Do I have too many solar panels?

Jamie.sanders

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Dec 1, 2019
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86
I have 10, 440 watt solar panels and 6 280AH lithium batteries, Do I have to many panels? how do I calculate this?
or does the charge controllers limit how many panels you can use?
 

Torch

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Aug 3, 2021
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Look at your charge controller info. It will tell you the panel limits.
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
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Is that 6, 12V 280 Ah batteries?

6 x 12V x 280 Ah = 20160 Wh storage

10 x 440w = 4400 W PV

4400W / 20160 Wh = 0.22C

That is a reasonable charge rate (at reasonable temperatures)
It only becomes a problem in rather cold weather.
Typically, LiFePO4 batteries are rated for 0.5C charge rate.
As temperature approaches freezing, max rate without damage drops to around 0.1C or 0.05C

Determine what temperature is OK for your battery to receive 0.22C, and set low-temperature charge disconnect to that temperature.

If your PV array is set up with multiple orientations, the peak could be reduced to about 0.7 as much, about 0.15C charge rate. Hours are extended.
 

Jamie.sanders

New Member
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Dec 1, 2019
Messages
86
Is that 6, 12V 280 Ah batteries?

6 x 12V x 280 Ah = 20160 Wh storage

10 x 440w = 4400 W PV

4400W / 20160 Wh = 0.22C

That is a reasonable charge rate (at reasonable temperatures)
It only becomes a problem in rather cold weather.
Typically, LiFePO4 batteries are rated for 0.5C charge rate.
As temperature approaches freezing, max rate without damage drops to around 0.1C or 0.05C

Determine what temperature is OK for your battery to receive 0.22C, and set low-temperature charge disconnect to that temperature.

If your PV array is set up with multiple orientations, the peak could be reduced to about 0.7 as much, about 0.15C charge rate. Hours are extended.
yes, it is six 12V 280 batteries I will wire to 24 volts.
 

rmaddy

Full-time Solar-powered Trailer Life
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What charge controller do you have?

What are the specs for the solar panels?
 

Hedges

I See Electromagnetic Fields!
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Mar 28, 2020
Messages
8,365
yes, it is six 12V 280 batteries I will wire to 24 volts.

There are systems which allow higher wattage PV while limiting battery charge rate. That can be good for supplying loads during sunlight.

Mine has AC coupled PV (Sunny Boy) and separate battery inverter (Sunny Island). PV could deliver > 0.5C, but charging is regulated to 0.2C (for AGM).
Victron systems can use a battery shunt and a monitor which commands the charge controller.
All-in-one systems should be able to support this as well.

It is just stand-alone SCC where you would want to limit harvested power to what battery can take.
It is OK to over-panel in order to help on days with poor sun, but size (or program) SCC for max current desired.
 

Jamie.sanders

New Member
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Dec 1, 2019
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What charge controller do you have?

What are the specs for the solar panels?
I don't have a charge controller yet, I want to run at least 2 of them, may have to run 3. But I want two so if one dies
I can still produce 1/2 the power.
the specs on the solar panel are

440watt
VOC49.62
VMP 40.99
STC 20.25%
short circuit currnet 11.35
maximum power current 10.74
 

MisterSandals

Participation Medalist
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Location
Silicon Valley
I don't have a charge controller yet
Have you figured out what your goals are for your system? An energy audit would reveal a LOT about your power use needs. If you figure out how many watt hours you need each day and what your largest loads are at any moment, suggesting workable SCCs will be easier (possible!).

You are on the right track matching panels to batteries so that’s a good second step.
 

Jamie.sanders

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Dec 1, 2019
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86
I have calculated I would need an 8,000 watt system for the entire house, however I know I cant afford that.
So I'm trying to build the biggest best system I can within my budget.
 

Jamie.sanders

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as for what I would like to be able to run, I have calculated, 3,806 watts to run my basic stuff in the house.
 

nogridhome

NoGridHome.com
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Location
Chapel Hill, N.C.
I want to say there is no such thing as "too many solar panels". You might do math like: how much would it take to fill your battery bank if f was empty, etc... There are sooooo many reasons you might want more power that you can't go wrong with extra panels.
What if your batteries are dead and you were also needing to do laundry, dishes, while running the AC the whole time| Oh, it's partly cloudy. What about those times when it is cloudy for a month! Run your life on solar for a while then consider what might constitute too many panels - no such thing unless you get rediculous. I have 11kw available from my 33 panels. My system was small and I added more as money permitted. I started with 2kw and 8 crappy car batteries. Now I have Lithium, 3 charge controllers, a main and backup inverter. This is real man, it works! Ground mounts complete, just need to mount the panels and bury the wire.
My 150ah Lithium is 12vdc x 150ah = 1800watt/hours. This means one will hold/provide 1.8kw (for 1 hour). I have 24 of them so I have 24 x 1.8kw = 43kw of power. This allows me to have a normal life with a refrigerator, freezer, dishwasher, AC and everything else. I have propane for all the heavy appliances like oven, dryer, water heater, furnace. On light nights my charge controllers throttle back after about 12 kw. You will be wanting more panels and batteries before you are done. GOOD LUCK, ALL THE BEST!!
 

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Jamie.sanders

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Dec 1, 2019
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86
Care to share how you got that number?
And just to be certain, while asked for watt hours, you gave a watt answer???
Is that a 8000 watt of solar panels or something with the wrong units?
Sir, as for how I got that number, I found a handy dandy page online that list the wattages of home appliances, and added up
everything I plan on using and then I bumped it up 10%.
 

Hedges

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Mar 28, 2020
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Sir, as for how I got that number, I found a handy dandy page online that list the wattages of home appliances, and added up
everything I plan on using and then I bumped it up 10%.

That works for a conservative estimate of continuous load.
So long as your appliances are similar - for instance, microwaves come in a range of wattages.
Check appliance labels for a better max load figure.

You may be able to get by with lower wattage inverter, for instance by not running microwave and coffee pot at the same time.
Most of us have quite a few high power appliances, but don't use many at once.

Do you have any appliances with large motors? That could include water pump, circular saw, etc.
Motors typically draw 5x their nameplate rating, for a fraction of a second. If the inverter can't supply this, it shuts off.
Some inverters give a surge rating. If the rating is for 30 milliseconds, that isn't long enough to help. If it is for 3 seconds, then it is good.

All this goes to size the inverter. And current draw the batteries must supply. It is in units of Watts, or of kW.

Beyond that, you need to know how many minutes or hours each will run in a day. Determine watt-hours or kWh.
That is used to size PV array and battery storage capacity.

as for what I would like to be able to run, I have calculated, 3,806 watts to run my basic stuff in the house.

That's a good number to work with, for inverter. But still a pretty good size inverter. How many minutes do you need to draw all 3800A? Some inverters can provide higher wattage for a few minutes before getting too hot, so maybe a 2500W or 3000W inverter could do it. Or, a 4000W to 5000W inverter could be used for continuous operation.

Any 240V loads, or all 120V?

Here's one of the lower cost brands:

 

Jamie.sanders

New Member
Joined
Dec 1, 2019
Messages
86
That works for a conservative estimate of continuous load.
So long as your appliances are similar - for instance, microwaves come in a range of wattages.
Check appliance labels for a better max load figure.

You may be able to get by with lower wattage inverter, for instance by not running microwave and coffee pot at the same time.
Most of us have quite a few high power appliances, but don't use many at once.

Do you have any appliances with large motors? That could include water pump, circular saw, etc.
Motors typically draw 5x their nameplate rating, for a fraction of a second. If the inverter can't supply this, it shuts off.
Some inverters give a surge rating. If the rating is for 30 milliseconds, that isn't long enough to help. If it is for 3 seconds, then it is good.

All this goes to size the inverter. And current draw the batteries must supply. It is in units of Watts, or of kW.

Beyond that, you need to know how many minutes or hours each will run in a day. Determine watt-hours or kWh.
That is used to size PV array and battery storage capacity.



That's a good number to work with, for inverter. But still a pretty good size inverter. How many minutes do you need to draw all 3800A? Some inverters can provide higher wattage for a few minutes before getting too hot, so maybe a 2500W or 3000W inverter could do it. Or, a 4000W to 5000W inverter could be used for continuous operation.

Any 240V loads, or all 120V?

Here's one of the lower cost brands:

sir, some of the items, like the air fryer and microwave will only be used for minutes. and of the 3 TV's only 2 would ever be on at the same time.
I calculated 60 watts for lights for every room, but they should not all be on at the same time. my big power drawers that run constant are the refridge and deep freeze,
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,365
So sharpen your pencil, determine how many watts are on for a long time. How many minutes of how many watts for the cooking appliances.
Consider specs of batteries and inverter to see if they meet those needs. (Tier-1 brands should deliver what they promise, while cheaper brands best to "derate", use for less than full rated power.)

Fridge and deep freeze of course are plugged in all day. Consider nameplate ratings for inverter capacity. But they cycle on and off - see consumer energy labels for estimate of average power consumption. For instance, a typical full-size fridge will use about 1500 Wh/day.

No motors other than refrigeration? In that case an inverter which can supply your 2kW to 3kW loads should be able to start them, no concern with surge capability.
 

Jamie.sanders

New Member
Joined
Dec 1, 2019
Messages
86
That works for a conservative estimate of continuous load.
So long as your appliances are similar - for instance, microwaves come in a range of wattages.
Check appliance labels for a better max load figure.

You may be able to get by with lower wattage inverter, for instance by not running microwave and coffee pot at the same time.
Most of us have quite a few high power appliances, but don't use many at once.

Do you have any appliances with large motors? That could include water pump, circular saw, etc.
Motors typically draw 5x their nameplate rating, for a fraction of a second. If the inverter can't supply this, it shuts off.
Some inverters give a surge rating. If the rating is for 30 milliseconds, that isn't long enough to help. If it is for 3 seconds, then it is good.

All this goes to size the inverter. And current draw the batteries must supply. It is in units of Watts, or of kW.

Beyond that, you need to know how many minutes or hours each will run in a day. Determine watt-hours or kWh.
That is used to size PV array and battery storage capacity.



That's a good number to work with, for inverter. But still a pretty good size inverter. How many minutes do you need to draw all 3800A? Some inverters can provide higher wattage for a few minutes before getting too hot, so maybe a 2500W or 3000W inverter could do it. Or, a 4000W to 5000W inverter could be used for continuous operation.

Any 240V loads, or all 120V?

Here's one of the lower cost brands:

I want to run 2 inverters for redundancy, if one dies I still have 1/2 my power.
I would like to figure out how to run my well, its 240V. not sure how I can do that? another inverter pushing 240V?
 
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