Osmotic power source from salt + fresh water?
http://www.aftenposten.no/english/local/article2027794.ece
"According to Statkraft, their PRO (pressure retarded osmosis) power plant generates power in a process "similar to a reverse osmosis desalination plant running backwards".
The plant uses seawater and fresh water separated by a membrane. The fresh water creates pressure as it enters the seawater via the membrane and this pressure is converted to energy."
This is pretty cool. It seems feasible. Brackish mixed water would have a lower free energy than the original salt + fresh water, and there should be a way to make an engine to extract that energy. I wonder how it works, and how much energy* can be extracted? I can imagine either slow pistons or some kind of ionic electrical power generator.
The downside, I guess, is that you're ruining good fresh water by mixing it with seawater. But if you've got a river of fresh water pouring into the ocean anyway, why not make a little energy off it first?
*Aha! here we go.
http://www.ese.iitb.ac.in/aer2006_files/papers/157.pdf
Apparently 300-400 watts per square meter of membrane surface is possible, assuming you start out with a concentrated salty brine. Compare to ~200 watts per square meter for a good solar cell in bright sunshine. It's not bad, especially if you have a ready source of brine and can manufacture the membrane at lower cost than solar cells.
4-6 watts per square meter starting with ordinary seawater. Not so great, but potentially viable depending on membrane cost and lifetime.
I wonder if you could make a closed-cycle osmotic power plant using solar or other heat to distill the brackish water back to brine and fresh water again.
"According to Statkraft, their PRO (pressure retarded osmosis) power plant generates power in a process "similar to a reverse osmosis desalination plant running backwards".
The plant uses seawater and fresh water separated by a membrane. The fresh water creates pressure as it enters the seawater via the membrane and this pressure is converted to energy."
This is pretty cool. It seems feasible. Brackish mixed water would have a lower free energy than the original salt + fresh water, and there should be a way to make an engine to extract that energy. I wonder how it works, and how much energy* can be extracted? I can imagine either slow pistons or some kind of ionic electrical power generator.
The downside, I guess, is that you're ruining good fresh water by mixing it with seawater. But if you've got a river of fresh water pouring into the ocean anyway, why not make a little energy off it first?
*Aha! here we go.
http://www.ese.iitb.ac.in/aer2006_files/papers/157.pdf
Apparently 300-400 watts per square meter of membrane surface is possible, assuming you start out with a concentrated salty brine. Compare to ~200 watts per square meter for a good solar cell in bright sunshine. It's not bad, especially if you have a ready source of brine and can manufacture the membrane at lower cost than solar cells.
4-6 watts per square meter starting with ordinary seawater. Not so great, but potentially viable depending on membrane cost and lifetime.
I wonder if you could make a closed-cycle osmotic power plant using solar or other heat to distill the brackish water back to brine and fresh water again.