"Spatial Footprint" Challenges of Solar Energy Use

http://www.salon.com/news/feature/2008/04/14/solar_electric_thermal/

Solar electric thermal, also known as concentrated solar power ... makes use of the most abundant and free fuel there is, sunlight, and key countries have a vast resource. Solar thermal plants covering the equivalent of a 92-by-92-mile square grid in the Southwest could generate electricity for the entire United States. Mexico has an equally enormous solar resource. China, India, southern Europe, North Africa, the Middle East and Australia also have huge resources.

No energy is free energy. To gain energy from some active source, you must extract it from an environment that depends on that developed energy source. What is the impact of stopping light from reaching the ground or sea surface. How much light do these environment require to support adequate levels of life and diversity. How does the loss of heat collected and stored in the water or soil effect the climate, currents, weather patterns. Also, while 5.5 million acres of land sounds like a lot, does your calculation include the efficiency of energy conversion for solar systems and energy conveyance (and some factor for undefined system losses or inefficiencies beyond the materials losses). How many KW per year can you generate from 5.5 million acres of solar cells? What happens at night? How many batteries do we need to buy?

Karl:

Well said. Nothing is really "perfect". Everything has its limits. Spatial Footprints of Solar Systems clearly takes up Land Space - in competition with other productive uses. Perhaps, Archipelagic Countries (i.e. Philippines, etc) may offset its Land Limitations with Sea-installed Solar Systems. Is there a model anywhere in the world existing today?

I read several years ago about methods of agriculture in india. One thing that they had was shade to prevent plants drying out or getting too hot. It may well be that certain plants welcome the shade of a shared place with panels! Often the limiting factor in plant growth is water or fertilizer. Not light. In that case low density panels would be useful. Brian

I am quick to accept that this idea of "Spatial Footprint" of Sun & Shade would have complimentary benefits as applied to Agriculture, et. al. All it takes to maximize use of Solar Energy is for more and more people to have an open mind - and the willingness to adapt to new technologies.

The development and use of "solar concentrators" to harness solar energy will help solve the challenge of space requirements.

This link

http://peswiki.com/index.php/Directory:Concentrated_Solar_Power

will tell more about this development in solar energy technologies.

Good Link. Thanks for sharing.

Please check this out www.solarthermalelectric.org Another form of solar.

Thanks, Nick

Since the area of solar cells require to power a home and charge batteries for nighttime use with significant power left over for the grid is the same area as one's roof, what need is there for using valuable agricultural land? This also applies to building tops and sun facing window shades. In fact, the Australians have developed PV cells for the windows themselves. Why, we could live in glass houses so long as our neighbors don't throw stones. The only real problems with either passive and active solar power is the costs. Most peoples have neither the knowledge nor money for "do it yourself" solar projects. If, however, we could convince our governments to put in the same effort and money to get to the moon into covering the world with both active and passive solar energy, it would go a long way toward solving SOME of our energy problems and reducing our carbon foot-print.

Then, there is the problem of our transportation infrastructure. There is several Sustainability projects already started on this forum to develop renewable fuels to replace fossil fuels for the world. This whole SEP system is doable if only were were willing to put our minds and moneies to it. We can no longer ignore the problems, talk is not enough, it is time for real action and effort.

Solar is not always the best answer due to its high cost and large footprint. Small wind generator systems have a very small footprint if placed on a monopole with no guy wires (4'x4' maximum). In class 2 or greater wind conditions the output is usually one half to 2/3 that of the rated. With most net metering programs, wind generators can "bank" power during the "windy" season which can be "withdrawn" during non-windy months. The payoff period is comparatively short, as well. Small wind technology has advanced exponentially in recent years becoming more efficient in harnessing energy. Unfortunately, there are a number of individuals claiming to have designed "breakthrough" machines which are more efficient than the horizontal axis, lift profile machines. Usually these "breakthrough" machines are a reinvention of the square wheel. Since the "heavy" (read utility scale) wind generator industry is highly competitive and profitable, the technology is always at the cutting edge. Therefore, small systems should simply be scaled down versions with only a few small modifications. Check your local weather station, or locate a wind map of your area (www.awea.org or www.nrel.gov). Keep in mind that wind maps are simply a general overview of your area's wind profile and may not accurately reflect your particular site. A local Mesowest weather station and/or an anemometer reading would be more suitable. If the average wind speed is 8 mph or above, small wind may be a good idea. Also, depending on your climate and financial situation, a wind/solar hybrid system may be the best option for a zero balance utility bill.

Some talk about the "Noise Factor" coming out of Wind Farms. Has this been resolved?

Indeed. The technological advances in wind generator technology mentioned in my previous posting include noise reduction. Wing airfoil and tip design, as well as scale increase (thereby reducing rotation speed) all contribute to a virtually noiseless wind farm. Thank you for the question.

Given the technical advances in Wind Power, I solicit your reply to my Discussion Thread - http://cr4.globalspec.com/thread/20153/Aternative-Energy-AE-Solutions-for-Philippine-Factories-Which-is-ideal. Given my Case Study # 1 and Case Study # 2, would you recommend Wind Power? How much would it cost to swift to Wind Power for both cases?

I have a question for your, WIndGenMan; has anyone investigated a rear mounted turbine with a shroud around the blade tips. It would seem to me that such an arrangement would provide a better control for keeping the turbine pointed into the wind even on gusty days and also help to increase the velocity of the wind across the surface of the turbine blades. This would make the system more like a true turbine. Also, if the alternator were set in the vertical rather than in the horizontal, it could be driven by a 90 degree gear and the alternator could be set at a more accessible level. This would, however, result in some vibration (balancing) and friction loss if the drive shaft were unreasonably long. Since the power produced with solar or fuel cells is direct current and would be used in combination with a wind turbine farm, it is likely that the power produced with an alternator would likely be converted from AC to DC with added into the system that would be then put into the inverter. This is the most practical means of establishing a uniform 50 or 60 cycle feed to the grid. Please supply us with some research and/or understanding of this situation, either positive or negative. We are most interested in finding those systems that can most practical for use in undeveloped nations using semi-skilled labor that can be trained to maintain an energy producing system. Thus, reliability, safety and simplicity is a must and cost is a major factor.

Thank you for your question. The configuration to which you refer is called a "downwind" wind generator. These machines do have the advantage not requiring a tail vane or a mechanical yaw system. However, they are susceptible to tower shadowing, which causes severe stress on the hub bearings due to the unequal wind loads placed on the blades as one passes the tower's lee side. This phenomenon can reduce the life span of the machine. One American manufacturer has attempted to address the problem by curving the blades so that only a fraction of its surface is shadowed at any one moment. There are no studies determining if this is effective in reducing the load variance. It is also not certain if blades curved as such are as efficient in harnessing energy from wind. High winds, especially those which come in gusts, are not always a good thing. Proponents of "downwinders" claim their machines have no cut-out speed. Yet most have some mechanism (blade feathering or pitching) for slowing the blades down in high winds to prevent over-speeding the generator. These mechanisms are basically doing the same thing as a tail vane on an upwind machine except much more expensively. Tail vanes on more modern upwind machines are designed to gradually yaw the blades out of the wind after reaching a certain speed. Gradual yawing allows the machine to continue producing far beyond the rated speed--just as feathering and pitching do on "downwinders." As for the shroud you mention, many individuals before you, including myself, have thought of ways to increase the wind speed as it approaches the blades using tunnel effect. However, wind obeys the same laws of momentum as liquids. Therefore, as wind approaches the turbine blades a high pressure zone is created. Some of the pressure is dissipated as wind is allowed to pass through the spinning blades. Some pressure is relieved when the wind is diverted off of the blade tips. Since the shroud you are talking about is very short in length and is located around the wing tips, it would only serve to prevent the excess pressure from dissipating, which would create more lateral load on the machine. This would offset any benefit from the minute increase in wind speed you may get from the tunnel effect. In order to create a true wind tunnel effect, a shroud would need to be quite long. One would then need to ask whether the material required for such an effect would be worth the small increase in wind speed. In regards to the vertical alternator I would need some clarification. Are you talking about using the alternator and gear system in a machine where the blades rotate around a vertical axis? Ken

you might consider the the support staff to be, as we use in the jet engine, as a part of the vaining, i.e., as a guide to the wind to direct the airflow at a reasonable angle to improve the flow to the turbine vains. Since I suggest a tip shroud, you can easily see a series of fixed vains to direct the airflow and to support the shroud. This shroud and the central shaft will also tend to increase the velocity of the airflow, thus increasing the shaft rpm.

now, I shall read on, as this is just the reply to your shadowing problem.

OK, the second part: I am considering this the same as I would consider any turbine, it is an engine. Many of the "problems" you suggested are much the same as with the turbine jet engine, and these have been overcome. As for placing the "generator" in the vertical, may I suggest a hydraulic drive. This, with a volume pressure tank, can also address the "overspeed" problems, too, one, by not being critical to shaft speed changes, and two, as the hydraulic pressure increases, it acts as a brake on the shaft speed, forcing the wings to develop more horse power to overcoming the braking action. I also find that a hydraulic drive might produce less energy loss to the generator.

These are simply suggestions but I would like to see some research figures with such a configuration.

The suggestions you make are great. I respect your knowledge of turbo jet engines and have no doubt there are many things we can learn from them. However, in your original question, if I understood you correctly, you are were interested in distributing power systems in rural areas needing electricity. I am guessing that you would appreciate a system that is both cost effective and efficient. As I mentioned in one of my earlier postings, the heavy wind industry is the best model for both cost effectiveness and technological innovation since the field is highly competitive. Blade technology on the larger systems have yet to be improved upon. They have come closer to extracting the maximum amount of energy from wind (i.e. reaching the Betz limit) than any other design. Utility scale wind turbines do employ an enormous amount of technology for overspeed protection, including hydraulics. They have to. Remember, the blades are extremely efficient in what they do. However, scaling these systems down and making them affordable to the average citizen requires simplifying the over-speed technology. This is where the discussion about upwind vs downwind, and passive yaw systems comes in. Since cost in raw materials continues to increase, it makes sense to reduce and simplify where you can. Regarding vertical axis turbines: the first wind powered grain mills employed by the by the Egyptians as long ago as 3000 B.C. were vertical axis machines. This configuration lasted thousands of years until the Europeans discovered a more efficient way of capturing energy from wind--hence the windmills of Scandinavia. Since then, humans have made several attempts to reintroduce the vertical axis machine and brand it as new technology.

Reading your Exchange-of-Replies with ChTank is encouraging to me - although, I must confess that I can't fathom your Technical Discussion. In any case, I await your reply to my Reply Post # 12. Thanks.

Okay, on to Reply Post #12. I hope I can be helpful.

Let me pass this along as an explanation of my viewpoint:

http://freepages.genealogy.rootsweb.ancestry.com/~chtank/homepower.html.

Also, Manilaman does need some hard facts and costs. He is working to bring the Philippines forward in alternate and green energy.

ManilaMan, Please feel free to use My Earthbound Space Station as you find fit. As for detailed plans, I am unable to provide. However, I have tried to give a written outline of the design I would use for each module. I do believe that any engineer or engineering company can take my "text" and convert it into a reasonable design to fit the local conditions. I offer My Earthbound Space Station to you and the world without reservation need for compensation. My reward will always be the inspiration. As you may note, the bio-digestion part(s) are much like that of APIX.

One thing that comes to mind now is that the manufactured building material of the APIX project could also be used in the habitat construction, providing that it remains rot, varmint, and flame retardant. This could be an outstanding alternative to our over-use of wood, i.e., help save our forests.

gaiatechnician makes the excellent point that solar "footprints" can be useful rather than harmful if applied intelligently.

Here in the southwest US we are actually seeing better pasture under the panels, partial shading seeming to benefit the soils and grasses.

I'm working on using panels mounted 15 feet up so cattle can still graze beneath.

And what will happen when we take the technology to the barren overgraze of northern Arizona remains to be seen.

Emmett

As i undertsand your statement, the State of Arizona is severely mismanaging the natural environment allowing business applications to severely deplete the natural environment for supporting the native ecosystem of northern Arizona. So installation of the solar panels would allow the people of the State to modify the environment to provide better conditions to utilize the resource more greatly. The question then becomes what is the impact on the natural ecosystem when you dramatically alter the environment to such a degree from one that is apparently already adversely impacting the ecosystem. does it improve the environment, or adversely impact it even further? Do invasive species not suited to the climate or solar conditions proliferate? Do species limited by the climate previously now proliferate? Does the proliferation of one species endanger the food chain and ecology of others? Could a person utilize this to develop land? Run cattle on the land for 5 years and determine the land has been so adversely altered by the cattle that it is no longer suitable as to support the natural ecosystem, and thus now can build homes on the property. Are cattle the only cause of such impacts, how about sheep, or tourist. Intriguing prospect on a method to get around the EIR significant impacts process. I have seen farming used in this kind of manner.

To further your discussions, perhaps this will be of interest: http://www.sciencedaily.com/releases/2008/04/080430103117.htm