What solar power proponents need to do:
- Demonstrate that solar power can be a baseload provider. How: Recruit a city of 50,000-60,000 to be powered by solar power (and maybe wind) with no fossil fuels or nuclear power as backup.
- Construct a modeling study from now until 2050 where:
- No new nuclear has been constructed and fossil fuel energy generation has
been reduced to at least 0-5% of 2011 levels (assuming some potential for
application of CCS).
- Slow, but rational rates of growth for biomass and geothermal (0.5-1.5% per year).
- Assume three principle scenarios of future global energy use: down 10%, up 10% and up 33% (despite the publicity about the gains that could be made by improving efficiency it is reasonable to anticipate more global energy use in the future due to continued economic development in Brazil, parts of
Africa, India and China).
- Wind power can represent anywhere from 3% to 15% of global energy generation with an average real-world generation capacity of 25%.
- Model energy demand over four distinct periods: early morning, early
afternoon, late afternoon/evening and late night and how available energy
generation technologies would meet this demand;
- Create a specific plan for the construction of solar power infrastructure asking exactly where, how much, at what cost, etc. This information must be very detailed, ‘this area here from latitude coordinates x and y and longitude coordinates a and b will house x number of mirrors, PV or whatever generating an average of x between hour x and hour y’ instead of ‘built a lot in the Mojave Desert over some arbitrary x by x area’.
- Calculate how much raw materials, including rare earths, will be needed to construct all of infrastructure for solar power including material extract rates relative to construction rates. In addition determine where these materials will come from and what production rates will be required to ensure stable and clean acquisition streams;
- Identify the best storage system apart from pumped hydro, which will normally not have applicable association with high quality solar locations (not a lot of pumped hydro availability in deserts). Calculate storage scale requirement and associated economical costs for this storage medium for required backup amount (still uncalculated due to lack of real-world large scale solar applications).
What wind power proponents need to do:
- Demonstrate that wind power can actually significantly contribute to the energy profile of a future energy infrastructure. Currently most wind power, even in countries with very high wind power penetration like Denmark and Germany, is heavily supported by the existing fossil fuel baseload. Due to this support most anti-wind individuals argue that for all of the wind power that has been installed, very little actual absolute carbon emission reduction has occurred in response. Wind power proponents need to produce a very specific report describing exactly how highly variable would operate without the fossil fuel baseload backbone to fill in the gaps.
- Create new energy generation models accounting for future wind speed predictions based on the anticipated change in global wind speeds due to the shrinking deltaT between Arctic and Temperate regions. There appears to be information that wind speed in most scenarios will decrease with larger standard deviations from the mean average due to the higher probability of tornadoes and hurricane formation. More Information
- Plan out the necessary elements balancing production between further wind power penetration and manufacture of electrical vehicles due to competition between rare earths and their potential shortages, especially yearly production shortfalls in neodymium and dysprosium. More Information
- Determine if constructing more conventional wind turbines is practical due to the increasing demands for conventional raw materials such as steel and concrete. The inherent low MW/single structure ratio of wind power will especially become difficult to manage in their production and transport if the issue of Peak Oil comes to pass. Therefore, is it even relevant to continue to produce convention wind turbines when other energy alternatives are available?
What geothermal power proponents need to do:
- Significantly increase the number of experimental EGS-Geothermal test pilot plants to determine future problems that may arise from EGS systems. The construction of these plants is also needed to generate further experience EGS system design to potentially lower economic costs.
- Demonstrate future drilling techniques that can be used to meet the increased depth demands of EGS systems over those depths used for oil or gas extraction, will be viable.
- Develop better heat pumps or other heating systems to optimize power generation from EGS systems as well as reduce potential seismic side-effect activity.
What biomass power proponents need to do:
Nothing, because there is no rational reason to pursue any further increase in biomass based energy. Economically viable biomass demands the use of land which will be in direct competition with food production and potential carbon sequestration through bio-char production. In such a competition biomass based energy finishes a distant third in importance. Non-economical biomass based energy can evade excess land use, but there is no reason to invest in expensive trace energy sources over other alternatives. Basically biomass-based energy fails because there are other energy generation alternatives available, but no legitimate food generation alternatives available with regards to required land use.
What tidal power proponents need to do:
Nothing, because there is no rational reason to pursue offshore hydro (tidal) power at all. Tidal power is not economical and will take a technological miracle for tidal power to produce large amounts of uninterrupted energy.
What nuclear power proponents need to do:
Three major reasons are used to justified opposition to nuclear power: cost, residual nuclear waste and its storage and pure personal morality. The first two reasons can be and should be addressed.
- Discuss the variance of cost between countries for construction nuclear power plants including the potential for global safety recommendations that will apply to all nuclear power plants around the world. These recommendations could also involve an independent inspection organization to ensure compliance.
- Develop a storage strategy for nuclear waste. Nuclear proponents cannot simply rely on the hope for the future development and commercialization of Type III and Type IV generation technology to address future nuclear waste accumulation as the possibility does exist that nuclear power will be needed, but these advanced nuclear technologies will not be readily available.
In addition to answering these issues the environmental community itself needs to be much more proactive in addressing the number of reports that come out from various institutions both in objective criticism and publicity. Currently there appears to be no ‘warehouse’ of sorts where individuals can go online to view any major report on a given energy medium regardless of what individual or organization produced it. One would think that if an organization like the newly merged 1sky/350.org actually cares about the environment organizing such an archive would be one of the first things they would do, but yet no easily accessible archive exists. Basically the environmental movement needs to create a ‘Cochrane Collaboration’ for energy putting all of its personal bias aside and look for the best solution.
Overall the important goal that solar, wind and geothermal proponents need to accomplish is demonstrate that at least one of these technologies can provide baseload electricity in a future energy infrastructure. If not then there exists almost no point in constructing these technologies over nuclear, despite any ‘excessive’ costs associated with nuclear power because it makes more sense to develop a future energy infrastructure around an expensive, but capable baseload provider than an expensive or inexpensive, but incapable baseload provider.
Showing posts with label Geothermal. Show all posts
Showing posts with label Geothermal. Show all posts
Tuesday, May 31, 2011
Wednesday, September 8, 2010
Determining the Future of the U.S. Electrical Grid
Although the official position of the government is not to attempt to select winners and losers through application of certain policy, the situation involving the environment is becoming dire. It is time for the government to realize that the free market is not capable of developing the appropriate grid demographic to substitute for the electricity provided by coal in the necessary allotted time frame to avoid severely detrimental consequences. This failure of the market is largely because of all of the lobbyists and the ‘so-called experts’ that are unwilling to accept the potential shortcomings in their preferred power medium. Normally even in the face of this common market bias people have faith in the market that the best option will outmaneuver the lesser options eventually controlling the market; however, on the doorstep to the end of ‘cheap oil’ with the era of ‘no oil’ not that far behind, decisions need to be made now, something the market is incapable of doing.
Almost all infrastructure is dependent on oil for its construction due to material transportation and construction operation and in an era of constant $150+ a barrel oil it will be incredibly difficult to construct an effective new electricity grid when the market is still deciding upon a winner because of its inefficiencies and imperfections. A wide range of piecemeal energy infrastructure (solar plant there, wind farm here, nuclear plant there, geothermal plant here) will not solve the energy problems of the future and yet that is exactly where the market is leading energy infrastructure. Therefore, the government MUST convene a legitimate and thorough energy conference to determine what one or two power mediums will be supported by government funds and which power mediums will be left out in the cold (from a government funding and subsidy perspective). It is time for the U.S. government to step-up, do its job and stop relying on the ‘all-powerful’ market to do a job that it is ill-equipped to do. Below are some concerns regarding most of the viable candidates to replace coal to get the ball rolling.
--
Some Issues about Nuclear Power –
1. With the lack of commercially viable Generation IV plants and none predicted to be available until 2021 at the very earliest, can Generation III plants carry the load for nuclear investment in the near-future from a cost prospective for clearly the cost effectiveness of Generation II plants is lacking.
2. Generation III plants do not appear to be able to create a negative radioactive waste load, so until Generation IV plants are created and fully commercialized in, at the earliest, 2025 where does all the excess radioactive waste go?
3. Although the probability of nuclear accident/meltdown is extremely small in modern nuclear plant designs, there are still lingering questions about who will foot the bill in the case of an accident.
Note the issue of ‘target for terrorist theft or strike’ seems irrelevant as no nuclear power plant has been destroyed by terrorist attack in decades of operation and with Pakistan, North Korea and in due time Iran all having nuclear bomb capacity, the impact and probability of terrorists stealing substandard and improperly enriched materials from a nuclear plant seems significantly unlikely when they can more easily acquire it from these countries.
Some Issues about Geothermal Power –
1. Without enhanced geothermal systems (EGS) is geothermal even worth pursuing as a baseload power source?
2. Can EGS be commercialized fast enough for geothermal to become a chief baseload provider warranting a rapid ramp-up of geothermal or should expansion be slow and steady pursuant to a back-up baseload provider?
Some Issues about Solar Power –
1. Will storage mediums ever move from uneconomical proof-of-concept plants to something which is actually realistic for a 500 – 1000 MW plant?
2. When will transmission lines be upgraded to dramatically reduce efficiency losses to warrant the massive economic investment of solar power in out-of-the-way desert and other high sun-low functional regions?
3. Will solar power ever become affordable relative to other options or will proponents continue to sell the yet-to-be-proven idea of scale-up significantly reducing prices? For decades solar proponents have professed that if only given a fair chance solar power could economically compete with fossil fuels and yet this proclamation for all intensive purposes remains false.
4. How will large-scale deployment of solar power handle large volcano erruption events? What is the attitude regarding the confliction between using solar power and the geo-engineering technique of seeding the atmosphere with sulfur dioxides?
Some Issues about Tidal Power –
1. Can tidal derived power even begin to produce any meaningful level of power required within the appropriate time frame of climate change? Basically is it even worth talking about tidal power?
Some Issues about Wind Power –
1. No one, wind proponents or wind opponents, seem to address the very real possibility of slower average wind speeds in the future due to higher average air temperatures in the Arctic brought on by climate change taking a significant bite out of wind power generation potential. Here
2. The concern that cost per MW for wind power is actually moving upwards not downwards as the best land-based locations for wind power have already been developed. Note: Offshore wind farms have yet to materialize in any significant capacity to develop a real and valid cost estimation to how their future development would influence overall wind prices per MW.
3. There is still the issue regarding how much emission savings wind power actually generates. Initial intuition leads to the conclusion that additional wind power that directly replaces coal or natural gas should reduce carbon emissions and while correct that intuition could be too simplistic. The problem with wind power relative to coal or natural gas is that wind power has only intermittent capacity, which demands backup power from more reliable sources (coal, natural gas, nuclear, geo-thermal or some form of storage medium). Unfortunately wind power advocates continue to downplay this need for effective and efficient power storage strategies to augment widespread wind power deployment on legitimate scale up grounds. Most pro-wind arguments make very optimistic estimates about the ability to scale up wind power via potentially unrealistic assumptions, like an average wind power failure with a very low standard deviation a la Diesendorf’s “the wind is always blowing somewhere” comment. Exactly how much backup is needed? Not surprisingly wind proponents cite almost nothing and wind opponents cite almost 100%. What is actually the right answer?
Also there is the issue of natural gas. Natural gas proponents feature natural gas as a cheaper and more reliable source of electricity over alternatives like wind, geothermal, solar and nuclear in the short-term. Such a strategy could be troublesome because widespread expansion of natural gas could be viewed as a significant waste of money because natural gas is not an endpoint energy solution, even if society wanted it to be one. While switching all coal plants to natural gas would cut total U.S. carbon emissions anywhere from 10.5 to 13.1% (derived from 2007 EIA data depending on natural gas plant efficiency), such a strategy is only a stop-gap measure because if emission targets to evade the worst consequences of global warming are to be met natural gas use as an electricity source must be minimized. With that reality would any significant scale-up of natural gas use for electricity be regarded as a waste of money if it has to scale back down 10 years later when that investment could have better been distributed to a cleaner and more permanent energy generation technology like geothermal, nuclear or solar?
Almost all infrastructure is dependent on oil for its construction due to material transportation and construction operation and in an era of constant $150+ a barrel oil it will be incredibly difficult to construct an effective new electricity grid when the market is still deciding upon a winner because of its inefficiencies and imperfections. A wide range of piecemeal energy infrastructure (solar plant there, wind farm here, nuclear plant there, geothermal plant here) will not solve the energy problems of the future and yet that is exactly where the market is leading energy infrastructure. Therefore, the government MUST convene a legitimate and thorough energy conference to determine what one or two power mediums will be supported by government funds and which power mediums will be left out in the cold (from a government funding and subsidy perspective). It is time for the U.S. government to step-up, do its job and stop relying on the ‘all-powerful’ market to do a job that it is ill-equipped to do. Below are some concerns regarding most of the viable candidates to replace coal to get the ball rolling.
--
Some Issues about Nuclear Power –
1. With the lack of commercially viable Generation IV plants and none predicted to be available until 2021 at the very earliest, can Generation III plants carry the load for nuclear investment in the near-future from a cost prospective for clearly the cost effectiveness of Generation II plants is lacking.
2. Generation III plants do not appear to be able to create a negative radioactive waste load, so until Generation IV plants are created and fully commercialized in, at the earliest, 2025 where does all the excess radioactive waste go?
3. Although the probability of nuclear accident/meltdown is extremely small in modern nuclear plant designs, there are still lingering questions about who will foot the bill in the case of an accident.
Note the issue of ‘target for terrorist theft or strike’ seems irrelevant as no nuclear power plant has been destroyed by terrorist attack in decades of operation and with Pakistan, North Korea and in due time Iran all having nuclear bomb capacity, the impact and probability of terrorists stealing substandard and improperly enriched materials from a nuclear plant seems significantly unlikely when they can more easily acquire it from these countries.
Some Issues about Geothermal Power –
1. Without enhanced geothermal systems (EGS) is geothermal even worth pursuing as a baseload power source?
2. Can EGS be commercialized fast enough for geothermal to become a chief baseload provider warranting a rapid ramp-up of geothermal or should expansion be slow and steady pursuant to a back-up baseload provider?
Some Issues about Solar Power –
1. Will storage mediums ever move from uneconomical proof-of-concept plants to something which is actually realistic for a 500 – 1000 MW plant?
2. When will transmission lines be upgraded to dramatically reduce efficiency losses to warrant the massive economic investment of solar power in out-of-the-way desert and other high sun-low functional regions?
3. Will solar power ever become affordable relative to other options or will proponents continue to sell the yet-to-be-proven idea of scale-up significantly reducing prices? For decades solar proponents have professed that if only given a fair chance solar power could economically compete with fossil fuels and yet this proclamation for all intensive purposes remains false.
4. How will large-scale deployment of solar power handle large volcano erruption events? What is the attitude regarding the confliction between using solar power and the geo-engineering technique of seeding the atmosphere with sulfur dioxides?
Some Issues about Tidal Power –
1. Can tidal derived power even begin to produce any meaningful level of power required within the appropriate time frame of climate change? Basically is it even worth talking about tidal power?
Some Issues about Wind Power –
1. No one, wind proponents or wind opponents, seem to address the very real possibility of slower average wind speeds in the future due to higher average air temperatures in the Arctic brought on by climate change taking a significant bite out of wind power generation potential. Here
2. The concern that cost per MW for wind power is actually moving upwards not downwards as the best land-based locations for wind power have already been developed. Note: Offshore wind farms have yet to materialize in any significant capacity to develop a real and valid cost estimation to how their future development would influence overall wind prices per MW.
3. There is still the issue regarding how much emission savings wind power actually generates. Initial intuition leads to the conclusion that additional wind power that directly replaces coal or natural gas should reduce carbon emissions and while correct that intuition could be too simplistic. The problem with wind power relative to coal or natural gas is that wind power has only intermittent capacity, which demands backup power from more reliable sources (coal, natural gas, nuclear, geo-thermal or some form of storage medium). Unfortunately wind power advocates continue to downplay this need for effective and efficient power storage strategies to augment widespread wind power deployment on legitimate scale up grounds. Most pro-wind arguments make very optimistic estimates about the ability to scale up wind power via potentially unrealistic assumptions, like an average wind power failure with a very low standard deviation a la Diesendorf’s “the wind is always blowing somewhere” comment. Exactly how much backup is needed? Not surprisingly wind proponents cite almost nothing and wind opponents cite almost 100%. What is actually the right answer?
Also there is the issue of natural gas. Natural gas proponents feature natural gas as a cheaper and more reliable source of electricity over alternatives like wind, geothermal, solar and nuclear in the short-term. Such a strategy could be troublesome because widespread expansion of natural gas could be viewed as a significant waste of money because natural gas is not an endpoint energy solution, even if society wanted it to be one. While switching all coal plants to natural gas would cut total U.S. carbon emissions anywhere from 10.5 to 13.1% (derived from 2007 EIA data depending on natural gas plant efficiency), such a strategy is only a stop-gap measure because if emission targets to evade the worst consequences of global warming are to be met natural gas use as an electricity source must be minimized. With that reality would any significant scale-up of natural gas use for electricity be regarded as a waste of money if it has to scale back down 10 years later when that investment could have better been distributed to a cleaner and more permanent energy generation technology like geothermal, nuclear or solar?
Wednesday, October 7, 2009
Loading up on Wind Power: The Wrong Strategy?
In 1824 Jean Baptiste Joseph Fourier in effort to explain why the Earth was warming faster than expected theorized that elements in the atmosphere were trapping solar radiation and reflecting it back to Earth. Later Svante Arrhenius expanded upon this explanation and coined the term ‘greenhouse effect’. When global warming was first proposed as a threat to the Earth, most rejected or ignored it, despite the fact that it was backed by solid science and some intriguing initial data, largely in favor of theories attributing the warming to changes in solar or orbit cycles, theories that have no valid evidence of support now. Other individuals elected to not out-and-out reject global warming and while gathering further data hypothesized that perhaps there was a much shorter lifespan for carbon intensive energy producing methods, like burning coal and natural gas due to their association with a future unmanageable temperature increase. In response to the potential loss of fossil fuels, trace/zero emission energy alternatives had to be developed and deployed to fill the eventual energy gap. From the trace/zero alternatives that have become available, wind power has seen significant growth in the last decade easily outpacing growth of all other trace/zero alternatives (solar, biomass, geothermal, fusion, hydroelectric) combined. However, there may be a problem with this massive wind deployment that harkens back to carbon intensive energy, in that wind may not actually be self-sustainable at the level that would be required to meet future energy demands in the United States. Is wind just another type of coal?
At the turn of the century wind power only accounted for 5.6 million MW-h of utilized electricity (approximately 0.29% of the total U.S. demand at the time).1 That abysmal statistic changed over the last decade largely due to the application of a government tax subsidy. The Federal Renewable Energy Production Tax Credit is designed to aid in the development and deployment of renewable energy technologies. Specifically for wind power it provides a 2.1 cent tax credit for every kw-h of energy produced from an operational wind turbine and utilized by a different source.2 Under most conditions the tax credit is only applicable to a given project for the first ten years of operation. A new portion of legislation that passed in early 2009 also allows renewable operators to instead of taking the production tax credit to opt for a federal business energy investment credit which typically covers approximately 30% of initial capital costs.2 However, unlike most of the major subsidies for the fossil fuel industry, which have permanent status unless explicitly eliminated, the Federal Renewable Energy Production Tax Credit has a typical lifespan ranging from 1-3 years and if not directly renewed it naturally expires. The current wind power subsidy was renewed earlier this year and is slated for expiration Dec 31, 2012.2
A vast majority of the success in wind power development and deployment can be attributed to this subsidy because first, despite the so-called risk-reward attitude that is supposed to drive capitalism, private companies have become more and more squeamish when taking investment risks unless the government footing a significant portion of the bill. Second, and more obvious, the years in which the subsidy had expired deployment of wind power fell substantially as shown in the figure below.3
The universal nature, albeit not universal value, of the renewable subsidies does demonstrate that the principal reason for selecting wind power over another trace/zero emission source like geothermal is a lower capital and/or operation cost. However, these economical considerations only focus on the short-term present value to both the producer and the country as a whole, but unfortunately such thinking is common. Also it is important to understand that all major domestic energy providers receive subsidies with those given to fossil fuel derived industries dwarfing those given to alternative energy sources, thus alternative energy sources are not receiving any type of governmental advantage over fossil fuels. In fact they are still actually at a significant disadvantage.
While wind power growth has been impressive over the last decade, an important question is how much of the future electricity demand can be reasonably provided by wind power with current technology? To calculate the required perimeter landmass a reference average of acres per MW will use Horse Hollow Wind Energy Center in Taylor and Nolan Counties in Texas, which can produce 735 MW of peak power from 421 turbines that cover a landmass of 47,000 acres equaling approximately 64 acres/MW.4 The fact that wind speeds in West Texas are above the national average and the peak power production, not the average power production, is being used makes the use of the above value as a reference value more than valid. Realistically the land value derived from this example more than likely will be an underestimation.
Next assume an average nameplate potential (average operational capacity) of 2200 hours per year (which is a little higher than current existing wind capacity)1, which would generate an average of 0.029 acres/MW-h or 34.4 MW-h per acre. Then assume that over the next decade total overall electricity demand drops by 22.5% from the demand of approximately 4,000,000,000 MW-h in 20071 due to incorporation of new energy efficiency technologies into the residential and commercial sectors and any new structures. Taking all of those assumptions into account, how much land would be required for wind power to replace 50% of the electricity provided by only coal-based sources in 2007 within a decade? Recall that replacing coal with a trace/zero energy source (not just natural gas) will be essential to warding off catastrophic climate change. With current technology wind power would require 45,795.2 square miles of land to generate the approximate 1.008 trillion kW-h (458 GW) produced by part of the coal industry in 2007, which would account for 32.5% of the anticipated electricity demand in this scenario.
That land value seems excessively high doesn't it? The reason that wind farms like Horse Hollow need to be so large is that if wind turbines are built within close proximity of each other overall energy output drops significantly because of elements like wake turbulence, which can interfere with the pressure variations that produce wind. Basically the proximity of turbines is related to the overall average wind speed in that the closer together the turbines the higher the probability that the average wind speeds those turbines experience will decrease.
Wind proponents argue that the total landmass devoted to wind power can be misleading due to the distribution pattern and chief vertical nature of wind turbines. Basically a large portion of the landmass attributed to a wind farm can be regarded as void space, which can be used for other tasks. The primary use of this void space is as farmland because any large vertical structures, even trees, disrupt wind speed as previously discussed. However, farmland conversion can be sub-optimal because wind farms are largely situated on land where high wind speeds are the primary concern and quality soil, water availability and distribution infrastructure are all distant seconds. Fortunately for wind proponents, some of the best pieces of land for wind farms are in the Midwest which already handle a large agricultural sector. Overall the true amount of ‘land use’ for wind power lies somewhere in between the distribution perimeter and the total amount of space occupied by the turbines themselves, but any wind farm will put significant constraints on the land used within its perimeter. Finally computer modeling is used before actually building a wind farm in order to predict the number of turbines and their placement within a given perimeter to maximize overall energy generation.
Note that EIA information from 2007 is being utilized in this analysis because electricity generation and demand from 2008 and 2009 are heavily skewed because of the economic recession. It is rational to believe that electricity demands will increase once again in 2010-2011. It is unknown whether or not future demand will rival that seen in 2007, unlikely but still unknown, but to suggest that 2007 demand will be significantly higher than any future demand seems naïve and unreasonable.
In even the most optimistic scenario of wind growth generating approximately 458 GW of wind power in a reasonable time period (the next two decades) seems unrealistic. If a lower goal were established, under the above scenario parameters wind power would still require approximately 282 GW to provide only 20% of the hypothesized demand. Unfortunately although the total costs and land use appear daunting, they may not be the biggest problem. There is reason to believe that wind power may not have the staying power once thought. In wind advocate circles the United States has been referenced as “the Saudi Arabia of Wind” in effort to describe its vast wind resources and the fact that it could easily be the world leader in wind power generation if current levels of investment continue. However, wind already suffers from the concern of intermittence, the reason behind its low capacity, but is this concern smaller than it should be?
A potentially groundbreaking study documented wind patterns in the United States from the mid 70s to the present and came to the conclusion that there has been an overwhelming dominance of decline in wind speeds at both the 50th and 90th percentile (basically average and top-end wind speeds).5,6 There is little information to evaluate if low-end wind speeds are changing because uncertainty values encapsulate a significant amount of those speeds. Placing a quantitative value on the above research, across portions of the Midwest and regions east of the Mississippi an approximated 10% drop in average wind speed has occurred just in last decade. It is not surprising that this drop in wind speed comes within the same time period that the Earth has experienced its most rapid pace of warming. Clearly this finding, if valid, is extremely important for the future growth and sustainability of the wind industry, but how could this decrease in wind speed be happening and exactly what influence will it have on wind power in the future?
Recall that wind is primarily the result of variance is air pressure brought on by two factors: differential heating between the equator and the poles, which influences the jet stream, mid-latitude westerlies, trade winds and polar easterlies, and planetary rotation, which creates circular motion of air (Coriolis Effect) and leads to monsoons. Unfortunately the rate of accelerated global warming is higher at the North and South poles than other regions of the Earth, which is closing the temperature difference between regions, in turn altering wind patterns and generally increasing the probability of slower wind speeds, for the greater the temperature variance the greater the maximum wind speed.
Although there is too little information to completely confirm whether or not this drop in wind speed is an aberration or a trend, most of the rationalities that have been suggested to explain these wind speed drops without acknowledging the legitimacy of the decrease are rather weak. Some argue that measurement technologies have evolved in the last 35 years and the different nuances in each device creates a level of error that could lead to these conclusions. Really, so the entire drop in wind speeds can be primarily attributed to instrumentation? Others claim that measurement devices, that were once in open space, have recently become obstructed by buildings and new trees which misrepresent wind speeds in that localized region. Such a rationality seems improbable based on the number of different regions that seem to be experiencing significant drops in average wind speed. Finally others claim computer models do not necessarily predict a decline in wind speed. When did the results of computer models take precedence over direct empirical measurements? Also computer models have predicted wind speed reductions in Europe, which creates some level of contradiction because there are similarities between the stock sources that drive wind patterns between the U.S. and Europe.7 Overall what all skeptics of this information seem to be forgetting is the physics behind wind generation as described above. The fact that the temperature variance between regions is shrinking demonstrates increased viability for the conclusion that wind speeds throughout the world should decrease in kind.
So how does a decrease in wind speed affect the power generation of a wind turbine? A wind turbine functions under the premise of transforming the kinetic energy of the wind into either mechanical or electrical energy (depending on the type of system used). The original mechanism of wind energy was the mechanical wind pumper which converted the kinetic energy into mechanical energy as a means to pump water. However, wind turbines and their associated wind power now more commonly convert kinetic energy into electrical energy. There are two types of wind turbines for electrical generation: horizontal-axis or vertical-axis. Horizontal-axis turbines are much more popular in industry most likely because they are more cost effective in maximizing blade diameter which is tied directly to the amount of energy that a wind turbine can produce.
The overall efficiency of a generic wind turbine is actually rather skewed in that the maximum efficiency is attained at approximately 18 mph, but the turbine reaches maximum power output at between 56 to 57 mph. The reason maximum power is not attained at maximum efficiency is because recall the equation governing kinetic energy (E = ½*m*v^2) as wind speed increases the amount of energy relative to only the velocity is squared. In addition the mass of air moving through the turbine also increases proportionally to its velocity, thus the change in the amount of energy available for collection is proportional to the cube of the wind speed. Note that the above explanation does not directly deal with calculating the power generated from a wind turbine, but addresses how the energy available in the wind changes with wind speed. Specifically calculating the power derived involves incorporating momentum flow rates, continuity principles and power equations, a level of applied physics that goes beyond the scope of this post.
Under normal circumstances efficiency of a given system is extremely important, but in the case of wind power due to the fact that wind is not a controllable finite resource, i.e. changes in wind are heavily outside of the control of humans, efficiency is much less important vs. maximum power output. Therefore, when discussing wind turbines, efficiency is an issue that is not imperative. With relation to the ability of a turbine to absorb energy from passing wind, the Betz limit (59% transfer) is the maximum level. The graph below illustrates the change in power generation in relation with wind speed. Note that the graph is not a mathematically perfect representation of the generic 2.1 MW wind turbine, but it is accurate enough that one can get a general idea of the relationship and make fairly accurate calculations.
Suppose that the conclusion that average wind speed is dropping is correct, what does that mean for the wind power industry? Well, if it is assumed that an 8% drop in wind speed can be universally applied, a significant drop-off in power production can be expected. For example if the average wind speed in a given generic wind farm containing 300 2.1 MW turbines falls from 15 mph to 13.8 mph the annual total power loss, when using the performance information from the above figure, is approximately 310,143.32 MW-h or about 27.76%.
The two primary reasons for the significant drop-off with such a small reduction in wind speed is the cubing property associated with the kinetic energy transfer and the low capacity of wind power. Regarding the second reason, suppose a wind turbine was constructed in an environment that had an average wind speed of 40 mph, the 8% reduction would have no effect on wind power (an average speed of 36.8 mph still attains a maximum level of power generation). Unfortunately the second reason is a problem because wind turbine technology is not cost-effective enough to construct turbines that exist at a high enough altitude to capture wind gusts with such a high average speed.
Another problem with the potential reduction of wind speed is early results localize it primarily in the Midwest which is the region that has the highest average wind speeds and is the principal construction venue for wind farms due to both the high average wind speed (12-17 mph) and the relatively flat and open spaces which lend themselves well to cultivating, if not already, wind farm void space. Therefore, if the wind reduction trend is accurate, there will be a significant reduction in power generation within the optimal region of power generation.
Understand that this analysis is not to say that wind power should be abandoned because such a stance would be silly and irresponsible. Instead it is important to remember to diversify the mix of energy generation for the United States in the future. If no new trace/zero emission energy sources become scientifically and economically available, most of which seem unlikely (anti-matter, greater than break-even hot fusion, cold fusion, space-based solar power, etc.), the total available trace/zero emission options are limited. In fact it stands to reason that significant future growth in trace/zero emission energy can be confined to four unique options: wind, solar, geothermal and biomass. A vast majority of the potential that exists for hydroelectric has already been realized as secondary tidal generation systems do not look promising in pushing hydroelectric power far beyond that which is already generated as well as account for any losses accrued from further drought conditions in the West, thus hydroelectric does not appear to be a valid candidate for significant further growth.
Unfortunately growth in geothermal and biomass has barely budged in the last decade and despite vast improvement in manufacturing, solar power is still heavily dependent on photovoltaic costs. There has been a lot of talk surrounding thermal solar plants, especially in the Mojave Desert, but very little has come from this so-called vast potential. In fact solar energy incorporation into the grid could grow at 30% annually over the next two decades and still be a relative non-factor in electricity production (255,533,901 MW-h in 2030; approximately 8.24% of the total electricity demand in the previously hypothesized demand scenario). The sad state of trace/zero emission energy source growth is demonstrated in the table below.1,8
* delineates annual growth rate from last year to current year;
Looking at the above table is rather disconcerting as wind power is generating double-digit growth rates from 1999 to the present in all years in which a government-based wind subsidy was available. However, the growth rates or absolute energy generation for the other three major alternative sources are completely and utterly pathetic. Although solar has an impressive growth rate over the last two years, the recession has limited the availability of capital for the solar industry, so unless something like the ACES is signed into law, it is rational to expect those growth rates to decrease significantly. Also the absolute energy generation of solar is extremely small comparative to the other alternatives, thus high growth rates are easier to achieve (note that the absolute gains in solar vs. geothermal from 2007 to 2008 were nearly identical, but solar grew at 37.75% and geothermal grew at 1.5%). Regardless, as previously mentioned, it is unlikely barring a technological miracle, that solar will become a major contributor to the grid in the next two decades. This reality is unfortunate because the next two decades will be the most critical time in both avoiding an energy crisis and serious detrimental climate change. Geothermal and biomass have significant capacities, but need a huge shot in the arm from a funding, infrastructure and willingness to actually undertake new projects standpoint, all which do not appear to be forthcoming.
If the trend of wind speed reduction continues, at the moment there is no reason to dismiss such a conclusion, then with the current rate of fossil fuel energy/electricity substitution relying so heavily on wind power, the United States will either almost definitely face an energy crisis of significant proportion in the future or be guaranteed significant detrimental climate change. To avoid such a crisis, energy diversity is essential, instead of giving huge subsidies to coal, oil and natural gas, a significant percentage of those subsidies need to be siphoned off and directed towards geothermal, biomass and solar-based sources. Unless specific quotas are assigned, the simple administration of a renewable energy standard will not drive this diversity because most producers will simply direct efforts to wind power to fill the requisite percentage. The current and future energy market is just like the stock market the key to long-term growth and stability in the overall portfolio is diversity, such an ideal is not achieved by throwing all the alternative energy eggs into the wind power basket.
==
1. “Electric Power Annual 2007: Table ES1. Summary Statistics for the United States, 1996 through 2007.” Energy Information Administration. January 2009.
2. http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US13F
3. Original Source: American Wind Energy Association [Secondary Source - Climate Progress: “Energy and Global Warming News for September 1: Big Money returns to Wind Power.” http://climateprogress.org/2009/09/01/energy-and-global-warming-news-for-september-1-big-money-returns-to-wind-power/]
4. Mims, Christopher. “The World's 10 Largest Renewable Energy Projects.” Scientific American Magazine. June 4, 2009.
5. Pryor, S, et, Al. “Wind speed trends over the contiguous United States.” J. Geophys. Res. 2009. 114: D14105 - doi:10.1029/2008JD011416.
6. Pryor, S, Barthelmie, R, Takle. “Wind speed trends over the contiguous USA.” IOP Conf. Series: Earth and Environmental Science. 2009. 6: doi:10.1088/1755-1307/6/9/092023.
7. Hennemuth, B, Hollweg, H-D, Schubert, M. “Change of Wind Speed in Europe in
Regional Climate Model Scenario Projections.” Service Group Adaption – SGA. Model & Data / MPI-M, Hamburg, Germany. 2008.
8. Preliminary Energy Data for 2008. Energy Information Administration. 2009. http://www.eia.doe.gov/cneaf/alternate/page/renew_energy_consump/rea_prereport.html
At the turn of the century wind power only accounted for 5.6 million MW-h of utilized electricity (approximately 0.29% of the total U.S. demand at the time).1 That abysmal statistic changed over the last decade largely due to the application of a government tax subsidy. The Federal Renewable Energy Production Tax Credit is designed to aid in the development and deployment of renewable energy technologies. Specifically for wind power it provides a 2.1 cent tax credit for every kw-h of energy produced from an operational wind turbine and utilized by a different source.2 Under most conditions the tax credit is only applicable to a given project for the first ten years of operation. A new portion of legislation that passed in early 2009 also allows renewable operators to instead of taking the production tax credit to opt for a federal business energy investment credit which typically covers approximately 30% of initial capital costs.2 However, unlike most of the major subsidies for the fossil fuel industry, which have permanent status unless explicitly eliminated, the Federal Renewable Energy Production Tax Credit has a typical lifespan ranging from 1-3 years and if not directly renewed it naturally expires. The current wind power subsidy was renewed earlier this year and is slated for expiration Dec 31, 2012.2
A vast majority of the success in wind power development and deployment can be attributed to this subsidy because first, despite the so-called risk-reward attitude that is supposed to drive capitalism, private companies have become more and more squeamish when taking investment risks unless the government footing a significant portion of the bill. Second, and more obvious, the years in which the subsidy had expired deployment of wind power fell substantially as shown in the figure below.3
The universal nature, albeit not universal value, of the renewable subsidies does demonstrate that the principal reason for selecting wind power over another trace/zero emission source like geothermal is a lower capital and/or operation cost. However, these economical considerations only focus on the short-term present value to both the producer and the country as a whole, but unfortunately such thinking is common. Also it is important to understand that all major domestic energy providers receive subsidies with those given to fossil fuel derived industries dwarfing those given to alternative energy sources, thus alternative energy sources are not receiving any type of governmental advantage over fossil fuels. In fact they are still actually at a significant disadvantage.
While wind power growth has been impressive over the last decade, an important question is how much of the future electricity demand can be reasonably provided by wind power with current technology? To calculate the required perimeter landmass a reference average of acres per MW will use Horse Hollow Wind Energy Center in Taylor and Nolan Counties in Texas, which can produce 735 MW of peak power from 421 turbines that cover a landmass of 47,000 acres equaling approximately 64 acres/MW.4 The fact that wind speeds in West Texas are above the national average and the peak power production, not the average power production, is being used makes the use of the above value as a reference value more than valid. Realistically the land value derived from this example more than likely will be an underestimation.
Next assume an average nameplate potential (average operational capacity) of 2200 hours per year (which is a little higher than current existing wind capacity)1, which would generate an average of 0.029 acres/MW-h or 34.4 MW-h per acre. Then assume that over the next decade total overall electricity demand drops by 22.5% from the demand of approximately 4,000,000,000 MW-h in 20071 due to incorporation of new energy efficiency technologies into the residential and commercial sectors and any new structures. Taking all of those assumptions into account, how much land would be required for wind power to replace 50% of the electricity provided by only coal-based sources in 2007 within a decade? Recall that replacing coal with a trace/zero energy source (not just natural gas) will be essential to warding off catastrophic climate change. With current technology wind power would require 45,795.2 square miles of land to generate the approximate 1.008 trillion kW-h (458 GW) produced by part of the coal industry in 2007, which would account for 32.5% of the anticipated electricity demand in this scenario.
That land value seems excessively high doesn't it? The reason that wind farms like Horse Hollow need to be so large is that if wind turbines are built within close proximity of each other overall energy output drops significantly because of elements like wake turbulence, which can interfere with the pressure variations that produce wind. Basically the proximity of turbines is related to the overall average wind speed in that the closer together the turbines the higher the probability that the average wind speeds those turbines experience will decrease.
Wind proponents argue that the total landmass devoted to wind power can be misleading due to the distribution pattern and chief vertical nature of wind turbines. Basically a large portion of the landmass attributed to a wind farm can be regarded as void space, which can be used for other tasks. The primary use of this void space is as farmland because any large vertical structures, even trees, disrupt wind speed as previously discussed. However, farmland conversion can be sub-optimal because wind farms are largely situated on land where high wind speeds are the primary concern and quality soil, water availability and distribution infrastructure are all distant seconds. Fortunately for wind proponents, some of the best pieces of land for wind farms are in the Midwest which already handle a large agricultural sector. Overall the true amount of ‘land use’ for wind power lies somewhere in between the distribution perimeter and the total amount of space occupied by the turbines themselves, but any wind farm will put significant constraints on the land used within its perimeter. Finally computer modeling is used before actually building a wind farm in order to predict the number of turbines and their placement within a given perimeter to maximize overall energy generation.
Note that EIA information from 2007 is being utilized in this analysis because electricity generation and demand from 2008 and 2009 are heavily skewed because of the economic recession. It is rational to believe that electricity demands will increase once again in 2010-2011. It is unknown whether or not future demand will rival that seen in 2007, unlikely but still unknown, but to suggest that 2007 demand will be significantly higher than any future demand seems naïve and unreasonable.
In even the most optimistic scenario of wind growth generating approximately 458 GW of wind power in a reasonable time period (the next two decades) seems unrealistic. If a lower goal were established, under the above scenario parameters wind power would still require approximately 282 GW to provide only 20% of the hypothesized demand. Unfortunately although the total costs and land use appear daunting, they may not be the biggest problem. There is reason to believe that wind power may not have the staying power once thought. In wind advocate circles the United States has been referenced as “the Saudi Arabia of Wind” in effort to describe its vast wind resources and the fact that it could easily be the world leader in wind power generation if current levels of investment continue. However, wind already suffers from the concern of intermittence, the reason behind its low capacity, but is this concern smaller than it should be?
A potentially groundbreaking study documented wind patterns in the United States from the mid 70s to the present and came to the conclusion that there has been an overwhelming dominance of decline in wind speeds at both the 50th and 90th percentile (basically average and top-end wind speeds).5,6 There is little information to evaluate if low-end wind speeds are changing because uncertainty values encapsulate a significant amount of those speeds. Placing a quantitative value on the above research, across portions of the Midwest and regions east of the Mississippi an approximated 10% drop in average wind speed has occurred just in last decade. It is not surprising that this drop in wind speed comes within the same time period that the Earth has experienced its most rapid pace of warming. Clearly this finding, if valid, is extremely important for the future growth and sustainability of the wind industry, but how could this decrease in wind speed be happening and exactly what influence will it have on wind power in the future?
Recall that wind is primarily the result of variance is air pressure brought on by two factors: differential heating between the equator and the poles, which influences the jet stream, mid-latitude westerlies, trade winds and polar easterlies, and planetary rotation, which creates circular motion of air (Coriolis Effect) and leads to monsoons. Unfortunately the rate of accelerated global warming is higher at the North and South poles than other regions of the Earth, which is closing the temperature difference between regions, in turn altering wind patterns and generally increasing the probability of slower wind speeds, for the greater the temperature variance the greater the maximum wind speed.
Although there is too little information to completely confirm whether or not this drop in wind speed is an aberration or a trend, most of the rationalities that have been suggested to explain these wind speed drops without acknowledging the legitimacy of the decrease are rather weak. Some argue that measurement technologies have evolved in the last 35 years and the different nuances in each device creates a level of error that could lead to these conclusions. Really, so the entire drop in wind speeds can be primarily attributed to instrumentation? Others claim that measurement devices, that were once in open space, have recently become obstructed by buildings and new trees which misrepresent wind speeds in that localized region. Such a rationality seems improbable based on the number of different regions that seem to be experiencing significant drops in average wind speed. Finally others claim computer models do not necessarily predict a decline in wind speed. When did the results of computer models take precedence over direct empirical measurements? Also computer models have predicted wind speed reductions in Europe, which creates some level of contradiction because there are similarities between the stock sources that drive wind patterns between the U.S. and Europe.7 Overall what all skeptics of this information seem to be forgetting is the physics behind wind generation as described above. The fact that the temperature variance between regions is shrinking demonstrates increased viability for the conclusion that wind speeds throughout the world should decrease in kind.
So how does a decrease in wind speed affect the power generation of a wind turbine? A wind turbine functions under the premise of transforming the kinetic energy of the wind into either mechanical or electrical energy (depending on the type of system used). The original mechanism of wind energy was the mechanical wind pumper which converted the kinetic energy into mechanical energy as a means to pump water. However, wind turbines and their associated wind power now more commonly convert kinetic energy into electrical energy. There are two types of wind turbines for electrical generation: horizontal-axis or vertical-axis. Horizontal-axis turbines are much more popular in industry most likely because they are more cost effective in maximizing blade diameter which is tied directly to the amount of energy that a wind turbine can produce.
The overall efficiency of a generic wind turbine is actually rather skewed in that the maximum efficiency is attained at approximately 18 mph, but the turbine reaches maximum power output at between 56 to 57 mph. The reason maximum power is not attained at maximum efficiency is because recall the equation governing kinetic energy (E = ½*m*v^2) as wind speed increases the amount of energy relative to only the velocity is squared. In addition the mass of air moving through the turbine also increases proportionally to its velocity, thus the change in the amount of energy available for collection is proportional to the cube of the wind speed. Note that the above explanation does not directly deal with calculating the power generated from a wind turbine, but addresses how the energy available in the wind changes with wind speed. Specifically calculating the power derived involves incorporating momentum flow rates, continuity principles and power equations, a level of applied physics that goes beyond the scope of this post.
Under normal circumstances efficiency of a given system is extremely important, but in the case of wind power due to the fact that wind is not a controllable finite resource, i.e. changes in wind are heavily outside of the control of humans, efficiency is much less important vs. maximum power output. Therefore, when discussing wind turbines, efficiency is an issue that is not imperative. With relation to the ability of a turbine to absorb energy from passing wind, the Betz limit (59% transfer) is the maximum level. The graph below illustrates the change in power generation in relation with wind speed. Note that the graph is not a mathematically perfect representation of the generic 2.1 MW wind turbine, but it is accurate enough that one can get a general idea of the relationship and make fairly accurate calculations.
Suppose that the conclusion that average wind speed is dropping is correct, what does that mean for the wind power industry? Well, if it is assumed that an 8% drop in wind speed can be universally applied, a significant drop-off in power production can be expected. For example if the average wind speed in a given generic wind farm containing 300 2.1 MW turbines falls from 15 mph to 13.8 mph the annual total power loss, when using the performance information from the above figure, is approximately 310,143.32 MW-h or about 27.76%.
The two primary reasons for the significant drop-off with such a small reduction in wind speed is the cubing property associated with the kinetic energy transfer and the low capacity of wind power. Regarding the second reason, suppose a wind turbine was constructed in an environment that had an average wind speed of 40 mph, the 8% reduction would have no effect on wind power (an average speed of 36.8 mph still attains a maximum level of power generation). Unfortunately the second reason is a problem because wind turbine technology is not cost-effective enough to construct turbines that exist at a high enough altitude to capture wind gusts with such a high average speed.
Another problem with the potential reduction of wind speed is early results localize it primarily in the Midwest which is the region that has the highest average wind speeds and is the principal construction venue for wind farms due to both the high average wind speed (12-17 mph) and the relatively flat and open spaces which lend themselves well to cultivating, if not already, wind farm void space. Therefore, if the wind reduction trend is accurate, there will be a significant reduction in power generation within the optimal region of power generation.
Understand that this analysis is not to say that wind power should be abandoned because such a stance would be silly and irresponsible. Instead it is important to remember to diversify the mix of energy generation for the United States in the future. If no new trace/zero emission energy sources become scientifically and economically available, most of which seem unlikely (anti-matter, greater than break-even hot fusion, cold fusion, space-based solar power, etc.), the total available trace/zero emission options are limited. In fact it stands to reason that significant future growth in trace/zero emission energy can be confined to four unique options: wind, solar, geothermal and biomass. A vast majority of the potential that exists for hydroelectric has already been realized as secondary tidal generation systems do not look promising in pushing hydroelectric power far beyond that which is already generated as well as account for any losses accrued from further drought conditions in the West, thus hydroelectric does not appear to be a valid candidate for significant further growth.
Unfortunately growth in geothermal and biomass has barely budged in the last decade and despite vast improvement in manufacturing, solar power is still heavily dependent on photovoltaic costs. There has been a lot of talk surrounding thermal solar plants, especially in the Mojave Desert, but very little has come from this so-called vast potential. In fact solar energy incorporation into the grid could grow at 30% annually over the next two decades and still be a relative non-factor in electricity production (255,533,901 MW-h in 2030; approximately 8.24% of the total electricity demand in the previously hypothesized demand scenario). The sad state of trace/zero emission energy source growth is demonstrated in the table below.1,8
* delineates annual growth rate from last year to current year;
Looking at the above table is rather disconcerting as wind power is generating double-digit growth rates from 1999 to the present in all years in which a government-based wind subsidy was available. However, the growth rates or absolute energy generation for the other three major alternative sources are completely and utterly pathetic. Although solar has an impressive growth rate over the last two years, the recession has limited the availability of capital for the solar industry, so unless something like the ACES is signed into law, it is rational to expect those growth rates to decrease significantly. Also the absolute energy generation of solar is extremely small comparative to the other alternatives, thus high growth rates are easier to achieve (note that the absolute gains in solar vs. geothermal from 2007 to 2008 were nearly identical, but solar grew at 37.75% and geothermal grew at 1.5%). Regardless, as previously mentioned, it is unlikely barring a technological miracle, that solar will become a major contributor to the grid in the next two decades. This reality is unfortunate because the next two decades will be the most critical time in both avoiding an energy crisis and serious detrimental climate change. Geothermal and biomass have significant capacities, but need a huge shot in the arm from a funding, infrastructure and willingness to actually undertake new projects standpoint, all which do not appear to be forthcoming.
If the trend of wind speed reduction continues, at the moment there is no reason to dismiss such a conclusion, then with the current rate of fossil fuel energy/electricity substitution relying so heavily on wind power, the United States will either almost definitely face an energy crisis of significant proportion in the future or be guaranteed significant detrimental climate change. To avoid such a crisis, energy diversity is essential, instead of giving huge subsidies to coal, oil and natural gas, a significant percentage of those subsidies need to be siphoned off and directed towards geothermal, biomass and solar-based sources. Unless specific quotas are assigned, the simple administration of a renewable energy standard will not drive this diversity because most producers will simply direct efforts to wind power to fill the requisite percentage. The current and future energy market is just like the stock market the key to long-term growth and stability in the overall portfolio is diversity, such an ideal is not achieved by throwing all the alternative energy eggs into the wind power basket.
==
1. “Electric Power Annual 2007: Table ES1. Summary Statistics for the United States, 1996 through 2007.” Energy Information Administration. January 2009.
2. http://www.dsireusa.org/incentives/incentive.cfm?Incentive_Code=US13F
3. Original Source: American Wind Energy Association [Secondary Source - Climate Progress: “Energy and Global Warming News for September 1: Big Money returns to Wind Power.” http://climateprogress.org/2009/09/01/energy-and-global-warming-news-for-september-1-big-money-returns-to-wind-power/]
4. Mims, Christopher. “The World's 10 Largest Renewable Energy Projects.” Scientific American Magazine. June 4, 2009.
5. Pryor, S, et, Al. “Wind speed trends over the contiguous United States.” J. Geophys. Res. 2009. 114: D14105 - doi:10.1029/2008JD011416.
6. Pryor, S, Barthelmie, R, Takle. “Wind speed trends over the contiguous USA.” IOP Conf. Series: Earth and Environmental Science. 2009. 6: doi:10.1088/1755-1307/6/9/092023.
7. Hennemuth, B, Hollweg, H-D, Schubert, M. “Change of Wind Speed in Europe in
Regional Climate Model Scenario Projections.” Service Group Adaption – SGA. Model & Data / MPI-M, Hamburg, Germany. 2008.
8. Preliminary Energy Data for 2008. Energy Information Administration. 2009. http://www.eia.doe.gov/cneaf/alternate/page/renew_energy_consump/rea_prereport.html
Subscribe to:
Posts (Atom)