Solar panel configuration for a small 2KVA system: advice needed!

Hi,

I'd very much appreciate some expert advice on the correct panel configuration for my rather lean 2 KVA system with inbuilt MPPT.

Context:

My system is small and low budget compared to the very, very impressive stuff I've seen here (e.g., I'm using 4x 100Ah AGM batteries, no fancy Lithium Ion, and a small 2KVA RCT inverter). And I also have no plan to go off-grid: I merely installed this little setup 6 months ago to prepare our  2-person private household for load shedding, and to date it has been working like a charm. We practically don't feel load shedding other than having to check when we can run certain appliances. All the essential low consumption items such as lights, fridge etc. are on a dedicated DB circuit that can be separated from the mains supply via a changeover switch. The batteries are configured to output 24 Volt, so their total capacity is 24 V x 200 A = 4.8 Kw, and I set the inverter to cut out automatically at a max of 50% capacity usage. We never got anywhere near that: out of curiosity I isolated the inverter from the AC supply and let the system run for 12 h hours using whatever I wanted to use (lights, TV, PC etc. to which my wife then accidentally added a 1.8 kw hair dryer for 10 minutes...) After that I could only measure a 20% capacity loss = so over 12 hs just 0.96 kw used or 80W / h. Makes sense when I calculate back from our metered electricity consumption: we normally use about 20 kwh/d = 833 w/h INCLUDING all the bigger appliances, geyser top-up heating, pool pump etc. - So it seems to me that all in all my little system is right sized to begin with.

Requirements:

OK, so I now want to add some solar panels, and I also want to stick to my 'lean engineering' approach. These are my requirements:

a) Be able to charge the batteries from solar via the inverter during the day if needs be. Let's assume continuous stage 6 load shedding as worst case: if we draw 80W / h over 6 hs from the batteries we'll use 480W per day. So if I can install 1000 W panel capacity and conditions are ideal I should be able to make it and recharge my battery bank to 90% plus. (Of course realistically I should be preparing for stage 16 🤓 .)  - But more than that I want to be able to...

b) ... add our 550 w pool pump to the dedicated circuit and power it from solar when there isn't load shedding - because in our household the pool pump has turned out to be the single biggest consumer of electricity. And this while it is practically the only machine that is absolutely guaranteed to run only during the day....  The pump is set to run for 4 h/d, so that means 2.2 kwh consumption per day. Seems realistic to cover that need from a 1kw panel array too, yes?   

So my overall requirements are really quite limited - namely to be able to cover the energy requirements of either a) or b).

Configuration options

Here are the inverter parameters:

• Inverter: RCT-AXVM2K, 24 Volt
• Max PV Array OC Voltage = 102Vdc
• PV Array MPPT Range = 30-80Vdc
• Rated Power Solar Charger = 1000 W

Option a)

My initial idea was to use 2x JA Solar 540W in series to obtain 1 KW under ideal conditions, with high voltage and amps as low as possible. But I now realise that the combined  max Vmp could then reach 2 x 41.64 = 83.28 Volt, which exceeds the 30-80 Volt range specified for the MPPT. Of course only theoretically and on a very cold day, but still...

Question 1: Are the theoretical 3.28 Volts something to worry about? 

Option b)

Use 3 x JA Solar 365W in parallel .  This configuration would then give me the 1 KW output at a comfortable, if not even rather low Vmp = 33.96V which is at the bottom end of the MPPT range. But more problematic perhaps is that it would require me to also run cables to my inverter that can handle a whopping 3 x 10.75 = 32.25 Amp current if need be, if my maths is correct. 

Question 2: Is this a (more) advisable approach?

Option c)

Downscale to a 2 x 2 series&parallel configuration that uses 250 - 300 W panels. Drawback seems to be a rather low efficiency in the 18% region, plus I didn't find any 250 W panels here at the power-forum store...

Many thanks for your patience in reading through all of this!

Chris

Edited September 27, 20223 yr by Chris M