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

[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.

[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.

[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.

[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.

[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.

[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 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?

[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.

[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.

[lkruper]

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.

Solardreamer and Solarddy are a tag team. When one makes a comment that is refuted, the other comes and moves away from that line of thought. Now they have abandoned the premise of the OP. I think they are trolls.

This last post is rhetorical nonsense.

[solarddy]

Enphase M250 works for battery-less daytime micro-grids (mostly) But could be better.

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.

Actually I said there were fluctuations in voltage. My off-grid testing showed that there is a small voltage surge 1-2 volts and a frequency increase but my system didn't shut down until it was massively overproducing and then it did shut down my primary grid sine producer. However Micro-inverters operate without batteries in a normal grid-tied situation. It really wouldn't be much of a thing to make them work without batteries in an islanding situation.

The problem is typical design guidelines show a BIG battery bank where all solar goes through it first. I think that piggy-backing the micro-inverters on the output of the primary sine wave inverter is the best way, load balancing is the issue, but like I said, it took massive overproduction to shut down my off-grid array, if balanced, there is no shut down. Do you "need" batteries? No. The solar panel provides a D.C. source and the sun shines every day.

Let's look at the problem another way: If load demand increased, and there was an intelligent microprocessor program monitoring the line voltage, when the line voltage dropped below a certain level, another micro-inverter(s) which was already powered up and waiting to sync would sync to the 0 crossing and shore up the power on the next cycle. Intelligent load balancing would take a snapshot of the demands and look for patterns and map the drops and peaks to anticipate the loads such as Air conditioning or other motors which have a distinct signature when coming on over discrete periods of time, such as per sec, 5 seconds, 10 seconds, 30 seconds, and 5 minutes.
An entire array of micro-inverters would only be utilized if/when the load demanded them to be used. This would significantly increase the lifespan of the micro-inverters, because peak demand differs from continuous load.
In the case of a load so great it looks like a dead short, as long as the protection devices installed are correct, the micro-inverters should push till those weak points blow which they would in the case of a dead short. Separation of each string of M250's is limited to the wire rating on the Enphase cable.

In a grid-interactive manner intelligent load balancing would limit your credits in "islanding" mode but would maintain power during the day if it was available. Surge output can be many times the rated output of the normal inverter, so the surge of 300 watts could likely be accomplished by a M250 if the load was limited to a few seconds and the M250 was connected to a 300 Watt solar panel. A new micro-inverter array would be developed that would not produce more than the local customer demanded when switched to Islanding mode.

And in the case of too-much power being generated in islanding mode the micro-inverters could sense this and turn their outputs off in one cycle or less utilizing a line sniffer program.

I think the next generation of micro-inverters could accomplish the goal of battery-less micro-grids during the day which eliminate their power bills during daytime hours. Oh wait they already do. Enphase M250. Just not in off-grid mode for several of the above listed reasons.

Using batteries to power the base sine wave inverter for a 90%+ floating M250 micro-grid tied is something like I mentioned earlier, if you Y the output from the solar panels, one to a PWM or MPPT controller and the other to the micro-inverter, the batteries for the base sine wave grid generator get charged till they are full and then the power goes to the micro-inverters, no generator needed. If we only had load balancing micro-inverters there would be no question as to which was superior.

Why are Micro-inverters better: lower Cost, massive scalability, less downtime on individual failure, TCOO is going to be cheaper if you keep them cooler. You lose a string inverter and you lose 1/3 or more of a small array production, you lose 250 watts, you can shrug it off and it takes minutes to install a new one.

[SunEagle]

Solardreamer and Solarddy are a tag team. When one makes a comment that is refuted, the other comes and moves away from that line of thought. Now they have abandoned the premise of the OP. I think they are trolls.

This last post is rhetorical nonsense.

Except for a the presumption of why Enphase is building their micro inverters with anti-islanding software, I agree with what Solarddy stated concerning a micro inverter grid being better.

IMO the biggest issue is the chance of a long string of days without sunshine which would put you in the dark without any device working. So there needs to be a balance of what the micro grid can generate when the sun is out and some other power source to cover the periods of time when the sun is not out. At this time batteries are not economical but running a gen set every day will also be very costly.

So the grid is still the best power source to use when the sun is not out with the availability of having a short term form of emergency power generation (gen set, battery, squirrel cage, etc.). What that source is will depend on what is best for the user which will not be the same for everyone.

[solardreamer]

Solardreamer and Solarddy are a tag team. When one makes a comment that is refuted, the other comes and moves away from that line of thought. Now they have abandoned the premise of the OP. I think they are trolls.

This last post is rhetorical nonsense.

You are way off base. I am not part of any tag team. Your comments about generators show you are mainly interested in being argumentative and not worthy of response. I am looking for constructive comments to address the shortcomings in OP's original proposal to make a more robust solar energy backup solution. So, my position remains the same that gas (or other non-renewable) generator is not the answer for a solar (or other renewable) energy backup solution.

[lkruper]

Except for a the presumption of why Enphase is building their micro inverters with anti-islanding software, I agree with what Solarddy stated concerning a micro inverter grid being better.

IMO the biggest issue is the chance of a long string of days without sunshine which would put you in the dark without any device working. So there needs to be a balance of what the micro grid can generate when the sun is out and some other power source to cover the periods of time when the sun is not out. At this time batteries are not economical but running a gen set every day will also be very costly.

So the grid is still the best power source to use when the sun is not out with the availability of having a short term form of emergency power generation (gen set, battery, squirrel cage, etc.). What that source is will depend on what is best for the user which will not be the same for everyone.

Perhaps I am lost in this discussion, but I don't think so. This is what I understand, so please correct me if I am wrong.

The OP was proposing that grid-tie solar is fed into a battery system that mimics the grid exactly. Naptown asked what happens if the loads cause the pseudo-grid (battery system) to be depleted. That is a valid concern that I have not seen addressed by the proponents of this proposal.

I suggested that using a generator for the case where something happens to the battery bank makes a lot of sense. Others including the OP seem to have great objections to using a generator and made the comment that one could run out of gas and then what? My response is that the generator is a way to save the system as a last resort, because the battery backup is a single point of failure.

And when I one can get in the car to buy gas if it suns out then they say they can get more batteries! So I ask if they are going to buy more batteries every day if they get two weeks of cloudy weather. Of course that is ridiculous, and I said it to make a point, that they have no way to fix this situation if it happens.


So, am I not understanding what they are proposing? But now the OP says no batteries are involved. I don't understand that at all. So then what does the grid-tie inverter feed when the actual grid goes down?

[SunEagle]

You are way off base. I am not part of any tag team. Your comments about generators show you are mainly interested in being argumentative and not worthy of response. I am looking for constructive comments to address the shortcomings in OP's original proposal to make a more robust solar energy backup solution. So, my position remains the same that gas (or other non-renewable) generator is not the answer for a solar (or other renewable) energy backup solution.

As I stated earlier a gas gen set may not be the best (or most economical) energy backup system for everyone. But as of today in the US it is cheaper to run a gen set(s) using multiple fuel types (gas, propane, natural gas) then a comparable sized battery system.

If you need to run electrical loads all day long it doesn't matter how much a pv system can generate because there is ALWAYS a limited number of useable sunlight hours. So for other parts of the day you need to either generate the power from something beside pv or "store" the excess energy your pv system has generated during the day that you did not use.

So pick your poison. When it is dark and you need power, you can produce it from a gen set, battery, wind power, and a few other places that are probably not practical. Or you get the power from the grid.

If you don't want to use non-renewable power source then as of this time expect to pay more for the power being generated then what you can purchase from your POCO.

What is confusing is that the OP started this thread suggesting batteries and now is stating you really don't need batteries until you expand your pv system.

So unless you do not run any electrical devices at night (or on rainy days like today for me in Florida) you need need to use the grid or generate the power by some other means.

I am not being argumentative. I am simply stating the physical and scientific facts concerning solar technology. It only works when the sun is shining on the solar cells.