay attention to a CPA who becomes a mayor and takes an objective look at how he can save money for the citizens of his community, even if it means ignoring ideological presuppositions about fossil energy. Especially when the mayor in question is in the heart of oil and gas country.”
Low Temperature Geothermal[29] refers to the use of the outer crust of the earth as a Thermal Battery to facilitate Renewable thermal energy for heating and cooling buildings, and other refrigeration and industrial uses. In this form of Geothermal, a Geothermal Heat Pump and Ground-coupled heat exchanger are used together to move heat energy into the earth (for cooling) and out of the earth (for heating) on a varying seasonal basis. Low temperature Geothermal (generally referred to as "GHP") is an increasingly important renewable technology because it both reduces total annual energy loads associated with heating and cooling, and it also flattens the electric demand curve eliminating the extreme summer and winter peak electric supply requirements. Thus Low Temperature Geothermal/GHP is becoming an increasing national priority with multiple tax credit support[60] and focus as part of the ongoing movement toward Net Zero Energy.[61][30] New York City has even just passed a law[62] to require GHP anytime is shown to be economical with 20 year financing including the Socialized Cost of Carbon.[63][64]
In the United States, one of the main problems with purchasing green energy through the electrical grid is the current centralized infrastructure that supplies the consumer’s electricity. This infrastructure has led to increasingly frequent brown outs and black outs, high CO2 emissions, higher energy costs, and power quality issues.[89] An additional $450 billion will be invested to expand this fledgling system over the next 20 years to meet increasing demand.[90] In addition, this centralized system is now being further overtaxed with the incorporation of renewable energies such as wind, solar, and geothermal energies. Renewable resources, due to the amount of space they require, are often located in remote areas where there is a lower energy demand. The current infrastructure would make transporting this energy to high demand areas, such as urban centers, highly inefficient and in some cases impossible. In addition, despite the amount of renewable energy produced or the economic viability of such technologies only about 20 percent will be able to be incorporated into the grid. To have a more sustainable energy profile, the United States must move towards implementing changes to the electrical grid that will accommodate a mixed-fuel economy.[91]
From 1978 to 1996, the National Renewable Energy Laboratory experimented with producing algae fuel in the "Aquatic Species Program."[112] A self-published article by Michael Briggs, at the University of New Hampshire Biofuels Group, offers estimates for the realistic replacement of all motor vehicle fuel with biofuels by utilizing algae that have a natural oil content greater than 50%, which Briggs suggests can be grown on algae ponds at wastewater treatment plants.[113] This oil-rich algae can then be extracted from the system and processed into biofuels, with the dried remainder further reprocessed to create ethanol. The production of algae to harvest oil for biofuels has not yet been undertaken on a commercial scale, but feasibility studies have been conducted to arrive at the above yield estimate. During the biofuel production process algae actually consumes the carbon dioxide in the air and turns it into oxygen through photosynthesis.[114] In addition to its projected high yield, algaculture— unlike food crop-based biofuels — does not entail a decrease in food production, since it requires neither farmland nor fresh water. Many companies are pursuing algae bio-reactors for various purposes, including scaling up biofuels production to commercial levels.[115][116]
However, it has been found that high emissions are associated only with shallow reservoirs in warm (tropical) locales, and recent innovations in hydropower turbine technology are enabling efficient development of low-impact run-of-the-river hydroelectricity projects.[17] Generally speaking, hydroelectric plants produce much lower life-cycle emissions than other types of generation. Hydroelectric power, which underwent extensive development during growth of electrification in the 19th and 20th centuries, is experiencing resurgence of development in the 21st century. The areas of greatest hydroelectric growth are the booming economies of Asia. China is the development leader; however, other Asian nations are installing hydropower at a rapid pace. This growth is driven by much increased energy costs—especially for imported energy—and widespread desires for more domestically produced, clean, renewable, and economical generation.
When a turbine is mounted on a rooftop the building generally redirects wind over the roof and this can double the wind speed at the turbine. If the height of a rooftop mounted turbine tower is approximately 50% of the building height it is near the optimum for maximum wind energy and minimum wind turbulence. While wind speeds within the built environment are generally much lower than at exposed rural sites,[29][30] noise may be a concern and an existing structure may not adequately resist the additional stress.
What? You are still reading? If we did not talk you out of a wind turbine by now there may still be hope! There certainly are situations where a small wind turbine makes perfect sense: If you are off-grid you should definitely consider adding a wind turbine. Wind and solar tend to complement each other beautifully; the sunny days tend to be not very windy, while the windy days tend to have little sun. Wind turbines generally produce most energy in the winter, when solar panels fall short.
“California Invests in ‘By Location’ Distributed Energy Resources” • California leads the US with several pilot projects to reward rooftop solar energy generators and other distributed energy resources in specific locations as an alternative to having utilities meet needs by investing in upgrading their electricity generation networks. [CleanTechnica]
Small-scale turbines are expensive (one manufacturer says a typical system costs $40,000 to $60,000 to install), though some of that outlay can be offset by federal and local tax credits. Experts recommend that you buy one certified by the Small Wind Certification Council. Turbine manufacturers include Bergey Wind Power, Britwind and Xzeres Wind; look on their websites for local dealers.
According to the International Energy Agency, new bioenergy (biofuel) technologies being developed today, notably cellulosic ethanol biorefineries, could allow biofuels to play a much bigger role in the future than previously thought.[41] Cellulosic ethanol can be made from plant matter composed primarily of inedible cellulose fibers that form the stems and branches of most plants. Crop residues (such as corn stalks, wheat straw and rice straw), wood waste and municipal solid waste are potential sources of cellulosic biomass. Dedicated energy crops, such as switchgrass, are also promising cellulose sources that can be sustainably produced in many regions of the United States.[42]
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Many residential PV systems are connected to the grid wherever available, especially in developed countries with large markets.[10] In these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are often added as back-ups. Such stand-alone power systems permit operations at night and at other times of limited sunlight.