Question about upgrading to 3 phase

[monkey5]

Just as a side note, what about solar and battery storage and have hot water tank with imersions.

 

[Geoff Toms]

Just as a side note, what about solar and battery storage and have hot water tank with imersions.

Oh yes. That's all part of the overall plan. We're very aware that electric boilers cost more to run than gas, but when you're generating some of that electricity yourself it's not so bad.
We've looked into solar. In fact we might have had it installed by now but were let down. We're an ideal location, in the south of the country and with one face of our roof pointing south too.
Of course, there's another conversation to be had about whether to go 3 phase to allow selling more electricity back to the grid at the best rate, but I didn't mention that earlier because I didn't want to over-complicate things - and the solar has been put back now - probably until next year. All of the installers are very busy!

 

[binky]

Oh yes. That's all part of the overall plan. We're very aware that electric boilers cost more to run than gas, but when you're generating some of that electricity yourself it's not so bad.
We've looked into solar. In fact we might have had it installed by now but were let down. We're an ideal location, in the south of the country and with one face of our roof pointing south too.
Of course, there's another conversation to be had about whether to go 3 phase to allow selling more electricity back to the grid at the best rate, but I didn't mention that earlier because I didn't want to over-complicate things - and the solar has been put back now - probably until next year. All of the installers are very busy!

how big an array do you think you can get on the roof?

 

[truffle pig]

just be mindful if you are going to go 3 phase, if you have single phase solar PV it will only feed that phase of your installation!!

 

[binky]

What you're all saying is very heartening, but I do want to be safe too. I certainly don't want to fall into the trap of having a system where it all works but the cables get warm and plastic starts to melt. I'll get someone to work out our loads, and they'll hopefully agree with you that it either doesn't need an upgrade - or if it does, it'll be limited to a single phase increase from 100 to 125.
A question about fuses / MCBs: Our DB has printed on it (I'm sure they all do) "Do not exceed 100A total load". Does that mean I shouldn't have all my MCBs/RCCDs adding up to more than 100A - or is that irrelevant and it's just talking about the calculated total load? (I hope it's the latter, cos we're going to be well over 100A on fuses/MCBs/RCCDs)

you probably have a 32 Amp circuit for the upstairs sockets, but all you ever plug in is a few side lights and the hoover, and occasionally the hair dryer. As I said before it's not about the circuit protection and what the numbers are on those, it's about the overall load on the system.

 

[GM at CA UK]

As others have said it is likely that you don't actually need the 3 phase upgrade. We have been involved in a lot of maximum demand surveys and you would be surprised how little domestic installations draw from the grid at any point in time, even with electric heating, showers, cooking, etc. The diversity calculations in the regs. are way out of date. Of course a problem you have is that you haven't got some of the new loads installed yet and so any max demand survey done now would not include them. Here's an example I have posted before of where a DNO recommended 3-phase supply was proven to not be required saving the customer a small fortune. https://issuu.com/hamervillemediagroup/docs/pe_july_august_2023/52 Furthermore, if you add solar panels and battery storage your need for power from the grid will reduce further.

 

[Geoff Toms]

how big an array do you think you can get on the roof?

13 panels (including 3 on the garage roof) and we looked at different sizes as the first deal started to fall apart. The total capacity was going up from about 5.3kW to about 5.5kW. After it fell apart we started to ponder whether an AC system was better than the DC they were selling us.

just be mindful if you are going to go 3 phase, if you have single phase solar PV it will only feed that phase of your installation!!

Oh. OK. That never came up at the time, probably because everyone assumed we would remain single phase (and they would cap the feed to the grid)

you probably have a 32 Amp circuit for the upstairs sockets, but all you ever plug in is a few side lights and the hoover, and occasionally the hair dryer. As I said before it's not about the circuit protection and what the numbers are on those, it's about the overall load on the system.

Ha ha! Yes. Very true - although in this house the upstairs would include a bunch of computers, some of them with PSUs up to 1kW!

As others have said it is likely that you don't actually need the 3 phase upgrade. We have been involved in a lot of maximum demand surveys and you would be surprised how little domestic installations draw from the grid at any point in time, even with electric heating, showers, cooking, etc. The diversity calculations in the regs. are way out of date. Of course a problem you have is that you haven't got some of the new loads installed yet and so any max demand survey done now would not include them. Here's an example I have posted before of where a DNO recommended 3-phase supply was proven to not be required saving the customer a small fortune. https://issuu.com/hamervillemediagroup/docs/pe_july_august_2023/52 Furthermore, if you add solar panels and battery storage your need for power from the grid will reduce further.

Thank you very much! I'll download that and have a read (and show my wife too) As I was saying above, anything that helps prove that we *don't* need to spend a fortune going to 3 phase is very welcome here!

 

[johnb2713]

Oh yes. That's all part of the overall plan. We're very aware that electric boilers cost more to run than gas, but when you're generating some of that electricity yourself it's not so bad.

Seriously, forget that idea if youre talking about a straight, resistive electric boiler, it will bleed you dry. Solar energy will be in very short supply when you need it most (winter).
Put your money into a Tepeo boiler or similar and you can then at least use off peak energy (mine is 7.5p kWh) and solar when it's available.

 

[Geoff Toms]

Seriously, forget that idea if youre talking about a straight, resistive electric boiler, it will bleed you dry. Solar energy will be in very short supply when you need it most (winter).
Put your money into a Tepeo boiler or similar and you can then at least use off peak energy (mine is 7.5p kWh) and solar when it's available.

Point taken. Will definitely be looking into those Tepeo ZEB. Very interesting (if we can find space for them in a small house!)

 

[Geoff Toms]

just be mindful if you are going to go 3 phase, if you have single phase solar PV it will only feed that phase of your installation!!

This has sparked off a lot of thought here. So, how would a solar pv system be wired into a CU if you *had* gone to 3 phase? You obviously need the solar to feed all of your circuits, but the 3 phase input will be split between circuits (or am I just betraying my ignorance? I don't mind if I am, of course. I'm learning about this from a very low starting point!)

 

[Geoff Toms]

As others have said it is likely that you don't actually need the 3 phase upgrade. We have been involved in a lot of maximum demand surveys and you would be surprised how little domestic installations draw from the grid at any point in time, even with electric heating, showers, cooking, etc. The diversity calculations in the regs. are way out of date. Of course a problem you have is that you haven't got some of the new loads installed yet and so any max demand survey done now would not include them. Here's an example I have posted before of where a DNO recommended 3-phase supply was proven to not be required saving the customer a small fortune. https://issuu.com/hamervillemediagroup/docs/pe_july_august_2023/52 Furthermore, if you add solar panels and battery storage your need for power from the grid will reduce further.

More thoughts, inspired by your final comment. (And I freely admit we don't know a lot about solar - although it turned out we had learned a lot more than the guys who were going to be fitting the system we ordered back in the spring) So ... how does the solar pv system wire into our DB? Is it like a secondary electricity supplier, which is protected by its own mains fuse of about 24A or 32A? If so, then couldn't we potentially have more than the 100A that the DB is rated for coming in? I'm sure I'm thinking about this all wrong.

 

[GM at CA UK]

More thoughts, inspired by your final comment. (And I freely admit we don't know a lot about solar - although it turned out we had learned a lot more than the guys who were going to be fitting the system we ordered back in the spring) So ... how does the solar pv system wire into our DB? Is it like a secondary electricity supplier, which is protected by its own mains fuse of about 24A or 32A? If so, then couldn't we potentially have more than the 100A that the DB is rated for coming in? I'm sure I'm thinking about this all wrong.

I'm no expert on how such a system is exactly implemented (I'm sure others on here could tell you) but in logging energy use in the field we have come across a couple of situations where a complete installation is running from a big "off grid" PV inverter (so no feed in), with any excess going to charge batteries, and with the incoming supply only feeding into the inverter. They are set so that the installation runs off the PV, unless there is not enough sun, in which case it then also draws power from the batteries, and if the PV and batteries are not enough, the balance is drawn from incoming mains supply. For large parts of the day they generate more from the PV than they use, which charges the batteries, and during the evening they run from the batteries, with the mains there ready if they don't have enough charge. During the peek charging months they generally use no power from the grid, and a little when its gloomier. That really depends on how big a PV array and how much storage capacity they have. Maybe you could do something like that? Or maybe you could split your installation so some of it runs from the existing single phase DNO supply and the other part is entirely off grid PV / Battery. However, as I mentioned at the start, I'm no expert in this area and I'm sure there are others in here that know all about such things.

 

[GM at CA UK]

I'm no expert on how such a system is exactly implemented (I'm sure others on here could tell you) but in logging energy use in the field we have come across a couple of situations where a complete installation is running from a big "off grid" PV inverter (so no feed in), with any excess going to charge batteries, and with the incoming supply only feeding into the inverter. They are set so that the installation runs off the PV, unless there is not enough sun, in which case it then also draws power from the batteries, and if the PV and batteries are not enough, the balance is drawn from incoming mains supply. For large parts of the day they generate more from the PV than they use, which charges the batteries, and during the evening they run from the batteries, with the mains there ready if they don't have enough charge. During the peek charging months they generally use no power from the grid, and a little when its gloomier. That really depends on how big a PV array and how much storage capacity they have. Maybe you could do something like that? Or maybe you could split your installation so some of it runs from the existing single phase DNO supply and the other part is entirely off grid PV / Battery. However, as I mentioned at the start, I'm no expert in this area and I'm sure there are others in here that know all about such things.

.... and there is still every chance you won't need any of it and the existing 100A supply will be fine for your intended loads

 

[binky]

More thoughts, inspired by your final comment. (And I freely admit we don't know a lot about solar - although it turned out we had learned a lot more than the guys who were going to be fitting the system we ordered back in the spring) So ... how does the solar pv system wire into our DB? Is it like a secondary electricity supplier, which is protected by its own mains fuse of about 24A or 32A? If so, then couldn't we potentially have more than the 100A that the DB is rated for coming in? I'm sure I'm thinking about this all wrong.

it will be wired as it's own circuit into the distribution board, and as it's back feeding the board, it will reduce the load being pulled from the grid, thereby reducing the ampage going through the main switch.

 

[Geoff Toms]

Seriously, forget that idea if youre talking about a straight, resistive electric boiler, it will bleed you dry. Solar energy will be in very short supply when you need it most (winter).
Put your money into a Tepeo boiler or similar and you can then at least use off peak energy (mine is 7.5p kWh) and solar when it's available.

Update! Yes. Really liking this ZEB. I've been reading up on it all afternoon (and realised we missed out on a trial that OVO were doing where they paid for installation!) We've now got in touch with tepeo to register our interest, and are waiting for them to give us a call.
Thanks for the recommendation.

 

[johnb2713]

Update! Yes. Really liking this ZEB. I've been reading up on it all afternoon (and realised we missed out on a trial that OVO were doing where they paid for installation!) We've now got in touch with tepeo to register our interest, and are waiting for them to give us a call.
Thanks for the recommendation.

Its a really good solution.

Have a look here if you havent seen it already.....

 

[Geoff Toms]

Its a really good solution.

Have a look here if you havent seen it already.....

Thanks. Yes, I did watch that video. It went a long way towards convincing me.

 

[binky]

Its a really good solution.

Have a look here if you havent seen it already.....

reminds me of the old centralised night storage heaters.

 

[johnb2713]

reminds me of the old centralised night storage heaters.

The principle is the same but the technology used is way better. It's great that it can use conventional flow temperatures around a wet central heating system and due to very high temperatures in the core can store a lot of energy which is contained in a very well insulated enclosure with minimal losses until needed.
No, I havent bought one yet, I'll wait and see how the heatpump manages first