rudolphsteiner (< 20)

which renewable energy technologies will power the future? part 1

June 17, 2008 – Comments (14)

Wind

Although wind power only accounts for about 1% of global electricity production, it is one of the fastest growing energy sectors. Installed capacity of wind generation grew by about 25% globally in 2006, to 74 GW. Between 1997 and 2006 wind energy increase by a factor of 10. Wind energy has a huge potential for electricity generation. For instance, the power of the wind, if harnessed, could supply all of the United States electricity needs. However, because wind is not an entirely dependable resource, using existing infrastructure wind power is expected to supply no more than 20% of electricity needs in any given region. If, in the future, wind power were stored in the form of hydrogen, pumped water, compressed air, or other means, it could have a much greater share of energy production.

More information: World Wind Energy Association

Solar

Arguably, all energy used on earth, except nuclear, tidal, and geothermal, comes from the power of the sun. The fossil fuels that drive our economy are the result of millions of years of solar energy stored in transformed plant materials. Even fossil fuels are renewable, but the energy we are consuming in a matter of centuries will take millions of years to renew. However, there are options to begin harvesting the power of the sun more directly to meet our energy needs. It is hard to quantify, but solar energy provides roughly 10% of the energy used worldwide, most of which is in the form of solar heating.

Solar Electricity

Currently, solar electricity generation accounts for less than 0.01% of total Global primary energy production, but like wind it is growing very rapidly. Generation of electricity from the sun can be accomplished either by concentrating solar heat and using steam to generate electricity, or using solar photo-voltaic panels, the majority of the growth is in the latter technology. Worldwide photovoltaic capacity increased by 1,460 MW in 2005 (from 1,086 MW installed in 2004) - in 1985, annual solar installation demand was only 21 Megawatts.

Solar photo-voltaic panels are undergoing a technology revolution, with many emerging companies and technologies competing for market share. Historically, most solar cells have been designed around crystalline silicon (c-Si) semiconductors to collect light and convert it to electricity. However, crystalline silicon needs a considerable thickness (several hundred microns) of material in order to work, and is relatively expensive to produce. To overcome this problem solar technologies are moving in two new directions. The first is the addition of solar "concentrators" that focus light onto the silicon material, increasing the efficiency of the conversion to electricity. The second direction of research is "thin-film" solar cells, which use far less materials, and are most commonly based on either amorphous silicon (a-Si, silicon in a different form), or the polycrystalline materials: cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS). Thin-film solar cells are now being commercially produced, and the production capacity coming largely from startup companies is expected to grow significantly over the next few years.

More information: Solar Buzz

Solar Thermal

Solar thermal energy is another hot item in the energy toolkit. The power of the sun has been used to heat buildings since the first crude shelters were erected, however with modern efficient windows solar space-heating has started to become a very practical option. This type of heating, termed "passive solar," largely depends on placement of windows to maximize heat gain in winter and minimize it in summer. Passive solar design can greatly reduce the need for heating, but generally cannot replace it. Solar hot water heating is an extremely practical way to use the sun's energy. Solar hot water heaters have a very significant presence in China, which accounts for 70-80% of the solar hot water heating market, and also in Germany, Greece, and Austria. On average, the solar thermal market grew 14% per year between 1990 and 2001. Installing a solar hot water heater is something any homeowner can do with a relatively low investment and reasonable pay-back time.

Hydro-Electric Power

Hydropower provides about one fifth of the world’s electricity supply (about 700 GW), but the potential for new expansion is limited. Also, while hydropower is a completely renewable energy source, large hydro projects have been shown to have significant greenhouse gas emissions for many decades after construction due to methane emissions from flooded areas. Small hydro projects, especially "run of the river" hydro-electric generation (without reservoirs), offer the greatest potential for new climate-friendly capacity. New hydro potential, including hydro "mega-projects" is estimated at 1 400 GW of capacity, roughly twice the present installed capacity. The development of all of this potential would undoubtedly have large social and environmental consequences, including greenhouse gas emissions from reservoirs.

Ocean Power Tidal Power

Tide mills are actually a very old form of power, that was used along the coasts of western Europe in the Middle Ages, and was only abandoned with the initiation of the fossil fuel era. In modern times, a tidal dam was built across the Rance estuary in Brittany, France, in the 1960’s. This project has an installed capacity of 240 MW, and has operated successfully for over thirty years. The cost of tidal generation is higher than traditional hydro-electric and can have impacts on marine estuarine environments. Deep marine currents, which are largely driven by tidal movements, offer a very stable energy source with low environmental impacts, but the technology has been very little studied. This type of generation is most comparable to wind, but has the advantages of predictability and high power-output per size of turbine. The future of tidal power is uncertain, but likely to grow.

Wave Power

Wave energy has only been harnessed in a scattering of pilot projects around the world, without any major commercial application to date. However, that will likely change over the next few years, with projects potentially coming on-line in Portugal, The United States, South Africa, and elsewhere. Wave power is most commonly harnessed several km out from shore, where the waves are most consistent. Often some form of buoy is used, which generates electricity as it bobs up and down, however a long snake-like structure has also been created by one company that generates power as the wave moves along it.

More information: World Energy Council

Biofuels

Biofuels are an extremely fast-growing, but also very controversial form of alternative energy. Two key questions remain unclear regarding the use of biofuels: do biofuels provide more energy than it takes to grow, harvest and transform them? And, is there enough land available for biofuels to grow any meaningful quantity? The answers to these two questions are linked.

Current biofuel crops and processes are extremely inefficient. For instance, the U.S. department of energy concludes that "the 'net energy balance' of making fuel ethanol from corn grain is 1.34; that is, for every unit of energy that goes into growing corn and turning it into ethanol, we get back about one-third more energy as automotive fuel." However, other studies, including a 2005 study from a Cornell University researcher, conclude that it actually takes more fossil fuel energy to create ethanol than you actually get back in the resulting fuel. In short, according to these studies, using a litre of ethanol actually contributes more to global warming than just using a litre of gasoline. Biodiesel has similar controversy, although the energy returns are somewhat better. Also, According to the USDA, amount of the total corn crop consumed to make ethanol will rise from 12 percent in 2004/05 to 23 percent in 2014/15. This will likely drive up the price of corn used for food, and even while using almost a quarter of the U.S. corn crop, ethanol will make up a fairly small proportion of the fuel used in the United States. The food to fuel problem is the strongest argument against the current generation of biofuels. Globally we have been using more food than we are growing most of the last decade, and literally eating away at grain inventories, which are now at historically low levels. The implications for human misery are significant. A report from PotashCorp on this trend in agriculture reads as follows:

"Grain consumption has outpaced production in seven of the last eight years, the only exception being a single year of excellent growing conditions in almost every major global agricultural region. With the growing demand for food and now a surge in the production of biofuels, the annual increase in grain consumption has grown from its historical rate of 1.2 percent to 2.0 percent. That has led to a widening gap between consumption and production – one that would become even more pronounced if production failures or other supply disruptions occur."

Biofuels only have a meaningful future if the means of production are shifted away from agricultural crops. For ethanol this means using cellulose materials such as straw or wood and breaking them down into sugars using enzymes. The efficiency of "cellulosic" ethanol will likely be significantly better than corn or wheat-based ethanol. For biodiesel, or vegetable oil production, the future may lie in growing the oil in algae ponds, where the theoretical rate of oil production can be up to 100 times as great per hectare, and will likely have much lower fossil fuel inputs.

Hydrogen

Hydrogen is not an energy source, it is an energy carrier, and potentially a means of storing energy. Currently, most of the world's hydrogen is produced from natural gas by a process called steam reforming. Using this process, Carbon Dioxide is still released leading to climate change, and non-renewable resources are still consumed. There is another way to make hydrogen, however, which is the use of electricity to break water down into hydrogen and oxygen. If this is done using renewable energy sources, the 'hydrogen economy' is born. Hydrogen can be used to very efficiently generate electricity in fuel cells. Fuel cells are based on the chemical reaction in which hydrogen and oxygen combine to make water, but instead of letting the reaction happen explosively, it happens in a controlled process that generates large amounts of electricity and relatively little heat. Because it can be stored and transported without losses, hydrogen may be an important intermediary in going from our fossil-fuel economy to one based on renewable energy, and because it is a high-energy fuel it may be particularly important in tranport, although batteries may instead fill this role.

More information: The Hydrogen Economy

Geothermal

Geothermal energy is the energy of the core of the earth. This energy is replenished by the slow decomposition of nuclear isotopes in underground rocks. The core of the earth is at about 4,000 degrees Celcius, and hot springs near the Earth's surface can reach 350 degrees Celcius. This energy can be used to heat homes or generate electricity in areas of geological activity where it is most readily available. Today, 22 nations are generating geothermal electricity, in amounts sufficient to supply 15 million houses. Geothermal energy is also used as a direct heating source in areas where it is available. Most modern geothermal electricity plants use a binary technology, where a heat exchanger transfers the heat from subsurface water to a liquid with a lower boiling point than water, which is then used to generate electricity. This has the advantages of no emissions to the atmosphere and low consumption of water, and allows power generation from lower temperature reservoirs. A huge advantage of geothermal electricity is that it can provide baseload power, which sets it apart from almost all other renewable technologies (the most notable exception being hydroelectricity)

A second, unrelated type of geothermal heating system uses the relatively small amounts of heat in the ground in non-geologically active areas to generate heat in a system quite similar to a refrigerator. These heat pump systems, while relatively efficient, are costly to install and still require significant amounts of electricity to run.

This is from my website - comments and criticisms welcome!