Then recently I was driving on I 380 between Waterloo and Cedar Rapids, and off to my right I noticed the white, puffy column of steam and hot air rising from cooling tower of the nuclear power station at Palo, Iowa. And I also noticed that the sky that day was nearly covered with white, puffy cumulus clouds that had occurred naturally.
The Palo Nuke has been there 40 years, and is Iowa’s first and only nuke, and the second powerhouse I ever helped to build. At full power, it produces just under 500 megawatts. And the steam cloud that rises from its cooling tower is about the size one expects from that size reactor. You see, for any given set of atmospheric conditions, there is a fixed relationship between the size of reactor and the size of the steam cloud. A nuke is a heat engine, and its efficiency limited by the Carnot equation. (Efficiency is equal to the absolute temperature of the heat source, minus the absolute temperature of the heat sink, all over the absolute temperature of the source.) Since there are limits to the maximum temperature that a steam turbine can withstand, and since a heat sink much colder than ambient air is unlikely, this means that in the real world, no more than about 40% of the heat energy can be harvested as mechanical power. The heat generated by the nuclear reaction produces steam, which flows through the turbine and is then condensed in a condenser cooled by water from the cooling tower. This coolant water absorbs heat from the waste steam and becomes warmer, only to be re-cooled as some of it is evaporated in the cooling tower. In the cooling tower, the warm coolant water flows over open slats, like a huge venetian blind, as ambient air is blown through it. Evaporation takes place, and that’s where most of the heat goes. In fact, except for the 40% of the original heat energy that is converted into mechanical power to drive the generator, nearly all of the heat is lost to evaporation. The more heat the nuclear reaction produces, the more heat removed by evaporation in the cooling tower, and the bigger the cloud produced.
I wrote that rather tedious paragraph to establish one point: In any heat engine large enough to have a cooling tower, you can tell the size of the heat source by the size of the cloud arising from the cooling tower. But the atmosphere is also a heat engine, and behaves by the same rules. As I have stated, on this day the entire sky was filled, from horizon to horizon, with cumulus clouds. And the solar energy required to boil moisture out of the ground to produce those clouds is precisely the same, for every gram of water, as the heat required at the Palo Nuke cooling tower. To evaporate a gram of water always takes precisely 540 calories. While the size of cloud produced for any level of power will vary from day to day because of local atmospheric conditions, both the power house and the cloud bank are using the same air on the same day. I stopped my car on the road shoulder, and as I looked at the clouds I estimated that the small plume rising from the nuke was less that a hundredth of the total cloud mass which I could see, just in the small patch of sky visible where I was standing. Not all of the solar energy striking the earth evaporates water. Most of it warms the ground, and some of it is reflected back into space. But just the small amount that was boiling water out of the ground, in just that area, had a hundred times as much energy as the nuke. And yet people continue to question whether renewable sources can supply our needs. Are they insane?