Where does the heat go?  I can imagine using a refrigeration cycle to transfer a high amount of heat to air, which may be the purpose of the Kalina cycle but doesn't sound like it from your description.  In order to generate energy you need a heat source (nuclear material, geothermal, burning coal, etc.) and a heat sink (evaporating water, exchanging cold water with oceans, etc.).  You describe the heat source (difference in temperature of water from ground) but not the heat sink.

This issue resurfaces periodically but I don't understand why this is any real problem. Power plants do not "use" water in the sense that it becomes unavailable. The water is merely a mechanism to transfer heat to the environment. That total heat is insignificant in the big picture. If a lake, river, or ocean is used for cooling, the water if very slightly warmer. If a cooling tower is used, a certain amount of the water is evaporated faster than it ordinarily would be.

If this is considered to be a real problem, dry condenser power plants are already in use. In these plants, a closed condenser (like the radiator in a car) is used to directly transfer the heat to the air. The cost is slightly higher and the efficiency slightly lower, but there is no technical challenge at all.

No water use.  Another big advantage.

Hydro electric storage for wind and solar can even help restore wetlands and aquifers by capturing flood waters.

http://amazngdrx.blogharbor.com/blog

All:  You can always air-cool a steam cycle (e.g., all coal plants, nuke plants and combined cycle gas plants), but remember that your air temps are going to be higher than your water temps, especially in the summer time when you can have a spread of 30+ degrees.  This means that you have to raise the exhaust pressure from the steam to maintain a sufficient temperature differential to condense, and therefore drop the efficiency of the power plant.  For economic reasons, this drives most to water-cooled plants.  For environmental reasons, we ought not advocate solutions that drive down operating efficiency.  

The beauty of a cogen plant is that you "square this circle" by using a local building/factory/etc as your condenser, thereby eliminating this penalty.  (Or at least substantially reducing.)  

And yes, you don't have to worry about this at all with wind & solar - or, for that matter, simple cycle gas turbines, stirling engines and a host of other techs.

Both carbon intensive and nuclear fuel costal power plants can recapture much of that lost energy and produce fresh water at the same time by cogenerating with multistage flash distillation plants. Aquatic heating is minimized and increased salinity is only a minimal local issue.

L.A. should loose some of its water rights to other people's water and they could do it.

Potable city water offers a free heat sink.  Who needs cold water except those few who still drink from the tap?  Warm water for showers, clothes washing, etc. would reduce domestic water heating bills.  City water supply is transported through uninsulated ground coupled buried pipes.  An enormous amount of heat dumped into city water supply and water towers would become a free geothermal heat sink while, at the same time, heat up domestic water a few degrees.  As Sean wrote, industrial process heat is also a negative cost heat sink.  This makes solar power from cogeneration cheaper than dedicated solar power plants isolated in the desert with large and expensive dry heat rejectors.

I think the idea here is we need closed loop cooling systems instead of using raw water and discharging it.  Some studies seem to hint that thermal pollution of the Hudson River and Long Island Sound could be as much 0.5 degrees per year, although taken together with global warming and other confounders.  Seemed like the average power plant used at least 300,000 gallons of water a day.  Refineries can use more, since water is also used to distill product in distillation columns and pump product in pipelines (and becomes contaminated).  Thermal pollution is wave of the future, mon, and we need to do something about it quick.  /sam

Onward through the fog