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 I’d 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 city’s laborers are working tiles and producing 38 shields, 6 of which are lost to waste, leaving 32 shields available; (2) the city’s 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 city’s production to 64 shields; (4) adding a Nuclear Plant would instead add 32 additional shields (100% of base), bringing the city’s 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 plant’s 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 city’s 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) doesn’t 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 doesn’t 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, let’s 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 city’s 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.
Thoughts on Power Plant Options / Tactics
I routinely build an available power plant in those cities that already contain a factory. If I have already made the determination that a the boost to production afforded by a factory justifies the factory’s upkeep cost and pollution effects, it is likely to deserve an additional boost to productivity offered by a power plant. There are two broad exceptions to my general rule of thumb.
First, if I am reasonably certain that I will successfully build the Hoover Dam, I will likely not incur the extra production cost of building Coal Plants in those cities that will benefit from Hoover Dam. I may still build a Coal Plant in one or more cities to help their production solely for the purposes of completing the Hoover Dam, Theory of Evolution, or the Universal Suffrage great wonders, but upon the completion of the Hoover Dam, I will immediately sell such Coal Plants to eliminate the upkeep cost and pollution.
Second, in those instances in which either Hoover Dam is not built or in which I have productivity centers on a continent other than that which built Hoover Dam, I will first determine the effectiveness of manually building an available power plant. By and large, by the time power plants become available in the tech tree, most productive cities will already have a full complement of needed improvements – such cities’ likely building orders will be units: either infantry, artillery, tanks, or aircraft. If a city with a factory already produces 57 shields (after waste), meaning that its base production is 38 shields (with an additional 19 shields coming from the factory), adding a conventional power plant will bring production levels to 76 shields. For the purpose of building any of the Industrial Age units described above, production of either 57 shields or 76 shields makes no difference as all build projects will still require two full turns to complete. In such a case I am unlikely to add a power plant to the city. Of course (exceptions to the exception!), the raw boost in productivity would be attractive in completing more expensive build projects such as wonders or spaceship parts, and so even in the above hypothetical one or two cities may push forward and build an available plant. Some players also like to use older units to “short-rush” building projects (too much micromanagement for me). With a production of 76 (instead of 57) a player could disband an old pikeman, netting 7 shields, and then complete an artillery unit in one turn instead of two. Using such a play style would cause me to evaluate the benefits of a power plant differently.
In those games that remain competitive in the age of nuclear power a Nuclear Plant will often be more advantageous than ignoring the opportunity to build one because of the need to build multiple spaceship parts. The great drawbacks to Nuclear Plants are the upkeep cost and the potential for meltdown. But meltdowns are pretty rare and are not particularly painful. As explained above, a meltdown doesn’t damage units or improvements, and since the underlying terrain improvements like RR and mines/irrigation are left intact, available worker groups can usually clean up the polluted tiles fairly quickly. Where a Nuclear Plant would bump a city’s production over a “turns to build” hurdle, or would appreciably help in building spaceship components, I build the Nuclear Plant with little fear of a meltdown – employing the AI governor to manage citizen moods or otherwise carefully ensuring that no civil disorder descends on a city with a Nuclear Plant and is allowed to continue can effectively prevent any meltdowns.