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grid tied systems useless when grid is down per NEC?

MTM98290

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I am fairly new to solar and have no experience with grid tied systems. We have an off grid cabin that we have successfully implemented a full off grid setup so I understand the basics.

I am now looking to set up a backup system at our full time residence so that if the power goes out we don't have to immediately start a generator to keep a few lights and pellet stove powered up.

This prompted me to start wondering about "grid tie" and what it really means. I am assuming that it means back feeding the grid with excess AC created by a grid tied array. Other than potentially paying less for electricity bills I do not understand this logic.

If I for instance set up an array, an AIO, and a battery bank I can hook up the grid to the AC input of my simple AIO off grid unit. I now have a system that is able to draw from the grid when needed and available.

With this simple system I can have power at all times. I will never be able to get paid a dollar per day or whatever for my excess electricity but it will function when I need it.

The way I understand it, If we had a grid tied system we would have nothing when redundancy was most important.

So is grid tied really only for generating money/credits toward utility bills? Is there really no way to separate from the grid that is not safe for the utility workers etc? Why is a transfer switch adequate for a generator but not a solar backup system? What am I missing here?
 
This prompted me to start wondering about "grid tie" and what it really means. I am assuming that it means back feeding the grid with excess AC created by a grid tied array. Other than potentially paying less for electricity bills I do not understand this logic.

Yep.

If I for instance set up an array, an AIO, and a battery bank I can hook up the grid to the AC input of my simple AIO off grid unit. I now have a system that is able to draw from the grid when needed and available.

With this simple system I can have power at all times. I will never be able to get paid a dollar per day or whatever for my excess electricity but it will function when I need it.

Yep, but the system would have to be carefully sized to be able to pass through all your loads as well as power them off-grid. More commonly, the system is smaller and only powering a separate critical loads panel.

The way I understand it, If we had a grid tied system we would have nothing when redundancy was most important.

Correct. SOME GT systems like the IQ8 microinverters can be grid forming and work without batteries.

So is grid tied really only for generating money/credits toward utility bills?

Yes, and any environmental motivations. Worth noting that GT tends to be markedly less costly than a system with battery backup. Additionally, there are folks like me who have maybe had a half dozen significant power outages in 25 years, so backup isn't a big deal.

Is there really no way to separate from the grid that is not safe for the utility workers etc?

Yes, but most GT inverters do not form their own grid by default.

Why is a transfer switch adequate for a generator but not a solar backup system? What am I missing here?

It likely is, but again, most GT inverters do not form a grid in the absence of the grid.
 
Thank you for the simple but complete clarification.

If we could just build enough storage capacity to store all of the daytime PV production capacity made in the middle of the day while the demand is low we would be set.

Storage is always the most expensive and resource intensive part of these systems it seems.
 
SOME GT systems like the IQ8 microinverters can be grid forming and work without batteries.

Most GT inverters do not form their own grid by default.
Thanks..
Could you elaborate a little bit more on this? It sounds like some systems can still work when the grid is down without batteries? I assume this grid forming technology is quite new?
 
Thanks..
Could you elaborate a little bit more on this? It sounds like some systems can still work when the grid is down without batteries? I assume this grid forming technology is quite new?
Some grid tied systems can island when the grid goes down, and provide power to the home. Some grid tied systems cannot. Get a system that can work off grid too.
 
Questions to ask yourself.
How often do I lose power?
Is it often enough to be concerned about?
Why spend so much more on batteries and a hybrid inverter to have power when a stand by generator with transfer switch is cheaper?
 
Questions to ask yourself.
How often do I lose power?

once last 12 years
Is it often enough to be concerned about?
not at all
Why spend so much more on batteries and a hybrid inverter to have power when a stand by generator with transfer switch is cheaper?
simply put : generators suck, rules and payback on grid tie depend on politicians, powerco's and their ever increasing greed, and changing of rhe rules.
i can very much imagine that credits/return on generation will disapear in the very near future ( here in my location ( eu ) , 2026 , credits will go away, and payback for generation goes to the gross bulk rate (0,05 c/kwh), one them still has to pay transport fees and taxes over what one generates
they cannot charge or tax you for what you dont use from them.

so in short, the grid is my generator ( or rather backup source)
 
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For a grid-tie inverter to operate when grid is down, there must be a transfer switch or at least a pass-through relay to isolate the grid.

Some GT PV inverters can provide batteryless backup, and some hybrids (PV + battery + grid) are battery optional.

Given the cost of batteries, I think batteryless backup should work for many cases and be a better deal. Sunny Boy offers "Secure Power", 120V 2kW while the sun shines. That could chill your fridge/freezer during the day, get you through extended power outages. Use a 12V AGM battery and charger for communication gear.

Much more money, I think SolArk is batteries optional. For little money, other hybrids do too. That leaves you the option of adding batteries later. Of course starting surge is limited to PV and capacitors unless small batteries are added. 4x car batteries made the difference for one forum member to be able to start a Skillsaw with an inexpensive hybrid.

I'm going to be looking at the SMA Smart Energy hybrid when details come out later this month, instead of Sunny Boy. I expect price to be in $2500 to $3500 range, should provide the same functionality without batteries, or peak-shaving with.
 
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