Multiple MPPT Solar Charge Controllers to the same battery bank

[Supervstech]

Why limit yield?

You must be an old dog, said you had 4 decades of the same experience and haven't learned the new tricks.

Well, how are you going to have enough solar to cover loads in poor conditions, and not be overpaneled in strong conditions? unless you have enough scc's to handle production when full strong sun is out, overpaneling will overwhelm the controllers.
And if you do have enough scc's for the strong sun production, you will have more solar production than the batteries can store. Or you will be limiting usage in poor conditions, or ramping up usage in strong...

 

[Zwy]

Well, how are you going to have enough solar to cover loads in poor conditions, and not be overpaneled in strong conditions?

You would have to ask those that advocate overpaneling about the latter part of your question. I don't advocate overpaneling, I don't see the need.

As for the first part of your question, I pull all available production from the array at any time. I also advocate large battery banks, enough for 4 to 5 days capacity of limited sun. This plays into the next question.

unless you have enough scc's to handle production when full strong sun is out,

Yes, that is correct. Enough SCC's to handle all production with peak sun. Pull that energy off the panels and put it in batteries or power loads. For example, a 10Kw array equipped with a pair of 5.5Kw SCC's. Large battery bank to soak up high array output.

overpaneling will overwhelm the controllers.

I don't advocate overpaneling although originally I had overpaneled the SCC's in the 6500EX. At peak sun they clipped and that potential yield was lost. The yield could have been used for a dump load if batteries were full, one example would be home heating using a heat pump or even resistance heating.

And if you do have enough scc's for the strong sun production, you will have more solar production than the batteries can store.

That is the purpose of a large battery bank and dump loads. Yesterday's example was heavy overcast sky until 11 am, then clear skies as the front pushed those clouds south starting at 10 am. At 9:58 am, my 58 Kwh bank was at 36% SOC. I pulled full array capacity thru peak sun and any available PV power until 5:14 pm. My wife did 2 loads of laundry, ran the dryer for both loads, ran the dishwasher and battery reached 74% SOC with 24.9 Kwh charged into the batteries. Those peak sun periods can really push power thru the system. Highest charge rate was 8.02 Kw (156A) with periods of lower charging depending on washing machine and dryer. Loads powered from 10 am to 5 pm were 11.8Kwh.

The larger battery bank makes a huge difference. The highest charge rate for the bank was 156A, divided by 4= 39.16A per battery. I was able to store all excess production. I did contemplate running a dump load later in the day as the next day is forecast to be sunny and I'll probably hit full charge. I'm not anywhere near the 1C rate.

Or you will be limiting usage in poor conditions, or ramping up usage in strong...

Our battery is large enough to run the house for 5 days with very little PV yield during the day. One more battery will get me over the 6 day hump. This past winter if I had 6 days of storage I would not have needed any grid power for some periods. With poor sun conditions in forecast, usage is cut to a minimum so no laundry and no dishwasher. Heat pump not ran. Any unnecessary usage is cut but we live life normally, we just wait until good days of sun to do laundry which is normal routine.

As for usage when PV is strong, we use the heat pump as a dump load but if outside temps are below 0°F, I will run resistive heating until battery is 100% SOC, then I might run the heat pump. Take for instance the week after the blizzard here in January. My tilting array at 65° was clear the morning after the blizzard and I even charged a little over 2Kwh plus ran household loads from 8.4Kw of array during the blizzard which one might think is poor conditions. Skies were clear starting Sunday and I could produce 60Kw per day. I heated my house during the day and evening using resistive heat (and some days ran the heat pump) with outside temps never getting above 0°F for the next week. Cold temps like that make for clear skies, it certainly was a change from the last 2 weeks of December and first 2 weeks of January with heavy overcast skies with only 3 days of sun.

I've been a strong advocate of large battery banks and a smaller PV array, although I planned my system for winter production if there is sun 1 out of 3 days. It might take a day or two to reach full SOC but LFP doesn't care. I did this thread last October https://diysolarforum.com/threads/get-a-big-battery.70751/ and also commented in this post. https://diysolarforum.com/threads/feast-or-famine-the-off-grid-solar-dilemma.63293/post-790832 Once a large bank is put in with a ratio of battery to PV of at least 5 to 1, life becomes much easier. No need to overpanel, capture any available PV yield and enough reserve to go thru several days of limited sun.

 

[Supervstech]

Well, ya spend the money where ya want to.

Options for staying energized in weak production months are either buy enough batteries to hold you over till sun recovers, a fairly expensive endeavor, but sure, it'll get ya through a few days, add scc's overpanel, and have production in weak times, but waste in strong times, or overpanel the scc's ya have, and have the energy clipped in strong times.

Not sure where the arguments are comming from.

Ya do what ya can.
Choose.

 

[Bop]

Economically, overpaneling is the better choice in most cases, buying batteries is expensive compared to buying panels and most of us don't have the last name of Gates, so want the 'best bang for the buck'- and thats overpaneling..

 

[Zwy]

Well, ya spend the money where ya want to.

I ended up with $7800 in my battery after the tax credit. I thought was a bargain at the time. I'm currently in the process of another 96 280Ah cells, 16 or 32 will be for the house, the remainder for my shop. I'm adding another heat pump in the house and 4Kw of array as I move more towards using heat pumps to heat the house in spring/fall.

Options for staying energized in weak production months are either buy enough batteries to hold you over till sun recovers, a fairly expensive endeavor, but sure, it'll get ya through a few days,

I get more than a few days, 5 days to be exact. One more 280Ah will get another day if not almost 2. Cells that ordered are $91 each shipped. That will get me 72Kwh. We can cut usage to an absolute minimum of 7Kwh per day if needed such as grid down and no grid backup. The battery will be cheaper this time and will bring overall cost per Kwh to $115/Kwh.

add scc's overpanel, and have production in weak times, but waste in strong times, or overpanel the scc's ya have, and have the energy clipped in strong times.

Not sure where the arguments are comming from.

Good question.

Ya do what ya can.
Choose.

This morning battery bank was at 55% with heat pump heating the house all night, I do turn the heat down at night as I don't like a hot house when sleeping. I started running dump loads before daybreak so I can pull battery bank down and convert that to heat for the house so the propane furnace didn't run.

By 7:45 am the SCC's were pulling 1300W off the 8.4Kw array and now at 8:30 am I'm powering 1600W of dump load and charging batteries at over 1800W. I like the free heat, the large battery bank allows me to run dump loads when I want if I know what the weather wil bring. Normally use 800 gallons of LP and I've cut that in half as the propane truck topped off both 500 gallon tanks the other day. We had used 394 gallons since July of last year and the usage includes hot water.

Life is good.....

 

[Zwy]

Economically, overpaneling is the better choice in most cases, buying batteries is expensive compared to buying panels and most of us don't have the last name of Gates, so want the 'best bang for the buck'- and thats overpaneling..

If you quit buying LYP cells, it might help buy more capacity in LFP. https://www.alibaba.com/product-detail/TSWB-LYP400AHA-B-winston-lifepo4-3_1600820926815.html

Without shipping that is $383/Kwh.

Just one 400Ah battery costs more than the 96 LFP 280Ah "Grade A matched" cells from Luyan that I purchased without shipping. My cells were $7,488 without shipping. That comes to $87/Kwh with 86 Kwh of capacity compared to 20.4 Kwh for your LYP.

 

[Supervstech]

I ended up with $7800 in my battery after the tax credit. I thought was a bargain at the time. I'm currently in the process of another 96 280Ah cells, 16 or 32 will be for the house, the remainder for my shop. I'm adding another heat pump in the house and 4Kw of array as I move more towards using heat pumps to heat the house in spring/fall.



I get more than a few days, 5 days to be exact. One more 280Ah will get another day if not almost 2. Cells that ordered are $91 each shipped. That will get me 72Kwh. We can cut usage to an absolute minimum of 7Kwh per day if needed such as grid down and no grid backup. The battery will be cheaper this time and will bring overall cost per Kwh to $115/Kwh.




Good question.


This morning battery bank was at 55% with heat pump heating the house all night, I do turn the heat down at night as I don't like a hot house when sleeping. I started running dump loads before daybreak so I can pull battery bank down and convert that to heat for the house so the propane furnace didn't run.

By 7:45 am the SCC's were pulling 1300W off the 8.4Kw array and now at 8:30 am I'm powering 1600W of dump load and charging batteries at over 1800W. I like the free heat, the large battery bank allows me to run dump loads when I want if I know what the weather wil bring. Normally use 800 gallons of LP and I've cut that in half as the propane truck topped off both 500 gallon tanks the other day. We had used 394 gallons since July of last year and the usage includes hot water.

Life is good.....

It is good the bank is handling your loads.
Many have weeks in a row where production is below 10% of capacity.

Conservation helps, but even twice the battery you have wouldnt cover those times.
Its generator time then. Or pull from the grid if available.

Overpaneling helps bridge the gap of extended weak production.

Putting off laundry helps too.

Conservation, capacity, production, and backup.
All play a part.

 

[Texas-Mark]

Enlighten me on this power availability.

If the 10Kw array is outputting 3Kw when cloudy, how does overpaneling a SCC make this "power availability" more than 3Kw?

If you have a 10Kw array, but have overpanneled to lets say 11Kw, on that cloudy day when 10Kw would have given you 3Kw, you will now get about 3.3Kw . How can you not understand that?

And lets not talk just about cloudy days, People with fixed angle arrays may also overpanel for the winter when the sun is lower. As for clipping, even on a matched system (i.e. 10Kw array and 10Kw SCC), the array will only output max on a perfect day when the temperature is good and the angle is perfect. So overpaneling a bit will most likely not have much clipping at all except when conditions are great, but will allow for more production when conditions are not ideal.

I really don't think you are understanding what overpaneling even means.

 

[Zwy]

If you have a 10Kw array, but have overpanneled to lets say 11Kw, on that cloudy day when 10Kw would have given you 3Kw, you will now get about 3.3Kw . How can you not understand that?

If I have 11Kw of panels, I'll pull the full 3.3 Kw. I installed panels to use them and pull all power from the panels I can. If it takes another SCC, I'll add one and just feed the output to my DC bus.

And lets not talk just about cloudy days, People with fixed angle arrays may also overpanel for the winter when the sun is lower.

I tilt my array in winter for a few reasons. Snow and albedo from snow cover. I'm getting over panel rating with albedo and full sun.

I really don't think you are understanding what overpaneling even means.

I know what it is and it doesn't make any sense if you have battery capacity or loads that can take any power produced.

I want every watt I can when I have the battery capacity and loads to use it.

 

[Zwy]

It is good the bank is handling your loads.
Many have weeks in a row where production is below 10% of capacity.

Conservation helps, but even twice the battery you have wouldnt cover those times.
Its generator time then. Or pull from the grid if available.

Overpaneling helps bridge the gap of extended weak production.

You can only get what the panels in array can produce. Overpaneling would do the same during times weak production. I get the bonus under peak sun however and can use that power for multiple uses. Overpaneling can't do that.

Putting off laundry helps too.

Conservation, capacity, production, and backup.
All play a part.

 

[Texas-Mark]

If I have 11Kw of panels, I'll pull the full 3.3 Kw.

You asked where more than 3Kw was going to come from and I told you. Now you are agreeing it is there from overpaneling. Glad you finally understand. It only took 4 pages.

 

[Texas-Mark]

I know what it is and it doesn't make any sense if you have battery capacity or loads that can take any power produced.

The problem is you have been trying to convince everyone that your way was the only way. Not everyone has a tilting array or wants to spend extra money on more batteries, or even another SCC.

This whole "argument" started when you suggested someone underpanel a system, and I asked how that was better than overpanneling for cloudy days.

 

[Zwy]

You asked where more than 3Kw was going to come from and I told you. Now you are agreeing it is there from overpaneling. Glad you finally understand. It only took 4 pages.

When you install more panels, you always increase output. I never denied it wouldn't.

But I'm going to pull any yield from those same number of panels regardless without any clipping.

You seem hung up on some semantics or did not understand my original question for you. Which will produce more from X number of panels when comparing overpaneling or under paneling (which probably should be called excess SCC capacity).

When you add panels, if the SCC capacity is there, it still will outproduce overpaneling.

The problem is you have been trying to convince everyone that your way was the only way. Not everyone has a tilting array or wants to spend extra money on more batteries, or even another SCC.

It isn't the only way, some can get by with what they have. Many have more SCC capacity than panels. Overpaneling is a waste of resources, panels and mounts which cost money. I'm looking long term to get the highest return for the dollars spent. Overpaneling on the other hand requires having panel capacity that sits idle part of the time. I don't consider that efficient use of resources or money long term.

One member purchased high priced battery cells, then complained about not having enough battery capacity to be able to take all power from an array because he couldn't "afford" more battery capacity. He could have purchased 4 times the capacity with LFP and still had money left over to purchase more SCC's. Who wasted their money? And who will get the highest return on the solar investment?

This whole "argument" started when you suggested someone underpanel a system, and I asked how that was better than overpanneling for cloudy days.

It appears you and one other member are arguing for arguments sake, you want me to tell you your way is the right way or that I am wrong. Everything I've stated is correct, I gave the 2 reasons for underpaneling the EG4 MPPT's which you must not understand. I can't help you in that regard, that only comes from you.

Having enough SCC capacity will always outproduce overpaneling SCC's. You can't admit it, want to argue the point that somehow the laws of energy work differently with overpaneling and somehow you think you get more energy from the same number of panels. It isn't going to happen. Your excuse is you will have more panels which wasn't what I asked. I'll simply add the SCC capacity to pull any power from any extra panels.

My suggestion to you and the other member is to put me on Ignore. You can't handle the truth.

 

[Texas-Mark]

Everything I've stated is correct,

LOL

 

[Zwy]

LOL

 

[Texas-Mark]

Having enough SCC capacity will always outproduce overpaneling SCC's.

Nobody ever said that it wouldn't. Once again, you have totally missed the point. <sigh>

In any case, I'm done here. I feel confident most other people here are smart enough to understand the reasons that people overpanel.

 

[Supervstech]

Having enough SCC capacity will always outproduce overpaneling SCC's.

If setup to do so, yes.

However...
An scc configured withpanels in a fixed position, for best overall gain, or if the home roof angle is poor for some seasons...
Perfectly full SCC may not be able to output even 1% of array size without overpaneling that array.

There is no ONE way that is always right.

 

[Supervstech]

Heck, with microinverters on grid tie, overpaneling is the only way to get best production most of the time.

Lotsa options and setups.

Lets all try helping members with their specific problems, and not tout the recommendeded theoretical best way.

 

[Zwy]

Heck, with microinverters on grid tie, overpaneling is the only way to get best production most of the time.

If on net metering, why not push any production onto the grid as it is an infinite battery?

One of the arguments made and even you mentioned it was battery capacity would be a case for overpaneling.

Now it isn't when the grid is an infinite battery?

A Kwh put on the grid at any time is a Kwh that can be pulled out later.

I guess you will have to explain why overpaneling with grid tie would give the best production. This only applies if there isn't a cap on production (such as limiting how many Kwh per hour) which some utilities could possibly have(?), in that case overpaneling would allow the production under the cap. My next question is if there are limitations on how much can be exported at any time? I'm not grid tie and have no intentions of having grid tie.

If no limitation exists, why overpanel? You say with microinverters but what if one had string inverters? And why with microinverters?

Inquiring minds would like to know........ you opened the can of worms.

Lotsa options and setups.

Lets all try helping members with their specific problems, and not tout the recommendeded theoretical best way.

 

[Supervstech]

Mocroinverters are a set output device.
Installing 360W on a 360W microcontroller will only produce 360W at peak production.
Installing 660W on a 360W controller gets you 360W 99% of the time...
But never 660W...
Its all about what you can produce.