Replacing AC coupled inverter with hybrid, maybe

I have a FIT solar system of 3.6Kw already installed, and an AC coupled inverter with a 9.5 battery. The system works well but due to my array of panels facing a little east of south, the output tails off a bit in the afternoon. I have a roof facing southwest and could put panels on here, which would give additional output, particularly in the afternoon. My options as I see it are firstly to install panels and a cheap inverter and let the additional energy improve the pm charging via the AC inverter. Also I would get some useful output into the house. The other option would be to replace the AC coupled inverter with a hybrid and take the DC from the new panels directly to this - it would be about a 5m run. More expensive but better integration, although lower overall output into house during the day if needed(two inverters not three). Can anyone comment on the two alternative courses of action? And if I replaced the AC inverter, do I need to inform the DNO?
Thanks for any help with this!

Chris

CleoBattery subject to agreement with your FIT provider, you could add the new panels to the existing inverter. They would then pro-rate your generation payments to reflect the extra energy being recorded by the FIT meter. DNO approval not rewuired and lowest cost solution.

Either an additional inverter or replacing the AC with a Hybrid needs DNO approval.

If you take the hybrid approach, losing the ability to capture export from the FIT system may be an issue. It wouldn't be my choice.

stevelewis Nor mine. But it depends on which FIT your are on. Additional inverter would be my choice. Simplest solution all around. The DNO issue is solution agnostic. Any additional potential export over your current approval would need resolving. Deepends on how much overlap there is in generation of the two arrays. Maybe you could size it to keep it all under your export limit. Otherwis bite the bullet and get your limit upped.

CleoBattery I agree pretty much with what Steve says.

You can definitely add extra panels to your existing FIT inverter and you will still be paid for your FIT generation (and deemed export), on a pro-rata basis. You have to get approval for this change from your FIT supplier (i.e. whover you give your FIT meter readings to).
If you are adding more panels that take you above the 4kW limit then you will separately need DNO approval for the extra micro-generation. They may impose a limit on how much you can export so as to not overload the grid in your area. Or they may not - I have 10.4kW of generation and no limits.

You can change your FIT inverter if you want to. Definitely would need approval from your FIT supplier for this change as they will need to record the old and new meter readings when the inverter is changed. I’m not sure whether you need DNO approval for this change as well, probably as its a new device feeding the grid.

Whilst installing a hybrid inverter for your FIT is going to be more efficient as there’s less power conversions, the trouble with this is that you need to be able to identify your FIT generation and potentially you could charge the battery from grid mains and then discharge this into the house which would mess up the meter readings. I believe it may be possible to do if you have a ‘net meter’ that separately records import and export, but its adding complexity.

If you already have a working FIT inverter and AC coupled inverter I would leave these as-is. Either add extra panels to your existing FIT inverter or add a separate inverter for the non-FIT generation. You may well have to put scaffolding up for the extra panels, in which case its worth getting as many extra panels as you can, even in non-optimum positions. This could well push you more towards getting a second inverter to handle the extra generation capacity.

geoffreycoan Thanks. I cannot add extra panels to the FIT system - the roof is 'full'. And I would have to change up the inverter and apply for DNO approval. And the reason for extra panels is because I can fit them to a more westerly workshop roof which will give me better generation in the afternoon. I am going to have to apply for DNO approval in any case whatever I do, but as I understand it all items including the AC inverter must have a limiter to prevent export of more than 4kW. Obviously these devices sense the current flowing to the grid(from whatever source) and limit their output. The proposed additional separate inverter(or the hybrid inverter) would still do this.

Discharging the battery into the house(desirable!) is not a problem for FIT. There is a separate generation meter on the FIT system. So any additional input doesn't affect this - unless such input takes the power fed to the grid over 4Kw, then the FIT inverter may limit output and reduce my income! If I can prioritise or set up the new inverter to limit first, before the FIT, this would solve the problem; or increase the permitted output overall so that both inverters can render full output without loss of FIT income. Any other observations welcome, and comments on the above.....!

CleoBattery As an additional comment on the above, I believe that the AC inverter can only deliver 2.5kW to the house; a 5kW hybrid would up this to 5kW with the support of solar. But retaining the AC inverter and adding a new inverter would give me another 3.6kW alongside the 2.5kW of the AC inverter(from battery) and the original 3.6kW of the FIT system. So more power available overall when the sun shines, and also to charge batteries(9.5kW Givenergy and Audi hybrid) when the house(500w base load) does not need it.

CleoBattery r/e adding extra panels to the FIT system. Even if the roof it physically full you may still be able to add the extra panels that are on the workshop roof onto the same FIT inverter. I don’t know what the DC cable limits are, but potentially you could add the workshop roof panels into the existing FIT strings. Would save you having to buy another separate inverter, but the extra panels might exceed the capacity of the inverter. Just a thought.

r/e “must have a limiter to prevent export of more than 4kW”. No, its not “must”, its “maybe”.
The DNO’s have to give you a 4kW export allowance and there’s no approval required for that. Its one of the reasons why many FIT arrays (including mine) were sized at 4kW.
If your array is bigger than 4kW you have to apply to the DNO for approval for the extra export capacity. Its called (I think) a G99 or G100 approval. Whether you get approval or not depends on the DNO, how much other solar there is in the local area, and the size of the cabling in the area. As I said, I have a 10.4kW PV array and my G99 approval didn’t limit my export.

If you are given an export limit then yes the inverter must ensure you can’t exceed the limit. I don’t know how the limits are applied if you have multiple inverters because even if each inverter had a 4kW limit then two independent inverters could both be generating the 4kW and you’d be on double the export limit. As you say such a limit on your FIT inverter would reduce your income.

r/e Discharging the battery into the house is not a problem for FIT. My reply about how it could be a problem was assuming you were considering replacing the existing FIT inverter with a hybrid inverter with connected batteries. Then the (AC) meter that is used to record generation that is downstream of your FIT inverter could be eroneously reporting any grid to battery charging up as FIT generation which it shouldn’t be doing.
If you keep the FIT inverter as is with its own generation meter and add a second inverter for the extra panels then this’d be fine.

geoffreycoan Thanks for your helpful comments Geoffrey. Yes there is no way to add the panels to the existing installation, it would exceed inverter capacity, and would have a long DC run.

Having done some poring over the application forms and conditions, I think I am going to go for G99 A1-3 fast track which if you use type approved equipment will allow a 32A export, eliminating any limiting on the inverters. By disengaging from the export part of the FIT I can then take on an export tariff.
I am thinking of installing a Givenergy Gen1 hybrid which would allow for increased battery storage in the future but it can be used for just solar generation at first with the workshop panels. This installation should be very straightforward with inverter in workshop.

CleoBattery Sounds like a plan.

I’ve been through the process of getting an export MPAN, turning off FIT deemed export and getting paid for Octopus Flux export. Took about 2 months, finally started getting my payments on August 10th. Was quite painful but eventually successful so I can share my experiences to hopefully get it through quicker when you get to it.

geoffreycoan Thanks Geoffrey. Did you go the full G99 route? Do they limit your export?
And how was the process of disengaging from the export component of FIT?
Chris

CleoBattery My installers submitted the DNO paperwork on my behalf. Looking at the DNO application form it looks like it as was a G100 application they did because at the bottom it says:

`Generation Details
Agreed export capacity (including G100 devices) per phase: 10.00 kW
G100 export limiting scheme on premises? No

G99 A1.1
I declare that the relevant Micro-generators and the installation which together form a Micro-generating Plant within the scope of EREC G99 at the installation address, conform to the requirements of EREC G99. This declaration of compliance is confined to Micro-generating Plant tested to EREC G99 or EREC G59 as applicable at the time of commissioning.
Response: Yes`

The FIT process was long winded. I applied to Octopus to go onto Flux and about a day later I got a response from their export team, identifying that I had a FIT array and asking me what I wanted to do. I elected to leave the FIT with the existing supplier (not move the FIT supply to Octopus) and that I would cease FIT deemed export - the form said that this would be the quickest route. Octopus said they would be in contact when it was time to cease the FIT.
After 6+ weeks having heard nothing I started chasing Octopus, and having heard that there were backlogs in the DNO to issue the export MPAN, I contacted my DNO directly to chase them as well. A couple of days later I heard back from the DNO, they had got the application from Octopus but had sent a query back to Octopus about my DNO approval. I was able to resolve the DNO’s query and they issued the export MPAN the next day which I passed back to Octopus.
Octopus then said that because I was on FIT they couldn’t progress the export application until I had ceased by FIT export supply. So over to my FIT supplier (Eon), telling them I wanted to cease the export. Took them about a week to do it, had to provide photos of the export meter and my house meter, sign a new FIT agreement, and I received a FIT payment with the final generation figure.
Having got the FIT closed down I then had to repeat most of this back to Octopus, giving them photos of the start export meter reading and they confirmed my export start date as being 10th August. Initially they then said that they couldn’t get half-hourly export readings due to a DCC issue (despite collecting half hourly import readings from the same physical meter) and I’d have to go onto the 15p/kW export rate, not Flux, but they started collecting half hourly readings OK and I commenced on Flux export.

geoffreycoan As an update to this thread I applied for G99 proposing the installation of a 3.6kW hybrid inverter and 3.24kW of panels, and a 5.2kWh battery. Response from the DNO was quick and helpful and they approved the installation with an export limit of 7.48kWh.

So I now have 1) a FIT installation with 3.6kW of panels, 2) An AC coupled inverter with 9.5kWh battery, and 3) a 3.6kW Generation 3 hybrid inverter coupled to 3.2kW of panels with an additional 5.2kWh Gen 1 battery. (3) is nearly installed but as yet uncommissioned. The FIT export has been changed to SEG export(currently with GoodEnergy who initiated the change due to the presence of a smart meter). Following commissioning and notification of MCS certification the DNO will grant me an export MPAN number.

I am less concerned with export than with the efficient use of the system in meeting the house demand and charging a hybrid vehicle without consuming grid energy. At the moment using the installed FIT solar and the AC inverter the system works pretty well coupled with a Zappi charger. An export limit is set on the Zappi which means that the AC inverter won't discharge to the vehicle, leaving the battery empty and unable to contribute to the house load in the evening.

I have two EM115 meters running into the AC inverter which tell the inverter when there is grid import, and also what the solar output is. I also have three myEnergi CTs linked to the Zappi via Harvi wireless links; one which monitors grid import/export, one which gives the solar output, and one which monitors the AC inverter. An additional complication is that the Zappi, AC inverter and now the hybrid are wired to the garage consumer unit which is fed from a 63A MCB in one of the house consumer units.

I have a couple of questions re the additional CT/meters I may need to install and where.
1) Presumably the RS485 bus carrying the modbus info from the EM115 meters can just be connected from the AC inverter to the hybrid, giving the hybrid the same info as the AC inverter(grid import/export and FIT solar output)? Or will I need separate meters - I cannot see why that might be the case since the info would be identical?
2)I would also install an additional CT for the hybrid output to the Zappi to show the solar output and enable charging when available?
3) I would install an additional CT on the hybrid output for the AC inverter? Can this be done in addition to using the EM115 meter information?
So with a combination of monitoring solar output and grid import/export by the Zappi charger, and timed charge/discharge settings in the inverters, I should be able to charge the car when there is an excess of solar, but preserve some or most of the battery charge for the evening house load. I would also be able to top up the batteries using the cheap overnight tariff on Octopus Go at night. An additional advantage of the two battery connected inverters is the ability to deliver higher power levels to the house in the evening.
It is somewhat complicated but basically using the Zappi to limit charging when there is the possibility of battery drain is the aim, whilst having both inverter/battery sets to reserve energy for evening house loads.
Am I on the right track here? Any comments or help greatly appreciated as ever.

CleoBattery the Zappi will be able to monitor the AC coupled batteries and solar effectively with appropriately placed CT clamps. You’ll be able to use avoid drain option in the Zappi to charge the car without draining the battery during the day as it can differentiate between solar and battery there. The joker is that you also have a DC battery (hybrid) as well, as a different strategy is required with DC coupled to avoid this as the Zappi can’t tell the difference between the energy streams with a hybrid. (Can’t use the same avoid drain options already in the Zappi)

This normally involves export limits/thresholds I think, but would basically counter your ability to solar charge via the AC side? I don’t have a hybrid myself so happy for those who have to correct me if wrong.

Smk82 yes I think you have nailed the dilemma there. It might have been better to have gone with a standard solar inverter and another AC coupled battery. But a total of four inverters seems a step too far. The hybrid and battery was a new/unused purchase at a very good price. Plus I think with some judicious choice of charging times the system might work pretty well.

One of my main questions is whether I can connect the two existing EM115 meters to the new hybrid as well as the AC inverter. Since it is a bus system, I think this should work ok?

CleoBattery I don’t have any practical experience either way on the EM115, but I think there are some considerations as to which is the master and which is the slave if you’re connecting multiple inverters to the same ct clamp. Might be something you’d need to ask GivEnergy about as this isn’t covered in the installation manual.

For the small cost of the em115, adding an extra one for the new inverter might just be simpler. I have two hybrid inverters and my installers put one em115 on each.

Glad to hear you got your export approved. Whilst not a priority for the winter you might want to look at a better export tariff than seg for the summer when you’ve got excess solar

geoffreycoan Thanks Geoffrey. Actually I had a reply from Givenergy on this and yes, you can daisy chain the bus connection from the EM115, this is an established protocol it seems in power management and monitoring. Also established is that you can use a direct connected CT sensor at the same time in the same inverter as the EM115 modbus connection.

CleoBattery Your comments on SEG are noted and after commissioning and MCS certification I can then get an export MPAN from the DNO and sell to the highest bidder. Actually I am hoping for the beta integration on the Zappi EV with Octopus to emerge into the public domain soon and will probably do everything through Octopus who I regard as the most innovative energy company out there. I had hoped to be invited as a beta or early adopter but that didn’t happen. The Zappi is pretty clever when fed with the right info - but interestingly Givenergy’s new EV has a modbus/RS485 connection which can be linked to a hybrid inverter - opening up the possibility of control that eliminates unwanted drain from the DC coupled battery.