2 hours ago, Scorp007 said:

@Sc00bs

"It is very important not to go over 425V on each string, otherwise you can have smoke & fire from your MPPT controller. "

With the sweet spot 125-425V and the maximum only at 500V why do you think one could have smoke exceeding 425 but still below 500V as per the specs. Is it not that you might loose just a percentage or 2 between 425 and 500V?

I don't think you'll find a panel arrangement with a Voc of 500V and a Vmp of more than 425V. At least not with the panels currently on the market...

I suppose you could get in trouble if you add so many panels that you don't ever get down to Vmp at the inverter's rated power, but that would be silly.

2 hours ago, P1000 said:

I don't think you'll find a panel arrangement with a Voc of 500V and a Vmp of more than 425V. At least not with the panels currently on the market...

I suppose you could get in trouble if you add so many panels that you don't ever get down to Vmp at the inverter's rated power, but that would be silly.

Thanks for that one. I never looked at the combination of Voc and Vmp. Clever 👌

On 2022/06/13 at 7:15 PM, Scorp007 said:

@Sc00bs

"It is very important not to go over 425V on each string, otherwise you can have smoke & fire from your MPPT controller. "

With the sweet spot 125-425V and the maximum only at 500V why do you think one could have smoke exceeding 425 but still below 500V as per the specs. Is it not that you might loose just a percentage or 2 between 425 and 500V?

Hi Scorp007

On every panel spec you should see a value called (Temperature Co-Efficient of VOC) 

My understanding is that this gives you the % that the VOC voltage will increase per degree C the temperature reduces. 

On my JA Solar panels for example the value is 0.275%, say my normal string voltage is 450v with the panels at a temperature of 40c.

Now picture a very cold winters day, panels are sitting at an icy 0c and the sun comes out . 0.275% x 40c difference = an 11% increase in panel voltage and we go from 450V @ 40c to 499.5V

I am not sure what the chances of this actually happening and doubt that damage would start happening at exactly 501V but I personally would prefer to be a bit more conservative on my string voltages but everyone to their own I suppose. 

12 minutes ago, Sc00bs said:

Hi Scorp007

On every panel spec you should see a value called (Temperature Co-Efficient of VOC) 

My understanding is that this gives you the % that the VOC voltage will increase per degree C the temperature reduces. 

On my JA Solar panels for example the value is 0.275%, say my normal string voltage is 450v with the panels at a temperature of 40c.

Now picture a very cold winters day, panels are sitting at an icy 0c and the sun comes out . 0.275% x 40c difference = an 11% increase in panel voltage and we go from 450V @ 40c to 499.5V

I am not sure what the chances of this actually happening and doubt that damage would start happening at exactly 501V but I personally would prefer to be a bit more conservative on my string voltages but everyone to their own I suppose. 

I have been watching a few of Keith's (CEO Sunsynk) videos on YouTube. He emphasized a few times that VOC is most critical and must not exceed 450v per mppt string. And correct, temperature does play a role in increasing this voltage. 

19 minutes ago, Sc00bs said:

Hi Scorp007

On every panel spec you should see a value called (Temperature Co-Efficient of VOC) 

My understanding is that this gives you the % that the VOC voltage will increase per degree C the temperature reduces. 

On my JA Solar panels for example the value is 0.275%, say my normal string voltage is 450v with the panels at a temperature of 40c.

Now picture a very cold winters day, panels are sitting at an icy 0c and the sun comes out . 0.275% x 40c difference = an 11% increase in panel voltage and we go from 450V @ 40c to 499.5V

I am not sure what the chances of this actually happening and doubt that damage would start happening at exactly 501V but I personally would prefer to be a bit more conservative on my string voltages but everyone to their own I suppose. 

You are correct. You should leave some margin. In practice though, all the components on the input of the MPPT need to handle the PV voltage + ripple. So it should detect overvoltage and disable itself without blowing up (disabled MPPT = no ripple). That said, I am not guaranteeing that all MPPTs are designed correctly. So the components are certainly rated at least 10% higher, but whether all the safety features are there is not a given.

10 hours ago, Solarcrazy said:

I have been watching a few of Keith's (CEO Sunsynk) videos on YouTube. He emphasized a few times that VOC is most critical and must not exceed 450v per mppt string. And correct, temperature does play a role in increasing this voltage. 

I find the statements from Keith very interesting. A spec of 500V max is given by which one will do calcs and then he says it should never go over 450V???

I did not see the video so I can't comment under what scenario he stressed the point.

I find temps very interesting when we follow discussions around this topic.

@Sc00bs

I think we must remember that the spec around temps are in lab tests and not that easy to calculate and relate it to our strings. Yes we must not be blind to not allow for temps.

De-rating of inverters being in house is a real problem on some. I have never found lower output of my MPPTs in the inverter on warmer days. This is on an inverter with only natural cooling. So far on the limited inverters that I know of my make is the only one that is rated above 4kw that has no fans. Perhaps a clever design and lots of heat sink.

My favourite thing is cold panels are meant to produce a higher output. But here comes the real life thing. As panels produce more power they generate their own heat so they can never be close to the outside temp. Due to this increase in temp the output will drop. My own actual figures show the best output at high irradiation during the peak period at times when the panels are at high temps.

I will place some data around this later. Also will give the Voc on a few very cold mornings recently.

Edited June 16, 20224 yr by Scorp007

8 hours ago, Scorp007 said:

I find the statements from Keith very interesting. A spec of 500V max is given by which one will do calc and then he says it should never go over 450V???

I'm did not see the video so I can't comment under what scenario he stressed the point.

I find temps very interesting when we follow discussions around this topic.

@Sc00bs

I think we must remember that the spec around temp are in lab tests and not that easy to calculate and relate to our strings. Yes we must not be blind to not allow for temps.

De-rating of inverters being in house is a real problem on some. I have never found lower output of my MPPTs in the inverter on warmer days. This is on an inverter with only natural cooling. So far on the limited inverters that I know of my make is the only one that is rated above 4kw that has no fans. Perhaps a clever design and lots of heat sink.

My favourite thing is cold panels are meant to produce a higher output. But here comes the real life thing. As panels produce more power they generate their own heat so they can never be close to the outside temp. Due to this increase in temp the output will drop. My own actual figures show the best output at high irradiation during the peak period at times when the panels are at high temps.

I will place some data around this later. Also will give the Voc on a few very cold mornings recently.

With the current cold spell it is perhaps a good time to chat about temperature affects. Bear in mind this is not advice but just actual inputs to consider based on real data.

As irradiance is not taken into account as it has a very small effect on voltage but a direct correlation to the current produced.

Firstly consider the temp of the panels on a chilly day. Maximum temp about 16 degrees yet the panels are at over 40 degrees. The maximum power is generated when the sun hits the panel at the best angle from east to west. Panels are at 28 degree fixed angle. All power is used and not dependent on load or battery. This is what I meant in my previous post that I feel the lower temp earlier/later in the day does not produce more power. We have no control over it so no need to try and alter it.

 

Power generated at the temp of the above graphic.

This table below adds to the post from @Sc00bs @P1000 and @Solarcrazy and the specs for the panels used is for a Canadian Solar which is used as a 6 in series single array. I used the lowest temp during the day from 19 May up to today. I normally look at the ambient temp in the morning and no chill factor is needed. We had at least 5 days where the temp was zero or lower up to minus 4 just before 07h00. Calculated Voc at a temp of zero works out at 247V. Actual figure shown does not get even close to it. This deviation from calculated to real life is what I have been observing over the 40 months that I have data available. Further to this I have also never had a Voc as per STC at 25 degrees at temps below zero. This does not mean Voc cannot go so high purely because it has not been the case in 40 months even on below zero ambient temperature.

Specs for the panels.

 

Table with the calculations and real measured Voc values on a few zero and below mornings. Today the Voc was not early in the morning but in the late afternoon.

If the post is too long just page down

So I looked at the spec sheet of the Canadian panels. There seems to be 2 specs (Standard test conditions (STC) and Nominal Operating Temp (NMOT), each have different VOC value. Which one do I use for my calculations of my max string? 

 

17 minutes ago, Solarcrazy said:

Which one do I use for my calculations of my max string? 

If you want to be safe, use the worst case scenario/the highest voltage...

If one has an east and west bank of panels do you need some form of change over switch to connect the most efficient bank during the day and what is the best option.

Thanks.

James 

If I install an east and a west bank of panels how do I ensure the most efficient bank is in use as the sun moves from one bank to the next.

Is a second inverter/charger required or can one install an MPPT on the one bank direct to the batteries?

Thanks,

James

Edited June 26, 20223 yr by JRW

1 hour ago, JRW said:

If one has an east and west bank of panels do you need some form of change over switch to connect the most efficient bank during the day and what is the best option.

Thanks.

James 

If the 2 banks are in parallel you don't need any switch over. Each bank will provide the power based on the power it can provide.

The only thing is these 2 strings should not be in series as the lower output would throttle the high output string.

If you have 2 MPPTs each string can be directly connected provided each string has a voltage high enough to start each MPPT.

Edited June 26, 20223 yr by Scorp007

4 hours ago, JRW said:

If I install an east and a west bank of panels how do I ensure the most efficient bank is in use as the sun moves from one bank to the next.

Is a second inverter/charger required or can one install an MPPT on the one bank direct to the batteries?

Thanks,

James

Just check what is the max wattage the mppt can handle  also the VOC of each panel and therein the string. Depending on how many panels you place on each side.. You can run each string connected to one mppt if you have 2 or connected then all together in a single string taking note of the limitations noted above. 

What inverter you have and how many panels and want to place on each side? You knw the wattage and VOC of each panel? 

3 hours ago, Solarcrazy said:

Just check what is the max wattage the mppt can handle  also the VOC of each panel and therein the string. Depending on how many panels you place on each side.. You can run each string connected to one mppt if you have 2 or connected then all together in a single string taking note of the limitations noted above. 

What inverter you have and how many panels and want to place on each side? You knw the wattage and VOC of each panel? 

I would not use a single string if there is only 1 MPPT. The morning the west side will throttle and in the afternoon the east will throttle. Too much waste if one only get a good yield around the middle of the day.

One will get the same as per the problem @Nicolas Strachan had with 2 panels of a string lying flat in a series string.

Edited June 26, 20223 yr by Scorp007

Presently have 12 x 330W panels in series and parallel, facing NE connected to 2 x 2.4 batteries via a 5kVA inverter charger, thinking of increasing  to 3 batteries and 4 panels facing west. could I just run those west panels to an MPPT and to the batteries?

2 hours ago, JRW said:

Presently have 12 x 330W panels in series and parallel, facing NE connected to 2 x 2.4 batteries via a 5kVA inverter charger, thinking of increasing  to 3 batteries and 4 panels facing west. could I just run those west panels to an MPPT and to the batteries?

Yes you could. Without knowing what 5kw inverter you using one cannot be sure if this is the way to connect those 4 x west panels via another MPPT. . Also not sure when you mention you have 12 x 330W connected in series parallel how they are connected.

 

Got a East & West String 
7 pannels on each side of 455W Ja Solar 
21.5Kw a day now. 

The West string is weaker though 24' Angle 

East being the one close to 7.73

i am going to try 12 panels west and 12 panels east.... (545w) - should get 50kwh per day i hope...

what you think..

On 2022/06/10 at 5:55 AM, Sc00bs said:

Hi @Solarcrazy

According to the specifications, the Deye 5kw has 2 x MPPT controller with optimum voltage of between 240V-425V, starts working at 125V. So you can support two strings of panels

It is very important not to go over 425V on each string, otherwise you can have smoke & fire from your MPPT controller. 

Maximum amps is 11A (I think that they have raised this to  12A, not sure). You can overwatt your panels within reason as the inverter is able to restrict the Amps coming from the panels by increasing resistance. Something it can't do with the Voltage

Maximum DC input power is 6500W (the total of both strings combined)

Canadian Solar panels produce 17.15A max @ 34.7V, you will however not be able to use more than 12A so you are paying for 5.15A of power that you won't be able to use. 

Would be better to go with the JA Solar panels 535W panels which are rated at 12.97A @ 41.47V, 8 panels would be well within the max voltage, you would loose a small amount of efficiency at max production as you would not be able to use the last bit of power and you would benefit from the extra production on more overcast days. 

 

So you chart would have a flat top at 12A on high solar radiation days

East and West facing strings are preferable if possible due to the longer hours of production if slightly lower total than a N facing string. The yellow part of the chart if from an North-East facing string the green part is from a  NWest facing string

 

@Sc00bs if you split the 8 panels on the 2x MPPTs will the voltage not too low, and will happen with the watage if you conect them on 1 MPPT? 

13 minutes ago, Inverter said:

@Sc00bs if you split the 8 panels on the 2x MPPTs will the voltage not too low, and will happen with the watage if you conect them on 1 MPPT? 

4 panels per MPPT is a risk on the output side. 8 in series on 1 x MPPT should be within the MPPT levels but if the panels have a Imp over 12.5A expect some waste due to clipping. 

Specs of panels needed to know the clipping or not. 

Edited January 28, 20242 yr by Scorp007

4 minutes ago, Scorp007 said:

4 panels per MPPT is a risk on the output side. 8 in series on 1 x MPPT should be within the MPPT levels but if the panels have a Imp over 12.5A expect some waste due to clipping. 

Specs of panels needed to know the clipping or not. 

I want to install 8x JA's 455w which will be 3640w.

Edited January 28, 20242 yr by Inverter

1 hour ago, Inverter said:

I want to install 8x JA's 455w which will be 3640w.

What inverter are you using? 

On 2024/01/28 at 2:55 PM, Scorp007 said:

What inverter are you using? 

@Scorp007 sorry for the late reply. It is 5kw deye inverter 

1 hour ago, Inverter said:

@Scorp007 sorry for the late reply. It is 5kw deye inverter 

All 8 in series is within the peak range on 1 MPPT. Using 4 per MPPT you will fall quite a bit below 200V at times and have a low output. 

8 in series will give a far better yield and even more so on cloudy days. 

18 hours ago, Scorp007 said:

All 8 in series is within the peak range on 1 MPPT. Using 4 per MPPT you will fall quite a bit below 200V at times and have a low output. 

8 in series will give a far better yield and even more so on cloudy days. 

@Scorp007 what will happens with the wattage will it not be to high for the MPPT if the load is for instance 2,2kw and the batteries were drained during the night?

1 hour ago, Inverter said:

@Scorp007 what will happens with the wattage will it not be to high for the MPPT if the load is for instance 2,2kw and the batteries were drained during the night?

This is where you have to manage the power left in the batteries if you want to use such high loads before the PV kicks in. 

For most areas your 8 panels will only provide 2900W from 10h30-14h00 during sunshine. You also have to ensure the chosen battery/ies can deliver this power. Some are only 0.5C which means a 5kWh battery can not provide more than 2.4kW of load if only 1 battery.