Looking for some guidance on how I should go about adding a parallel string inverter for additional solar panels to install on my garage roof.
I have a GE gen 3 5kW hybrid with 2 strings of panels and 2x gen 1 batteries on the house. My garage is connected with a 40A supply on a separate spur from the main DNO fuse to the building (parallel to the house CU). I’m hoping to DIY install the panels and have a sparky hook the inverter up.
What things do I need to consider? Can I have the gen 3 be aware and account for external generation? Will this skew metrics?
If you add a second inverter the good news is that your existing inverter will see any excess export and (if there is room), charge the batteries with it.
The bad news is that your GivEnergy inverter will be completely unaware of the generation from the second inverter, it will see it as being a reduction in house load. And if you are exporting more than you are consuming the house load will go negative. The graphs in the portal and app will be of limited use in summer
I have two GivEnergy inverters and have this problem. Here’s today’s graph for example
This was part of why I decided to get Home Assistant to read the inverters directly and produce my own (accurate) consumption and generation data. Here’s today’s data in Home Assistant, far more sensible!
Good to know. So there’s no way of adding an external MPPT measure, or is that something that’s an AIO thing?
I presume that the generation would still be able to power the house in that arrangement, and be pulled to battery also?
I decided to use HA and Predbat to maximise ROI for the deployment. I estimate I could accelerate that further with the additional array, especially if done DIY.
Yes, solar generation from both arrays would power the house, the excess going to the battery (if inverter capacity & space), and then exported. The GE inverter tries to balance to zero grid import/export, so your second inverter would just help it in that respect.
In HA you’d just need to create a custom template load sensor from import - export + discharge - charge + generation and use that in dashboards/predbat. That’s exactly what I do, I have two givenergy inverters and an older FIT inverter and it all works fine together (see the 3 generation lines in the energy graph).
DIYing a second install is interesting idea. Certainly a lot cheaper than paying someone, and if its a garage roof then would be do-able. Charlie DIYte did a similar self install on his garage roof as part of re-roofing it, he has a video on Youtube about it, IIRC he concluded that he would have probably been better off paying someone to install the panels as it would have been much quicker than he could do.
You’d need to work out what to do about DNO approval as well for the second inverter.
The customisation of HA is very much a learning curve for me.
The install on the roof isn’t looking too terrible realistically. Most installers wouldn’t want to touch it because of the fact it’s a timber / OSB / EPDM wrap over an original asbestos concrete roof.
Pragmatically though, as long as I get sufficient means to mount, it shouldn’t be that hard. I’ve found some reasonably priced mini rails, can get some panels for relatively reasonable price too. Talking maybe £750 to get panels, second hand inverter and mounting - 8 panels totalling around 3500Wp. The issue comes with the cable route into the garage for DC, and then the hooking up to the AC and making sure the RCD is appropriate. Would need to find a sparky prepared to undertake that work, and guessing it’s be another £400 - £700. So should be able to get it done for £1500. Export increase about £500 a year, plus improved generation in winter to offset costs, should payback in 2 years or so at that price.
DNO isn’t necessarily too bad. Currently could deploy outside MCS on that roof. Just need to register the inverter with the DNO in addition to existing G99 approval.
Well, I sort of got the go ahead. Close enough anyway…
Is there a way of having Predbat limit rate of givenergy system export to ensure overall cap on export - don’t want to throttle generation, so want the GE to handle the control aspect and not the secondary inverter.
You can configure an export limit in apps.yaml but Predbat only uses this to model the impact of the limit in the plan, it doesn’t control that on your inverter, it relies on your inverter applying any export limit set.
So what I believe happens in a setup like yours is if your new string inverter is generating and exporting solar, the GivEnergy inverter will throttle its output to keep within any export limit it has configured. If it can’t charge the battery and keep within the limit it will reduce its solar generation.
Solcast limit is 2 sites as you know. My roof is East West aligned so I have two sites setup in Solcast, one for the East facing panels and the other for the West facing panels.
Power output across the 3 arrays as the sun moves round:
The grey gives the total forecast and the orange the total power generation. Total power generation is a time based trigger template that updates itself every 5 minutes which is good enough granularity for viewing on a graph and using in predbat.
For interest I created some template entities to track the forecast of my G array which is 16 out of 22 East facing panels, that’s the purple line vs red line actuals.
The solcast and predbat forecast doesn’t understand the subtlety’s of potential inverter clipping so I have to fudge that a bit, but otherwise it works fine.
If you have 3 different roof orientations you either have to create a fudge twin site setup in solcast (which is what @Rbor does) or you have to create a second Solcast account with the extra orientation (but this does break Solcast’s terms and conditions so isn’t really recommended).
So I did fudge it to see what it looked like - and today I’d be getting circa 140% of current install if I’d had it there. Seems reasonable on the estimate and pattern, so guess I’ll have a look at it again once installed.
Predbat does 1, it plans to use your battery capacity to minimise your electricity bill through minimising import, maximising export, but at the same time being aware of your export limit and forecast generation.
2 has to be done by your inverter. If installer has configured your export limit on your inverter and it has CT clamps on the grid supply, it will see what is being exported and will reduce any forced discharge to keep within your export limit.
[Well that is what I believe should happen, I have never personally seen it happen but my export limit is my inverter capacity, 10kW, so I wouldn’t]
I have a 5kW export limit. My battery is set to do a timed export each morning. It starts off at 4kW. As more sun gets on my SE facing panels the inverter reduces the battery export to stay within the 5kW limit. Hope this helps.
Interestingly, I was looking through my DNO authorisation letter today, and noted that I appear to already have an IDC permitted installation allowance of up to 7.36kW, so seems that I won’t be limited presently because current system is well within this.
I guess that I’ll need to have the GE system limitation configured to limit total export. I presume this is something that can be done on the Inverter settings, or is this a call to GE support?
Your export limit will be determined by what your inverter is set at. You can check under Settings - Grid Settings on the GivEnergy app or the Export Limit in HA. The settings on the portal my limit is set to 3680w which is wrong.
I’m not sure what the 7.36kW you refer to represents. Is it the Maximum Export Capacity granted by the DNO or the maximum generation capacity of your PV panels? Normally the DNO will let you export to the maximum of your inverter.
My understanding is that you will need to notify the DNO and get permission before you can connect any additional generation equipment to the grid.
DNO has approved installation, and require G100 enforcement at 7.36kW. I’ve asked GE support to enable that G100 enforcement (they have set the value, just checking following some other research that they may or may not have enabled G100 enforcement mode).
I’ve also configured Predbat to model the export limit, and have primed the value for the aggregate solar inverter maximum for when I’ve installed this system. (Plan is this weekend!)
Thanks for all the pointers and guidance chaps. I’ve learned a lot about G99 Type A, DNO interactions and something around G100 in this process, so some good time spent!
All completed on Saturday. Got most of the stats sorted out this morning after API access enabled for the other inverter. I am at 43.9kWh generated today with more trickling in at around 300W.
I have pretty much added another 80% yield or more to the system.
Exports seen over 6kWh peak today. I lost a few kWh from cloud cover.
Great result. As well as the equipment and install costs you mentioned above, did you have to pay the DNO for the G100 application? I’ve heard that some DNO’s can charge a few hundred pounds for the approval.
There’s definitely part of me that would be interested in extra panels myself, there is some spare roof space at the front of the house and by moving the existing garage panels up I could get another couple on there as well.
Whether it’s worth it though I am less sure. I already get issues with high solar generation causing the grid voltage to spike above 258V which shuts the inverters down, so another array would just exacerbate this. Of course could go back to the DNO and get them to look at my grid voltage but I suspect its caused by me and my neighbours generation as it’s only high during the day
