Hi all I have a axpert 5000w inverter with 3 poly US2000 lithium batteries. 

I have 4 x 450 watts solar panels connected in series and parallel 

On a sunny day here in Portugal the system starts up and charges without a problem  on cloudy day the system works but does not charge up the batteries 

Would it be best to buy 2 or 4 more panels for cloudy days so the system does not run out of battery

1 hour ago, jason compo said:

Hi all I have a axpert 5000w inverter with 3 poly US2000 lithium batteries. 

I have 4 x 450 watts solar panels connected in series and parallel 

On a sunny day here in Portugal the system starts up and charges without a problem  on cloudy day the system works but does not charge up the batteries 

Would it be best to buy 2 or 4 more panels for cloudy days so the system does not run out of battery

Let me supply this info. The graph below shows some PV that will produce 1400W+ on a sunshine day. Around 260W on a rainy and heavy cloudy day in sunny South Africa. 

If panels were doubled it will still only provide 520W. More panels do help on days with broken cloud and some blue skies. This will still be much lower than a normal sunshine day. This day provided less than 20% of normal yield. 

Horizontal scale at 250, 500, 750W.

These days I rely on the power grid. 

1 hour ago, jason compo said:

Hi all I have a axpert 5000w inverter with 3 poly US2000 lithium batteries. 

I have 4 x 450 watts solar panels connected in series and parallel 

On a sunny day here in Portugal the system starts up and charges without a problem  on cloudy day the system works but does not charge up the batteries 

Would it be best to buy 2 or 4 more panels for cloudy days so the system does not run out of battery

@jason compo  I have 4 x 450 watts solar panels connected in series and parallel 

How are they connected? is it 4 in serries or 4 in parallel?  

I am not on the power grid so I have to us only the system. I have 4 solar panels.

 

I am currently in the middle of an off-grid test with my solar. Switched the MCB off on 15 February 2023, and will only switch it back on on the 15 March 2023.

You definitely need as many panels and batteries as finances will afford, especially for those bad weather days, when it rains for days. So far to date I've only had to run the generator once to top-up the batteries. I'm doing a full simulation of off-grid, no cheating with the MCB.

So I suggest getting as many panels as you can afford, all depending on your "base load".

39 minutes ago, Antonio de Sa said:

@jason compo  I have 4 x 450 watts solar panels connected in series and parallel 

How are they connected? is it 4 in serries or 4 in parallel?  

I have the 4 connected

14 hours ago, jason compo said:

I have the 4 connected

@jason compo I just want to make sure of one thing, is this the type of inverter you have?   =  Axpert 48v/5000w Off Grid Inverter with 4000w MPPT

If that is the case, I am not sure about the specifications of your panels but from what you show on your drawing above, you would be better of connecting your 4 panels in series. looking at your inverter 

MPPT Range @ Operating Voltage

60VDC ~115VDC

 

15 hours ago, jason compo said:

I have the 4 connected

Is this image showing your panel specifications, or is it just a momentary snapshot?

You've said that there are 4x450W panels attached, however in the image above, at 20V and 5A, each panel is just producing just 100W, with a total of 400W.

 

56 minutes ago, GreenFields said:

Is this image showing your panel specifications, or is it just a momentary snapshot?

You've said that there are 4x450W panels attached, however in the image above, at 20V and 5A, each panel is just producing just 100W, with a total of 400W.

 

This is a basic diagram is just an idea on how I connect up the panel

57 minutes ago, GreenFields said:

Is this image showing your panel specifications, or is it just a momentary snapshot?

You've said that there are 4x450W panels attached, however in the image above, at 20V and 5A, each panel is just producing just 100W, with a total of 400W.

 

Let's wait for an answer but I am sure the pic is just a snap shot to give the configuration that was mentioned in the OP. 

Can you give us the specifications of your panels, that way we would be able to suggest the most efficient way to run your system. 

7 minutes ago, Scorp007 said:

Let's wait for an answer but I am sure the pic is just a snap shot to give the configuration that was mentioned in the OP. 

This is just to show how I completed the panels

7 minutes ago, jason compo said:

This is just to show how I completed the panels

These are the panels

@jason compo what is important is the Voc voltage in your case the way you show in your drawing 2 in series + 2 parallel you should in theory get +_ 100 V out of you set up, that is in line with your inverter. You can add more panels just make sure you don't exceed the inverter MPPT.

MPPT Range @ Operating Voltage

60VDC ~115VDC

Edited March 5, 20233 yr by Antonio de Sa

1 minute ago, Antonio de Sa said:

@jason compo what is important is the Voc voltage in your case the way you show in your drawing 2 in series + 2 parallel you should in theory get +_ 100 V out of you set up, that is in line with your inverter. 

MPPT Range @ Operating Voltage

60VDC ~115VDC

The problem I am getting is the system is working but on a cloudy day the inverter does not show the the batteries are charging

I do not see on the screen of the inverter any charging

7 minutes ago, jason compo said:

The problem I am getting is the system is working but on a cloudy day the inverter does not show the the batteries are charging

I do not see on the screen of the inverter any charging

That is the reality. on cloudy days the voltage generated by your panels is probably bellow 60 V or there about, not enough to trigger the inverter MPTT.  

Just now, Antonio de Sa said:

That is the reality. on cloudy days the voltage generated by your panels is probably bellow 60 V or there about, not enough to trigger the inverter MPTT.  

So what would be the minium panels I would need on a cloudy day ?

2 minutes ago, jason compo said:

So what would be the minium panels I would need on a cloudy day ?

@jason compo   Difficult to say, knowing Portugal, my native country, one could have cloudy days for weeks, especially in winter. Your biggest problem is the limitation of your inverter MPPT. You could possibly add another panel in serries = 115 V. in a nice sunny day and you will still be within the limits.

2 minutes ago, Antonio de Sa said:

@jason compo   Difficult to say, knowing Portugal, my native country, one could have cloudy days for weeks, especially in winter. Your biggest problem is the limitation of your inverter MPPT. You could possibly add another panel in serries = 115 V. in a nice sunny day and you will still be within the limits.

 

If I buy 2 x 450w will it at least trigger the inverter to charge on a cloudy day ?

@jason compo

The best answer I believe is already given by @Scorp007

19 hours ago, Scorp007 said:

Let me supply this info. The graph below shows some PV that will produce 1400W+ on a sunshine day. Around 260W on a rainy and heavy cloudy day in sunny South Africa. 

If panels were doubled it will still only provide 520W. More panels do help on days with broken cloud and some blue skies. This will still be much lower than a normal sunshine day. This day provided less than 20% of normal yield. 

Horizontal scale at 250, 500, 750W.

These days I rely on the power grid. 

The point is, you are running into one of the major limitations of solar power. It works well and produces a lot of power when the sun is shining and there's lots of solar radiation, but obviously when the sun is low, there is very little you can do with solar. The difference between sunny days and dark cloudy days is so big that it is probably not worth it to add extra panels.

Here for example is the solar radiation in Lisbon, Portugal for today. You can see that at around 10-11am the solar radiation is at its peak at around 190-195W/m^2 for today.

Now looking at the specification sheet for your panel below, you can see that at radiation of 200W/m^2, the bottom curve in dark blue/(purple?), at the peak Voltage of around 41V, the current will be just below 2 Ampere, and it will actually never go above 2.5A if the solar radiation is that low.

From 100% peak power at 1000W/m^2 you can drop as low as 15-20% of peak power on cloudy days. As a high-level thumbsuck you would have to add five or six times as many panels to make up for the lost power. One or two panels won't be enough. And it is not practical to put that many times more panels on, because it's firstly very expensive, and secondly you may exceed the power capacity of your inverter when the sun comes back. Sure you could add double the panels, 4 more of the 450W panels, but on cloudy days you will still only get up to 40% of the peak power you are getting on sunny days now with the first 4 panels. It might not be worth it to give you enough power, but at least it's a little bit extra.

So if it's not for so many days in the year, it's probably cheaper to just keep the grid as a backup (I understand you don't have that option), or else maybe more batteries could help up to a point (but that's also expensive and at some point the battery runs out, and it doesn't help anyway if there's not enough power generation), or a petrol or diesel backup generator might be an option (but that goes against the ideal of clean green energy).

 

Sorry, I don't think there is a better answer like what you might have wanted.

 

Edited March 5, 20233 yr by GreenFields

19 minutes ago, GreenFields said:

@jason compo

The best answer I believe is already given by @Scorp007

The point is, you are running into one of the major limitations of solar power. It works well and produces a lot of power when the sun is shining and there's lots of solar radiation, but obviously when the sun is low, there is very little you can do with solar. The difference between sunny days and dark cloudy days is so big that it is probably not worth it to add extra panels.

Here for example is the solar radiation in Lisbon, Portugal for today. You can see that at around 10-11am the solar radiation is at its peak at around 190-195W/m^2 for today.

Now looking at the specification sheet for your panel below, you can see that at radiation of 200W/m^2, the bottom curve in dark blue/(purple?), at the peak Voltage of around 41V, the current will be just below 2 Ampere, and it will actually never go above 2.5A if the solar radiation is that low.

From 100% peak power at 1000W/m^2 you can drop as low as 15-20% of peak power on cloudy days. As a high-level thumbsuck you would have to add five or six times as many panels to make up for the lost power. One or two panels won't be enough. And it is not practical to put that many times more panels on, because it's firstly very expensive, and secondly you may exceed the power and Voltage capacity of your inverter when the sun comes back. Sure you could add double the panels, 4 more of the 450W panels, but on cloudy days you will still only get up to 40% of the peak power you are getting on sunny days now with the first 4 panels. It might not be worth it to give you enough power, but at least it's a little bit extra.

So if it's not for so many days in the year, it's probably cheaper to just keep the grid as a backup (I understand you don't have that option), or else maybe more batteries could help up to a point (but that's also expensive and at some point the battery runs out, and it doesn't help anyway if there's not enough power generation), or a petrol or diesel backup generator might be an option (but that goes against the ideal of clean green energy).

 

Sorry, I don't think there is a better answer like what you might have wanted.

 

I understand where you are coming from 

I tried connecting up a small generator but it did not work the inverter kept cutting off as I am not to sure the setup for a generator to kick  ( start the generator by hand  ) when  the batteries are down to there limit

Just now, jason compo said:

I understand where you are coming from 

I tried connecting up a small generator but it did not work the inverter kept cutting off as I am not to sure the setup for a generator to kick  ( start the generator by hand  ) when  the batteries are down to there limit

I was told the generator had to be a pure sin wave 

@jason compo where is Pt are you? Roughly? The reason why I ask is that weather patterns differ from region to region. We can get some fairly accurate results if we snarf weather info from stations on Ambient.net  

The problem with the Axpert-type inverters is that they do not have sufficient latitude on their MPPT controllers to safely cater for sunny as well as overcast days. That's why Sunsynk released the 3.6K Hybrid with a whopping 7K MPPT controller, it's for the UK and I would assume the northern parts of Portugal as well:

  

 

My own situation in South Africa: I have a 5K Sunsynk with a maximum PV input of 6.4K, which I populate with just over 6K panels. I find that it is great on most days, but on cloudy days I get about half that (3K) if I am lucky. On heavy cloud days (raining) I get 10% (600W) maximum from my 6K array. This is in SA where my weather station records up to 1200 W/m2 . I can only image Pt to be far worse than that, so you may want to consider another MPPT controller or even a new inverter. 

5 minutes ago, jason compo said:

I was told the generator had to be a pure sin wave 

Many struggle to get a generator working with an inverter, and due to its design most (if not all) are pure sine wave. You can try to fiddle with the revolutions, this has an effect on voltage and frequency. Needs to be within the range that the inverter is able to accept, so if you have settings to adjust this on the inverter, then try to increase the latitude of acceptable voltage and frequency.