So here I am preparing for the next SoCal fire season weighing my options for backup power sources. A backup gas generator is of course on the table, but it would be nice to be able to tap into my existing 9kW SolarEdge solar array and avoid dealing with fuel and noise. I'm not looking for anything fancy, just want to be able to power my home from solar/charge a modest battery during a power outage. Ideally I envision a poor-man's setup that consists of a backup power inlet feeding the main panel and a mechanical interlock installed on the main breaker. In case of an outage I flip the main breaker OFF/connect the battery to the backup power inlet/turn on the battery and flip the backup power breaker ON, this fools the solar inverter into thinking the grid is connected, it starts to produce power that powers the home and charges the battery. The battery naturally buffers any reductions in solar output and takes over when dark. Are there any simple solutions that allow something like that?
Simplest AC coupling for backup power on an existing SolarEdge system?
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timselectric
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Solar Wizard
AIO as already stated.
Or you can grab an XW Pro that is currently on sale, there's an AC coupling guide by Schneider you could consult before you buy, they go over a lot of stuff.
When you say "modest battery" what do you mean?
A 9KW AC coupled will require AT LEAST 10KW in batteries at pretty low SOC to be able to absorb the current.
if it really is a small battery bank then the other concern is the self consumption of the inverter, most AIO units are not best known for low consumption.
The good thing is you got enough panel capacity to allow you to do most of the "heavy" stuff while the sun shining and just coast along overnight with a modest battery bank.
State the exact requirements you have in mind and someone will give you better idea of how to fulfill them.
Or you can grab an XW Pro that is currently on sale, there's an AC coupling guide by Schneider you could consult before you buy, they go over a lot of stuff.
When you say "modest battery" what do you mean?
A 9KW AC coupled will require AT LEAST 10KW in batteries at pretty low SOC to be able to absorb the current.
if it really is a small battery bank then the other concern is the self consumption of the inverter, most AIO units are not best known for low consumption.
The good thing is you got enough panel capacity to allow you to do most of the "heavy" stuff while the sun shining and just coast along overnight with a modest battery bank.
State the exact requirements you have in mind and someone will give you better idea of how to fulfill them.
Which means a new inverter? Sounds expensive. Is it possible to somehow use my current inverter with a manual transfer switch?
Quattrohead
100% off grid - EG4 Electronics
Unfortunately it is not possible. The solaredge inverter is not capable of being run with a battery and it needs to see the grid to produce power, otherwise as you have probably found out it will shut down your solar system if it loses grid.
Well, I can try. I'm not really interested in having grid interaction for TOU reasons as I'm lucky to be on symmetric NEM for 10 more years. All I need is a backup power solution to get through outages, that are becoming the norm as Edison now prefers to pull the plug over being sued for starting fires during wind events. I think a 6kWh battery is all I need to pull through a night until the next day, the hope I can somehow integrate it with my current system so I don't need to buy a new inverter and have the solar and battery work together during the day to power the home. Won't run any big loads like ac/oven, so I'm guessing 3kW power is sufficient for everything I need. Cost is an issue, I don't see spending more than 3-4k on a setup that I get to use 2-3 times a year, if that's impossible I might just stick with a portable generator.
So there isn't a battery-powered solution that can generate AC to simulate the grid that works with SolarEdge?
timselectric
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One would think a solution that uses a smaller battery and a space heater used as a load to dissipate extra power already exists
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Quattrohead
100% off grid - EG4 Electronics
It can get really complicated very quickly, have a read-up around here on AC coupling and you will start to see what it's all about.
timselectric
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Solar Wizard
XW Pro - 900$ at NAZ
Mini PDP - 300$
10KW batteries about 2K (more or less depending on what you get).
Read the AC coupling guide published by Schneider and see if that will work for you, the inverter will handle any surges that could happen in your scenario.
transfer switches or a panel and some breakers can be used to even set it up so it's bypassed at all times unless you purposefully connect it.
Mini PDP - 300$
10KW batteries about 2K (more or less depending on what you get).
Read the AC coupling guide published by Schneider and see if that will work for you, the inverter will handle any surges that could happen in your scenario.
transfer switches or a panel and some breakers can be used to even set it up so it's bypassed at all times unless you purposefully connect it.
SplitUniverse
Solar Wizard
One would think a solution that uses a smaller battery and a space heater used as a load to dissipate extra power already exists
That's just asking for trouble or involves as much effort and automation that will cost the same as the larger battery; remember, you need an inverter and battery that provide enough "stiffness" to simulate the grid and full the current ongrid system into thinking that everything is hunky dory. (don't ask me how I know, I have a Solark that messes up with the micros every time the conditions are not ideal).
SplitUniverse
Solar Wizard
Looked over Schneider docs, this looks like exactly what I need. I can land XW Pro's AC Out on a breaker in my main panel that's mechanically interlocked with the main breaker to prevent back feeding the grid. Switch to backup power will be manual but that's fine and I don't need a critical loads panel as the XW Pro will be feeding the main panel. Not yet sure how I will connect the XW Pro to the grid to charge the batteries from the grid, but it should be doable. Interoperability with my SolarEdge is an open question, need to research if it supports frequency-watt controls. Any recos for the batteries? Is that 10kWh capacity or 10 kW charging rate, or both assuming 1c? Sounds like this all can be done for about $3,500, this is about 2-3x of a cost of a portable backup generator, but I think it's worth it.
SplitUniverse
Solar Wizard
You want to keep the C rate as low as you can with any batteries, they work better and last longer with low C rates. Look at the specs for the batteries you have in mind; they will specify charging and discharging rate.
To charge from the grid you would need a way to power the grid side of the XW without connecting the grid to the Load side, various schemes can be used for that, a transfer switch is probably the easiest.
To charge from the grid you would need a way to power the grid side of the XW without connecting the grid to the Load side, various schemes can be used for that, a transfer switch is probably the easiest.
ASword
Solar Enthusiast
You also need to consider how to manage the battery state of charge throughout the year — they don’t like to sit around fully charged nor empty for long periods of time. If you have them just for rare outage events, you need to consider how to manage them the rest of the time (which is most of the time).
Also, the Schneider unit is cheap right now because it has been discontinued. They will “support” it for a decade (whatever that means… there are stories about their levels of support), and they may be getting hard to source. A very robust unit though, by all accounts.
Also, the Schneider unit is cheap right now because it has been discontinued. They will “support” it for a decade (whatever that means… there are stories about their levels of support), and they may be getting hard to source. A very robust unit though, by all accounts.
timselectric
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AIO = All In One
Inverter, SCC (Solar Charge Controller), AC charger, and a transfer switch, all in one unit.
Inverter, SCC (Solar Charge Controller), AC charger, and a transfer switch, all in one unit.
Is that a PV Inverter, battery inverter, or both?
timselectric
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Hedges
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Solar Edge means optimizer per panel.
To move the PV panels over to an AIO, you have to remove the optimizers and possibly rearrange string.
The string might presently be 24s, too high a voltage without optimizers. In that case 12s2p or 2x 12s might work for an AIO.
If RSD is required (likely for a newer installation) then you ought to replace the optimizer MLPE with something like Tigo RSD MLPE. Works without, but more recent regulations require.
SolarEdge can AC couple. It can do so gracefully if it can be reconfigured for Rule-21 frequency-watts (or maybe already is.) Without that it will cycle on/off and battery will charge/discharge rather than sitting at float.
Some AIO also support AC coupling. Because they are HF inverters, they typically need the SolarEdge connected to "Gen" relay for rapid disconnect. They behave most gracefully if AIO has DC coupled PV panels in excess of AC coupled.
I would use 2x SMA Sunny Island 6048US, the original AC coupling implementation. Because I'm a 100% SMA shop. I do that with Sunny Boy, not SolarEdge.
Schneider should be good too; I just don't have hands on experience.
I think but don't know for sure that if battery gets drained Schneider could connect to grid to charge back up. Sunny Island must wake up on battery first. Either way, it is preferable to shed non-critical loads so AC power stays on for critical loads and AC coupled grid-tie inverters.
Battery is an important decision. I've been using AGM which is dumb and simple. LiFePO4 has many benefits, including same or lower purchase price for 5x the cycle life. (my system was grid-backup so not many cycles needed.) You can run lithium batteries open-loop, telling inverter they are VRLA. That is simplest. Closed-loop can be a can of worms. Closed-loop can be done by EG4 PowerPro, Midnight (I think), BYD (expensive), and various DIY solutions.
And finally, SolarEdge may have a much higher failure rate than other brands. Not all models or installations do, but we've seen some reports. A reason to consider replacing with a hybrid/AIO.
To move the PV panels over to an AIO, you have to remove the optimizers and possibly rearrange string.
The string might presently be 24s, too high a voltage without optimizers. In that case 12s2p or 2x 12s might work for an AIO.
If RSD is required (likely for a newer installation) then you ought to replace the optimizer MLPE with something like Tigo RSD MLPE. Works without, but more recent regulations require.
SolarEdge can AC couple. It can do so gracefully if it can be reconfigured for Rule-21 frequency-watts (or maybe already is.) Without that it will cycle on/off and battery will charge/discharge rather than sitting at float.
Some AIO also support AC coupling. Because they are HF inverters, they typically need the SolarEdge connected to "Gen" relay for rapid disconnect. They behave most gracefully if AIO has DC coupled PV panels in excess of AC coupled.
I would use 2x SMA Sunny Island 6048US, the original AC coupling implementation. Because I'm a 100% SMA shop. I do that with Sunny Boy, not SolarEdge.
Schneider should be good too; I just don't have hands on experience.
I think but don't know for sure that if battery gets drained Schneider could connect to grid to charge back up. Sunny Island must wake up on battery first. Either way, it is preferable to shed non-critical loads so AC power stays on for critical loads and AC coupled grid-tie inverters.
Battery is an important decision. I've been using AGM which is dumb and simple. LiFePO4 has many benefits, including same or lower purchase price for 5x the cycle life. (my system was grid-backup so not many cycles needed.) You can run lithium batteries open-loop, telling inverter they are VRLA. That is simplest. Closed-loop can be a can of worms. Closed-loop can be done by EG4 PowerPro, Midnight (I think), BYD (expensive), and various DIY solutions.
And finally, SolarEdge may have a much higher failure rate than other brands. Not all models or installations do, but we've seen some reports. A reason to consider replacing with a hybrid/AIO.
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