# Power factor effect on grid/ hybrid inverters

Solar Expert Posts: 35
Having experienced bad power factor figures using petrol/ diesel generators as result the generator labours heavily with a reactive load. With power factor correction the generator is more efficient. Now take the case of running a washing machine or an air conditioner what happens to the reactive current. The old disc meters and the new smart meters only record KW. In my mind the Grid gets the power for free. I have noticed that some hybrid battery inverters claim to handle reactive loads. So, what happens to the reactive power? Could an electrical engineer make some comments please?

• Solar Expert Posts: 3,741 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
phred01 wrote: »
Having experienced bad power factor figures using petrol/ diesel generators as result the generator labours heavily with a reactive load. With power factor correction the generator is more efficient. Now take the case of running a washing machine or an air conditioner what happens to the reactive current. The old disc meters and the new smart meters only record KW. In my mind the Grid gets the power for free. I have noticed that some hybrid battery inverters claim to handle reactive loads. So, what happens to the reactive power? Could an electrical engineer make some comments please?

An appliance with poor power factor (PF) uses only insignificantly more power than the same appliance with good PF. That's why the power company doesn't charge residential customers for low PF appliances.

However, the currents that are flowing in a poor PF circuit are higher than in a good PF circuit. This means that the wires, transformers, generators, inverters, etc need to be heavier. There will be slightly higher losses in the circuits of a poor PF appliance because higher currents means higher I2R losses, but these losses are generally insignificant.

You ask "what happens to the reactive power?". The answer is nothing... there is no reactive power... it's imaginary and can best be modeled with imaginary numbers.

One way to think about this is consider a motor with a PF of 0.6. If the motor draws 600 watts, that means the inverter (or generator) needs to be rated for 1000 watts. But only 600 watts is actually being used. If the "missing" 400 watts were real power, there would be 400 watts of heat being dissipated in the motor or the inverter. Your motor or inverter would be very hot!

When an inverter claims to handle reactive loads, that means it can handle the higher currents and current surges that occur in reactive loads.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
vtmaps wrote: »
When an inverter claims to handle reactive loads, that means it can handle the higher currents and current surges that occur in reactive loads.

--vtMaps
And hopefully that it can recover the power coming back in during the two portions of each cycle where the current is flowing in opposition to the output voltage. Not all output circuits can recover onto the DC bus the energy which went out for part of the cycle (real energy, being stored in the reactive load) and then came back in again later in each cycle.
SMA SB 3000, old BP panels.
• Solar Expert Posts: 3,741 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
inetdog wrote: »
And hopefully that it can recover the power coming back in during the two portions of each cycle where the current is flowing in opposition to the output voltage. Not all output circuits can recover onto the DC bus the energy which went out for part of the cycle (real energy, being stored in the reactive load) and then came back in again later in each cycle.

If the output circuit can't recover the real energy, then that energy is converted to heat. That would make for one very hot output circuit.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 891 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
vtmaps wrote: »
If the output circuit can't recover the real energy, then that energy is converted to heat.
Agreed, but in many low-PF circuits, there's no energy being transferred to the output stage. The current just circulates.
• Registered Users Posts: 1
Re: Power factor effect on grid/ hybrid inverters

Well here goes...putting my helmet on now.

The reactive power simply flows back and forth, and serves only to heat the components
it flows through. Poor power factors are a problem to electric utilities, since they require
larger wires and transformers to support this flow, but the utility cannot charge for it.
Utilities regularly penalize industrial users for poor power factors.

In the case of an inverter, I would think a poor power factor would result in inverter heat,
and perhaps push the inverter closer to rated load, without doing any useful power delivery.

In my case, since we have very poor utility service here, and the cost of utility power is
very high, I intend to integrate my battery inverter system with a power management system,
switch all high reactive power loads with the management system, and place tailored power
factor correction capacitors BEHIND the switching provided by the power management
system. Clearly there are reactive loads which this scheme could not be applied easily,
such as refrigerators.

OK...lemme have it !!

Regards to all.
• Banned Posts: 17,615 ✭✭✭
Re: Power factor effect on grid/ hybrid inverters

Welcome to the forum Steve.

You're pretty much spot on.

The issue which seems to have been ignored here is whether it is a GTI (hybrid or standard) feeding a circuit which is active to the grid, in which case its output is unaffected due to the electrical 'mass' of the grid, or a hybrid inverter operating in back-up mode in which case it takes the full hit of the PF problem. This is why inverter output is actually expressed as Volt Amps, even though the term Watts is used almost everywhere.
• Super Moderators, Administrators Posts: 33,567 admin
Re: Power factor effect on grid/ hybrid inverters
The reactive power simply flows back and forth, and serves only to heat the components
it flows through. Poor power factors are a problem to electric utilities, since they require larger wires and transformers to support this flow, but the utility cannot charge for it Utilities regularly penalize industrial users for poor power factors.

Pretty much true... However, utilities can charge for poor power factor, and do it all the time for (some?) larger commercial customers... Basically, if a customer averages 0.67 PF, the pricing is 1/0.67 * \$/kWH rate (as I recall). So, for large customers that have lots of induction motors (like oil refineries), they do put in (switched) capacitors to keep the PF much closer to 0.95 (lagging). There are reasons they don't go for 1.0 (or even "leading") PF, basically the capacitors+induction motors can generate large voltage spikes when the motors are power cycled (capacitor helps the slowing induction motor act like an alternator with no load).
In the case of an inverter, I would think a poor power factor would result in inverter heat,
and perhaps push the inverter closer to rated load, without doing any useful power delivery.

Yep--As Marc/Cariboocoot says, Inverters (and generators) are really rated for Peak VA (or kVA) loads--Not really peak KWatt loads (although, in some cases, and many commercial sized gensets, the kVA rating will be larger than the kWatt rating).
In my case, since we have very poor utility service here, and the cost of utility power is very high, I intend to integrate my battery inverter system with a power management system, switch all high reactive power loads with the management system, and place tailored power factor correction capacitors BEHIND the switching provided by the power management system.

That is the right way of doing it--You don't want a bunch of capacitors sitting on AC lines when the motors are turned off--It just pushes the phase problem to the "other side of 1.0 PF" (current lags with inductive loads, and leads with capacitive loads--Both are "bad" for utilities).
Clearly there are reactive loads which this scheme could not be applied easily, such as refrigerators.

In California (and probably most all utilities), the utilities install large capacitor banks out around their service area. And in California, they "turn on" the capacitor banks to "locally correct" bad power factors from water pumping and air conditioning use in the Central Valley.

A simple refrigerator is easy to "fix" the power factor with a capacitor (need to match capacitor size to motor size and PF error).

However, what cannot be "fixed" with capacitors are non-linear loads such as switching power supplies--Which are used in most consumer computers, electronic gadgets, and CFL/LED lighting. That power factor can be as bad as 0.5 PF--And the current wave form is not just "shifted" by the inductive (or capacitive) load--But a series of sharp current peaks near the voltage sine wave peaks.

For example, the cheap CFL (compact florescent lamps) that are being pushed by government may use 1/4 the electric power, but with a PF~0.5, they only use 1/2 the current (VA or kVA)--So, for residential customers, the utility gets 1/4 the price for the same light, but has to supply 1/2 the amount of current (VA).

Electric lighting a very significant load on the utility--And poor/uncorrectable power factor is a big issue. The poor PF CLF/LED use 2x the VA vs the Watt*Hours they consume. Leaving the utility with less money from customers to pay for infrastructure.

There are now laws that require larger loads to be power factor corrected. However, it did not (or does not?) apply to smaller loads like CFL/LED lighting, smaller computers/electronics, etc.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 9,583 ✭✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters

now I want to build a test fixture to plug all my LED bulbs into for the killwatt to test.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Super Moderators, Administrators Posts: 33,567 admin
Re: Power factor effect on grid/ hybrid inverters

I should add that for Grid Tied inverters, Power Factor of the loads/utility/etc. is a "don't care".

A standard, configured for defaults, GT Inverter simply outputs a sine wave current in proportion to the AC Sine Wave Voltage. This is a PF=1.0 situation. And as far as the GT inverter is concerned PF=1.0=VA*1.0=Watts is the most efficient method to operate.

However, some (a few, some, all?) newer GT inverters can be programmed for leading/lagging PF of as much 0.8 (as I recall). A utility may be very happy to have people put GT Inverters with leading PF of 0.8 turned on--This would help the GT inverter carry the poor PF loads, such as motors.

Of course, operating with PF=0.8 will cause more current to flow through the GT inverter and wiring--So the inverter + wiring would need be sized 1/0.8 x larger because of the PF adjustment.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 114 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters

Save your fixture building time Mike95.
The Kilowatt is not going to read it right.

There are two things that go wrong with AC distributions.
One is the power factor where the current gets out of phase with the voltage.
Every body seems to know about pf.
The second problem is so called "harmonic" loads.
They are called harmonic because they can be described by a Fourier series, hence the name harmonic.
These are not well understood.
In harmonic loads the current is not usually out of phase with the voltage.
Correction methods used for pf correction will not correct harmonic loads.
The largest producer of harmonics is rectifiers charging batteries or biased capacitors.
Examples are CFLs, Computer power supplies, VFDs and motor controllers.

BB
Your description reminded me many years ago when I had the responsibility of a city power distribution system.
We had a capacitor bank to reduce the pf lag and hence not be penalized for low pf.
It was switched in steps but we ended up leaving it all on all the time.
So most of the time our pf was leading.
Our power suppliers liked it this way and did not penalize us for a leading pf.
Most of their customers and their own transformers had lagging pf so we were helping them out.
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
Ken Marsh wrote: »
Save your fixture building time Mike95.
The Kilowatt is not going to read it right.
The type of low power factor which does not correspond to an overall phase shift between voltage and current is usually referred to as distortion power factor (because the current is not a clean sine wave, or even close to a sine wave) or, as you mentioned, harmonic power factor.
The effect on the power measurement is the same in that any device which integrates the product of the voltage and the current over the course of many samples within one cycle of the AC will be able to read the true power, and by also measuring the RMS voltage and RMS current can tell you what the overall power factor is.
As for the behavior of the Kill A Watt (TM) device, I have seen reports of it measuring the real power of LED or CFL loads correctly within 10% over a wide range of lighting equipment makers and models, as well as occasional reports of the KAW giving totally off the wall readings for some lamps.
YMMV, but for sure the KAW gives good results on both inductive and capacitive linear loads.

Mike, I would say it is probably worth the effort, but take the results with a grain of salt and check your model KAW by measuring some bulbs with published energy draw figures to see how well it is doing.
SMA SB 3000, old BP panels.
• Registered Users Posts: 1
Re: Power factor effect on grid/ hybrid inverters

I thought grid-tie just sampled the AC wave form and out the current to match ..Ie PF of 1.0 but it was programmed to lag ( or lead ) it put out a a known PF... It could be used for PF correction if programmed to do so,, but i don't think any are ~~~~

~~~So that does a Grid-Tie inverter putout for PF ... ~~it is an output device right ??

One more thing ~~

Is a Grid-Tie inverter a demand inverter (or may be a sinking inverter needs to have sinked ie the grid)~~~If there is no place to sink ( use the energy ) as in the grid where would the energy go back into the inverter... ~~~Demand type inverter = stand-a-lone
inverter only making power when needed ??~~how can you change them ??

BB. wrote: »
Pretty much true... However, utilities can charge for poor power factor, and do it all the time for (some?) larger commercial customers... Basically, if a customer averages 0.67 PF, the pricing is 1/0.67 * \$/kWH rate (as I recall). So, for large customers that have lots of induction motors (like oil refineries), they do put in (switched) capacitors to keep the PF much closer to 0.95 (lagging). There are reasons they don't go for 1.0 (or even "leading") PF, basically the capacitors+induction motors can generate large voltage spikes when the motors are power cycled (capacitor helps the slowing induction motor act like an alternator with no load).

Yep--As Marc/Cariboocoot says, Inverters (and generators) are really rated for Peak VA (or kVA) loads--Not really peak KWatt loads (although, in some cases, and many commercial sized gensets, the kVA rating will be larger than the kWatt rating).

That is the right way of doing it--You don't want a bunch of capacitors sitting on AC lines when the motors are turned off--It just pushes the phase problem to the "other side of 1.0 PF" (current lags with inductive loads, and leads with capacitive loads--Both are "bad" for utilities).

In California (and probably most all utilities), the utilities install large capacitor banks out around their service area. And in California, they "turn on" the capacitor banks to "locally correct" bad power factors from water pumping and air conditioning use in the Central Valley.

A simple refrigerator is easy to "fix" the power factor with a capacitor (need to match capacitor size to motor size and PF error).

However, what cannot be "fixed" with capacitors are non-linear loads such as switching power supplies--Which are used in most consumer computers, electronic gadgets, and CFL/LED lighting. That power factor can be as bad as 0.5 PF--And the current wave form is not just "shifted" by the inductive (or capacitive) load--But a series of sharp current peaks near the voltage sine wave peaks.

For example, the cheap CFL (compact florescent lamps) that are being pushed by government may use 1/4 the electric power, but with a PF~0.5, they only use 1/2 the current (VA or kVA)--So, for residential customers, the utility gets 1/4 the price for the same light, but has to supply 1/2 the amount of current (VA).

Electric lighting a very significant load on the utility--And poor/uncorrectable power factor is a big issue. The poor PF CLF/LED use 2x the VA vs the Watt*Hours they consume. Leaving the utility with less money from customers to pay for infrastructure.

There are now laws that require larger loads to be power factor corrected. However, it did not (or does not?) apply to smaller loads like CFL/LED lighting, smaller computers/electronics, etc.

-Bill
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
sparkskard wrote: »
I thought grid-tie just sampled the AC wave form and out the current to match ..Ie PF of 1.0 but it was programmed to lag ( or lead ) it put out a a known PF... It could be used for PF correction if programmed to do so,, but i don't think any are ~~~~

~~~So that does a Grid-Tie inverter putout for PF ... ~~it is an output device right ??

One more thing ~~

Is a Grid-Tie inverter a demand inverter (or may be a sinking inverter needs to have sinked ie the grid)~~~If there is no place to sink ( use the energy ) as in the grid where would the energy go back into the inverter... ~~~Demand type inverter = stand-a-lone
inverter only making power when needed ??~~how can you change them ??

A lot of questions.
1a. A GTI will put out power into the combination of loads and the grid with a PF as close to zero as its circuitry can get. Since it has no way of knowing what the load current is, it has no way to know to source/sink current out of phase with the voltage so that is can directly supply the current to that load. If you have a 2kW GTI output and a 2kW load which has a power factor of .5 and so is pulling 4kVA, then all of the reactive power will be supplied only by the grid while the real power is coming only from the GTI.
This puts a serious strain on the POCO facilities and is one of the interesting downsides of GTI power from the utility's point of view.
A stand alone inverter, on the other hand, knows exactly how much current the load it drawing at each point in the AC cycle, and it will (within its operating limits) deliver whatever power factor is needed to match the demands of the load.
1b. A GTI could be programmed to put out current at whatever power factor the designers wanted, but it would be a fixed or selectable phase angle, not one which reacts to the loads. I do not know of any GTI that allows you to set the PF. Possibly large commercial units?
2. The GTI will always produce as much output as the solar DC input will allow. Some GTIs like the SMA SunnyBoy are designed to accept feedback from a separate device (the SunnyIsland) to regulate their output based on the information (in the form of line frequency) that the SI supplies. This allows the SB/SI combination to be used off grid, unlike most GTIs.
3. The circuitry for off-grid and for grid tie is very different on the control and drive side, even though the power handling components are very similar. There is no practical way to convert one to the other unless the unit was designed to do both, as some hybrid inverters (like some Xantrex models) are.
SMA SB 3000, old BP panels.
• Super Moderators, Administrators Posts: 33,567 admin
Re: Power factor effect on grid/ hybrid inverters

Here is a large SMA system (~500-900 kVW) 3 phase GTI system:

http://www.sma.de/en/products/solarinverters/sunny-central-500cp-us-630cp-us-720cp-us-750cp-us-800cp-us.html

Here is a tech paper about some of the reactive power capabilities of the system:

http://files.sma.de/dl/18858/Q-at-Night-TI-en-11.pdf

Only 9 pages, but not a quick read. Some basic information in the first sections about power factor.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
BB. wrote: »
Here is a large SMA system (~500-900 kVW) 3 phase GTI system:

http://www.sma.de/en/products/solarinverters/sunny-central-500cp-us-630cp-us-720cp-us-750cp-us-800cp-us.html

Here is a tech paper about some of the reactive power capabilities of the system:

http://files.sma.de/dl/18858/Q-at-Night-TI-en-11.pdf

Only 9 pages, but not a quick read. Some basic information in the first sections about power factor.

-Bill
Now that is impressive! If I am understanding it correctly, the inverters can, without any solar panel input, operating just on the utility connection, "borrow" current in phase with the line voltage to source current out of phase with the voltage to help the utility deal with high reactive loads.
But, as I stressed, any production of reactive power by the inverter depends on outside input (either active control or setup) to tell it what to do.
SMA SB 3000, old BP panels.
• Super Moderators, Administrators Posts: 33,567 admin
Re: Power factor effect on grid/ hybrid inverters

That is how I read it... Seems like capacitors may be cheaper to run (and repair) vs cycling the GTI system.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Power factor effect on grid/ hybrid inverters
BB. wrote: »
That is how I read it... Seems like capacitors may be cheaper to run (and repair) vs cycling the GTI system.

-Bill
Especially since without incoming DC the GTI system will have to use capacitors for DC storage to make the desired reactive power transfer happen. What it really is, to some degree, is an infinitely variable capacitor bank (with a maximum size of course) that can be switched in and out smoothly without annoying transients.
The paper only mentions (I think) phase shifted reactive power, but with the right software this technique could also cancel out third harmonic currents and other results of non-linear loads. No capacitor bank can do that.
SMA SB 3000, old BP panels.