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Old 12-18-2012, 10:54 PM   #1 (permalink)
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check my math?

someone wanna help check my idea?

So I wanted to try something but I had to put it on hold.

I enlisted in the military in navspecwar, and that obviously didn't pan out as of today so I have a lot more free time on my hands going forward. Thats what stopped me. Moving forward.

Alright so I want to go solar, not because I am concerned about the environment but because I wanted to save money and wanted grid independence. Solar is way too expensive to be a viable options right now. wind isn't really and geothermal is only an option for ground sourcing for HVAC. So I started looking for ways to get around it and do it myself instead of buying something.

If you're familair with solar concentration then you'll see I am not asking anything too weird...

The array is a series of mirrors(mylar) that direct the light onto a galvanized steel pipe. heat transfer fluid is oil(motor). I'm aiming for somewhere in the neighborhood of 350-400 degrees C. turbine working fluid is water(steam) at hopefully superheated conditions to avoid any turbine blade damage. Turbine itself is a car turbo. Found gears to spool the turbine down from its peak operating RPM down to 3500 rpm to run a generator. so far so good huh? Thats because none of that is anything new so I didn't get a chance to screw up yet :-).

Now we go off track.

Instead of venting the heat from the array into the air and losing some actual operational power, I want to vent the waste heat into another turbine. Not another water steam turbine. A gasoline(steam) turbine. So the heat exchanger for the water turbine dumps(closed deaerater) into the boiler of the gasoline(steam) turbine.

You might have a couple of questions at this point and thats reasonable... so ask away but any suggestions are massively helpful.

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Old 12-19-2012, 08:02 AM   #2 (permalink)
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You'd be better off buying a few solar panels.

What you are thinking of can be done, there are power plants that use this technology to generate power. However, its really not that simple. You're working with VERY hot things and VERY high pressures to get any real power out of it. This ends up meaning expensive components. Also, a turbo is going to be horribly inefficient at capturing that energy. Most likely less than a solar PV panel. Steam turbines usually have a large number of turbines to capture as much of the steam energy as they can. Here is an example:



Honestly, a much better idea is to head over to EcoRenovator and take a look at their 60+ energy saving tips list that is the equivalent of the 100+ hypermiling / 65+ ecomods lists we have here on EM. There is way more you can do on the conservation side before even considering generating your own power.
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Old 12-19-2012, 08:59 AM   #3 (permalink)
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Sounds like a good project, but electricity is only about 10c/kwh. A backup generator? Im all for it. Replacing the grid?...... good luck
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Old 12-19-2012, 09:55 AM   #4 (permalink)
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How long can a device like that run without needing attention?
Most solar panels have a 25 year warranty and pay for them selves in about 10 years, the warranty is based off their half life, so 50+ year life span meaning that the long term cost of electricity produced by solar is less then 2 cents per kwh and that is the installed cost, paying someone else to do all of the work.
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Old 12-27-2012, 03:13 PM   #5 (permalink)
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I'm with ya on generating some power from concentrating solar and producing steam. I wish there were cheap sterling engines. I think a car turbo wouldn't capture much energy. If you were looking for the math, take the following example...

Power = Work / Time

Work = Volumetric Flow * Pressure Drop ... so

Power = Volumetric Flow Rate * Pressure Drop

Example: Power is 283 watts = 0.028 (m^3/s or 1 ft^3/s) of steam * 10132.5 Pascals (10th of an atmosphere... so you raise the pressure in front of the turbine slightly less than 1.5 psi).

But don't let the man keep you down! Build it, I want to see pictures.
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Old 12-28-2012, 12:40 PM   #6 (permalink)
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I have 6 panels and 2 grid tie inverters, 3 panels each. I save 50 bucks a month in power or about 120 kilowatts.
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Old 12-28-2012, 01:57 PM   #7 (permalink)
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Quote:
Originally Posted by Cobb View Post
I have 6 panels and 2 grid tie inverters, 3 panels each. I save 50 bucks a month in power or about 120 kilowatts.
And there is a good chance that you will never have to touch that system for the rest of your life, it will just sit there quietly producing electricity for the next 50+ years, no adding water, no changing oil, no greasing bearings, nothing other then checking every few years to make sure everything is still on and there.
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Old 12-30-2012, 04:03 PM   #8 (permalink)
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While you're deciding on a primary, efficient DIY off-grid power supply, why not reduce dependence on the grid with the following:

Added insulation at key points throughout the house for better R-value.
Thermal barrier for the windows(my solution was $20 of office-grade bubble-wrap).
More insulation around water heater and pipes, along with a timer.
Build one or more solar thermal window units or a solar Thermal false wall-the easiest unit I have found consists of an old, large window, windowbox cut to size and filled with rows of soup cans painted black, PVC intake and outflow ports, wrapped conduit and window block, with one way valve on outflow to prevent heat losses at night. A false wall can be rendered inert in summer with an awning and window units can be disconnected and repurposed as food dehydrators, solar cookers and the like.
I have heard of designers reengineering horizontal freezers into super-effecient refrigerators-my budget and space hasn't allowed me to explore that option yet though, so I can't add personal testimony.

Get the house efficient enough and you won't need nearly as much of any power source for grid independence. BTW-are you near any sources of running water that don't dry up in the summer? The only option I didn't see listed above was Hydroelectric..
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Old 12-30-2012, 04:03 PM   #9 (permalink)
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While you're deciding on a primary, efficient DIY off-grid power supply, why not reduce dependence on the grid with the following:

Added insulation at key points throughout the house for better R-value.
Thermal barrier for the windows(my solution was $20 of office-grade bubble-wrap).
More insulation around water heater and pipes, along with a timer.
Build one or more solar thermal window units or a solar Thermal false wall-the easiest unit I have found consists of an old, large window, windowbox cut to size and filled with rows of soup cans painted black, PVC intake and outflow ports, wrapped conduit and window block, with one way valve on outflow to prevent heat losses at night. A false wall can be rendered inert in summer with an awning and window units can be disconnected and repurposed as food dehydrators, solar cookers and the like.
I have heard of designers reengineering horizontal freezers into super-effecient refrigerators-my budget and space hasn't allowed me to explore that option yet though, so I can't add personal testimony.

Get the house efficient enough and you won't need nearly as much of any power source for grid independence. BTW-are you near any sources of running water that don't dry up in the summer? The only option I didn't see listed above was Hydroelectric..
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Old 12-30-2012, 09:50 PM   #10 (permalink)
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Quote:
why not reduce dependence on the grid
That's what I did. I improved the efficiency of my house until my electric bills were typically less than $20 a month, or less than 100 kwh a month. Then I added photovoltaic panels to my house.

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