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New Solar Installation. Need Some Help.


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Hi all.

So about a week ago, I got my solar system up and running. I'm running a growatt 3kv 24v inverter with inbuilt mppt. I have 2 x narada 200ah 12v batteries and I have 3 x 330w solar panels. I have a few questions that I'm hoping someone here could help me with.

Firstly, some background info. The inverter is powering 1 x plasma TV (I know I need to get an LED), 1 x small freezer (186w), and a few led lights and a few sockets used for charging phones, router etc. If I have no power after 4.30pm, I will switch off the freezer to prevent it being powered by the battery without solar energy to keep the battery charged. I've set my inverter output priority to utility first and my charging priority to solar first. My thinking behind these settings is that I want to make sure that during the day, if I have grid power available, solar is dedicated to charging my battery while the grid power is used to power the loads. On the other hand, when solar is not available in the evening, if I have grid power available, it can charge the batteries as well. Either way, I'm trying to make sure that my batteries are fully charged as often as possible considering that I experience load shedding of between 8-12 hours a day every day.

So thats the background info. Here's what I've noticed and what I require some assistance with...

1. I've noticed that if I have no grid power during the day, solar will charge my battery and supply load. The weird thing is that according to the monitoring software for the inverter, and the inverter display screen, the solar output isn't constant. It's continuously jumping from 0w to 350w and then back to 0w every 10-20 seconds. This occurs whether or not the TV or freezer are on. Is this normal? I was under the assumption that the solar output would be constant.

2. I've noticed that if I have grid power available during the day, the solar output isn't constant as explained in question 1. However, when the solar output drops from 350w to 0w, the grid power will charge the battery until the solar output kicks back in. The charge priority settings state that solar energy will be prioritized if solar is available and if it isn't available, utility power will be used. I was under the assumption that, based off the output priority settings and charge priority settings, if the grid power is available and powering the loads, solar would be dedicated to charging the battery. Are my assumptions incorrect?

I would appreciate any assistance and I am happy to provide more information if necessary. Thanks.

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the difference between an LED and a Plasma imo isn't as bad as it is made out to be, my 42" Plasma at max draws 150W, my 42" LED draws 100W.

The solar should follow the load pretty well, it will be delayed to start up but if there is a constant load and clear skies the solar is generally pretty constant.

where do your panels face? and at the time is there any shadowing or clouds in the sky etc?

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The wattage rating on the sticker on the plasma is 410w though I have energy saving enabled on the tv so I'm sure it's probably approximately 300w or so.

The panels are facing north. I have a flat roof on a double story house and the panels are mounted at an angle. The inverter is downstairs so I had to run about 25 meters of solar cable from the roof to where the inverter is placed. Not sure if that makes any difference. Also, the panels are wired in parallel.

As far as the weather, it's been very hot with no cloud cover for the last week. There is no shade on the roof during the day.

The load on the inverter is very low even with the TV and freezer on. It only hits about 20% load. So I'm thinking it might be something to do with how the mppt is controlling the voltages in regard to the load required. Do you think that could be the case for the panels constantly cycling between 0w and approximately 350w and back down to 0w every 10 to 20 seconds?

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30 minutes ago, Darknight said:

The wattage rating on the sticker on the plasma is 410w though I have energy saving enabled on the tv so I'm sure it's probably approximately 300w or so.

The panels are facing north. I have a flat roof on a double story house and the panels are mounted at an angle. The inverter is downstairs so I had to run about 25 meters of solar cable from the roof to where the inverter is placed. Not sure if that makes any difference. Also, the panels are wired in parallel.

As far as the weather, it's been very hot with no cloud cover for the last week. There is no shade on the roof during the day.

The load on the inverter is very low even with the TV and freezer on. It only hits about 20% load. So I'm thinking it might be something to do with how the mppt is controlling the voltages in regard to the load required. Do you think that could be the case for the panels constantly cycling between 0w and approximately 350w and back down to 0w every 10 to 20 seconds?

wowsers it must be an old one 😛
 

what is your inverters min and max pv input? I can't  find much info, is that a purely off grid inverter?

 

have you ever seen more than 350W pv input?

Edited by Dex_
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I got the tv about 8 years ago lol. It's been good to me.

So according to the sticker on the inverter, the max pv input voltage is 102vdc. I'm not sure where to find the min pv input.

I've set the maximum charging current to 70a based off a formula I found online. Basically 990w / 24 = 41.25 * 20% (for reflection etc) = 51.56. The inverter manual says the maximum charging current should include the maximum utility charging current. So 51.56 + 20 = 71.56. Do you think I should set it to 75a or should I lower it?

As far as the pv output wattage I've seen, it varies between 115w and 380w. So it's constantly jumping between 0w and anything between 115w and 380w before dropping to 0w every 10 to 20 seconds. This constant jumping only occurs when solar is available during the day. 

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32 minutes ago, Darknight said:

I got the tv about 8 years ago lol. It's been good to me.

So according to the sticker on the inverter, the max pv input voltage is 102vdc. I'm not sure where to find the min pv input.

I've set the maximum charging current to 70a based off a formula I found online. Basically 990w / 24 = 41.25 * 20% (for reflection etc) = 51.56. The inverter manual says the maximum charging current should include the maximum utility charging current. So 51.56 + 20 = 71.56. Do you think I should set it to 75a or should I lower it?

As far as the pv output wattage I've seen, it varies between 115w and 380w. So it's constantly jumping between 0w and anything between 115w and 380w before dropping to 0w every 10 to 20 seconds. This constant jumping only occurs when solar is available during the day. 

I don't know lead acid / gels etc too well but i beleive charge current is meant to be 8-15% so i would expect it to be far lower but lets see what someone who knows more says. I highly doubt you will ever get 50Amps out of 2 panels so this is likely your issue. (note this is my guess with very limited knowledge.)

 

while you are at it what is your bulk charge/float voltages etc

Edited by Dex_
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Thanks for the help. Appreciate it. The original max charging current was set at 60a so maybe I should drop it back to that or maybe even drop it down to 50a.

My bulk charging voltage is set at 28.2v. Thats the default setting on the inverter. The float voltage is at 27v which is also the default setting. The sticker on the battery states that the float is 2.25vpc so the setting checks out to be correct.

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6 hours ago, Darknight said:

I have 3 x 330w solar panels.

Can you please tell us how these panels are connected, all 3 in series or all of them in parallel. 

I missed that part, I think that is your problem. 

Although your loads are low, the system will take all it can from the panels to try and charge the batteries.

 

6 hours ago, Darknight said:

I have 2 x narada 200ah 12v

 

1 hour ago, Darknight said:

Thanks for the help. Appreciate it. The original max charging current was set at 60a so maybe I should drop it back to that or maybe even drop it down to 50a.

According to the spec sheet, the max charging  limit is 45 amps. Its better if you don't exceed that. 

 

2 hours ago, Dex_ said:

what is your inverters min and max pv input?

30-102Volt. That is why i am worried, If the panels were connected in parallel, and you look at a Vmp of 34-35 volt (NOCT), it might be that the MPPT starts when the volts exceeds 34Volt but as soon as it draws current the voltage falls below the startup voltage and the MPPT switches off. Without load the volts goes above 30, and the cycle repeats itself. 

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All 3 panels are connected in parallel. The 2 x narada 12v batteries are connected in series. The strange thing about these inverters is that the spec sheet differs with the manual for certain settings. The spec sheet for the inverter shows that the maximum solar charge current is 50a. The manual for the inverter states the max charging current is 80a. Maybe they're two different settings. The manual states that the setting for max charging current is the total charging current for solar and utility chargers (max charging current = utility charging current + solar charging current). The max utility charging current is set at 20a which is why the max charging current setting is so high (because it includes the max utility charging current value). Would you recommend setting the max charging current to 50a or 45a? Do you think this setting might be a cause of why the solar output is constantly jumping during the day?

I'm a complete noob at this, so for all I know, the constant jumping of solar output might be normal and correct. I wouldn't really know. I have a video of the inverter screen if that helps to explain what I'm querying.

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29 minutes ago, Jaco de Jongh said:

I missed that part, I think that is your problem. 

Although your loads are low, the system will take all it can from the panels to try and charge the batteries.

Sorry, please could you explain that a bit more. If the system is trying to take all it can from the panels wouldn't that mean the solar wouldn't be jumping from 0w to anywhere between 115w and 380w and then back down to 0w every couple of seconds?

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So after browsing another board on this site, I came upon this post. 

Sounds a bit like a reason for why my solar input is constantly jumping up and down. I may not be putting enough load on the inverter which is causing the mppt to discard the excess output from the panels. Not sure if that makes any sense. Would anyone be able to back that up? What I have also noticed is that when the battery bank is fully charged, and the grid is powering the load during the day, the solar feed to the battery will be constant.

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2 hours ago, Jaco de Jongh said:

30-102Volt. That is why i am worried, If the panels were connected in parallel, and you look at a Vmp of 34-35 volt (NOCT), it might be that the MPPT starts when the volts exceeds 34Volt but as soon as it draws current the voltage falls below the startup voltage and the MPPT switches off. Without load the volts goes above 30, and the cycle repeats itself. 

Sorry, didn't see this part. From what I've seen from the readings on the inverter screen, my input pv voltage from the panels during the day is is usually between 31v and 35v. 

When the mppt draws current from the panels, does that reduce voltage? 

By wiring the panels in series, that would increase my voltage but leave my amperage the same. Each panel has a Vmp of 29.4v (NOCT) and an imp of 8.34a (NOCT). If I wire the panels in series won't I be restricting how many panels I can run because the max pv input on the inverter is 102vdc and by wiring my 3 panels in series my voltage would already be 88.2v?

Do you think adding another panel, while keeping the panels wired in parallel (or series-parallel) would prevent the mppt from switching off after drawing current?

Or should I just try to add more load to the inverter during the day?

Edited by Darknight
Added the last question
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2 hours ago, Darknight said:

When the mppt draws current from the panels, does that reduce voltage? 

Yes, certainly.

2 hours ago, Darknight said:

By wiring the panels in series, that would increase my voltage but leave my amperage the same. Each panel has a Vmp of 29.4v (NOCT) and an imp of 8.34a (NOCT). If I wire the panels in series won't I be restricting how many panels I can run because the max pv input on the inverter is 102vdc and by wiring my 3 panels in series my voltage would already be 88.2v?

Yes, I believe that your inverter is designed for pairs of nominally 24 V panels in series. What is the Voc rating of the panels? How cold does it get in winter?

If your panels' Voc is 31 V or less, and you only go down to 0°C in winter, and they have normal temperature coefficients, you should be OK with 3 panels in series. But with Vmp = 29.4, this seems unlikely.

2 hours ago, Darknight said:

Do you think adding another panel, while keeping the panels wired in parallel (or series-parallel) would prevent the mppt from switching off after drawing current?

Yes, this is likely the solution to your problem. Wire two panels in series for now, and get a fourth panel to have two strings of two panels in series. Both strings should have their own fuses or breakers.

2 hours ago, Darknight said:

Or should I just try to add more load to the inverter during the day?

No, the load isn't your problem at all.

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7 hours ago, Coulomb said:

Yes, I believe that your inverter is designed for pairs of nominally 24 V panels in series. What is the Voc rating of the panels?

The VOC (NMOT) rating of the panels is 36.7v. In the case that I'm not able to get the exact same panel for the fourth panel, I was told by my electrician that I should get a higher wattage panel. Is this correct and would I still be able to wire this higher output panel with the existing 3rd panel in series?

So, just to wrap my head around this, if I have 2 pairs of 2 panels wired in series that would make each pairs output (at a rating of about 36.7v per panel) equal to about 73.4v and 8.73a. These two pairs of panels would be then be joined in parallel with an output of 73.4v and 17.46a. Is my math correct?

7 hours ago, Coulomb said:

How cold does it get in winter?

It hardly gets that cold in winter. In fact this winter was probably the warmest winter in a few years. I'd say the minimum I've ever seen the temperature drop to is probably 2 degrees Celsius.

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2 hours ago, Darknight said:

So, just to wrap my head around this, if I have 2 pairs of 2 panels wired in series that would make each pairs output (at a rating of about 36.7v per panel) equal to about 73.4v and 8.73a. These two pairs of panels would be then be joined in parallel with an output of 73.4v and 17.46a. Is my math correct?

That is correct. 

As for the bigger panel, chose one as close to the original as what you can get. 

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24 minutes ago, Jaco de Jongh said:

That is correct. 

As for the bigger panel, chose one as close to the original as what you can get. 

Awesome. I'll hopefully be able to get another panel within the next week or so. My current panels are canadian solar 330w. I'm going to try and get the fourth panel from the same supplier but if they're out of stock, I'll have to go with another supplier who has canadian solar panels, but his are 385w if I'm not mistaken. I'll post an update once I've got the panel installed etc.

Thanks everybody for the help.

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3 hours ago, Darknight said:

The VOC (NMOT) rating of the panels is 36.7v. In the case that I'm not able to get the exact same panel for the fourth panel, I was told by my electrician that I should get a higher wattage panel. Is this correct and would I still be able to wire this higher output panel with the existing 3rd panel in series?

I have some of the 335 Watts in stock. Specs included. Where are you based. 

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On 2019/10/22 at 3:30 AM, Coulomb said:

Yes, this is likely the solution to your problem. Wire two panels in series for now, and get a fourth panel to have two strings of two panels in series.

So, just a quick update. I wired two of the panels in series yesterday and as specified by Coulomb, this solved the problem I was having. I now have a steady stream of solar energy coming into the inverter. I am working on securing another panel so that I can wire my third panel and the new fourth panel in series-parallel. I'll update once it's put up. Would it be possible for me to have 3 pairs of series wired panels joined in parallel?

 

On 2019/10/22 at 11:10 AM, Darknight said:

Yes, I believe that your inverter is designed for pairs of nominally 24 V panels in series

My solar installer said something  similar to me yesterday and I have no idea what he meant. Would you mind explaining this to me. As far as I know, solar panels aren't specifically designed for 12v / 24v / 48v systems are they? When I bought my panels, no one said anything to me about my panels being compatible with a 24v inverter. So, hypothetically, if I had a small 800w 12v inverter, would I be able to connect it (via an mppt) to a pair of 330w panels wired in series if each panel was rated at ~35v? If my current inverter is a 24v inverter, and the voltage of my series wired panels at the moment is ~60v, does that adversely affect the battery bank?

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7 hours ago, Darknight said:

So, just a quick update. I wired two of the panels in series yesterday and as specified by Coulomb, this solved the problem I was having. I now have a steady stream of solar energy coming into the inverter. I am working on securing another panel so that I can wire my third panel and the new fourth panel in series-parallel. I'll update once it's put up. Would it be possible for me to have 3 pairs of series wired panels joined in parallel?

 

My solar installer said something  similar to me yesterday and I have no idea what he meant. Would you mind explaining this to me. As far as I know, solar panels aren't specifically designed for 12v / 24v / 48v systems are they? When I bought my panels, no one said anything to me about my panels being compatible with a 24v inverter. So, hypothetically, if I had a small 800w 12v inverter, would I be able to connect it (via an mppt) to a pair of 330w panels wired in series if each panel was rated at ~35v? If my current inverter is a 24v inverter, and the voltage of my series wired panels at the moment is ~60v, does that adversely affect the battery bank?

The guys here know their stuff :) @Coulomb ecspecially.

 

What is the model on your inverter, as far as I know there are 2 axpert 24V models, one that has a 600W pv limit and one that has a 3000W pv limit, a model number would confirm.

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5 hours ago, Dex_ said:

The guys here know their stuff :) @Coulomb ecspecially.

Good to know! Thanks @Coulomb!

5 hours ago, Dex_ said:

What is the model on your inverter, as far as I know there are 2 axpert 24V models, one that has a 600W pv limit and one that has a 3000W pv limit, a model number would confirm.

I have a Growatt 3kv 24v inverter. The datasheet says that the maximum pv array power is 1000w but I've read that oversizing the panel array is a good thing because you generate more power on days when the sun isn't that strong.

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5 hours ago, Darknight said:

Good to know! Thanks @Coulomb!

I have a Growatt 3kv 24v inverter. The datasheet says that the maximum pv array power is 1000w but I've read that oversizing the panel array is a good thing because you generate more power on days when the sun isn't that strong.

ah sorry i was confusing it with one of many other threads.

Guys generally say you can cater for 20% more, frankly though i would be very careful because on a cooler day with some clouds you could see a little more than you expect and poof goes your controller, this is why it is always better to oversize so that you can grow your system. Personally i think 4 panels is slightly pushing it already, 6 would definitely be too much. You could possibly look at a separate charge controller though?

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18 hours ago, Darknight said:

... this solved the problem I was having.

Excellent, always good to hear.

Quote

Would it be possible for me to have 3 pairs of series wired panels joined in parallel?

It would be possible, but I would not recommend it. As @Dex_ has just posted, 4 330 W panels is already pushing it, and 6 would be of little to no benefit except on the darkest of cloudy days. The main problem is the overshoots; the Axperts aren't great at responding quickly to changes in load and/or solar availability. When you put on too many panels, those overshoots (and there are undershoots as well) could damage your battery and/or inverter. So best to stop at roughly 25% "overclocking"; 4 panels is already 32% overclocking.

Quote

As far as I know, solar panels aren't specifically designed for 12v / 24v / 48v systems are they?

No, they aren't. Nearly all panels these days, apart from a handful designed for camping, are so-called 24 V nominal. That is, they have 72, 60, or occasionally 54 silicon cells in series. You could connect that directly across a 24 V battery, with no solar charge controller, and it would charge the battery (with terrible efficiency, but it would work). Really, "24 V" is just to distinguish them from the toy camping panels (which are usually "12 V" nominal, with Vmp around 17 V or so).

Quote

So, hypothetically, if I had a small 800w 12v inverter, would I be able to connect it (via an mppt) to a pair of 330w panels wired in series if each panel was rated at ~35v?

It depends entirely on the design of the MPPT (solar charge controller), whether built-in with the inverter, or separate. The smallest Axpert inverter is a 1000 W 12 V model, which will take up to 102 V at the PV terminals. So two panels in series would work with that one, but may be too much for others. But if two panels in series is too much, then you could just wire two in parallel. It would be a strange charge controller indeed that could not handle a single "24 V" panel, unless it was designed just for camping, not home rooftops.

Quote

If my current inverter is a 24v inverter, and the voltage of my series wired panels at the moment is ~60v, does that adversely affect the battery bank?

Not at all. It's designed to "buck" the voltage; it's a bit like a DC transformer. It can "transform" say 60 V @ 10 A to say 27 V @ 22 A; that's 600 W in and 594 W out, there is always some loss, though charge controllers are usually quite efficient. Other solar chargers boost the panel voltage up to some 400-500 V, which the inverter-charger can use in a very different way (more efficient for generating 220 V AC, but less efficient charging the battery). All the Axperts with about a 450 V max solar charge controller work that way.

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5 hours ago, Dex_ said:

Personally i think 4 panels is slightly pushing it already, 6 would definitely be too much. You could possibly look at a separate charge controller though?

Thanks. I was just wondering if it was possible. I agree with you that 6 panels would be pushing it too much. I do have another 40amp mppt controller sitting in a box at home which I intend to use for another inverter to power a part of my house that couldn't be powered by my 3kv. For interests sake, how does it work to have 2 mppt controllers on a single inverter. I didn't think that was possible or necessary.

 

6 hours ago, Coulomb said:

It would be possible, but I would not recommend it. As @Dex_ has just posted, 4 330 W panels is already pushing it, and 6 would be of little to no benefit except on the darkest of cloudy days. The main problem is the overshoots; the Axperts aren't great at responding quickly to changes in load and/or solar availability. When you put on too many panels, those overshoots (and there are undershoots as well) could damage your battery and/or inverter. So best to stop at roughly 25% "overclocking"; 4 panels is already 32% overclocking.

Thanks for explaining everything for me. I think I'll stop at 4 panels. I need to have the 4th panel so that I can make use of the 3rd panel which I already own and is not currently connected. Also, so that I can have enough power available from the panels to charge the battery and feed the load sufficiently.

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