On Fri, 4 Oct 2002 13:54:47 -0500, Dan Minette wrote: >Well, it would be very hard to believe. Lets look at some numbers. The >general efficiency of an internal combustion engine is given in >http://ecen.com/content/eee7/motoref.htm >at around 40%. The initial efficiency of a big power plant goes up to >about 60% >http://www.ecoling.ch/englisch/thermal_power_plant.htm
I am not sure how you could have attempted to reach a conclusive efficiency number by this method. It is an extremely complex calculation and then only valid in the particular case that you analyze. Your efficiency number for internal combustion engines above is based on extrapolated data taken prior to 1975. It is also an analysis of efficiency IMPROVEMENT and does not necessarily reflect the efficiency of converting btu's to usable work. I will also note that this was a Brazilian web page and that Brazil gets I think at least 75% of its energy from hydroelectric :) (I only point this out to note that the situation will be different in every locale). Anyhoo, here is one that says the IC engine is 20% efficient. http://ffden-2.phys.uaf.edu/102spring2002_Web_projects/Z.Yates/Zach's%20 Web%20Project%20Folder/EICE%20-%20Main.htm This one gives 26% thermal efficiency and doesn't give a number for mechanical efficiency(which would make it even lower) http://www.auto-ware.com/combust_bytes/eng_sci.htm I am not trying to prove you wrong here, I am just trying to show you that there is not much agreement on precise numbers and you can't write off a potentially beneficial technology based on a back of the napkin calculation As this last web site states: "The four stroke engine is the backbone of the automotive and racing industries. Yet the basic scientific concepts of volumetric efficiency, thermal efficiency and mechanical efficiency and how they relate to engine performance is not well known." >So, the electricity that gets to the pumps that compress the air is about >30%. I am not sure where you are getting 50% transmission loss. It may be valid in some but not in all cases. I would bet that it represents close to a worst case. If you wish to compare to natural gas plants, you should note that most are located near urban centers and will suffer less transmission loss to wherever these cars are being fueled. I can not find a source of easily interpreted data on transmission loss right now. Maybe you can. >so a generous efficiency is probably 80% for the compressor itself. , we are >down under 25% by the time the air is in the car. Assuming 90% in the car I'll buy that >, and we are close to >20%. So, for rough numbers, we are talking around > 20% efficiency. I can play with numbers here too. If I reduce the transmission loss number to 30% the air car becomes 30% by your method. Also, the option is now in the fleet owners hands to have a power plant on site using whatever generation method appears feasible. This is also an apple and oranges comparison. Gasoline powered IC and gas vapour turbines use different fuel sources with different extraction, delivery and processing costs. >1) Electrical power will not just be used for air conditioning. I'm not >totally unfamiliar with Africa, BTW. I think I remarked here that I have >an African "daughter" from Zambia (her church is a mission partner with our >church and we're her home in the 'States while she goes to school nearby). >Most people are not at the point where the incremental use of electricity >will be AC. The per capita use is very low, and they will be able to use >up all of their remaining hydro capacity without massive use of AC. I was oversimplifying about AC. You probably also know that the photovoltaic industry is booming in Africa as there is many places where the grid has yet to reach. But, if their transportation needs are met, and they have a steady supply of cheap fuel, they may have little need to change. >2) Addition commutes. That is to say it doesn't matter what order the >consumption comes on line. So, if the additional use for purposes other >than transport is greater or equal than the additional capacity available >from non fossil fuel sources, then it is fair to say that the use of these >cars will result in additional use of fossil fuels, no matter what the >temporal sequence is. It is not fair to say that unless we have determined that they are less efficient than IC (you have not convinced me yet :) or it is an additional transportation service. >3) Air quality is cities is a different question than consumption of fossil >fuels. It may very well be reasonable to use more fossil fuels to have >cleaner air. >The US does this by having pollution control equipment on >autos. They both decrease the fuel efficiency of the cars and >significantly reduce pollution. I don't follow you here. Burning more fossil fuels, whether they are emitted either way will not result in cleaner air than burning less fossil fuels. >I never really argued for a step function. Aren't these vehicles >compressed air? My guess is that fuel cells would be a more likely source >for electric cars. That may be feasible. Among other things, they don't >have the transmission loss problem associated with a car that is "refueled" >at home. The car doesn't have to be refueled at home. First applications will likely be fleet operators. They could have diesel or propane powered compressors at their base, eliminating the electrical link all together. Public filling stations could also be configured the same way. >That's perfectly valid. I have no problem with that. I do have a problem >with the sales pitch for these vehicles that includes false statements. >The reality is that the use of zero emission vehicles will result in lower >energy efficiency. I looked at the article originally posted here and it makes no claims to its efficiency other than the 1 cent/km figure. I assume this is based on current costs of electricity and an efficient compressor. If this figure is correct, it indicates one or more of the following. 1. It is very efficient 2. power generation is very efficient or heavily subsidized 3. gasoline costs are expensive or over-inflated. The Fool made no claims as to its efficiency either and only suggested a shift in fuel sources would be opposed by the fossil fuel industries. Also, I don't agree with you that they are notably less efficient. >You could argue that they are lighter, and will thus be more efficient. >However, the power source has, historically, actually been heavier for >comparable output. The fact that a small electric vehicle is more >efficient than an 8 passenger SUV isn't really relevant. A small gas >powered car is still more efficient; but people want the big cars. They want the big cars in the US and Canada because fuel costs are low. Most of the rest of the world drives smaller cars (or scooters or bicycles) because fuel is too expensive. Actually, everyone WANTS big cars but sometimes they just aren't practicle. >>, it may make Houston smell better. :) > >Actually, not. Houston smells the way it does because of the petrochemical >industry. It will make _Houston_ smell worse, because there will be >greater output at the petrochemical plants. I'll retract that then. It was a poor attempt at a light hearted tie-back to a recent thread. Criteria smog pollutants have little odor. I have never been to Houston and have no idea what it smells like. >>politicians. Wind has no immediate large profit potential, as did, or >>does, nuclear, in an economy with an established oil and coal >>infrastructure. >Huh? Any type of plant can plug into the infrastructure. The >infrastructure is the transmission lines. Which has limited capacity at many sites ideal for expansion of wind power. Actually, I was referring to the fuel supply side. The mines, wells, transportation and processing industries are in place, running efficiently and cheap. Alternatives require a very large investment up front and do nothing for local economies that rely on these industries. >>Wind has been far less subsidized than nuclear and has been growing at a >>phenomenal rate over the past 10 or so years. >Actually, not. Wind energy now gets a 1c per kwhour subsidy. Nuclear gets >nothing like that. 1.7c/Kwh I believe. However, wind power subsidies will most likely be removed in the next couple of years as it has been proven to be self sustainable. Meanwhile they will be building a $58b wine cellar at Yucca Mountain. I can't find any numbers for nuclear right now. Alot of the current subsidy appears to be clouded in insurance and risk assumed by the government. I'll adjust my statement by saying that large scale wind power is relatively new and has been far less subsidized than nuclear over its history or at a similar stage in its development. >>Worldwide wind energy output doubling every 3 years or something like >>that. >Well, it is politically popular and subsidized. I couldn't get world >figures, but at the present time it is 0.05% of the total energy supply. >At that level, subsidized wind farm construction can be better seen as >cheap political cover more than economically viability. I'll assume you meant 0.5% in the US. It is somewhere around there. Is it politically popular because it is what the people want? If it is, why not subsidize it more to get capacity up. >>However, for oil companies and politicians, everything is PR, right? :) > >No. Let me take a moment to point out that the oil industry has cut >overhead overwhelmingly over the last 20 years to significantly reduce the >price of oil. Even with the war scare raising prices to an artificially >high level, oil prices are about half of what they were 20 years ago in >inflation adjusted dollars. Indeed, one of the problems for other energy >suppliers is that the oil companies are extremely good at providing very >cheap energy. Agreed. the infrastructure is in place and the bugs have been worked out. >>>IMHO, articles such as this one shows the power of wishful thinking. >> >>What the air car offers is a clean energy storage option. > >If there is a tremendous demand for fuel cells, then wind power usage may >increase 100x in the next 30 years to 5% of energy usage. Large scale use >of wind power also suffers from the fact that there are few places with high >sustained winds. After those are "harvested," it will be hard to find other >good > Remember, wind power goes as v^3. Fuel cells will initially be powered by natural gas or other hydrocarbons. It is currently far too inefficient to liberate hydrogen from other sources using electricity. They will find applications, perhaps in vehicles with longer range or larger payload requirements. I think the first ones will be far too expensive though. >>This is the technology needed to make intermittent renewable like solar >and wind >>viable for transportation. >But with 20% efficiency? Now, if fuel cells can be made in an economically >feasible manner, then they might provide a good source of stored energy for >transportation. Then, we may see wind power climb into the few % of the >total energy budget. That would be a step forward. I have a feeling it will provide more opportunity for de-centralizing power generation and micro-griding using combinations of small gas turbine plants, wind and solar. Also a good strategy for a country worried about terrorist attacks. Let me clarify my position here. The only reason I got involved in this discussion is because I object to people using terms like "PR" and "wishful thinking" to immediately write off potentially beneficial technologies. I believe the subject deserves exploration. When I read about things like this I immediately set to thinking about its benefits and if beneficial, how it could be made viable. I'm not an engineer but I would like to play one on TV :). I don't have the time to get into a war of numbers or brain size here (I will concede on that one quite early:). You are welcome to prove the futility of this technology to me. I would consider you doing so a service to me. Dean _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
