Adding more PV and battery storage to existing system

I have 4.4 KW of PV, a 3.6KW hybrid inverter (Gen 1) and 2 x 2.6 KWh batteries. I'm considering putting ₂.2KW on the flat garage roof which is detached from the house and 8m away as well as more battery capacity. There is a decent electrical wire to the garage (it has an electric roller shutter door and the previous owner had a water heater for a hot water tap). This is all hypothetical, firstly on the proviso that this battery discharge issue gets sorted, whether the cost/benefit is good enough (I haven't had a deep dive on the numbers, but my gut instinct is that it would be), getting planning permission etc...

I assume that I would need another inverter and would it be better located in the garage close to the new PV? If so another 3.6 KW? Get a Gen 2 and swap it with the Gen 1 so that I could charge/discharge at 3.6 KW from the larger array? Would the new battery be better located in the garage if the inverter goes in there? If I get wifi to the garage, then will both inverters work together?

Your 1st hurdle, will be your DNO, will they approve another inverter? Assuming they do.

Stick it in the garage with its battery. So you have 2 hybrids, one in the house, and one in the garage. The existing EM115 Import Export meter can feed both inverters the same data. So a run of Cat6 will be needed from teh current EM115 to the new Garage inverter.
Then set them up as a plant of 2, or keep them separate, your choice

If you don't want any more battery in the garage, then just get a regular non Hybrid Solar inverter, such as a Solax Mini. Good for 2kw of PV, 2.2 should be fine too

TheDragon (GivEnergy) Thank you, yes I would prefer that the battery went in the garage as will probably get 5 or 8KW, so hauling it into the loft will be a pain as well as siting it.

I'm awaiting a call back from my DNO as its been 6 weeks since the notification was sent and nothing back yet, so will ask then. My roof with the 4.4KW currently on will take another 4 panels, so would it be worth getting a 5KW inverter?

TheDragon (GivEnergy) The existing EM115 Import Export meter can feed both inverters the same data.

@TRBob If you have hybrids, they each need their own EM115 if you want them to work properly. AC-coupled inverters are designed to be connected together as a single plant, but hybrids not. Whether this changes with the EMS is another matter.

TRBob a call back from my DNO as its been 6 weeks since the notification

They'll probably limit you to 3.68kW. If you volunteer to limit to 3.68kW, it could have gone on a G99 fast track which should be turned round in a couple of days.

TRBob My roof with the 4.4KW currently on will take another 4 panels, so would it be worth getting a 5KW inverter?

Add the panels and see how often the existing inverter is clipping. It's likely to only clip at peak season (if at all), but the extra panels will increase your PV harvesting throughout the day and extend your harvesting through the year.

TRBob I'm considering putting 2.2KW on the flat garage roof

If necessary, you could move your existing 3.6kW hybrid inverter to the garage and replace the existing one with the bigger 5kW. But just check that with the orientation and shading that you can reach the threshold for voltage that the inverter can use (maybe 120V?)

Tim If you have hybrids, they each need their own EM115 if you want them to work properly. AC-coupled inverters are designed to be connected together as a single plant, but hybrids not. Whether this changes with the EMS is another matter.

Thank you Tim, I got a call back from my DNO (they managed to send my acknowledgement straight away...), they said that the installer would need to send a proposal for a G99, the design team would generate a quote which is £660 and then if connection reinforcement is required that is some further amount.

Tim They'll probably limit you to 3.68kW. If you volunteer to limit to 3.68kW, it could have gone on a G99 fast track which should be turned round in a couple of days.

So having two hybrids, it wouldn't function as a single system? I would need two instances of the app to see what is going on, or is there functionality for two systems in there?

Tim Add the panels and see how often the existing inverter is clipping. It's likely to only clip at peak season (if at all), but the extra panels will increase your PV harvesting throughout the day and extend your harvesting through the year.

Ok, I don't really understand how many panels and inverters are married up, tbh I was surprised that I could have 4.4 KW of panels with just a 3.6 KW inverter.

Tim If necessary, you could move your existing 3.6kW hybrid inverter to the garage and replace the existing one with the bigger 5kW. But just check that with the orientation and shading that you can reach the threshold for voltage that the inverter can use (maybe 120V?)

I don't have the technical knowledge to understand the last sentence. Maybe its not totally relevant but I've been thinking about fabricating a single axis tracker for the panels on the garage roof, provided that planning allows it and it doesn't scupper MCS rules. But that's going off topic a bit.

TRBob
I was told that axis tracking increases the height of the panels above what is allowed without planning permission. i do not know if that is true though

TRBob the installer would need to send a proposal for a G99

Just get the installer to submit a fast track G99 with voluntary restriction of output to 3.68kW. The DNO want to know what capacity you have installed but as long as you choose to limit the output, the application should be a formality. In practice, the amount of time you would be able to exceed 3.68kW from PV, and get a decent SEG payment is so small, that (IMO) it's not worth paying the £660 for survey etc.

TRBob So having two hybrids, it wouldn't function as a single system?

Although separate, they behave as a single system (at least ours do). They respond like any demand-led generator, irrespective of how many there are; they see grid import (on their own EM115), they increase output to reduce import; they see export, no problem until 3.68kW when they ramp down to limit output. The hybrids know nothing of each other but as they measure the same parameters (at least in my experience), they drive output up and down at the same rate effectively meeting instantaneous demand such as a kettle in half the usual time (each only has half the work to do). They both appear on the same portal/app, figures already consolidated by Givenergy. There are some portal anomalies with summing which they are aware of but it doesn't stop them operating well together. The data for each inverter is shown on separate inverter tabs on the portal. The app doesn't give you the granularity but ultimately, the portal and web are window dressing for what they actually do, and do well.

WRT to panels, we have 6kWp on each of our 5kW hybrids. Ours don't clip even at the height of summer. We have seen generation of 12kW several times for a few minutes and 10kW+ for hours this year. So far total generation (according to the portal) is 8.9MWh since the end of January.

positor1 I was told that axis tracking increases the height of the panels above what is allowed without planning permission. i do not know if that is true though

It definitely will, on a flat roof you need planning permission anyway when they are mounted in a static position, you will need them to be inclined to make the most of the Sun, which will put part of them above the 0.2m that is permitted development.

Thank you Tim for that information

So after a bit of research, you size the inverter according to what your peak load is right? At the moment 3.6KW is fine, but say I got an EV, I believe that the chargers are 7KW, so in order to use this and have a bit of spare capacity if we wanted to use something else, a 5 and a 3.6KW might be best? Also I have a low roof at the roof of the house which would take at least 4 panels (maybe 6 at a push), so if I added 8 panels in total to the house that would give me in the region of 7.6KW peak, would a 5KW inverter handle this amount of PV?

It is possible paying the DNO fees might come in handy, if you get approval for higher export than 3.68. With Agile, you could be literally making money!
My export cap by DNO is 8.8KVA

TRBob The cost of a solar installation is a combination of the PV on the roof, the inverter and battery, if specified. If you tweak the spec to add a bit of solar, it nudges the price up. Similarly, if you opt for a slightly higher capacity inverter or battery, the price creeps up. Nobody (AFAIK) ever regretted putting too much PV on the roof. There are people who rue the day when they skimped on the number of panels installed. Even if your inverter clips on the sunniest days, there will be plenty of days in the early/late season when the added panels will extend your harvesting season as well as days when the added panels will extend the length of the day you can harvest. The panels are expensive, but when installed the major cost is the manpower and scaffolding. Whether they install ten or fifteen, the labour/access cost is the same; it's just the cost of the panels that increments. Once you have the largest array you can afford/justify, go for the inverter that gives best price/performance for your situation, but don't worry too much about peak generation and clipping because that happens for a few hours on a few days each year.

We started out with the aim to meet our annual consumption except we were planning to buy an EV. Our consumption was quite high at 6,000kWhpa. We maxed out and installed 12kWp PV with two 5kW inverters and two 8.2kWH batteries. Since installation in January this year, we have generated 8.9MWh, consumed about 1.2MWh on EV charging and exported 4MWh at SEG rate, the rest supporting our daily routines. Our average daily grid import since commissioning is less than 1kWh but we will have to rely on our EV off-peak tariff to support EV charging and load shifting over the winter.

My two pen'orth is to install as much PV as you can and match that with the largest battery and inverter that makes sense to you. Especially with an EV, the more you have on the roof, the lees you will need to import, at whatever tariff.

Tim
Hi Tim,
This may be a noob question. I've recently just had my solar system fitted. You mentioned about checking whether the inverter is clipping. Can you see this from the GivEnergy dashboard?

althanator You probably can but would have to work it out. The days when we have 6kW+ from each of our arrays is when the batteries are charging (up to 2.5kW-gen1) and we have the EV on charge as well (varies from 1.4-7.3kW to soak up diverted export) and possibly some export. If the batteries are fully charged, the maximum we can produce from PV is 5kW/inverter.

If we have sufficient light to produce 12kW across the two arrays and the batteries are fully charged and we have little house load and the export is limited to 3.68kW, which happened on many occasions this summer, the inverters are clipping - reducing output despite there being surplus PV. When this happens, the inverter does something clever with the string voltage and current, moving it away from the optimum, causing PV input to reduce. I have no idea how this is done but someone on here will have a much better answer on the technicalities.