Growatt or MPP All In One - Charge and Use at the same time?

[OnGrid]

How do I figure out how much excess power (panels) I would need during the "day" to utilize the additional power as well as charge a 48V 5.12kWh (Lithium EG4 or SOK) battery?

For example, suppose I have a 3000W All-In-One inverter (not tied to the grid) and I want to run a 120v hot tub using 1200 watts with the "heater on" for 5 hours during the day, with the idea of not discharging my battery, but using the "excess" solar panels to run this during the day. So at the end of the 5 hours, my battery would be close to fully charged. And just for this example, after 5 hours i shut the hot tub OFF.

AND FOR MY EXAMPLE LETS SAY IT'S A PERFECT "NO CLOUDS OR SHADE DAY DURING THESE 5 HOURS.

How would I calculate this?
48V Lithium 5200W / 5 = 1040W (bump up array with extra - good practice) so maybe 1200W panels just to charge battery and then would need 1200W more panels to run hot tub heater? 2400W

 

[BentleyJ]

Typically the battery should not be discharged more than 80% of its capacity.
5200Wh x 0.8 = 4160Wh to charge the batteries.
1200W x 5hr = 6000Wh to operate the hot tub.
Total is 10,160Wh needs to be produced during that 5 hr period which is assumed to be perfect solar conditions.
Typically a solar array does not produce 100% of the STC rating in real world conditions. So lets use a factor of 1.25.
You need 10,160Wh/5hr = 2032W. 2032W x 1.25 = 2540W.

So your guestimate of needing a 2400W solar array was good. I would upsize to a 2500W to 2600W array just to make sure all the efficiency losses in the inverter and MPPT charger are accounted for.

 

[OnGrid]

Typically the battery should not be discharged more than 80% of its capacity.
5200Wh x 0.8 = 4160Wh to charge the batteries.
1200W x 5hr = 6000Wh to operate the hot tub.
Total is 10,160Wh needs to be produced during that 5 hr period which is assumed to be perfect solar conditions.
Typically a solar array does not produce 100% of the STC rating in real world conditions. So lets use a factor of 1.25.
You need 10,160Wh/5hr = 2032W. 2032W x 1.25 = 2540W.

So your guestimate of needing a 2400W solar array was good. I would upsize to a 2500W to 2600W array just to make sure all the efficiency losses in the inverter and MPPT charger are accounted for.

So either the Growatt or MPP could do this with no limitations ( keep my battery fully charged and run off just the solar).

 

[BentleyJ]

I'm not understanding your follow up question completely.
1) The Growatt has an MPPT charge controller built in. If you are asking if the math still applies with a stand-alone inverter and a separate MPPT charge controller instead of the AOI Growatt then yes the math is the same.
2) There is absolutely a limitation in that the solar conditions were assumed to be perfect.

 

[OnGrid]

No, I"m trying to get a better understanding of how this works, my followup question is:

1) In the Hot tub example is the excess solar power to the Hot Tub "actually" working directly from the solar or is it working off the battery inverter or both?

2) And if the excess solar power is going directly to the hot tub (as in my example with a Growatt / Mpp 3000w All-in-One Inverter), let's say for example I had a more powerful hot tub with 2800w needed for 5 hours, could I just add more solar panels (or over panel them if needed) to run in without utilizing much of my battery too as outlined in my first post on this thread?

 

[12VoltInstalls]

No, I"m trying to get a better understanding of how this works, my followup question is:

1) In the Hot tub example is the excess solar power to the Hot Tub "actually" working directly from the solar or is it working off the battery inverter or both?

If the hot tub load doesn’t exceed the solar power available in the moment then the battery is not being used.

2) And if the excess solar power is going directly to the hot tub (as in my example with a Growatt / Mpp 3000w All-in-One Inverter), let's say for example I had a more powerful hot tub with 2800w needed for 5 hours, could I just add more solar panels (or over panel them if needed) to run in without utilizing much of my battery too as outlined in my first post on this thread?

Well there’s some efficiency losses and solar wattage under hot sun and stuff, but running a 3000W inverter at full tilt imho ain’t a good plan.

Then overpaneled: there’s the limits of the SCC amperage output… I think your expectations might exceed reality by at least 31.749%

Then the hot-tub motor may have startup amps taller than the 3000W aio.

There’s a lot to actually work on first.

 

[BentleyJ]

1) Most All-in-One Inverters give the user 2 or 3 choices for setting output priority. For example SBU would be Solar first, Battery second and Utility third. In your example this would be the chosen setting. Specifically your question can only be answered completely by having the inverter specifications and schematic. You could then follow the current path through the various components.

2) Excess solar power is NOT going directly to the hot tub. Solar input power gets adjusted and regulated then directed to the inverter and/or battery charger circuits based on user settings, firmware and it depends on the internal components and circuit design.

 

[OnGrid]

If the hot tub load doesn’t exceed the solar power available in the moment then the battery is not being used.

Well there’s some efficiency losses and solar wattage under hot sun and stuff, but running a 3000W inverter at full tilt imho ain’t a good plan.

Then overpaneled: there’s the limits of the SCC amperage output… I think your expectations might exceed reality by at least 31.749%

Then the hot-tub motor may have startup amps taller than the 3000W aio.

There’s a lot to actually work on first.

" there’s some efficiency losses and solar wattage under hot sun and stuff, but running a 3000W inverter at full tilt imho ain’t a good plan"

Thanks, if I buy a 3000w inverter why do you think it would be not a good idea to run it "full tilt".?If that's what it's rated for, I would think a manufacturer has done diligent testing.

 

[BentleyJ]

Thanks, if I buy a 3000w inverter why do you think it would be not a good idea to run it "full tilt".?If that's what it's rated for, I would think a manufacturer has done diligent testing.

This is where the discussion of Low Frequency vs. High Frequency inverters begins. Generally speaking, its not a good idea to operate a value brand inverter at its full rated capacity. Especially not a HF type. The same applies to gasoline and diesel generators. Any good engineer designing a commercial or industrial system will size generators and many other electrical components at 50% of the manufacturers ratings.

 

[12VoltInstalls]

I buy a 3000w inverter why do you think it would be not a good idea to run it "full tilt".?If that's what it's rated for, I would think a manufacturer has done diligent testing.

Because the world - especially the US - no longer has the perception of value in durable manufactured goods.
Once was a time when ‘repairable’ and ‘still going strong’ were more valued by consumers than “bargain price” and “instant gratification.”

There are top shelf products that are shelf-priced brands not price-point or bargain brands that you could run full tilt probably without issue. Like a Ferrari at speed on a track versus a Ford sedan trying to keep up. The motor in the Ford is going to blow…

Even boat motors: you should run ‘em 75-80%, not WOT all the time (unless you’re a bass tournament guy LOL) and you don’t turn up a stereo to max volume non-stop without blowing something.

Having said that, the 1012LV-MK I’m running right now has a measly 1kW inverter. Making coffee (750W) and the fridge cycles on (900W-ish surge) and it seems to take it but the fridge starts slow. Though that ain’t 24/7 either.

 

[Lost_One]

I also think that it is a good idea to consider that there is a idle consumption when sizing inverters and batteries. That eats away at wiggle room.

 

[OnGrid]

If the hot tub load doesn’t exceed the solar power available in the moment then the battery is not being used.

Well there’s some efficiency losses and solar wattage under hot sun and stuff, but running a 3000W inverter at full tilt imho ain’t a good plan.

Then overpaneled: there’s the limits of the SCC amperage output… I think your expectations might exceed reality by at least 31.749%

Then the hot-tub motor may have startup amps taller than the 3000W aio.

There’s a lot to actually work on first.

The new EG4 3000 AIO is rated for 3000W Continuous Output

 

[DThames]

There is no "excess" solar power. There is "available" solar power at any one instant, depending on temp and light conditions. Your load is your battery charger and your AC load. If output source is configured for "solar first" and your load does not exceed the available solar, then solar is powering the load. At the same time, if the battery needs charging it should be seeing "available solar power minus load" going to the battery.

Looking at your original question, my approach is this. "How many amp hours do I want to put into the battery in 3 hours. I feel like on an average day, 3 hours of sun is not unusual. I size charging watts based on my charge rate. If I want to put 100 amps to the battery for 3 hours, I will need panels that can deliver 100 amps to the battery. If I also want to run my window AC unit or my hot tube, I would figure the watts needed to carry that load. Those watts, I will need over and above my charging watts. That is a fairly simple and easy to understand approach.

Add to that the fact that during the 8 hour day that I am running my window AC unit, some clouds come by and then early in the day and late in the day the sun angle is less, I found out that my AC unit digs into my battery a bit during the day, so maybe I will add a few more watts to help the charger make up for that. Basically overdo it on panels if you want to charge and carry a load in less than ideal solar conditions.

A few months ago we did a practice "power out" run when I saw a week coming up with clouds at least some part of most every day. We went to emergency power with freezer, fridge, microwave, CPAP, lights, etc on our emergency system. About day five, we got behind the curve and had to get out the generator for about 3 hours of charging so the battery could carry the night load. Need more panels! Cloudy days are real.

 

[DThames]

More info on available solar power.

I turned on the window AC unit in the garage and let it take down the battery a bit. Then I turned the solar power to the Growatt. Below is a graph of part of the PV and load data. Notice the solar watts (blue) that are being used. On one of the cloud events, there was not enough solar for the demand and the battery had to give a little. There is never excess, only what is available when needed.

edit...So if the battery can take it, the charger is pushing all it can to the battery. The inverter is then delivering what the load demands, from the battery. Because the battery, inverter power input, and charger output (to battery) are all the same point, electrically, you get a sum of the amps either coming out of the battery or going into the battery, depending on the situation.

 

[Lost_One]

More info on available solar power.

I turned on the window AC unit in the garage and let it take down the battery a bit. Then I turned the solar power to the Growatt. Below is a graph of part of the PV and load data. Notice the solar watts (blue) that are being used. On one of the cloud events, there was not enough solar for the demand and the battery had to give a little. There is never excess, only what is available when needed.

edit...So if the battery can take it, the charger is pushing all it can to the battery. The inverter is then delivering what the load demands, from the battery. Because the battery, inverter power input, and charger output (to battery) are all the same point, electrically, you get a sum of the amps either coming out of the battery or going into the battery, depending on the situation.

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