adding a second inverter to the same solar array

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mufaddalk
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adding a second inverter to the same solar array

Post by mufaddalk »

Currently i have solar array (2 strings of 10 each) connected to my PIP5048GK inverter. This setup has been running fine for a year now.

I have 100ah battery to the above setup, and my total solar max output of the 20 panels is 4kw. On a good day my batteries are charge in couple of hrs and the solar output is wasted for the rest of the day as my inverter will reduce the charge current and stop when the batteries are charged.

I have hot water heater tank that is not powered via my inverter as it don't want to trigger the output more then the inverter max i.e. 5kw. This runs on 4kw itself and its the biggest contributor for my electricity bill.

I am thinking of getting another Inverter and battery setup that will power my hot water and few other appliances. My question is, can i connect 2 inverters to the same solar input. is there any additional circuit or device needed in the middle.

Thanks for help
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coulomb
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Re: adding a second inverter to the same solar array

Post by coulomb »

mufaddalk wrote: Sat, 31 Oct 2020, 08:53
Currently i have solar array (2 strings of 10 each) connected to my PIP5048GK inverter.
For other readers, the PIP-5048GK (Axpert VM III) cannot be paralleled; there is nowhere to add the paralleling boards and the firmware doesn't support paralleling the outputs.
I have 100ah battery to the above setup, and my total solar max output of the 20 panels is 4kw. On a good day my batteries are charge in couple of hrs and the solar output is wasted for the rest of the day as my inverter will reduce the charge current and stop when the batteries are charged.
I used to fret over the wasted panel energy too. But now I realise that you just can't use it all on the good days, if you have enough panels to power your loads on most of the bad days.
I am thinking of getting another Inverter and battery setup that will power my hot water and few other appliances. My question is, can i connect 2 inverters to the same solar input.
No. The panels have to be connected to one and only one inverter; PV inputs can never be connected to each other.

You have to strings of panels, so you can just put one string on one inverter and the other string on the other inverter, sharing only the battery and AC-in connections (not the AC-out connections). If you need more than one string's worth of energy on any particular day, the PV energy will flow from one inverter's solar charge controller through the battery connection to the other inverter. You may want to switch your hot water over to mains, but even if you don't, you won't be wasting PV energy. Any mains energy that you use, you will need to use one way or the other. Depending on circumstances, since your inverters won't be paralleled, one may be in bypass while the other is in battery mode. I don't believe that there would be any problem with that.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
mufaddalk
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Re: adding a second inverter to the same solar array

Post by mufaddalk »

Hi @coulomb thanks four your feedback.

sorry i wasn't clear in my earlier post, the 2 inverters will not be in parallel. The they will each have a separate battery and connect to separate AC output.

My only question was if they can be powered from a single solar source. Thanks for clarifying that it cant be done.

It is doable to have then each connected to its own solar string, however it would be preferable for me if possible to have them both connected to same panel set.

Is anyone able to explain the reason why it cant be done, my electrical knowledge is only that great. Also is there any device i can use, maybe reverse polarity protection or something to allow it to happen.
Also is there is no way to achieve this, I am also thinking about having a smart switch/relay or something that i can control, i.e. if my first inverter battery is fully charge at 53.8V, switch panels to second inverter. finding a switch that will work with 450vdv is a separate thing :)
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Re: adding a second inverter to the same solar array

Post by antiscab »

Why not just common the batteries? Then it doesn't matter which inverter the solar is on.
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Re: adding a second inverter to the same solar array

Post by mufaddalk »

antiscab wrote: Sat, 31 Oct 2020, 13:55 Why not just common the batteries? Then it doesn't matter which inverter the solar is on.
currently i have 100ah battery (16x100ah calb cells). with the next inverter its unlikely i will be going with the same brand. Wont be able to parallel them to increase capacity. and i need more capacity.
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Re: adding a second inverter to the same solar array

Post by coulomb »

mufaddalk wrote: Sat, 31 Oct 2020, 13:41 Is anyone able to explain the reason why it cant be done, my electrical knowledge is only that great. Also is there any device i can use, maybe reverse polarity protection or something to allow it to happen.
I'll try. The problem is the lack of isolation. Each side of the so-called "DC bus" connects alternately to active and neutral at some 20 kHz. Most but not all of the 20 kHz voltage square waves, of 300 - 500 V amplitude, are filtered out, but that leaves the 230 VAC 50 Hz component on both PV leads. Despite the best effort to synchronise these, they will be slightly different in amplitude, especially with the Solar Charge Controllers operating at different boost levels, so connecting the PV inputs will lead to damaging current flows.
Also is there is no way to achieve this,
If it was AC, you use an isolating transformer. But PV is DC, so you'd have to have a DC to AC converter, followed by an isolating transformer, then an AC to DC rectifier, which is just too inefficient and costly.
I am also thinking about having a smart switch/relay or something that i can control...
It's possible but messy. I have two EV200s on the inputs of my inverters (4 total for 2 inverters), but they are single pole single throw. You would need 4 of these to act as changovers for one string of panels. They need power and something to control them, so it gets complex pretty quickly. They can handle 800 V and 200 A, but they are expensive. For a while, they could be bought for only some $60, but that source seems to have dried up.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
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Re: adding a second inverter to the same solar array

Post by paulvk »

For high current relays/contactor albright engineers you can get 125 amp single pole ones for AU $35 from element 14
I use these as I have some already, they are big units with 10mm dual contacts for single pole to give large air gap
they have a current breaking capacity of 400 amp at 80 volt dc so at lower currents they can handle a higher voltage
and if two are used in series you can nearly double the voltage.
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Re: adding a second inverter to the same solar array

Post by T1 Terry »

coulomb wrote: Sat, 31 Oct 2020, 15:27
mufaddalk wrote: Sat, 31 Oct 2020, 13:41 Is anyone able to explain the reason why it cant be done, my electrical knowledge is only that great. Also is there any device i can use, maybe reverse polarity protection or something to allow it to happen.
I'll try. The problem is the lack of isolation. Each side of the so-called "DC bus" connects alternately to active and neutral at some 20 kHz. Most but not all of the 20 kHz voltage square waves, of 300 - 500 V amplitude, are filtered out, but that leaves the 230 VAC 50 Hz component on both PV leads. Despite the best effort to synchronise these, they will be slightly different in amplitude, especially with the Solar Charge Controllers operating at different boost levels, so connecting the PV inputs will lead to damaging current flows.

Also is there is no way to achieve this,

If it was AC, you use an isolating transformer. But PV is DC, so you'd have to have a DC to AC converter, followed by an isolating transformer, then an AC to DC rectifier, which is just too inefficient and costly.

I am also thinking about having a smart switch/relay or something that i can control...
It's possible but messy. I have two EV200s on the inputs of my inverters (4 total for 2 inverters), but they are single pole single throw. You would need 4 of these to act as changovers for one string of panels. They need power and something to control them, so it gets complex pretty quickly. They can handle 800 V and 200 A, but they are expensive. For a while, they could be bought for only some $60, but that source seems to have dried up.
If the solar PV was converted to AC, then through the isolating transformer, could that also be wound to drop the voltage to 240vac that would better suit the water heater element and thermostat? The water heater already runs on AC, so no need to rectify back to DC, the DC to AC could be square wave if there are no electronics being powered by this converted DC from the solar, a heater element doesn't really care what wave form it receives .... or have I got that wrong?

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coulomb
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Re: adding a second inverter to the same solar array

Post by coulomb »

T1 Terry wrote: Mon, 02 Nov 2020, 09:00 If the solar PV was converted to AC, then through the isolating transformer, could that also be wound to drop the voltage to 240vac that would better suit the water heater element and thermostat? The water heater already runs on AC, so no need to rectify back to DC, the DC to AC could be square wave if there are no electronics being powered by this converted DC from the solar, a heater element doesn't really care what wave form it receives .... or have I got that wrong?
I guess if you really did go to all that trouble, you could step it down to ~230 V RMS. But that (as a square wave) would rectify to under 230 VDC, which is a bit on the low side to boost back up to ~350 VDC for the DC bus. Also, I worry that such a high amplitude square wave would cause massive noise in electrical and radio systems, and the inductance of the leads might cause significant voltage drop. In other words, I suspect there's a good reason that no-one does it that way.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.
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Re: adding a second inverter to the same solar array

Post by shallowal »

Why not replace the water heater element with a smaller wattage one. I recently reduced ours from a 4.8Kw to a 1.8Kw, to better suit the solar system. The longer heating time doesnt much matter for me.
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Re: adding a second inverter to the same solar array

Post by TyTower »

shallowal wrote: Mon, 09 Nov 2020, 05:08 Why not replace the water heater element with a smaller wattage one. I recently reduced ours from a 4.8Kw to a 1.8Kw, to better suit the solar system. The longer heating time doesnt much matter for me.
I've got a 1K 240v element on the way to try exactly that too.
How will you run it? Just put it on a timer 10 to 4 or some sort of voltage point control?
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Re: adding a second inverter to the same solar array

Post by solamahn »

Mine operates via the inverter dry contact and a contactor. On at 58v, off at 51v
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