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quoyshakes avatar image
quoyshakes asked

UK G100 workaround

Looking to get some advice on the operation of the Multiplus 2.

As MP2 does not have a G100 Cert. I have been looking at way to remove the need.

We have a small farm in the UK with a single phase 230v supply so do not need a massive system but more than your average family home.

Our DNO has advised an initial export limit of 3.68Kw on enquiry.

I should be able to install a MP2 (firmware 510) as G98 with the 16A limit.

Would it be possible to operate 2 or 3 MP2 5k in parallel. But have only one unit connect to the incoming supply, providing charging to a battery system and passthrough. the other units would operated as off grid, using a battery (system would also have DC coupled PV).

As operating in parallel all AC out would be combined to provide a single phase output.


multiplus in parallel
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matt1309 avatar image matt1309 commented ·

Is MP2 not G100 compliant?

Microsoft Word - G100 declaration Multi vii (midsummerwholesale.co.uk)

Looks old but maybe worth chancing it and asking your DNO before you design a more comlpex system.


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quoyshakes avatar image quoyshakes matt1309 commented ·

Sadly the requirements for G100 have been updated since that Declaration.

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matt1309 avatar image matt1309 quoyshakes commented ·

I'd still chance it if I were you and ask them... Worse case scenario they confirm you're right and say no you need another solution. Best case they pass it and you have more basic easier to install (and cheaper) setup.



My other guess (I've never done this so not 100% sure if it's possible but agian DNO will be able to tell you either way). But could you not get the unit tested ie a one off installation.

I believe this is how installations are complete when manufacturers have inverters that are not type tested. ie the unit needs to be tested on installation rather than relying on manufacturer specs


You might have to pay DNO/electrician to come complete the test.

ie can you comply with G100 even if G100 type testing hasnt been complete assuming the G100 requirements are met even if not type tested (ie the specific installation is tested to comply).

I've not read up on them recently but when i last looked the G100 requirements boiled down to how fast the system reacted when limiting export was required. I imagine the multiplus complies with this easily but it might just not have the certificate/type testing for it.

Imagine it'll cost you more for DNO/electrician but might work out cheaper than buying/designing a more obscure complex system.


Before spending money definitely give your DNO a ring see if they have suggestions. I've had some scarily good luck doing that in the past


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Craig Chamberlain avatar image Craig Chamberlain matt1309 commented ·
Good advice I'd say - and I strongly suggest phoning the DNO and talking to them rather than communicating via email. I found email "ping pong" with my DNO very slow and prone to misunderstandings but a 5-10 minute phone call could achieve the same as a month worth of email back and forth!
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quoyshakes avatar image quoyshakes Craig Chamberlain commented ·

I agree that the perfect solution is to work with the DNO, but one aim is to keep this totally DIY (I have qualified electricians and solar installers in the family) and costs down.


The other aim was to allow future trials of G100 set-ups to test how they worked, but without exceeding the 3.68Kw DNO export limit.

basic-concept-layout.jpg I have added a basic diagram.

Simplicity is the key here and replies on the MP2 48/5000 having a 16A export limit in the newest firmware so falls into G98.

In the future i can add the grid meter etc, to achieve G100 operation with all 3 units grid ties.

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sharpener avatar image sharpener quoyshakes commented ·
Back to the OP's original question.

I am no expert on parallel operation but as I recall reading a Master-Slave setup requires identical units running the same Assistants. But I think for your schematic you would need ESS on the Master but not on the slaves. @Alexandra may be able to help on this.

Alternatively you could have a series arrangement with a 5k multi on the grid and an 8 or 10k unit connected to its ACOut1, this would still limit the export to 16A and give you the same 50A feedthrough from the grid. Not sure if they could share the same battery though but that might not be a complete barrier. AC or DC PV could go in various places in such a system.


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Craig Chamberlain avatar image Craig Chamberlain quoyshakes commented ·
Installing your system on a DIY basis doesn’t mean you can’t work with the DNO. I installed my entire system myself and got G99 approval no problem. Actually it was a bit of a faff at the time but only because I got caught in the middle of a battle between Victron and the ENA to restore type approval for the Multiplus which had been revoked. Once that issue was resolved I got G99 approval pretty quickly. As a bonus, I then managed to get an export tariff despite not having MCS certification. My export limit is 4.4kW but only because that is the limit of my MP-II 48/5000/70-50. I’m pretty sure I could get that limit raised to 8kW if I asked.
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matt1309 avatar image matt1309 Craig Chamberlain commented ·
Just out of interest Craig how you finding life without MCS? You with Octopus or have other providers also relaxed this?

Or do you just give away the exported power for free?


I do find it frustrating that MCS is seen as a requirement by so many.


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Craig Chamberlain avatar image Craig Chamberlain matt1309 commented ·
It's working out great for me. I was lucky to be one of the first (actually I was told by my Octopus agent that I was the very first) to get onto an export tariff without MCS certification. I didn't even have to pay the £250 fee that was introduced afterwards, and all I had to give Octopus was my DNO approval proof.

Right now (just after noon) my inverter is exporting to the grid flat out at 4kW and my PV is pulling in nearly 6kW off the roof so my batteries are at 75% and rising. I've already exported 10.8kWh this morning out of the 17.8kWh of total solar absorbed. And this is central Scotland in April! :)

I try to prevent the batteries reaching 100% while there is still more than 4kW of PV power available otherwise my PV absorption rate is restricted by how fast I can export which is only 4kW or so. So I manually set a -4000w grid set point in the mornings before peak solar activity to ensure I still have battery capacity to spare. I have also stopped charging my batteries fully overnight and just charge them to 25% now to get me through to sunrise. Even on a cloudy day now I have enough solar energy to cover my base load. I know "Gary Does Solar" just did a YouTube video on why it's better to always charge your batteries overnight on Intelligent Octopus Go, but his calculations didn't take account of the clipping effect I mentioned above where my export rate restricts PV absorption rate. I would rather get all the solar energy available even if it means exporting a bit less. Also, the round trip conversion losses have an impact when I charge overnight only to then export again. I think it's easy to lose sight of my original aim which was to just do self consumption and I don't want to end up obsessing over how I can make a few extra pence per kWh by doing this or that. There is something very satisfying about just running entirely from solar energy.

I'm also about to install a heat pump to replace our oil boiler and am awaiting a decision from the government on my grant and interest free loan. During that application process I was asked if I had PV and/or an ESS and I said yes. I was then asked for my PV & Battery installer's MCS number which was a mandatory field! That gave me a bit of a sinking feeling but when I queried it, I was told that this was only relevant if I was also applying to add additional PV or battery capacity. So shouldn't be a blocker. I'll hopefully hear from them in the next day or two so fingers crossed!

But yeah, I've certainly not missed having MCS certification so far and although I'm not aware of any other energy companies following Octopus's lead on this, I also have no reason to leave Octopus. Even if I did want to leave them, I'm pretty sure the fact I already have an export meter number would allow me to get an export tariff elsewhere. Not sure though.

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atebee avatar image atebee Craig Chamberlain commented ·

Do Octopus give you access to all the export tariffs they have available? When I enquired last October the canned response I suggested that Octopus Flux wasn't available.


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The breakeven point given the application fee plus the other hoops changes quite a bit depending on the export tariffs.

I'm focusing on self consumption and at the moment hot water diversion is actually soaking up a surprising amount of excess (also on an oil boiler, west coast Scotland).

With a small system (3.2kW peak) and perhaps a few hundred kWh/pa exported I'm thinking it's not worth trying to get a non-MCS export setup with Octopus.

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Craig Chamberlain avatar image Craig Chamberlain atebee commented ·
I'm not aware of any restrictions on export tariffs for me, but bear in mind I got my tariff as part of the trial process at Octopus so might be different to the finalised non-MCS process.

Initially I only had the basic SEG tariff which yielded 4.1p/kWh but this was later doubled to 8p/kWh out of the blue by Octopus to recognise higher energy costs. Then later I was invited to join Intelligent Octopus Go because I was already on Octopus Go. That is what caused the switch from the "Outgoing Octopus 12M Fixed Lite" tariff to the "Outgoing Octopus 12M Fixed May 2019" tariff which yields 15p/kWh.

I have looked into switching to Flux but to be honest I don't think it would work out better for me due to having an EV. Intelligent Octopus Go has been working really well so far.

As for whether it's worth the cost, for me it absolutely is, even if I had been required to pay the £250 fee. So far I've exported 1134kWh in total and 658 of that was in 2024. Total generation is 3876kWh so I've only exported about 30% of what I've generated.

Total export income has been £92.59 so far which comes from a mix of 4.1p, 8p and 15p tariff rates, and that doesn't count the income I got from saving sessions. This is also mostly winter generation which was obviously a lot less than I will get in the spring and summer. For example, today I've exported 27kWh and it's still going at over 3kW so will probably hit 30kWh before sunset. That's 27kWh exported from a total of 42kWh generated from my 6.8kWh array.

I expect my exports to go down once I get the heat pump, which has now been approved for government funding by the way, but given that peak solar generation happens when heat pump demand is lowest, I still expect to be exporting a lot in the coming months.

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atebee avatar image atebee Craig Chamberlain commented ·

Thanks for the detailed response. Final question; did your DNO charge you for the G99 application?


Considering upgrading from a MPII 3k to a 5k or 8k.

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Craig Chamberlain avatar image Craig Chamberlain atebee commented ·
Hi, my DNO initially charged me £300 to complete the G99 application but later refunded it at my request because they admitted they utilised the wrong process. I also used g59projects.co.uk to assist with preparing my G99 application because I initially went through a lot of back and forth with my DNO over the application details and just wanted to get it moving. That fee was something like £259 but to be honest I could easily have done the application myself because the main issue at that time was the lack of type testing approval from the ENA. This was later resolved.

In general I think the DNOs have streamlined the G99 fast track process significantly since I submitted my application so I wouldn't expect any fees to be charged now.

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matt1309 avatar image matt1309 Craig Chamberlain commented ·
Sounds amazing glad it's worked out so well for you. I'm moving house at the moment and considering not going MCS route. My current place I installed and had electrician "plug it in" and provide MCS. Was eye wateringly expensive for what was provided so would quite like to replicate your approach at the next place.


That's good to hear about the heatpump MCS reference not being needed. I'm a few years from affording one but good to hear it's not impacted things.

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2 Answers
slartybart avatar image
slartybart answered ·

I was recently allowed to install the larger 8000vA model under a g99 fast track. I was told my export limit is 3.68kW and lo and behold the grid code in the new software 510 states it’s now automatically limited to 16amps and G98 compliant. I’ve sent off screen shots of that and await a response to my commissioning letter. As far as running three units in parallel, I don’t think that would work as the three work together….. so one connection serves all…. To the capacity of the three. That said, with the new grid code setting they may be more relaxed about it.

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slartybart avatar image slartybart commented ·
To update: selecting the G98 gridcode in the Multiplus settings seems to limit not just feed in, but production, so I’ve reverted to the G99 grid code and set the export limits elsewhere. However, I have now received my final ‘all’s good’ letter. The original principle was choosing an inverter under a 32amp capacity meant qualifying for the G99 fast track process, which allowed me to use the larger 8000vA model, despite being subject to a 16a export limit. Its notional capacity is 6.4kW. I also applied to install the bigger 10000vA model but was told no. The original application pointed out that the export limits are installer options and locked and therefore not changeable by the user (although here both are me). The use of an external meter (et112) in the system satisfied them my system would be compliant. Although I also sent them the G100 sheet (the one someone posted above), this wasn’t needed in the end.
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spazpeker answered ·

I have 2x 5k Multiplus in parallel for simplicity my drawing only shows one,

The export limit doesn’t change with more units.

I did get approved.

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