So if I stick to 14KW I don't need a new fuse

[plugwash]

Furthermore these changes will probably markedly alter the timing of 'peak' periods

If people get home from work, and immediately start charging their electric car, turn on their heat pump to warm up the house and start cooking dinner on their electric cooker then that will just be adding more demand at what is already the peak time of day.

It seems clear to me that some kind of scheme is needed to incentivize matching demand to supply, but I'm no expert on the details of how that can best be made to work. "Agile Octopus" uses a system where pricing is based on "day ahead" wholesale rates but the problem I see with that is it could cause everyone to dogpile on whichever hour happens to be cheapest.

Perhaps a tariff where you get a set number of hours each day at each price, but the supplier determines which hours have which prices (and can assign different cheap hours to different customers to balance load).

 

[Steven Prentice]

I think you'll find that the average is quite a lot less than that.

Probably John, yes, the actual real world demand is probably a lot less than 20A, but somewhere in the back of my head that figure is the design value for the system.

It seems clear to me that some kind of scheme is needed to incentivize matching demand to supply, but I'm no expert on the details of how that can best be made to work. "Agile Octopus" uses a system where pricing is based on "day ahead" wholesale rates but the problem I see with that is it could cause everyone to dogpile on whichever hour happens to be cheapest.

To an extent the price concious will alter their behaviour to the cheapest hour, however there will always be peaks and troughs in the system, few people I know will get up at 4:00 in the morning just because it is cheapest then to make a cup of tea, or be up past midnight in the winter to get the clothes washed and put in the drier. So you'd get car charging and heating overnight, but the early evening peak will be much the same, or greater as we switch to all electric and no gas.

 

[JohnW2]

Probably John, yes, the actual real world demand is probably a lot less than 20A, but somewhere in the back of my head that figure is the design value for the system.

Quoting from (this) ...

".... After diversity maximum demand (ADMD) is used in the design of electricity distribution networks where demand is aggregated over a large number of customers. ADMD accounts for the coincident peak load a network is likely to experience over its lifetime and as such is an overestimation of typical demand. ... Network peak demand, considering diversity between customers is time coincident where within each household there are times, mainly the 4-8pm period, in which electricity is used simultaneously, for example when all appliances are used at the same time. An ADMD is normally 2kW when electric heating isn’t present

. So, for houses without electric heating, the "design value" appears to be about 8.7A [2kW at 230V).

To an extent the price concious will alter their behaviour to the cheapest hour, however there will always be peaks and troughs in the system, few people I know will get up at 4:00 in the morning just because it is cheapest then to make a cup of tea, or be up past midnight in the winter to get the clothes washed and put in the drier. So you'd get car charging and heating overnight, but the early evening peak will be much the same, or greater as we switch to all electric and no gas.

All that can be achieved by playing with prices at different times of the day is to try to iron out those peaks and troughs as much as possible. However, as I said, the total amount of available energy still has to be adequate to satisfy demand and, even if demand could be made to be almost constant (which is obviously the optimum situation), I don't think that would be the case with existing generation/distribution capabilities if widespread deployment of all these 'new' loads were to happen 'per 'government targets'.

It's only a few years ago when, before anyone was giving any significant thought to EVs or heat pumps, that serious concerns were being expressed about the adequacy of electricity availability in the 2020s, particularly because of the impending decommissioning of all our existing nuclear facilities and, as far as I am aware, still only one replacement being worked on.

Kind Regards, John

 

[JohnW2]

If people get home from work, and immediately start charging their electric car, turn on their heat pump to warm up the house and start cooking dinner on their electric cooker then that will just be adding more demand at what is already the peak time of day.

Someone (quite possibly you) made that very same point recently.

Most people's behaviour is driven/incentivised by money. If it cost them twice (or 5 times!) as much to charge their car if they started the charging as soon as they got home from work than if they delayed the start of charging for, say 4-5 hours, I don't think that a lot would behave as you suggest.

It seems clear to me that some kind of scheme is needed to incentivize matching demand to supply,

Indeed - as above.

It always has been (since long before people had heard about EVs or heat pumps), and always will be, in the interests of generators and distributors to achieve as constant a demand during the 24h as they can - and that's obviously the reason why tariffs such as E7 and E10 came into existence. As you suggest, the tariffs will undoubtedly become more complex, and more 'dynamic' (to some extent facilitated by 'smart' meters), but the concept and purpose will remain the same.

However, as I keep saying, even if one could completely remove variation in demand during the 24h, one would still need there to be enough total energy available to satisfy the demand - and, as things currently look, it seems unlikely (at least to me) that that will be the case if switching to EVs and heat pumps etc happens as rapidly as is being suggested.

Kind Regards, John

 

[Vicario]

All very interesting. I didn't expect my question to generate three pages (so far) of debate. Can I ask one more thing? My street has about 50 three-bedroom semis. Would these all rely one big DNO fuse further down the line? I have read on this forum that tampering with the main cutout can 'blow the fuse at the substation'. This would presumably need to be 500A or more assuming 10A per property is the median expected usage per home.

 

[Steven Prentice]

All very interesting. I didn't expect my question to generate three pages (so far) of debate. Can I ask one more thing? My street has about 50 three-bedroom semis. Would these all rely one big DNO fuse further down the line? I have read on this forum that tampering with the main cutout can 'blow the fuse at the substation'. This would presumably need to be 500A or more assuming 10A per property is the median expected usage per home.

Yes, there will be a 'big fuse' in the substation supplying you and your neighbours. Whether it is a fuse or circuit breaker isn't so relevant here, it's purpose is to protect the cables in the street. Increasing one fuse in one house in a street of 50 and that single house using more is unlikely to cause problems. If all the 50 houses did this then you could cause problems. The supplier should know how close to the limit the cable is and what the 'big fuse' is rated at, and that's why you need to talk to them about it. Might be simple that they just replace your fuse, might be that they have to also replace the 'big fuse' in the substation, might be they need to dig up the street to replace their cables.

 

[Harry Bloomfield]

I think you'll find that the average is quite a lot less than that.

I agree and it is fairly easy to work out a personal average current value. Most people know roughly how many Kwh they use per year. From that annual consumption an actual average current can easily be calculated. Last time I bothered to check, mine averaged out from memory at less than 2amps.

 

[Steven Prentice]

Quoting from (this) ...
. So, for houses without electric heating, the "design value" appears to be about 8.7A [2kW at 230V).

Just for the point of the discussion. If I read the report correctly that 2kW (8.3A? the system was mostly installed many years ago, at 240V) is the maximum demand calculated for all the houses. As you use a smaller number of houses then the average maximum demand per house increases (bigger peaks and troughs). This value could double for a smaller number of houses depending who is living in them (5kW was quoted for young people, 3kW for old people). This is also per phase, in a street 1/3 of the houses will be on each phase, e.g. 30 houses from that circuit, 10 houses per phase, a greater variation in peak demands. Going with the larger figures quoted at about 4kW per house, 25 houses (gives a 'street' of 75 houses), 17A per house? The design engineer will also have added a factor on top of that, 10%? and possibly rounded up too, and suddenly that design amps is getting closer to the 20A in the back of my mind. I think the big difference is averaging the maximum demand for all the thousands of houses, and the maximum demand for a single phase of a single circuit in 1 street being the 2 extremes of the scale.

 

[Steven Prentice]

I agree and it is fairly easy to work out a personal average current value. Most people know roughly how many Kwh they use per year. From that annual consumption an actual average current can easily be calculated. Last time I bothered to check, mine averaged out from memory at less than 2amps.

However the system is designed to supply your maximum, what is it when you jump into your 10kW power shower?

 

[Harry Bloomfield]

However the system is designed to supply your maximum, what is it when you jump into your 10kW power shower?

That is not the point, we are discussing average demand, not instantaneous demand. My 10Kw shower is maybe on for a couple of minutes per day.

 

[Adam_151]

The other thing worth thinking about, is traditionally highest demand came when it was cold outside with most of the heavy demand being heating*, its becomming not so simple now, EV charging is not dependant on temperature, and while heat pumps largely are atm, its probably only a matter of time before someone figures they might be able to sell a good few ducted heating systems if they included a reversing valve and could offer a system that cools the whole house for not much more than one that simply heats.

*Short term overloads are epected and as long as it averages out to a sensible value then its not too much of a problem, the transformers are oil filled so have a capacity to sink quite a lot of heat, especially when its in the cool night air, and the cables in the cold wet ground will have a similar effect

 

[Steven Prentice]

That is not the point, we are discussing average demand, not instantaneous demand. My 10Kw shower is maybe on for a couple of minutes per day.

My apologies, I had got the discussion all wrong, I thought it was whether the OP would be able to have a larger fuse and then onto how the system was designed a bit. That's OK though, 2A average current and say, 25 houses in the street per phase, I guess the Electricity company only needs a 50A supply from it's distribution board? (My road has 5 supplies, if they followed what you are suggesting 2A average current for the design, my 10kW shower would trip the power every time I jumped into it). Might want to find the paper that John was referring to earlier, Average Max Demand is the figure to use, not average demand (including the time you are out at work or asleep).



Adam, heat pumps.... they can run in reverse

 

[Harry Bloomfield]

My apologies, I had got the discussion all wrong, I thought it was whether the OP would be able to have a larger fuse and then onto how the system was designed a bit. That's OK though, 2A average current and say, 25 houses in the street per phase, I guess the Electricity company only needs a 50A supply from it's distribution board? (My road has 5 supplies, if they followed what you are suggesting 2A average current for the design, my 10kW shower would trip the power every time I jumped into it). Might want to find the paper that John was referring to earlier, Average Max Demand is the figure to use, not average demand (including the time you are out at work or asleep).

There is a massive difference between average demand and the maximum.

 

[Steven Prentice]

There is a massive difference between average demand and the maximum.

I can see this going around and around but never mind. Yes and also a big difference between average demand and average maximum demand... which is the values quoted above, and what the system designs are based on. I suspect you are looking for a 'discussion' for the sake of a discussion.

 

[Harry Bloomfield]

I can see this going around and around but never mind. Yes and also a big difference between average demand and average maximum demand... which is the values quoted above, and what the system designs are based on. I suspect you are looking for a 'discussion' for the sake of a discussion.

No, merely trying to explain some of what is involved..