AC solar and inverter

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
It seems that the market is slowly figuring out how to solve using micro-inverter -equipped solar arrays with onsite battery storage. This inverter has a clever solution:


It apparently has a separate input for the AC output of a grid-tied solar array. It will "fool" the microinverters into thinking they're tied to the grid by providing a 60Hz sine wave at the solar array input so they produce. The inverter uses this power to charge connected batteries and (I think) power connected AC loads. If charging is complete as signaled by an external battery management system, the inverter will raise it's frequency above 60Hz to force the microinverters into shutdown.

I like the solution, though I'd want a unit that's UL listed before I even thing about installing one. That's way too much power to have running around in your basement or garage unlisted.

The above linked unit seems to need an external voltage sensing setup to figure out when the batteries are charged; it doesn't do it internally and shut down the microinverters. I'm also not to fond of needing to externally switch the power from the solar array to/from the grid connection if and when the grid supply goes down.

Anyone doing something similar, but UL listed and actually safe to install in a home? Perhaps a little better integrated too, with internal AC switching and battery monitoring?



SceneryDriver
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Um, everyone is doing this. SMA, Tesla, Enphase, Sonnen. And yes, all listed. I'd say that thing doesn't hold a candle to them.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Um, everyone is doing this. SMA, Tesla, Enphase, Sonnen. And yes, all listed. I'd say that thing doesn't hold a candle to them.
You can tell I don't do much solar. I didn't realize this was common practice; it's the first time I came across that topology. Good to know others are doing it better.


SceneryDriver
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Um, everyone is doing this. SMA, Tesla, Enphase, Sonnen. And yes, all listed. I'd say that thing doesn't hold a candle to them.
Also, the battery inverter in a setup like this and the others isn't "fooling" the inverter(s). It produces a legit AC waveform and the batteries provide a buffer to coordinate the production of the PV system with the usage of the customer.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Also, the battery inverter in a setup like this and the others isn't "fooling" the inverter(s). It produces a legit AC waveform and the batteries provide a buffer to coordinate the production of the PV system with the usage of the customer.
Yes, and not only that but in the better setups (e.g. Enphase) the solar inverters can throttle their output appropriately depending on the load and battery charge, or even to compensate for grid conditions.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Yes, and not only that but in the better setups (e.g. Enphase) the solar inverters can throttle their output appropriately depending on the load and battery charge, or even to compensate for grid conditions.
Does Enphase use powerline communications to their microinverters for PV throttling, or do they rely on frequency shifting?

Cheers, Wayne
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Read the instructions for storage systems before buying or installing a storage system in a dwelling...at least one brand has instructions that the storage system can only be installed in a room that has 5/8" Class X drywall on the walls and ceilings of the room.
 

SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Yes, and not only that but in the better setups (e.g. Enphase) the solar inverters can throttle their output appropriately depending on the load and battery charge, or even to compensate for grid conditions.
Does Enphase allow an AC-tied array to charge storage batteries, and export to the grid once the batteries are charged? I'm closing on a house on Friday that has an 8kW array installed. I finally got a look at the single line in the docs package, and it's (25) Enphase IQ7 microinverters and an Envoy IQ combiner box. Does Enphase have a central inverter/charger solution that allows for battery recharging when the grid isn't present? I'm considering a battery/solar solution for critical loads in lieu in of a generator after the mess we got with the remnants of Ida.



SceneryDriver
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Does Enphase allow an AC-tied array to charge storage batteries, and export to the grid once the batteries are charged?
Yes.

I'm closing on a house on Friday that has an 8kW array installed. I finally got a look at the single line in the docs package, and it's (25) Enphase IQ7 microinverters and an Envoy IQ combiner box. Does Enphase have a central inverter/charger solution that allows for battery recharging when the grid isn't present?

It's not 'central', but otherwise yes. Enphase takes the same modular/microinverter approach to batteries as they do with solar inverters. The equipment you mentioned supports it.

I'm considering a battery/solar solution for critical loads in lieu in of a generator after the mess we got with the remnants of Ida.



SceneryDriver
Enphase's solution should do well for you. It can also incorporate a generator.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
That system would also integrate nicely with a Powerwall, which supports frequency shifting. The newer IQ7 micro-inverters will throttle their output based on the frequency provided by the battery inverter, but the older Enphase micros will not. They are only on or off.
 

analog8484

Member
Location
CA
Occupation
Tech
Read the instructions for storage systems before buying or installing a storage system in a dwelling...at least one brand has instructions that the storage system can only be installed in a room that has 5/8" Class X drywall on the walls and ceilings of the room.
That's just one of many potential issues. Some jurisdictions only allow outdoor installations now. These are generally large lithium based batteries that are inherently flammable and difficult to extinguish after burning starts. It's always odd to me that people install them in garages that can get very hot.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
That's just one of many potential issues. Some jurisdictions only allow outdoor installations now. These are generally large lithium based batteries that are inherently flammable and difficult to extinguish after burning starts. It's always odd to me that people install them in garages that can get very hot.
Here in Texas there were a lot of people who thought that they were prepared for the outages caused by the Polar Vortex in February with their Powerwalls only to find that since they were installed outside they quit working when it got too cold for them to function.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
That's just one of many potential issues. Some jurisdictions only allow outdoor installations now. These are generally large lithium based batteries that are inherently flammable and difficult to extinguish after burning starts. It's always odd to me that people install them in garages that can get very hot.
That's arguably a reason that LiFePO should be more favored over NMC.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Here in Texas there were a lot of people who thought that they were prepared for the outages caused by the Polar Vortex in February with their Powerwalls only to find that since they were installed outside they quit working when it got too cold for them to function.
What is the roll-off curve like? Steady slope or fall off a cliff? Considering that the Powerwalls are just the Tesla car cells in a different form factor, how does that work for folks in, say, Minnesota?
 

analog8484

Member
Location
CA
Occupation
Tech
That system would also integrate nicely with a Powerwall, which supports frequency shifting. The newer IQ7 micro-inverters will throttle their output based on the frequency provided by the battery inverter, but the older Enphase micros will not. They are only on or off.
Tesla only sells Powerwall with their solar systems now.
 

analog8484

Member
Location
CA
Occupation
Tech
Here in Texas there were a lot of people who thought that they were prepared for the outages caused by the Polar Vortex in February with their Powerwalls only to find that since they were installed outside they quit working when it got too cold for them to function.

I also heard Powerwalls in TX that drained overnight and wouldn't boot up following day even with lots of sun. Also, people couldn't monitor Powerwall SOC when cell service was down so they couldn't tell how much battery charge was left.
 

retirede

Senior Member
Location
Illinois
What is the roll-off curve like? Steady slope or fall off a cliff? Considering that the Powerwalls are just the Tesla car cells in a different form factor, how does that work for folks in, say, Minnesota?

EVs have battery temp management systems. They will try to maintain the battery temp in its operating range even when parked. If not plugged in, this comes at the expense of range.
When powering down an EV when the temp is below freezing, most will give you a message: “Please plug in, if possible.”
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What is the roll-off curve like? Steady slope or fall off a cliff? Considering that the Powerwalls are just the Tesla car cells in a different form factor, how does that work for folks in, say, Minnesota?
Sorry, I don't know. All I do know is that our residential operations guys got a lot of calls from customers with externally mounted Powerwalls.
 

myspark

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
Read the instructions for storage systems before buying or installing a storage system in a dwelling...at least one brand has instructions that the storage system can only be installed in a room that has 5/8" Class X drywall on the walls and ceilings of the room.
If you are installing batteries in a room—Class X drywall on walls and ceilings is the least of your worries.
Lead acid batteries give off hydrogen gas while charging and even more so when overcharged.

Of course you can use sealed AGM or Lithium-Ion Batteries that don’t give off explosive hydrogen gas—but I don’t think OP is well prepared for that. Also fire danger is ever present.

Lithium-Ion Battery cost ten times as much compared to a garden variety LEAD-ACID battery. One 100Amp- hour Lithium-Ion costs over $1000 a pop--while a lead-acid is about $115.

Here’s more info:

 
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