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Pete,
Thanks for the
great summary of solar's potential. In a few
paragraphs you demonstrated, using simple "back of the envelope"
calculations, the basic theoretical limits of solar power. Why these kinds
of facts are not more widely disclosed has always baffled
me.
As for your
alternative to combustion-based technologies, go ahead and tell us! There must
be ways in which complexity figures into it. :)
Regards,
Tim
(...Yeth, thatth the plural of "myth" with a lithp.) Judith is correct in her preference for using renewable resources like solar energy wherever they are appropriate. Tim is correct in his assertion that intensive, reliable, on-demand power generation is not one of those applications. NOTE:The economics of installing engine-driven generators must indeed be balanced by the ROI such an investment would make. In addition to the capital cost of the power generating, distribution, & switching equipment, and the facilities to house it, there's the expense of storing and recycling fuel (usually Diesel No. 2) -- with all its associated regulatory hassles. Add to that the personnel cost of maintenance & operations, and you have to have a very compelling reason to load that kind of cost into the goods/services you offer your customers. In fact, if your competitors decide against going that route and the market prefers the resulting lower prices of their goods/services, you won't have any customers. Gas turbine technology has improved, but it's more costly in capital & maintenance. Regardless, if you want reliable backup and your market provides the economics to support it, you're going to be going with some form of combustion engine-driven generating plant. Solar energy works pretty well in a thermal application -- that is, for heating water and living space. Electrical power generation from solar energy is an entirely different matter. It can be used to generate electrical energy via photovoltaic conversion, as long as one is willing to accept conversion losses on the order of 90%. Even if such losses are acceptable, you still can only collect and store enough energy to operate things like radios, stereos, and high-efficiency lighting (e.g., fluorescent or metal halide vapor lamps; forget about incandescent -- thermal losses are too high). But if you want to do a lot of intensive usage (e.g., air conditioning, electrical appliances, power tools), you're not going to be able to run that kind of stuff using photovoltaic conversion without prohibitive equipment & maintenance costs. The cost in lead-acid storage batteries alone would eat you alive -- assuming you even wanted to have that much hazardous stuff lying around. I sympathize with the hopes of solar energy enthusiasts, but they would perhaps be better served by a somewhat more realistic appraisal of the ability of solar-powered infrastructure. As a source of large-scale, intensive, reliable power generation, solar/photovoltaic conversion is more mythology than technology. Consider the physical constraints. The maximum terrestrial incident power flux of solar radiation is ~1 kW per square meter when the sun is directly overhead and is unobstructed. The sun's output imposes that physical limitation, given the radius of Earth's orbit, and there isn't much we can (or should) do about it. Perhaps some concrete examples will help to illustrate how that limitation affects our ability to use the sun as a practical source of electrical energy. To convert the incident solar power to energy, multiply by the amount of time that the 1 kWh/m^2 condition is in effect. First, you must account for the seasons. The maximum solar collection time that you can squeeze out is 12 hours per day, twice per year... if your latitude is somewhere between the two tropics. The rest of the year you have considerably less daylight, and more atmospheric interference as the sun's path drops to the horizon seasonally, so on average you have maybe 10 hours of usable sunlight per day, under ideal conditions. If your location is between one of the tropics and the nearest pole, it goes downhill from there. Now you must also account for the daily rotation of the Earth. Even under the best of conditions (desert, during the summer, with no cloud cover), you have that condition for maybe one hour before plus one hour after the sun is at zenith. Of course, the sun isn't directly overhead for the other 22 hours in the day, but let's say that you can devise some complicated tracking mechanism to keep the perpendicular axis of your solar collector(s) always pointed directly at the sun. However, the average incident power won't be the full 1 kW/m^2 for the entire 10 hours. Call it 0.70 -- again being generous. That gives you ~0.7 kW/m^2 x 10 hr/day = 0.7 kW-hours/m^2/day of incident solar energy. Assume that you fill the entire 1-meter area with photovoltaic cells and capture all the incident energy. With a conversion efficiency of ~10% (that's typical of current technology), here's your maximum electrical generating capacity, under ideal conditions: Now, since we've already accounted for the seasons in our average daily capacity, we can annualize that capacity: 0.07 kW-hours/m^2/day x 365 days/year = 25.55 kWh/m^2/year Now, compare that capacity to the energy-intensive sources that we typically find in fossil-powered electrical generating technology. That's how Southern California Edison generates most of its power... by burning fuel oil or coal, so for comparison, the same capacity can be converted to the equivalent amount of fuel oil or coal: Fuel Oil: Anthracite Coal:My average annual usage over the last 36-month period is 20,385 kWh. Allowing for peak usage months, and based on my existing 0.25-acre lot size, I could replace the energy I'm currently getting from the grid if I were to cover 98% of my property with photovoltaic cells... if I had ideal conditions, and the money to spend on such things, and the desire to live amidst that sort of ugly junk, and the inclination to spend my time or my money servicing/maintaining such a preposterous facility. I don't. Most people don't. More to the point, neither do the most vocally active "public figures" who advocate the mythology of "soft energy" technology, and mislead others to believe that such technologies are feasible. I find the idea of energy self-sufficiency attractive as a means of sustaining oneself when living in a remote location, but even then, I would require a small generating plant if I wanted to maintain the quality of life that I currently enjoy. The maximum conversion efficiency attainable with current non-nuclear technology is approximately 50%, provided by high-speed gas-fired turbines. I suppose that when they can be made reliable enough and can be mass-produced cheaply enough, it would be feasible for individuals to own them. Nevertheless, such a decentralized system would sacrifice the economies provided by large-scale, centralized power generation and distribution. As long as we rely on combustion-based technologies, we might as well minimize the combustion by-products via economies of scale. I should think that would be an article of faith among anyone who is concerned with global warming (I'm not). Of course, the longer-term solution is to drop our reliance on combustion-based technologies altogether. We have the capability to do that safely right now, but (sigh) I'm not inclined to pursue such a controversial subject in this forum... and besides, the content of this post has probably wandered too far off-topic for this list as it is... PVG |