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330 messages, Last post on Nov 13, 2008 at 12:13 PM
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Replying to: lightminer (Mar 04, 2007 11:03 pm) This in answer to " You can't compare generating power at the 80 - 300 hp level to the efficiencies you can get at 100 - 600,000 kW! Any comparison is really just laughable when you get all the facts on that one. " Sure you can, a thermal plant at the level of 500MW depending on equipment runs 31-33% efficiency. My source is somewhat dated from the Yorkshire Electricity Generating Board. But it also relects night time running at 5% load when the magnetising current of the distribution system has to be maintained. Most of the auxiliaries like boiler feedwater pumps and furnace blowers have consumption that is load independent. An Otto cycle engine gets close to 36% at full load and a diesel 44%. That's two years of study in thermodynamics. The power companies have a vested interest in a captive load of vunerable consumers which is very lucrative. What residential consumers should be doing is to burn natural gas in a reciprocating engine about 10HP should do it rather than in a gas furnace. This will yield 15kw of waste heat which can be used for space heating. Ever wonder why power stations are built by lakes rivers oceans ? That's right, to dissipate the 70% of thermal energy they have no use for. Cheaper than cooling towers. Of course steam turbines can be scaled up to 500mw LEVELS MORE easily than positive displacement reciprocators but to the small user at the wrong end of a monopoly this is of small consequence. GM should have retained the EV-1, battery boxes could have been insulated for sales to those of us in the north. Also a knowledge of hi-power electronics is key to the evolution of the automobile is another reason. Toyota is probably the largest manufacturer of electronic servo drives purely by producing the Prius. I am expecting Toyota to use its expertise in this area to challenge pricepoints established by suppliers to the industrial market one of these days. T2 |
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Replying to: toyolla2 (Mar 05, 2007 11:56 am) Wouldn't this entail using a battery storage system so the generator doesn't have to run constantly? AFter all refrigerators click on and off. Also what about the months when excess heat is not needed? Is all this practical? Both in terms of expemse and how a mechanical failure would leave you out in the cold, so to speak. Seems to me some good old yankee ingenuity could capture a lot of this energy at the power plant source.
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Replying to: reddroverr (Mar 05, 2007 5:00 pm) I agree completely and that is exactly what's going on. The newer coal powerplants operate at close to 40% efficiency and that is going up. These gains are being achieved by recapturing the lost heat and figuring out how to use it. Also, efficiency is only one variable in the equation. Even if a diesel engine can operate at 44% efficiency that doesn't make it better if diesel fuel costs twice as much as coal. |
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Replying to: reddroverr (Mar 05, 2007 5:00 pm) Yes, but not at the 21kw level of the HV battery in the Prius. I would envisage a system similar to that adopted by the photovoltaic panel industry with an intermediary 24 volt lead acid accumulator. In practice the variable output voltage from a variable speed alternator genset would feed into a controller which would maintain a float charge on that battery storage. A crystal locked oscillator - needed to support those consumer appliances with line frequency derived digital clocks - would then feed a single phase inverter of around 7kw capacity. Then "good old yankee ingenuity", as you like to put it, could determine a control strategy to minimise generator startups. You get one chance to use the exergy of natural gas and if you are going to consume it, an engine is a better solution than an open flame. Natural gas distribution to the home is already in place so it has a higher exergy than diesel or home heating oil which would need to be delivered. My suggestion is that we should build on that legacy infrastructure. "what about the months when excess heat is not needed? " You have a good point, this scheme doesn't have quite the efficacy in summer, but that is no reason to discount the "free" home heating that is available in winter if we so choose to 'roll our own' electricity at that time. Our engine would also need the ability to run on propane, to keep the gas company in check, after all with governments that continually roll over on the pricing of staple commodities we have to remember that we live in a capitalistic society that loves monopolies. As for possible mechanical failures we have tens of thousands of homes without power for a day or two already this winter because our distribution system is proving to be extremely vulnerable to storms, more so than I can ever remember as this particular infrastructure continues to age. Underground gas piping has the advantage of avoiding large transient swings in temperature and the debilitating effects of solar exposure suffered by the overhead installations of the electrical system. This winter I personally have experienced a two hour electrical outage but with gas I have to go back about ten years and that service interruption was pre- announced with a flyer ! Maybe in future the power plant could recapture more energy but in the meantime I like "free". The relevance to the thread is that in winter the waste heat from your residential generator being used at night to recharge your PHEV, would be heating your house. It's as if all that heat blown to the elements from a normal car radiator could be utilised in your home instead. T2 |
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Replying to: toyolla2 (Mar 05, 2007 11:56 am) To discuss 'efficiency' we'd have to be in the same room - I also have around 2 yrs thermo behind me in college and most of the discussion would be symantics - once those are all worked out we could make statements and we would probably agree. (Some examples are do we include transportation costs for the fuels, do you compare natural gas in a plant generating electricity for an EV to natural gas in a vehicle and which goes farther as one question as which has higher emissions as a second question - that would really be the only way to compare efficiency, can't put coal in a car  - so comparing the theoretical energy (enthalpy? Gibbs free energy? we don't even know which energy...) of a brick of coal compared to what gets done with gas, etc. - it goes on forever about what exactly are we talking about and I wouldn't be interested in that online) - For those reading and interested in practical aspects of the subject I would send them to: http://en.wikipedia.org/wiki/Fossil_fuel_power_plant this is a great overview of the situation with current generation, efficiencies, etc. Oh - and at Stanford we do exactly what you mention above to some degree - there is a great cogeneration facility where the excess steam is pumped underground and does all the heating for the dorms. I agree completely! For a side project in a thermo class I actually modelled how efficient we could make a plant if we had 5 additional power plants using the temp differential of the effluent stream from the previous plants. It was fun! Of course only the first additional power plant would be even remotely cost efficient to build... But that fifth one did get power!
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Replying to: lightminer (Mar 06, 2007 1:35 pm) Large diameter pipes carrying steam at up to 1000 F pressurized to 3000 psi absolutely boggle my mind. Then I have read about transformers exploding without warning and spewing hot oil on workers. The facts in the Wikipedia entry make my head spin. I am resolved to reduce use. For residental water heating we replaced our tank with a gas fired, minimally sized, tankless water heater and use it sparingly. I should have put in a solar set-up with storage tank using a tankless as backup, but I wouldn't go for the upfront cost. We are actually nore intent on reducing our consumption of city water than our energy use which is already pretty low. The City of Dallas wants to dam-up the last remaining free flowing rivers to allow its citizens to water turfgrass lawns. |
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That was the headline, Tues March 6th, on our community newspaper. Apparently 15 power line poles toppled in our neighbourhood during last Thursdays ice storm. There were pix of the activities of our electric utility coming to the rescue with a giant web of some of the tallest "cherrypickers" I've seen. Quite a demonstration. Even so 12 businesses didn't get power back until Sunday it says.The story goes on to quote the Mayor that the new civic admin building - currently under construction - will be equipped with backup generators. I guess he's right, you can't have government come to a halt just because the whole area might get destroyed. Hell no, there might be some rebellious cinders ! Central distribution of electrical energy is an idea that should have come and gone. For those millions of homes that have a natural gas supply the the residential equipment needed for conversion into electricity is many times less complex than a laptop and only slightly more complex than a lawn tractor. Posters contributing here are contemplating connecting up thousands of grid fed PHEVs. On the first outage thousands of vehicles will be out looking to top up their tanks but how many gas stations have the necessary standby apparatus also ? That's why I think you have to go through to residential cogeneration if energy security is to be realized with PHEVs. T2
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Replying to: toyolla2 (Mar 07, 2007 7:19 am)
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Replying to: toyolla2 (Mar 05, 2007 11:56 am) The power companies have a vested interest in a captive load of vunerable consumers which is very lucrative. What residential consumers should be doing is to burn natural gas in a reciprocating engine about 10HP should do it rather than in a gas furnace. This will yield 15kw of waste heat which can be used for space heating. I assume you envision a liquid cooled, spark ignition engine driving a generator. Sounds expensive, but isn't everything? Would there be a noise problem if all the houses in a residential neighborhood of 10,000 sq ft lots had this set-up? Is anything like this currently available?
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Replying to: jim314 (Mar 07, 2007 11:38 am) |
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