Grid Tie with no batteries

[RainbowKraut]

I'm still trying to understand how a grid tie system works. I want to tie to the grid, and use net metering, and have no batteries. But I'm being told by one solar company that I can't use my solar to power my house if the grid goes down. I don't get it. Seems to me that if it's a sunny day, and the grid goes down, my array is still producing power, so why can't it power my house? Please educate me.

 

[sunshine_eggo]

I'm still trying to understand how a grid tie system works. I want to tie to the grid, and use net metering, and have no batteries. But I'm being told by one solar company that I can't use my solar to power my house if the grid goes down. I don't get it. Seems to me that if it's a sunny day, and the grid goes down, my array is still producing power, so why can't it power my house? Please educate me.

Let's look at the words...

Grid-tie = tied to the grid. The operation of your system is dependent on the grid. The inverters must sense a grid before they will engage. If there is no grid, there is nothing to synchronize to, so they don't function.

This is a safety feature. If grid is down, and your system is live, you're actually the grid thus potentially shocking anyone working on the system.

Some inverters like the IQ8 microinverters can be made to operate in a grid down situation. I don't know the details.

A way around this is by providing an off-grid inverter with batteries to provide the "grid" to which the GT PV inverter can synch to. This is called AC coupling. High quality inverters capable of AC coupling can sense the surplus power on their output and use the GT PV to charge their batteries.

 

[Bud Martin]

BTW, once you understand how it works, you should also ask the solar company if the system can be integrated with battery now or later or not.

 

[ImAnIdiotPleaseBePatient]

BTW, once you understand how it works, you should also ask the solar company if the system can be integrated with battery now or later or not.

Second this, but also ask them if it can be integrated with the *cost effective* batteries now or later, because some (enphase etc) are reeeaaally expensive.

 

[RainbowKraut]

Okay, so it's an intended design limitation. I get the safety aspect. For my standby generator there is a transfer switch. The generator can not supply power to my house unless the connection to the grid is first disconnected. I would think that at least one manufacturer would be smart enough to build in a transfer switch or some other device into the inverter so that PV power would not flow into the power grid if the grid was down. I can't be the only person who wants to do this.

 

[sunshine_eggo]

Okay, so it's an intended design limitation. I get the safety aspect. For my standby generator there is a transfer switch. The generator can not supply power to my house unless the connection to the grid is first disconnected. I would think that at least one manufacturer would be smart enough to build in a transfer switch or some other device into the inverter so that PV power would not flow into the power grid if the grid was down.

At least one has. Have you looked into the aforementioned IQ8 microinverters?

I can't be the only person who wants to do this.

Definitely not. Most GT PV owners think they're going to have power during an outage, until they discover they don't during their first outage.

 

[RainbowKraut]

Sunshine-eggo,

Yes, I did look into the Enphase option. There are several extra pieces of equipment the must be added to make it work, and at a significant cost. I'll have to weigh that option against just adding batteries and using a hybrid inverter. I have also learned that the array must have a "reference" for frequency and voltage in order to operate, so the tie to the grid and disconnect from same is not just a safety feature, it's functional.

One other manufacturer has an "emergency power" option on their inverter, but it is only a 15 amp outlet.

Thanks for all the info. I'm slowly learning how much I don't know about solar.

 

[dcg9381]

I'm still trying to understand how a grid tie system works. I want to tie to the grid, and use net metering, and have no batteries. But I'm being told by one solar company that I can't use my solar to power my house if the grid goes down. I don't get it. Seems to me that if it's a sunny day, and the grid goes down, my array is still producing power, so why can't it power my house? Please educate me.

The only part you are missing:

PV solar is not allowed to be connected to the grid (AT ALL) if the grid is down. The idea behind this is that we don't want PV arrays electrifying the grid when we've got linemen working on it. All grid tie inverters (that are legal) shut down when the grid is offline.

Grid tie, no batteries, and net metering is likely the most cost effective way to have a PV solar install pay back.

If you want power back up, you have to isolate from the grid via a transfer switch and use a hybrid inverter than can switch to battery power. Direct to PV solar (no battery) - it's too unstable to keep up with variable loads in the house, especially as clouds pass by.

 

[sunshine_eggo]

Thanks for all the info. I'm slowly learning how much I don't know about solar.

Same!

 

[GregTR]

In addition, the PV only systems that will provide power in a grid down situation without batteries have some additional stipulations, such as limited power output.

The issue you face with a PV only backup is that it will only work when the sun is out, it will have no ability to handle larger loads (unless you have a large PV system) and it will be at risk of losing instant power the minute a cloud rolls in front of the sun. These are deterrents for most people and manufacturers to even consider such a setup.

Your best bet is to buy a hybrid inverter and put a small-ish 5kWh battery on it. This will allow backup functionality in a grid down situation for not that much more money. Then again "not that much more" is a personal valuation.

 

[solar8484]

Okay, so it's an intended design limitation. I get the safety aspect. For my standby generator there is a transfer switch. The generator can not supply power to my house unless the connection to the grid is first disconnected. I would think that at least one manufacturer would be smart enough to build in a transfer switch or some other device into the inverter so that PV power would not flow into the power grid if the grid was down. I can't be the only person who wants to do this.

You are certainly not the only one who wants to do this. Unfortunately, the manufacturers want to sell you batteries. The Enphase iQ8 is a good example that can provide sunlight only power without batteries but the solution requires lots of add-on's that basically get you ready for the batteries that they want to sell to you.

 

[dcg9381]

Okay, so it's an intended design limitation. I get the safety aspect. For my standby generator there is a transfer switch. The generator can not supply power to my house unless the connection to the grid is first disconnected. I would think that at least one manufacturer would be smart enough to build in a transfer switch or some other device into the inverter so that PV power would not flow into the power grid if the grid was down. I can't be the only person who wants to do this.

I have a house with a 20kw generator, 6kw grid tie solar, I did it a few years ago - at the time it was very difficult to integrate solar and generator with them both active. So I have a transfer switch (automatic) - which kicks in the generator, but solar is tied in up stream of the transfer, so it shuts off.

Today, you can do what you're talking about, but it's expensive. You essentially need enough inverters to be able to cover your home's entire power needs.. So if you're expecting to cover a 200A main, that's over 40KW of inverter capacity necessary. That's a bunch of inverters. Modern "hybrid" inverters can do batteries, grid tie, perhaps generator power (some are picky about the power being clean) - but you need a bunch of them...

 

[Hedges]

Sunny Boy has "secure power", manually enabled PV direct 120V 2000W outlet to use during grid failures.
For a while, was said it did not work with "Rapid Shutdown" now required for rooftop panels. But I think I read there was a way with 9V batteries to wake the panels up and use it anyway.

https://files.sma.de/downloads/SBxx-US-DS-en-41.pdf

You can add a battery inverter later, for a not-insignificant price.

Coming soon to an SMA near you is a PV/Battery hybrid inverter
We don't know its capabilities yet, but can guess similar to European 3-phase Smart Energy.

Discover the Sunny Boy Smart Energy | SMA America

The hybrid inverter at the heart of the SMA Energy System, with three backup options: Sunny Boy Smart Energy ► Discover now!

www.sma-america.com

Other brands offer similar features today, from Growatt, Outback, SolArk.

 

[xjaw4]

There are inverters that work without the grid and without batteries.

ACDCX Hybrid Asymmetric Inverter (1.25 kW) - Practical Preppers

The ACDCX asymmetric inverter allows you to run any Air Conditioner or other A/C load appliances directly with solar. You can even use the grid as a back-up!

practicalpreppers.com

Also in hotspot energy.com

Sol-ark and others can run without batteries or with batteries but you need batteries to have power without the grid. Since even a small automotive 12v inverter can power lights after dark and cheaply a off grid no battery inverter is tough to justify.

 

[RainbowKraut]

dcg9381;

I understand the safety issues. And I understand the need to isolate from the grid in the event of an outage. I have a large house. 400 amp service from the grid ( 2-200 amp panels). I have a 5kw generator, with a manual transfer switch that will run everything that is 120V. If we lose power in the winter, I have a wood stove for heat. I was hoping to be able to supplement the generator with solar to be able to power up my heat pump in the summer for air conditioning. I'm planning 17.5kw in solar.

I'm intrigued by the suggestion from Greg to use a hybrid inverter and just get a basic battery so that the array can function. It would be great If I could find an inverter that would also allow me to connect up my generator.

 

[GregTR]

Sol-Ark inverters allow both battery and generator to be connected. It does require a 240V generator though and the generator will be used to charge the battery and the battery will be used to power the loads. This is ideal as it allows the generator to run at a constant optimal load and the battery will provide the ebb/flow of the load balancing.

Sol-Ark inverters are not cheap but they are versatile with a TON of options and they're also battery agnostic and can use any 48V battery storage system which makes it economic when you consider the price of brand specific battery storage like Enphase or SolarEdge.

 

[sunshine_eggo]

Sol-Ark inverters allow both battery and generator to be connected. It does require a 240V generator though and the generator will be used to charge the battery and the battery will be used to power the loads. This is ideal as it allows the generator to run at a constant optimal load and the battery will provide the ebb/flow of the load balancing.

Please elaborate. I know of no other inverter that works this way or can even work this way.

 

[Hedges]

Either charge batteries from generator or powers loads from generator at any given instant, I presume.

I think SolArk wants a generator big enough to run all loads.

Sunny Island (not cheap) can take any size generator, limit what is drawn from generator by drawing from batteries, or charge batteries from generator while passing through power to loads and producing AC from DC cocupled or AC coupled batteries.

 

[GregTR]

Please elaborate. I know of no other inverter that works this way or can even work this way.

TL;DR: Sol-Ark has multiple ways to hook up a generator. One particular way is to use the AC coupled PV input as gen input and use a backup generator with much less power than what your batteries could provide.

With Sol-Ark (at least with the 15K I have) you set the maximum power (you set maximum current) of the generator and it will charge your batteries with that power. If the batteries reach the set charge level (90% for example) the generator will be shut off (if you have a 2 wire signal input, closed for on, on your generator) and it will be on battery until the battery depletes to another set value (30% for example) at which point the generator will kick back on and charge the batteries.

Since the Sol-Ark 15K can provide 12kW of power from batteries it is generally far more than a portable generator would/could provide in and of itself that would be connected to the generator input of a grid-tied Sol-Ark 15K.

Now should you have an off-grid setup where you'd put the generator on the grid input side and have one that is much more capable than 12kW then that would definitely power your whole house in excess of 12kW. You could also do the same with a manual/auto transfer switch in a grid-tied situation too with a whole house backup generator, but I wonder why you'd want to invest in that if the generator is truly for emergencies only and not for regular use. You could also do a gen/grid shaving and have the generator provide most of the power on the grid/main input side for your house and use the batteries to provide power that is in excess of the generator's rating.

 

[GregTR]

I think SolArk wants a generator big enough to run all loads.

It precisely doesn't. You can have a significantly smaller generator that just needs to provide your "average" consumption rather than your peak consumption and you can have it on either the gen input or on the grid input and have Sol-Ark use the battery as the buffer for higher demand or as the dump load when your load side is less than what the generator outputs.

 

[GregTR]

The generator A/C produced does not get bypassed to the load side in either of these scenarios, the sine wave on the load side is from the inverter itself. Sol-Ark will work with some pretty gnarly generator output. "THD of less than 15% is preferred but not required"

 

[GregTR]

Sunny Island (not cheap) can take any size generator, limit what is drawn from generator by drawing from batteries, or charge batteries from generator while passing through power to loads and producing AC from DC cocupled or AC coupled batteries.

This is exactly how Sol-Ark works too except you can use different inputs depending on whether you're off-grid or on-grid and depends on what size generator you want to use.

 

[dcg9381]

Please elaborate. I know of no other inverter that works this way or can even work this way.

I think most hybrid inverters work this way. Just substitute "generator" for "grid" on the source side.
Note, I'd make DARN sure that my inverter would work with "dirty" generator input - not all will.

The limitation is that you're going to need to isolate "some" of your house load or you'll need inverters with enough power to cover the entire load of the house.

And from what I'm finding personally, a 6KW inverter needs a single $1.6K battery just to turn on.. More inverters are going to need more minimum battery.

It's really not practical to supplement with solar alone in a case where an inverter is necessary. Solar by itself on anything other than a cloudless day can be pretty up/down in terms of output. You need something to buffer (like a battery). The EG-4 inverters that I'm starting to use seem to switch between sources, not sure they can mix sources, but not 100% sure. IE - as long as you've got enough solar, they'll stay on solar.. But overcast for a minute, they'll switch to another source.

 

[dcg9381]

dcg9381;

I understand the safety issues. And I understand the need to isolate from the grid in the event of an outage. I have a large house. 400 amp service from the grid ( 2-200 amp panels). I have a 5kw generator, with a manual transfer switch that will run everything that is 120V. If we lose power in the winter, I have a wood stove for heat. I was hoping to be able to supplement the generator with solar to be able to power up my heat pump in the summer for air conditioning. I'm planning 17.5kw in solar.

I'm intrigued by the suggestion from Greg to use a hybrid inverter and just get a basic battery so that the array can function. It would be great If I could find an inverter that would also allow me to connect up my generator.

I have 320A service - basically the same 2 x 200A panel setup. I'd recommend getting a load tool on your panel and looking at how much variation there is in power use. My house can idle at 1100 watts for hours, but can also suddenly peak up to 8000-12,000 watts also.

I dunno where you are, but heat pumps are efficient in the cold until a certain point, then they lose massive efficiency and most residential systems are designed to kick on "heat strips" - those heat strips in my home are like 90A at 240V, so it's massive amount of power.

And heat pumps have substantial in-rush start up current required. This can be mitigated by "soft start" capacitors, but you're going to be very limited to how much HVAC you can start with a 5.5k generator... Assuming it is 240V.

I also suggest you look at the parts diagram on your generator. Figure out what the 240V breaker is ACTUALLY rated at. I've had issues with generators in that KW range not really being setup for 5000 watts continuous and having breakers that will sustain less.

To accomplish what you want, would it be possible to isolate loads? Otherwise you're looking at a pretty big investment in hybrid inverters.

 

[RainbowKraut]

DCG9831: The load tool is a good recommendation. I really don't know what my daily fluctuations are. What device do you recommend? As to the heat pump, yes LRA is high, but it works fine in cold weather ( well cold for the pacific northwest - 20F or so). My strip heat never comes on. And no, my generator will not run it.

Greg: I looked at the Sol-Ark, but I'm also looking at the EG4 8KEXP. For the price, I can get two and still be cheaper than the Sol Ark 15. Just need to figure out how much battery capacity I'll need to make them happy.