battery grid feedback

[GXMnow]

$3,000 is on the cheap side for an arm and a leg... But I get where you are going with this.

That is where the problem comes in. Any device that can "legally" push power back to the grid has to meet some strict standards. The cheap grid tie inverters rarely bother with all of the requirements. I am not even sure the Sol-Ark can do it. The OutBack SkyBox does, but it costs more than my Schneider. But the OutBack has much better software and a built in MPPT charge controller, but only a 5,000 watt inverter. The Sol-Ark is also quite expensive and has some excellent features and specs, but I could not tell from their online manual if it can grid sell from battery.

I came close to doing a "roll my own" setup with a combination of grid tie and off grid inverters and chargers and having a micro controller tie it all together, but in the end, I was not going to be saving much over the Schneider. The one thing that bugs me though, is the Schneider software has some rather dumb limitations. All of my solar is currently AC coupled on the output of the Schneider XW-Pro inverter. And with their current software, it is not able to trigger a battery charge cycle on it's own. If I start it charging, it fully charges, taking power from my existing grid tie solar inverters, and at 4pm, it switches to "Grid Support" mode and starts powering all of the loads in my backup panel, and pushing 900 watts (my setting) back to the main panel, up until 9 pm. It will then keep running my backup loads without exporting until the battery runs to my low cutoff set point. That all works great. But then the next morning, it won't start another charge cycle, it just sits at the low batter point. They expect you to also use a solar charge controller to do the charging.

Pushing power out to the grid is actually kind of tricky. From Solar, you have a limited current source, so the output current is also inherently limited. It keeps trying to pull as much power as it can from the solar panel, an then pushing it to the grid. It keeps adjusting the current, while monitoring the voltage from the solar panel. If it pulls too much current, the voltage falls, so it knows it past the maximum power point. When you connect a battery to the input of the same inverter, the MPPT search fails. As it increases the current it draws, the power just keeps climbing. If the MPPT is not well designed, it could actually pull enough power to burn out. This is why MPPT controllers have a maximum ISC input rating. That is the safe current limit. I watched a video where a guy was trying to feed a grid tie solar inverter from a battery, and it kept tripping the BMS current limit.

 

[fafrd]

I actually don't care about the limiter part, exporting to the grid is OK. Those, if appropriately used, should not impose a threat to anybody as the inverter shuts down if the grid is down. The one linked above however doesn't seem to have a battery option.

Are you talking about exporting to grid under an agreement or without?

Without an agreement, many locals / utilities charge for exported power just as much as they do for imported power (no credit).

As far as the GTILs, even though it is not documented / advertised as much as it should be, they run fine off of batteries. The MPPT-capability is wasted in n that case so you will need a separate SCC…

I’ve got 2 1000W GTILs powered by a 560Ah 24V LiFePO4 battery getting charged by a 60A Epever SSC fueled by 1.1kW PV array.

I have had very close to 0kWh of consumption during peak hours since I set up the system (mainly consume when running the 3kW electric oven which exceeds my 1.7kW generation capability).

 

[fafrd]

I do not have any experience with GroWatt or MPP inverters, but I can say for sure that the Schneider XW-Pro will sell to grid from the battery. There are not many that will because of the grid code requirements. When the grid is up, I have mine set to push 900 watts back out the grid input side. This allows it to help power the loads that are in my main panel. You can tell it how many amps to push back and time limit it. I only have it push to my main panel during the peak rate which is about triple my off peak rate. When I am running my air central conditioner, pushing that power to the main panel can save me close to $3.00 a day. It drops to about $1.50 to $2.00 on days with less load in my main panel, as I try not to export to the grid from battery, but it will do it without a problem. I may end up adding a "WattNode" which measures the power on the grid input to my home, and it can auto adjust the output of the XW-Pro to meet the demands in the main panel while limiting the export that goes out to the grid.

This is not a cheap system by any means. The XW-Pro inverter runs about $3,000 for a 6,800 watt low frequency inverter. But it is fully UL rated and meets the grid codes for legal use just about anywhere. The WattNode box that I need to true grid zero export control is about $500 more with the current transformers.

The budget GTIL inverters may sort of do the job, but the ones I looked at did not meet the code requirements and did not have safety lab testing listing. When you are talking about pushing a couple thousand watts around your home, be careful what you connect. Time shifting the power to peak time will not pay for the inverter and batteries, but being able to time shift the power is helping to pay for having backup power when the grid goes down.

This is absolutely correct.

It’ll be interesting to see whether the ‘Powers That Be’ ever authorize GTILs for use here in the US.

Until then, the best way to think about them is like an all-in-one solar generator such as those sold by Jackary used to power certain loads such as a refridgerator.

Not exactly the same but these GTIKs just plug into a standard 120V outlet like a toaster oven, the main difference being that they will push rather than pull current / power.

 

[fafrd]

Can you think of a model? I have an agreement to export so the limiter part is not even very relevant.

If you have an export agreement and have a way to stay ‘within’ its limits (max kW of export), I think jus about any Microinverter can be powered from a battery rather than PV…

The GTIL inverters can also export - just uncheck the ‘limiter’ function and set the maximum power you want the inverter to generate…

 

[minerva]

Yes, I do have an agreement and I can stay within its limits since I want to time the discharge of the battery when my consumption is high. A microinverter won't do the job because I need to be able to charge the battery and time those processes.
This is my conundrum. I have a 137,000 BTU/h pool heat pump. The ideal way to use it would be to power between noon and 6 pm when the air temperature is high. My electricity super-peak rate approaches $0.30 while I pay about $0.05 at night. Time-shifting almost never pays off but it may be worth it with a 6-fold rate difference. So I need to charge my batteries at night and discharge them during the day. I don't want to sell that energy but I can use the grid as a buffer. I have a separate grid-tie solar system and an agreement with the POCO. I would hate to put a 5kW heat pump behind a hybrid inverter.

 

[minerva]

$3,000 is on the cheap side for an arm and a leg... But I get where you are going with this.

That is where the problem comes in. Any device that can "legally" push power back to the grid has to meet some strict standards. The cheap grid tie inverters rarely bother with all of the requirements. I am not even sure the Sol-Ark can do it. The OutBack SkyBox does, but it costs more than my Schneider. But the OutBack has much better software and a built in MPPT charge controller, but only a 5,000 watt inverter. The Sol-Ark is also quite expensive and has some excellent features and specs, but I could not tell from their online manual if it can grid sell from battery.

I came close to doing a "roll my own" setup with a combination of grid tie and off grid inverters and chargers and having a micro controller tie it all together, but in the end, I was not going to be saving much over the Schneider. The one thing that bugs me though, is the Schneider software has some rather dumb limitations. All of my solar is currently AC coupled on the output of the Schneider XW-Pro inverter. And with their current software, it is not able to trigger a battery charge cycle on it's own. If I start it charging, it fully charges, taking power from my existing grid tie solar inverters, and at 4pm, it switches to "Grid Support" mode and starts powering all of the loads in my backup panel, and pushing 900 watts (my setting) back to the main panel, up until 9 pm. It will then keep running my backup loads without exporting until the battery runs to my low cutoff set point. That all works great. But then the next morning, it won't start another charge cycle, it just sits at the low batter point. They expect you to also use a solar charge controller to do the charging.

Pushing power out to the grid is actually kind of tricky. From Solar, you have a limited current source, so the output current is also inherently limited. It keeps trying to pull as much power as it can from the solar panel, an then pushing it to the grid. It keeps adjusting the current, while monitoring the voltage from the solar panel. If it pulls too much current, the voltage falls, so it knows it past the maximum power point. When you connect a battery to the input of the same inverter, the MPPT search fails. As it increases the current it draws, the power just keeps climbing. If the MPPT is not well designed, it could actually pull enough power to burn out. This is why MPPT controllers have a maximum ISC input rating. That is the safe current limit. I watched a video where a guy was trying to feed a grid tie solar inverter from a battery, and it kept tripping the BMS current limit.

What Schneider do you have?

 

[minerva]

If you have an export agreement and have a way to stay ‘within’ its limits (max kW of export), I think jus about any Microinverter can be powered from a battery rather than PV…

The GTIL inverters can also export - just uncheck the ‘limiter’ function and set the maximum power you want the inverter to generate…

Without the limiter, I basically need a grid-tied inverter with the ability to charge a battery and discharge it into the grid.

 

[minerva]

Are you talking about exporting to grid under an agreement or without?

Without an agreement, many locals / utilities charge for exported power just as much as they do for imported power (no credit).

As far as the GTILs, even though it is not documented / advertised as much as it should be, they run fine off of batteries. The MPPT-capability is wasted in n that case so you will need a separate SCC…

I’ve got 2 1000W GTILs powered by a 560Ah 24V LiFePO4 battery getting charged by a 60A Epever SSC fueled by 1.1kW PV array.

I have had very close to 0kWh of consumption during peak hours since I set up the system (mainly consume when running the 3kW electric oven which exceeds my 1.7kW generation capability).

Which inverters do you have? Can you charge the battery off the grid?

 

[fafrd]

If you have an export agreement and have a way to stay ‘within’ its limits (max kW of export), I think jus about any Microinverter can be powered from a battery rather than PV…

Yes, I do have an agreement and I can stay within its limits since I want to time the discharge of the battery when my consumption is high. A microinverter won't do the job because I need to be able to charge the battery and time those processes.

You can control a batter-driven Microinverter or a GTIL using a lamp timer (but assure it’s rated for the maximum power output). This is how I control my GTILs to generate only during peak hours…

This is my conundrum. I have a 137,000 BTU/h pool heat pump. The ideal way to use it would be to power between noon and 6 pm when the air temperature is high. My electricity super-peak rate approaches $0.30 while I pay about $0.05 at night. Time-shifting almost never pays off but it may be worth it with a 6-fold rate difference. So I need to charge my batteries at night and discharge them during the day. I don't want to sell that energy but I can use the grid as a buffer. I have a separate grid-tie solar system and an agreement with the POCO. I would hate to put a 5kW heat pump behind a hybrid inverter.

Time-shifting becomes much less sensible charging off of AC (but probably worthwhile at 6X) - do you have a DC Array or can you set one up?

I also have a NEM agreement and a 4kW AC-coupled Microinverter-based grid-tied array.

I set up a new 1.1kW DC-coupled array that does nothing but charge a 14kWh 24V battery.

That battery feeds 2 850W GTIL inverters connected through lamp timers so they are only on / connected during peak hours.

I don’t know how many Watts a 137,000 BTU heatpump requires, but a similar approach would allow you to charge all morning then power your heatpump between noon and 6pm from a combination of remaining PV power and stored battery power…

 

[minerva]

You can control a batter-driven Microinverter or a GTIL using a lamp timer (but assure it’s rated for the maximum power output). This is how I control my GTILs to generate only during peak hours…

Time-shifting becomes much less sensible charging off of AC (but probably worthwhile at 6X) - do you have a DC Array or can you set one up?

I also have a NEM agreement and a 4kW AC-coupled Microinverter-based grid-tied array.

I set up a new 1.1kW DC-coupled array that does nothing but charge a 14kWh 24V battery.

That battery feeds 2 850W GTIL inverters connected through lamp timers so they are only on / connected during peak hours.

I don’t know how many Watts a 137,000 BTU heatpump requires, but a similar approach would allow you to charge all morning then power your heatpump between noon and 6pm from a combination of remaining PV power and stored battery power…

The heat pump is about 5kW. I do have a DC array. There is no point for me to charge the battery with the solar. I can send it to the grid. The difference between day-time and day-time super peak is not worth it. I need to be able to charge it at night. What GTIl do you use again?

 

[fafrd]

The heat pump is about 5kW. I do have a DC array. There is no point for me to charge the battery with the solar. I can send it to the grid. The difference between day-time and day-time super peak is not worth it. I need to be able to charge it at night. What GTIl do you use again?

Oh, do you have a super-cheap middle-of-the-night rate like for EV charging?

Then yes, you want an AC charger that gets your battery filled during that ultra-cheap rate window.

Your heat pump burns 5kW but for a full 100% duty cycle over those 6 hours of peak? That would be 30kWh of capacity but you’ve also got to figure in inverter efficiency.

The GTIL inverters have only ~80% efficiency driven by 24V batteries (might be higher driven off 48V batteries) so that would mean 37.5kWh of storage to power your 6kW load through 6 hours of continuous use.

The GTIL inverters I am using are 1000W 120V models: https://www.amazon.com/Inverter-Lim...ocphy=9032080&hvtargid=pla-523294429130&psc=1

I use one per leg because my load is 120V.

If your heatpump is 240V, you can use one or more of the 2kW models (that require 48V battery).

They can be ganged and only put out ~85% of rated power when battery-driven, so you’d need 4 of these in parallel to supply 6kW @ 240V.

Growatt also appears to have GTIL inverters but only for 240V (no 120V) so that might be a better option for you (believe they have higher-power models to at least 5kW if mot above 6kW).

 

[minerva]

Oh, do you have a super-cheap middle-of-the-night rate like for EV charging?

Then yes, you want an AC charger that gets your battery filled during that ultra-cheap rate window.

Your heat pump burns 5kW but for a full 100% duty cycle over those 6 hours of peak? That would be 30kWh of capacity but you’ve also got to figure in inverter efficiency.

The GTIL inverters have only ~80% efficiency driven by 24V batteries (might be higher driven off 48V batteries) so that would mean 37.5kWh of storage to power your 6kW load through 6 hours of continuous use.

The GTIL inverters I am using are 1000W 120V models: https://www.amazon.com/Inverter-Lim...ocphy=9032080&hvtargid=pla-523294429130&psc=1

I use one per leg because my load is 120V.

If your heatpump is 240V, you can use one or more of the 2kW models (that require 48V battery).

They can be ganged and only put out ~85% of rated power when battery-driven, so you’d need 4 of these in parallel to supply 6kW @ 240V.

Growatt also appears to have GTIL inverters but only for 240V (no 120V) so that might be a better option for you (believe they have higher-power models to at least 5kW if mot above 6kW).

Yes, it's TOU rates, 5 cents at night. The heat pump kicks in intermittently depending on the water temp, season. I am planning on investing in a 12-14 kWh battery system. May expand as needed. I don't need to cover every single kWh. I can and do run it at night. I do want to be able to run it for 2-3f in the middle of the day heat though.

 

[fafrd]

Yes, it's TOU rates, 5 cents at night. The heat pump kicks in intermittently depending on the water temp, season. I am planning on investing in a 12-14 kWh battery system. May expand as needed. I don't need to cover every single kWh. I can and do run it at night. I do want to be able to run it for 2-3f in the middle of the day heat though.

For your application, you’d probably be better off with a Hybrid Inverter. A 6kW model (or 5kW with boost-from-grid) connected to your heat exchanger as the only ‘critical load’. You don’t need MPPT since you don’t have PV but most have an integrated AC charger and will allow you to program the time to switch from AC-pass through to battery power as well as the time to charge the battery.

Schneider or Magnum are two top-tier brands to consider (in addition to Outback Radian or Solark). If you are looking to spend less, there are a few Chinese brands to consider including Growatt and MPP Solar with US presence and a growing following…

In addition to the 6kW (or 5kW) inversion from battery, the other key spec you’ll face will be the power of the AC battery charger (to get your battery fully recharged during your ultra cheap EV-charging window).

Some of these hybrid inverters can be ganged (giving you both 2-4x power output as well as 2-4x battery charging power) and in any case, you may need a separate AC battery charger in parallel (depending on how long your ultra-cheap EV window is).

 

[GXMnow]

I have the Schneider XW-Pro 6848 6,800 watts at 120/240 volt split phase. And I now have a usable 36 KWHs of Chevy Bolt battery modules wired in a 14S12P arrangement of 60 amp hour cells LG cells. That makes 720 amp hours at a nominal 51.8 volts. It's about 58% of a complete Chevy Bolt battery pack. Yes, I am following the recall news.

Since you want to run your pool heater during the day, I would just add more solar with microinverters. That is by far the most efficient, to use the power as it is being produced. Charging is 95% efficient, at best, and inverting is also about 93% efficient, and the batteries lose a little as well. I lose a full KWH when I move 10 KWH from solar to peak rate evening time here. And my rates go from 17 cents a the cheap time to 43 cents at the peak rate. Moving that 10 KWH in theory saves me 10 x 0.42 - 10 x 0.17 = $2.50 cents a day. I figure I average moving about $2.00 a day for 300 days a year to account for days of weak sun or other reasons I can't push the full 10 KWH in the peak window. I may actually do better than that. But that still means I am saving $600 a year by time shifting the power. But I spent $3,000 on the inverter, and probably something like $5,000 on the batteries. Maybe a little more with the cases, BMS units, and wiring etc. So taken totally separate from the solar power, the battery system will take 15 years to pay off. But I am only expecting the batteries to last about 10 years. So yup, at the peak to off peak rate here, it won't pay off, but it sure does cut down on the cost of having backup power.

But if you take the entire cost of my solar installation into the equation, and figure on what I am saving, then my system pays off in about 11 years. My Enphase solar PV system has already produced 16.9 MEGA watt hours. And it has just been running a bit over 2 years. In the full year of 2020, it made 7.9 MWHs. If I just figure that half of it was used at peak, and half off peak, so we average the value of the electricity, that is 30 cents per KWH x 7,900 = $2,370 per year chopped off of my electric bill, but that is with the battery doing the time shifting. Adding up everything I spent on the solar panels, inverters, installation, and my battery system, I spent $26,000 over a span of 2.5 years. Divide by the 2,370 per year = 10.97 years to cover the whole cost of everything just from electric bill savings. Production may fall off some, but I also expect So Cal Edison to jack the rates more. So that may end up a wash.

I do plan to add another 2,000 to 3,000 watts of solar to DC couple charge the battery bank. I am still working on the budget for that upgrade. If I do the ideal 9 x 330 watt panels, It will easily provide all of my night time power and improve y system efficiency while freeing up the microinverters to export more or run my air conditioning during the day. That would add about 60% to my total solar production. So kick my annual energy production to over 12.5 MWHs a year. I should then be able to shift more like 14 KWHs to the evening peak rate time. Yes, our peak rate for solar customers is 4 pm to 9 pm as the sun goes down. They do offer a 13 cent overnight rate for EV charging, but then they charge an increased fixed per day rate. I have to do that math to see if it is worth changing ones I am producing 90% of my own power.

 

[mrzed001]

I have to check but I think the Voltronic/ MPP Solar one unit hybrid can not function as battery-to-grid inverter.

But the Sol-Ark / Deye / SunSynk hybrid inverters seems to have this option:

 

[minerva]

I have the Schneider XW-Pro 6848 6,800 watts at 120/240 volt split phase. And I now have a usable 36 KWHs of Chevy Bolt battery modules wired in a 14S12P arrangement of 60 amp hour cells LG cells. That makes 720 amp hours at a nominal 51.8 volts. It's about 58% of a complete Chevy Bolt battery pack. Yes, I am following the recall news.

Since you want to run your pool heater during the day, I would just add more solar with microinverters. That is by far the most efficient, to use the power as it is being produced. Charging is 95% efficient, at best, and inverting is also about 93% efficient, and the batteries lose a little as well. I lose a full KWH when I move 10 KWH from solar to peak rate evening time here. And my rates go from 17 cents a the cheap time to 43 cents at the peak rate. Moving that 10 KWH in theory saves me 10 x 0.42 - 10 x 0.17 = $2.50 cents a day. I figure I average moving about $2.00 a day for 300 days a year to account for days of weak sun or other reasons I can't push the full 10 KWH in the peak window. I may actually do better than that. But that still means I am saving $600 a year by time shifting the power. But I spent $3,000 on the inverter, and probably something like $5,000 on the batteries. Maybe a little more with the cases, BMS units, and wiring etc. So taken totally separate from the solar power, the battery system will take 15 years to pay off. But I am only expecting the batteries to last about 10 years. So yup, at the peak to off peak rate here, it won't pay off, but it sure does cut down on the cost of having backup power.

But if you take the entire cost of my solar installation into the equation, and figure on what I am saving, then my system pays off in about 11 years. My Enphase solar PV system has already produced 16.9 MEGA watt hours. And it has just been running a bit over 2 years. In the full year of 2020, it made 7.9 MWHs. If I just figure that half of it was used at peak, and half off peak, so we average the value of the electricity, that is 30 cents per KWH x 7,900 = $2,370 per year chopped off of my electric bill, but that is with the battery doing the time shifting. Adding up everything I spent on the solar panels, inverters, installation, and my battery system, I spent $26,000 over a span of 2.5 years. Divide by the 2,370 per year = 10.97 years to cover the whole cost of everything just from electric bill savings. Production may fall off some, but I also expect So Cal Edison to jack the rates more. So that may end up a wash.

I do plan to add another 2,000 to 3,000 watts of solar to DC couple charge the battery bank. I am still working on the budget for that upgrade. If I do the ideal 9 x 330 watt panels, It will easily provide all of my night time power and improve y system efficiency while freeing up the microinverters to export more or run my air conditioning during the day. That would add about 60% to my total solar production. So kick my annual energy production to over 12.5 MWHs a year. I should then be able to shift more like 14 KWHs to the evening peak rate time. Yes, our peak rate for solar customers is 4 pm to 9 pm as the sun goes down. They do offer a 13 cent overnight rate for EV charging, but then they charge an increased fixed per day rate. I have to do that math to see if it is worth changing ones I am producing 90% of my own power.

With your rates in SoCal, solar is a no-brainer You are positive that 6848 can export battery power to the grid, right? To be fair, I have to agree with you that $3,000 is not an arm and a leg. However, to make time-shifting work, the cost of the equipment is crucial. If I don't use the inverter for solar (which I might but with only 1,800W), this investment will never pan out. Not even just a matter of a long time.

 

[minerva]

I have to check but I think the Voltronic/ MPP Solar one unit hybrid can not function as battery-to-grid inverter.

But the Sol-Ark / Deye / SunSynk hybrid inverters seems to have this option:

View attachment 67858

Are Sol-Ark / Deye / SunSynk the same just rebranded?

 

[mrzed001]

Are Sol-Ark / Deye / SunSynk the same just rebranded?

Yes, all three have the same hardware. SunSynk makes a special firmware for the SunSynk "branded" inverter.

 

[minerva]

Yes, all three have the same hardware. SunSynk makes a special firmware for the SunSynk "branded" inverter.

That's good news. I don't know much about Deye but it's pretty affordable.
PS: No more split-phase Deye inverters for the US market. What a pity.

 

[GXMnow]

That's good news. I don't know much about Deye but it's pretty affordable.
PS: No more split-phase Deye inverters for the US market. What a pity.

I remember reading something about Deye making the hardware, and Sol-Ark wrote their own firmware, and spent the money to get UL listing. As part of their deal, Sol-Ark was to have exclusive rights to sell the product in the USA. I think they held some legal action against Deye when their inverters started showing up here.