Trick enphase into working off-grid as well?

lairdreed

I am about to get approval to put 3kw up on the roof of my house in VA but will have some shading issues on one of the strings so would like to go the micro-inverter route.

Live in countryside so also need batt backup a few times a year

Have seen lots of chatter around the web about trying to trick enphase into working off grid. Is such a thing possible with the right combination of hardware?

Thanks,

Laird

Cariboocoot

Re: Trick enphase into working off-grid as well?

Yes, but no.
Yes as in some people have managed to use a pure sine wave off-grid inverter or generator to "trick" a grid-tie inverter into synch and use the power.
No as in its not meant to work that way and may not work if things aren't just right so you end up with no power and/or fried equipment.
Since you have to have some other source of power to begin with, it's probably not worth the trouble/risk just to add the potential for extra Watts. Others may have a different opinion on this.

The Sunny Boy inverter system has the famous (and expensive) Sunny Island which is designed to work with their grid-tie inverters and convert them into a usable off-grid/emergency back-up system. I'm not sure it works with the really small (700 Watt) units they make.

The other choice is the hybrid inverters like the Xantrex XW series. This is not a microinverter, so would not help with your shading issues.

XRinger

Re: Trick enphase into working off-grid as well?

The trick has been done on low end Chinese GTIs..

http://www.youtube.com/watch?v=R9uK_mDFzmM&feature=mfu_in_order&list=UL

I've tried to trick a 1200w PowerJack using a 400w sinewave inverter
and it would not stay up. The pair kept shutting off and restarting.
I plan to do some more experiments when the weather gets better.


I've read some of the EnPhase specs and they look pretty tight.
My 'guess' is, it's going to take a really clean (to spec) sinewave to trick an EnPhase.

ggunn

Re: Trick enphase into working off-grid as well?

Cariboocoot wrote: »

The Sunny Boy inverter system has the famous (and expensive) Sunny Island which is designed to work with their grid-tie inverters and convert them into a usable off-grid/emergency back-up system. I'm not sure it works with the really small (700 Watt) units they make.

I have built a system with a SI5048U and SB700U. It works fine.

Cariboocoot

Re: Trick enphase into working off-grid as well?

ggunn wrote: »

I have built a system with a SI5048U and SB700U. It works fine.

That's good to know! Someone could build a pseudo-microinverter system with the 700's and run an island for emergency back-up potential. It's always good to have options.

lairdreed

Re: Trick enphase into working off-grid as well?

Thanks for the replies guys; it seems there are a few solutions but perhaps not off the shelf & pure sine wave & using microinverters (for shading...) Might have to call enphase and see what they have up their sleeve as they say they are investigating off-grid applications on the website. Will advise if I learn anything.

Thanks again,

Laird

stephendv

Re: Trick enphase into working off-grid as well?

Any grid tied inverter will work fine with the sunny island system - as long as it disconnects from the grid at a reasonable over frequency, e.g. +2Hz of regular grid frequency. The only issue is that when the batteries are fully charged, the sunny island will kick the GTIs off the mini-grid. Then when the battery's charge drops a bit, it will re-engage them, and then repeat the process, so what you get is this all-or-nothing cycling of the PV array.

I still don't really understand why one would want to construct an entire array out of microinverters. If it's a shading question, then stick microinverters only on the shaded panels and use a regular GTI on the rest.

In any case, what could be interesting with microinverters and the sunny island, is if you can program the over-frequency limit on each microinverter independently. So if you could have 25% of the inverters drop off the grid at 50.5 Hz, the next 25% drop off at 50.1Hz, etc until all of them drop off at 52Hz. Then you'd have a system very similar to the sunnyboy's variable power output.

ggunn

Re: Trick enphase into working off-grid as well?

stephendv wrote: »

Any grid tied inverter will work fine with the sunny island system - as long as it disconnects from the grid at a reasonable over frequency, e.g. +2Hz of regular grid frequency. The only issue is that when the batteries are fully charged, the sunny island will kick the GTIs off the mini-grid. Then when the battery's charge drops a bit, it will re-engage them, and then repeat the process, so what you get is this all-or-nothing cycling of the PV array.

The Sunny Island tweaks the frequency of the AC connection to a Sunny Boy when the SB's output exceeds the demand, and (if it is set to "off grid") the SB throttles down its output as the frequency goes up. I don't recall the exact numbers, but it is a ramp, not a off/on point. I don't know how/if that would work with another type of GTI.

stephendv

Re: Trick enphase into working off-grid as well?

ggunn wrote: »

The Sunny Island tweaks the frequency of the AC connection to a Sunny Boy when the SB's output exceeds the demand, and (if it is set to "off grid") the SB throttles down its output as the frequency goes up. I don't recall the exact numbers, but it is a ramp, not a off/on point. I don't know how/if that would work with another type of GTI.

Hehe, yeah I know. What I'm saying is that it WILL work with any other GTI except that you won't get the variable output of the SB, instead you'll get an all-or-nothing on off from the GTI.

stephendv

Re: Trick enphase into working off-grid as well?

The new Xantrex XW firmware also uses line frequency to kick GTI off the grid, but it's not variable.

http://www.global-download.schneider-electric.com/852577A4005D7372/all/8FA29D94B918A0FB8525781F0072FCA7/$File/ac-coupling-app-note(976-0240-01-01_rev-a).pdf