diy solar

diy solar

Grid tie inverter power generation in blackout/offgrid

mrzed001

Voice of reason
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Apr 10, 2020
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Hungary - EU
Hi
I am searching for a solution.
I want to make a grid tie system, that sells power to the grid. And a separate UPS system with MPP Solar inverter and lithium batteries.

The possible grid tie inverters are limited, so no MPP Solar for example, but many Huawei, Fronius, SMA, Solaredge, SAJ, .... also no hybrid inverter is allowed by utility (EU).

The main problem is when there is a blackout (no power from grid) the grid tie inverters stop. Does not produce power (not to shock linemen).
And so no solar power can be used by the MPP Solar inverter to store in the battery or used directly by the house.
(I can not use the MPP Solar's PV possibility, because I can not use it grid tie ... I need to use a separate grid tie inverter)

Is there a solution (manual is alright) so I could shut down grid connection, and produce a sinus wave ... so the grid tie inverters start generating power again ? (in an off grid situation)

I saw some videos but nothing serious.
This guy used a 1000W pure sine wave inverter to start grid tie inverters (like a micro grid). But had nothing to stop the backfeed from grid tie to the 1000W inverter, so it does not seem very reliable

I know there is the Victron 8000, but that cost a lot (and not compatible with DIY battery cell-s).

Any other solution maybe ?
Thanks
 
Put in a grid-tie inverter (with Rapid Shutdown, if required to let firemen isolate roof panels if required), like a good boy.
After system is complete, signed off, inspected, etc., insert a suitable battery inverter (Sunny Island, Skybox, etc.) between the breaker panel and the GT inverter (or it's separate disconnect, if there is one.) When grid goes down, battery inverter disconnects from grid and lights up the GT inverter.
You can now run critical loads off the battery inverter, with GT inverter helping out.
Add an interlocked (normally for backup generator) backfeed breaker in your main panel. You can manually shut off main breaker and enable backfeed so anything in the house can be powered as well.

Many of these systems use frequency shift by battery inverter to tell GT inverter to throttle production, in order to match load.

A simpler no-battery solution is SMA's "Secure Power", up to 2000W direct from PV to 120V AC (maybe 220V for Europe). That is manually enabled, has its own separate outlet. It is only usable if you do not have "Rapid Shutdown", which opens switches between individual PV panels when AC goes away.
 
I can't tell what sort of grid-tie inverter those things are due to the use of a Sorny Unsteady-cam. Can a grid-tied inverter be tricked into running islanded? Yes. It's not necessarily as straight forward as what is being shown though as decent grid-tie inverters do tests against what they think is the grid to make sure it really is the grid and not another inverter. This is how it's possible to have multiple grid-tied inverters in parallel feeding the same installation and still have anti-islanding protection.

There are other issues to consider so all up I'd not recommend going down this path even though it is technically possible.
 
I am searching for a solution.
I want to make a grid tie system, that sells power to the grid. And a separate UPS system with MPP Solar inverter and lithium batteries.

The possible grid tie inverters are limited, so no MPP Solar for example, but many Huawei, Fronius, SMA, Solaredge, SAJ, .... also no hybrid inverter is allowed by utility (EU).

Where are you located? Why is no Hybrid inverter allowed?

The main problem is when there is a blackout (no power from grid) the grid tie inverters stop. Does not produce power (not to shock linemen).
And so no solar power can be used by the MPP Solar inverter to store in the battery or used directly by the house.
(I can not use the MPP Solar's PV possibility, because I can not use it grid tie ... I need to use a separate grid tie inverter)

Is there a solution (manual is alright) so I could shut down grid connection, and produce a sinus wave ... so the grid tie inverters start generating power again ? (in an off grid situation)

There are certainly other ways of using solar power for backup. Have you figure out how much power you would need in Watts at any given time? And how much energy in Watt Hours while you are without grid power?

Since you say you do want to sell power to the grid, do you already have a net energy agreement with your local power utility company? This is normally the hardest part. In most places, you can pretty much build anything you want in your own home, but once you start to push power back out to the utility, then you have to make sure you do not violate any rules. Many grid tie and hybrid systems are able to be set in a "zero export" mode where they can help power your home without ever pushing current back out to the grid. But if you can push power out, you can save some cost if the net energy agreement is decent.

Do you have existing equipment now? For any normal amount of power during a blackout, you will need a battery bank. Some inverters are claiming they will be able to make a stable grid without batteries, but they are not doing it yet. Having a battery bank give your system a place to push extra solar power, or pull power if the solar production falls short of the demand. The size of the battery bank is normally determined by how much you want to be able to run overnight when the sun is not helping. Then you need enough solar to run the loads when the sun is up and enough extra power to also charge the battery back up from the night before.

Once we understand your requirements a bit more, we can help you try to figure out what gear you will need. There are only a few battery based inverters that can sell power from battery back to the grid, but for a backup power system, that should not be needed. I am doing it here with a Schneider inverter, but only a small amount as I am just trying to zero the grid, not actually sell much out. During the day, when my battery bank is fully charged, my grid tie solar inverters do sell a fair of bit of power out to the grid though. If you just want to top up and float the batteries until there is a power failure, there are many inverter options that can work for you.

Let us know what you are trying to do in more detail.
 
After system is complete, signed off, inspected, etc., insert a suitable battery inverter (Sunny Island, Skybox, etc.) between the breaker panel and the GT inverter (or it's separate disconnect, if there is one.) When grid goes down, battery inverter disconnects from grid and lights up the GT inverter.

I know this solution, but it costs extra +4000$

I already plan to use MPP Solar MK5048 inverter (+16piece 3,2V 280Ah cells) as an UPS. Both together is less than 2000$.

So I only need some small separate thing to go around the islanding.
It can be a separate inverter also connected to the 48V battery


Many of these systems use frequency shift by battery inverter to tell GT inverter to throttle production, in order to match load.
And to lower production too. That is important because if battery is full and low usage then overload
 
Where are you located? Why is no Hybrid inverter allowed?

EU - Hungary. Utility have a list of tested and enabled inverters.

There are certainly other ways of using solar power for backup. Have you figure out how much power you would need in Watts at any given time? And how much energy in Watt Hours while you are without grid power?

My plan is a small 5 kWp PV system to use the grid like battery. (1 phase 230V) ... so at the end I almost do not pay anything for utility power.

And separate MPP Solar 5kW inverter with 14 kWh battery to power necessary equipments UPS mode.
It can do bypass and online double conversion UPS modes.

Yes, I could go like offgrid with the MPP Solar system ... but that is not the goal.
The goal is to have an all the time 80% loaded UPS system and a separate money making solar system (ok not make money but zero pay to utility).
But in an emergency (like big blackout) I want to use the solar system to power the UPS system.


Since you say you do want to sell power to the grid, do you already have a net energy agreement with your local power utility company? This is normally the hardest part. In most places, you can pretty much build anything you want in your own home, but once you start to push power back out to the utility, then you have to make sure you do not violate any rules. Many grid tie and hybrid systems are able to be set in a "zero export" mode where they can help power your home without ever pushing current back out to the grid. But if you can push power out, you can save some cost if the net energy agreement is decent.
Do you have existing equipment now?

This is not an issue thank god.
Utility company has procedure for it (government regulated) so they accept all system with allowed and tested inverters.
Only in the planing phase ... I want to make the whole system first in my head and then make it.
 
I can't tell what sort of grid-tie inverter those things are due to the use of a Sorny Unsteady-cam. Can a grid-tied inverter be tricked into running islanded? Yes. It's not necessarily as straight forward as what is being shown though as decent grid-tie inverters do tests against what they think is the grid to make sure it really is the grid and not another inverter. This is how it's possible to have multiple grid-tied inverters in parallel feeding the same installation and still have anti-islanding protection.

There are other issues to consider so all up I'd not recommend going down this path even though it is technically possible.
Just to revive an old thread:
are you aware of special requirements to the master inverter in order to work as being the pseudo-grid?
Have you seen models that will produce the magic smoke when back-fed by a grid tie inverter?
Normally a grid tied inverter should take care of matching phase/voltage, but what happens if the "pseudo grid" cannot take all the power available?
 
Hi
I am searching for a solution.
I want to make a grid tie system, that sells power to the grid. And a separate UPS system with MPP Solar inverter and lithium batteries.

The possible grid tie inverters are limited, so no MPP Solar for example, but many Huawei, Fronius, SMA, Solaredge, SAJ, .... also no hybrid inverter is allowed by utility (EU).

The main problem is when there is a blackout (no power from grid) the grid tie inverters stop. Does not produce power (not to shock linemen).
And so no solar power can be used by the MPP Solar inverter to store in the battery or used directly by the house.
(I can not use the MPP Solar's PV possibility, because I can not use it grid tie ... I need to use a separate grid tie inverter)

Is there a solution (manual is alright) so I could shut down grid connection, and produce a sinus wave ... so the grid tie inverters start generating power again ? (in an off grid situation)

I saw some videos but nothing serious.
This guy used a 1000W pure sine wave inverter to start grid tie inverters (like a micro grid). But had nothing to stop the backfeed from grid tie to the 1000W inverter, so it does not seem very reliable

I know there is the Victron 8000, but that cost a lot (and not compatible with DIY battery cell-s).

Any other solution maybe ?
Thanks
According to what I understand from inverters; If you have an off-grid inverter, during blackouts, you can FIRST AND MOST IMPORTANT, disconnect your house net from the grid and then connect the inverter to a plug. This one will produce AC for the house only. When you are done, SUPER IMPORTANT, disconnect first the inverter and then you can turn on the grid fuses.

If you are connected to the grid and connect an off-grid inverter, somebody can get hurt receiving a AC 220V discharge in case the blackout is due to grid repairs. Also, when the grid comes back to life, then it dumps electricity on your inverter and kills it.

What did you do at the end?
 
According to what I understand from inverters; If you have an off-grid inverter, during blackouts, you can FIRST AND MOST IMPORTANT, disconnect your house net from the grid and then connect the inverter to a plug. This one will produce AC for the house only. When you are done, SUPER IMPORTANT, disconnect first the inverter and then you can turn on the grid fuses.
Not exactly :)
If you buy an all-in-one off-grid inverter then it has an AC in and AC out port.
You connect (permanently) the grid to AC in, and your house to the AC out port.
When a blackout comes the inverter internally switches from grid power to its inner (DC/AC) inverter power.

The stupid example I cite was for running a grid-tie inverter in a blackout (in an emergency situation)

If you are connected to the grid and connect an off-grid inverter, somebody can get hurt receiving a AC 220V discharge in case the blackout is due to grid repairs. Also, when the grid comes back to life, then it dumps electricity on your inverter and kills it.
Off-grid means that its OUTPUT is off the grid. You should never connect it to grid (not in a blackout, not ever).
So you need like a transfer switch to ensure it.

What did you do at the end?

I am considering now the Deye inverters (Sol-Ark in US)
That has a third separate port for AC coupling grid-tie inverter to it.
So in a blackout it gives power to grid-tie inverter to work, but does not give to grid. Only to house/load.
 
Off-grid means that its OUTPUT is off the grid. You should never connect it to grid (not in a blackout, not ever).
So you need like a transfer switch to ensure it.
You are correct, but what I understood is that If you disconnect the fuses from your house, so therefore you make it off-grid manually, you could use a regular off-grid inverter. Somebody explained that in another post.

That this is recommended, safe, etc... that is another story. Things could go wrong easily...

My answers are always heading into frugality, ideally the best is to use smart systems indeed such as the one you mentioned.
Thanks for sharing, good to learn that such all-in-one inverters exist :)
 
You are correct, but what I understood is that If you disconnect the fuses from your house, so therefore you make it off-grid manually, you could use a regular off-grid inverter. Somebody explained that in another post.

That this is recommended, safe, etc... that is another story. Things could go wrong easily...

My answers are always heading into frugality, ideally the best is to use smart systems indeed such as the one you mentioned.
Thanks for sharing, good to learn that such all-in-one inverters exist :)

With the breaker panels we have in the U.S., an interlock is available so we have to turn off main breaker before turning on a backfed "generator" breaker. That lets us safely feed our house from an off-grid inverter.

In Europe or U.K. with DIN rail breakers, you can find some which are an interlocked pair packaged together.
I found some really cheap ones on eBay coming from China, but they made a buzzing sound, didn't trust them.
There are some name brands available. Midnight sells some.

You can also buy battery inverters which serve as a UPS, pass through the grid (and GT PV), then disconnect during grid failure to feed the house. Some of them perform frequency shift to control output of GT PV inverters with frequency-watts feature.
I use SMA Sunny Island, which does that. There are several other brands including Schneider and Outback Skybox.

Of course the hybrid or all in one can do the same in a single package.
 
Pardon me: off grid generally means you have no grid in the house at all.

What you mean is a backup fo outages: That is a completely different challenge.

Nope.
Off-grid means that its output is off the grid (can not connect output to grid because it is not synchronized to it).
It can have grid input too.

So there is 2 off-grid system:
- Off-Grid with grid support (has AC_in and AC_out port)
- Separated Off-Grid (only has AC_out port or only that is used)
 
The short version here is that the original poster wants to be able to make a rid tied solar PV system work when the grid goes down.

There is no cheap way to do it safely. Grid tie solar inverters need to see a stable grid to produce output. To fake them into seeing a local micro grid, you need a battery inverter that can do three things.

First it has to be a pure sine wave inverter that is more powerful than the peak solar power.

It needs to be bidirectional, meaning it can absorb power back into the battery if the solar is producing more than the loads are using.

And third, it needs some way to be able to reduce the output of the solar inverters when the battery is full

To make an inverter that can do all of these, it needs to be well designed and use some quality high power components. And since you are likely dealing with a few thousand watts of power, do you really want to do a cheap solution that might not be safe?

People have thrown together systems with inverter type generators that will wake up the solar, but if the solar ever makes more power than the load, it can go bad in a big way. Same thing with trying to just use any old off grid battery inverter. AC coupling to make a grid tie inverter function off grid (during a grid outage) is not a simple task. I would not try to use any inverter that is not rated for AC coupling in the instructions. At the very least, it needs to be able to accept back feed current and do frequency shifting to control power. Once you have those functions, the cost of adding the transfer relay is not a big deal, so most of the ones capable have it built in.

If the existing grid tied system is a string inverter, why not use a transfer switch on the DC side to an off grid style charge controller to charge a battery feeding an off grid inverter for backup power?
 
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