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I have a three-phase supply and am looking to install solar panels and a Home Energy Storage battery. Would I need a Single-phase or Three-phase inverter?

  • 22 October 2021
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Mark C
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We have a three phase supply with an Aclara SGM1433-B smart meter 

We are looking at Solar PV with a storage battery and have had a number of companies provide initial information and quotations.

One thing nobody seems to agree on is if we should have a single phase or three phase inverter.  
We have been asked if our meter supports phase vectoring but cannot work this out…

Has anyone else come across this type of question or considered this position?

Thanks in anticipation

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Best answer by Blastoise186 23 October 2021, 10:16

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Blastoise186
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Hiya!

Did you mean the Aclara SGM1433-B by any chance? If so, that's definitely a Three-Phase SMETS2 Smart Meter  I can double check it if you would like me to though. All I'll need are a few photos of it and I'll be able to identify it in a jiffy 

I would imagine a Three-Phase inverter would make more sense than a Single-Phase inverter with your setup. I'll dig through some resources in the morning and get back to regarding phase vectoring if possible  

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Mark C
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@Blastoise186 Yes, well spotted, my first proper post and I got the model number wrong! 😜

It is the 1433-B, any help is appreciated and the fact you know what they meant by vectoring is also a positive. 

Blastoise186
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Hehehe, it helps when you’ve written a guide or two. Here’s one I made earlier! :stuck_out_tongue:

And also this very handy user manual which I umm… “Borrowed” from Aclara. It’s hosted on a website called SmartMe, which is a resource we make use of a lot here but it’s run by a group of engineers who are unrelated to any of the forum volunteers here. Feel free to share the links to all of these with basically anyone you wish. I’m sure you’ll know a few people who would definitely be interested in them!

While my understanding of the technical details is somewhat limited, I would still have reason to think that if you’re already on a Three-Phase Supply, you’ll want to go Three-Phase everything to match that. Not least because your Distribution Network Operator will probably thank you for it later.

As for phase vectoring, I can’t find anything specific in the user manual I have access to, but then again it is for the Single-Phase versions and SmartMe doesn’t have the Three-Phase version available. However, my understanding is that the Aclara SGM1433-B should be capable of handling exports anyway so I wouldn’t have thought there’d be any problems as long as everything is installed and wired up correctly.

But I also have a secret weapon or two up my sleeve. May I introduce you to a new friend of ours here. @Lukepeniket_OVO is an OVO/SSE Engineer who actually installs Smart Meters on behalf of OVO and SSE. If anyone might know this answer, it’s possible he does.

And then there’s also @Transparent who absolutely loves to discuss really technical stuff like solar panels and microgeneration. It’s actually one of his favourite topics on this forum too!

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Transparent
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Hi @Mark C - and you’ve definitely arrived at the right place!

The rules for grid-connection of generators, such as PV Solar Panels, are described here.

The starting point is that you may normally export only 16A per phase (3.68kW). So if you have 3-phase, then you can triple that figure!

Moreover, one of the important constraints on grid-export is the losses caused at the substation due to phase-imbalance. If you have a 3-phase inverter, then you won’t be contributing to those losses. So in some circumstances your Distribution Network Operator (DNO) may permit you to operate above the 16A/phase limit.

You’re right on the northern edge of Western Power’s region. So your starting point is to look at their G98 Application Form and then assess your normal Maximum Demand (MD) for the house (excluding the PV Panels at this stage).

Ask here again if you require clarification.

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Transparent
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Vector-phase metering is used when you might be exporting on one or two phases whilst importing on the corresponding other one or two. It allows the Energy Supplier to bill you for only the difference between the import and export.

It is more commonly referred to as “Vector sum” in the UK, and was previously discussed here on the Forum at a time when none of us knew what it was!

Further investigation since that topic suggests that a Smart Meter could not gain approval for connection to the National Smart Meter Network unless it supported vector sum metering.

Model SGM1433-B is currently the top-end model of Aclara’s 1430-series. You can download its Aclara Product Description PDF and a more detailed 1430-series specification document running to over 100-pages. The SGM1433-B terminal layout is referred to on page-81, but its features are otherwise little different to the rest of the series.

Vector-sum wouldn’t be an issue if your PV Inverter was 3-phase. But it would be relevant if you decided to store some of that energy in a single-phase Storage Battery.

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Mark C
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Vector-phase metering is used when you might be exporting on one or two phases whilst importing on the corresponding other one or two. It allows the Energy Supplier to bill you for only the difference between the import and export.

It is more commonly referred to as “Vector sum” in the UK, and was previously discussed here on the Forum at a time when none of us knew what it was!

Further investigation since that topic suggests that a Smart Meter could not gain approval for connection to the National Smart Meter Network unless it supported vector sum metering.

Model SGM1433-B is currently the top-end model of Aclara’s 1430-series. You can download its Aclara Product Description PDF and a more detailed 1430-series specification document running to over 100-pages. The SGM1433-B terminal layout is referred to on page-81, but its features are otherwise little different to the rest of the series.

Vector-sum wouldn’t be an issue if your PV Inverter was 3-phase. But it would be relevant if you decided to store some of that energy in a single-phase Storage Battery.

Thanks for this….

One of the PV solution provider was suggesting “…if you have phase vectoring on the meter that would cancel out the need for a three phase PV system to utilise the solar electricity over all three phases”

We are not sure if this means they really know there stuff, they haven’t got a clue or they only sell single phase solutions!!!

We think our best option is to stick with three phase solar with an AC coupled battery storage

Transparent
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That PV Installer hasn’t understood the way the Grid works, nor how Energy Suppliers create bills for customers with 3-phase.

He is correct if the only consideration is the ability to produce correct billing. But it’s not!

When you think about it, apart from your proposed 3-phase Solar Panel installation, everything else in your house is likely to be running on single-phase electricity. So you are already causing phase-imbalance every time you switch something on.

At present there is no financial penalty for causing phase-imbalance at the substation. But it is highly likely that Ofgem will place it as a high level priority in a year’s time when Western Power is given its targets under the forthcoming RIIO-ED2 contract. The UK simply can’t go on squandering energy when we’re trying to reach net-Zero with increased use of renewables!

In the meantime a DNO can (and will) restrict what a customer can feed back onto the Distribution Grid if that would take the electricity supply outside its statutory limits.

I’m in precisely this position myself.

I was recruited onto the OVO trial of Storage Batteries from PowerVault. An 8kWh unit was installed here in Jan’21 and I proceeded to monitor how it operated in close coordination with Western Power area engineering staff.

OVO/Kaluza have now concluded that their Trial cannot operate at this site due to it already having a high supply voltage. That’s something I already knew, but was not picked up during the pre-installation survey.

Initially the Storage Trial would’ve been ok because the PowerVault battery was DC-connected. But software issues remained unresolved and PowerVault changed the installation to AC-connected by installing a PV Inverter.

The presence of two AC generation devices on the same site meant that a new Application was submitted for G99. That hasn’t been forthcoming and the Trial has been abandoned.

And you’ve just stated that you want AC-connected Battery Storage! :scream:

Have a look at the diagrams I’ve posted here on the topic about PV Installation…

and then let’s discuss this further.

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Mark C
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@Transparent I will take a look…

it was a different installer that advised I need AC coupled if I ever want to export to the grid and take advantage of variable rate / times tariffs… Maybe this isn’t correct either!

I can feel another reply coming along…

Transparent
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Have a look also at the Solis Inverter here which is being discussed by a customer with billing anomalies.

He and I have both posted diagrams. These show that the inverter sits in the middle of a 3-way junction between the Solar Panels, the Storage Battery and the mains/grid.

There is a 3-phase version of the Solis inverter. I haven’t yet checked whether it is certified for use in the UK, nor how a 3-phase inverter handles battery connections. But I’m happy to do so if this is of interest.

For the moment you can ignore the difficulties being discussed by the customer. They’re nothing to do with the functionality of the inverter. His photos also show a high-quality installation by an electrician who understands the safety requirements and the way to properly attach cabling.

Growatt also offer an inverter which operates in the same fashion. It is not a design strategy unique to just one manufacturer.

You have no need to install everything at the outset. Once you’ve selected an inverter  with adequate capacity, you can add more batteries and PV panels over time.

 

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Mark C
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@Transparent we are looking to ‘fill the roof’, between 15 and 18 panels depending on the provider, and want to take advantage of the scaffolding installation.  Additionally the starting battery can take advantage of the 5% vat rate.

One of the most difficult challenges is sizing the battery requirement, our usage has changed a lot recently along with expansion plans we have for early next year.  Who was it who said Solar is easy 😝

Transparent
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That’s understandable. Scaffolding is expensive.  Fortunately I have my own! :slight_smile:

There will be lots of advice here about the ‘correct’ size for the battery. As a rough guide my 8kWh unit is clearly too small for my house. Tesla have done their homework and concluded that their base-unit should be 13kWh. That’s more like it… and they also score well for the £ per kWh evaluation.

But Tesla only have AC coupled units and their Li-ion battery chemistry is the same as their vehicles (LiMNC). That C stands for Cobalt, not carbon. This raises ethical considerations because it’s mostly mined in the Congo where it helps to buy arms.

Moreover for a static battery you don’t need the high-currents and fast responses which are required by an Electric Vehicle. You can opt for LiFePO4 cells which will also last 5x longer!

 

As you had expected I absolutely disagree with the installer who suggested you required an AC-coupled battery in order to export and have the opportunity to choose a Time Of Use tariff. These are completely separate issues, unrelated to the technology.

The more relevant questions are:

a: what are your aspirations towards having an EV with its charger?

b: what are the electricity implications of the ‘expansion’ you are contemplating.

Put all the cards on the table before trying to choose battery sizes and connectivity!

 

Right I’m signing off for the night and opening a beer! :beer:

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Mark C
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The more relevant answers are:

a: what are your aspirations towards having an EV with its charger?

> not in the short term

b: what are the electricity implications of the ‘expansion’ you are contemplating.

> sauna - 9kW heater (expecting regular short duration usage 1hr max inc. warm up)

> indoor endless pool (heated / powered swim lane) - not sure if diverter can help here

> garage conversion to gym (with air con)

 

Current usage about 8,000 kWh, very difficult to predict ‘future usage’

Looking at 18 panels initially, so far quoted between 370W to 455W from various manufacturers (still reviewing but advice seems to be ‘invest in inverter rather than panels’)

Also considering water heating via a diverter

Looking at this list I know why this isn’t easy…

Transparent
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Thanks @Mark C - and this topic suddenly looks like it’s going to be huge!

We’ve already got a tutorial and a topic discussing Load Diverters. 3-phase Diverters are available, but haven’t yet been researched/discussed here on the Forum.

Let me also point out that there are significant benefits in running electric heating devices from 3-phase.

Consider a heating element through which we will pass 2-amps:

 

The heat output for three single-phase devices is lower because there’s only 240v between phase and neutral. But there’s 440v between phases if you don’t require a neutral.

3-phase immersion heaters are available at 6kW, 9kW and 12kW with ‘standard’ 2¼” BSP threaded base. Prices are £120 - £250 and don’t vary much wrt the wattage, but there are large variations depending on the material from which the element casing is constructed. This depends on the characteristics of water in your area.

You obviously need to check that an immersion heater specified by an Installer uses the elements in ‘delta’ pattern (as shown above) and does not require the neutral. There will be some which are effectively three single-phase units in one package. :face_palm_tone1:

 

When choosing a load-diverter, it is important to note that you require one which varies the amount of energy being sent to the immersion heater. You don’t want a cheap one with a relay!

Suppose you have a 9kW immersion heater and your PV panels were generating 5kW more than could be exported to the Grid. If a relay simply switched on the heater, then it would take the 5kW plus another 4kW imported from the Grid !

A Diverter must operate using pulse-width modulation (PWM). This has transistors which are pulsed rapidly to chop the mains frequency on/off many times for each AC cycle.

The higher proportion of time that the transistor is ON, the more power will be sent to your immersion heater.

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Transparent
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Ok…. next concept - Thermal Store:

A thermal store looks like a hot water cylinder from the outside, but the main body of water is simply a reservoir of heat.

 

When you turn on a hot tap it passes cold water through a coil to pick up the heat which is required.

Thermal stores may have a number of different coils and one or two points for immersion heaters. The column of water exhibits thermoclines, so you use the lowest coil to input energy from the coolest source. The diagram above is merely illustrative. In practice all the input coils would be lower in the tank, and the immersion heaters just above them.

The general idea is to select a tank capacity according to the amount of heat you need to store, and then specify as many coils as you envisage having as heat-inputs.

Here’s my 300-litre thermal store which is slightly more complex than most because we use a well rather than mains water(!):

 

If I was choosing my TS now, I’d want a second port for an immersion heater. The present 24v one is a ‘dump-load’ in case there’s too much energy arriving at my main off-grid battery-stack.

This means I no longer have a 240v mains immersion-heater which could be fed via a load-diverter.

 

@Mark C- it may help your planning if you consider both your swimming-pool and the sauna as secondary ‘thermal stores’. Either could act as a reservoir from which you draw heat when not being used in its primary role.

From that viewpoint you are absolutely correct to be thinking of a diverter for the swimming pool… especially so if there is insulation between the pool walls and the ground.

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Mark C
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@Transparent We live in a village, you missed off the oil boiler and the Oil Aga!!!😜

We do have underfloor heating, but rarely use it due to the heat from the Aga, but hadn’t really considered that as a separate element to our overall system  

The pool will be well insulated, including the cover, hence considering it in a similar way you our hot water system. 
I really appreciate this content as it enables me to understand so much more from a single location rather than trawling through all sorts of websites / you tube content

 

Transparent
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Ah… thanks for reminding me!

So your Aga can be considered as another possible input to a Thermal Store.

And if it dies in 10-years time and you install a wood-gas boiler (or whatever is the best solution at that time) then it simply takes over the same heat input coil in the cylinder.

 

May I also pick up your comment about the gym in the converted garage having air conditioning?

Where would the heat go?

What about using a Mechanical Ventilation with Heat Recovery (MVHR) unit such as discussed here?

An MVHR unit would also be able to re-capture heat from the sauna of course. The water in the air would be expelled through the condensate drain, and the heat transferred to fresh incoming air for the house.

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Mark C
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@Transparent  Added to my list to review… The gym will be adjacent to the pool.

The plan was to have a dehumidifier in the pool area as it will get quite humid with the powered lane running and air-con in the gym as it can get hit in the summer. 
For the brief reading I may be able to replace this with an MVHR taking the warm moist air from the pool area…

Transparent
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Precisely, @Mark C. When you’re spending money to bring in energy in the first place, you should then try to use it several times within the house.

I don’t know how busy you are, but I would strongly suggest you take a day out to visit one of the Homebuilding and Renovation Exhibitions. There’s one in Harrogate at the end of next week (5-7th Nov).

When I moved to our current home it required extensive renovation and I applied to Devon Building Control to install a new sewer pipe as a matter of some urgency!

The Surveyor/Inspector agreed to visit that very same afternoon and arrived on the doorstep with two free tickets for the next Homebuilding & Renovation Show. It was truly inspiring! :slight_smile:

The Harrogate exhibition will be full of supplier-experts in all the technologies we’re discussing here. So in the space of a few hours you can not only get to see the equipment, but also grill them with questions about efficiency, maintenance and failure rates.

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Mark C
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@Transparent Great idea, I will head up and have a look 👍

Transparent
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@Mark C  I’ve been taking a look at electricity data for the Retford area.

You have an amazingly low carbon footprint, with almost all power coming from local renewable sources, even tho’ these are actually flagged as low generation for today!

 

Energy mix snapshot; 10am Thur 28oct21

Your Bulk Supply Point is at Checkerhouse, where the Mansfield Road crosses the railway line, west of Retford. That’s where the transformers take an input of 132kV and send 33kV to the 9 Primary substations in the area.

You can get loads of data from your BSP by entering a post-code into the Carbon Tracer website for Western Power Distribution.

Here’s the snapshot showing how much of that renewable generation is local, as opposed to being imported from the National Grid.

 

 

Were you aware of such large scale renewable generation in your area?

As the country moves towards customers having variable Time Of Use tariffs, this data will affect how ‘valuable’ are any exports you may wish to send back to the local Distribution Grid.

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