I was recently informed by a supplier that I couldn't use 605 watt solar panels with the Sunsynk 5kVa.

(I'm familiar with max. solar input voltage, series solar panel connection, Voc and the increase in Voc that cold weather and no load can cause).

So I sent a few messages to Sunsynk support .

Below are some of the responses that I received:

"As stated in the technical specification you cannot exceed 13A on the mppts"

"You cannot use panels that exceed 13A voc as this will damage the Inverter and void the warranty"

"you cannot use panels that exceed 13A voc"

"This is because if a fault was to occur that caused the panels to reach the Isc, if the Isc is higher than the MPPT rating over current damage can be caused to the inverter"

I was then told that the issue had been resolved and the "ticket" had been closed.

So I had a little rant and sent them the following:

Quote "

The whole point of a MPPT is to keep the solar array performing at its most efficient.

This sweet spot of maximum efficiency is as close to the solar panel Imp and Vmp as possible

The MPPT does this by controlling the amount of power available to its load (the MPPT's load).

The MPPT does not "know" what solar panels are connected to it and it doesn't "care", as long as the voltage is above the start-up voltage and below the maximum input voltage.

NB. 

The MPPT in an inverter system is NOT connected directly to any external load, - the loads that your MPPT is connected to are your battery charge system and the actual inverter DC input.

 

The reason a sophisticated maximum power point tracking system is needed for solar applications, is that the amount of energy that a solar panel receives from our sun is constantly changing (time of year, time of day, temperature and changing atmospheric conditions ie.clouds & pollution).

and

Ever changing load requirements of the inverter system (effectively R in the equation V=IR).

 

So for example, if the output of the MPPT was connected directly to a pure resistive load (let's ignore inductive or capacitive loads for simplicity).

This would be your R, or pure electrical resistance.

Let's say that the solar panel Imp is 10 amps and the Vmp is 50 volts.

The MPPT will adjust its own resistance "seen" by the solar array to about 500 ohms(V=IR=10x50).

 

The MPPT adjusts its own effective input impedance to keep the solar array voltage and current as close to Vmp and Imp as possible.

(impedance because your MPPT is using high frequency switching to keep the panels at Vmp & Imp as well as to control and limit current to load).

But now if for some reason the load increases as a result of the load resistance decreasing. 

The MPPT is going to try to keep the solar array as close to its Maximum Power Point.

The MPPT does this by limiting the amount of current to the pure resistive load, if it is unable to do this then it's not a MPPT or it's broken

 

If the Sunsynk MPPT can't limit its output current then there are some serious hardware design flaws or firmware stupidity.

I find the possibility of either of those very unlikely. " - end quote

 

I would be very grateful for some "perspective" from other forum members.

If I'm misunderstanding things or I'm just plain wrong then please feel free to tell me.

24 minutes ago, Mitmat said:

I was recently informed by a supplier that I couldn't use 605 watt solar panels with the Sunsynk 5kVa.

(I'm familiar with max. solar input voltage, series solar panel connection, Voc and the increase in Voc that cold weather and no load can cause).

So I sent a few messages to Sunsynk support .

Below are some of the responses that I received:

"As stated in the technical specification you cannot exceed 13A on the mppts"

"You cannot use panels that exceed 13A voc as this will damage the Inverter and void the warranty"

"you cannot use panels that exceed 13A voc"

"This is because if a fault was to occur that caused the panels to reach the Isc, if the Isc is higher than the MPPT rating over current damage can be caused to the inverter"

I was then told that the issue had been resolved and the "ticket" had been closed.

So I had a little rant and sent them the following:

Quote "

The whole point of a MPPT is to keep the solar array performing at its most efficient.

This sweet spot of maximum efficiency is as close to the solar panel Imp and Vmp as possible

The MPPT does this by controlling the amount of power available to its load (the MPPT's load).

The MPPT does not "know" what solar panels are connected to it and it doesn't "care", as long as the voltage is above the start-up voltage and below the maximum input voltage.

NB. 

The MPPT in an inverter system is NOT connected directly to any external load, - the loads that your MPPT is connected to are your battery charge system and the actual inverter DC input.

 

The reason a sophisticated maximum power point tracking system is needed for solar applications, is that the amount of energy that a solar panel receives from our sun is constantly changing (time of year, time of day, temperature and changing atmospheric conditions ie.clouds & pollution).

and

Ever changing load requirements of the inverter system (effectively R in the equation V=IR).

 

So for example, if the output of the MPPT was connected directly to a pure resistive load (let's ignore inductive or capacitive loads for simplicity).

This would be your R, or pure electrical resistance.

Let's say that the solar panel Imp is 10 amps and the Vmp is 50 volts.

The MPPT will adjust its own resistance "seen" by the solar array to about 500 ohms(V=IR=10x50).

 

The MPPT adjusts its own effective input impedance to keep the solar array voltage and current as close to Vmp and Imp as possible.

(impedance because your MPPT is using high frequency switching to keep the panels at Vmp & Imp as well as to control and limit current to load).

But now if for some reason the load increases as a result of the load resistance decreasing. 

The MPPT is going to try to keep the solar array as close to its Maximum Power Point.

The MPPT does this by limiting the amount of current to the pure resistive load, if it is unable to do this then it's not a MPPT or it's broken

 

If the Sunsynk MPPT can't limit its output current then there are some serious hardware design flaws or firmware stupidity.

I find the possibility of either of those very unlikely. " - end quote

 

I would be very grateful for some "perspective" from other forum members.

If I'm misunderstanding things or I'm just plain wrong then please feel free to tell me.

With the MPPT rated at 13A one would not use panels with a higher than 13A Imp. The inverter should clip current higher than 13A but perhaps not ideal to use panels with a higher than 13A current. 

Thanks Scorp007, - that's what the Sunsynk support guys in Randburg JHB are saying but no one can say why.

Would you not agree that you cannot try to "force" current into a MPPT (or any other appliance for that matter) without increasing the voltage of the current source?

1 hour ago, Mitmat said:

Thanks Scorp007, - that's what the Sunsynk support guys in Randburg JHB are saying but no one can say why.

Would you not agree that you cannot try to "force" current into a MPPT (or any other appliance for that matter) without increasing the voltage of the current source?

In theory I agree but once we get above the starting level of the MPPT even a 150V made up of say 10 parallel string could in theory supply more current than say 5x50V=250V panels at a much lower voltage. The impedance of the MPPT based on the maximum power point as well as the level at which the MPPT throttles will determine what current can flow as well as the actual source being the panels.

Theory only holds if it is a fixed resistance. A MPPT is not a fixed resistance module.

Here are a number of guys who have shown how their Sunsynk / Deye throttles once the maximum is reached with damaging the MPPT. Some inverters like my Solis would switch off if the current from the panels are much higher than the maximum allowed. As an example trying to put 18A instead of the maximum of 13A would cause it to turn off - a great feature.

Edited October 8, 20241 yr by Scorp007

Generally speaking, I agree with Scorp007.

Just for the sake of correctness, 2 comment:

"You cannot use panels that exceed 13A voc as this will damage the Inverter and void the warranty"

"you cannot use panels that exceed 13A voc"

 

At OC, current is 0 amp. If circuit is open no current flows. They should refer to Isc, not Voc.

 

The MPPT will adjust its own resistance "seen" by the solar array to about 500 ohms(V=IR=10x50).

 

Review the formula: For V=50 and I=10 then V=I*R  ->  50=10*R -> R=50/10 = 5 ohm

Edited October 10, 20241 yr by Mauritius B

Thanks Mauritius, yes you're quite correct, - should be V/I to get the 5 ohms.

The replies from Sunsynk in Johannesburg were mostly nonsense and seemed to lack depth of knowledge (unlike my own attention to detail regarding the highly complex Ohm's law 🤣).

Would you not agree with the following:

An MPPT by design will limit current to its load to keep the solar array as close to Vmp/Imp as possible?

"Over panelling" Is a common practice that allows for better solar performance early in the day, late in the day and during overcast weather (as long as you don't get close to or exceed the inverter maximum input voltage)?

Saying that you cannot use solar panels that are able to deliver more than 13 Amps is a bit like saying that you can't use a 500kVa generator to power a clock radio?

 

 

 

 

 

 

Give these a read and listen to what Keith says , it's in quite a few threads on the forum. 👍

 

 

38 minutes ago, Mitmat said:

Thanks Mauritius, yes you're quite correct, - should be V/I to get the 5 ohms.

The replies from Sunsynk in Johannesburg were mostly nonsense and seemed to lack depth of knowledge (unlike my own attention to detail regarding the highly complex Ohm's law 🤣).

Would you not agree with the following:

An MPPT by design will limit current to its load to keep the solar array as close to Vmp/Imp as possible?

"Over panelling" Is a common practice that allows for better solar performance early in the day, late in the day and during overcast weather (as long as you don't get close to or exceed the inverter maximum input voltage)?

Saying that you cannot use solar panels that are able to deliver more than 13 Amps is a bit like saying that you can't use a 500kVa generator to power a clock radio?

 

 

 

Over panelling is quite common but maximum input voltage must never be exceeded. Many inverters can clip input current when it reaches maximum level but overvoltage will damage the mppt for sure. This is a red line that must not be crossed.

I cannot be sure if your inverter can limit input current so, unless someone else has tested it and verified it, I would be cautious.

Edited October 11, 20241 yr by Mauritius B

Get an email from Sunsynk/DEYE confirming that they are ok with the configuration would be my recommendation. 

On 2024/10/08 at 7:38 PM, Mitmat said:

I would be very grateful for some "perspective" from other forum members.

If I'm misunderstanding things or I'm just plain wrong then please feel free to tell me.

In an ideal world, your rant might be correct.  But you are ignoring a number of real world practicalities.

Solar input is variable. In cloudy+windy conditions, you can get very sudden Isc changes from 0 to 130% (or sometimes more) of rated Isc.

Also, where is the MPPT point?  With partial shading, it could be just about anywhere within the parameter space, and sampling algorithms can go to very high duty cycles at times.

So, the MPPT needs to be able to reliably withstand a sudden current increase from almost 0A to Isc x 1.3, even while the PWM is operating at high duty cycles.  This maximum withstand current will be determined by the transistor rating, inductor size (current ramp rate) and current sense feedback speed.

So, in order to guarantee reliable operation, MPPT manufacturers must either heavily over-design the hardware (expensive), or set input current limits.

Generally max input Isc will be quite a bit higher than max continuous input current (because you really don't do an MPPT scan _that_ close to 100% duty cycle).

Newer Sunsynk spec sheets reflect this:

But I don't know if that higher Isc rating is related to hardware/software revisions, or generally applicable to all 5kW inverters.

Even then, 17A is still lower than Isc of 605W panels, so if you do go there, don't expect any warranties to be honoured.

 

1 hour ago, JustinSchoeman said:

But I don't know if that higher Isc rating is related to hardware/software revisions, or generally applicable to all 5kW inverters.

Even then, 17A is still lower than Isc of 605W panels, so if you do go there, don't expect any warranties to be honoured.

 

I think it would be interesting to ask Sunsynk/DEYE what the size panels /max Isc (Short Circuit Current) is that they will cover under the warranty on the 5kw inverters 

My first observation is that the MPPT is actually a DC-DC converter with a 50V output, with an algorithm to adjust the input current to extract the maximum power from the panels.
I have also been wrestling with ignorance. The MPPT is designed to only draw the maximum power it is designed for and throttle back once the battery SOC reaches the specified level. Just keep the Voc below the spec taking into account the possibility of extremely cold weather which would cause a rise in Voc.
I take the point that sudden changes in solar voltage could cause a problem, but the device should be spec'd to take changes.

The spec that puzzled me for a while was the inclusion of Isc. If the MPPT controls the current, so what is the reason for including it?
Here is the answer. If the MPPT input polarity is reversed, the MPPT creates a short circuit to protect itself. However if the Isc available exceeds the design, the input circuitry will overheat and destroy the device. The moral of the story is, don't swap the DC cables of a multi-string array.

On 2024/10/08 at 7:38 PM, Mitmat said:

I was recently informed by a supplier that I couldn't use 605 watt solar panels with the Sunsynk 5kVa.

(I'm familiar with max. solar input voltage, series solar panel connection, Voc and the increase in Voc that cold weather and no load can cause).

So I sent a few messages to Sunsynk support .

Below are some of the responses that I received:

"As stated in the technical specification you cannot exceed 13A on the mppts"

"You cannot use panels that exceed 13A voc as this will damage the Inverter and void the warranty"

"you cannot use panels that exceed 13A voc"

"This is because if a fault was to occur that caused the panels to reach the Isc, if the Isc is higher than the MPPT rating over current damage can be caused to the inverter"

I was then told that the issue had been resolved and the "ticket" had been closed.

So I had a little rant and sent them the following:

Quote "

The whole point of a MPPT is to keep the solar array performing at its most efficient.

This sweet spot of maximum efficiency is as close to the solar panel Imp and Vmp as possible

The MPPT does this by controlling the amount of power available to its load (the MPPT's load).

The MPPT does not "know" what solar panels are connected to it and it doesn't "care", as long as the voltage is above the start-up voltage and below the maximum input voltage.

NB. 

The MPPT in an inverter system is NOT connected directly to any external load, - the loads that your MPPT is connected to are your battery charge system and the actual inverter DC input.

 

The reason a sophisticated maximum power point tracking system is needed for solar applications, is that the amount of energy that a solar panel receives from our sun is constantly changing (time of year, time of day, temperature and changing atmospheric conditions ie.clouds & pollution).

and

Ever changing load requirements of the inverter system (effectively R in the equation V=IR).

 

So for example, if the output of the MPPT was connected directly to a pure resistive load (let's ignore inductive or capacitive loads for simplicity).

This would be your R, or pure electrical resistance.

Let's say that the solar panel Imp is 10 amps and the Vmp is 50 volts.

The MPPT will adjust its own resistance "seen" by the solar array to about 500 ohms(V=IR=10x50).

 

The MPPT adjusts its own effective input impedance to keep the solar array voltage and current as close to Vmp and Imp as possible.

(impedance because your MPPT is using high frequency switching to keep the panels at Vmp & Imp as well as to control and limit current to load).

But now if for some reason the load increases as a result of the load resistance decreasing. 

The MPPT is going to try to keep the solar array as close to its Maximum Power Point.

The MPPT does this by limiting the amount of current to the pure resistive load, if it is unable to do this then it's not a MPPT or it's broken

 

If the Sunsynk MPPT can't limit its output current then there are some serious hardware design flaws or firmware stupidity.

I find the possibility of either of those very unlikely. " - end quote

 

I would be very grateful for some "perspective" from other forum members.

If I'm misunderstanding things or I'm just plain wrong then please feel free to tell me.

 

14 hours ago, IanO said:

My first observation is that the MPPT is actually a DC-DC converter with a 50V output

Not quite - it's output is the DC bus voltage, which should be around 330V (the exact voltage depends on your AC voltage and some other factors). Apart from that, it's under software control, meaning that the response time is limited. So there exists the possibility that the current might overshoot the capability of the hardware - possibly saturating the inductor and killing the IGBT before the software even knows about it - that is why there is a Isc limit.

After all that, I'm still curious as to why there's this desire to fit a panel with 17A Imp on an inverter that is rated for 13A. It just seems like a waste of money and roof space because of 25% of the panel's rated capacity that can never be used.

Latest specs from DEYE on the 5kw shows: 

Max. Input Short-Circuit Current (A) of 17A

Max. Operating PV Input Current (A) of 13A

Would get confirmation from Sunsynk that they are happy with an ISC of up to 17A. 

19 minutes ago, GreenFields said:

After all that, I'm still curious as to why there's this desire to fit a panel with 17A Imp on an inverter that is rated for 13A. It just seems like a waste of money and roof space because of 25% of the panel's rated capacity that can never be used.

Hi @GreenFields

I think that there are two reasons why it just makes sense to install the bigger panels if you can. 

1. On overcast days when production is not at the max, you will be getting 25% more power with the bigger panels. 

2. The Wattage of the panels is not proportional to price, there is such a small price difference between the lower/higher wattage panels that it just makes sense in most cases to just get the larger ones. 

I agree that if space is very limited then you may need to look at smaller panels but unless you live in a garden shed 🙂  is not usually that much of an issue though. 

50 minutes ago, Sc00bs said:

Hi @GreenFields

I think that there are two reasons why it just makes sense to install the bigger panels if you can. 

1. On overcast days when production is not at the max, you will be getting 25% more power with the bigger panels. 

2. The Wattage of the panels is not proportional to price, there is such a small price difference between the lower/higher wattage panels that it just makes sense in most cases to just get the larger ones. 

I agree that if space is very limited then you may need to look at smaller panels but unless you live in a garden shed 🙂  is not usually that much of an issue though. 

Fair points but I still don't see compelling reasons to opt for the 605W panel.

I'm just comparing two panels now from the Powerforum site, as of today:

A: Canadian Solar 605W Super High Power Mono PERC HiKU7 with EVO2 at R1897.50 Incl. VAT

B: Canadian Solar 555W Super High Power Mono Perc HiKu6 with MC-4 EVO2 and New-Frame Length at R1674.40 Incl VAT.

 

To be fair there are other brands and other versions of Canadian Solar panels to consider, but in this case I can't see the 605W panel being better, for the following reasons.

1. To cater for overcast days you can over-panel the 5kW inverter with for example 5 or 6x555W per MPPT, and then the inverter will cap AC output to 5kW and DC to 6.5kW. With the 605W panel you just don't fall as neatly and symmetrically into a configuration near to the inverter's rated parameters, leading to possibly more wastage.

2. The price per Watt is lower on the 555W panel than on the 605W panel. This might not always be the case, but it is today.

3. As I said, on sunny days at mid-day the 605W panel should be capped to around 460W output per panel because you can never reach Imp.

4. With say 5 or 6 of the 605W panels, your operating Voltage is on the lower end of the inverter's optimum range. Not impossible to run, but possibly less efficient, especially on cloudy days. 41.5Voc and 35.1Vmp at STC.

5. The Isc of the panel being above the inverter's rated maximum Isc, as said above by others.

The bottom line, maybe someone will do it with the 605W, and maybe it will sort of work okay and wastefully and with risk, but there are better-suited panel options for the 5kW Deye that are more of a no-brainer to me.

2 hours ago, P1000 said:

Not quite - it's output is the DC bus voltage, which should be around 330V (the exact voltage depends on your AC voltage and some other factors). Apart from that, it's under software control, meaning that the response time is limited. So there exists the possibility that the current might overshoot the capability of the hardware - possibly saturating the inductor and killing the IGBT before the software even knows about it - that is why there is a Isc limit.

 I was referring to the MPPT which is DC coupled at 50V as in the hybrid inverter such as Sunsynk and Deye. The same with Victron system.

3 hours ago, IanO said:

I was referring to the MPPT which is DC coupled at 50V as in the hybrid inverter such as Sunsynk and Deye.

Me too. The MPPT in the Sunsynk/deye goes to the HV DC Bus. There is another isolated DC/DC bridge (bidirectional) that couples the battery to the HV DC bus. It's not the same as with the low frequency Victron solution (although the new RS is probably a similar topology).

@GreenFields The new DEYE 5kw will handle much higher amperages so it will no longer be an issue

I think that we will see the price for panels probably staying at around R1500 but the Watt size of the panels increasing as they become bifacial 

Would be looking for panels with a 55V VOC as the ISC Amperages they give obviously less. 

Have seen 675W Panels with a max amps of 13.95 @ 55.67V 

 

 

The mppt wil not attempt to load the PVs if batteries are full and there is no/low AC load, then on bright day,Voc can be approached by PV strings if Voc spec of inv. is too low.