Having taken care of food, water and housing, all that remains is to find some source of lights and POWER for the people of the city. After all, you're going to need lights and some form of heat. (Cooling likely won't be a problem. Food storage isn't really an issue, the ambient temperature's probably going to be in the mid 50's.)
Let's look at lighting first.
The movie version of "City of Ember" showed incandescent lighting suspended over the city. In the book, reference was made to 'storerooms full of light bulbs of all kinds'. That's what we've got to work with. Now, there's a certain advantage to incandescent lighting that might not be apparent at first in a cave - it throws off a lot of heat, too.
The only problem is - there's no way to really catch it. That heat is going to go... up, when it's needed down below. (Hey, ambient temperature below 60, remember?) (Hmm, heat ducts above light fixtures with fans? No, that's something else to break. Maybe heat pipes? Nothing to break there...)
Currently, there's three commercially viable types of interior lighting. You've got incandescent lights, flourescent lighting, and LEDs. Sulfur bulbs have seen some commerical use, but they're a bit on the touchy side, needing a magnetron and forced air cooling. Again, there's plenty of heating from it, perhaps air ducting would work? There's other bulbs available, like halogen and sodium bulbs - but we'll go with what was seen in the movie. Incandescent, tungsten filament it is.
Now - how do you get an incandescent bulb to last as long as possible? (You only have a limited supply, after all...) The obvious way would seem to be de-rate the thing - take a 130 volt bulb and run it at 120 volts - and you should get longer life, right? (Increasing it by a factor of about 2.8, it says here.) Of course, your brightness goes down also, by 25%, but your wattage decreases by 14%. Regulate your input to about 100-110 volts, and you'll have a VERY long lasting bulb.
(How long? Well, how about 106+ years? I did a brief search to see what frequency and voltage the bulb was designed for, with no luck. It's a 4-watt bulb with a .08 in. straight filament, not thinner and coiled the way they make tungsten filaments today. So an 'eternal' incandescent with a 5-10 year life isn't inconceiveable.)
So you've got a bulb. Big whoop - what are you going to power it with?
The 'Generator' seen in the movie was a very LARGE thing (easily the size of a 10 story building, and about half as wide and deep as it was tall) - occasionally throwing off sparks. (Guess the insulation was breaking down, too...) But in reality, high-output generators aren't all that large. A 10 megawatt generator is about the size of a large minivan, sans power unit. Let's see what something like Ember would actually NEED.
Okay, Let's start with lighting. 500 1kw bulbs for external lighting - that's 500kw.
You've got 400 buildings. (Judging by the map at the front of the book, that's probably overcounting by a factor of 4, but we'll run with it.) 10kw per building should do - about 1 kw for lighting, 4 for cooking and refrigeration, 5 for general heating.
10kw x 400 buildings - (not all of which will be running that load at the same time) you're looking at 4 MW.
4.5 MW so far. Add in an extra MW for city infrastructure, and you're up to 5.5 MW, leaving you 4.5 MW spare capacity. Add on two megawatts for the greenhouses, and you're at 3/4ths load for one generator.
So put in 10 for redundancy. (What the heck, you've got a BIG generator building, gotta have something to fill it, right?)
Use magnetic levitation bearings so there's minimal to no metal-metal contact, or engineer it to use fatty wastes from the city as bearing lube.
What powers the generator? Let's look at options.
A nuclear power plant's probably out of the question. Admittedly, radioisotope generators exist for long-term power supply needs - but they're relatively low-wattage compared to the needs here. There's other options - but I'm not aware of any low-maintenance nuclear plant that could go 250 years with barely skilled operators. (The Hyperion comes close, though.)
Coal? Nah. Solar? Nope. Wind? Don't think so...
Water? Well, there's this handy river...
Hydroelectric power might be the way to do it. Engineer 10 water turbines, with massive (and I mean MASSIVE) pipes supplying them. Magnetic bearings again - that'll reduce wear. Make everything oversized and overthick - if the usual engineering practice calls for a tube of X diameter with a tubing wall thickness of Y, make it 10Y thick.
Yeah, it's overkill. But this system CAN'T be allowed to fail.
Without power, the City is doomed.
Your thoughts?
J.