Questions about power plants and how they work seem to come up pretty frequently and I just had a chat via PM with someone regarding how power plants work I though Id post the substance of the chat for others. The following information is accurate as of Civ 3 PTW v1.21f (and to the best of my knowledge has been accurate for all prior version of PTW and Civ 3). Everything You Wanted to Know about Power Plants There are four different power plants available to the player: Coal Plant, Hydro Plant, Solar Plant, and Nuclear Plant. Power plants add a production bonus to the city in which they are built. To build a power plant, a city must first build a factory. All but the Nuclear Plant add a 50% production bonus to base shield output; the Nuclear Plant adds a 100% production bonus to base shields. The production bonus is calculated on base shields available which works as follows: (1) assume that a citys laborers are working tiles and producing 38 shields, 6 of which are lost to waste, leaving 32 shields available; (2) the citys factory adds 50% of 32, or 16 shields, meaning the city produces 48 shields; (3) adding any of the Coal Plant, Hydro Plant, or Solar Plant would generate an additional 16 shields (50% of the base of 32), increasing the citys production to 64 shields; (4) adding a Nuclear Plant would instead add 32 additional shields (100% of base), bringing the citys total to 80 shields (32 base, 16 factory, 32 Nuclear Plant). Each of the available power plants become available at different points in the tech tree, and each comes with its own benefits and drawbacks. Coal Plant. The Coal Plant becomes available at the same time as factories, with the tech Industrialization. In order to build a Coal Plant, a given city must have a factory and must have a supply of coal within its strategic resources box. A city with a Coal Plant continues to enjoy the production bonus of the plant even if the supply of coal originally needed to build the plant subsequently depletes, just as a city building a Coal Plant can complete the build even if the source of coal depletes prior to the plants completion. A Coal Plant generates pollution 2 pollution icons. The Coal Plant costs 160 shields. Hydro Plant. The Hydro Plant becomes available with the tech Electronics. In order to build a Hydro Plant a city must have a factory and a river must be present within the citys 21-tile city radius. Note that the requirement is a river a lake will not suffice. A city has a river within its radius if any tile within the radius enjoys the river commerce bonus. The Hydro Plant does not generate pollution. The Hydro Plant costs 240 shields. Solar Plant. The Solar Plant becomes available with the tech Ecology. In order to build a Solar Plant, a city must have a factory. The Solar Plant produces no pollution. The Solar Plant costs 320 shields. Nuclear Plant. The Nuclear Plant becomes available with the tech Nuclear Power. In order to build a Nuclear Plant, a city must have: (1) a factory; (2) a supply of uranium in its strategic resources box; and (3) a source of fresh water within its 21-tile city radius. Note that the requirement is fresh water either a river or a lake will suffice. A city with a Nuclear Plant continues to enjoy the production bonus of the plant even if the supply of uranium originally needed to build the plant subsequently depletes. The Nuclear Plant does not generate pollution, but may meltdown (see below). The Nuclear Plant costs 240 shields. One way to think about the various power plants involves imagining the chain of three conventional power plants as delivering increased benefits and reduced restrictions as you move up the tech tree. The first plant (Coal) requires a strategic resource (coal) and pollutes. The second plant (Hydro) doesnt require resources, but does require specific terrain features (a river) and does not pollute. The third plant (Solar) requires neither a resource nor a terrain feature, and does not pollute. The final plant (Nuclear) offers a new production boost over the prior plants, but reverts to needing both a resource (uranium) and a terrain feature (fresh water); and while it doesnt pollute, it can meltdown. A city may have only one power plant. Any city that already has a power plant and then builds any additional power plant, will automatically sell the prior plant the sale price in gold will be added to your treasury (and the recycled shields to your production box if you have discovered the tech Recycling). For example, if the player builds a Solar Plant in a city that already has a Coal Plant, the Coal Plant will be sold automatically and be replaced by the Solar Plant. Once replaced, an older power plant is gone for good i.e., in the above example, if the newly built Solar Plant were sold or destroyed, the older Coal Plant would not reappear. Meltdowns. According to the original Civ 3 manual, a nuclear plant has a 50% chance of melting down during any turn in which the host city experiences civil disorder. However, empirical testing indicates that the correct changes are about 10% - 15% (assuming the meltdown chances are a discrete variable, i.e., not influenced by unknown factors such as size of empire, number of city improvements, etc.). Furthermore, it seems as if the nuclear plant will never melt down on the turn that the host city enters into disorder only if a city is allowed to continue through a full turn in a state of civil disorder is there a chance of meltdown. Although a meltdown graphically looks a lot like the effects of a nuclear blast, the actual effects are far less destructive. A city that experiences a meltdown will have its eight surrounding city tiles polluted and will have its population cut in half. However, neither units nor city improvements (not even the Nuclear Plant itself) will be damaged or destroyed. Furthermore, the pollution in the eight surrounding city tiles will not destroy the underlying terrain improvements such as railroad, roads, mines, etc., and will not cause the terrain itself to degrade (i.e., plains turning to desert). Once the pollution is cleaned up, the city will again grow and eventually return to the state it enjoyed before the meltdown. Hoover Dam. The Hoover Dam great wonder provides the effects of a Hydro Plant to every city on the same continent. Even cities without a river in their 21-tile city radius or without a factory will have a Hydro Plant icon listed in their city improvements window. However, unless a city has a factory, the effects of the Hoover Dam will not operate on the city. For example, lets assume that you have just completed the Hoover Dam great wonder. A nearby city that does not have a factory and that produces 30 shields will continue to produce 30 shields even though the Hydro Plant icon appears in the city improvements window. When that city subsequently builds a factory, the citys production will jump to 60 shields 15 shields from the new factory and 15 shields from the now-effective Hoover Dam effects. Additionally, cities that already have a different power plant (i.e., a Coal Plant) will also have a Hydro Plant icon in the city improvements window; however, each city enjoys the effects of only one power plant despite the appearance of two power plant icons in the city improvements window, i.e., the city will not enjoy both a 50% production bonus from its Coal Plant and an additional 50% production bonus from the effects of Hoover Dam. In cases where a city enjoys the effects of Hoover Dam but also has a Nuclear Plant, the city will enjoy the greater 100% production bonus of the Nuclear Plant. You should note that the city will continue to experience the burdens of any other power plants after the construction of Hoover Dam a city with a Coal Plant on the same continent as the Hoover Dam great wonder will still incur the 3 gold upkeep cost of the Coal Plant and will still suffer the pollution generated by the Coal Plant, even though the sale of the Coal Plant would not change the productivity of the city since it would still enjoy the effects of Hoover Dam. Manufacturing Plant. The Manufacturing Plant is not a power plant. Think of it as an improved factory. Like the factory, the Manufacturing Plant will add 50% to the production of a city. A city must have a factory to build a Manufacturing Plant, but may build a Manufacturing Plant despite the absence of a power plant. Again using our 32-shield city as an example: (1) such city would produce 48 shields with a factory; (2) such city would produce 64 shields with a factory and a Manufacturing Plant; (3) such city would produce 80 shields with a factory, a Manufacturing Plant, and any of the three 50% power plants (Coal, Hydro, or Solar); and (4) such city would produce 96 shields with a factory, Manufacturing Plant, and a Nuclear Plant.