On Fri, Sep 23, 2005 at 11:08:33PM +0300, Peter wrote: > > Oops, the previous message went out unfinished and uncut. Wrong key. > Sorry. Here is the sequel: > > Water requires about 2.2 MJ/kg to boil. There is no way around that. If you > think of the engine in terms of mass flow, it takes about 0.05 kg of fuel > to boil a kg of water in an unspecified amount of time. It also takes a 1 > meter m^2 I presume? 0.05 kg of which fuel? Each delivers is different amount of energy per unit. Natural Gas: 105.5 MJ/therm Electricity: 3413 MJ/kWh liquid propane has its own value. > mirror in full sun (1kW) about 37 minutes to boil the same amount of > water (assuming no losses in either case). > > So 1 sq. meter of mirror used for an hour will equal ~0.03 kg of fuel > (about 1 oz). You can take this as a base for cost calculations I think. I > don't think that mirror life can be counted on to be longer than 2 years. With the mylar sheet on the form I referred to before the replacement cost are minimal. Also James pointed out a stability issue. There's no reason such a plant simply could not be housed to minimize wind effects. Clear polycarbonate panels are inexpesive and sturdy. > With 200 days of sun/year and 8 hours of usable sun/day = 3200 mirror hours > (not so bad). The fuel equivalent is 96 kg (~36 gallons at density 0.7). At > $2.6/gal ~= $94. Say $100. The equivalent in heating costs is probably half > that. This does not take into account system losses for the sun system, > which are going to be huge. All true. However you are missing the point that the engine also serves as a heat sink. So it'll retain some of the previous heat energy that was previously captured. A huge thermal mass will assist in the process of heating the water. > So assuming the solar system efficiency is 50% (a good figure imho) Too good. > the equivalent gas price equivalent of a 1 sq. meter mirror for 200 sun > days/year, 2 years, and 8 hours/day is about $50 over 2 years. Again which gas? Is it possible for you to recalculate your figures in MJ? It's important because the cost of fuel is all over the place. My Natural Gas price has nearly doubled in a year's time, and it's likely that it'll start moving toward tripling depending on the damage of Hurricane Rita upon the refinery and distribution supply from East Texas. > If I read > heating costs correctly for USA the bills are about $150/month per > (small) house so $150/month in mirrors would be at least 81 square > meters of sun collectors (about half floor surface of the liveable part > of the house ?) not counting the storage arrangements. $150/month for electricity? At what time of the year? What rate plan? Dollars isn't a good measure here. Too variable. What I've been doing is converting everything to MJ. You also need to take those losses into effect. Here's an example: Last winter in December I used 160 therms of natural heating the house. Each therm produces 105.5 MJ. I'm going to be generous to my furnace and give it 70 percent efficiency (though at its age, it's really probably 65%). To equalize cost with electricity I have to know the equivalent number of kWh that matches up with those therms. Electricity generates 3.6 MJ per kWh. You can find such figures on pages like this: http://www.combust.com.au/tips/hottips.htm Electricity burns with 100% efficiency. So the equivalent amount I would need is 160(therms)*105.5(MJ/therm)*0.7/3.6(MJ/kWh) = 3282 kWh. Now we can talk price. And it's all over the place. Currently I'm at the end of a 12 month contract paying 0.88 USD/therm for Natural Gas. So that 160 therms right now costs $140.80. But today I'm choking on the price. Fixed rate prices for the next 12 months are averaging $2.50 a therm! So that same 160 therms would now cost me $400! See why you can't compute solely with costs. You need to know the energy requirement. Now onto electricity (which here in Georgia, USA is a regulated utility). The price per kWh depends on the time of year and time of day you use it. The Summer fixed rate is about 9 cents a kWh. However there is a time of use plan where the price is lowered for off peak usage, and raised very high during peak usage times. For example from 2-7PM M-F from June to September has a 19 cents/kWh charge! However in the winter, from October to May, any kWh after the first 650 only costs 5.1 cents/kWh with a fixed extra charge of 2.2 cents/kWh for the first 650. So let's compare with that number. 0.051$/kWh *3282 kWh = $167.38 + 650*0.022 (fixed charge) = $181.68 So the dollars are meaningless without the MJ behind them. You can see why I'm purchasing an electric furnace and having it installed. Also I just got an additional insulation estimate today. I hope I don't choke on it when I get it next week. I may have to blow it in myself. > > >How much is it going to cost? > >How much electricity can I get out of it? > > I don't think that a 10% efficient (with heat recovery and very high > temperature steam) steam engine is practicable in garage build mode, > even if using a burner with fossil fuel. > > I also think that using solar for heating makes a lot of sense but using > it for making electricity (at least via steam) is not a good > proposition. That didn't answer the questions. But let's take a stab at it. Full Sun is 1 kW/m^2. Say we get 5 percent efficiency. so we get 50W/m^2. A reasonable collect is about 3 m on a side. So we can collect 9 m^2 and concentrate it on the engine. So in full sun we can expect to get 450W of power. With 5 full sun hours per day the engine can produce 2.25 kWh of power per day. Anemic. Solar space heating is a much better bet. James, this is why efficiency is important. If we can get the efficiency up we can get useful power during the time that the sun is out. > I would think in terms of sun heat + heat storage for heating and > cooling (adsorbtion process) and co-generation for electricity, with the > extra heat from co-generation supplied to the sun system. The fuel for > co-generation will have to be fossil but may be supplemented with > vegetable oil, biogas etc. > > I think that efficient electricity generation is reserved for large > plants whoch can afford the hardware to maximize efficiency (I heard > 60+% is possible using diesel + steam turbine or gas turbine + steam > turbine). I'm looking at this because I know that next summer I'll be facing 19 cents/kWh costs at certain times. Any useful output I can get from solar during those times would help. My game plan there is to build a battery charge bank. I'll charge the batteries during off peak hours, and use that charge during peak hours. The off peak price is 2.5 cents cheaper than the regular price of electricity (6.5 cents/kWh vs. 9 cents/kWh) while the 19 cents/kWh is flat off the chain. Any solar electrical supplement would help. I'm wondering about concentrated solar onto a PV panel now. BAJ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist