What can I realistically expect from my panels / would it make sense to add more?

[wolfandy]

Hi all

I've recently upgraded my Axpert backup solution with solar and am now running the following:

• 5kVA Axpert (PF 0.8)
• 1x 3.5kWh Pylontech
• 9x JA Solar 315W panels (3x3s) (thanks to Coulomb for panel advice on AEVA)

In theory, this should give me 2,835W of PV capacity for the max 3,000W PV array that the Axpert can handle. However, I understand that these are theoretical values under lab conditions and that in reality due to heat these values will be lower (which I am now also experiencing).

So my first question would be what max PV Watts I can realistically expect from my system in local CPT conditions? So far, the max PV output that I have seen is just over 2,500W on a sunny (no clouds) and hence hot day. This is a roughly 12% loss, which at my panels Temperature Coefficient of Pmax of 0.380%/℃ seems roughly right to me. Is that correct or am I wrong somewhere? Are you guys having similar experience?

If the above is correct, would it make sense to add more panels (I am easily getting to the point where I am fully utilising my PV production)? Adding another 3s would take me to a total theoretical capacity of 3,780W. At the 12% loss that I am experiencing, it would mean 3,326W. I understand that during peak period I would not be able to utilise more than 3,000W - but it would get me closer to utilising the full PV capacity of the Axpert for the majority of the time. My questions here:

• Would I actually be allowed to install 3,780W of capacity? I remember my installer mentioning something about a 3.5kW limit in CPT
• Would I be running a risk by adding that much capacity? Many places on the web mention oversizing PV capacity to maximise production as a viable option (with numbers ranging from 10% to 33%). As they will be added in parallel, my Voc should not change, right? 
• Would it be a simple mount-and-connect on the roof or would I also need to run additional cabling down to my inverter? If I am not mistaken, the installer ran 6mm cables

I am also contemplating of adding a 2nd Pylontech (if our load-shedding continues as it is at the moment, then most definitely) - which obviously could then also utilise additional PV capacity for charging

Thanks and cheers

 

[Jaco De Jongh]

12 minutes ago, wolfandy said:

So my first question would be what max PV Watts I can realistically expect from my system in local CPT conditions? So far, the max PV output that I have seen is just over 2,500W on a sunny (no clouds) and hence hot day. This is a roughly 12% loss,

If you get 2500 wh from a 2835 whp array, you should be very pleased. Realistically you can expect 80% of the total array size.

I would not advice on over-sizing the array on a voltronic inverter although some members have said that its safe. To what level, I am not sure. 

[KLEVA]

<RantOn>
As a complete aside - How come so many people on this forum can afford to buy PylonTech battery arrays, but then buy an Axpert Invertor? I am happy that people take batteries seriously, but that is a huge financial leap to go from the "cheapie" invertor to the "expensive" batteries??? Not completely knocking the Axpert, it is extremely capable, but I just don't see the point on spending R50+k on batteries, and then cheaping out on a R9k invertor???
<Rant Over>

[KLEVA]

Now seriously on your Solar Panels. This is one of the few times I disagree with @Jaco de Jongh.

Solar panels are rated based on a certain amount of light (or lux) per meter square output. For many places around the world, they don't quite get the same amount of light (or lux) per meter square of solar panel, so they can either be rated lower for market or they specify (most specify). You will always see on a panel specification sheet exactly how they calculated the fact that it would deliver 280W or so in an environment.

In places like South Africa and Australia, our sunlight level is far higher (I say sunlight to simplify, it is slightly more complex than that). So the panels we install that are maybe rated as 280W, can actually deliver a much higher Wattage than expected (even over 300W) - because we get better sunlight than the European countries that it is rated for. But then we have the reverse situation, if they "cheated" (my emphasis), then they can use the South Africa maximum conditions to spec the panels (ArtSolar based in Pinetown, South Africa do this with their spec sheets, but with limited detriment to the purchaser as they show many other Lux levels for the advised purchaser). At the end of the day, it means that depending on the source, certain panels will behave the same if they are rated 250W or 280W. When you buy panels, or especially if you need to add panels to your array, stick with the same size and supplier. If you can't - then try get them properly tested and matched to your array. I happily run 280W panels with 250W panels from 2 different suppliers, but other than a volt difference of 1V or less, they perform identically.

[RikH]

@wolfandyCan you please upload or just write down the specs of your inverter and you panels? Important to know is Voc and Isc of panels at STC (= STC:1000W/m²irradiance,25 ̊Ccelltemperature) and temp coeff. Voc. Also max VDC and Amps of the MPPT input on the inverter. What is the lowest temperature you can expect there? After that I can give you a better advise.

Edited December 10, 2019 by RikH

[wolfandy]

Thanks for the feedback, all 

8 hours ago, KLEVA said:

<RantOn>
As a complete aside - How come so many people on this forum can afford to buy PylonTech battery arrays, but then buy an Axpert Invertor? I am happy that people take batteries seriously, but that is a huge financial leap to go from the "cheapie" invertor to the "expensive" batteries??? Not completely knocking the Axpert, it is extremely capable, but I just don't see the point on spending R50+k on batteries, and then cheaping out on a R9k invertor???
<Rant Over>

In my case, this has historical reasons. I bought my Axpert back in 2015 with a bunch of lead acid batteries to survive the load-shedding at the time. Batteries eventually reached their end of life earlier this year and I replaced them with the Pylontech. And when I then decided to add solar, why should I throw out a working inverter? It does what I need it to, so I'm going to get as much mileage out of it as I can...

Quote

When you buy panels, or especially if you need to add panels to your array, stick with the same size and supplier

This would not be a problem as I only purchased the panels a couple of weeks ago and can source exactly the same panels again

@RikH: Here are the details you've requested:

• Inverter: MPPT range operating voltage 60VDC - 115VDC; max 145VDC; max SolaR Charge Current 60A
• Temperatures: Lowest during morning probably around 2 degrees Celsius
• Panels: 
  

 

[Jaco De Jongh]

12 hours ago, KLEVA said:

Now seriously on your Solar Panels. This is one of the few times I disagree with @Jaco de Jongh.

Solar panels are rated based on a certain amount of light (or lux) per meter square output. For many places around the world, they don't quite get the same amount of light (or lux) per meter square of solar panel, so they can either be rated lower for market or they specify (most specify). You will always see on a panel specification sheet exactly how they calculated the fact that it would deliver 280W or so in an environment.

In places like South Africa and Australia, our sunlight level is far higher (I say sunlight to simplify, it is slightly more complex than that). So the panels we install that are maybe rated as 280W, can actually deliver a much higher Wattage than expected (even over 300W) - because we get better sunlight than the European countries that it is rated for. But then we have the reverse situation, if they "cheated" (my emphasis), then they can use the South Africa maximum conditions to spec the panels (ArtSolar based in Pinetown, South Africa do this with their spec sheets, but with limited detriment to the purchaser as they show many other Lux levels for the advised purchaser). At the end of the day, it means that depending on the source, certain panels will behave the same if they are rated 250W or 280W. When you buy panels, or especially if you need to add panels to your array, stick with the same size and supplier. If you can't - then try get them properly tested and matched to your array. I happily run 280W panels with 250W panels from 2 different suppliers, but other than a volt difference of 1V or less, they perform identically.

Very nice explanation, but you left out, temperature losses, wire losses, connection losses and conversion losses. Taking all that into consideration you can effectively expect 80% of the Array size and I have the history on multiple sites to prove that figure. The only time ever i have seen an array giving more than its rated wattage is with cloud edge effect on a cool day. 

@KLEVA, If you found a way to get 300 Watt out of a 280 watt panel, please share it, the industry need to know that secret. 

[stoic]

hehe... i like where this conversation is going  

[ChristoSnake]

An example of over 9kW from an 8kW array on a partly cloudy day...

[___]

22 minutes ago, Jaco de Jongh said:

the industry need to know that secret

Easy... cool it down! (and use less energy to do the cooling than the gain on the module, cause you need a net increase in energy... kinda like a Turbo/blower on a car engine... it robs the engine of some power, but it makes up for it ).

South Africa does have a very high insolation. Where Europe averages 100W/m^2 (over 24 hours) and some parts of the US reaches 150, we can do 220. But that's an average, and given our relatively long days which doesn't shorten much in winter (compared to Europe!) it's not too much of a surprise. My point is that there is some merit in this "more insolation" claim. I'd like to quantify it though.

I've located a value from a Cape Town weather station, indicating an all time peak of 1446W/m^2. So one can reasonable estimate that South Africa could have as much as a 50% higher peak, which is to say that I can imagine a PV module making more than its design rating for maybe an hour a day (or so)... IF you keep the module cool enough.

Incidentally we already have the information we need. The panel specs has the temperature coefficient right there: between -0.35% and -0.5% per degree centigrade. So a PV module at 50°C runs at (50-25)*0.35 ~= 9V lower. Take your average 300W module that pushes around 8A at 37V (ish), and multiply out the 8A with your 9V lower voltage. That's 72W, or 24% lost.

So even at a nice 1500W/m^2, I will get only 1125W peak for that hour over noon, and pretty close on 1000W once I lost another 5% on the MPPT (very optimistic).

So... uuuhm... no. You ain't getting more than the advertised rating... except maybe during exceptional circumstances. I remember such a day when I was a young boy. It was probably around October. I was in the South of Namibia at a place called Koës, it was colder than a dead Kudu's nuts that day with a wind that cut through everything... and the brightest sunshine you can imagine. On that day... maybe... :-)

[Luminous]

I have to agree, don't oversize the panels that much.

My panels are setup quite far west facing and I have seen them topping out past their rated capacity a few times already. Normally cold and rainy days. 

 

[___]

13 hours ago, KLEVA said:

afford to buy PylonTech battery arrays, but then buy an Axpert Invertor?

Well of course people do it for legacy reasons, as already noted. But I too sometimes marvel at this sort of thing in new installations. I put it down to man-with-a-hammer syndrome. Every problem starts to look like a nail.

[Jaco De Jongh]

1 hour ago, plonkster said:

Easy... cool it down! (and use less energy to do the cooling than the gain on the module, cause you need a net increase in energy... kinda like a Turbo/blower on a car engine... it robs the engine of some power, but it makes up for it ).

No , not at all that easy, I had many birdbrained ideas in my live and cooling panels were one of them. I just could not get the balance right, the water you need to cool down 24 panels in Phalaborwa to gain 300 watt vs the power you need to get the water up there. I could have used the council pressure to achieve that but then i had to pay for the water, I wanted to circulate my swimming pool water, but after a while just stopped trying. 

[___]

16 minutes ago, Jaco de Jongh said:

No , not at all that easy,

Yeah... I was being rhetorical. Of course it isn't easy

[hancock]

19 hours ago, ChristoSnake said:

An example of over 9kW from an 8kW array on a partly cloudy day...

@ChristoSnake are the 24x330w Canadian solar panels connected to just one infinisolar 5Kva inverter in your setup?

That thing has like a maximum PV size of about 4000w according to the spec sheets.

[wolfandy]

Ok - I understand now that a panel can produce more than it's rated capacity (however only under very specific conditions and most likely only for short peak periods under real-life conditions)

And that the average max output of 2.5kW that I am getting from my 2.8kW array is in line with general expectations (so there is nothing 'wrong' with my setup)

My question that remains is whether there are any risks of adding another 3s panels (same type) to my array - which would take total nameplate capacity to 3.8kW on an inverter that can handle max 3.0kW of PV. Would this carry an increased risk of damaging my inverter? 

[ChristoSnake]

12 hours ago, hancock said:

@ChristoSnake are the 24x330w Canadian solar panels connected to just one infinisolar 5Kva inverter in your setup?

That thing has like a maximum PV size of about 4000w according to the spec sheets.

Indeed!

They are connected as two strings of 12x330W panels,  each to a separate MPPT.  The inverter can actually handle 5kW per MPPT for a total of 10kW.

[Coulomb]

12 hours ago, wolfandy said:

which would take total nameplate capacity to 3.8kW on an inverter that can handle max 3.0kW of PV. Would this carry an increased risk of damaging my inverter? 

I don't believe that it will endanger your inverter-charger, but it could cause problems with overvoltaging the battery, possibly causing the BMS to trip off. So this is a nuisance factor mainly.

But that's just my opinion. I run 3.2 kW nominal into one of my PIP-4048MS inverter-chargers (with 60 A / 3000 W PV capacity,  one of the last 60 A models manufactured). But 3.8 kW is a significant "overclocking". Personally, I would not do it.

[wolfandy]

Thanks Coulomb

Would it be possible to connect another MPPT with panels in parallel to the Pylontech, so that it would be charged both from the Axpert and the extra MPPT? Obviously this would not increase the PV available to feed the loads on the Axpert, but it should provide extra capacity to charge the Pylons, right?

Or would this cause issues?

 

[___]

9 hours ago, Coulomb said:

overvoltaging the battery

My advice is to set charging voltage to 52.5V (instead of the recommende 53.2V) if you're going to oversize on the PV. Leave a bit of room. The battery recommendations ask for a charge voltage of 53.2V and they switch off at 54V. That's 0.05V per cell (full at 3.55V, overvoltage at 3.6V). That's really just too close for comfort.

[GVC]

1 hour ago, wolfandy said:

Thanks Coulomb

Would it be possible to connect another MPPT with panels in parallel to the Pylontech, so that it would be charged both from the Axpert and the extra MPPT? Obviously this would not increase the PV available to feed the loads on the Axpert, but it should provide extra capacity to charge the Pylons, right?

Or would this cause issues?

 

Yes, you can easily add an external MPPT, but bear in mind what @Coulomb has said about putting too much voltage / current into your one pylontech battery.

If I am not mistaken the 3.5kW Pylontech can take a max of 74A Charge/Discharge. This would equate to 3552W if my math serve me correctly. If you do add an external MPPT you can probably also set the battery voltage to stop charging at say 52.0V.

[Coulomb]

1 hour ago, wolfandy said:

Would it be possible to connect another MPPT with panels in parallel to the Pylontech... Or would this cause issues?

Yes. In fact I did this for years, and actually still do in a way.

The issue is that you have two "bosses". They both want to decide when to bulk charge and when to float charge. So I have to put the bulk and float voltage settings on one of them 1 or 2 tenths of a volt lower than the other. I note that when Axperts are paralleled, one declares itself the master and there is only one boss after all.

However, with the current trend of using a float voltage setting that is nearly as high or equal to the bulk voltage setting, this doesn't matter.

With two MPPTs (one internal to the inverter-charger, one external), you now have twice the chances of over-voltaging the battery. So I'd take @plonkster's advice and keep the voltage setting further away from the 54.0 V never-exceed point than the manufacturer recommends. I use the 16-cell equivalent of 51.8 V, but 52.5 V is probably fine.

[___]

46 minutes ago, Coulomb said:

I use the 16-cell equivalent of 51.8 V, but 52.5 V is probably fine.

@Youda posted a long explanation as to why at least 52.2V should be used, and ideally a bit more. In my own testing at @Ironman's site I determined that 52.4V seems to be the lowest voltage that yields good results. As a result, this was logged and implemented yesterday, so if all goes well it will make it into a future release.

[wolfandy]

Thanks all

I will most likely be adding another Pylontech to the system - so now I know how to scale charging capacity if required

Quote

@Youda posted a long explanation as to why at least 52.2V should be used, and ideally a bit more. In my own testing at @Ironman's site I determined that 52.4V seems to be the lowest voltage that yields good results. As a result, this was logged and implemented yesterday, so if all goes well it will make it into a future release.

Just to make sure that a novice like me understands correctly: This means 52.4V for Bulk Charging, correct? And then Float Charging slightly lower (e.g. 52.2V)?

[KLEVA]

@Jaco de Jongh - Definitely can get a higher Wattage from a panel that has been calculated with lower Lux values (to define Watts/sq meter). Lux is calculated in the 0.3-2.4 micro meter range of the Solar Spectrum (some is outside visible light) and then multiplied by approx 0,0079 to give Watts/sq meter. Yet in South Africa there are some days we can easily exceed a Lux of 100000 (standard industry used AKA Peak Sun, but some countries reduce this to cater for their own latitudes - So they can exceed their Lux value calculation if used elsewhere).

Note: For the purpose of this discussion I am using Lux, not Lumens (they are slightly technically different), and W/sqM is weird because it depends on their entirety of the product build.

Here is why:

• As mentioned Peak Sun is 100000 Lux
• Full Sun is 108000 Lux (if nothing is between you and the sun, and Sunburn/Skin Cancer is near), South Africa can get very close to that on some days, not just because we think so but because it has been measured by people with far more "Dr"'s behind their name than I have.. And the SA Weather Service.
• Good Solar Panel manufacturers will always use Peak Sun for their calcs. It is what most of the world gets at 12 midday with (was without until edit, sorry)out direct sun.
• So even if we have a good quality product, tested at 100000 Lux, you will can get an increase in the Wattage output above Manufacturer specs - Highly unlikely to be larger than 10% though. Max reported by SAWS is 104000, until they provide the datasheet I requested. That is already 4% higher - 250W Panel becomes 260W output at the same Panel.
• A worse quality product may be rated at 250W based on 80000 Lux - If you give that product a 15% increase in Lux, then it can drastically out-perform its specs, or just break because it can't operate at the temperature difference created by that 15%

Edited December 13, 2019 by KLEVA
typos & dutchman translation failure (mine)