I've been running my system for about 11 months (the inverter and first battery were a lucky gift from my brother-in-law). It's great in summer, but the short days and low winter sun here in the Garden Route mean I'm struggling to cover usage and fully charge my batteries. My self-sufficiency fell from 81% in April to 64% last month, and I'm sitting on 52% at the moment.

I want to add 2 more panels purely to boost my winter generation, but I'm worried about inverter safety.

Current Setup:

• Inverter: 5kW Sunsynk

• Batteries: 2x Revov R100

• Panels: 12x 550W Trina (6.6kWp total) (TSM-550DE18)

• Split: 6 East / 6 West (24° roof pitch)

If I add one 550W panel to each string (making it 7E / 7W), my total array becomes 7.7kWp. I know the extra capacity will clip in summer, which is fine, I just need the winter bump.

My questions:

1. Will just 2 extra panels actually make a noticeable difference to my winter battery charging?

2. Given the East/West split (meaning the inverter never sees peak wattage all at once), is 7.7kWp safe on the 5kW Sunsynk, or is this pushing the hardware too far?

Thanks!

1. You're increasing your array by 7.7/6.6=16.6%. Only you will know if the cost of adding two panels justifies an extra 16% production. You can look at your current generation, increase it by 16% and work out how much those extra units would be to buy from Eskom. Then look at your ROI and added resilience. That being said, I'm always a fan of adding more panels, especially if you can't fully charge your battery currently. Just make sure the new panels match the old panel specs.

2. I ran the same size array for a few weeks on my home system (although arrays were 6x550W NE and 8x550W NW). Had no issues while it ran, although did get clipping midday at 6500W as it was summer. Soon afterwards I added a second 5kw in parallel so split the arrays and have since added another 6x600W.

   Out of interest, how many kWh are you generating on clear days?

28 minutes ago, sproete_za said:

Given the East/West split (meaning the inverter never sees peak wattage all at once), is 7.7kWp safe on the 5kW Sunsynk, or is this pushing the hardware too far?

Given the East/West split, you won't see the full 7.7kWp anyway, the peak should be lowered to around 7kW at mid-day in high summer (you can check it on an online solar calculator). Maybe calculate by another route and compare it to your current mid-day peak in summer, then add another 17% on-top of that.

I'm not in a position to give a comment on the safety.

2 hours ago, sproete_za said:

1. Will just 2 extra panels actually make a noticeable difference to my winter battery charging?

2. Given the East/West split (meaning the inverter never sees peak wattage all at once), is 7.7kWp safe on the 5kW Sunsynk, or is this pushing the hardware too far?

1. it should make a difference, how noticeable, is tough to predict, if there is no partial shading on either of the strings, when they should be producing energy, it should be worthwhile, I'd say

2. the inverter should throttle the power back to what it is able to consume/charge the batteries

3. the more important one is the strings Voc, which should be ok, I think, just a hair under 50Voc per panel * 7 = 350Voc per string, which, I believe, the Sunsynk would be ok with, maybe double check this, I don't have a Sunsynk here anymore...

2 hours ago, sproete_za said:

My questions:

1. Will just 2 extra panels actually make a noticeable difference to my winter battery charging?

2. Given the East/West split (meaning the inverter never sees peak wattage all at once), is 7.7kWp safe on the 5kW Sunsynk, or is this pushing the hardware too far?

In my opinion:

1. I'm sure it will...

2. As @Kalahari Meerkat said, the panels will only produce what is demanded, and unless your consumption exceeds the inverter's rated power, the panels won't exceed that (plus losses...), so it's unlikely to be a problem. It would, however, be wise to set your battery charging current at a value that this plus your house load will not exceed the inverter rating (i.e. don't charge at (say) 200A for two hours - rather charge at 50A for 8 hours).

2 hours ago, JaseZA said:

Out of interest, how many kWh are you generating on clear days?

Thanks for your feedback and opinion! My total daily consumption is just shy of 20 kWh, though in summer it's around 23 kWh. I haven't had a clear day recently—as you can see below, the most I've generated in the past 30 days was 18.5 kWh. This will really help with the cloudy winter weather as well.

51 minutes ago, Kalahari Meerkat said:

1. it should make a difference, how noticeable, is tough to predict, if there is no partial shading on either of the strings, when they should be producing energy, it should be worthwhile, I'd say

2. the inverter should throttle the power back to what it is able to consume/charge the batteries

3. the more important one is the strings Voc, which should be ok, I think, just a hair under 50Voc per panel * 7 = 350Voc per string, which, I believe, the Sunsynk would be ok with, maybe double check this, I don't have a Sunsynk here anymore...

Yes, I've checked now and the safety limit on the Sunsynk is 500V, with the optimal working range being 150V - 425V. We seem to fall well within that, which I assume is safe. My only concern was that the inverter cannot throttle the voltage, if I'm correct, but it seems to be okay.

34 minutes ago, HennieL said:

As @Kalahari Meerkat said, the panels will only produce what is demanded, and unless your consumption exceeds the inverter's rated power, the panels won't exceed that (plus losses...), so it's unlikely to be a problem. It would, however, be wise to set your battery charging current at a value that this plus your house load will not exceed the inverter rating (i.e. don't charge at (say) 200A for two hours - rather charge at 50A for 8 hours).

Thanks for the tip.

I just received the quote from the installer and it comes to R9,650. Since my initial install, panels have gone up by R389 each, and labor increased by R500 for a half-day's work, but the rest has stayed the same. They assured me they're the same panels as what's on the roof. I know the two extra panels will be useless in summer, but my main issue is winter, so I'm fine with that because that's when I need the boost.

According to my calculations, the ROI goes from 2.86 years to 3.38 years, which is still very acceptable since I received the inverter and battery as a gift.

4 hours ago, sproete_za said:

I've been running my system for about 11 months (the inverter and first battery were a lucky gift from my brother-in-law). It's great in summer, but the short days and low winter sun here in the Garden Route mean I'm struggling to cover usage and fully charge my batteries. My self-sufficiency fell from 81% in April to 64% last month, and I'm sitting on 52% at the moment.

I want to add 2 more panels purely to boost my winter generation, but I'm worried about inverter safety.

Current Setup:

• Inverter: 5kW Sunsynk

• Batteries: 2x Revov R100

• Panels: 12x 550W Trina (6.6kWp total) (TSM-550DE18)

• Split: 6 East / 6 West (24° roof pitch)

If I add one 550W panel to each string (making it 7E / 7W), my total array becomes 7.7kWp. I know the extra capacity will clip in summer, which is fine, I just need the winter bump.

My questions:

1. Will just 2 extra panels actually make a noticeable difference to my winter battery charging?

2. Given the East/West split (meaning the inverter never sees peak wattage all at once), is 7.7kWp safe on the 5kW Sunsynk, or is this pushing the hardware too far?

Thanks!

Somewhat tricky, because of the E/W split, and you have cooling coastal winds to contend with that could cause both voltage and amps to fluctuate. You say that you have 11 months worth of data, but if you can at least look at a full 12 months' worth of MPPT data (not just power, but voltage and amperage), then you could do your calculations based on that.

Also you don't say where on the Garden Route (a 300 km stretch from Witsand to Tsitsikama!) you are: minimum temps could be vastly different, especially at different altitudes, for example a ridge on the Outeniqua or Swartberg would have different lows to Storms River Mouth. This is important because minimum temperatures increase voltage, and maximum temperatures increase amperage.

As pointed out by @Kalahari Meerkat the main concern is exceeding the max voltage of the MPPT which is 500V, so nothing 450-480V. Using 0°C to +2°C as the minimum gives ~52.9–53.2 V per panel, so OK even if you are on a low-ish slope on the Swartberg.

• 7 panels: ~370–372 V → still in MPPT operating range (425V);

• 8 panels: ~423–426 V → marginally over MPPT operating range, but still workable;

So theoretically you can go for up to 8 panels per series string, provided that it does not get to -5°C during a cold snap with some wind (that cool coastal breeze can turn into a frozen gale 🥶).

Long story short: You can safely add 2 panels to each string, provided no sub-zero temps.

Another scenario worth considering, if you have the garden space, is a North-facing ground mount structure with 4-6 panels. You can use a Hoymiles or Deye microinverter or two to pump the AC to the Sunsynk's Aux port.