Question - any GT inverters out there with remote disable/throttling?

bill von novak

Does anyone know of any grid tie inverters that support either a remote disable (say via a contact closure or serial message) or a remote method of throttling (say a 0-10V input that reduces max power output) ?

Cariboocoot

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

Does anyone know of any grid tie inverters that support either a remote disable (say via a contact closure or serial message) or a remote method of throttling (say a 0-10V input that reduces max power output) ?

Why would you want to?

The standard GTI is meant to deliver as much power as is available from the array at any time. Since it is connected to the grid there is always a place for this power to go and no reason to reduce it.

If you are looking to use one only to offset loads (no grid sell-back) it probably isn't worth doing.

If you are looking to negate household usage and not sell back to the grid, the battery-based hybrid inverters can do this. Again, probably not worth the investment.

If you are looking to use a GTI to supplement power output from an off-grid inverter you need to choose one that can control the GTI output, which is usually done by skewing the frequency so that the GTI drops out.

So the real question is: what exactly are you trying to achieve?

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

Cariboocoot wrote: »

Why would you want to?

To reduce or stop generation on an AC coupled off grid system. Some systems use relays for this purpose, but that's a brute-force approach to a problem that could be solved a lot more simply.

ggunn

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

To reduce or stop generation on an AC coupled off grid system. Some systems use relays for this purpose, but that's a brute-force approach to a problem that could be solved a lot more simply.

To what end? What is it that you are trying to accomplish? What do you mean by "simply"?

If you are trying to run a grid tied system only to power your local loads without exporting power to the grid, I submit that this is NOT a simple task. A grid tied inverter has no way of distinguishing between your local loads and the grid. Regulating the output of a GT inverter based on the magnitude and direction of current flowing through your meter would be a non-trivial task. I believe you could do it with the addition of a Sunny Island and a battery bank if the GT inverter were a Sunny Boy, for example, but that could double (or more) the cost of your system.

One of the things that grid tied systems have going for them is that they are relatively cheap, but they do what they do and they are not very flexible.

EDIT: I just saw the "off grid" in your question. The short answer is that you cannot use a grid tied PV system off grid by itself. The Sunny Boy/Sunny Island system is designed to do what you describe but it ain't cheap.

Cariboocoot

Re: Question - any GT inverters out there with remote disable/throttling?

Yes; SMA does it "a lot more simply" by being more complex at it. Their Sunny Boy & Sunny Island combination is the industry's best for AC coupling.

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

ggunn wrote: »

To what end? What is it that you are trying to accomplish? What do you mean by "simply"?

Here's the brute force approach:

http://solarprofessional.com/articles/products-equipment/inverters/ac-coupling-in-utility-interactive-and-stand-alone

See figure 3 for how to do it 'brute force.' If there were a discrete line that could be used to disable a GT inverter you would not need the relay.

If you are trying to run a grid tied system only to power your local loads without exporting power to the grid, I submit that this is NOT a simple task. A grid tied inverter has no way of distinguishing between your local loads and the grid.

Right. You need either a separate distribution system or an isolating inverter (with transfer switch) to accomplish this.

Regulating the output of a GT inverter based on the magnitude and direction of current flowing through your meter would be a non-trivial task. I believe you could do it with the addition of a Sunny Island and a battery bank if the GT inverter were a Sunny Boy, for example, but that could double (or more) the cost of your system.

I am considering the case where someone with a solar GT system wants to add backup. One option is to rewire the ~500 volt array to the 150-200 volt range that most charge controllers can handle, then add a large (equal to the capacity of the solar system) charge controller, plus a large (equal to the capacity of the former GT inverters) Outback GTFX type inverter, plus a large battery bank. You'd also have to add an essentials load center that included the GT inverter. So that would require:

New wiring for solar array
New charge controller that can handle the entire array
New inverter that can handle the entire array's output
New large battery bank
New essentials load center

This is expensive.

An alternative way to do this is to do a conventional AC coupled array. This would allow the user to keep his GT inverters per figure 3 in the above referenced design. He would also need:

New smaller GTFX style inverter (can be smaller since it does not need to invert full array power)
New smaller battery bank (can also be smaller since max load will be smaller)
New load panel
Relay

This option is considerably less expensive, since it does not require as much new hardware, and the required hardware can have lower power ratings. If the GT inverters could be disabled via a discrete signal, the relay could be eliminated as well.

stephendv

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

New smaller GTFX style inverter (can be smaller since it does not need to invert full array power)
New smaller battery bank (can also be smaller since max load will be smaller)
New load panel
Relay

This option is considerably less expensive, since it does not require as much new hardware, and the required hardware can have lower power ratings. If the GT inverters could be disabled via a discrete signal, the relay could be eliminated as well.

This seems like a nice solution, don't see why you have a problem with the relay? Since the relay is switching AC, it can be a run of the mill cheap-o device, no need for anything fancy.

The other option mentioned in the article is to use a PWM diversion controller + dump load like the morningstar tristar. This will give a much better charging profile for the batteries while the system is off-grid. Depends on how much time the system is going to spend off-grid vs. grid tied. If it goes off-grid for a few hours year, then the additional expense of diversion controller + dump loads isn't worth it IMO.

ggunn

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

Here's the brute force approach:

http://solarprofessional.com/articles/products-equipment/inverters/ac-coupling-in-utility-interactive-and-stand-alone

See figure 3 for how to do it 'brute force.' If there were a discrete line that could be used to disable a GT inverter you would not need the relay.



Right. You need either a separate distribution system or an isolating inverter (with transfer switch) to accomplish this.



I am considering the case where someone with a solar GT system wants to add backup. One option is to rewire the ~500 volt array to the 150-200 volt range that most charge controllers can handle, then add a large (equal to the capacity of the solar system) charge controller, plus a large (equal to the capacity of the former GT inverters) Outback GTFX type inverter, plus a large battery bank. You'd also have to add an essentials load center that included the GT inverter. So that would require:

New wiring for solar array
New charge controller that can handle the entire array
New inverter that can handle the entire array's output
New large battery bank
New essentials load center

This is expensive.

An alternative way to do this is to do a conventional AC coupled array. This would allow the user to keep his GT inverters per figure 3 in the above referenced design. He would also need:

New smaller GTFX style inverter (can be smaller since it does not need to invert full array power)
New smaller battery bank (can also be smaller since max load will be smaller)
New load panel
Relay

This option is considerably less expensive, since it does not require as much new hardware, and the required hardware can have lower power ratings. If the GT inverters could be disabled via a discrete signal, the relay could be eliminated as well.

If your customer has relatively consistent grid power, he needs to take a hard look at how important it really is to him for his GT PV system to keep operating during an outage. It is a whole lot cheaper and simpler just to get a generator and automatic transfer switch for backup and leave the GT PV system outside the switch.

A GT system is a strategic solution to counteract high electric bills over the long haul. A grid outage is a tactical problem. If outages are relatively rare and short lived, the GT PV system's contribution to his bottom line during those outages would be minuscule. A PV system that keeps chugging along irrespective of the state of the grid has a lot of geek appeal, but it may not be good economics.

EDIT: To answer your initial question - SMA GT inverters have the capacity to throttle back their output in response to changes in the frequency of the line voltage they are referencing, which is the heart of the AC coupled interaction between Sunny Boy and Sunny Island inverters.

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

ggunn wrote: »

If your customer has relatively consistent grid power, he needs to take a hard look at how important it really is to him for his GT PV system to keep operating during an outage. It is a whole lot cheaper and simpler just to get a generator and automatic transfer switch for backup and leave the GT PV system outside the switch.

That makes good sense when compared to a 'standard' battery backed grid tied system. However, a smaller system (as outlined above) might well be cheaper than a generator.

A GT system is a strategic solution to counteract high electric bills over the long haul. A grid outage is a tactical problem. If outages are relatively rare and short lived, the GT PV system's contribution to his bottom line during those outages would be minuscule.

Agreed. However, the value to the homeowner is not the same as the monetary cost of the power. This was brought home to me pretty dramatically a year ago when Sandy hit New York. Several friends and family on Long Island and New Jersey were without power from a few days to two weeks. None of them had grid tie solar power systems, but many of their neighbors did. Of those neighbors, none understood why they could not generate power with the sun out and their system intact. The cost to to them of flooded basements (with no power to pump them out) spoiled food and the lack of light at night was very high, and when gasoline for the few generators in the neighborhood ran low, they were out of luck. Thus the value to them of a system that could provide backup was high as well*.

After power was restored, they talked a lot about the generators they were going to buy, and several were planning to spend upwards of $5000 to get a generator/transfer switch. If there were a cheaper option that worked with their solar power system that would a) save them money and b) end worries about gasoline supplies during such an emergency.

(* - Fortunately there is now one option on the market (the SMA secure power supply) that allows some backup power, but only during daylight hours.)

ggunn

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

That makes good sense when compared to a 'standard' battery backed grid tied system. However, a smaller system (as outlined above) might well be cheaper than a generator.

Agreed. However, the value to the homeowner is not the same as the monetary cost of the power. This was brought home to me pretty dramatically a year ago when Sandy hit New York. Several friends and family on Long Island and New Jersey were without power from a few days to two weeks. None of them had grid tie solar power systems, but many of their neighbors did. Of those neighbors, none understood why they could not generate power with the sun out and their system intact. The cost to to them of flooded basements (with no power to pump them out) spoiled food and the lack of light at night was very high, and when gasoline for the few generators in the neighborhood ran low, they were out of luck. Thus the value to them of a system that could provide backup was high as well*.

After power was restored, they talked a lot about the generators they were going to buy, and several were planning to spend upwards of $5000 to get a generator/transfer switch. If there were a cheaper option that worked with their solar power system that would a) save them money and b) end worries about gasoline supplies during such an emergency.

(* - Fortunately there is now one option on the market (the SMA secure power supply) that allows some backup power, but only during daylight hours.)

"None of them had grid tie solar power systems, but many of their neighbors did. Of those neighbors, none understood why they could not generate power with the sun out and their system intact. "

Do you mean to tell me that none of the folks who had GT systems knew that their PV systems wouldn't work without the grid???? If so, that tells me that they were all the victims of unscrupulous PV salesmen; that point should have been made VERY clear in the sales pitch. I know that such things go on, though; I was told by an SMA rep that every time there is a big grid failure somewhere their tech support lines light up with calls from from irate GT PV system owners that don't understand this.

"After power was restored, they talked a lot about the generators they were going to buy, and several were planning to spend upwards of $5000 to get a generator/transfer switch."

A Sunny Island alone will cost them nearly that much, and we haven't even started in on batteries. Every time this comes up there are questions about "fooling" a GT inverter into thinking the grid is up with a tiny battery and inverter. It won't work. The SMA inverters with the auxiliary power outlet is a great idea that solves some problems, but it's just 1500W max (and varies with the system size and irradiance of the array) and only works when the sun is shining. It isn't going to run their AC in any case.

There are solutions out there but they are not cheap or simple. Anyone who expects to have 24 hour whole house backup power for the price of a GT PV system is going to be disappointed.

Cariboocoot

Re: Question - any GT inverters out there with remote disable/throttling?

The big problem with battery-based back-up power for occasional outages is that the batteries age whether they are used or not. Come the power failure they could be dead already, or at least reduced in capacity enough to not deliver the expected service.

There is also Xantrex's (and soon Morningstar's) 600 Volt MPPT controller which could be switched in to a central GTI system's array to recharge batteries when the grid goes down. (While utility power is available they would be maintained from that.)

stephendv

Re: Question - any GT inverters out there with remote disable/throttling?

For backup supply in the Americas, I'd go with the Xantrex XW or Magnum energy battery inverters that support shifting the frequency to knock the GTI offline when the batts reach a certain voltage. You can then use any GTI and you get a split phase battery inverter for half the price of a sunny island. The charging profile for the batteries won't be smooth like the SMA solution, but it's good enough for occasional use IMO.

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

ggunn wrote: »

Do you mean to tell me that none of the folks who had GT systems knew that their PV systems wouldn't work without the grid????

I don't know if that was true of everyone. Of the people my friends and family knew, none of them were aware that their systems could not do anything without a working grid. One of them was asking around for an electrician who was able to "reconnect their solar generator" which had gone off-line.

I think this is going to get more and more common as more people install solar. As with the Internet, there used to be a barrier to entry; you had to be fairly technical to play in the first place. Nowadays you just need a credit card.

But that's beside the point; you can always educate them. To me it's more interesting to examine methods of solving their problem, rather than methods of explaining why they have a problem in the first place.

A Sunny Island alone will cost them nearly that much, and we haven't even started in on batteries.

I know. My point is that a Sunnyboy with a SPS output will not cost them anywhere near that amount, and an AC coupled system with a very small battery bank might cost them half of that - and the end result will be a useful solar power system with backup, not just a propane fueled generator that might be used once every five years.

Every time this comes up there are questions about "fooling" a GT inverter into thinking the grid is up with a tiny battery and inverter. It won't work. The SMA inverters with the auxiliary power outlet is a great idea that solves some problems, but it's just 1500W max (and varies with the system size and irradiance of the array) and only works when the sun is shining. It isn't going to run their AC in any case.

I've "fooled" my 10kW GT system into working with an Outback GTFX2524 with a 100 amp hour battery bank. It worked, although I wouldn't want to try it without me there watching it (and in my case manually shutting down GT inverters when sources were close to exceeding loads.) That function can be replaced with a relay or the disable input that is the subject of this thread. Also keep in mind the goal in general is not to "run their AC" - it's to keep their food from spoiling, charge their radios and cellphones and have some light at night.

ggunn

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

I've "fooled" my 10kW GT system into working with an Outback GTFX2524 with a 100 amp hour battery bank. It worked, although I wouldn't want to try it without me there watching it (and in my case manually shutting down GT inverters when sources were close to exceeding loads.) That function can be replaced with a relay or the disable input that is the subject of this thread. Also keep in mind the goal in general is not to "run their AC" - it's to keep their food from spoiling, charge their radios and cellphones and have some light at night.

Maybe a compromise system would be a battery inverter with a charge controller and a switching system to reroute some of their PV from their grid tied system to the CC in the event of an outage. The switching would be somewhat complex because it would have to change the string length from what a GT inverter uses to what would work with a CC, but I'll bet it could be done.

solar_dave

Re: Question - any GT inverters out there with remote disable/throttling?

Some one around here talked about using micro-inverters to add to a small battery system with a TSW and an Ardunio controller to switch a relay to engage each one individually. SSR are pretty cheap and some thing like this might be able to work if the load was known. The premise was that it would not really carry the loads off the battery but mostly off the micro-inverters. Of course it would only be good while the sun was shining.
http://www.ebay.com/itm/Solid-State-Relay-SSR-40DA-40A-250V-3-32VDC-/261257784697?pt=LH_DefaultDomain_0&hash=item3cd42d6d79

It might require a transistor to pull the relay from the TTL level control board. You would probably want to opto-isolate it as well.

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

ggunn wrote: »

Maybe a compromise system would be a battery inverter with a charge controller and a switching system to reroute some of their PV from their grid tied system to the CC in the event of an outage. The switching would be somewhat complex because it would have to change the string length from what a GT inverter uses to what would work with a CC, but I'll bet it could be done.

Yeah, that might work out. Right now the cleanest way to do that is with an SMA SPS system, with the backup power source going straight into an inverter's input. Second cleanest is with an XW-MPPT 80-600 charge controller (can accept up to 600 volts) but that's a $1200 device that you don't need 99% of the time. (A cheaper 600V to 12/24/48V MPPT controller would solve this problem.)

The switching system you mention might indeed work but there are some arcing problems when trying to switch 400-500 volts under load. So you'd need a way to ensure that there's no current in the string before switching, which would add to complexity. Question there - how would you segment your typical array? If you assume a 550 volt maximum and a 450 volt operating point you could cut it in half, parallel the two halves and feed a Midnite 250KS charge controller. Going into 48 volts they can handle up to ~300 volts so you'd have some margin. Or perhaps just tap the array at the halfway point and use half the array; that would require no switching.

Thanks for the suggestions.

ggunn

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

The switching system you mention might indeed work but there are some arcing problems when trying to switch 400-500 volts under load. So you'd need a way to ensure that there's no current in the string before switching, which would add to complexity.

It's not a problem when the grid goes down; the inverter shuts off so there's no current in the DC conductors. When the grid returns you'd want to shut off the CC before switching, though, if you didn't use load break rated switches.

It seems to me that the biggest issue is that it would be a significant expense no matter how you slice it, and the decision would have to be made if the odds of an extended grid outage support the expenditure. Sure, many of the folks who went through Sandy wish they had spent the money for a sustainable backup for grid power, but that's hindsight; what are the odds of it happening again?

boB

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

Yeah, that might work out. Right now the cleanest way to do that is with an SMA SPS system, with the backup power source going straight into an inverter's input. Second cleanest is with an XW-MPPT 80-600 charge controller (can accept up to 600 volts) but that's a $1200 device that you don't need 99% of the time. (A cheaper 600V to 12/24/48V MPPT controller would solve this problem.)

The switching system you mention might indeed work but there are some arcing problems when trying to switch 400-500 volts under load. So you'd need a way to ensure that there's no current in the string before switching, which would add to complexity. Question there - how would you segment your typical array? If you assume a 550 volt maximum and a 450 volt operating point you could cut it in half, parallel the two halves and feed a Midnite 250KS charge controller. Going into 48 volts they can handle up to ~300 volts so you'd have some margin. Or perhaps just tap the array at the halfway point and use half the array; that would require no switching.

Thanks for the suggestions.

I would use a SSR (triacs) rather than a relay with contacts.

I agree that GT inverters should have a power control input. It's just too easy to do !

As the battery voltage goes higher than it is supposed to in an AC coupled system, the battery based
inverter's AC voltage will eventually go high enough that the PV GT inverter will drop out due to
that high voltage, ~maybe~ even before anything bad happens to the batteries... Depending on
the size of the batteries.

Regarding splitting up the array to two MidNite controllers, they don't have to be KS's, they can be
regular 250's but they will not turn on with the input above 250V. Hopefully the total Voc of the
un-split up array is less than 500 volts DC. This is another idea of course besides using a
single 600V input controller which isn't a bad idea either.

Lots of different alternatives and ways to go here if you're looking for things to try.

boB

bill von novak

Re: Question - any GT inverters out there with remote disable/throttling?

bill von novak wrote: »

Does anyone know of any grid tie inverters that support either a remote disable (say via a contact closure or serial message) or a remote method of throttling (say a 0-10V input that reduces max power output) ?

After doing a bit of research I've discovered that many SMA Sunnyboy inverters can be ordered with an option called the power control module. It can (among other things) be used to throttle the Sunnyboy back. It can set discrete power levels of 0%, 30%, 60% or 100% of full power. Assuming the throttling is real time (for their purpose - feed-in management - it would seem it would have to be) that potentially reduces the size of inverter you need to provide the "island" that the inverters feed.