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DIY Grid Tie Without Batteries

Solargrow

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Dec 12, 2021
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Hello All,
Hypothetical... If I wanted to install about 8Kw panels and have it power my house during the day and switch to the grid at night, without the use of batteries or sending power to the grid, would that be possible? I guess basically it's your standard grid tie system but I don't want to coordinate anything with the utility company.
I know people have done it and I see a lot of similar systems but the ones I'm finding all use batteries. I will add batteries later but panels are cheap and I'd like to take advantage of this Arizona sun. I just want it to switch to the panels during daylight and automatically switch to the grid when the sun goes down.
What type of transfer switch would I need and where would I find more specific info on that type of system?
Thank you
 
Hypothetical... If I wanted to install about 8Kw panels and have it power my house during the day and switch to the grid at night, without the use of batteries or sending power to the grid, would that be possible?
Anythings possible!
I guess I have 1/2 the specs you state running batteryless for the last 6 weeks since my old lead acids finally died and were disconnected.
PWMs, 1500w 12v/240w inverter, a lot of 12v items.
A 1500w 12v-240v PSU and supercaps seem to replace the battery ok for when the sun don't shines.
 
For grid tie the grid is the battery

For off grid the battery is the battery

Basically you cannot do what you suggest...there must be some sort of energy storage.

An off grid system only generates AC as you need it, it stores its extra solar power in the batteries

A grid tie system uses all the solar power available and converts it to AC, it needs the grid to dump the power that you generate and do not use.
 
Now we're talking. I'm definitely going to look into these. Thank you.

Yeah, there are inverters from MPP Solar and other brands which officially support operation in batteryless mode, however, usually only in single-inverter topology, and not in a parallel-stacked topology.

So if you need split-phase (240v/120v output), you'd need to find an inverter that can support it with single-inverter (not requiring a pair to operate in split-phase) and operate in batteryless mode, or get an EU style inverter (with single-phase output 230v-240v), which supports batteryless operation, and add in an auto-transformer (external center-tap transformer) if you'd wish to provide output in split-phase operation...
 
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Yeah, there are inverters from MPP Solar and other brands which support operation in batteryless mode, however, usually only in single-inverter topology, and not in a parallel-stacked topology.

So if you need split-phase, you need to find an inverter that can support it with single-inverter (not requiring a pair to operate in split-phase) and operate in batteryless mode, or get an EU style inverter (with single-phase output 230v-240v), and add in an auto-transformer (external center-tap transformer) if you wish to provide output in split-phase 240v/120v operation...
Great info! So if I want to use it batteryless with my 220v air conditioner I would need to find a single inverter and possibly add the transformer (for the eu models).
Is there a minimum battery bank size if I wanted to parallel inverters to get my 220? Do I have to have a full size bank or can I just get enough to balance out the system?
 
Yeah, there are inverters from MPP Solar and other brands which officially support operation in batteryless mode, however, usually only in single-inverter topology, and not in a parallel-stacked topology.

So if you need split-phase (240v/120v output), you'd need to find an inverter that can support it with single-inverter (not requiring a pair to operate in split-phase) and operate in batteryless mode, or get an EU style inverter (with single-phase output 230v-240v), which supports batteryless operation, and add in an auto-transformer (external center-tap transformer) if you'd wish to provide output in split-phase operation...
Would the lvx6048 MPP work?
 
Great info! So if I want to use it batteryless with my 220v air conditioner I would need to find a single inverter and possibly add the transformer (for the eu models).
Is there a minimum battery bank size if I wanted to parallel inverters to get my 220? Do I have to have a full size bank or can I just get enough to balance out the system?

You could run a small bank, just need 4x 12v batteries. There is probably a policy you can set in the firmware to make it favor grid or solar power over battery power...

It would just be like a UPS that would give some time (like an hour, just guessing, pulling out of rear), if it was nighttime and the grid power went down, it could still run for some limited time as a UPS to get through smaller grid outages.
 
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Batteryless and off-grid, PV has to support surge current to start motors (5x running current).
That could work for small motors like refrigerators.
The AIO systems people have mentioned could do that, but if you can have a small battery for starting surge it could run bigger loads.
SMA inverters offer "Secure Power" up to 2kW PV direct when grid down.

I think grid tie "zero export" would be better. PV supplies the lesser of 100% of loads or 100% of available power from the sun. Grid supplies the rest.
 
Batteryless and off-grid, PV has to support surge current to start motors (5x running current).
That could work for small motors like refrigerators.
The AIO systems people have mentioned could do that, but if you can have a small battery for starting surge it could run bigger loads.
SMA inverters offer "Secure Power" up to 2kW PV direct when grid down.

I think grid tie "zero export" would be better. PV supplies the lesser of 100% of loads or 100% of available power from the sun. Grid supplies the rest.

Yeah, I would agree that having even a small bank would be optimal to meet the surging demand.

That guy from the above video demonstrates this point about how having even small bank helps with surging:

(Automatically starts on 19:10)

Even good to have for a motor load like a saw where it will run for a couple minutes and power exceeds solar power, the battery makes a good buffer to fill in the solar power supply gaps (like his example where the clouds came over for a minute).
 
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Without a battery, how are you proposing for supply to match demand?
Solar panels will do that themselves.
For grid tie the grid is the battery

For off grid the battery is the battery

Basically you cannot do what you suggest...there must be some sort of energy storage.
I think the misunderstanding between 'voltage' and 'power' and the operation of solar panels compared to other power generators may be the cause of why we see the above wrong statement a lot!

In actual operation solar panels only cause the voltage difference....we determine the energy use by plugging something in!
 
One of my solar systems is dead simple.....4 ea. First Solar CdTe panels in parallel wired directly to 4 ea. home depot 48 inch 2 tube fluorescent T-8 lamps in parallel...., no fuses, no CC, no regulator, no battery, no switch, nada, sun comes up lights come on, sun sets ,lights out,


I was referring to whole house systems that work day or night
 
Grid Interactive and Grid Sharing are not the same. In grid sharing the grid picks up what the solar can't provide. They work together. (Watch the GroWatt video again). The GroWatt 3000 & 5000 do that. I can't find out if the MPP does it or not. Manufactures and Retailers don't seem proper documentation is important so you have rely on individuals documenting their experience. Really pathetic. You have to buy it to find out what it will do. Sound Familiar?
 
Solar panels will do that themselves.
Yes some solar inverters can manage to keep power supply going without a battery but what happens when a cloud comes over and generation capacity is instantly cut by 80% or more and suddenly you have insufficient power?

e.g. here's what the output of my grid tied system looked like one day a week or so ago:

Screen Shot 2022-01-01 at 12.06.33 pm.png
Being grid tied of course the arrays are producing the maximum they can at any given moment, but it does highlight challenges of managing when output capacity is so variable.
 
Yes some solar inverters can manage to keep power supply going without a battery but what happens when a cloud comes over and generation capacity is instantly cut by 80% or more and suddenly you have insufficient power?

e.g. here's what the output of my grid tied system looked like one day a week or so ago:

ItView attachment 77839
Being grid tied of course the arrays are producing the maximum they can at any given moment, but it does highlight challenges of managing when output capacity is so variable.
Valid concern. It looks like the growatt and mpp inverters someone else posted here will do grid sharing where they draw from the grid when pv power gets too low.
 
Valid concern. It looks like the growatt and mpp inverters someone else posted here will do grid sharing where they draw from the grid when pv power gets too low.
Correct on the GroWatts. As I stated before. I don't know if the MPP can do that or not. Maybe Ian at Watts247 can step in and answer that question on the MPP.
 
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