How many solar panels can I safely connect to my inverter,below is the spec sheets for both, I have been given different answers?

ecco specs

Sorry forgot to mention, I have the 3.5KVA inverter

15 minutes ago, Elro said:

Sorry forgot to mention, I have the 3.5KVA inverter

9
8 to be absolutely safe

Edited June 12Jun 12 by Denns

Your panels VOC is a bit too high. I have 650W panels and each has a VOC of 45V and Vmp of 42 so I could overspec my inverter quite a bit. 9 with your panels would be around 470VOC but with 10% leeway you overshoot the 500Vdc limit. So 8 would be the safest.

If you had similar panels to me you could have done 10 panels very easily and hit about 6500W. Not the 4480W you will potentially hit now. Not bad though as you are still over-paneling your inverter decently well.

Thank you Denns, was told by a solar installer that the 6 panels (have 5 currently installed) I want to install would create at least a burnt inverter and at most a mini chernobyl disaster. I have 4 x 200a/h (+-20kwh) batteries and a Inge geyser solar system with 4 x 460w panels and fortunately a gas stove, everything in the house runs of solar/batteries except kitchen appliances which are connected directly to grid. My power consumption from grid averaged 35 units per day and has dropped to an average of 8.9units per day. A large saving and couldn't be happier, I installed everything myself and had a COC done. The story concerning installation from beginning to end is a story for another day. LOL

8 minutes ago, Elro said:

Thank you Denns, was told by a solar installer that the 6 panels (have 5 currently installed) I want to install would create at least a burnt inverter and at most a mini chernobyl disaster. I have 4 x 200a/h (+-20kwh) batteries and a Inge geyser solar system with 4 x 460w panels and fortunately a gas stove, everything in the house runs of solar/batteries except kitchen appliances which are connected directly to grid. My power consumption from grid averaged 35 units per day and has dropped to an average of 8.9units per day. A large saving and couldn't be happier, I installed everything myself and had a COC done. The story concerning installation from beginning to end is a story for another day. LOL

Lol, we have similar setups. I have a 3.6kW 24V with 7 panels, a GeyserTech controller with 4 panels for the geyser, also gas stove. I also have 10x100ah 12V batteries connected in 5S2P to make 24V. I literally went off-grid with just that and had my kitchen on that 3.6 lol. Self-installed, also like you. I have since added a 5kW/5kWh inverter I got off builders for cheap to supply the kitchen, which allows my 3.6 to coast now and more freedom to run kitchen appliances, whereas I used to only run 1 appliance at a time in the kitchen to avoid overloading it.

The only thing you need to look at really is your voltage. You have a 500 VOC limit. So the number of panels is dictated by that. Not the wattage limit of your MPPT. I am running 4500W on my 4000W limit on the inverter, but am well below the voltage limit on it. Has been like that for 1.5 years now.

The remaining 3 panels you can put on an MPPT, or, since MPPTs are pretty pricey, just get another inverter on a deal if you don't want to spend too much and hook it up to the 3 remaining panels. Then you can boost your AC output and supply the kitchen with solar power also. I have 1 extra panel, which is connected to a Victron MPPT, since I couldn't add any more to the 3.6kW. My 5kW has no panels on it and is charged off my 3.6, but that's on the cards in the next 3 years. Will boost my array to some 13kWp when I do add to that inverter, as I still have the whole house roof to add panels on, as they are all currently on top of the 3 garages.

1 hour ago, Elro said:

How many solar panels can I safely connect to my inverter,below is the spec sheets for both, I have been given different answers?

The "spec" label does not tell the full story. Look in the actual specifications sheet for your PV panels (download it from the internet if you do not have it) for something called "Temperature coefficient (VOC) or something in that line. You should see a small % value - something like (0.30%/°C). You must also know the Open Circuit (VOC) voltage (52.27V according to the lable that you provided).

Here's an example of then calculating the maximum number of panels per serial string:

If:

• Panel Voc = 52.27 V at STC (i.e. at 25°C) (from your label)

• βVoc = −0.30%/°C (assumed)

• Lowest expected temperature = −5°C

Then:

• Temperature difference = −30°C

• Voc increase = -0.3% x -30 = 9%

So the panel Voc could reach approximately:

52.27 × 1.09 = 57.0 V (per panel)

Your inverter states a maximum PV Array open circuit voltage of 500V. So:

Maximum number of solar panels = 500/57.0 = 8.77 panels... so the maximum safe number of panels per string would be 8 (don't round the 8.77 up to 9...)

Please note that this example is based on some assumptions - you must get the accurate figures and do your own calculations!

Edited June 15Jun 15 by HennieL
Corrected signs in formula to make the maths work

My road to the system I have now has a few kinks, son works from home and where we live power outages are a way of life so bought a system to keep him going, 3.5kw inverter/ 6 x 460w panels/ 1 x 100a/h battery, it was just not enough to keep him going overnight, he has a pc that needs a nuclear power station to run. Realised we were actually saving on electricity. First mistake, no stock in SA to add to this battery, sold it for the same price I bought and decided lets get 4 x 200a/h batteries and also install the geyser system and upgrade the solar panels, sold the old ones(6 months old) what a rabbit hole. I was enjoying myself until I slipped on the coated IBR roof and cracked my coccyx on the ridge and in slow motion proceeded to slide down, fortunately thru the tears was able to hook my heels in the gutter to stop from going splatt. Mistake 2 and 3, realised I could not upgrade the 24v 3.5kw inverter to 5kw( maybe you can explain the problem?) and to make things worse my inverter cannot be paralleled with another. The reason I only have 5 of the 6 panels up is there is no stock of the low mounting steel brackets for the steel rails I used. so have made my own now and will install the 6th panel this coming week.

2 hours ago, Elro said:

My road to the system I have now has a few kinks, son works from home and where we live power outages are a way of life so bought a system to keep him going, 3.5kw inverter/ 6 x 460w panels/ 1 x 100a/h battery, it was just not enough to keep him going overnight, he has a pc that needs a nuclear power station to run. Realised we were actually saving on electricity. First mistake, no stock in SA to add to this battery, sold it for the same price I bought and decided lets get 4 x 200a/h batteries and also install the geyser system and upgrade the solar panels, sold the old ones(6 months old) what a rabbit hole. I was enjoying myself until I slipped on the coated IBR roof and cracked my coccyx on the ridge and in slow motion proceeded to slide down, fortunately thru the tears was able to hook my heels in the gutter to stop from going splatt. Mistake 2 and 3, realised I could not upgrade the 24v 3.5kw inverter to 5kw( maybe you can explain the problem?) and to make things worse my inverter cannot be paralleled with another. The reason I only have 5 of the 6 panels up is there is no stock of the low mounting steel brackets for the steel rails I used. so have made my own now and will install the 6th panel this coming week.

I just had to laugh at your description, picturing you slipping down the roof with a very sore backside - apologies for laughing, but you do paint a vivid picture... glad you managed to stop the splat from happening...

Best of luck with the upgrade - just ask on the Forum before you buy, hopefully the combined wisdom on the forum can save you from making another expensive mistake.

The inverter which you have has a maximum solar power input of 4000W and 500V DC so if your solar panel is 560W and 52.27V Open Circuit then you can have a maximum of 7 solar panels in series before exceeding the 4000W power and with 7 solar panels in series the open circuit voltage is round about 365V so that is below the 500V.

4 hours ago, Elro said:

Mistake 2 and 3, realised I could not upgrade the 24v 3.5kw inverter to 5kw( maybe you can explain the problem?) and to make things worse my inverter cannot be paralleled with another.

High power low voltage single phase inverters are not common because if the power increases and the battery voltage remains the same the current also increases which means thicker cables and more components which can handle the current, e.g. 3000W @ 24V is 125A and 6000W @ 24V is 250A and to safely handle the current then the cable must be at least 35mm2 for the 3Kw and 70mm2 for the 6Kw inverters.

If more than one inverter is used in parallel on the same phase then the inverters must be able to communicate with each other because the sine wave output must be in phase otherwise you face other problems with the inverters.

1 hour ago, GerhardK83 said:

The inverter which you have has a maximum solar power input of 4000W and 500V DC so if your solar panel is 560W and 52.27V Open Circuit then you can have a maximum of 7 solar panels in series before exceeding the 4000W power and with 7 solar panels in series the open circuit voltage is round about 365V so that is below the 500V.

High power low voltage single phase inverters are not common because if the power increases and the battery voltage remains the same the current also increases which means thicker cables and more components which can handle the current, e.g. 3000W @ 24V is 125A and 6000W @ 24V is 250A and to safely handle the current then the cable must be at least 35mm2 for the 3Kw and 70mm2 for the 6Kw inverters.

If more than one inverter is used in parallel on the same phase then the inverters must be able to communicate with each other because the sine wave output must be in phase otherwise you face other problems with the inverters.

The 4000W solar power rating is not really important.

I have seen my inverter pull 4000W and no more. The extra 550W on it it’s there for extra generation during cloudy days that’s all. His would do the same, just pull up to a max of 4kW when he installs the 8 panels on it.

Even if he had 6000W on his 4000W MPPt it would be fine.

8 hours ago, Denns said:

The 4000W solar power rating is not really important.

Even if he had 6000W on his 4000W MPPt it would be fine.

I agree with @Denns for the following reasons:

• Unless the panels are installed at exactly the optimum angle (and that changes daily throughout the year...), it is very unlikely that the panels will produce their rated current/power.

• Unless one is exporting power to the grid, it is unlikely that the demand will be at the 100% power rating in any case - and one can simply limit the PV input power by slightly limiting the power demand during the peak solar period (12:00 - 14:00)

• Even if the panels do produce their rated power, the inverter will simply limit the power to the maximum that it can handle. This will produce extra heat, though, and one should ensure that the inverter is installed where it can dissipate heat properly - but that is good practice in any case...

It is common practice to install slightly more PV than the inverter's power rating, as long as the VOC limit is respected, but it is also just common sense to not go overboard with this.

I would like to ask the forum what 24v hybrid inverter would you recommend, to replace my existing, one that can be paralleled with a second one. I would like to start budgeting as the idea of been self sufficient is really appealing. Had no idea a year ago that I would be so far down this road

5 hours ago, Elro said:

I would like to ask the forum what 24v hybrid inverter would you recommend, to replace my existing, one that can be paralleled with a second one. I would like to start budgeting as the idea of been self sufficient is really appealing. Had no idea a year ago that I would be so far down this road

Not worth it in my opinion.

You can’t parallel them per se. But you can supply different circuits in the house with 2 inverters without them being in parallel.

Can you not convert your battery bank to 48V? Then you just buy a larger inverter?

otherwise you can do what I did.

Edited June 13Jun 13 by Denns

The manufacturer of the batteries warns not to try and connect in series to convert them to 48v, so I agree will have to go your route Denns and get another inverter and have a separate circuit for the kitchen appliances, looks like the easiest route.

You could check whether a 24V Victron Multiplus setup would work for you, but in the long run it's a strong consideration to transition to 48V or even HV batteries, if you want to increase the system power.

What exact batteries have you got, and what's the spec for lifespan or number of cycles ? That might also help guide the level of expense to incur now for the 24V path.

Maybe you could look at options for the best use-case, if you would dedicate this 24V / 3.5kW / 20kWh system to a feed a specific 15A sub-circuit in the house, and get a different 48V inverter system to feed the main circuit breaker. Similar to how you have an MPPT dedicated to a geyser. Meaning, maybe use this exclusively for running an aircon, or a pool pump, or get an electric vehicle.

1 hour ago, Elro said:

The manufacturer of the batteries warns not to try and connect in series to convert them to 48v, so I agree will have to go your route Denns and get another inverter and have a separate circuit for the kitchen appliances, looks like the easiest route.

If I may suggest: plan from the start to buy a good quality inverter, and larger than what you think you need. I know, cost always come into the equation, but so does having to upgrade again in a year or two at additional costs.

A solar power system should be designed to provide for your (expanding) needs for at least 10 years, in my opinion. I am fortunate that I was given this advice before I upgraded from my 2.2kW 24V inverter 21 months ago - I had considered a 5kW system to be "more than I needed" at the time, but was convinced to rather upgrade to a 12kW single-phase inverter, with 8kWh PV panels and 20kWh 52V LiFePO4 batteries. I have been practically off-grid for the last 6 months, with the grid feed to the inverter switched off at the DB board. I am able to run my full house, including a 200l geyser and a large oven without any grid input, only switching the grid on on Sundays for a few hours to keep the utility meter "ticking over", and if rain & heavy clouds lasts for more than 48 hours.

Thanks for the advice everyone. Have a clearer picture of what I should do. My main aim was to have power for son and wife during outages, that was achieved but then the solar bug bit(I should have known). It will take awhile but my path will be to install a larger 48v system seperately and go from there. It will take awhile as I am a pensioner and have to count the pennies LOL

9 hours ago, Elro said:

Thanks for the advice everyone. Have a clearer picture of what I should do. My main aim was to have power for son and wife during outages, that was achieved but then the solar bug bit(I should have known). It will take awhile but my path will be to install a larger 48v system seperately and go from there. It will take awhile as I am a pensioner and have to count the pennies LOL

Some great answers to the way forward. Without knowing your location the current system can generated a average of 13kWh per day in Gauteng from PV. It would then depend what the power requirements are for the sons pc to get through the night.

One can get a system that caters for the end state. I did not and got a grid tied system without batteries when I started. Only save the day time grid power and at night used grid. Then came a 3kw with battery system to take me through LS. The grid tied paid for itself in 3 yrs.

The lastly I git a 48V 5kw Deye. I am still using the 24V batteries in series to the Deye. No wasted capital.

Equipment can be reused without dumping if you ask around how to do it.

My 3kw 24V I still have and is a back up for essential loads should my 48V 5kW give up the ghost. Just need to rewire the batteries and some load circuits.

Just my different approach using less capital and a good ROI.

9 hours ago, Elro said:

Edited June 14Jun 14 by Scorp007

11 hours ago, Elro said:

Thanks for the advice everyone. Have a clearer picture of what I should do. My main aim was to have power for son and wife during outages, that was achieved but then the solar bug bit(I should have known). It will take awhile but my path will be to install a larger 48v system seperately and go from there. It will take awhile as I am a pensioner and have to count the pennies LOL

If money is something to strongly consider then the cheapest is to just get a second 24V. Split the DB.

they both share the same battery bank. A 4kW 24V is under 4000 rand.

Then you will have about 7.5kW of AC capacity.

What specs are the batteries btw? The C rating for discharge in particular

Hi Denns, attached is the specs for my 4 x batteries

28 minutes ago, Elro said:

Hi Denns, attached is the specs for my 4 x batteries

Your batteries can handle having 2 inverters on them without issues.

So the most budget friendly thing I see you can do is just hook up a second 24V inverter. There are 4kW inverters for under 4k available and same MPPT ratings as yours.

so just split the DB and have each inverter supply certain breakers there.

You have 11 panels in total also so you can have you 8 on 1 and out the other 3 on the other (just check the minimum voltage required for the MPPT for the second inverter in case 3 panels aren’t enough to turn it on but I think you should be good otherwise just split them half and half on each inverter, just add the 6 on new inverter)

You could put the 4kW to supply just the kitchen. Then the whole house will be on solar.

Edited June 15Jun 15 by Denns

Denns, this will definately be cheaper. I could do this much quicker than having to wait 3 years to go the 48v route. Another question, how would you split the batteries to the 2 inverters?

3 hours ago, Elro said:

Denns, this will definately be cheaper. I could do this much quicker than having to wait 3 years to go the 48v route. Another question, how would you split the batteries to the 2 inverters?

I assume you are using busbars for the positive and negative?

It will be as simple as connecting the other inverter to those busbars and ensuring both have the same charge voltages set.

do you have comms to the batteries by any chance or are you just running in voltage mode?

51 minutes ago, Denns said:

I assume you are using busbars for the positive and negative?

It will be as simple as connecting the other inverter to those busbars and ensuring both have the same charge voltages set.

do you have comms to the batteries by any chance or are you just running in voltage mode?

@Elro You should also make sure that the battery connection cables going to the busbars are the same length and diameter (cross-sectional area, actually) for both sets of batteries. Even though cable resistance is normally very low, the high current flowing when charging and/or discharging the batteries can result in the set of batteries with the longest cables being charged slightly less, and thus develop an imbalance with respect to the other set. Over time this can get gradually worse, and could lead to damage to your batteries in the long run (especially if they are lithium ion batteries...).