Topping up the National Grid?

[WRT]

I grew up on an island where you had to gather/generate/grow everything yourself, which has given me a bit of an interest in alternative methods of supplying electricity (amongst other things). After reading the thread “Is it time we went nuclear? (http://www.kiwibiker.co.nz/forums/showthread.php?t=67724&page=6)” I’ve been having a bit of a think about the power generation shortage we currently have here in NZ, and might have an idea for part of the solution.

Despite the initial damage done to the environment for the reservoir, I’ve always been a bit of a fan of hydro. Thing is, it’s pretty hard these days to find a whole valley you can flood just to build a new dam. Hard work to convince a farmer to give up his land, or the greenies to let you flood a national park. And let’s not even start on the hassles of resource consent.

But what if the dam is already there? What if you have already flooded the valley/moved the farmer/appeased the greenies? As it happens, there are 10 dams around Auckland alone – 5 in the Waitak’s, and 5 in the Hunua’s.

These are the dams that supply most of the drinking water for Auckland – around 315,000 cubic meters a day, or an average of around 3.5 cubic meters a second. Why can we not put a turbine in each of the supply pipelines?

By way of comparison, the power station at Manapouri uses 80 cubic meters a second to produce 945MVA, so we aren’t talking the be all and end all solution here, probably only around 40MVA directly from the dams around Auckland by my rough (and amateurish) calculations. But, there are some quite nice benefits to it.

One is we are using a source that is already there, it’s not like we are taking water from another purpose – merely borrowing it for the length of time it takes to spin a turbine. There’s next to no environmental impact (compared to other methods of generating electricity), you won’t need to run power pylons the length of the country to transmit the power (as it’s generated right next to where the demand is), and the best bit is you can use the same water more than once.

According to the Metrowater website, there are 51 reservoirs around Auckland. Not all of these would be suitable for power generation, but there are quite a few “header tanks” on the tops of hills that you could plumb a turbine into. Mt Eden, St Johns, etc. And that’s just Auckland. Why not also put one on the reservoir on the hill above Tokoroa? Or any other town/city around the country?

I’m not talking a major hydro scheme here, just lots of little ones, so that shouldn’t reduce the pressure/flow in the pipes by too much. Just put them everywhere you can, some sort of standardised design, purchased in bulk, monitored centrally.

It wouldn’t replace our main stations, but it would provide small amounts of power all over the show, next to where it is actually needed. Plus, a lot of our power demand is tied in to water usage. For example, early mornings, when people are having showers for work, you’re generating power to compensate for all the hot water cylinders kicking in. Sunny weekends, when they’re doing the laundry. They’d be both drawing water and generating power.

So, why hasn’t Metrowater or Watercare clicked to this “untapped” source of water? What have I missed?

Note: all figures were obtained from the Watercare, Metrowater and Meridian Energy websites. My calculations as mentioned are rough and amateurish at best. But I do think the idea is sound.

Perhaps someone could offer input on how efficient lots of small turbines would be in comparison to one large one. Or how feasible it is to have lots of small generators adding power back into the national grid (I’ve heard of people producing power privately and selling it back to the grid, so it must be possible). The only hiccup I can see is efficiency – generally speaking, a turbine needs a high rate of flow rather than just sheer pressure or volume. But there are systems that would work on lower flow rates, they might just not be as efficient.

So, what do you all think? And who wants to go in to business with me manufacturing the turbines?

[Mikkel]

It's a nice thought. However...

I'll try not to get too nerdy here.

Anyway, when producing hydro power you convert potential energy (gravitational to be exact) into kinetic energy (rotating turbine) into electrical energy(generator).
Energy has to be conserved - it doesn't appear out of nowhere and it can't disappear either (basic law of thermodynamics).

When you're using raised reservoirs to supply drinking water you use the potential energy to move the water to the taps in your house. This is very efficient - and only a small amount of energy is lost due to friction and pressure loss in the pipes.

Let's say you put a turbine in there - this would reduce water pressure at your tap since the restriction (turbine) in the piping will eat potential energy. This is of course a very simplified explaination - but in the end the energy has to come somewhere and if you want to maintain the same pressure at your tap then you need to chuck more pumps into the system and these will eat more power than you can produce (since efficiency can not exceed 100% ;) ).

[Jantar]

Mikkel is correct. Any turbine in the pipe will reduce the pressure downstream. However there are many water reservoirs that are too high to use directly, and the pipelines have pressure reducing valves in them. Replacing those PR valves with small turbines does make sense. It produces some power for the local network (KW rather than MW) and provides a cash return to the water company.

[Mikkel]

Mikkel is correct. Any turbine in the pipe will reduce the pressure downstream. However there are many water reservoirs that are too high to use directly, and the pipelines have pressure reducing valves in them. Replacing those PR valves with small turbines does make sense. It produces some power for the local network (KW rather than MW) and provides a cash return to the water company.

Hmm, it couldn't be too many...

Besides the added maintenance costs of running a turbine might not make the solution lucrative in the long run. Then you have the risk of oil contamination of the drinking water from leaky oil seals... I'm sure someone thought about this before and found it a "not-so-good" idea.

[Pwalo]

A big potential problem is where, and how you 'back feed' energy into the national grid.

[Jantar]

Hmm, it couldn't be too many...

Besides the added maintenance costs of running a turbine might not make the solution lucrative in the long run. Then you have the risk of oil contamination of the drinking water from leaky oil seals... I'm sure someone thought about this before and found it a "not-so-good" idea.

No problem with leaky seals. Turbine seals are graphite and water cooled, They have water on one side, and just air on the other. Turbine guide bearings (on large turbines) are water cooled with pressurised water so if there is a leak it is water leaking into oil, not oil leaking into water.

Maintence costs on hydro turbines are miniscule.

As for "I'm sure someone thought about this before and found it a "not-so-good" idea" It is already in use in many areas.

[Dargor]

While were at we could put a turbine in every loo, every time i take a piss i could be generating power.

[Jantar]

While were at we could put a turbine in every loo, every time i take a piss i could be generating power.
Now THAT does sound like a load of 54!T. The maintence costs would be horrendous every time you take a dump.

[FROSTY]

I've been wondering about wind power. Not those huge wind farms but more a individual domestic mill.
Mum and dad have one up at mangawhia--it's used to charge their deep cycle batteries -but pumps out 240v

[Jantar]

I'm in favour of that approach as well. But I'd go further and ask why full size wind turbines can't be sited in industrial areas in cities, particularly coastal cities where there is often a sea breeze most evenings. Two or three wind turbines in each industrial area would soon add up to a formidable distributed generation source.

[FROSTY]

Industrial areas makes really good sense--noisy daytime and uninhabited nighttime

[homer]

Ummm If its clean and green your going to pay
if its dirty its cheap

unfortunately the govt of this country has fucked us all with the whole no nukes thing

its a major going to happen and when we NEED IT theres going to be a big fuck round session of back peddling by the govt

and by the way its actually a very clean process these days
and theres little waste and it can be recycled

[Bren]

lets get nuclear, nuclear
i wanna get nuclear
lets get into nuclear
let me hear your atoms talk
your atoms talk
let me hear your atoms talk

[Mikkel]

No problem with leaky seals. Turbine seals are graphite and water cooled, They have water on one side, and just air on the other. Turbine guide bearings (on large turbines) are water cooled with pressurised water so if there is a leak it is water leaking into oil, not oil leaking into water.

Maintence costs on hydro turbines are miniscule.

As for "I'm sure someone thought about this before and found it a "not-so-good" idea" It is already in use in many areas.

Ah, I wouldn't know if it was in use already. What I meant was that if it wasn't then surely someone would have found it to be a NSG idea ;)

Cheers for the heads-up on hydro turbines. I, obviously, thought they were running on oil bearings. :yes:

[WRT]

When you're using raised reservoirs to supply drinking water you use the potential energy to move the water to the taps in your house. This is very efficient - and only a small amount of energy is lost due to friction and pressure loss in the pipes.

Let's say you put a turbine in there - this would reduce water pressure at your tap since the restriction (turbine) in the piping will eat potential energy.

This is great description for the layperson, and something I'm well aware of. As mentioned, I'm very much an amature, I can't quote you the calculations or formula for working out the friction loss etc, but I've spent half my lifetime working with domestic water supplies (up to four houses off one system) and do have a fair idea of what is involved in getting water from catchment to tap.

Generating hydro power is something I'm not so familar with, I've only worked with a couple of home-made domestic systems (none of which were in my own household), but as mentioned it's an area I'm quite interested in. I'm actually starting to gather equipment to build a system for my mother's property - speaking of which, if anyone has an old F&P smart drive that they are throwing out, could I please have the motor? :niceone:

Now I know that there is a world of difference between gathering water for a household and having to supply it for an entire nation. However (and correct me if I'm wrong), the basic principles are the same - you have a catchment area, a filtration/treatment system, a header tank/reservoir, pressure control and finally a tap. All of which are joined by pipe.

Now here's the bit where I'm looking for feedback/insider knowledge. My understanding of Auckland's water system, is that 85% starts from catchment in dams in hilly country. It is then piped to treatment facilities, where (amongst other things), it sits for a while in settling tanks. Then it's piped to a filtration plant, where it runs through sand filters. Chlorine, flouride and lime are added, before it is run to the reservoirs dotted around the city that act as header tanks for final supply.

I'm thinking there are two places we can put the turbines, one is on the way to the settling tanks. I'm no watercare engineer, but surely this bit of piping would be done solely by gravity feed wherever possible, and I'm guessing that the settling tanks are not pressurised. Where it is done by gravity feed, surely there is sufficient additional pressure to allow some of it to be used to drive a turbine?

The second potential place is between the header tank reserviors that are around the city. Not all of these would be suitable, but I'm sure there would be quite a few that would. Anyone that has a mains shower can attest to how much pressure there is in that system, and that's after it's been run through a half inch pipe. I'm sure there would be generation systems out there that could sit at the base of the water reservior itself, that wouldn't take too much of the pressure away to limit end delivery. In fact, the only places I can think of (again, not being a Metrowater engineer) that would be effected would be the high rise buildings - and I believe most of them use there own pump system anyway.

Jantar - you mentioned that there are similar systems to what I've described in use already? Would this be in NZ?

[Mikkel]

This is great description for the layperson, and something I'm well aware of. As mentioned, I'm very much an amature, I can't quote you the calculations or formula for working out the friction loss etc, but I've spent half my lifetime working with domestic water supplies (up to four houses off one system) and do have a fair idea of what is involved in getting water from catchment to tap.

Quoting the equations is the easy part - solving them is slightly harder.

Fluid mechanics is an extremely complicated matter because it's very difficult to disentangle or seperate a problem in the system from the entirety of the system. In that regards it's similar to quantum mechanics where you have to include the entire system in your equation...

I can't recall all of the lecture we had on fluid mechanics - it was enough to give me a headache mind you - but I believe the equations are the Navier-Stokes equation and it revolves around considerations of flowlines. And coming to think of it I think that it might actually be limited to the case of laminar flow - i.e. no turbulence, which you would have in a turbine.

To give an example - some years ago they held an international competition where different departments in fluid mechanics from around the globe modelled a certain system, then the system was built and the modelling data was held up against the emperical observations. I believe that the department of fluid mechanics at the Technical University of Denmark (where I got my M.Sc. btw) won the competition - they were off by a factor of TWO! So there you go. :)

[Coyote]

I've been wondering about wind power. Not those huge wind farms but more a individual domestic mill.
Mum and dad have one up at mangawhia--it's used to charge their deep cycle batteries -but pumps out 240v
http://www.turby.nl/

Saw that on Beyond Tomorrow. Seems like a brilliant idea.

[rainman]

I’ve heard of people producing power privately and selling it back to the grid, so it must be possible

As I understand things, this is not currently a possibility in NZ.It s Green Party policy to establish feed-in tariffs (what you're describing) to encourage development of renewables, but everyone's so keen to bash the greenies on principle that much of their sensible policy (like this) is overlooked.


Disclaimers:
1. I'm not saying there is not some silly policy in there too - they're politicans, thus not perfect. But more sensible than given credit for, by far.
2. There may be significant engineering issues with feeding lots of small power sources back into the grid. Or maybe the guys who manage it are just lazy. I dunno.