Energy efficiency in historic homes

[Flyfisher]

Micro-generation (is this the right term for locally shared plants or just for individual households?) is certainly an interesting concept, although the economics of biodigesters would worry me somewhat because of the uncertain nature of the input costs. Although effluent is currently regarded as a waste product, free to anyone who wants it, who knows how this will change if a market for the stuff develops? Farmers are always complaining about the profitability of their businesses and might start to see their bio waste as a potentially valuable commodity. How would this affect the economics of bio-digesters? Interesting stuff though.

Mind you, I suspect that any scheme that relies on the mass migration of people once a year is unlikely to be truly sustainable when overall energetics are taken into consideration. Probably 'greener' to cancel the event in the first place?

I'll also be interested in learning how your heat pump performs next winter. I'd love to hear that it outperforms a fossil fuel based system! Have you considered fitting a meter to the heat pump power circuit to measure it's true energy consumption?

I also like Biff's idea (well, maybe not his personally!) of solar generated electricity from deserts being transmitted over high-efficiency grids. We all know that the sun delivers more energy than we need so there must be a good reason why it's not being actively pursued. Economics and politics is my guess.

 

[Lime]

Africa supplying electricity to Europeans in the north?
An interesting idea if africa was unpopulated.
As it is I cannot see Africans wishing to supply us with power, they hardly manage to do it for themselves, so why would this be any different?
Also a very large proportion of the political establishment would enjoy watching us freeze.
The idea of cables running from Africa to Europe supplying anything like what we will require is utopian pie in the sky I'm afraid, whether it makes physical sense or not.

 

[Flyfisher]

I take your point about political sensitivities and animosities, but might the African nations not see the opportunity to develop a very lucrative energy economy? The middle east has done quite well out of oil, couldn't Africa do the same with solar power? Still, I suppose the Arabs didn't actually exploit their oil themselves, so perhaps Africa will need a similar helping hand?

I'm not sure about cables from Africa to Europe being pie-in-the sky. I remember visiting the Porthcurno museum in Cornwall where the first transatlantic cables came ashore in the 1800's. By the end of that century they had quite a network of communication cables running throughout the British Empire, including India and Singapore I seem to recall. Fast forward 100 years or so and it must surely be possible to lay power cables across the straits of Gibraltar - it's narrower than the English Channel and we don't have any trouble importing electricity from France.

 

[Jon Maine]

Couldnt agree more about the enviromental impact of the event, but I am not going to change that. Although it would be nigh on impossible to process that ammount of effluent through a biodigester you would need some major storage facility.

Dc from Africa, interesting have not heard that one before.

I also agree more value will be held in compostable/organic waste as more biodigesters come on line. The generators have a life expectancy of only 2 years for the top end of the engines too due to the caustic nature of the methane produced even after scrubing it.

Maybe time to buy that mill............

 

[Penners]

it must surely be possible to lay power cables across the straits of Gibraltar - it's narrower than the English Channel and we don't have any trouble importing electricity from France.

My concern is not so much the technicalities of supplying power from Africa to Europe, but the security of it. Many African states are not known for high levels of political or social stability, so I can see ransom demands becoming a part of everyday life. Just think back a couple of years to the Russia/Georgia gas supply debacle.

And guess where your average terrorist would plant his bomb, if he wanted to cripple us?

 

[Ian Bond]

And guess where your average terrorist would plant his bomb, if he wanted to cripple us?

Steady on Penners!!! You are going to bring PPUK to the attention of MI5, the CIA, and perhaps even MFI with talk like that :lol:

They'll be coming for us in the night, and seizing our tubs of lime putty if we're not careful.

:|

 

[biffvernon]

solar generated electricity from deserts being transmitted over high-efficiency grids. We all know that the sun delivers more energy than we need so there must be a good reason why it's not being actively pursued.

Oh but it is being very actively pursued. Start here for info: http://www.trecers.net/

As it is I cannot see Africans wishing to supply us with power, they hardly manage to do it for themselves, so why would this be any different?

For the same reason that they supply us with oil even though they can't afford to use much of it themselves. Sad but true.

An HVDC grid connecting Iceland to Morocco and Egypt is about a certain as heavier than air flying, which some folk thought would never work.

 

[Penners]

They'll be coming for us in the night, and seizing our tubs of lime putty if we're not careful.

Ah, you've obviously heard of the secret formula involving a lime putty/sanatogen mix. Highly explosive, I understand.

 

[Flyfisher]

Interesting link Biff, thanks.
What I find a bit depressing though is all the talk about the difficulty of finding 45bn euros of funding for the grid system when, apparently at the drop of a hat, the UK can find around £50bn to bail out a bank. Of course, Northern Wreck was an immediate problem and so couldn't be avoided whereas climate change/peak oil is something for the future and can be safely ignored. :roll:

We managed to get to the moon with fairly primitive technology (by today's standards) and little or no cost-benefit or return-on-investment analysis simply because of strong political vision and a motivated nation. Sure, everyone was in the grip of cold war paranoia back then but we seem to be increasingly in the grip of climate change paranoia, so what's the difference?

Perhaps if we discovered a comet on a collision course for Earth and the only way to save ourselves was to build a global power grid powered by a solar powered electrical repulsion system then it might concentrate minds. I'm sure Bruce Willis would chip in to help save mankind (again).

 

[Lime]

As it is I cannot see Africans wishing to supply us with power, they hardly manage to do it for themselves, so why would this be any different?

For the same reason that they supply us with oil even though they can't afford to use much of it themselves. Sad but true.

An HVDC grid connecting Iceland to Morocco and Egypt is about a certain as heavier than air flying, which some folk thought would never work.

It is not the concept or installation of a high voltage DC supply that I have doubts about although the size of the structure in order to take the load would be something to see.(!)
It is the fact that at any point of this long structure damage could be done relatively easily.
It would only take a minor event to cause a major dc discharge that would destroy most of the installation.
With that length of cable carrying dc the inductance would bring about catastrophic arcing and electromagnetic disturbance/movement.

A video of a much more minor event is here:

http://www.youtube.com/watch?v=MAlyEMQxTN0

This shows what reactance can do (the ac equivalent of dc inductance) on an *unloaded* stretch of overhead cable when a reactor is disconnected (to the right of the video).
(One of the "puffers" on the swing switch did not operate and caused an arc to continue instead of being quenched.
It was disconnected further up the overhead line remotely)

That system is ac.
A dc system with a large inductance would give a much more powerful arc.

 

[Penners]

It would only take a minor event to cause a major dc discharge that would destroy most of the installation.

Are you saying that a DC supply infrastructure such as Biff is suggesting could be potentially more dangerous than, say, a nuclear power station accident? If not, then surely we should consider such a supply as being safer than nuclear, shouldn't we?

It won't have escaped your notice that I'm debating above my weight, here!

 

[Flyfisher]

I tend to agree. Surely such things are 'mere' engineering issues (although anything above 12 volts tends to make me a bit twitchy!).

As for security issues, yes I take the point, but it's surely no more risky than existing gas and oil pipelines and certainly no reason NOT to do such things. Remember the Kuwait oil field carnage in the first gulf war? That required a whole hostile army yet I seem to recall that the damage was cleared up fairly quickly.

 

[Lime]

Are you saying that a DC supply infrastructure such as Biff is suggesting could be potentially more dangerous than, say, a nuclear power station accident? If not, then surely we should consider such a supply as being safer than nuclear, shouldn't we?

Not potentially more dangerous but very much more exposed to damage by accident or design.
Ring fencing a nuclear site is relatively easy compared to ring fencing 1000s of miles of cabling.

As for security issues, yes I take the point, but it's surely no more risky than existing gas and oil pipelines

No that is not true.
When a gas or oil pipeline is broken by explosion (or whatever) the gas/oil takes time to flow down the pipe.
The energy available is limited.
When damage occurs to a high voltage cable the maximum electrical energy is available instantaneously and for as long as the system can supply it.

It may help to understand the problem if I explain what inductance "does".
In a dc circuit inductance attempts to keep the current the same....it resists change.
So, for instance, when a cable carrying a load is suddenly broken or disconnected the inductance attempts to maintain the current that was flowing before.
In it's attempt to maintain the current it induces a very high voltage (often resulting in an arc similar to the video) very much higher than the normal voltage present in the cable.
So in a dc cable that normally carries thousands of volts under fault conditions inductance can create many millions of volts or more. In theory the sky is the limit.
The high voltage induced can result in explosion, the melting/vapourising of everything around it and a general breakdown of insulation throughout the cable dependent on where the weakest insulation may be. Also, where the insulation breaks down there are further induced voltages ... and so it can go on.
I think it will be impossible to protect the cable from wilful damage successfully.

Following on from that, surely the critical aspect of having a very long cable supplying Europe from Africa is what do we do when/if it fails?
How many runs of cable do we have to have before we have a secure supply?
....and how much will that cost?

Perhaps it would be better if we all moved to Africa or sat at home in the cold and dark?
It would cetainly be greener. :wink:

 

[MdB]

I think you are overplaying the dangers here. Sure there are dangers but the amount of power available is limited. Once the wire is damaged, a fault condition will occur which will be detected and circuit breakers will activate. The inductance of a cable is low so the energy storage in the line is low. Yes you will get arcing (at the fault point) and yes it could start a fire but otherwise it is not a major issue. 3GW travels 1300km down the west coast of the US as 500kV DC without problems. We also get 10%(?) of our power from France as DC I think. Its a solved problem.

 

[Flyfisher]

Come on chaps, where's the 'can do' approach? As MdB points out, there are such things as circuit breakers for fault conditions. And anyway, such things must happen to existing grids all the time; they get damaged, they get fixed. I'm no expert but I'd put money on the likelihood that politics and economics will be the sticking points, not the technology.

Er, having just read my previous post, my "I tend to agree" was not in answer to Penners' self-deprecating aside about him debating above his weight.
Just thought I'd clear that up

 

[Lime]

I think you are overplaying the dangers here. Sure there are dangers but the amount of power available is limited. Once the wire is damaged, a fault condition will occur which will be detected and circuit breakers will activate. The inductance of a cable is low so the energy storage in the line is low. Yes you will get arcing (at the fault point) and yes it could start a fire but otherwise it is not a major issue. 3GW travels 1300km down the west coast of the US as 500kV DC without problems. We also get 10%(?) of our power from France as DC I think. Its a solved problem.

None of which are exposed to terrorist attack or traverse other countries.

DC technology has been around since Edison, that doesn't make it safe under attack.

Besides it's not the damage I'd be worried about, it is the lack of juice on the end of the wire.

 

[MdB]

There is no need for DC anyway. It can be transmitted as AC. Invertors (which would be required anyway) are pretty efficient nowadays.

 

[biffvernon]

I'm no expert in these matters but I am assured that there are significant advantages in using a DC grid over long distances and that they do operate safely. The interconect between England and France is DC, as are most other undersea cables, and the Chinese are building a 2000 km HVDC line at present.

 

[Lime]

I'm no expert in these matters but I am assured that there are significant advantages in using a DC grid over long distances and that they do operate safely. The interconect between England and France is DC, as are most other undersea cables, and the Chinese are building a 2000 km HVDC line at present.

Yes you are quite correct.
DC has a distinct advantage over long distances compared to AC.
With DC the inductance of the line/wire only comes into play when the current changes.
If the load is kept constant, the current does not change, so the inductance need not effect the circuit at all.
Of course the resistance of the wire still creates some loss.
On the contrary, with AC the voltage and current are changing all the time (hence Alternating Current).
So the reactance of the line/wire (the AC equivalent of DC's inductance) cannot be discounted from the circuit and always will cause a loss of power.
The greater the reactance the greater the loss of power.
This loss is in addition to the loss caused by the resistance.
The reactance of a system can be balanced out so it's effect is minimised (which is the purpose of the reactors connected to the power lines in the video) but it is expensive to do so.

Another big advantage for DC transmission is that the generating source does not have to be synchronized with the load.
Thus a country with 60Hz generating frequency can supply a country that uses 50Hz (like the UK).
Similarly they can have the same frequency but be out of sync with each other.
With AC transmission any difference of frequency creates very big problems.
Many people never give it much thought but the frequency of the supply in John O'Groats has to be precisely sychronised with the supply in Land's End otherwise the grid system would fail.

 

[Flyfisher]

Er, right, so now you seem to be saying it is a solved problem?