Inverter PF

Status
Not open for further replies.
B

BR549

Member
Location
Boise
I'm looking at grid-interactive micro-inverters for PV applications; these are grid-tied inverters of about 200W that generate power from a PV panel. Specifically I was look at this datasheet: http://www.petrasolar.com/downloads/SunWave-AC-Module.pdf . What caught my eye is that it specifically lists both max Watts and max VARs, yet shows a power factor of >0.99. I haven't seen VARs listed on micro-inverter data sheets previously. This generated the following hypothetical question:

Assume the inverter operates in two modes: 1) near unity PF and max watts (VA=Watts), OR, 2) near zero PF and max VARs (VA=VARs). I think there wouldn?t be a demand penalty since VA doesn?t exceed Watts or VARs. Is this kind of behavior by a device OK from a utility perspective?

Thanks for comments.
 
impedance matching

impedance matching

I'm guessing the only way you could provide 100% VARs is if you attached half a pallet of accessory filter capacitors to the output circuit. Then you would have an impedance mismatch and VAR flow from your cap bank out to the utility.

The inverter natively probably wants to run at .99 pf and any VAR flow will likely be determined by how far the utility is from .99 pf. Not determined by the inverter, look at the micro inverter output filter section, if any, for the size of the capacitors. Any VAR flow capacity will likely not come from its IGBT's, it will come from the filter section caps, which are probably undersized. The inverter natively probably lacks capacity to to deliver VARs, it will deliver kW (.2 kW) if the utility pf is good.
 
Variable/Selectable VARs

Variable/Selectable VARs

__dan

Take a look at this one: http://www.xetenergy.com/solar/solutions/xpx.php The data sheet under product info (their website is somewhat broken so it may not load) shows a variable PF output of -0.64 to 1.0. Apparently they have a way that the user can specify the PF that the inverter operates at. Can't get their white paper up though.
 
BR549 said:
I'm looking at grid-interactive micro-inverters for PV applications; these are grid-tied inverters of about 200W that generate power from a PV panel. Specifically I was look at this datasheet: http://www.petrasolar.com/downloads/SunWave-AC-Module.pdf . What caught my eye is that it specifically lists both max Watts and max VARs, yet shows a power factor of >0.99. I haven't seen VARs listed on micro-inverter data sheets previously. This generated the following hypothetical question:

Assume the inverter operates in two modes: 1) near unity PF and max watts (VA=Watts), OR, 2) near zero PF and max VARs (VA=VARs). I think there wouldn?t be a demand penalty since VA doesn?t exceed Watts or VARs. Is this kind of behavior by a device OK from a utility perspective?

Thanks for comments.
Click to expand...

speaking from a utility perspective (I am from a utility), devices that use high pf is most welcome. residential consumers normally have low pf but they are not penalized as their kW demand is not that significant. large customers are penalized for having low pf and are provided discounts if they have high pf. so customers normally invest in high pf devices to avail of utility discounts

the first one (petrasolar) is correct, the pf of the panel is rated at >0.99. the other page didnt load for me but I would suspect that the thingamajig can correct pf as low as 0.64. which can be done by adding pf correction capacitors.
 
VAR's don't seem to be the issue. Load pf will probably have to be good and the units are rated for how much bad pf they can tolerate.

From the literature it looks like voltage matching is the issue. They are saying they can scavenge power from panels that are at a relatively lower voltage. There are lots of interesting things they could be doing in that regard but it's impossible to tell if they have great engineering or great marketing.

I will say that there's a lot of advanced and changing technology in power supplies, it's not a boring area. My fear would be that the small units, if they are built cheap to sell, that may not be an advantage over one large unit taking the aggregate on the DC side.

Really, the units need third party benckmark performance load testing with competitors to get an idea of what is saleable and what performs better.
 
BR549 said:
I'm looking at grid-interactive micro-inverters for PV applications; these are grid-tied inverters of about 200W that generate power from a PV panel. Specifically I was look at this datasheet: http://www.petrasolar.com/downloads/SunWave-AC-Module.pdf . What caught my eye is that it specifically lists both max Watts and max VARs, yet shows a power factor of >0.99. I haven't seen VARs listed on micro-inverter data sheets previously. This generated the following hypothetical question:

Assume the inverter operates in two modes: 1) near unity PF and max watts (VA=Watts), OR, 2) near zero PF and max VARs (VA=VARs). I think there wouldn?t be a demand penalty since VA doesn?t exceed Watts or VARs. Is this kind of behavior by a device OK from a utility perspective?

Thanks for comments.
Click to expand...

Such a very amazing link!
Thanks you for the post.

__________________
watch free movies online
 
BR549 said:
I'm looking at grid-interactive micro-inverters for PV applications; these are grid-tied inverters of about 200W that generate power from a PV panel. Specifically I was look at this datasheet: http://www.petrasolar.com/downloads/SunWave-AC-Module.pdf . What caught my eye is that it specifically lists both max Watts and max VARs, yet shows a power factor of >0.99. I haven't seen VARs listed on micro-inverter data sheets previously. This generated the following hypothetical question:

Assume the inverter operates in two modes: 1) near unity PF and max watts (VA=Watts), OR, 2) near zero PF and max VARs (VA=VARs). I think there wouldn?t be a demand penalty since VA doesn?t exceed Watts or VARs. Is this kind of behavior by a device OK from a utility perspective?

Thanks for comments.
Click to expand...

BR-
I think a better model is to look at the inverter as a generator. It really does not have a power factor, it just reacts to the load. The utility line does not have a power factor either. It just looks like a voltage source.

A grid tied inverter would never have to supply or take vars. So, the idea of a var penalty would never apply.

There is a note in the link that says, "Capable of sourcing reactive power". I suspect this means one of two things:
1. The inverter has a mode capable of running independent of the grid and can supply vars to an inductive load.

2. The inverter can be programmed to output vars to the grid. I am out of my area on this. However, it should be able to do this by changing the firing angle on the output thyristors.

Perhaps the mfg has an application guide.

W
 
I might be able to help you out here. In the last 4 years or so, I have designed quite a few off-grid systems and several grid-tied systems for commercial users (telco).

I have not used Petrasolar micro inverters, but I have used quite a few Enphase ones. All they are telling you in the spec is they will work all the way down from unity to .64

Grid interactive inverters are strange beast. They are current sources that lag or follow the utlity.
 
Last edited:
Status
Not open for further replies.
Top