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Amount of solar panels


Chris Louw
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Hi, I've been using solar power for the last 5 years but now I need some advice.  My electrical knowledge is basic. Currently I have a 5kva Axpert with 8 x 150ah Beta batteries (Lead Crystal). The system has been running for 3 years. I started with 12 (250watt) panels and in the last year I've run 15 (250watt) panels on the system, no problems. The system rarely reaches 3000 watt solar supply.  I now have another 3 (250watt) panels available.  Is there any way that I can limit the solar supply to 3000watt?  I can use the additional power in the mornings and late afternoon.  I can switch the panels manually but I must have protection against a power spike.  I have a 2nd 5kva Axpert inverter but would prefer not to install it for only 3 panels.

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I assume that the built-in MPPT is a 3kva unit and you are concerned about installing more than 3kwp of PV panels on this system. The good news is that the MPPT will automatically cap the power at its max rating, so even if you oversize the array a little the MPPT will simply cap it at 3kwp whenever it does make more.

It is advisable not to oversize by too much (it's not cost- effective anyway). Try to stick to around 120%. 3 additional panels should not be a problem.

Edit: Just watch out for the maximum open circuit voltage! I assume that this system is probably configured as 5 strings of 3 panels, so you'll be adding an extra string and won't be messing with any voltages... but it has to be said for completeness.

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It is a 5 kva unit with 3000 watt mppt . Currently running fine on 3750 watt , 125% . I have another 3 panels 250 spare  which will be 4500 watt . Is there a way to regulate it at 3000 watt . Currently the system is running good . We are pensioners and only use +/- 30 kwh grid power per month ( only to keep batteries above 80 % DOC ) , the rest is solar power . The extra panels will be usefull during the of peak hours for early charging and bad weather days . Thanks for your respons .

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10 hours ago, Chris Louw said:

Currently running fine on 3750 watt , 125% . I have another 3 panels 250 spare  which will be 4500 watt

That seems a tad much. I should have noticed that the first time round.

I usually try to temper my skepticism about these cheaper inverter/charger's ability to run at max for extended periods of time, but I've seen what a high end European MPPT does at 50% oversizing (it logs overcurrent events) and I doubt the cheaper ones are going to be better: so I stick to my general advice to stick to 20%, and you're already there.

So for your application it might be better to add an external MPPT charger for the extra panels (which is rather a lot of overhead cost for just three panels). But there are more complications. You have 300Ah of battery, so you're limited to 60 amps charging current (and that is pushing things a little), while 4500Wp gives you a potential 90A peak charge current. Now the internal MPPT in the Axpert can be configured to limit to a safe level, but the moment you add an external MPPT there is no such possibility.

I think what I would do is 1) add a second MPPT, 2) point the panels in a slightly different direction, for example point them North West so they make peak power around 3pm. You get the same energy, but a flatter curve instead of a very high peak, and you catch more of that late afternoon Summer sunshine.

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Thanks I will ad the extra akpert 5kva i have . Have checked firm ware , both U1 - 52 - 30 . I have a few questions .

1. I will now have 6 Strings of 3 panels . Must i split them in 2 strings on the roof before i take them down  to the inverters .

2 . Will i be able to switch 1 inverter of at nite to lower consumption during the nite . Currently the lowest we go on the batteries is 50.5 Volt . Want to keep it like that .

Thanks 

 

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1 hour ago, Chris Louw said:

Thanks I will ad the extra akpert 5kva i have . Have checked firm ware , both U1 - 52 - 30 . I have a few questions .

1. I will now have 6 Strings of 3 panels . Must i split them in 2 strings on the roof before i take them down  to the inverters .

2 . Will i be able to switch 1 inverter of at nite to lower consumption during the nite . Currently the lowest we go on the batteries is 50.5 Volt . Want to keep it like that .

Thanks 

 

Hi Chris 

Welcome

1. I think you mean two arrays. Where is your combiner box? I would just add a second combiner box perhaps with 2 of the 6 strings (ensuring that all the panels on a single MPPT face the same direction)

2 Yes one can do that just make sure that the one you switch off is the slave not the master.

 

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12 hours ago, Chris Louw said:

The combiner box is in the roof . Yes i dit mean 2 arrays . What i wanted to now is if i could split 1 array into 2 or must i have  2 seperate arrays . Sorry neither english or electrics are my language .

 

OK so you are going to need a second combiner box.

Each inverter is going to need separate panels dedicated to that particular inverter. I would probably split 4 strings on the one and 2 on the other. You have 4(actually 5) strings working well so I would not fiddle too much. One could have 5 and 1 but that really does not seem to clever taking into account the work involved setting up a second inverter so I would go 4 and 2 strings and if you get more panels you could just add them to the second inverter.

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