Optimum generator size.

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Optimum generator size.

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Hairyloon

Joined: 20 Nov 2008
Posts: 15425
Location: Today I are mostly being in Yorkshire.

Posted: Thu Oct 24, 13 10:40 am Post subject: Optimum generator size.

I was just having a debate with a chap who pointed out that it is obviously more efficient to have electricity made in one big power station than in lots of individual little ones.
While it is probably true in terms of economic efficiency, and certainly true if the individual generators are not grid connected, I'm not seeing any real reason it should be the case, and certainly not an obvious one.

Am I just being dense?

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Thu Oct 24, 13 6:00 pm Post subject:

Not sure I understand the question?

All engines need X amount of fuel just to make them work. Loading them to lightly means that the X is large in proportion to the load.

However over loading them takes them out of the efficiency sweet spot. Engines are tuned for a speed & load pattern. Make then run faster or under more load & it all goes wrong.

I dont know about big gennies but small ones run best (IE efficiently) at about 3/4 of the full rated load.

Pilsbury

Joined: 13 Dec 2004
Posts: 5645
Location: East london/Essex

Posted: Thu Oct 24, 13 6:16 pm Post subject:

RichardW wrote:

so i guess the question is is it more efficent to run 10 x 1000 w genies at 750 w or 1 x 10000 at 7500....

Hairyloon

Joined: 20 Nov 2008
Posts: 15425
Location: Today I are mostly being in Yorkshire.

Posted: Thu Oct 24, 13 7:24 pm Post subject:

Pilsbury wrote:

so i guess the question is is it more efficent to run 10 x 1000 w genies at 750 w or 1 x 10000 at 7500....

Yes, something like that...

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Fri Oct 25, 13 8:48 am Post subject:

Are you talking small or large engine for powering a workshop with several different machines, or power stations for powering large areas?

If the former, probably one large engine, if the latter, the opposite.

My father remembered before the National Grid very vividly. In fact the new house they moved into in London in the 1930s didn't have an electricity supply for a year. He was very much for the National Grid as it made it possible for nearly everywhere to be connected, distribute power round the country and utilise the more efficient power stations first, only bringing in the less efficient ones for high loads.

The down side is that because of losses in the cables, the amount of carbon dioxide generated by producing 1kw of electricity from the grid is currently far more than if you did it locally by using some sort of engine; diesel, gas, coal or wood. I looked into this in 2008 and at that time the ratios were something like 4 times as much carbon dioxide from grid electricity as burning wood directly. This would of course be reduced a bit if you used the burning wood to generate electricity on site, but even at something like 50% efficiency this would still be twice.

Hairyloon

Joined: 20 Nov 2008
Posts: 15425
Location: Today I are mostly being in Yorkshire.

Posted: Fri Oct 25, 13 12:59 pm Post subject:

Mistress Rose wrote:

Are you talking small or large engine for powering a workshop with several different machines, or power stations for powering large areas?

The discussion which provoked the question was comparing trolley-buses to diesel.
In that case, the power station would probably be more efficient as it should be running at optimum efficiency all the time, but how much more efficient?
Diesel buses are old hat anyway, and should be moving over to hybrids.

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Fri Oct 25, 13 3:53 pm Post subject:

If the power is locally generated and used within a town, perhaps the trolley buses would be more efficient. As far as I remember them, although they didn't have the disadvantage of spewing out diesel fumes, they did have the disadvantage of sparking which created ozone and coming adrift fairly frequently, particularly at busy junctions.

If you compare like with like, hybrid engines are more efficient, but if you compare a medium to large hybrid car with a smaller one, the fuel consumption can be similar.

Hairyloon

Joined: 20 Nov 2008
Posts: 15425
Location: Today I are mostly being in Yorkshire.

Posted: Fri Oct 25, 13 4:36 pm Post subject:

Mistress Rose wrote:

If you compare like with like, hybrid engines are more efficient...

I had assumed that hybrids were the most efficient option, but I didn't care enough to go chasing for figures to prove it.

Woodburner

Joined: 28 Apr 2006
Posts: 2904
Location: Essex

Posted: Fri Oct 25, 13 5:05 pm Post subject: Re: Optimum generator size.

Hairyloon wrote:

I've been pondering a similar thing but specifically with wind turbines. Smaller ones are less efficient, but safer, so can be closer to habitation. Bigger ones are more efficient, but dangerous, so have to be a long way away from people. Further away = more power lost. I had been wondering if it might be better if communities got together to have 'medium' sized turbines, but have finally managed to find how much is generated by such a turbine, and it's a mere 11kw

and I presume that's peak output too. Hardly enough for one household nevermind a community!

Mistress Rose

Joined: 21 Jul 2011
Posts: 15600

Posted: Sat Oct 26, 13 8:13 am Post subject:
Another thing to think about with wind turbines is the speed at which they operate. The small ones will operate at virtually all wind speeds, but the larger ones don't even start to generate unless the wind reaches a certain speed. I don't know what the figures are as I haven't studied it, but that was just on info gained on a visit.

Hairyloon

Joined: 20 Nov 2008
Posts: 15425
Location: Today I are mostly being in Yorkshire.

Posted: Sat Oct 26, 13 9:31 am Post subject:
Funny how definitions vary... The "small" wind turbines on the FIT banding are up to 150kW.

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Sat Oct 26, 13 6:22 pm Post subject: Re: Optimum generator size.

Woodburner wrote:

Smaller ones are less efficient, but safer, so can be closer to habitation. Bigger ones are more efficient, but dangerous, so have to be a long way away from people. Further away = more power lost. I had been wondering if it might be better if communities got together to have 'medium' sized turbines, but have finally managed to find how much is generated by such a turbine, and it's a mere 11kw

and I presume that's peak output too. Hardly enough for one household nevermind a community!

11kW is deff in the small band.

Where has the danger stats come from? From the few people I know that have small ones & from the very few problems with big ones that you hear about in the press I would say that small ones have more problems. Mainly due to lack of planned maintenance.

Woodburner

Joined: 28 Apr 2006
Posts: 2904
Location: Essex

Posted: Wed Oct 30, 13 8:49 pm Post subject:
Crikey, it's !!!!! huge compared to the domestic ones I've seen! I haven't seen any stats of failures of either domestic or industrial, though obviously both do have at least occasional failures. I'd rather be hit by something off a smaller one than a larger tho!

RichardW

Joined: 24 Aug 2006
Posts: 8443
Location: Llyn Peninsular North Wales

Posted: Wed Oct 30, 13 10:56 pm Post subject:

Woodburner wrote:

Crikey, it's !!!!! huge compared to the domestic ones I've seen!

Domestic ones are not small they are toys. Especially roof / house mounted ones.

Ty Gwyn

Joined: 22 Sep 2010
Posts: 4563
Location: Lampeter

Posted: Wed Oct 30, 13 11:09 pm Post subject:
Do they really do Roof mounted windturbines? Heard on the radio about a turbine on a roof in Ilfracombe blowing over in the wind the other day,i took it that it had blown over on to the roof, How tall would these be and how would one secure it properly? Bet the damage to the roof out ways an saving in electricity.

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