Converting Grid Tie to off Grid

cow_rancher · February 2014

OK,

I have several Sharp 240 watt panels that are currently Grid-tie thru Enphase inverters.

What do I need connector wise, and wiring to go to a MPPT converter with batteries to get prepared for loss of grid power?

I understand that you cannot excite those Enphase inverters from a generator, but could that be done by a small stand alone solar panel/controller/battery system to charge a larger converter/battery system?

Rancher

Cariboocoot · February 2014

Re: Converting Grid Tie to off Grid

cow_rancher wrote: »

OK,

I have several Sharp 240 watt panels that are currently Grid-tie thru Enphase inverters.

What do I need connector wise, and wiring to go to a MPPT converter with batteries to get prepared for loss of grid power?

I understand that you cannot excite those Enphase inverters from a generator, but could that be done by a small stand alone solar panel/controller/battery system to charge a larger converter/battery system?

Rancher

You can't do it with a generator, but you can do it with an inverter. How well it will work is debatable.

But you can use something like an SMA Sunny Island or Xantrex XW and AC couple the Enphase output to it to provide charging (and perhaps a bit of extra AC power during daylight).

The other option is a wiring nightmare: disconnecting the microinverters from the panels and reconfiguring the whole array as DC input to a charge controller. If it were a central GT inverter this is somewhat easier, but not a whole lot. The AC coupling method, despite its inherent faults, will be easier.

cow_rancher · February 2014

Re: Converting Grid Tie to off Grid

Cariboocoot wrote: »

You can't do it with a generator, but you can do it with an inverter. How well it will work is debatable.

But you can use something like an SMA Sunny Island or Xantrex XW and AC couple the Enphase output to it to provide charging (and perhaps a bit of extra AC power during daylight).

The other option is a wiring nightmare: disconnecting the microinverters from the panels and reconfiguring the whole array as DC input to a charge controller. If it were a central GT inverter this is somewhat easier, but not a whole lot. The AC coupling method, despite its inherent faults, will be easier.

Thanks Coot, I knew it would be a wiring nightmare, and now that I think about it, I wouldn't need a stand alone solar system, just the battery system and the MPPT controller, correct? Grid goes down, disconnect the incoming power and feed the house with the battery system and converter, then when the sun comes up the panels and Enphase will feed back thru the Xantrex/SMA into the battery system and feed excess to the house load. I have generators that could be used to re-charge battery system during days of rain/snow (not much snow in SE AZ).

OK size? I have 35 Panels, supposed to be 8.4 KW but I've never seen it go over 7.9 KW. So which controller, and how many batteries, and I know I will have to cut back on load. I was thinking about the Costco (I think they are eXide) 6 volt golf cart batteries since they have an unreal warranty period.

Rancher

Cariboocoot · February 2014

Re: Converting Grid Tie to off Grid

You won't need a charge controller at all with the AC coupling:

The Enphase inverters will detect power from the battery-based inverter and fire up, producing power. The battery-based inverter can use this power to recharge its batteries. But this is one of those cases where using the right battery-based inverter is important, because not all of them will regulate the incoming AC from the micros. The two I mentioned can 'turn off' the AC when there's no demand for the extra power (either for loads or charging). Use the wrong inverter and the power keeps flowing, overcharging batteries.

With the amount of power your showing from those Enphase units you will want something like the XW6048 here. Either that or do some more re-wiring to drop a few micros from the mix. The battery bank would need to be at least 600 Amp hours too.

I can't give you much real direction on how to wire this as I don't know how what you've got it wired and how easy it will be to integrate the XW for just some of the household loads (most important ones).

There are a lot of threads on here about the ins and outs of AC coupling; you're going to have to do a lot of research and see how well it can be adapted to your particular use.

cow_rancher · February 2014

Re: Converting Grid Tie to off Grid

Cariboocoot wrote: »

But this is one of those cases where using the right battery-based inverter is important, because not all of them will regulate the incoming AC from the micros. The two I mentioned can 'turn off' the AC when there's no demand for the extra power (either for loads or charging). Use the wrong inverter and the power keeps flowing, overcharging batteries.

Thanks, that's what I needed to hear!

Cariboocoot wrote: »

With the amount of power your showing from those Enphase units you will want something like the XW6048 here. Either that or do some more re-wiring to drop a few micros from the mix. The battery bank would need to be at least 600 Amp hours too.

I have 5 banks of 7 each so I could drop out some panels, thanks on the rough estimate of what I would need to do this.

Why won't a generator work, I've never figured this one out?

Rancher

Cariboocoot · February 2014

Re: Converting Grid Tie to off Grid

cow_rancher wrote: »

Why won't a generator work, I've never figured this one out?

Rancher

Whereas a generator would provide the necessary 'signal' (Voltage and frequency within range) to keep the GTI's turned on, there's no place for their power to go if the loads aren't taking it. Result: back-feed power to generator which has no way of regulating that power; generator burns up.

mike95490 · February 2014

Re: Converting Grid Tie to off Grid

cow_rancher wrote: »

....I have 5 banks of 7 each so I could drop out some panels....
....Why won't a generator work, I've never figured this one out?Rancher

Enphase are usually wired to a pair of breakers, with AC cable. Do you have 5 (or 10) breakers with 7 panels on each ?

A generator or simple inverter, won't work, because it only provide a 60.000Hz sync for the inverters. And that's fine, till your loads become light, and your batteries become full.

I believe the XW (not sure what firmware version is needed) will simply throttle back the 240VAC charging, but it will also just let the AC become unloaded, till the Enphase inverters start shutting down from Hi Line Voltage.

I think the SMA inverters shift the AC freq to 59.8Hz as a signal to the mini-inverters, that there is enough power, and for them (mini-inverters) to throttle back.

I'm off-grid, and never explored these features. Still working on tuning up my Generator Support settings.

cow_rancher · February 2014

Re: Converting Grid Tie to off Grid

mike95490 wrote: »

Enphase are usually wired to a pair of breakers, with AC cable. Do you have 5 (or 10) breakers with 7 panels on each ?

3 breakers, 2- 20 Amp, and 1-15 Amp, I assume it 14/7

Rancher

Blackcherry04 · February 2014

Re: Converting Grid Tie to off Grid

This a perfect thread for a Question I'v had. If you have a Enphase Inverter connected with MC-4 connectors and you have a " Y " in each one ( + / - ) and you shut the Enphase Inverter output off, would you now have to panel output available at the " Y ' ?? That output would go to a combiner and to a Charge Controller. With simple switching you could direct the panel output.

bill von novak · February 2014

Re: Converting Grid Tie to off Grid

Blackcherry04 wrote: »

This a perfect thread for a Question I'v had. If you have a Enphase Inverter connected with MC-4 connectors and you have a " Y " in each one ( + / - ) and you shut the Enphase Inverter output off, would you now have to panel output available at the " Y ' ?? That output would go to a combiner and to a Charge Controller. With simple switching you could direct the panel output.

In theory that works. In practice you have to be very careful WRT grounding issues, and it will only work if the Enphase inverter is completely isolated from the AC side connection.

Cariboocoot · February 2014

Re: Converting Grid Tie to off Grid

Blackcherry04 wrote: »

This a perfect thread for a Question I'v had. If you have a Enphase Inverter connected with MC-4 connectors and you have a " Y " in each one ( + / - ) and you shut the Enphase Inverter output off, would you now have to panel output available at the " Y ' ?? That output would go to a combiner and to a Charge Controller. With simple switching you could direct the panel output.

This has actually come up before. The flaw is in having the panel connected to two things at the same time: i.e. the Enphase MPPT input and a charge controller MPPT input. Since the actual electronics in either is not a known quantity there's no way to predict how one would affect the operation of the other.

Shutting off the output of a grid-tie inverter doesn't kill it completely; there is still circuitry active on the input powered by the panels (panels charge up, activate inverter which checks for valid AC on the output and if present begins producing power).

Having negative all in common and switching the positive from the Enphase to the combiner feed would be possible, but not very practical as you'd either have to climb up on the roof to switch the panels or run a lot of extra wire to where they'd be easily accessible. Though I suppose you could always rig remote relay reconfiguration (NO connection to micro-inverter, close relay to direct power to charge controller).

Blackcherry04 · February 2014

Re: Converting Grid Tie to off Grid

Cariboocoot wrote: »

This has actually come up before. The flaw is in having the panel connected to two things at the same time: i.e. the Enphase MPPT input and a charge controller MPPT input. Since the actual electronics in either is not a known quantity there's no way to predict how one would affect the operation of the other.

Shutting off the output of a grid-tie inverter doesn't kill it completely; there is still circuitry active on the input powered by the panels (panels charge up, activate inverter which checks for valid AC on the output and if present begins producing power).

Having negative all in common and switching the positive from the Enphase to the combiner feed would be possible, but not very practical as you'd either have to climb up on the roof to switch the panels or run a lot of extra wire to where they'd be easily accessible. Though I suppose you could always rig remote relay reconfiguration (NO connection to micro-inverter, close relay to direct power to charge controller).

When I did mine, I just did two separate systems. In hind sight maybe I could have played with it a bit. Just a question I'v wondered about. Good answers . I only wanted 4 panels, so it was easier in my mind at the time.

Converting Grid Tie to off Grid

Comments

Categories