Generating electricity
 

Not being very knowledgeable in the subject I will ask the experts. Would it be economically feasible to generate enough electricity for a small house in the Houston area using the earth as a heat sink and solar panels as a heat source with propane as the transfer medium. A piston type motor would drive the generator.

You need you a Gererator.

No idea - sounds pretty experimental, yes? Solar PV panels and solar water heating, that would be the proven technology.

Not sure what you're getting at. Are you talking about heat transfer of fluid? How would the piston move? Look up on wikipedia and search for gas refrigerator and tell us if that is what you're thinking about. I wouldn't use propane for a transfer fluid for anything.

"generate enough electricity for a small house in the Houston area"

No. Unless you plan to suffer along w/o a/c. People survived that way long ago - does not mean it is fun.

You could put up a bunch of PV panels, collect a govt. subsidy to help w/the cost; feel good about it; and sell to the elec. co. or keep the watts on site... it would likely be "booster power" not handle all your needs.

that would help quite a bit but not pay for itself over 10, or even 20 years.

Now if you wait 10 years, we will likely have some nice cheap PV panels out there... it's all relative.

Operation
 

The solar panel would vaporize the propane and the increased volume would drive the piston motor thereby driving the generator. The motor would exhaust the gas and the gas would be pushed into the earth cooling piping to condense the vapor back into a liquid. There would be a check valve to force the flow in one direction.

You'd want a series of successively smaller pistons to claim the rest of the enthalpy.

Re.: Operation
 

I believe the mechanical operation will work. I have read the earth has a constant temperature below a certain number of feet and all of this varies with the area of the country. Around Houston it is supposed to be some were about 55-60 degrees below 4-5 feet but I am not sure.The information I am lacking is the amount of piping in the earth to condense the vapor continually and the amount of solar panel area to absorb the required BTU. The propane would be at the required vapor pressure to operate within this temperature range.

Re: Hugh R - the would work like steam engines with variable diameter pistons for the same reason.

Texas certainly does have a good environment for solar more...http://www.seco.cpa.state.tx.us/re_solar.htm

...but you need lots of area and lots of equipment.

Yeah, if you want to use something really dangerous, like propane, why not just go for anhydrous ammonia? That's what commercial refrigerator used to use, they may still.

Propane - dangerous
Propane would be dangerous to use in a home or car AC due to the location of an ignition source but this system would be away from any ignition source and I do not think there would be that great of volume. It is also cheap and plentiful (relatively speaking).

which begs the question; why not just burn it for energy?

RE: The propane would be used much like a refrigerant, it would not be burned.

Depends on your definition of "enough electricity." With no modern appliances, you may barely make the mark.

I ran the numbers for using a small Lister diesel engine, biodiesel, and a generator for making electricity. The expense, complexity, and labor lost out to grid power at 11 cents/KW. I also considered buying an outhouse and diesel fired boiler to heat water and my home. Despite cost savings using homebrew biodiesel, it still could not match the cost of natural gas.

Sure, if I was off-the-grid, it would be more attractive, but I was faced with sacrificing time for no cost savings. Hard to justify the investment with infinite payback time.

The problem I see with your idea is you'd need significant pressure to move that piston. Or, you could make the piston larger, but then you'd need more vapor. More vapor = more solar panels. Your theory is very similar to solar vacuum tubes used for water heating. The tubes are placed under vacuum to minimize heat loss and increase efficiency. The medium is vaporized by the heat of the sun. The vapor rises and condenses on a manifold at the end of the tube. That heat is eventually transferred to water. Solar water heating should receive greater focus in America. It's proven, efficient, and can immediately reduce energy usage, particularly in the sunny Southern US.

Just tap in before the meter

I was curious about geothermal heating and cooling, so I did a little research (I did say 'a little'). I saw/heard/read someplace that Houston would be a hard place to manage it because of the heat. I know that my tap water comes out of the ground at over 80* during the summer. I think you'd need a lot of pipe, and it would have to be fairly deep.

100 ballons and flannel shirts.

My understanding is that you would use the 55-60 deg-F earth has a huge heat sink. In a normal A/C unit you have to compress the freon, this is where most of the energy cost comes from. If you install a bunch of underground piping that is filled with water or air you can move this air or water for a much lower cost than compressing refrigerant. No propane needed just air or water.

and a lot of land

But as far as generating electricity I would think you do not have enough of a temperature different to drive a turbine or piston type engine

Yep. That's where the low hanging fruit is.

But, why listen to engineers, when fantasy greeners are pitching better intent. :rolleyes:

"I will ask the experts"

you know, I think you should ask your local utility. They will likely tell you 'noo' as per above posts, but at least that will indicate some interest in this for them to log into their files...

In 10, maybe even 5 years, it could be a go.

Nobody accused you of being ridiculously optimistic, lately?

cel, checking vapor pressure chart for propane, there is no way you're going to condense the propane. Propane boils above -44 degrees F. Instead of a piston engine, you could use an air-driven pump (sort of like a air grinder or polisher, except much larger). At ground temp of 60 degrees, propane would be 90 psi. Your solar panels would heat to at least 110 degrees, giving you over 200 psi. Use that pressure differential to move the air-pump.

I still think you're looney, but you are thinking outside the box.

PV cells are chips - and not even highly complex ones - it is the conversion & power handling that are the issues here. You can look at the rates of progress in "computer" chips for an inkling of what will happen.

Add in the same subsidies that oil & coal get are you there even sooner.

You should probably contact David Heymann... if he knew how to do this...

http://www.snopes.com/politics/bush/house.asp

...me might know how to make your idea happen.

The answer is yes, but you would want to use a Sterling cycle, not a brayton or otto cycle which require compression. The "problem" is that the temperature difference is not great in Houston between your source and sink, so your collector and sink would need to be huge.

Never could figure out the old Sterling Fan I have, you use heat to keep you cool??:rolleyes:

But does it cycle? :cool:

PV cells are made from silicon ingots similar to other semiconductors, although lower quality. Only a few companies make the ingots, and they were slow to invest the hundreds of millions required to increase production. For the past few years, supply has been tight and this has supported the price of PV cells. Supply is now coming online and silicon wafer prices are falling steeply. As are PV prices. The other big cost in PV manufacture is the capital equipment, which is something like a semiconductor fab though simpler. Here too supply is increasing, as fabs become obsolete they or the equipment in them can be repurposed for PV cell production. I expect PV prices will fall by 50 pct in a few years. With even modest efficiency increases, the PV cell portion of a PV system's cost should decline, in $/watt terms, by over half in the next few years. Installation and inverter costs are slower to fall, but there are lots of under-employed residential construction workers out there.

$1.70 per watt, FOB Shanghai, is what I've been quoted, recently. I'm working with some people on reducing the cost of the inverter, by about 50%, and make it more efficient in the process. I expect that PV is going to be cost effective shortly.