Extinction Rebellion, ongoing disscussion.

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Re: Extinction Rebellion, ongoing disscussion.

Post by adam2 »

Lesson two.

Primarily about different utility voltages and different battery voltages.

Merits of lower voltages such as 120 volts in USA and of 127 volts in some other places. Cheaper and simpler installation. Earthing still a good idea but less important than at 220/240 volts.
Greater losses in cables unless thicker cables used at greater cost.
More transformers needed for lower supply voltage, greater capital AND running costs since many small transformers cost more to buy and to run than fewer larger ones.
Three phase supply briefly mentioned and relationship between voltages.
Single phase three wire supply, mentioned, common in USA, exists but much less common in UK.

Briefly mentioned many different supply voltages used in the past, and observed a general move towards 3 phase, four wire, at 230/400 volts in most places other than USA. Saudi Arabia to abolish 127/220 volts, other Arab countries to follow ?
127/220 volts ALMOST extinct in Europe.

Possible move toward 400/690 volt systems in industry.

Sensible limit as to distribution distance at different voltages, about one mile per thousand volts. "no law of man or nature" prevents greater distances, but a higher voltage is likely to be more sensible.
Also sensible limit to current being about 1000 amps, unless the distance is very short.

Moved on to battery voltages and merits of differing voltages according to size of system.

6 volts, obsolete for general use. Possibly worth considering for one or two lamps up to a few watts load. Gave example of such a system.
8 volts, even more obsolete !

12 volts= pretty much the standard in years gone by. Arguably still be best choice for small systems. Safer than 24 volts, very simple, good choice of equipment.only needs one battery. No shock risk. 12 volts can not sustain a continuing arc, unlike 24 volts. Sensible load limit about 200 watts.

16 volts-obsolete in general.

24 volts= increasingly popular for medium size systems. Almost no shock risk, significant fire risk without proper materials and workmanship. Good choice of equipment. sensible load limit one or two kw, unless used with an inverter.

32 volts- once popular in USA but now largely obsolete, limited choice of equipment.

36 volts- not common.

48/50/52 volts. Limited choice of equipment, primarily for larger inverter based systems. Borderline dangerous with regard to electric shock. Definitely dangerous as regards fire risk. Standard types of domestic light switch not recommended at this voltage.

110/120 volts- NOT DIY unless experienced. Special switches and socket outlets needed. SOME USA mains voltage equipment will work at this voltage.

220/240 volts . Definitely into dangerous territory. More applicable to community scale systems.

440 volts and up. Avoid domestically, this is utility scale stuff. Lethal.
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Re: Extinction Rebellion, ongoing disscussion.

Post by kenneal - lagger »

I have had a 300W 12V wind turbine sitting in the cellar for years because I can't work out how to get the power from the turbine to the battery store, a distance of about 30m including down the pole, affordably. The only way that I thought it could go is suspended along poles in the air but that causes a problem with an access. All the rest of my kit, about £6K+, which has been built up over about 30 years, is all 12V and I am beginning to wish that I had gone with 24V to start with. Ah! the benefits of hindsight!!
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Re: Extinction Rebellion, ongoing disscussion.

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Two answers occur to me.

Option one, simply use very thick cable. A scrap dealer might have something suitable for the value of the copper, not the makers list price.

Option two, In what condition is your battery ? when a one is required go for a 24 volt battery with a center tap so as to obtain a 3 wire DC system.
Split the existing 12 volt loads between the two 12 volt circuits, and split the existing PV charging between the two halves of the battery.
Use the wind turbine to charge the whole 24 volt battery, presuming that it is multi voltage.

Dont forget to double check what is the output voltage of the wind turbine. Some are 110 volt three phase between the alternator and the control box, and then a regulated DC supply suitable for charging a battery. The 110 volt circuit can be extended as needed in modest size cable. very thick cable is only needed between battery and control box.
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Re: Extinction Rebellion, ongoing disscussion.

Post by kenneal - lagger »

The turbine is definitely 12V as I had to chose when ordering it and they rewired it from 24V.

With a 24V battery system set up as two 12V banks connected in series can you take a connection from the 0v, the negative, and from the 12V + to an inverter and then take a connection from the 12V - to the 24V + to the same inverter to double the Ampere hours available, Adam?
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Re: Extinction Rebellion, ongoing disscussion.

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If it can not be changed back to 24 volt, and used with a 3 wire system, then I would look for some very thick cable.
70mm should suffice and may be affordable at scrap prices.
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Re: Extinction Rebellion, ongoing disscussion.

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Lesson three, again not a formal lesson but more of a round table discussion. Different means of generating electricity by burning fuel.

1) Burning coal or other fuel to raise steam that works a reciprocating steam engine. Largely obsolete, low efficiency, possibly worth considering in an emergency, esp if the engine already exists. Typical efficiency varies from 1% up to about 10%, maybe 15% under optimum conditions. Needs a lot of water.

2) Burning coal or other fuel to raise steam that works a steam turbine. Still in widespread use, but falling out of favour. works best on a large scale, efficiency from about 15% up to 35%. Little hope of improvement. Needs a lot of water.

3) Burning gas or liquid fuel in a gas turbine. Very popular, quick starting, not that efficient. no water needed. Low capital cost, can start and run unattended. Some types are dual fuel, burning natural gas normally but with light oil as an emergency alternative.
3b) As above but with a waste heat boiler that operates a steam turbine, highly efficient, 45% typically, has reached 50%. Very popular.

4) Diesel engines. Quick starting, can start and run unattended. fair efficiency in large sizes, usually needs no water.

5) Petrol engines poor efficiency, quick starting, dangerous fuel. Cheap, recommended for short term or emergency use.
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Re: Extinction Rebellion, ongoing disscussion.

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We then moved on to alternatives.

1) PV. simple to use and install, from a few watts up to megawatts. Much cheaper than previously. Manufacture of PV modules is a high technology operation. No moving parts long lasting and reliable.

2) Solar thermal. Useful when a lot of warm water is required, such as for hotels, hospitals, industrial laundries, heated bathing pools. Low tech.

2b) Solar thermal for steam raising to work a steam engine. Largely displaced by PV and electric drive.

2c) Solar thermal for desalination of sea water, low tech and user repairable, works fine but has been displaced by PV and reverse osmosis plant. Needs a lot of land.

3) Wind power, used on a large scale, domestic size turbines only worthwhile in very windy locations. Gave example of domestic wind turbine installation.

4a) Large scale hydro power, capital intensive, limited chance to expand in the UK as the best sites are already used. Note that the water is not consumed but is still available for other purposes. Dangerous if the dam breaks.

4b) Micro hydro. Has a lot of potential. Cost very variable.

5) Human powered generators. Excellent for short term or emergency needs. Limited to about 100 watts for cycle type machines, or about 15 watts for hand crank types.

6) Peltier generators, very low efficiency but this matters little if the waste heat is rejected to a room that needs heating in any case from a stove.

7) Fuel cells, still hugely expensive but show promise. Still need fuel despite often being listed as an "alternative" Silent. Possible "doom prep"

8) Disposable batteries, these ARE fuel of a type despite often being considered as an alternative. Simple, reliable, and safe. Hugely expensive at from £50 to £500 Per kilowatt hour compared to about 15 pence from a utility company. Useful for emergencies, for portable use, and economic for very small loads of up to a few watts short term or fractions of a watt long term.
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Re: Extinction Rebellion, ongoing disscussion.

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adam2 wrote: Thu Jul 08, 2021 7:57 pm 6) Peltier generators, very low efficiency but this matters little if the waste heat is rejected to a room that needs heating in any case from a stove.
How many watts can you get from a hot plate on a wood stove? 5-10W for a half decent LED lantern?

Datasheet for this gives a general idea, cooling the cool side might be tricky though.
https://uk.rs-online.com/web/p/peltier-modules/7650019/
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Re: Extinction Rebellion, ongoing disscussion.

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Yes, a peltier generator atop a wood stove and rejecting the heat from the cold side into the room air can achieve at least 10 watts and up to 15 watts in favorable circumstances. Some units sold on line claim greater outputs but I suspect chinese watts in such cases.

Note that whilst the efficiency is only about 1% to 2% that this does NOT imply the waste of 98% or 99% of fuel burnt. 2% into electricity and 98% into heating an otherwise cold room is a good result.

By water cooling the cold side of a peltier generator, greater output can be obtained, but this removes a lot of heat from the space that one wishes to heat. The pump consumes electricity, adds another point of failure, and plumbing is vulnerable to leaks and to freezing in severe weather.

Only worthwhile if you have a use for a lot of lukewarm water. Posibilities include a second hot water cylinder in cold mains water is preheated to say 35 degrees before passing into the second tank for heating to say 60 degrees.
Or limited central heating by use of HUGELY OVERSIZED radiators through which the warm water pumped. FIVE times the normal radiator area is about the minimum, bigger is better.

Both the above involve considerable capital cost and complication for marginal gains.
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Re: Extinction Rebellion, ongoing disscussion.

Post by kenneal - lagger »

Or underfloor heating instead of larger radiators.
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Re: Extinction Rebellion, ongoing disscussion.

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kenneal - lagger wrote: Mon Jul 12, 2021 1:33 am Or underfloor heating instead of larger radiators.
Yes that would work. Probably only worthwhile for a relatively large installation.
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Re: Extinction Rebellion, ongoing disscussion.

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Lesson four, again not a formal classroom type lesson but more of round table discussion.

Largely about older versus more recent technologies, there being a general belief that if it was old then it must be better.

Noted that steam engine drive and line shafting power distribution in factories is now almost extinct. Low efficiency of reciprocating steam engine noted, and losses in line shafting. Almost always replaced by individual or group electric drive of machines.
Merits of steam power as being relatively low technology, but these days unusual.

Briefly mentioned the famous American "liberty ships" of the last war. Driven by an obsolete type of reciprocating steam engine, long after the general use of steam turbines. Largely because the older type of engine was easier to make and needed no reduction gears, production of which was a bottleneck in wartime.

Briefly mentioned steam railway locomotives, largely extinct in most countries apart from limited heritage use. Fireless safety steam locomotives used until recently in munitions stores, petrol depots etc.

Moved on to traditional water wheels, interesting heritage, but insufficient power for most modern applications.

Moved on to traditional windmills, simple and low technology, need a lot of labour, not suitable for unattended operation.

Conversation diverged on to more general heritage versus modern.
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