Jump to content

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


Recommended Posts

On 2019/12/10 at 8:37 PM, KLEVA said:

. 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,

I beg to differ with this statement, ArtSolar and actually every other panel I have cared to check has its power rating specified at STC, which is 1000W/m2 at 25 deg C as an international standard.

This is done so that apples can be compared with apples.

I accept that nominal operating conditions may vary country to country, but the power rating of a panel is given at STC.

The NOCT rating however also seems to be standardized at 800W/m2, 20 deg C & 1m/s wind.

 

Link to post
Share on other sites

Interestingly, I learned yesterday that in Germany you are allowed to oversize your array to account for the lower insolation, provided that the system is limited to 70% of its capacity (either on demand, using a ripple signal, or permanently).

The reason for this is that most days of the year you are highly unlikely to make more than 70% of the STC-spec production of the array... but for a few days in the year (those days when the price of electricity goes negative and other European countries turn off power stations because Germany supplies them for free), you do get the full power. Based on a paper I read from Fraunhoffer, they calculated that this results in about a 2%-5% hit on the income of embedded generators.

Link to post
Share on other sites

@phil.g00 - Hope you misread my statements and comments, or I might not have been clear in what I was trying to say about the reverse (I was comparing them to manufacturer's who use the lower standard) - I was agreeing with the fact that ARTSolar use the higher value on their product. ARTSolar are brilliant when they have stock available, and I would definitely at least give them first shot locally. My only negative with them is that they only manufacture 2 sizes at a time, and keep no older stock to expand existing installations. So if you did an install 5 years ago, then sorry you have to buy completely new panels as none of there current stuff will work.

Link to post
Share on other sites

@plonkster - Sorry, I don't understand what that means to us. Are they getting any financial benefit or less payment to government? Sorry for my ignorance here, but I don't understand the current Germany situation and why it is now a benefit to add to their load? I fully understand that Germany's feedback to grid has nearly reduced their municipal power to 0, that I know... I just don't quite understand the politics/legalities/reason as to why your news article is good news?

Link to post
Share on other sites
17 minutes ago, KLEVA said:

I don't understand

It's just something interest I learned yesterday. No real direct lesson for us 🙂

When a bunch of embedded generators are dumping power into the grid and you have nowhere to go with it, it is a big problem, something the German authorities want to avoid. That's why the price of power goes negative on those days (it's a rare event, kinda like our own 1500W/m^2 coinciding with cold weather), in other words you are BILLED for what you feed into the grid.

To avoid this, pretty much like in Cape Town, the size of your PV setup is limited to some maximum. But that causes a new problem... which is that for most of the year your PV array will come nowhere near the max rating. So they needed a way to oversize the array AND not run into problems with too much power, and this was the outcome: You can either reduce to 70% on demand... or permanently.

If you reduce permanently, you will lose around 2%-5% of the money you would have gotten from your FIT vs on-demand.

The nice thing about it is the 70% rule is at your interface with the grid. If you can use 30% of the power yourself, then you can utilise 100% of the PV on that day... the trickery comes into the control systems to make this work nicely 🙂

Edited by plonkster
Link to post
Share on other sites
53 minutes ago, KLEVA said:

@phil.g00 - Hope you misread my statements and comments, or I might not have been clear in what I was trying to say about the reverse (I was comparing them to manufacturer's who use the lower standard) - I was agreeing with the fact that ARTSolar use the higher value on their product. ARTSolar are brilliant when they have stock available, and I would definitely at least give them first shot locally. My only negative with them is that they only manufacture 2 sizes at a time, and keep no older stock to expand existing installations. So if you did an install 5 years ago, then sorry you have to buy completely new panels as none of there current stuff will work.

Yes, I did misunderstand your statement. Apologies.

Regarding Artsolar, I have the same issue, regarding size availability. In their defense though,  PV specs are increasing that fast, that it must be a universal PV issue.

I suppose you'll still find old stock of the size you want from bigger international makes, but they have to move onto current production lines as well. It seems to be a very competitive market.

What I do like is that ArtSolar do seem to standardize on a physical size for their 60's and 72's.

I find some panels I got a few years back, no longer deserve have pride of place (North-facing perfect angle), as they are about 100W weaker than today's panels. Having a standard size means I can easily replace them with the more powerful panels, and redeploy the lesser panels to stand-alone direct PV pumping tasks or the like.

ArtSolar does a fair range now, but these days I buy by the pallet. (Cheaper price and enough PV to meaningfully mix and match).

 

Link to post
Share on other sites
On 2019/12/13 at 5:09 PM, KLEVA said:

@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%

This story really looks good on paper, I actuality want to offer this solution to all my customers, but sadly these panels dont get installed on paper, they get installed on a roof in Africa, under the African sun where there is a great chance that the panel will reach over 40 deg C (60deg plus in Phalaborwa) almost anywhere in SA at midday (Peak production). All the specs you mention is for temperatures below 25 deg C. So on a nice cold winters day , if your panels are mounted at the correct angle, your theory will be correct. 

The OP wants to know what he can realistically expect from his panels (installed on a roof in Africa).. and I promise you, it is not 110% of the array size, does not matter how much you want to believe that is true.  

Is his panels facing true north, at the correct angle (fixed on the roof), but what happens next month and the month after, if he did not adjust the angle/tilt of his panels to mach the time of year he would be 16 deg out. Guess what that does to his production? 

Link to post
Share on other sites
18 hours ago, Coulomb said:

Yes.

Thanks Coulomb

Quote

The OP wants to know what he can realistically expect from his panels (installed on a roof in Africa).. and I promise you, it is not 110% of the array size, does not matter how much you want to believe that is true.  

Thursday/Friday this week we had some sunny and hot days here in Cape Town. On those days I could not get more than 1,800W of sustained power out of my PV system (brief peaks of more yes). If my load exceeded that amount, the inverter would draw additional required watts from the battery.

I spoke to my installer and he explained the following:

  • In summer, can expect to generate 5x my installed array capacity per day if I have sufficient load attached. Then my system is working as expected. In my case (5 x 9 x 315W) it would be 14.2kWh. I did produce 15.49kWh and 14.21kWh on those days
  • The reason for not getting more than 1.8kW sustained power out of my 2.8kW array on those days are due to heat - in the panels, the cables, and the inverter
  • Panels: Heat losses as per spec sheet with cell temperature around 70 - 80 degrees
  • Cables: The MPPT in my older Axpert increase the Amps rather than the voltage, running more than 32A (I did see up to 36A on those days). This increases the temperature in the cables and the cable losses
  • Inverter: Those same high Amps also increase heat and losses in the inverter
  • Even though my losses are 1kW against capacity, he was not surprised by this number

He suggested the following:

  • Add a 2nd Pylontech to provide more sustained load during the day and 'better balance the system'
  • Disconnect the panels from the inverter and connect them to a standalone MPPT charging the batteries ('newer technology and better performance')

I would be curious about your opinions on this 😀

Link to post
Share on other sites
21 hours ago, wolfandy said:

Cables: The MPPT in my older Axpert increase the Amps rather than the voltage, running more than 32A (I did see up to 36A on those days). This increases the temperature in the cables and the cable losses

Addition to my post above: The MPPT was running at 50A and 84V today while providing 2.3kW of PV

Link to post
Share on other sites
On 2019/12/15 at 9:22 AM, wolfandy said:

Cables: The MPPT in my older Axpert increase the Amps rather than the voltage, running more than 32A

That's fine, as long as the cables are thick enough to provide reasonable voltage drop. My system (5565 W nominal) can charge at over 90 A (into the battery; that's over 60 A of panel current; I run 2S panels).

The main effect of ambient temperature is on the voltage output of the panels. You can run a hose over the panels to get a brief boost in panel power. This isn't a practical thing, but can be useful as a one-off to convince yourself that the panels are producing near their rated power when closer to 25°C.

In extreme temperatures, it's possible that the Solar Charge Controller will throttle back its maximum charge power to avoid overheating, but I'd expect that to be quite rare.

Link to post
Share on other sites

@Jaco de Jongh - On a 6 panel 250W/panel system, I have seen over 1500W according to an Axpert. I have also seen over 100W on my small PWM controller while out on the dam from a single 100W rated panel (3.85 A @ 27.2VDC = 104.7W, I recorded it on my phone) while charging 2 x 100Ah batteries, one of the reasons I switched back to a 50W panel - they started bubbling (@under 4A they never should have, but understood that they are cheap/nasty batteries). I also understand that temp and distance/cable size will make a difference and reduce it overall before the normal household input - but in my experience it does/can happen - So my opinion stands, set your solar panels as close to possible as the max, but be careful of exceeding the max your invertor/mppt controller can take.

Link to post
Share on other sites
  • 3 weeks later...

Hi all

I thought I'd just post a brief update on my experience over the last couple of days/weeks:

I added a 2nd 3.5kWh Pylontech just before Xmas, which definitely has helped to optimise my PV production.

I have seen PV production higher than my 'panel capacity' (2.8kW) at more than 3.2kW - however only for very brief periods.

Most of the time it sits around 2.2kW - 2.4kW.

The other day I managed to run sufficient loads throughout the day that I fully maximized my PV production capacity (under basically ideal conditions). My Pylontechs never got to 100% SOC that day and I had the 'perfect' curve in my PV production chart. My system produced 18.5kWh that day but never really went above 2.4kW (except for brief spikes mentioned above).

Am still contemplating my installers recommendation of adding a Victron MPPT to replace the Axpert MPPT - but will open a different thread on that

Link to post
Share on other sites
On 2019/12/10 at 7:08 PM, wolfandy said:

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

 

Hi, quick question, how many hours backup did the 1 pylontech give you ?What load are you running on the axpert?

Link to post
Share on other sites
2 hours ago, Shockin said:

What load are you running on the axpert?

I basically have my whole house connected to the Axpert with the exception of heat pump, dish washer, washing machine, and tumble dryer

2 hours ago, Shockin said:

Hi, quick question, how many hours backup did the 1 pylontech give you ?

This obviously depends on what loads you are running. My baseload is around 400W-500W, so 1x Pylon was easily sufficient for our normal 2.5h of loadshedding. But if the kids are playing Playstation in the evening and the TV/sound system is running for longer, then even my 2x Pylons are not sufficient to get fully through the night without switching over to Eskom

Link to post
Share on other sites
6 minutes ago, wolfandy said:

I basically have my whole house connected to the Axpert with the exception of heat pump, dish washer, washing machine, and tumble dryer

This obviously depends on what loads you are running. My baseload is around 400W-500W, so 1x Pylon was easily sufficient for our normal 2.5h of loadshedding. But if the kids are playing Playstation in the evening and the TV/sound system is running for longer, then even my 2x Pylons are not sufficient to get fully through the night without switching over to Eskom

I have ordered the axpert 5kva with prewired db board, I am looking at using it for loadshedding only at present, we get cutoff for around 4 1/2 hrs at a time, my base load with fridge averages around 350w   just need my led lights , tv, wifi, decoder to run for that time

Link to post
Share on other sites
On 2019/12/11 at 6:13 AM, wolfandy said:

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: 
    Panel.jpg

Hi @wolfandy, sorry but I completey forgot to answer you. The question was if you could add more panels. In theory yes but you have to keep in mind that it should be the same or similar panels. Make a extra string of 3 panels and contact the string in parallel to the other strings. They stay in range of the inverter specs. You could even double your array to stay within 60A but  your inverter would continue clipping. (shaving of the peak) since it can only use 3000W max in total. Did you add something already?

Link to post
Share on other sites

Thanks @RikH

Quote

Did you add something already?

No, I have not added anything yet.

Latest thinking is to rather add an external Victron MPPT 250/85 and change the panel configuration to 2x 5S (with 1 extra panel). But as performance in our current summer will most likely not be significantly different to the Axpert-internal MPPT, I have parked any further tinkering with the system until the fall

Link to post
Share on other sites

Hi from reading all the responses to the topic and topic heading I personally would not add more panels in this setup for the following reason.

If you are using the panels only for load shedding it does not make sense only to utilize the extra panels just to charge batteries.

The power generated is waisted if not used when mains power is utilized if a change over switch is used.

If you use mains power through the Axpert 5K there will be continual switching between pv and mains power which is certainly not ideal.

I had a similar setup and changed to a grid tied inverter to seamlessly integrate the pv panels power. This only works if the max household consumption at any one time is less than the inverter capacity.

To get the most out of pv panels they need to be utilized otherwise it is just a waist of generated power and not much return on a good investment.

2.url

Link to post
Share on other sites

You can also utilize your pv power when you load exceeds your inverter capacity when mains is used with a grid tied inverter. You need to switch off or isolate the inverter output and allow the inverter to feed back to mains power  while using mains power by bypassing the inverter output if you are wired appropriately and if you are allowed to feed back to mains.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...