People thinking that they are saving money from more energy efficient products

[scaryjim]

@scaryjim: Not quite true; modern condensing boilers are extremely thermally efficient, with claims of up to 98%.

Yeah, that occurred after I typed it, but figured someone would correct me so couldn't be bothered to click "edit" and do it myself (I'm so lazy ).

You're not getting anything for free, it's still a generator, turning some energy from the gas into electricity and I also don't really understand why such a thing is eligible for the FIT. Then again the whole FIT program never did make a great deal of sense to start with...

I think it's just down to the general point that electricity generation at home tends to be more carbon efficient than electricity generation centrally (far lower transmission losses for one thing). The feed-in-tarif is pretty much there to incentivise local, distributed electricity generation. It takes some of the load off the long-distance tranmission grid (which in turn also reduces transmission losses, which are proportional to current squared). Sure it might not make a huge difference at the moment, but the more it's incentivised the more it is taken up, the less electricity has to be transmitted hundreds of miles from centralised generation, and the greater our overall generation and transmission efficiency becomes.

[wasabi]

Would be interesting to see comparison of efficiencies in sending electricity over long distances from large power plants vs small consumer grade generators.

Wonder how far we can take it? Maybe fit a small generator in front of the taps to feed off mains pressure?

[DanceswithUnix]

This site says CHP is 8-10K to install, which takes us back to Cat's original topic: Will you ever get your money back.

http://www.yougen.co.uk/renewable-en...'26+Power/

Perhaps I should just go for solar water heating tubes on the roof, they seem cheap in comparison.

[RobbieRoy]

The family have baths. Lots of them, far more than my blokeish head can fathom.

Sounds like you live with a wife and daughters, as I do - not that I am making use of any particular gender stereotypes!

[peterb]

It says I pay 4p/kWh for gas and 11.5p/KWh for electricity. Makes me wonder if I can run my own generator off a gas turbine, if it is only 50% efficient my electricity would still be way cheaper.

Just need some car manufacturer to make these things mass produced so I can go down the scrappy and get myself a power plant. http://www.bladonjets.com/applicatio...pt-case-study/
If I could run the exhaust through a radiator I could have my own CHP system

You would be lucky to get 50% efficiency without vey careful system design. You would need a gearbox to reduce the output speed of the turbine to a reasonable synchronous speed - for a two pole generator, generating at 50Hz, the maximum rotational speed is 3,000 rpm.

You might want to read up about the Brayton cycle. http://en.wikipedia.org/wiki/Brayton_cycle

[wasabi]

Sounds like you live with a wife and daughters, as I do - not that I am making use of any particular gender stereotypes!

Just tell them they'll lose a lot of fat and be healther if they bathe in cold water - i.e. a bit of cold thermogenesis.

[RobbieRoy]

Just tell them they'll lose a lot of fat and be healther if they bathe in cold water - i.e. a bit of cold thermogenesis.

Would I be so foolish!!

[Top_gun]

This site says CHP is 8-10K to install, which takes us back to Cat's original topic: Will you ever get your money back.

http://www.yougen.co.uk/renewable-en...'26+Power/

Perhaps I should just go for solar water heating tubes on the roof, they seem cheap in comparison.

I looked into micro-CHP a few years ago. They are not as thermal efficient as normal condenser boilers. They were expensive but there was enough information out there to suggest that the micro-CHP would become more efficient and less expensive in time.

Would you get your money back? Possibly but you have to take into account British engineering as there was only one British made product on the market and whether the micro-CHP will last 10-15 years. Chances are probably not!

I believe micro-CHP is very popular in Japan.

[watercooled]

Would be interesting to see comparison of efficiencies in sending electricity over long distances from large power plants vs small consumer grade generators.

I agree it would be very interesting to see something along these lines, taking into account issues like intermittency and unbalance of local grids (as I've said in another thread, just shoving small, highly intermittent power sources on to the grid doesn't necessarily help) and vastly lower generation efficiency vs transmission losses.

Wonder how far we can take it? Maybe fit a small generator in front of the taps to feed off mains pressure?

In that case all you're doing is reclaiming some energy put into the system by the water utilities.

[peterb]

This site says CHP is 8-10K to install, which takes us back to Cat's original topic: Will you ever get your money back.

http://www.yougen.co.uk/renewable-en...'26+Power/

Perhaps I should just go for solar water heating tubes on the roof, they seem cheap in comparison.

The Baxi Ecogen is the first practical implementation -and costs (according to this site) around £7,000 - plus installation

http://www.thegreenage.co.uk/chp-boi...-buyers-guide/

But then you have to factor in servicing, which will cost more (my gas boiler is 20 years old - and has a flue fan, a gas solenoid valve and some very basic control circuity to operate the igniter and provide flame failure detection - the Ecogen is way more complicated!)

The same considerations apply - to some extent - to modern condensing boilers - more complicated, and to reduce the thermal inertia, the heat exchangers tend to be flimsier and more prone to corrosion, so corrosion inhibitors in the primary loop are essential thing to have, just just a good thing to have. Old cast iron boilers could last 25 years provided they were cleaned regularly - town gas was very dirty with high sulphur content.

[kalniel]

In that case all you're doing is reclaiming some energy put into the system by the water utilities.

The term 'watermill' comes to mind

[DanceswithUnix]

The same considerations apply - to some extent - to modern condensing boilers - more complicated, and to reduce the thermal inertia, the heat exchangers tend to be flimsier and more prone to corrosion, so corrosion inhibitors in the primary loop are essential thing to have, just just a good thing to have. Old cast iron boilers could last 25 years provided they were cleaned regularly - town gas was very dirty with high sulphur content.

That would be my worry. Modern boilers are far more delicate than the old one I currently have, but when it eventually fails (I hope it lasts a long time yet) then AIUI the current legislation forces me to get a condensing boiler with all the cutting out, unreliability and short life woes that they bring. If CHP boilers lasted 20 years, then I could get my money back. If it dies after 10 years (which I am told is typical of condensing types), then perhaps I am better off with just a standard condenser boiler rather than one 4 times the price.

All stupid IMO, how can you call making something last half the lifetime of older products environmentally friendly?

[DanceswithUnix]

I agree it would be very interesting to see something along these lines, taking into account issues like intermittency and unbalance of local grids (as I've said in another thread, just shoving small, highly intermittent power sources on to the grid doesn't necessarily help) and vastly lower generation efficiency vs transmission losses.

The grid has dealt with no real control over *consumption* of electricity for all this time with only the occasional bad hiccup, my gut feeling is that by doubling the uncertainty with uncertain generation you make the system 4 times worse, but is it really?

I do wonder at what point local storage will become mandatory for local generation, and some signalling to the grid like "I'm 3kW going offline in 60 seconds". I'm sure some maths could work out the instability points in such a system, but that involves Control engineering and I never got on with that.

In that case all you're doing is reclaiming some energy put into the system by the water utilities.

Ah, but if the utility company is putting the water in a local water tower then I wouldn't feel so bad about it as you aren't pushing back against their pumps (which would be on par with using the 50V line voltage on the phone line, I gather BT hate it when you do that).

I sometimes wonder when its raining how much power the water going down the drainpipe represents. A bit of rain across the roof of the house concentrated into that smallish pipe could be quite a flow rate.

[RobbieRoy]

That's the benefit of a national grid at present - supply can be managed to meet demand as both fluctuate.

Although it would be more complex to do the same thing at a more local level with a multitude of local generators, it's certainly possible.

[watercooled]

That would be my worry. Modern boilers are far more delicate than the old one I currently have, but when it eventually fails (I hope it lasts a long time yet) then AIUI the current legislation forces me to get a condensing boiler with all the cutting out, unreliability and short life woes that they bring. If CHP boilers lasted 20 years, then I could get my money back. If it dies after 10 years (which I am told is typical of condensing types), then perhaps I am better off with just a standard condenser boiler rather than one 4 times the price.

All stupid IMO, how can you call making something last half the lifetime of older products environmentally friendly?

We've had our Vaillant condensing boiler for several years and it genuinely hasn't missed a beat. The Brittony (granted it seems like a no-namer) conventional combi we had before that brought no end of trouble. Just go with a respected brand and I can't see it being a massive issue.

But I agree with your point in general - it's a false economy and another stellar example of greenwashing when you get 'efficient' products which last five minutes and need constant replacement parts.

The grid has dealt with no real control over *consumption* of electricity for all this time with only the occasional bad hiccup, my gut feeling is that by doubling the uncertainty with uncertain generation you make the system 4 times worse, but is it really?

Well it's certainly a concern that it may cause further issues, but even if not, there's still the debate as to whether random bits of energy added to the grid is of any tangible benefit.

I do wonder at what point local storage will become mandatory for local generation, and some signalling to the grid like "I'm 3kW going offline in 60 seconds". I'm sure some maths could work out the instability points in such a system, but that involves Control engineering and I never got on with that.

I see no potential for problem at all with such a massive-scale computerised control system.

Ah, but if the utility company is putting the water in a local water tower then I wouldn't feel so bad about it as you aren't pushing back against their pumps (which would be on par with using the 50V line voltage on the phone line, I gather BT hate it when you do that).

How much energy are you hoping to harvest though? You can already get kinetic-charged watches...

That's the benefit of a national grid at present - supply can be managed to meet demand as both fluctuate.

Although it would be more complex to do the same thing at a more local level with a multitude of local generators, it's certainly possible.

As above, it's one thing it not being an issue, but quite another whether it's actually beneficial overall.

[scaryjim]

... I sometimes wonder when its raining how much power the water going down the drainpipe represents. ...

Wonder no longer. Randall Munroe has dealt with this very question: third one down on this What If page: http://what-if.xkcd.com/23/

It's not very much at all, sadly