48 Volt Solar array question

[Wesleydeb]

I series stringed 4 12 volt 100 watt renogy PV panels into my 12 KW Growatt Off Grid inverter charging a Flooded Golf Cart Battery Bank.... Battery Bank is 8 x 6 volt Golf cart batteries that I recovered from a broken down Golf cart.. I purchased the batteries new thinking it would fix the old golf cart but found out the chassis was broken so I put them in the Solar System when I built it..

My question is; the contractor I purchased the Inverter from tells me that series stringing 4 renogy panels is not enough to full utilize the MPPT feature in the Inverter Charger... They recommend series stringing 6 panels...

Does anyone have any thoughts on this... Will Prowse this would make a good video for you to discuss benefits or cons to series stringing multiple panels and whether 4 each 12 volt panels in series is enough for a 48volt solar charger???

Thanks for any information regarding this.

 

[JoeHam]

As you likely know, series sums the voltages.

For any 48v nominal system you will charge your batteries to a voltage greater than 48v. In addition you need your panels to generate a voltage about 5 volts higher than that number to work. That is one reason why you want higher voltage. Frankly you would be better off with fewer higher voltage solar panels but what you have may work. You haven’t provided the panel specs so we can be sure.

In addition your Growatt PROBABLY can take up to 150v on the MPPT input side. Again, not enough information provided to be sure. One could argue that if you’re only generating say 75v you aren’t fully utilizing it’s capabilities. Double check your owner’s manual (you did read it, right) to be sure the Growatt doesn’t list a minimum required voltage for the MPPT to function. Obviously if it has a minimum requirement you must meet that but what you have now MAY do that.

 

[RCinFLA]

Need to know particular model of inverter and panel. He may be referring to the PV input operating voltage range of inverter/charger.

Having only four 100w panels and 215AH of batteries is not going to take a 12KW inverter very far. Idle power on inverter may eat up a significant percentage of solar production. Batteries will limit to about 4KW peak power load and limit consumption per charge to about 5 kWH's.

 

[MichaelK]

We can look at this issue from two different angles, the voltage optimized to charge your batteries, and the watts needed to charge your batteries. Assuming your panels are producing about 18Vmp, that would give you 18V X 4 panels = 72V. With 6 in series it would be 108Vmp. 72Vmp should be adequate even under cold-weather conditions when charge voltage is bumped up to about 60-61V. In the middle of hot summer though, your panel voltage will go down. If for example it drops to 16V per panel, then 4 in series would put out only 64Vmp. This might not be enough overhead to allow the MPPT of your particular unit to function properly. So, yes, he might be right about the voltage spread.

The charging watts is a separate issue and is much easier to answer. Let's assume your golf-cart batteries are somewhere in the 200-250Ah capacity range. Their optimal charging rate is going to be around 1/10 to 1/8 C, so depending on the battery, that works out to be.....
200Ah X 1/10C = 20A
200Ah X 1/8C = 25A
250Ah X 1/10C =25A
250Ah X 1/8C = 31.3A

What you can really expect your array to produce is (100W X 4 panels)/50V charging X .85% fudge factor = 6.8amps, far below what your batteries actually need. I would say you need to add far more than just an additional two panels. Depending on what your battery's capacity is you actually need is.....
(20A X 50V charging)/0.85 fudge factor = 1176W
(25A X 50V charging)/0.85 fudge factor = 1470W
(31.3A X 50V charging)/0.85 fudge factor = 1840W

The problem is that you started out with 12V panels, which was a mistake for a system of this size. 12V carries a price premium to fit into the 12V automotive market. You would have been far better off starting out with higher voltage grid-tie panels. So, now you have choice to make.

1) Get rid of the 12V panels completely, and buy 6 grid-ties at 30-36Vmp. Wire them so you get at least 90Vmp, so that might be 3 in series. You MUST pay careful attention though to what the Voc for your controller is. That would give you about 1500W. I can get this many W for about 330$ when buying 60 cell panels.

2) Buy an additional two 12V panels, wire them 6 in series to get 108Vmp, then parallel them with at least three 36V grid-tie panels that would put out 108Vmp in series. Typically what I see are 300W 72cell panels that produce that voltage. That would give you 600W + 900W =1500W total. You might have to pay a bit more for 72cell panels than standard 60cell, which right now are dirt cheap.

3)Buy one additional 12V panel, wire 5 in series to get 90Vmp, then parallel them with three 250W/30V grid-ties wired in series for 90Vmp. That would give you 500W + 750W = 1250W. That's on the low side of good, but completely adequate.

Whatever path you take, you'll need a LOT more watts to charge your batteries adequately. Look on Craigslist to find local sellers that market the panel types mentioned, then make a decision on what's locally available at low cost. You always pay far less for panels with local pickup, rather than shipped. And, some of my BEST panels are used grid-ties pulled off someone's roof. Look for those to get the best deal.

 

[Wesleydeb]

We can look at this issue from two different angles, the voltage optimized to charge your batteries, and the watts needed to charge your batteries. Assuming your panels are producing about 18Vmp, that would give you 18V X 4 panels = 72V. With 6 in series it would be 108Vmp. 72Vmp should be adequate even under cold-weather conditions when charge voltage is bumped up to about 60-61V. In the middle of hot summer though, your panel voltage will go down. If for example it drops to 16V per panel, then 4 in series would put out only 64Vmp. This might not be enough overhead to allow the MPPT of your particular unit to function properly. So, yes, he might be right about the voltage spread.

The charging watts is a separate issue and is much easier to answer. Let's assume your golf-cart batteries are somewhere in the 200-250Ah capacity range. Their optimal charging rate is going to be around 1/10 to 1/8 C, so depending on the battery, that works out to be.....
200Ah X 1/10C = 20A
200Ah X 1/8C = 25A
250Ah X 1/10C =25A
250Ah X 1/8C = 31.3A

What you can really expect your array to produce is (100W X 4 panels)/50V charging X .85% fudge factor = 6.8amps, far below what your batteries actually need. I would say you need to add far more than just an additional two panels. Depending on what your battery's capacity is you actually need is.....
(20A X 50V charging)/0.85 fudge factor = 1176W
(25A X 50V charging)/0.85 fudge factor = 1470W
(31.3A X 50V charging)/0.85 fudge factor = 1840W

The problem is that you started out with 12V panels, which was a mistake for a system of this size. 12V carries a price premium to fit into the 12V automotive market. You would have been far better off starting out with higher voltage grid-tie panels. So, now you have choice to make.

1) Get rid of the 12V panels completely, and buy 6 grid-ties at 30-36Vmp. Wire them so you get at least 90Vmp, so that might be 3 in series. You MUST pay careful attention though to what the Voc for your controller is. That would give you about 1500W. I can get this many W for about 330$ when buying 60 cell panels.

2) Buy an additional two 12V panels, wire them 6 in series to get 108Vmp, then parallel them with at least three 36V grid-tie panels that would put out 108Vmp in series. Typically what I see are 300W 72cell panels that produce that voltage. That would give you 600W + 900W =1500W total. You might have to pay a bit more for 72cell panels than standard 60cell, which right now are dirt cheap.

3)Buy one additional 12V panel, wire 5 in series to get 90Vmp, then parallel them with three 250W/30V grid-ties wired in series for 90Vmp. That would give you 500W + 750W = 1250W. That's on the low side of good, but completely adequate.

Whatever path you take, you'll need a LOT more watts to charge your batteries adequately. Look on Craigslist to find local sellers that market the panel types mentioned, then make a decision on what's locally available at low cost. You always pay far less for panels with local pickup, rather than shipped. And, some of my BEST panels are used grid-ties pulled off someone's roof. Look for those to get the best deal.

I am 71 years old... I went with the Renogy Panels after watching Will Prowse video comparing HQST, Rich Solar, Renogy and another brand that escapes my memory.... Also I went with the 100 Watt panels based on the South Facing Roof space I have available and I have to be able to lift them up a ladder by myself so I bought what I could handle by myself at my age...

I currently wired them in series 4 100watt panels to achieve the 48volts... Currently during peak Sun Conditions they produce around 70 volts each string... I then Paralleled 6 strings together... The 12 kw Off Grid Growatt inverter has 2 PV inputs so I put 3 strings into one input and 3 strings in the other... At Peak Sun conditions the best I have gotten current wise to the batteries is 42 watts...

I understand voltage and current as my background is as a Senior Telecommunication Specialist.. But I am a beginner to Solar Arrays and Off Grid systems such as these... In my day at the telecommunications towers we used Generators and battery backups.. All of our towers were gird tied so we used batteries and generator only during power failures.

Here is part of the reasoning the Solar Engineer I purchased my Growatt inverter explained that by adding at least 2 additional panels that in the early morning I would reach that 48+ volt requirement to start the battery charging process and in the late evening I would get additional charging minutes. My fear is during the peak of the day will the MPPT just clip off the extra production thus offsetting any gain he mentioned?

PS. the main reason I started this Solar Array project was to introduce my 3 pre-teen grand daughters to the PROs and CONs of Green Energy because their teachers have convinced them Fossil Fuels must end tomorrow.. So I want them to understand how systems work and what it would take to get us there and the time frame it will take to make this happen.. Plus to show them I am doing my part for their future!

 

[Wesleydeb]

Need to know particular model of inverter and panel. He may be referring to the PV input operating voltage range of inverter/charger.

Having only four 100w panels and 215AH of batteries is not going to take a 12KW inverter very far. Idle power on inverter may eat up a significant percentage of solar production. Batteries will limit to about 4KW peak power load and limit consumption per charge to about 5 kWH's.

I am a newbie to Solar Arrays,,, Building the system as I have the time and money... Plus something to keep me entertained and busy during this COVID madness... I started with a 4000 watt peaked at 8000 watt Giandel Inverter 12 volts... It ended up failing... I figured if I am going to get serious I would just upgrade and settled on the 12 kw Growatt Off Grid inverter meaning it does not do NET METERING. After I purchased on got it installed and running I only had about 2kw in the Solar Array roof mounted on South facing roof.. So I added a additonal 1 kw of panels... 100 watt Renogy 12 volt panels. The Growatt is a 48 volt system so I had to rewire the panels in series from the 12 volt parallel system for the Giandel Inverter.. This is when the Solar engineer I have been working with told me instead of 4 panels in series I should have at least 6 in series... The 4 panels in series was coming in at 70 volts Peak Sun Conditions... Because the panels are fixed to the roof it would take some time in the morning for the sun angle to hit a sweet spot for the 70 volts, stay there for several hours then drift back down during the evening hours.

 

[Wesleydeb]

As you likely know, series sums the voltages.

For any 48v nominal system you will charge your batteries to a voltage greater than 48v. In addition you need your panels to generate a voltage about 5 volts higher than that number to work. That is one reason why you want higher voltage. Frankly you would be better off with fewer higher voltage solar panels but what you have may work. You haven’t provided the panel specs so we can be sure.

In addition your Growatt PROBABLY can take up to 150v on the MPPT input side. Again, not enough information provided to be sure. One could argue that if you’re only generating say 75v you aren’t fully utilizing it’s capabilities. Double check your owner’s manual (you did read it, right) to be sure the Growatt doesn’t list a minimum required voltage for the MPPT to function. Obviously if it has a minimum requirement you must meet that but what you have now MAY do that.

Yes the Growatt is rated for 155 volts PV input. I am 71 years old and did not think I could manage the physical size and weight of the larger wattage panels... I am putting these on a south facing Roof climbing up and down ladders all by myself... My wife is to ill to provide any assistance so I have to select products I cam manage on my own...

PS,,, Owners Manuel,,, What's that? Do they even come with one anymore? all I got was a installation manual that does have a spec sheet... Since this thing is made in China even the installation manual is mostly pictures. I searched YouTube for some assistance but found nothing for this 12kw Growatt Model... The Technical Support team at Signature Solar have been great answering my questions and assisting me with the Menu and software setup...

Since my Finanaces are limited I am buy stuff piece meal as I can afford,,, My biggest purchases so far have been the Battle Born batteries and the 12 kw inverter. So far the battle born batteries have been a disappointment as the high rush of current at times kicks out the BMS. Now Battle Born says I need a $300 dollar current limiter. This system just gets more expensive day by day and really not giving me much in the way of ROI.

Thanks for your advice

 

[MichaelK]

Sorry to hear this. Well, I'm not a young guy either, I'll be 61 in three more months. At this point, I'm a bit confused about what you are telling me.

I currently wired them in series 4 100watt panels to achieve the 48volts... Currently during peak Sun Conditions they produce around 70 volts each string... I then Paralleled 6 strings together... The 12 kw Off Grid Growatt inverter has 2 PV inputs so I put 3 strings into one input and 3 strings in the other... At Peak Sun conditions the best I have gotten current wise to the batteries is 42 watts...

Are you saying that you put together a system with four 100W panels (400W), or a system with 6 strings of four 100 panels (2400W)? It seems to me you are saying 2400W? If it's the former, you very definately need more watts. If it's the later, it would be easy to just re-wire the panels from a 4S6P configuration into a 6S4P configuration. Assuming your panels have an Voc of 22.0V, six in series would not reach 155V till the outside temperature went down to ~-20F.

In the statement you're getting 42watts, I think what you meant to say was 42amps? Is that correct?

BTW, if in fact, you are wiring 3 strings together at one input terminal, that is considered to be an unsafe condition. Three independent strings should be on separate breakers/fuses. You should be using a combiner box. This is the Midnight one I use.

If you re-wired your arrays to 6S4P, you might be safe wiring the 4 strings in 2+2 configuration into the two inputs, though if it was me, I'd still use a combiner.

I'm not keen myself about going up on the roof, so what I've done is focused my attention on ground mounts that have the added benefit of tracking the sun over the course of the day. I built them myself, out of schedule 40 pipe, and Home-Depot uni-struts. Here's a pic of my fourth generation design, which I am very proud of.

Once the frame sub-assemblies were welded, final assembly, and solar panel attachment took only 2-3 hours. Assembly was accomplished by my son and myself only. Starting at maybe 8am, we were making power by noon. This is the 8th array I've built.

If you want something even simpler, just make a fixed ground mount facing south out of some lumber and unistruts. BTW, always paint galvanized uni-struts so you don't have galvanic corrosion between the aluminum panel frame, and the zinc coating of the uni-struts.

 

[schmism]

US supplier with growatt is watts247.com I bought my 2 units from him and he has good support.

Im guessing this is your unit.

Growatt 48V 12000T 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – Watts247.com

watts247.com

you note that he also lists links to the manual that you can download

http://watts247.com/manuals/gw/Growatt%20SPF%204000T-12000T%20DVM%20User%20Manual.pdf

You'll note on page 10 the PV array voltage range is 60-145v

Typically you don't run a 12kw inverter off 400w of panels. In fact even with a single 400w panel with a Voc of something like 90v my napkin math says you'd likely just break even in terms of the amount of energy you can pull in from 400w vs what the unit requires just to stay turned on.

 

[Wesleydeb]

Sorry to hear this. Well, I'm not a young guy either, I'll be 61 in three more months. At this point, I'm a bit confused about what you are telling me.

I currently wired them in series 4 100watt panels to achieve the 48volts... Currently during peak Sun Conditions they produce around 70 volts each string... I then Paralleled 6 strings together... The 12 kw Off Grid Growatt inverter has 2 PV inputs so I put 3 strings into one input and 3 strings in the other... At Peak Sun conditions the best I have gotten current wise to the batteries is 42 watts...

Are you saying that you put together a system with four 100W panels (400W), or a system with 6 strings of four 100 panels (2400W)? It seems to me you are saying 2400W? If it's the former, you very definately need more watts. If it's the later, it would be easy to just re-wire the panels from a 4S6P configuration into a 6S4P configuration. Assuming your panels have an Voc of 22.0V, six in series would not reach 155V till the outside temperature went down to ~-20F.

In the statement you're getting 42watts, I think what you meant to say was 42amps? Is that correct?

BTW, if in fact, you are wiring 3 strings together at one input terminal, that is considered to be an unsafe condition. Three independent strings should be on separate breakers/fuses. You should be using a combiner box. This is the Midnight one I use.
View attachment 29468
If you re-wired your arrays to 6S4P, you might be safe wiring the 4 strings in 2+2 configuration into the two inputs, though if it was me, I'd still use a combiner.

I'm not keen myself about going up on the roof, so what I've done is focused my attention on ground mounts that have the added benefit of tracking the sun over the course of the day. I built them myself, out of schedule 40 pipe, and Home-Depot uni-struts. Here's a pic of my fourth generation design, which I am very proud of.

Once the frame sub-assemblies were welded, final assembly, and solar panel attachment took only 2-3 hours. Assembly was accomplished by my son and myself only. Starting at maybe 8am, we were making power by noon. This is the 8th array I've built.

If you want something even simpler, just make a fixed ground mount facing south out of some lumber and unistruts. BTW, always paint galvanized uni-struts so you don't have galvanic corrosion between the aluminum panel frame, and the zinc coating of the uni-struts.

Sorry posting at 3am sometimes have brain fog,,,, Yes 42 AMPS not Watts is the max Charge to my batteries that I have seen so far... Unfortunately the way my 1/2 acre lost is laid out I don't have any ground space to mount Solar due to Trees, Workshop that has roof line east west, and multipule Trees for shade and tire swings for the Grand Kids. So a FIXED base system on the metal roof on the south facing side is my only option... I do plan on adding a Combiner in the future but thus far my system is so small I doing see the need... Right now each string is fused at 30 amps with a MP4 inline fuse. It's winter here in Columbus Ohio so any further upgrades or additions will probably have to wait till Spring. I can use this time to Study up and acquire product to be ready when the weather breaks.

 

[Wesleydeb]

US supplier with growatt is watts247.com I bought my 2 units from him and he has good support.

Im guessing this is your unit.

Growatt 48V 12000T 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – Watts247.com

watts247.com

you note that he also lists links to the manual that you can download

http://watts247.com/manuals/gw/Growatt%20SPF%204000T-12000T%20DVM%20User%20Manual.pdf

You'll note on page 10 the PV array voltage range is 60-145v

Typically you don't run a 12kw inverter off 400w of panels. In fact even with a single 400w panel with a Voc of something like 90v my napkin math says you'd likely just break even in terms of the amount of energy you can pull in from 400w vs what the unit requires just to stay turned on.

The Growatt PV OFF=grid inverter is "SPF 1200T DVM" Max PV input Voltage (VOC) 150VDC,,, MPPT voltage range 60 ~ 145 VDC,,,,, number of input strings 2,,,,,

Interesting just notice the input voltage requires a minimum of 60 VDC, I just assumed that would be 48 VDC,,, I guess that confirms I need to add more 12 volt 100 watt renogy panels to each string because right now I seem to be under volting the input except at Peak Sun condition when they output 20 volts per panel.. I hardly ever have Peak SUN conditions here in Mid-Ohio and when I do most likely the Sun angle is not optium for my roof mount fixed base system..

Thanks for sharing your knowledge,,, I just placed a order for more panels.

 

[Wesleydeb]

I am a newbie to Solar Arrays,,, Building the system as I have the time and money... Plus something to keep me entertained and busy during this COVID madness... I started with a 4000 watt peaked at 8000 watt Giandel Inverter 12 volts... It ended up failing... I figured if I am going to get serious I would just upgrade and settled on the 12 kw Growatt Off Grid inverter meaning it does not do NET METERING. After I purchased on got it installed and running I only had about 2kw in the Solar Array roof mounted on South facing roof.. So I added a additonal 1 kw of panels... 100 watt Renogy 12 volt panels. The Growatt is a 48 volt system so I had to rewire the panels in series from the 12 volt parallel system for the Giandel Inverter.. This is when the Solar engineer I have been working with told me instead of 4 panels in series I should have at least 6 in series... The 4 panels in series was coming in at 70 volts Peak Sun Conditions... Because the panels are fixed to the roof it would take some time in the morning for the sun angle to hit a sweet spot for the 70 volts, stay there for several hours then drift back down during the evening hours.

GROWATT PV Off-Grid Inverter,,, SPF 1200T DVM... My intent was not to do NET METERING as it require to much permitting.... We lost power for 14 days a couple of years back,,, My intent is to save a few bucks off the electric bill and give me a SOLAR GENERATOR backup during power outages.. Even though the unit will handle Split Phase 240 VAC 50 hz I never intended on adding the Electric Hot Water Tank, Well Pump, Electric Oven, or my workshop to the GROWATT INVERTER,, It's a low frequence Inverter so it will handle heavy duty motors but would just kill my battery bank to fast. I heat with Fuel oil so I did add the blower motor to the Inverter to keep us warm during a power outage. I did not add the heat pump that sits on top of the Fuel oil Furnace again I figured it would kill my battery bank to quickly..

 

[Wesleydeb]

US supplier with growatt is watts247.com I bought my 2 units from him and he has good support.

Im guessing this is your unit.

Growatt 48V 12000T 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – Watts247.com

watts247.com

you note that he also lists links to the manual that you can download

http://watts247.com/manuals/gw/Growatt%20SPF%204000T-12000T%20DVM%20User%20Manual.pdf

You'll note on page 10 the PV array voltage range is 60-145v

Typically you don't run a 12kw inverter off 400w of panels. In fact even with a single 400w panel with a Voc of something like 90v my napkin math says you'd likely just break even in terms of the amount of energy you can pull in from 400w vs what the unit requires just to stay turned on.

GROWATT PV Off-Grid Inverter,,, SPF 1200T DVM... My intent was not to do NET METERING as it require to much permitting.... We lost power for 14 days a couple of years back,,, My intent is to save a few bucks off the electric bill and give me a SOLAR GENERATOR backup during power outages.. Even though the unit will handle Split Phase 240 VAC 50 hz I never intended on adding the Electric Hot Water Tank, Well Pump, Electric Oven, or my workshop to the GROWATT INVERTER,, It's a low frequence Inverter so it will handle heavy duty motors but would just kill my battery bank to fast. I heat with Fuel oil so I did add the blower motor to the Inverter to keep us warm during a power outage. I did not add the heat pump that sits on top of the Fuel oil Furnace again I figured it would kill my battery bank to quickly..

 

[Wesleydeb]

We can look at this issue from two different angles, the voltage optimized to charge your batteries, and the watts needed to charge your batteries. Assuming your panels are producing about 18Vmp, that would give you 18V X 4 panels = 72V. With 6 in series it would be 108Vmp. 72Vmp should be adequate even under cold-weather conditions when charge voltage is bumped up to about 60-61V. In the middle of hot summer though, your panel voltage will go down. If for example it drops to 16V per panel, then 4 in series would put out only 64Vmp. This might not be enough overhead to allow the MPPT of your particular unit to function properly. So, yes, he might be right about the voltage spread.

The charging watts is a separate issue and is much easier to answer. Let's assume your golf-cart batteries are somewhere in the 200-250Ah capacity range. Their optimal charging rate is going to be around 1/10 to 1/8 C, so depending on the battery, that works out to be.....
200Ah X 1/10C = 20A
200Ah X 1/8C = 25A
250Ah X 1/10C =25A
250Ah X 1/8C = 31.3A

What you can really expect your array to produce is (100W X 4 panels)/50V charging X .85% fudge factor = 6.8amps, far below what your batteries actually need. I would say you need to add far more than just an additional two panels. Depending on what your battery's capacity is you actually need is.....
(20A X 50V charging)/0.85 fudge factor = 1176W
(25A X 50V charging)/0.85 fudge factor = 1470W
(31.3A X 50V charging)/0.85 fudge factor = 1840W

The problem is that you started out with 12V panels, which was a mistake for a system of this size. 12V carries a price premium to fit into the 12V automotive market. You would have been far better off starting out with higher voltage grid-tie panels. So, now you have choice to make.

1) Get rid of the 12V panels completely, and buy 6 grid-ties at 30-36Vmp. Wire them so you get at least 90Vmp, so that might be 3 in series. You MUST pay careful attention though to what the Voc for your controller is. That would give you about 1500W. I can get this many W for about 330$ when buying 60 cell panels.

2) Buy an additional two 12V panels, wire them 6 in series to get 108Vmp, then parallel them with at least three 36V grid-tie panels that would put out 108Vmp in series. Typically what I see are 300W 72cell panels that produce that voltage. That would give you 600W + 900W =1500W total. You might have to pay a bit more for 72cell panels than standard 60cell, which right now are dirt cheap.

3)Buy one additional 12V panel, wire 5 in series to get 90Vmp, then parallel them with three 250W/30V grid-ties wired in series for 90Vmp. That would give you 500W + 750W = 1250W. That's on the low side of good, but completely adequate.

Whatever path you take, you'll need a LOT more watts to charge your batteries adequately. Look on Craigslist to find local sellers that market the panel types mentioned, then make a decision on what's locally available at low cost. You always pay far less for panels with local pickup, rather than shipped. And, some of my BEST panels are used grid-ties pulled off someone's roof. Look for those to get the best deal.

Thanks for sharing your knowlege on this subject. Below was my intent for going Solar.

GROWATT PV Off-Grid Inverter,,, SPF 1200T DVM... My intent was not to do NET METERING as it require to much permitting.... We lost power for 14 days a couple of years back,,, My intent is to save a few bucks off the electric bill and give me a SOLAR GENERATOR backup during power outages.. Even though the unit will handle Split Phase 240 VAC 50 hz I never intended on adding the Electric Hot Water Tank, Well Pump, Electric Oven, or my workshop to the GROWATT INVERTER,, It's a low frequence Inverter so it will handle heavy duty motors but would just kill my battery bank to fast. I heat with Fuel oil so I did add the blower motor to the Inverter to keep us warm during a power outage. I did not add the heat pump that sits on top of the Fuel oil Furnace again I figured it would kill my battery bank to quickly..

 

[Wesleydeb]

US supplier with growatt is watts247.com I bought my 2 units from him and he has good support.

Im guessing this is your unit.

Growatt 48V 12000T 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – Watts247.com

watts247.com

you note that he also lists links to the manual that you can download

http://watts247.com/manuals/gw/Growatt%20SPF%204000T-12000T%20DVM%20User%20Manual.pdf

You'll note on page 10 the PV array voltage range is 60-145v

Typically you don't run a 12kw inverter off 400w of panels. In fact even with a single 400w panel with a Voc of something like 90v my napkin math says you'd likely just break even in terms of the amount of energy you can pull in from 400w vs what the unit requires just to stay turned on.

GROWATT PV Off-Grid Inverter,,, SPF 1200T DVM... My intent was not to do NET METERING as it require to much permitting.... We lost power for 14 days a couple of years back,,, My intent is to save a few bucks off the electric bill and give me a SOLAR GENERATOR backup during power outages.. Even though the unit will handle Split Phase 240 VAC 50 hz I never intended on adding the Electric Hot Water Tank, Well Pump, Electric Oven, or my workshop to the GROWATT INVERTER,, It's a low frequence Inverter so it will handle heavy duty motors but would just kill my battery bank to fast. I heat with Fuel oil so I did add the blower motor to the Inverter to keep us warm during a power outage. I did not add the heat pump that sits on top of the Fuel oil Furnace again I figured it would kill my battery bank to quickly..

 

[schmism]

We lost power for 14 days a couple of years back,,, My intent is to save a few bucks off the electric bill and give me a SOLAR GENERATOR backup during power outages..

Yep I know the use case. I have done the same. I put in a critical load panel which runs about 1/2 the house. Things like lights, fridge/freezer/furnace etc.

I would not recomend buying more 100w panels. The price per watt on them sucks. 250-350w panels are a much better price/watt deal.

 

[MichaelK]

Interesting just notice the input voltage requires a minimum of 60 VDC, I just assumed that would be 48 VDC,,, I guess that confirms I need to add more 12 volt 100 watt renogy panels to each string because right now I seem to be under volting the input except at Peak Sun condition when they output 20 volts per panel.. I hardly ever have Peak SUN conditions here in Mid-Ohio and when I do most likely the Sun angle is not optium for my roof mount fixed base system..

Thanks for sharing your knowledge,,, I just placed a order for more panels.

OK, could you please give us a firm answer on exactly how many panels you have right now? Rather than buying more over-priced 12V panels, I think the first option would be to wire the panels in a 6S4P configuration, rather than a 4S6P configuration. That would bump up the voltage to about 90V, which your unit would be very happy with.

It's good to hear that each string is fused. That is essential for building a safe system. Getting back to the combiner, the nice thing is that they are great for troubleshooting. There are times where I've suspected a loose connection, and flipping breakers on each string allows you to pinpoint problems.

I would really, really try to dissuade you from buying more 12V panels. Right now I can buy 250W 60cell panels for 55$ each. Three would cost 165$. That's 750W for 165$. How many 12V panels can you buy for 165$? Yes, I understand that you are 71, but you have adult children nearby, right? When putting panels on my roof, I enlisted my adult son's help. Even if they are not available/capable, you could go to your local Home Depot and hire a day laborer to do it for you. Even paying someone 100$ to go up on your roof to install grid-ties is going to be cheaper than spending all that money on 12V.

In terms of your split-phase 120/240V inverter, keep in mind that almost all American main service panels are wired for split-phase AC anyway, with L1 output going to one row of breakers, and L2 to the second. So, split-phase is the easiest to wire into a normal panel.

 

[Wesleydeb]

OK, could you please give us a firm answer on exactly how many panels you have right now? Rather than buying more over-priced 12V panels, I think the first option would be to wire the panels in a 6S4P configuration, rather than a 4S6P configuration. That would bump up the voltage to about 90V, which your unit would be very happy with.

It's good to hear that each string is fused. That is essential for building a safe system. Getting back to the combiner, the nice thing is that they are great for troubleshooting. There are times where I've suspected a loose connection, and flipping breakers on each string allows you to pinpoint problems.

I would really, really try to dissuade you from buying more 12V panels. Right now I can buy 250W 60cell panels for 55$ each. Three would cost 165$. That's 750W for 165$. How many 12V panels can you buy for 165$? Yes, I understand that you are 71, but you have adult children nearby, right? When putting panels on my roof, I enlisted my adult son's help. Even if they are not available/capable, you could go to your local Home Depot and hire a day laborer to do it for you. Even paying someone 100$ to go up on your roof to install grid-ties is going to be cheaper than spending all that money on 12V.

In terms of your split-phase 120/240V inverter, keep in mind that almost all American main service panels are wired for split-phase AC anyway, with L1 output going to one row of breakers, and L2 to the second. So, split-phase is the easiest to wire into a normal panel.

Do you have a link or source for those $55 Solar panels... I've checked Amazon and my searches only bring up $175..00 panels... My Son is afraid of heights so he is of no help on a roof. Also with this COVID Madness we are basically in Lock-Down here in Mid Ohio and since my wife is having Surgery in a couple of weeks to remove Cancer from her Breast her Surgeon does not want us to have any outside Contacts until after her surgery and Chemo treatments,,, so that could last for well over month... I could use this time to get a Combiner Box and panels. Also could you recommend a good Combiner Box..

Thanks so much for the information you have provided...

 

[MichaelK]

Do you have a link or source for those $55 Solar panels... I've checked Amazon and my searches only bring up $175..00 panels... I could use this time to get a Combiner Box and panels. Also could you recommend a good Combiner Box..

Thanks so much for the information you have provided...

Sorry, the 55$ panels are from a local seller in Corona, California, found on my local Craigslist. There's no shipping. It is simply cash and carry. You drive your truck up to the loading dock, hand him the money, and load the panels. I have to say though through testing, these panels are the best quality. You'll just have to find a comparable deal in your own location.

Look at the combiner pic in post #8. That's Midnight's 6 breaker combiner. That's what I have.

Hope your wife comes through OK! Good luck!!!

 

[Wesleydeb]

US supplier with growatt is watts247.com I bought my 2 units from him and he has good support.

Im guessing this is your unit.

Growatt 48V 12000T 12kW Split Phase 120V/240V output (100A at 120V ,50A at 240V) – Watts247.com

watts247.com

you note that he also lists links to the manual that you can download

http://watts247.com/manuals/gw/Growatt%20SPF%204000T-12000T%20DVM%20User%20Manual.pdf

You'll note on page 10 the PV array voltage range is 60-145v

Typically you don't run a 12kw inverter off 400w of panels. In fact even with a single 400w panel with a Voc of something like 90v my napkin math says you'd likely just break even in terms of the amount of energy you can pull in from 400w vs what the unit requires just to stay turned on.

I am running 4p7s right now but have been advised to up them to 6p5s for higher charging capacity... Right now weather is hindering me from getting on the roof and rewiring to the 6p5s config.. My panels are mounted on struts flat on the roof so each row has to be removed to rewire.