Three phase supply - need a three phase heat pump and battery system?

[lookseehear]

We're moving our electricity supply and National Grid said they only put in three phase in this situation. I initially was quite pleased about this - it felt future proof.

 

I'm now looking at solar and battery combinations, and installers seem less experienced with three phase systems and the cost seems higher. There's the benefit of being guaranteed ~12kW export balanced across the three phases. We're also planning to put in an ASHP and I assume that we would now need to put in a three phase ASHP to spread the load over the phases, and again there looks like there's less choice and potentially more cost involved.

 

It feels like going three phase has added cost and complexity at this point. Is it possible to run it all off one phase or push National Grid to put single phase in? It feels like an own goal with three phase to not have the heat pump and battery on the same phase, but then the system will be out of balance.

 

Am I missing something or does it all have to be three phase to play nicely together.

[markc]

3 phase supply and only use 1 phase if that covers your needs, if you do have a 3 phase heat pump and want that to run from the battery then you will need a battery on each phase. Or you have the 3ph heat pump running from grid and use a single phase battery for your domestic needs and export any spare to offset the heat pump requirements.

[Nickfromwales]

Net metering at the 3ph meter has been discussed here quite a lot, and makes for great reading. 
 

In a nutshell you can consume or export on any 1 of the 3 phases, or 2, or 3, and the sum of the activity affects the meter reading in balance.

 

So, you can have a solar system on 1ph, exporting, and be pulling in power over L2, and if it’s 1kw in and 1kw out, the meter stands still.

 

No need for a 3ph ASHP, but 3ph solar and batteries is now pretty easy to resolve, so don’t panic too much here just get the right advice off the right people.

@lookseehear If you want a very good designer and installer that doesn’t charge the earth let me know, (PM). 
 

If you choose well, then you can connect ASHP > solar > batteries > hot water > EV charger in one family of products that “talk”, with the advantage of rapid EV charging with 3ph.

 

You can have bigger solar and batteries on 1ph, just then you’d go for a hybrid system so the number of panels and size of batteries isn’t the value you ‘ask’ the DNO for permission to connect to the AC grid, aka “AC coupled equipment’”, just the size of the inverter is declared and whatever’s behind the inverter is then of no consequence.

 

Plenty of options and solutions, and I’ve done a good few domestic new builds where the clients had 3ph and large on site micro-generation, with a mix of 1ph and 3ph equipment on site. When I explain the many available options to my clients, with reason / rationale (and how the entire electric arrangement can be harmonised quite easily), the fog soon clears; it’s just folk don’t know what they don’t know, basically. Also, there’s way too many salespeople out there which is why I stay impartial.

 

Lots on here on the subject. 

[Tom]

We have a 3ph PV system for the 13kW we have on the roof and a single phase ASHP - as @Nickfromwales says the smart meter nets out the demand/generation. So if say you are generating 1kW on each of the three phases, but the ASHP is drawing 3kW on only one phase, the meter stays still. They call it "vector sum metering" I believe.

Edited 23 hours ago by Tom

[SimonD]

39 minutes ago, Nickfromwales said:

No need for a 3ph ASHP

 

Although you should listen to the language coming out of the mouth of the electrician I use for heat pump installs when a hp installer put in a 1ph hp cascade onto a 3ph system he'd installed without telling him and without balancing!

[Nickfromwales]

39 minutes ago, SimonD said:

 

Although you should listen to the language coming out of the mouth of the electrician I use for heat pump installs when a hp installer put in a 1ph hp cascade onto a 3ph system he'd installed without telling him and without balancing!

Nice.

 

I went bat-shit crazy balancing out a 3ph system in Leicestershire, as it not only makes sense by design, but also pays long term dividends for the client of the on-site generation and consumption are given proper consideration from the outset; I’d planned the 3ph CU and circuits well in advance of the house even being built, plus all the M&E requirements et-al, so there was a plan in place for when we were allowed on site to execute all of these works.

 

At that early stage I could plan penetrations through steels, ahead of them being delivered to site, but my favourite () bit was being able to see quite quickly that neither the architect nor the SE gave two hoots as to a) where plant was going to need to reside, and b) how pipes and ducts were to get about the building without significant compromise.

 

Getting your ducks (ducts) in a row early on (for power / other services entering and exiting the building) makes so much light work of 1st fix, it’s just a genuine shame to see missed opportunities when these details etc have not been discussed way in advance of the construction phase. 
 

 

Plan ahead people!!   

[ProDave]

So are ALL 3 phase meters installed now "net metering"?

[lookseehear]

OK I think I'm understanding the metering aspect, with import and export netting off, but does that play well with time of use tariffs? If I am exporting from the battery in the evening, but drawing from the grid during the day to run heating, those things won't surely net off in the same way that running the ASHP from the battery would do?

 

We're a bit limited on the size of our solar array because only one aspect makes sense and it's low pitch (30 degrees) which means that the max we can squeeze in would be 5-6kW peak. I was hoping to put in a large battery with scope to increase capacity in the future so that during the winter we're minimising running the ASHP off peak rates (eg using Octopus Cosy to top up the battery).

[Nickfromwales]

35 minutes ago, ProDave said:

So are ALL 3 phase meters installed now "net metering"?

I think these “should”, by the laws of physics, as in EMF passes through coils to register the flow of energy, so should work bi-directionally in principal.
 

Depends on whether the software is told to register the flow in each direction or not, eg it charges you but doesn’t (won’t) refund you.

 

So to answer the question, I’m not sure.

[Tom]

1 hour ago, ProDave said:

So are ALL 3 phase meters installed now "net metering"?

 

When I was researching this it seemed that this was the new standard for 3ph meters - so I'm guessing any new installation using a new meter should do this. This was based purely on internet research though - asking the ASHP installers/Octopus/electrician was just met with a blank stare. 

[Nickfromwales]

2 minutes ago, Tom said:

asking the ASHP installers/Octopus/electrician was just met with a blank stare. 

Likewise. 
 

My solar go to guy was as curious to know, but the industry in general (and the on site sparkies at the time) were clueless.

 

I even drew a picture on the wall, of the how the pickup coils were positioned and functioned, to show it should be a feature that comes regardless, but also got blank stares.

[ProDave]

I may be wrong but I would expect a 3 phase meter to have 3 metering coils, one per phase.  It would then be up to the software how it combined them.

 

The old spinning disk meters could do nothing other than net metering, even going backwards unless there was a ratchet mechanism to stop that.  From a legal perspective you might expect an electronic meter to give the same result as a spinning disk meter ?

[Dillsue]

I'm not certain on this but there was a long discussion on net metering a while ago and I think the upshot was the net metering only happened in real time ie you had to be importing on one phase and exporting on another at the same time for them to cancel each other out. If you imported one minute and exported the the same the next minute then you wouldn't get net metering??

[Tom]

1 hour ago, Dillsue said:

I'm not certain on this but there was a long discussion on net metering a while ago and I think the upshot was the net metering only happened in real time ie you had to be importing on one phase and exporting on another at the same time for them to cancel each other out. If you imported one minute and exported the the same the next minute then you wouldn't get net metering??

Correct.

[lookseehear]

So this means that if you had an ASHP on one phase pulling in 8kW and a battery on another phase exporting at 8kW, you'd effectively be saving at the current per kWh rate because they'd offset, but if you export for an hour, then run your ASHP for an hour you'd export at the export rate (eg 15p) and import at the current rate (which could be 28-30p/kWh).

 

Unless the system is tuned to import to the battery when electricity is cheap, then export to match usage during peak hours you would be losing out financially.

[Dillsue]

28 minutes ago, lookseehear said:

So this means that if you had an ASHP on one phase pulling in 8kW and a battery on another phase exporting at 8kW, you'd effectively be saving at the current per kWh rate because they'd offset, but if you export for an hour, then run your ASHP for an hour you'd export at the export rate (eg 15p) and import at the current rate (which could be 28-30p/kWh).

 

Unless the system is tuned to import to the battery when electricity is cheap, then export to match usage during peak hours you would be losing out financially.

Yes, assuming you'd charged the battery from solar. If you've charged the battery from grid eleccy then you need to deduct the unit cost of the energy in the battery from the import your offsetting or the 15p export rate.

 

When weighing all this up don't forget that when the ASHP is using the most energy in winter your solar will be generating at its lowest. Unless you've got a massive array its likely your solar will make only a negligible saving on your ASHP running costs. PVGIS will give you a monthly forecast so you can see what you're likely to generate in the winter and compare it to forecast ASHP demand.

[-rick-]

Also, assuming you have an 8kw ASHP, it's unlikely to draw any more than 3kw outside some unusual scenarios (assuming a well designed system). Normal operation should be much less than that. Electricity in should be less than 1/4 heat out (COP 4+) except during hot water cycle.

 

So it's easier to generate what you need on the relevant phase. Assuming you have 3phase solar then the ASHP will be on one of the phases.

Edited 17 hours ago by -rick-