How much does it take to power a city?

[Krases]

I am sort of looking for both ballpark estimates on what it takes to power a city and explanations on how power is measured (especially over time).

As I understand it, the three gorges dam will eventually produce something like 22.5 gigawatts of power while New York city uses 5 gigawatts of power while New York state uses around 140 gigawatts. Am I even close to correct? It doesn't feel like I am, I really need help visualizing what it takes to produce power for a city.

[Kelvin]

This is only my own casual observation for an industrialized city/country: approx. 5 GW per million people, but obviously there would be a natural +/- to that figure as well.

This is not anything but my own speculation and completely unsubstantiated!

From Wikipedia (of course): http://en.wikipedia.org/wiki/World_e...nd_consumption

World energy production 2005 was 16 TW (16,000 GW) for say 6.5 billion persons = 2.67 GW/million which obviously includes many lesser industrialized nations.

[mersar]

Yep, I've heard a number of 3-4GW/million in the past, how much industry though would be a huge factor in the +/- of that average.

Just taking a rough number from the current Alberta generation, for a population of 3.6 million the demand is currently sitting at 8.1 GW for the entire province, granted it is a Sunday afternoon. I believe our record for demand is around 9.7GW a couple years ago. So we're currently using 2.25GW/million and our record was around 2.7GW/million

[Krases]

Interesting. I am in the process of conceptualizing a nation of about 70 million people with one major metropolitan area surrounded by farms, mountains and suburbs. Four large rivers feed into a fairly large great lake that was formed out of the construction of either one or a series of massive dams.

The majority of the power comes from hydroelectric which is supported by both wide spread private solar power on roof tops and a few wind farms on some of the plains that flow down from the mountains.

The country pursues green solutions to consumption, it is not in a political position to pursue nuclear power and while it did have a history of coal power usage, it preferred to use hydro electric to kill three birds with one stone (produce a massive area of prime lakefront property, produce massive amounts of power and transform the formerly flood prone swamp area downstream from the lake into prime farmland).

So around 70 million people in a very modern 1st world nation need power. Can it be done with mostly hydro electric?

[vid]

Hydro-electric isn't a green solution, especially if you have displaced a significant amount of trees (which release methane as they rot in the reservoir for the first few years, probably polluting more per MW than a coal plant would for a time) and converted a wetland into farmland (wetlands filter water, farmland, unless it's just organic, tends to pollute waterways and watertables.) To power those 70,000,000 people, that hydro-electric dam has to be considerably larger than Three Gorges. It would be extremely expensive, unless your city is sitting on a lot of oil or a cheap labour pool.

[Krases]

Originally Posted by vid

Hydro-electric isn't a green solution, especially if you have displaced a significant amount of trees (which release methane as they rot in the reservoir for the first few years, probably polluting more per MW than a coal plant would for a time) and converted a wetland into farmland (wetlands filter water, farmland, unless it's just organic, tends to pollute waterways and watertables.) To power those 70,000,000 people, that hydro-electric dam has to be considerably larger than Three Gorges. It would be extremely expensive, unless your city is sitting on a lot of oil or a cheap labour pool.

I actually had this idea for the political evolution of the "super city-state" that I am developing. It would also help explain why the nation relied of hydroelectric power. In the valley were the reservoir would be built as part of the dam, there would be a major conflict zone were much of the forest would be destroyed by either deliberate fire bombings or accidental fires. As a result of the war with this adversary who I haven't really elaborated on yet, the city-state entered a alliance with a much larger super-power who in turn constructed the massive hydroelectric dam to both supply power to its ally (the city state) and to literally flood some of the adversaries hardened defensive positions in the valley. This eliminates the rotting tree problems and the environmental issues of the valley...seeing as the valley was obliterated in the war.

I don't know what to do about the farming issue. I kinda of want this city to be both great and yet have a few flaws to make it believable.

Well 15 years later and the war is over, the entire region belongs to the city state and the hydroelectric dam is turned over to the city much like how the panama canal was handed over to the Panamanians by the US. With a massive electricity monopoly in the region, the nation starts to accumulate wealth both from a large existing treasury, energy deals, large reserves of silver in the surrounding mountains and the end of a long hard war. The nation constructs a second, larger dam and builds smaller dams up in the surrounding mountains.

So with a recent modernization and upgrades, the first dam produces 20 gigawatts. The second dam produces around 25 gigawatts and the smaller dams in the surrounding mountains produce a combined 18 gigawatts of power. Perhaps if the required power-per million people was lowered by privately owned rooftop solar power, power for 70 million could be achieved.

I was also wondering about another idea. Is there a sort of dam that doesn't actually block the rivers flow, but still produces energy? Kind of like how a water wheel doesn't have to block the river, but produces energy. Is there a name for what I am describing?

[vid]

Those exist, but they're much less efficient at generating electricity. I'm not sure what they're called. It's similar to tidal power generation, where the movement of the water through tides turns the turbines.

[SFUVancouver]

Originally Posted by Krases

I was also wondering about another idea. Is there a sort of dam that doesn't actually block the rivers flow, but still produces energy? Kind of like how a water wheel doesn't have to block the river, but produces energy. Is there a name for what I am describing?

That is called "run of river" hydo and quite a bit of it is planned for British Columbia (BC). The real problem with it is that while the flow of the river isn't entirely interrupted, so much is diverted that salmon cannot swim up stream. One run of river hydro project near Squamish BC, on the way from Vancouver to Whistler, diverts 95% of the river for the distance of several kilometres. The dam company, since it is a private project, has promised to not divert that much during the salmon spawning season, which is good, but there is another problem with scouring of the river bed where the penstock returns the diverted water to the main channel. The other big problem with run of river hydro is that because it does not store up water in a dam, which does make it more environmentally friendly, the peak output times for the project are during and after major rain events during the winter and spring months. In BC this is when we need new supplies of electricity the least. The last problem with run of river hydro is that local opposition to several of the first projects prompted the Province of BC to change the municipalities act to prevent them from acting as an obstacle to the development of private run of river hydro projects within their jurisdiction. Run of river hydro is contentious, to say the least, in BC.

[Krases]

Cool stuff. Run of river, after looking at examples, looks a lot more destructive than I thought. I was literally picturing a giant waterwheel that just sat on the side of the river, but that is not the case.

Basically as part of the planned background history for this city I am designing, I could have them literally strip the forest that would be sitting on the future reservoir as a way to prevent waste that way. It would be a massive deforestation move though seeing as the reservoir along with the existing lake will likely become the size of Lake Victoria (although shaped more like Lago De Garde in Italy).

With a few major rivers feeding the existing lake (and later, reservoir) would it be possible to build additional dams up in the mountains?

By my calculations, there would need to be 200 gigawatts of power to supply 70 million people. That is a lot.

[Krases]

I know this thread is a little bit old, but I would rather post here than make a new thread on the same subject.

Is the following feasible: you have a large river flowing through a valley with some coastal cliffs in the way. The river has carved a way through the cliffs, though the cliffs already get reasonably low when you reach the coast. If the river were dammed to fill the valley as a reservoir, would it be able to supply power to multiple dams if water were diverted into additional paths?

So far, I only see the limit being the amount of water coming down stream. How big of a river are we talking to say, generate 100 gigawatts of power?

I made some images to illustrate my idea. I know it is kinda primitive, but assume that it is not to scale.

Before Dam's


After Dam's.