Hi there, I was wondering about the so called ‘factor 1.0’ rule. I understand the underlying idea that a Multiplus has to be able to process the maximum power coming from an AC-OUT coupled PV system. What I dont understand is the mathmatics behind it.
The usual claim is that a 3000VA Multi can handle 3000W of PV power, and that a 5000VA Multi can handle 5000W of PV power. But how is this calculated? The 3000VA has a charger that can only charge with 2016W (35A x 57,6V) and a 5000VA can only charge at 4032W (70A x 57,6V).
The 3000VA and 5000VA are multi-inverter ratings (DC to AC), but that is not what is used when converting power from an AC-coupled PV-inverter to a DC-coupled battery. It seems that looking at the multi-inverter ratings makes no sense, and if it does, why not look at the peak power of the inverter, that can be handled for aprox 1 minute?
So my question is: Where do the ‘max-PV-output’ ratings used for the ‘Factor 1 rule’ come from?
For AC coupled PV if the inverter is 5kVa then the expected backup AC load is 5kVa.
At most the AC PV should be sized to cover the expected max load. Your inverter cannot invert more than that.
What happens in scenarios such as sudden grid rejection and or causing the AC PV to cut out etc?
Then you have the opposite 8kva ac pv on the output feeding back, whrn the grid drops off? Who takes the hit? The inverter has to be able to sink the power somewhere or things will go pop and bang.
I understand the basics of the factor 1 rule, I just don’t get what the inverter in the MP has to do with it. The inverter does nothing in case of no grid power and an abundance of AC power. The charger in the MP has to covert al that AC power comming from the PV inverter to DC power to charge the battery.
So my question still remains: why do we need to look at the MP inverter (that coverts DC to AC) stats, when the MP charger (that coverts AC to DC) is doing all the work?
The inverter and the charger are the same, the multiplus uses a toroidal transformer and circuitry for both inverting and charging and can only do one of them at the time, either charging or inverting is 3000VA (3k mp2)
Because the sun doesn’t shine all the time, the power for the load will have to come from somewhere when it doesn’t
You unfortunately are only thinking if the oerfect run conditions. An engineer has to think about what happens when things aren’t going as expected.
It is why your car has brakes and a door has locks. And an oline platform has a login page. Things are never perfect.
Yes they are the same device, but inverting gives different specs than charging.
When you look at the datasheet, the inverter can deliver 3000VA (or 2400W) continue at 25degrees celcius. With a peak power of 5500W (for 1 minute. These are the stats for inverting power from DC to AC.
When looking at the charging stats they are a bit different. When charging in absorbtion mode, the charger can charge with 35A at 57.6V, which is aprox 2000W. This is the limit with which the multi 3000 can convert AC power to DC power.
So, lets say you have 3 x multi 3000, with 9000W of PV power coming in. You are on holiday, so no use from your home. Batteries are nearly full. In normal mode most of the 9000W will go to the grid. No problem so far.
Now the grid disconnects, PV is still producing 9000W. The three multis will each start charging, in best conditions this will use 6000W (3x2000W). Where is the other 3000W going?
its not 3000w of pv power that can be installed per multiplus its 3000wp of max solar power, that means you will never get 3000w from an ac inverter not even under best conditions
If there is too much pv power coming in from ac solar, than it will not be used, and the multi will throtthle down the ac inverter with freq, thats why ist important the ac inverter supports freq shift
Remember you can put more ac solar behind the multi if you want. But than it needs to be on ac out 2 and no more than the transfer relay can handle, ac out 2 will switch off if grid is lost
No, that is not correct. The Victron Factor 1 page clearly states (see below) that in case of oversized PV arrays you should take the Wp from the PV inverter. Lets say you take a Growat MIC 3000 PV converter, this converter can deliver 3000W on AC. When you have three of those you can get 9000W on AC. The 3 multi 3000VA cant handle this power.
So my question still remains, what is the theory behind the math of this Factor 1 rule. Why are we looking at the Multi Inverter specs, in stead of the Multi Charger specs?
2.4 Should you look at the total PV array, or the PV inverter rating?
The mentioned 3000 Wp and 8000 Wp is the Watt-peak which can be expected from the solar system. So for an oversized PV array, where the total Watt-peak installed PV panels exceeds the power of the PV Inverter, you take the Wp from the inverter. For example 7000 Wp of solar panels installed, with an 6000 Watt PV grid inverter, the figure to be used in the calculations is 6000 Wp.
And for an undersized PV array, where the total Wp of installed PV panels is less than the installed PV grid inverter, you use the Wp from the PV panels in your calculation.
Yes you are right about the oversizing and pv inverter wp, missed that part
but a growatt mic 3000 does not deliver 3000w, but 3000va thats about 2400w, so yes if you use a pv inverter with 3000w real capacity than its 9000w, so do we have to look for 3000w or 3000va pv ac inverter, that question is also
Your specific question remains unanswered from me better ask victron tech themself…
A 3kVa pv inerter will only produce 3kVa regardless of whether 6kw of pv is attached to it. (Maybe with a slight 5% over.) It is at the end of the day an inverter and can only invert its own power rating
Yes, but Victron is not speaking about an VA output of the PV inverter. The factor 1 rule states that a 3000VA Multi can handle 3000W of PV inverter output.
Then the documentation is wrong. And what about the 4k5 and 6k5? These dont have a VA rating, but a rating in Watt. Does this mean that a 6k5 can handle 6500W PV power? Does not comply with the charger specs, this can only charge with 5760W, where is the rest of the power gonna go?
This factor 1 rule is just a bit arbitrary in my opinion.
And can you explain to me why it has nothing to do with the charger? When there is an overload of AC power comming from PV, and grid is not available, then this can only be converted to DC power so it can flow to the batteries. It has no other place to go.
If the 1:1 rule states that a 3000VA can handle up to 3000Wp of PV inverter power, then that means that there can be a situation where PV is providing 3000W of power to AC, but the charger can only cover aprox 2000W. Until the moment frequency shifting has throttled down the PV inverter, where is the last 1000W going?
Mind you that Victron is stating that frequency shifting is not fast enough, that is why there is a 1:1 rule. If frequency shifting was quick enough, there would be no need for this rule, as a 6000W PV inverter can be throttled down just as good as a 3000W PV inverter.
If it was charging only it would already be throttled to what the charger can take.
If it was a dumb process, yes. It is a bit more involved that that though.
Problem - the ac PV takes the load off the inverter - inverter does not know there is a load. The processing centre does (GX) calculations and communication to and from then response and physical change all takes time.
A good efficient ratio of ac pv to inverter system is actually about 70 to 80% injection into ac loads and then battery charging saturated by DC PV.
System design is key. If you are expecting large load drop offs then change design accordingly.
This has nothing to do with expected large load drop offs. Neither can you expect any load on AC. This is a safety rule by Victron, a safetyrule is there for extreme situations, not for reguar expected situations. The rule by it self makes sense, the theory behind it as well. But if you really think about the numbers, it does not add up.
So again: What will happen when PV is delivering 3000W of power, and then grid fails? Where is the last 1000W going?
Or another Scenario: System is running in island mode (no grid), PV is delivering 3000W to AC and we have a load of lets say 4000W. What happens when load is shut off? Then in stead of delivering 1000W to the island grid, the charger has to take 3000W from PV. But it can only handle 2000W. What now?
18 posts in. Not sure what is unclear about the requirement. This seems fairly self-explanatory.
To understand the background, consider the following situation: the PV inverter is at full power, supplying a big load. The Multi is in inverter mode. Then, suddenly and at once, this load is switched off. At that moment the PV inverter will continue operating at full power until the AC frequency has been increased. Increasing this frequency will take a very short time, but during that time all power will be directed into the batteries as there is no other place for it to go. This causes the following:
When batteries are (nearly) full, the battery voltage will spike, possibly causing the Multi to switch off in DC over-voltage alarm.
The same spike will cause the AC output voltage of the Multi to spike, as these two are directly related, and when the spike on the battery voltage is high and fast enough, the Multi can never regulate its PWMs down fast enough to prevent the spike on AC. This spike can damage the PV inverter, the Multi and also any connected loads and other equipment.
Another problem is that the Multi starts charge current protection.
In the best case it might switch the grid inverter off immediately by setting the AC frequency to the disconnect frequency as configured in the assistant.
Again, what is unclear is why Victron creates a rule (the 1:1 rule) that uses the inverter-mode specs, for something that has absolutely nothing to do with these specs, as this situation is fully managed by de charger-mode specs.
It states that ‘all power will be directed into the batteries’. But how is the multy directing this power into the batteries if is is not capable of charging with the full load of de PV inverter?
As said before, the 3000VA multi can only charge with ~2000W, while the 1:1 rule clearly states that the 3000VA multi can handle 3000W of PV inverter power. During that short time (increasing this frequency will take a very short time), where is the other 1000W going?
I agree there is some word polishing that is needed here.
The chapter defines the limit as the amount of PV (Wp) that you have and that kWp should be mated to the kVA rating of the Victron system. This I can understand as actual generation from PV is below the laboratory-conditions rating they have.
It later contradicts this by saying it is absolutely fine to massively over-panel, which too makes sense as the generation limit is the PV inverter itself.
So they should both really be using kVA values, if you want to be pedantic and logical.
Still think this is somewhat implied by a 1 to 1 or factor 1 rule.
I will query this with the documentarian-in-chief.
