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Is a new electrical ecosystem needed and what could it offer?
Question
The migration from no electricity to plentiful, reliable, affordable electricity is not a smooth one.
This energy access staircase model is based on the Energy Access Tiers defined by the Energy Sector Management Assistance Program (ESMAP).


The 48VDC Realisation Forum exists to advocate filling this gap with an electrical ecosystem that is intermediate between the familiar 12VDC environment used in cars, caravans and boats and small Solar Home Systems, and 230VAC mains electricity.

Chris Moller shares his thoughts on why a new electrical ecosystem is needed in this blog. We want to hear from you! Read his blog and let us know your thoughts and ideas on 48VDC by commenting below.
 
10 Replies
mapj1
3413 Posts
I'm not sure about the need for this.

Also looking for gaps in that stair case I'd argue the other way, at least in the western world, 230V single phase will soon not be enough as we try to make rechargeable lorries etc,
If we want anything it is probably a layer above our common 230/400 and less common 400/690 single/three phase, perhaps adding a tier of 690/1k2  for longer distances, and better compatibility with electric vehicle voltages that need to be in the high hundreds to kV region, and modern solar panels where the string voltages are also a few hundred.

As a crude rule of thumb, for distributing significant currents  without needing to oversize cables relative to thermal ratings to mitigate excess voltage drop, one meter per volt is a good starting point. so a 10KV line may go no more than a small multiple of 10km before cable loss means it is worth having transformers at each end,  and in the same way 12V DC may go 10-20m and run out of steam.
This is based on copper or aluminium cables and 5% to 10% voltage drops. If the interest is high efficiency, and for this it should be than really you do not want to lose more than that in the cables. Equally if you want to use steel wires for reasons of economy, these are more resistive, and you may want to go the other way and use slightly higher voltages for a given distance - the SWER systems in parts of Africa deliberately have a higher voltage to distance ratio, to allow the use of what is in effect strands of galvanised steel fence wire as the single HV conductor. (though these systems are not without their own problems)

At 48v generation and load will need to be within a few tens of metres (perhaps up to 100m) of each other, so there is little scope for spatial averaging by interconnection between islands.

The 48V Telecom system is not such a great fit to that model , as at both ends clever electronics is working hard to change it into something else - in the handset circuitry that mostly runs in 3.3V and 5V CMOS has to step up the last bit to pretend to be a moving iron earpiece and carbon mike, and at the exchange, the carefully spoofed same voltages are stepped down again for digitisation.Of course it is also a signalling  system not power transmission, and  so the length to voltage consideration does not really apply. (and to show there is no real voltage distance link for signalling, for gigabit Ethernet, voltages of order 2Vp-p  go a few hundred metres on a good day.)

I am not familiar with the 48V cooker, I imagine there is a serious fire risk from the sort of currents needed to supply a few households cooking, and arranging reliable ADS on DC is not easy - welder like arcs can be drawn without the zero-crossing to aid extinction.

I suggest that more technical meat is needed to make a convincing argument - a comparably safe system in terms of shock risk, if the assumption is that there will be bare conductors, that would be far easier to integrate with grid equipment as well, might be something closer to the UK RLV 55-0-55 supplies used on building sites.
Mike.


edited 11/3/2021 to tidy up the explanation and assumptions of the voltage drop range limits.
Simon Barker
873 Posts
In a village setting, the voltage drop could become significant, and at 48V, a few volts is rather more significant that at 230V.  If everything uses DC/DC power supplies, the more the voltage drops, the more current they will draw.

If the supply is limited to 800W (about 16A) per household, then you're not going to be doing a lot of cooking.  That's one 800W electric ring, so long as you turn off everything else in the house.
Helios
143 Posts
Interesting post , quite a lot of thinking in HVDC or UHVDC and its potential in grids of the future , i dont think the electric HGV will happen ,i mean it looks nice as an idea , but it doesnt necessarily translate to the best choice for point to point transport on different driving conditions , lots of \hgv going to HGV going to LNG and LBG and its giving some favourable results most notably in non CO2 and particulates. I think 3 phase is here to stay but if we do settle on on UHVDC then we have a whole load of possibilities to think about and as you say we get some efficiencies in some places and some non transformation problems voltage problems in others. Generally given how much electricty is wasted , i hope we can think through the transmission losses , as these are the bulk/volume transports of electrical energy , so quite of lot of initial savings to be explained there. Being as the voltage drop affects pretty much every calculation in electrical energy networks and systems , then this might suggest we see some different thinking ,as long lines might not deliver the best solution , so perhaps localised generation and grouping .I think its about 1000km for HV lines before the calculation really shows. local renewables could change things taking some areas off grid, so the transmission grid of the future will be somthing possibly carrying a lot more at UHVDC , and if new housing is all electric , we have to plan for peak winter transmission flows being high , but once to distributon I think we will have to re specifiy at 600-800v ac (more than 3 phase is a very interesting thought), either that or think the unthinable and re specify every street cable in the uk dont forget a lot of the high energy individual loads could come off grid .   
Helios
143 Posts
mmm thinking about this a little more , cant use steel for conductors , specificying the generator units to be compatable is difficult and perhaps put this to one side at the moment , as like everything else generator tech has moved on.
I guess the big question is do we need an electricty transmission grid at all ?? You could have a sort of system where you have gas powered engines/generators generating to whatever you spec your big ring mains to 11kv and just run them to demands ??? so thats an interesting question.

A UHVDC grid could be specified to run to all the main cities , and if you have this it doesnt matter where you site your generation units so much , current thinking is for HV aluminium suspended wires , but obviously when things like the new sort of demands are thought about , then current conductor sizing probebly wouldnt do it . Given NJK cables have an undersea cable rated at 650kv and are working on a 750kv then one cable can now carry 3000mw and these are DC voltages , running temps at 70oC plus, so using these in an underground network , would probebely need some cooling and some very ingenious containment to last as infrastructure . 
The next question how much can be saved in transmission losses by going to UHVDC ??? and we all know it depends how high a volyage you can specify I would guess (and it is a guess) at least 1000mw possibly 2000mw at peak flows , however being as electricity looks like running cars and homes ,then at some point the gov are going to have to think about peak loads , and then there going to realise the current specification for the grid could not do it ,let alone the other fact that most on call generation is being replaced by renewables .
beyond transmission the question becomes more complex , if we have UHVDC transmission then we can run DC to distribution , but at the moment there isnt any HV DC demand (other than the efficiency of car charging) and the re specifyng the main 11kv grid main would be a difficult transition , even though it eventually would liberate previous electrical losses. beyond the 11Kv ring mains then things get very difficult , but my belief is ,if the gov does move to the fully electric/well designed  new build (and it may bee should have been done a long time ago)  then urban grids re specifying ,has to be done , but this will be very expensive and very difficult to tansition particulary where old inefficient housing is kept , as winter loads will be quite a lot higher perhaps 60GW or more .

I guess there are specialist engineers that model this sort of stuff , and I am having a go at very complex electrical engineering problem , but what sort of transmission grid is possible is quite exciting , however at distribution switiching to using more electricty , will need the efficiencies that a re specification can deliver , in short the shifting of energy use to electrical power (and this is useful) we have a distribution grid that cannot deliver the sorts of electrical quantities , that such a switch is outlaying as demand patterns.

My choice is to work out where you need to supply with a electricty transmission grid and where you dont , as a start and if the modern cabling can be routed  in an undergoround system , if we still cant get a coherent system for electricty transmission systems , then plan for a gas fired local generation .

I think this question will be one of the most important future engineering problems , that our best engineers can figure out , there are new specifcations to take adavantage of , but its a really difficult transition cost and challenge.
Actually, I wouldn't disagree with either @mapj1 or @Simon_Barker's points - the physics of voltage drop are unarguable.  There is no doubt that higher voltages for distribution make sense - not least because better insulation is cheaper than more copper - this may turn out to be the only way we can distribute enough power to charge all the electric vehicles we're going to have.  For a given insulation level, switching from AC to DC gives a 41% power advantage straight away.

What HAS changed is the ease with which voltage can be changed at point-of-load - and DC more easily than AC, so supply voltage stabilization is much less critical than it was.  Buck converters are amazingly small, cheap and efficient - at least for applications that don't require galvanic isolation.  

The other thing that has changed is a growing recognition that the very significant proportion of the 900 million or so world population currently without any form of electricity and who are likely always to be beyond reach of the grid, and the 500 million or so whose electricity is more often off than on, cannot afford self-contained grid-standard solutions.  If the affluent parts of the world take 48VDC seriously, this will help drive the economies of scale for a solution that is more versatile than 12VDC, and more affordable than 230VAC.

Cooking with 48VDC is not a serious option in the Developed World.  However, for the half of the world population that currently cooks with solid fuel, it is good enough to drive a green revolution.

Arcing is certainly an acknowledged concern for LVDC - though arc detection evidently still has some issues.  Some very imaginative ways are emerging for power semiconductors to break the current flow, both in switches and connectors.  This will be very important at higher voltages and currents.

The bottom line in my view is that our capabilities with solid state electronics and the complexities of what we need electricity to do for us justify a re-visiting of the "Battle of the Currents", and a very serious reconsideration of Low Voltage Direct Current as an attractive electrical ecosystem.  48VDC is but one possible point on that journey, and there will need to be others.
mapj1
3413 Posts
You may not be aware of  The 2020 Tracking SDG7 Report  which is relevant to this, including amongst much else some   up to date data on access to electricity and cooking facilities on a country by country basis, which make interesting reading.
Page 7 suggests that burning wood and bottled gas are the two main cooking fuels of choice rurally and in towns respectively for what may be considered as developing countries,so maybe what is really needed is a better gas bottle - experiments with blending hydrogen or bioderived methane with fossil fuels for example - I agree there is a real engineering problem to solve, but it may be the solutions are mechanical and chemical as well as electrical.
Mike.
Hi Mike,

Thank you for your words of good sense on cooking - a bit off the subject of 48VDC, but very interesting and really important for many parts of the world.  It's unfortunate that most people want to cook just after the sun has gone down.  On paper, it looks as though it's possible to generate low-pressure hydrogen using an electrolyser from your solar panels, store it in the roof space in a balloon perhaps a metre in diameter, and put a weight on the balloon when you want to run your gas cooker.  I suggested it to the MECS programme a while back, but I don't know if anyone has explored it. 
Helios
143 Posts
Isnt the problem with roof top low Hydrogen systems ,that you cannot use them in hot climates ??  perhaps this is what the research found 
Helios
143 Posts
Ok thinking about this a little further mainly from a historical perspective , the clean air act of 1960 was a way of dealing of dealing with all the coal burning in urban spcaes , the steam turbine had developed to larger power outputs , so the remote power generation station was possible , and once you had the remote power station you you needed the higher voltage cables.  The situation now is that we can have cleaner burning systems , some countries just have banks of gensets , that come on and off load as the daily loads rise and fall. be pretty staright forward to specify them to 11kv and connect them where the big HV transformers used to be , 
Favourite news was that Bill Gates was working super low ohm cables , although I dont think superccoled conductot cables would be easy to do in practice , however as in the way of yin and yang Bill Gates now backs spraying chalk powder into space to create a sort of sun dimmer , which would be a disaster as you would reduce the very thing that is capturing CO2 i.e. Photosynthesis.    Doh back to the drawing board on that one , and its been tried a few years ago where very thin mirrors were being touted .   Come on Bill ya all know its a Biochemistry problem in the end, not more data centres.

Bit puzzled by govs warm home spending spree , especially being as some insulation isnt exactly eco friendly (phenolic foams etc) but there arnt enough sheep to provide the more eco friendly version , actually given some other annoucments i am very unconvinced the gov understand the eco thinking at all , found another hydrogen promo "emissions free transport"   whats water vapour I thought ??? oh yes its an emission
having a big smile moment calculations for waste incineration now done , those bad boy inefficenct systems , some are even less than 30% converson of fuel energy to electricty , and they have to bury the ash residue as its toxic ...   
Simon Barker
873 Posts
Helios:

having a big smile moment calculations for waste incineration now done , those bad boy inefficenct systems , some are even less than 30% converson of fuel energy to electricty , and they have to bury the ash residue as its toxic ...   

The waste from the incinerator in my county is used as a building material.  They don't dump most of it.

Incinerating waste has got to be better than chucking it in a landfill to rot down over years.

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