Wednesday, December 17, 2008

Combat Global Warming with Evaporative Cooling

To combat global warming, wind turbines along the coastline could be used for the dual purposes of generating electricity at times when there is wind and evaporating water at times when there is no wind. Just a small breeze over the water can give the top water molecules enough kinetic energy to overcome their mutual attraction, resulting in evaporation of water and associated cooling of both water and air.

The evaporation will give some cooling effect, but the real impact on global warming will come from albedo change. When there's much wind at night, offshore wind turbines could produce more energy than is needed on the grid. Such surplus power could be stored and - at times when there's little wind - used to pump up sea water and have this sprayed by the turbines as a fine mist over the water. This spray will contain tiny particles of sea-salt that get sucked up into the air, especially when there's little wind and sunshine causes rising currents of air. These little salt particles will attract further droplets of water from the surrounding air, forming clouds that are lighter in color from space than sea water (see albedo comparison below, from Wikipedia).

In early 2006, I wondered to what extent such increased cloud coverage could mitigate global warming. On the one hand, the extra clouds will reflect more sunlight back into space, but on the other hand water vapor is itself a greenhouse gas. While the albedo difference between clouds and sea water is obvious, some of the evaporated water could rise higher up into the atmosphere and increase humidity of cirrus clouds at high
altitudes, thus trapping the heat underneath and heating up Earth even further through the greenhouse effect. Also, such evaporation could cause unwanted salty rain to fall over land.

Has anyone done any modeling on this?
Cheers! Sam Carana.


Sam Carana said...

I've discussed the evaporative cooling idea a bit more. Somebody mentioned the work of Ron Ace, as described at:

Others were concerned that such ideas will be used as excuses to continue the burning of fossil fuel, etc.

What worries me most is the possibility that Earth will start loosing hydrogen and oxygen to space, if we artificially increased humidity. I wrote about this danger at:

Sam Carana said...

Some people have asked me to explain how surplus energy from wind turbines could be stored.

There are many ways to store energy. There are flywheels, compressed air, molten salt, pumped-up water, hydrogen, car batteries, etc. Pumped-up water seems an obviously promising method. Surplus energy from wind turbines can first be used to pump up seawater and keep this seawater stored, either within the body of the wind turbine itself or within a separate water tower. At suitable weather conditions, gravity can then allow this water to be sprayed in front of the wind turbine, while gravity can also provide the energy needed to ensure that the seawater is spray out in the form of a fine mist, while the falling water could also power the rotor of the wind turbine to give this mist enough lift to rise high enough into the air to contribute to cloud formation.

As to car batteries, surplus electricity could be sold over the grid to charge spare capacity of car batteries, which becomes increasingly attractive with the rise of electric vehicles. As long as the vehicle doesn't need the energy, it could be attractive for the vehicle owner to sell the electricity back to the wind turbines when times are suitable to spray seawater into the air and power the turbines to allow this spray to go far and wide, and give it sufficient lift.

Another promising alternative is to use hydrogen. Surplus energy from wind turbines could - by means of electrolysis - turn seawater into hydrogen. The hydrogen could be stored as a gas in tanks next to the wind turbine - little or no compression of the hydrogen is needed, given that there is plenty of room for a large tank next to the wind turbine. A fuel cell next to the tank could - at suitable times - turn the hydrogen into electricity, powering the wind turbine, while pumping up seawater and spraying this in front of the rotor.

The latter method could also ensure that there is a steady supply of hydrogen, which could be used to power ships and boats - quite frankly, I see no better way to power ships and boats that travel long distances. It makes sense for offshore wind turbines to store surplus energy in the form of hydrogen and allow ships and boats - at commercial prices - to take such hydrogen on board. From there, it's a small step to use spare hydrogen to spray seawater when weather conditions are suitable.

I accept that there are other ways to spray seawater into the air, such as vortex towers. However, it is in the end a matter of what is the most economic way to do this. If surplus energy from wind turbines otherwise goes to waste, while wind turbines remain idle periodically, then there will be little cost involved in using this surplus energy to make the wind turbines spray seawater into the air.

In conclusion, I do not see engineering problems in making this work, but I suggest that each such method be explored further, to find out what the most economic approach is.

For now, the question is whether there will be a net benefit in regard to global warming. Clearly, this method will allow some latent energy to be carried into the sky, and some of that energy will be radiated into space. But the big question is: will the albedo change - as a result of increased cloud coverage - outweigh the greenhouse effect of water vapor.

Sam Carana