Enphase M250 Specs for off-grid, tips and tricks and results

[sensij]

A micro-inverter micro-grid is simple, if the sun is out you have power generated if not you don't, with no fussing around with batteries because they aren't needed in a pure micro-inverter grid-interactive array.

Huh? Your first post in this thread clearly talks about using batteries to create your micro-grid. Now battery free? It isn't just the islanding feature that prevents the micro-grid from working. As you sort of pointed out, if load isn't exactly matched to what is being generated, you've got nothing. Without some kind of storage to buffer the fluctuations, too much or too little load will knock the whole micro-grid voltage out of range and shut the whole thing down.

[solarddy]

Off-grid without gas- it's called solar power.

Well, yes I could buy more batteries, but then I will have too many batteries! Batteries are long term consumables and expensive and gas is a short term consumable and cheap.

As for a generator, I don't see how anyone can buy expensive batteries and charge them entirely from solar with never a need to use a generator. What happens when you get two weeks of rainy/cloudy weather? You are not going to buy new batteries every day, are you?

BTW- this is "solar panel talk", not bash solar threads with gas generator comparisons, so let's do one.

buy batteries every day? I've never seen that. Gas, aside from one day being there and the next day being $5 a gallon, is a controlled resource which is as volatile in many people's lives as any expense you can name. Nothing beats the sun for longevity, reliability, and cost effectiveness. The sun never raises it's prices, and if your solar system is so small that you are having issues charging batteries, then get more Micro-inverters and piggy-back some real power into the mix.

A micro-inverter system does not "need" batteries, so you have none to charge, or buy. Compared to a gas generator running 8-11 hours a day every day for a year I'd say solar has that nonsense beat. As for emergency off-grid power... It can be done many ways. I wanted to explore the benefits and methods of using micro-inverters off-grid as mini-grids, not argue which is better gas or battery for backup power. In a real emergency any power is good power, short term gas is nice, a week to a month and gas gets very expensive quickly, as in after a disaster in emergency conditions. What if there is no power regionally? The pumps at the station use electricity too. Working as a telecommunications diesel repair Genset field technician I learned a lot about backup power and how it is done by the telecommunication industries. They rely on very large batteries the size of refrigerators, and those are just the bridge for the diesel powered generators to turn on, the really cool stuff is what Walmart uses- Fuel cells for their server UPS! Fuel cells are obviously the best way to go considering they are using them en-mass, and there is a nice, $1 per watt tax incentive when you do.

I think it would be easiest to just have Enphase put a "Islanding" switch on their micro-inverters so you could have scalable emergency and non-emergency off-grid power. The fact that there is Islanding protection just means that someone in the power industry convinced someone at Enphase and at a local regulators office that "anti-islanding" should be required, when in fact it is more of an annoyance, comparing to other inverters that are off-grid capable and scalable, I don't see the point of not allowing islanding for remote micro-grid installations. They are definitely losing sales over it. Likely it was a competitor who hired an "expert" to squash Enphase a bit when the awesome specs and ease of use is fully understood by those in the know.

A micro-inverter micro-grid is simple, if the sun is out you have power generated if not you don't, with no fussing around with batteries because they aren't needed in a pure micro-inverter grid-interactive array. As you add more panels and micro-inverters you eventually have enough daytime over-production to warrant batteries in about phase 4 of solar expansions. So right out of the gate expect to have a system that will pay for itself in 5-8 years depending on how much you spent on labor. Then based upon real demand, you can expand the system to produce more than your peak usage. Then take the extra and charge some batteries when you have it, if you want night-time or emergency UPS available for your entire house.

As we go into the winter months, having extra solar power production is key when considering cloud coverage, and shorter days, but solar power works every day all day without having to fill up a gas tank.

[lkruper]

Not really. You seem to be implying that you can go get gas for the generator but you can't go get batteries? If you can get gas for a car then you have a backup charger for batteries.

I fully understand the need to design safe and reliable battery based backup for solar systems but I don't see how generator is the really the answer.

Well, yes I could buy more batteries, but then I will have too many batteries! Batteries are long term consumables and expensive and gas is a short term consumable and cheap.

As for a generator, I don't see how anyone can buy expensive batteries and charge them entirely from solar with never a need to use a generator. What happens when you get two weeks of rainy/cloudy weather? You are not going to buy new batteries every day, are you?

[solardreamer]

I think you are missing the point. Yes, a generator could run out of fuel, however if that happened your underlying infrastructure was poorly designed. I can easily see a number of likely scenarios how a set of backup batteries which are intended to mimic a grid could be depleted by a single accident and then you will need another outside source of power to "reboot" the service. That is because the batteries are a single point of failure. But for a generator to run out of gas, it would take a series of failures AND the inability to get more gas, such as driving to the gas station or siphoning it from a vehicle gas tank.

Not really. You seem to be implying that you can go get gas for the generator but you can't go get batteries? If you can get gas for a car then you have a backup charger for batteries.

I fully understand the need to design safe and reliable battery based backup for solar systems but I don't see how generator is the really the answer.

[lkruper]

Not sure how a generator would qualitatively change the scenario since you can also run out of generator fuel. In general, we are talking about only running critical loads in emergency situations where you are not supposed to discharge the batteries completely. The diagram does not show it but many of the Magnum (and other) inverter/chargers allow for a generator to be easily added but that does not eliminate the possibility of discharged batteries. You can also have a few spare charged batteries to ensure startup of the inverter/charger.

I think you are missing the point. Yes, a generator could run out of fuel, however if that happened your underlying infrastructure was poorly designed. I can easily see a number of likely scenarios how a set of backup batteries which are intended to mimic a grid could be depleted by a single accident and then you will need another outside source of power to "reboot" the service. That is because the batteries are a single point of failure. But for a generator to run out of gas, it would take a series of failures AND the inability to get more gas, such as driving to the gas station or siphoning it from a vehicle gas tank.

[ButchDeal]

I'm trying to understand the value of what Enphase is doing here, beyond increasing microinverter sales. If you want off-grid capability, it would be less expensive, more reliable, and safer to build a system based on an MPPT charge controller, batteries, and a hybrid inverter. The dump load is just a hack to make up for things that a normal charge controller would do that the microinverters apparently can't.

Yep, just an overly complicated AC coupled system thus doubling the inverter costs and lowering the efficiency, and greatly increasing failure points.

[solardreamer]

Again What happens when the batteries become overly discharged in a back up situation which can easily happen as most are not used to the energy diet required to run off batteries.
in this scheme there is no input for a generator to bring batteries up to at least a charge level that the magnum will work.
and the system is dead until the grid comes back on.
The addition of generator support would be a good thing but is not included in the schematic.

Not sure how a generator would qualitatively change the scenario since you can also run out of generator fuel. In general, we are talking about only running critical loads in emergency situations where you are not supposed to discharge the batteries completely. The diagram does not show it but many of the Magnum (and other) inverter/chargers allow for a generator to be easily added but that does not eliminate the possibility of discharged batteries. You can also have a few spare charged batteries to ensure startup of the inverter/charger.

[Naptown]

I share your feeling. It's an interesting time for innovation.

Attached is diagram from Magnum that shows how Magasine inverters would work with micro inverters similar to what the OP mentioned. However, it also shows the need for a dump load to soak up excess power to prevent overcharging the batteries as others have mentioned in the thread.

[ATTACH]7950[/ATTACH]


I wonder if it's possible to hook up central AC as the dump load.

Again What happens when the batteries become overly discharged in a back up situation which can easily happen as most are not used to the energy diet required to run off batteries.
in this scheme there is no input for a generator to bring batteries up to at least a charge level that the magnum will work.
and the system is dead until the grid comes back on.
The addition of generator support would be a good thing but is not included in the schematic.

[sensij]

I'm trying to understand the value of what Enphase is doing here, beyond increasing microinverter sales. If you want off-grid capability, it would be less expensive, more reliable, and safer to build a system based on an MPPT charge controller, batteries, and a hybrid inverter. The dump load is just a hack to make up for things that a normal charge controller would do that the microinverters apparently can't.

Energy storage in residential applications is fertile ground for development in the NEC, as higher voltage systems become more integrated and safer. It will be interesting to see how this all develops over the next several years.

[solarddy]

I would love to see more manufactures provide grid tie inverters that will continue to produce power from some portion of the pv system when the grid goes down. But except for SMA and some very expensive hybrid inverters there is not much to chose from.

One statement that the OP put out is "I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency on solar arrays employing micro-inverters". The reason for the lack of this type of equipment may have to do with safety or economics. The manufacturers may not feel there is a worthwhile market to produce that type of equipment.

What inetdog and I are trying to say is that some people might be able to "rig up" a system to fool a micro inverter but is it reliable or more important, is it safe? Neither of us feel the "tip" from the OP is safe or reliable.

Not yet understood is another way of saying that. Several products exist, but what I was referring to was a smallish inverter with dump load capability to allow for islanding, I never said to keep the system attached to the grid when doing so, I said to make it automatic so that that could not happen.
As for the rest of that, I'm here to explore new ideas and not discount safety so get off your high horses, you're trotting down the wrong path.

There is a need in the marketplace for a simple inverter that can do what I am talking about. I have a nice MPPT controller that also does wind with a resistor dump. Micro-inverters pose a new challenge to the market and I'm sure even with your skepticism, it will be answered.

Enphase has an article on islanding or using their products offline I suggest you read it. The suggest the 4024 by Magnasine, this tips and tricks post is to show that the specs to do it with are precise, as listed in my OP.

Thanks for the criticism, it keeps our solar world safer.

[solardreamer]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

I share your feeling. It's an interesting time for innovation.

Attached is diagram from Magnum that shows how Magasine inverters would work with micro inverters similar to what the OP mentioned. However, it also shows the need for a dump load to soak up excess power to prevent overcharging the batteries as others have mentioned in the thread.

Magnum AC Coupled Line Diagram with Micro Inverters.pdf


I wonder if it's possible to hook up central AC as the dump load.

[Naptown]

Enphase has come up with some sort of AC coupled system. This is fairly new as they would void the warranty in the past for these types of installs.
However it is still AC coupled.
A preferable hybrid system IMHO is one that schneider produces.
Array- charge controller-batteries- hybrid inverter.
Issues i have with AC COUPLED i already spelled out
Particularly for back up systems with no generator.

[J.P.M.]

What happens when one needs to sell a house with a complex non-standard system that is only supportable by the expert DIY that built it?

Perhaps it will affect the marketability ? Or the price ? Or limit the potential number of buyers in some way(s) ? While such a system may have some appeal to the DIY and survivalist sets, I'd SWAG it and say they are not a major market segment.

[lkruper]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

What happens when one needs to sell a house with a complex non-standard system that is only supportable by the expert DIY that built it?

[SunEagle]

I find this interesting and hope to hear all the sides of this. I am currently basing part of my purchase decision on my ability to get some sort of power out of my panels during a prolonged down grid. So far sunny boy is winning but this sounds interesting.

I would love to see more manufactures provide grid tie inverters that will continue to produce power from some portion of the pv system when the grid goes down. But except for SMA and some very expensive hybrid inverters there is not much to chose from.

One statement that the OP put out is "I am very surprised some inverter company hasn't created an "Island" inverter to be used in emergency on solar arrays employing micro-inverters". The reason for the lack of this type of equipment may have to do with safety or economics. The manufacturers may not feel there is a worthwhile market to produce that type of equipment.

What inetdog and I are trying to say is that some people might be able to "rig up" a system to fool a micro inverter but is it reliable or more important, is it safe? Neither of us feel the "tip" from the OP is safe or reliable.