Designing a 6kW Solar System and Need Some Help

I want to design a 6kw solar system and am trying to figure out some of the components. I want to start with an AIMS 6000W Pure Sine Wave Inverter and a
AIMS 60 amp MPPT charge controller. Where I get confused is the wattage of the solar panels. I want to try to keep it to about 16 panels. Do I need a combiner box? So what wattage should I use? And finally, I want a sealed lead-acid battery. How many amp-hours and how many? Thanks in advance for any tips.

Is this going to be a 48 volt system? I assume so since you're using a 6000 watt inverter. Only using 120 volt devices or do you need 240 as well? Is this a fully off grid system or grid tied?

The system needs to be sized for what you are going to be using the system to power. First thing is to do an energy audit. A Kill-A-Watt meter is very helpful for this.

Once you know the requirements of the devices you wish to use, we can help with battery bank size, solar panel array, etc.

This is a good video to start you off.

This is another good video to watch as is the rest of the videos on this channel. They refer to mobile systems because that is what they specialize in, but if you're building an off grid system the same concepts apply.

CraigK said:

I want to design a 6kw solar system and am trying to figure out some of the components. I want to start with an AIMS 6000W Pure Sine Wave Inverter and a
AIMS 60 amp MPPT charge controller. Where I get confused is the wattage of the solar panels. I want to try to keep it to about 16 panels. Do I need a combiner box? So what wattage should I use? And finally, I want a sealed lead-acid battery. How many amp-hours and how many? Thanks in advance for any tips.

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SLA battery probably has a preferred charge rate of 0.1C or 0.2C, so should be large enough to accept peak power/current from PV panels.
You want your batteries to at least last through the night, so that many Wh shouldn't exceed 70% of battery capacity.
Maybe you want to make it through three days without sunshine; in that case that many Wh shouldn't exceed 70% or perhaps 90%.

PV panels can be connected in series for more volts per string, and strings in parallel for more amps.
Voc must never exceed max spec of MPPT even after adjusting for record cold.
Isc of parallel strings added together shouldn't exceed Isc limit of MPPT.
If more than two strings into a single input of MPPT, each should have a fuse (possibly part of a combiner). Just 1 or 2 strings, can "Y" together.

Do you want 16, 500W panels for 8 kW? 100 W panels for 1600W?

Once you've done that energy audit, you can figure out how many watts of panels (considering less sun in winter, too).
Peak AC load, also surge load to start motors, typically 5x nameplate. That will determine if your inverter is good enough.

This system will be an off-grid system for a manufactured home to run a well pump, small to medium appliances, and a mini split ac unit. I was thinking a 24 volt system but maybe I need a 48 volt?

Can't go wrong starting with 48V

Well pump is likely the heaviest load. You need its ratings to estimate surge current requirement.
Both of these have a spec 18kW 20 seconds, which sounds good for up to about a 3500W motor.
Keep those battery cables short and fat, since these are 24V.

Initial charge current is usually around 60a for a 12v Sealed Lead Acid battery so .2C is about 12amp. For my system I want 6kwh ability per day and I want to charge using generator if there is no sun for only 2 hours per day. So, 6kw at 12v is 500ah. At 12a it will take 42 hours to charge. I want to charge for only 2 hours so I need 21 batteries. 21 batteries at 12a will get me 6kwh charge in 2 hours. Now these 21 12v batteries can be arranged in 48v and will still get charged in 2 hours.

Now let me check the capacity, let's say 24 batteries so we can make it a 48v system more easily. 24 * 12v * 100ah = 28.8kwh. if I want to use only .5 of this for battery longevity I have 14.4kwh capacity.

If I am ok with 4 hours per day generator charging I can get by with just 12 batteries, or 7.7kwh at .5 depth of discharge using .2C charge rate.

I like to work backwards from charge rate and generator time to figure out how many batteries I need.

Now I would look at solar panels. Basically I am replacing the generator with solar panels. For 4 hours of sun per day to charge at .2C for 12 batteries I will need 7.7kwh/4hrs = 2kw of solar panels minimum. You might want more panels to charge fully on less than perfect sun power. A good charge controller will keep from overcharging if there is too much sun for your battery bank to absorb.

I could be wrong, but that's what I think. 14.4 kwh capacity battery bank and at least 2kw solar panels for a 6kwh system.

I am in the process of building this, but I am using 16kwh of Lifepo4 in 48v and I already have 9.5kw solar in the roof. I could probably double the battery bank capacity with this much solar but am spending $$ on new Victron inverter/charger etc so don't have the budget for more capacity yet.

As Hedges said a 3 day reserve is also desirable. So multiply the capacity by a factor of three. So 48kwh seems appropriate. If I we're going to stay with Lead Acid I would use 6v 200ah batteries. This would make a whopping 40 batteries. 40 * 6v * 200ah = 48000wh. Maybe less if you are willing to discharge below 50 percent on occasion. I think 32kwh would be a good compromise. That would be 30 6v 200ah batteries. 8 Lifepo4 power blocks (24v 4kwh each) would be my desire. I pre-ordered 4 of them 2 days ago. Now thinking of adding another 4 before the pre-sale price goes away Nov 11th. 4kwh power blocks were $1349.00 each using "diysolar" discount code. $5399 for 4 and you get free shipping. I think that is a good deal for 5000 cycles compared to lead acid where you may get 500 cycles if you are careful.
$280 for 6v 486ah Rolls FLA batteries from the power store might work. Let's see, 32000/486/6= 11 cells . Make it 12 for simplicity of making 48v. 12 * $280 = $3360.00 not bad. A 12 battery system is a lot easier to deal with than a 30 battery system. I don't know what shipping would cost. 4s3p is pretty doable for a 48v system. That price is right around $1/watt. But only 500 cycles. The Lifepo4 system I described is $0.40 per watt and 5000 cycles. More cost up front though.

My worry with the Lifepo4 system is that battery technology improvements will continue to take place and I will be stuck with old chemistry technology in the future. Going lead acid now would be a cheeper way to get you up and running and then when the lead acid batteries need to be replaced you might have an even better battery option than now for changing battery type.

Crazyfrog said:

I think that is a good deal for 5000 cycles compared to lead acid where you may get 500 cycles if you are careful.

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This is utter nonsense! Abused/mistreated lead-acid batteries might last only 500 cycles. Properly cared for batteries last far longer. Right now, my Trojan L-16RE-B bank is on 1500 cycles, and still appears to be in "like new" condition. They typically measure 1.280 for S.G. That's because I'm serious about proper charging, and don't skimp on panels. My new Rolls batteries in system two are rated for 9000 cycles at the rate I deplete them. I'll get back to you in a decade or so to let you know how they are doing.

Crazyfrog said:

My worry with the Lifepo4 system is that battery technology improvements will continue to take place and I will be stuck with old chemistry technology in the future.

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But if it performs for what you need it to, and lasts for the time you want it to, does it matter?

Who said 6kWh?

6kW is inverter continuous output.

16 PV panels could be 8 kW (STC) or 1.6 kW, depending on whether they are 500W or 100W.

Battery could be small, just enough to supply starting surge. In that case, charging system has to limit battery current.
Or, it could be sized for several days without sun.

My (grid backup) system is 20 kWh battery and about 14 kW PV, 80 kWh/day.
Could probably have been 5 kWh battery if less nighttime load.

If you size for 3 days, that can be at 90% to 100% DoD and occurs rarely. Most of the time you only have one night, 16% if usage is constant around the clock, 5% DoD if nighttime usage is minimized.

If you have a generator to fire up anytime there's no daytime production, and if you generally draw little at night, your battery bank can be about 1/20th the size as needed for 3 days autonomy. Make hay while the sun shines, get through the night surviving on body fat.

The smaller the battery you buy up front, the less money you've tied up and the sooner you can discard it to get something new and improved as costs come down.

MichaelK said:

This is utter nonsense! Abused/mistreated lead-acid batteries might last only 500 cycles. Properly cared for batteries last far longer. Right now, my Trojan L-16RE-B bank is on 1500 cycles, and still appears to be in "like new" condition. They typically measure 1.280 for S.G. That's because I'm serious about proper charging, and don't skimp on panels. My new Rolls batteries in system two are rated for 9000 cycles at the rate I deplete them. I'll get back to you in a decade or so to let you know how they are doing.

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Great first hand information! Glad to hear the FLAs can have more life than I was aware of. Which Rolls batteries did you go with?

Crazyfrog said:

Which Rolls batteries did you go with?

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MichaelK said:

8 CS 17P | Rolls Battery

www.rollsbattery.com

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9000 cycles to 10% DoD
4300 cycles to 50%
2200 cycles to 100%

At the shallow end, about 2x what the SunXtender AGM I use are rated for,
At the middle, 4x
At the deep end, about 6x

Same price per Wh capacity.
The Rolls winds hands-down for price per Wh of lifetime use. (Forklift batteries will be similar.)
I went with AGM as a better fit for my lifestyle (install it and forget it), because I could accept relatively low capacity.

I don't have personal results to report, however. My 100 Ah bank has been standby for 10 years, haven't measured capacity. 405 Ah bank is new.

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GMB said:

Is this going to be a 48 volt system? I assume so since you're using a 6000 watt inverter. Only using 120 volt devices or do you need 240 as well? Is this a fully off grid system or grid tied?

The system needs to be sized for what you are going to be using the system to power. First thing is to do an energy audit. A Kill-A-Watt meter is very helpful for this.

Once you know the requirements of the devices you wish to use, we can help with battery bank size, solar panel array, etc.

This is a good video to start you off.

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I am very interested in building a panel for my house how do I get started

I am very interested in building one for my house how do I get started thank you

British kid said:

I am very interested in building one for my house how do I get started thank you

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First decide what you want it to do.
On-grid net metering?
Backup during occasional power failures?
Power the house 365 days per year off-grid?

Second do an "energy audit",
catalog what devices you want to run.
Determine how much continuous power draw at one time.
Determine start-up surge for motors.
Determine how many watt-hours per day you will consume. How many at night?

You could start with that video and energy audit link in the post you replied to.

Start a new thread describing what you've figured out.