EnPhase on batteries?

XRinger

If you had a charged up bank, could you run an EnPhase inverter on batteries?

Or, would the GTI see the bank as a super high amperage PV and go nuts pulling amps, until it smoked?

Blackcherry04

Re: EnPhase on batteries?

See if this helps you.

www.global-download.schneider-electric.com/.../ac-coupling-app-note(976-0240-01-01_rev-a).pdf

XRinger

Re: EnPhase on batteries?

Blackcherry04 wrote: »

See if this helps you.

www.global-download.schneider-electric.com/.../ac-coupling-app-note(976-0240-01-01_rev-a).pdf

Nope, I could find nothing there directly related to my question.

I'll add more detail to my question. Do the Enphase inverters self-limit their power input?

If you were testing one with a large power supply, that could supply
0 to 56vdc at 250 amps. Would it self-limit, or start melting?

Looking at some of the M190 specs,

Recommended input power (STC) 230W
Maximum input DC voltage 56V
Peak power tracking voltage 22V – 40V
Max. DC short circuit current 12A
Max. input current 10A

It seems like if more than 10A were supplied, it could fail or maybe shut itself off..

Blackcherry04

Re: EnPhase on batteries?

Now I see what your asking, no clue. Sounds like a test till destruct is in order.

stephendv

Re: EnPhase on batteries?

Helps to think of it this way: You can't apply current, you can only draw it. So in a circuit with PV panels and an enphase, the enphase will draw current from the panels. It will only draw as much as it's designed for, won't matter how much current the PV can potentially supply.
In principal I think that it'll work fine with a battery instead of PV panel, but best to let someone more knowledgeable confirm

BB.

Re: EnPhase on batteries?

In theory, all you should have to add is a fuse/breaker to limit short circuit current if something fails.

-Bill

Blackcherry04

Re: EnPhase on batteries?

The next question would be, without a qualifying grid connected to it, how would you know.

XRinger

Re: EnPhase on batteries?

Blackcherry04 wrote: »

The next question would be, without a qualifying grid connected to it, how would you know.

Of course, the Enphase would do absolutely nothing without being connected to the grid.


When connected to the batteries, I would assume the Enphase would MPPT itself to max power out.
The power could be monitored using a clamp-on amp meter or wired-in meter.



I would be worried that watts-out would zoom up in a few seconds
and you wouldn't have much time to switch it off.
Maybe a fast blow 10a fuse?

BB.

Re: EnPhase on batteries?

The rating is something like 10 amp maximum at 22 volts => 220 watts...

At the very least, probably fuse around 1.25x to 1.56x Imax (1.25^2).

Remember, you are just protecting the wiring--I am not sure that the fuse would protect the Enphase from self destruction if it had a tendency to try that.

Certainly would not hurt anything to try a 10 amp fast blow fuse... I am assuming that the Enphase will wait ~5 minutes after DC power is applied before ramping up the AC output current. I don't think the MPPT would overwhelmed by the "unlimited" input current and lose control of the total power transfer equation.

-Bill

XRinger

Re: EnPhase on batteries?

I could make another fast acting circuit breaker.

http://i46.photobucket.com/albums/f147/Xringer/NCL/AB2011.jpg

Just set it for around 240 watts and keep my fingers crossed..
Once it kicked in, the Enphase would jump into anti-island mode and turn off.
Seems like it would be safer than a fuse, or an electromechanical breaker.

BB.

Re: EnPhase on batteries?

I would not worry about over current during normal operation...

For me, I would be slightly concerned about the initial current surge (flip on battery switch, current surge into the front end/capacitors). The Enphase may never have been designed to be connected to a virtually zero ohm voltage source. Could affect reliability.

It is also possible that during development and test that Enphase does connect their units to standard voltage based power supplies and they work just fine.

-Bill

Brianellul

Re: EnPhase on batteries?

Hi

Please post your results if you decide to try it out!

Regards

Brianellul

Re: EnPhase on batteries?

Hello

Wondering if anyone has any updates on this old tread!

Has anyone tried connecting the Enphase inverters directly to batteries. The Enphase M190 has a startup voltage of 28v so it would make it ideal to start 'selling' when 28v is reached, and the batteries (for a 24v system) are fully charged.

Regards
Brian

ggunn

Re: EnPhase on batteries?

Brianellul wrote: »

Hello

Wondering if anyone has any updates on this old tread!

Has anyone tried connecting the Enphase inverters directly to batteries. The Enphase M190 has a startup voltage of 28v so it would make it ideal to start 'selling' when 28v is reached, and the batteries (for a 24v system) are fully charged.

Regards
Brian

The only DC in an Enphase system is in the conductors between the microinverters and their respective modules, and each one is its own separate PV system. There is no DC bus to which one could connect a battery.

Brianellul

Re: EnPhase on batteries?

ggunn wrote: »

The only DC in an Enphase system is in the conductors between the microinverters and their respective modules, and each one is its own separate PV system. There is no DC bus to which one could connect a battery.

That's why I'm asking because it's not the normal way to connect these inverters. The title 'Enphase on batteries' is exactly what I'm questioning

ggunn

Re: EnPhase on batteries?

Brianellul wrote: »

That's why I'm asking because it's not the normal way to connect these inverters. The title 'Enphase on batteries' is exactly what I'm questioning

I think the original question was whether or not an Enphase system would play nice with something like a Sunny Island battery inverter. There is no way to connect Enphase microinverters directly to batteries. Even if you could you would need a separate battery for each module.

BB.

Re: EnPhase on batteries?

If you wish to connect an Enphase inverter directly to the appropriate voltage battery bank--yes is probably would work fine (use the correct fuse between battery and inverter DC input).

Of course, then you need to think about how to "throttle" the Enphase unit so that it is only drawing power when the battery bank is in the desired state (charging, >20/50/75% sate of charge, etc.).

You will need to look at the battery specs. vs Enphase inverter input requirements... For example the M215:

• 96% CEC efficiency
• Output power: 215W
• Recommended max input power: 260W
• MPPT Range: 22-36V
• Low-voltage operation capability
• Works with 60-cell modules ONLY

A 60 cell panel probably is around Vmp~30 vdc, Vmp-min~24 volts, and Voc-cold ~48 volts or so...

It would appear you would have to use a 24 or 36 volt battery bank.

Of course, using an Enphase inverter on a battery bank would "not be legal" to connect to utility/grid power.

I don't think the Enphase inverter have an "inhibit" input you can control--so that leaves you with either a relay on the DC input or a relay/electronic switch on the AC output to allow you turn the Enphase units "on" and "off" to protect the battery bank.

It is possibly you will have secondary issues... Who knows if Enphase requires some sort of input voltage profile that looks more like a solar PV panel vs the on/off of a battery bank, or how accurate is the "starting voltage" set point. What if you leave the Enphase running for 24 hours or more straight that it will hit an internal software or hardware timer error (since they are not designed to operate 24x7--Enphase engineers may not bother with the ability to "count" more than XX hours per day).

Lots of unknowns.

I don't think you will "blow an Enphase Inverter up" by connecting it to the appropriately sized and fused battery bank... But that and $5 will buy you a cup of coffee from Starbucks.

Why/how would you like to use an Enphase on a battery bank?

-Bill

A big PS: One issue that I don't know the answer too... I would guess that the Enphase is an isolated inverter (DC input is isolated from the AC output)--I but I do not know that. And I do not know how it handles DC Ground / Ground Fault detection (if any) of the DC panel power... I would be very careful about how I handle and connect the inverters. You may end up with issues if you attempt to connect to Enphase inverters to one battery bank--plus it is possible that the Enphase could energize the battery bank DC bus with some lethal amount of voltage/energy.

I just do not know.

XRinger

Re: EnPhase on batteries?

ggunn wrote: »

I think the original question was whether or not an Enphase system would play nice with something like a Sunny Island battery inverter. There is no way to connect Enphase microinverters directly to batteries. Even if you could you would need a separate battery for each module.

Here in America, Ebay can provide us with the proper PV connectors.

So, connecting a battery to an GTI isn't much of a problem.
If I have the parts and wire, it would take me a few minutes to connect an Enphase to batteries.
(But, I don't own any Enphase products yet).


I don't understand why, "you would need a separate battery for each module"..
If you connect a GTI to a battery bank, how would it know that another GTI was also connected to the same bank?? Why would it care? :roll:

BB.

Re: EnPhase on batteries?

You may have missed my post--but it may matter if the Enphases are not isolated inverters (i.e., there is not a transformer between the DC input and the AC output.

If you get the phasing wrong, or put the Enphase on different AC breakers/fused output/loads--You could end up with some weird current paths with the common DC bus input (typically "weird" in electrical power terms is not a good thing).

It really depends on how Enphase designed their units--and they are not likely to tell us what they did.

With a couple of Enphase units and a fused connection to the battery bank--you can probably do your own testing and figure much of it out with some testing... A pair of Enphase inverters is not that expensive (if you end up trashing them).

But you do have to be careful.

And, again, battery powered Enphases is (most likely) not a "legal" configuration in North America.

Out of curiosity, why would you want to Battery Connect small inverters like the Enphase to utility power (I presume). It is not going to save that much money on the utility bill vs the risks involved (utility could turn off your power, let alone safety questions) and if you end up cycling your battery bank (drain below ~25.2 volts), you will cut some cycle life off of the batteries themselves.

-Bill

XRinger

Re: EnPhase on batteries?

Hi BB,
I made a little circuit to monitor one of my 12v batteries (in a 48v bank).

http://i46.photobucket.com/albums/f147/Xringer/Solar/12vdump.jpg

It turns on an SSR when the battery is up around 14 volts and shuts off the SSR when the battery gets too low.
Kinda like a Load-Dump..

The SSR connects the AC from the inverter to light loads in the house, using IOTA relays.

http://i46.photobucket.com/albums/f147/Xringer/Solar/z206.jpg

The circuit doesn't work real well, but it keeps the bank from going too low after sundown.
As the voltage drifts back up (with no load), the inverter comes back on, only to shut off a few minutes later, repeatedly, until I go down and put it in standby.

A little programmable controller (w/ a RTC) would be much better.. 8)

Anyways, I think this sort of rig could be used with any kind of inverter with an AC output.

The reason anyone would want to do this? I'm not sure, but people who maintain a battery back-system (like I have), might like the idea of using
the extra PV power that is normally not used after the bank is charged (in float).

BB.

Re: EnPhase on batteries?

I understand why people would want to do hybrid systems (grid tied / off grid capable) and dump the power to the grid to save money...

However, I do not see this being legal and of questionable safety unless you get support from Enphase (not likely).

The draw of rolling your own GT capable battery backup system is strong. And I would like to read about your road towards achieving that goal.

HOWEVER, beating a dead horse, it is not legal and possibly of unknown safety concerns.

It sounds like you may have enough experience to address the safety issues... But the legal problems are difficult and expensive to address.

About the only way to get the utility issue addressed would be to install a GT system of some sort, get it approved by building and the utility so you get on Net Metered billing system--Then start playing with getting the DC Backup up system running.

-Bill

XRinger

Re: EnPhase on batteries?

Okay BB,

Yeah, I understand the legal ramifications (and the problems that could occur with home owners insurance, if there was an accident).

I don't plan on ever pushing power onto the grid illegally.
Even if I wanted to, my modern meter does not 'spin backwards' and would set a flag,
informing NStar that I was connecting a power source to the grid.
Even if they didn't notice the flag, the meter (LCD) would actually spin forward,
and I would be charged for any power put out on the grid!


The questions about using Enphase off-grid comes from Enphase system owners
and people who are thinking about becoming Enphase owners.
It's always, "What if the grid goes down, I've all this PV and it can't be used."

If the power goes out for a few days, it must be pretty frustrating to be outdoors
on a sunny day, looking up at a roof covered with PV that's not doing anything.

BB.

Re: EnPhase on batteries?

Yea--I got 3.5 kW on my roof through a GT inverter--And a eu2000i genset in the shed for the end of the world (I assume that will be an earthquake for us).

And I might have generator power for 10-20 days of light usage... I would guess our neighborhood would be pretty much empty/unlivable after that long with no outside support (San Francisco suburb--no water, food, heat, fuel, sewage, red-tagged homes and apartments, etc.). Either things will be better after that, or we would have to go elsewhere (some of the governments were pretty heavy handed after the 1989 Loma Prieta quake about keeping people out of damaged structures).

At least with earthquakes--The damage tends to be heavy in "small clusters" unlike a huge storm or flood which takes out square miles at a time. Plus earthquakes are more likely to happen during nice weather;).

In more rural areas--Long term outages may not be as dire.

-Bill

Brianellul

Re: EnPhase on batteries?

Thanks to all for your feedback.

I have contacted Enphase to seek if this is not possible or not. I'm currently exchanging emails and will post their responses when I have an answer. I think it's the best solution... will also ask them about connecting multiple inverters to the same battery bank... never though about it!

My queries on all this started some time ago when I noticed that my batteries are loosing capacity. I basically got my fork-lift deep cycle batteries 3 years ago from the trash since they were going to be thrown away. They had been sitting idle/ discharged for some time and some cells were low on water so I knew that I'll be getting a much reduced capacity battery set, however it was OK for my needs considering that I only have 320w of panels dedicated for the batteries.
This system is lightly used since I just power my house lights and other small items. When the batteries are < 80% charged I manually change over to grid-power. In Summer (well ~ 7 months) I'm usually OK and never need to switch over while I'll keep an eye open in the Winter when the days are shorter for the SOC. The problem now is that the batteries are not even holding for a night. I fully charge them (solar + charger) but they loose charge quickly. In the morning by 10:00, the batteries would already be > 26v, and they will fall to 24v by 20:00, this clearly showing the reduced capactity. I say 'clearly' because I closely monitor the batteries and know by charge-load pattern... there was no change in loads lately.
I checked regarding new batteries and unfortunatly right now I can't justify spending $$$$ on another set of batteries. Therefore, what's happening now is that I'm loosing power from these panels! I'm basically wasting the power into a set of batteries. I'm charging them in during the day BUT can't use/find that charge in the evening! I don't know when I'll be buying a new set of batteries and therefore was thinking of a way to yes continue replensihing the batteries (for backup purposes only now) and at the same time export some power which otherwise would be wasted.
Regarding legal issues, I already have a 2KW grid-tie system so exporting an extra 190W should be of a concern (in my opinion).

Regards

XRinger

Re: EnPhase on batteries?

I don't know what Enphase modules cost over there in Malta, but you should
compare the price with how many battery AH you can buy with that money.

I would try troubleshooting your battery bank. Maybe something can be done.
I'll bet there are a lot of battery experts who post here.

Your GT production looks pretty good for 2011! Your PV install has that Professional look!

Cheers,
Rich

ggunn

Re: EnPhase on batteries?

XRinger wrote: »

I don't understand why, "you would need a separate battery for each module"..
If you connect a GTI to a battery bank, how would it know that another GTI was also connected to the same bank?? Why would it care? :roll:

Because each Enphase microinverter has its own MPPT capacity and if you parallel all the modules and connect them to a battery bank there is no telling what they will do.

As a matter of fact, I don't know what an MPPT circuit is going to do with with even a single battery and PV module in parallel. With grid tied battery backup systems, the PV is not directly in contact with the batteries, so the MPPT doesn't see the batteries. Batteries act like voltage sources and PV modules are mostly current sources; their IV curves are completely different. When you put them directly in parallel and run MPPT dynamic loading on them, who knows what the result will be? I don't; maybe you do. At the very least, what you put together won't be UL listed for that application, so you'll likely have trouble convincing your AHJ to give you permission to connect to the grid.

Someone earlier said that they didn't think this could blow up an Enphase; I am not so sure. PV is systemically current limited but batteries are not.

XRinger

Re: EnPhase on batteries?

ggunn wrote: »

Because each Enphase microinverter has its own MPPT capacity and if you parallel all the modules and connect them to a battery bank there is no telling what they will do.

As a matter of fact, I don't know what an MPPT circuit is going to do with with even a single battery and PV module in parallel. With grid tied battery backup systems, the PV is not directly in contact with the batteries, so the MPPT doesn't see the batteries. Batteries act like voltage sources and PV modules are mostly current sources; their IV curves are completely different. When you put them directly in parallel and run MPPT dynamic loading on them, who knows what the result will be? I don't; maybe you do. At the very least, what you put together won't be UL listed for that application, so you'll likely have trouble convincing your AHJ to give you permission to connect to the grid.

From what I know about MPPT, the GTI will likely look for the PV's sweet spot.
By continuously sampling the amount of power that can be taken from the PV,
it will track to the optimum voltage range (depending on the clouds etc),
and take power from the PV using the voltage level as it's trigger to draw power.
If it sees the power is dropping off, it will self-adjust the time window between input power pluses.
(It's quickly connecting and disconnecting it's internal 'load' to the PV).

It's going to harvest every single watt it can, even when clouds move in..

But, if you connected the Enphase m190 to (peak power tracking range 22v to 44v),
to a 36 volt battery bank, it's going to track right to 36v and start sucking out max power. It's input pulse window is going to max out.

If the battery bank is large, looking at it's DC output with your scope is not going
to show any little square waves (like you would see on a PV).

So, connecting another Enphase to the battery isn't likely to cause any weird problems.

But, like BB said, you might want the AC outputs of the Enphase units, to be in-phase.
You could just use the daisy-chain connectors provided.

solarix

Re: EnPhase on batteries?

All MPPT devices are basically variable impedance loads which can adjust their input resistance to match the optimum impedance of the source.
(study the subject of impedance matching sometime - maximum power transfer is only achieved when the impedance of a source and load is matched)
This is why you have transmission gearing in your car.
When fed by a low impedance source (battery), the Emphase will ramp up its current until it sees the battery voltage droop too much (which won't happen) and will only stop when it hits its current limit, which it does have. The common size of Emphase has been the 190 watt size which they allow using on panels larger than that, so this overcurrent possiblility already happens. All inverters and charge controllers have current limiting inherently as a result of their MPPT capability.
Now, why you would want to do this I don't know, as the only time you need battery backing is if the grid is down and the Emphase won't work then.

BB.

Re: EnPhase on batteries?

Other thing to look into... 36 VDC battery banks are a bit odd ball these days for solar PV systems. It might be difficult to find mass market inverters, battery chargers and DC direct loads (pumps, etc.) that run at 36 volts nominal.

-Bill

solar_dave

Re: EnPhase on batteries?

I can see where using battery to off set usage at night (sell back) might be a nice feature, but a regular grid tie inverter wants generally a higher voltage input. The Enphase lower input voltages could make that possible.

Does it make sense economically? Big question, the costs of operating a battery system is pretty steep. In my case with TOU rates it certainly would not make sense @ $0.055 a kWh, but I could see maybe some high dollar rates like some of the posters have said the get like on Long Island might be there. I suppose you could also have a backup system wired into the same battery bank for outages. It gets pretty complicated I am sure.

Just a rambling from a guy who sat in the sun to much this summer!

BB.

Re: EnPhase on batteries?

I have several times "ran the numbers" to buy an inverter/charger and battery bank, plus add replacing batteries every 10 years--and it always looks like ~$0.45 per kWH (over 20 year system life) just to "time shift" your power ("buy" power at night rates, sell at day time rates).

With our very high Time Of Use rates, the best spread is around $0.20 to $0.30 per kWH. A best, right now, it appears I would break even or only loose a small amount of money per month.

-Bill