Is there any reactive power gained in pv systems ??

ahmedzein · July 11

If so what are the reasons and sources for generating reavtive since pv sytstem only output is active power? I have read also that some inverters produces reactive power to reduce the power factory .is that true?

mike95490 · July 12

Most inverters where I've seen a PF spec, is 1.0 as it's ideal output.

Loads are what bring things down, enough loads with poor PF, can drag an inverter down out of it's best efficiency range, and eventually cause a shutdown, even though loads are not at max, the poor PF throws things out of whack.

My small diesel generator with brushless alternator has a nameplate .99 PF, but in reality, my 1/2 hp well pump pushes it's ability right to the limit, any extra loading, and the pump protector circuit shuts the pump down from dirty power

BB. · July 12

Is the question Grid Tied or Off Grid inverters... GT, I addressed my thoughts in the other thread.

If off grid, the loads define the PF, not the inverter.

However, any generation source has its own output abilities. When the PF/load waveforms exceed the capabilities of the inverter (highly inductive, highly capacitive, non-linear wave forms, etc.), then the output of the AC power source will become distorted too--And this distortion also affects the loads too--Causing further distortions.

-Bill

ahmedzein · July 12

> @BB. said:
> Is the question Grid Tied or Off Grid inverters... GT, I addressed my thoughts in the other thread.
>
> If off grid, the loads define the PF, not the inverter.
>
> However, any generation source has its own output abilities. When the PF/load waveforms exceed the capabilities of the inverter (highly inductive, highly capacitive, non-linear wave forms, etc.), then the output of the AC power source will become distorted too--And this distortion also affects the loads too--Causing further distortions.
>
> -Bill
So what i understood that the power factor and the reactive power depend on the type of the grid itself? So that power factor of the off grid system depend on the loads not the inverter ,but for the grid ties system the powerfactor depend on the inverter ?
I hope i am right
Thanks in advance

Dave Angelini · July 12

BB. said:

Is the question Grid Tied or Off Grid inverters... GT, I addressed my thoughts in the other thread.

If off grid, the loads define the PF, not the inverter.

However, any generation source has its own output abilities. When the PF/load waveforms exceed the capabilities of the inverter (highly inductive, highly capacitive, non-linear wave forms, etc.), then the output of the AC power source will become distorted too--And this distortion also affects the loads too--Causing further distortions.

-Bill

The XW+ from Schneider has a screen where the power factor can be adjusted up or down 20% BTW. I have heard that the new offering from Outback this fall will have that also.

BB. · July 12

More or less yes... The Grid Tied Inverter (I believe Dave is talking about the GT configuration menu for a Hybrid AC inverter--One that does both GT and Off Grid depending on the needs of the user and what power may be available--I.e., emergency backup or pure off) can be programmed to "inject" sine wave current offset with respect to the Voltage Waveform from the utility... More or less the typical GT inverter is a "Current Mode or Current Source" power supply (injects current based on programming--PF=1.0 -- The current is a sinewave following the voltage sinewave. PF=0.80, the current is "typically" delayed by Cos^-1 (0.80=) 38 degrees... 90 degree delay would be PF=0.0).

Note that I am "ignoring" a whole class of Voltage source type generators (and inverters) that can be paralleled/connected to the grid. For example, the utility has many voltage source generators paralleled together and look very much like one giant genset. Backup genset at hospitals (for example) can also connect directly to the grid and feed energy "backwards" as a voltage source. A different animal than this present discussion. The differences between Voltage and Current sources is actually quite amazing from a circuit theory/electronics point of view. "We" normally work with voltage sources all day long (utility power, batteries, small power supplies, etc.). The concepts behind current sources is something that can be difficult to wrap your brain around without a lot of study.

For us, the only "current source" we normally deal with here are Solar Panels... They output (first approximation) a constant current based on the amount of sun they receive (output load/voltage from zero to Vmp volts--Above Vmp volts to Voc, the current falls to zero amps).

This thread goes into pretty good detail about Solar Panels as DC Current sources:

http://forum.solar-electric.com/discussion/5458/two-strings-in-parallel-with-unequal-string-voltages

Off Grid Inverters are "Voltage Sources" (like batteries). They (attempt) to generate a sinewave that goes from 0 volts to +170 volts peak to 0 volts to -170 volts peak to 0 volts (sinewave peak is equal to sqrt(2)*120 VRMS volts root mean square).

So, the ideal voltage source would output exactly the predicted sinewave voltage. And the loads (resistive, inductive, capacitive, non-linear) would "take the current" according to their "nature". (inductor delays taking the current, the capacitor takes the current as the voltage changes).

"The Grid" (utility power) is a pretty good approximation of a sinewave voltage source (utility generators and distribution systems) can supply a lot more power than the typical house can consume (without tripping breakers, melting wiring).

The Off Grid power systems are typically generators and inverters that are not much bigger than their loads--And so their design and physical limitations come into play. If the well pump starting current is higher than the current output of the inverter/genset, then the voltage waveform will collapse--And look like something else. Also, how much you pay for your energy source (genset/inverter) affects the "quality" of the AC output power.

A couple of years ago, @Mike95490 posted this link from a person that supports Hollywood's remote set power needs. It is weighted towards generators, but does a really good job of "explaining everything" regarding making your own 120/240 VAC power:

http://www.screenlightandgrip.com/html/emailnewsletter_generators.html

-Bill

Dave Angelini · July 12

No Bill

I am talking about the Inverter, no mater what the configuration. Here is mine below. I was told this was added for a very particular Military requirement. I think people mix up the power factor of the Charger and the power factor of the Inverter. The charger in the inverter charger is not adjustable. At least not yet....

Image: https://us.v-cdn.net/6024911/uploads/editor/tm/zmse9nr65xt9.png

BB. · July 12

I am not talking about the "battery charger" function either... I believe that this is configuration the Grid Tied function when the inverter is feeding energy back (utility interactive mode) to the utility (or larger genset).

In general, a sinewave output AC inverter cannot be programmed to have a particular Power Factor on its output--Other than as a limit (i.e., disconnect of PF is less than 0.50--Not that I have seen anyone do that).

The "ideal" Off Grid is an inverter and only can drive the output waveform (PSW/TSW or MSW, Square Wave, approximation of a Sine Wave, etc.). The current taken from the inverter is purely a function of the load(s) (motors, computer power supplies, lighting, etc.).lity

At least to me, the only way that programming the PF on an inverter is when it is in Grid Tied (Utility Interactive) Mode and feeding current (aka power) back into an AC Voltage Source (utility, large genset, another Off Grid inverter in "voltage source" mode--aka normal operation).

A typical home is (roughly, guessing) around -0.80 PF ... But individual loads can be down towards 0.8 to 0.6 (induction motors) to 0.50 or worse (cheap CFL lamps and other non-linear loads). So a setting for 1.0 to +/-0.80 (technically -0.80 PF is for inductive loads) does not make sense as a limit (shut down if not -0.80 PF?) to me.

It only makes sense for Grid Tied operation where you want the GT inverter to pickup some of the reactive load. The "standard" GT Inverters from times past (to near present?) only output PF=1.0 current (vs utility sine wave voltage waveform). And left the utility to supply the "reactive" power for "free" (standard home utility meter does not bill for reactive power).

Taken to extremes, that a utility could have their customers with nice/clean GT solar power systems with PF=1.0 supplying 100% of the billable loads (i.e., zero revenue to the utility) and yet they would still have to supply 20% to 50% or so of the reactive loads (current) with their generators.

I first saw this out of Germany (specifications) of a GT inverter with programmable PF output (SMA) a number of years ago. It makes sense because now the local home GT system would also supply the "average" reactive current too... And would off load the utility of having to provide reactive current (and larger wiring, transformers, switching, etc.) for something that they did not bill for.

Now--I could be wrong. Dave does this for a living, and I (apparently) do this for a hobby

. But that is how I see the issue(s).

-Bill

BB. · July 12

To bring this down to everyday experiences... Imagine a bicycle and you put a spring on the pedal and attach it to the frame. During part of the cycle you are stretching the spring (adding energy to the system). The other part of cycle the spring is pulling the pedal up[ through the rest of the cycle.

Another would be to add ankle weights. The weights slow your feet as you press down on the peddle and add their momentum as you get to the bottome of the cycle (gain/loss of stored energy), and do nothing at the bottom or the top of the cycle.

Sort of like how Capacitors and Inductors store and release energy.

In both cases, the storage and release of energy adds up to zero over the whole cycle. The "real" energy is what you pay for doing work. The "reactive" energy is this stored/released energy where the sum of work is ~ zero. The "apparent energy" is that portion where it is the "sum" of both real and reactive energy.

You (the utility, the inverter, the generator) has to be "strong enough" to support both the "real work" and this "temporary" store/release of energy. That is why it is not really "free" (poor power factor).

I think I got those terms correct--My weakness is English and technical terms....

-Bill

Dave Angelini · July 12

In General! All I am saying is the inverter in an XW+ can adjust its output power factor no matter if there is a utility or not like me!
I am the utility

Almost all of my loads (inverter heat pumps, toaster ovens, hot water for tea, hair dryers, etc) are pretty much 1.0. So we are not typical

When I turn on my 2 extra centrifugal fire pumps I get a power factor hit. At that point I could care less.

I get what you are saying also Bill, just saying.... Maybe the military has a need for this in an application where the XW+ is used. It was not on the old grey box XW, so this is new in the last few years. I do spend time with alot of power engineers and they do influence me,
like it or not. I always like your take!

In the old days that was all done by an electrician with discreet components (caps mostly) for commercial power. Also people tried to do this in residential for their air conditioning loads.

BB. · July 12

Dave, no problem... I am here to learn too.

I cannot think, off hand, of how one could program the AC output of an off grid inverter's PF. I guess it could be done if the XW does wave shaping on the AC voltage sinewave...

However if somebody has a need, this stuff can be done in electronics (programming) relatively easily.

-Bill

Dave Angelini · July 12

Bill, you program it by selecting the highlighted area below on one of the 11 screens. It is called the inverter screen.
Sorry, I just could not resist.... have a good day! Three hours until Happy Hour!

The XW+ is totally digital signal processed. There is not much that can't be added later or made ship shape in firmware. Very little hardware has been changed since the DoD funded the project and tested it in Livermore at Sandia or Lawrence. Can't remember which one. Circa 2004.

Is there any reactive power gained in pv systems ??

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