Sizing inverter to array size

I plan to install a small solar system at my home. The panels add up to 3840 watts. One 1800 string and one 2040 string. I would like to use a SMA SB3.8-1 SP-US=41 3.8 kw inverter. Would this work or do I need to go to a larger inverter

Inverters handle appliance loads. Size the inverter for your required loads plus a % more 25-50%?

Charge Controllers handle energy from the solar panels into a battery.

Some inverters also have a built in charge controller, many do not. Some with built in charge controllers, like mine, do not handle DC solar voltage but only AC voltage, as from a liquid fuel generator or the grid. Some inverter / chargers can handle solar DC and grid or generator AC.

I don't know what an SMA SB xxx is and don't have time to look it up. Could you tell us instead?

So your post is somewhat vague as to what you are referring to.

Up to 150% DC to AC ratio the standard recommendation for most grid tied string inverters. It's on the spec sheet. So you could even use a 3.0.

Last summer SMA stopped supplying WIFI with their inverters due to a chip shortage so if it was me I'd be looking for some older stock that still had WIFI. They may back to including them so just make sure you know what you're getting.

FWIW: You get three MPPT strings with the 5.0 and larger so if there's even a remote chance you might expand that's the one you'd want.

E. Cho said:

Inverters handle appliance loads. Size the inverter for your required loads plus a % more 25-50%?

Charge Controllers handle energy from the solar panels into a battery.

Some inverters also have a built in charge controller, many do not. Some with built in charge controllers, like mine, do not handle DC solar voltage but only AC voltage, as from a liquid fuel generator or the grid. Some inverter / chargers can handle solar DC and grid or generator AC.

I don't know what an SMA SB xxx is and don't have time to look it up. Could you tell us instead?

So your post is somewhat vague as to what you are referring to.

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All correct for a battery based application but the OP appears to be asking about a battery-less grid tied application.

Not going to install batteries. Just tie to the grid. I don't care about wifi. I did see that SMA had dropped wifi.

I lived off the grid on my sailboat for 9 years. The last 7 years with 100% solar for my electricity. That was a low voltage 12 volt system where I charged a battery bank and then drew power from the batteries. Lucky to get 6 to 7 years from batteries before needing replacement if you don't screw up the charging. You would need a huge battery bank in a house. Not going that route.

Thanks for the info on inverter size verses array size.

mickri said:

Not going to install batteries. Just tie to the grid. I don't care about wifi. I did see that SMA had dropped wifi.

I lived off the grid on my sailboat for 9 years. The last 7 years with 100% solar for my electricity. That was a low voltage 12 volt system where I charged a battery bank and then drew power from the batteries. Lucky to get 6 to 7 years from batteries before needing replacement if you don't screw up the charging. You would need a huge battery bank in a house. Not going that route.

Thanks for the info on inverter size verses array size.

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You knew about the WIFI but never looked at the spec sheet??

You'll care about WIFI when you learn how clumsy it is to set that inverter up without it. Adios

I looked at the spec sheet. I asked one of the companies I talked to about buying an inverter from and they were a little iffy on using a 3.8 kw inverter on my proposed array. So I am doing more research. I saw the max PV power on the spec sheets and wondered why the max PV power was so much greater than the inverter size. I will get this figured out before I buy the inverter.

After doing more research it seems like the inverter should be around the size of the array. Can be a little smaller or bigger. So a 3.8 kw inverter should work with the size of my array.

So future readers that stumble on this post can make an educated choice about what size of grid tied inverter they need.

7.65 kW array on 4 different inverters ranging size from 5.0kW to 7.7kW from SMA's design tool. We do several dozen projects like this a year so I had the software already pulled up. There's no appreciable difference in production from clipping until you go past 150% DC to AC ratio and even then it's really not that bad. Where it really makes sense is when you compare the cost of adding a 2nd inverter vs. staying with one inverter. In these single inverter projects it's more a matter of what inverter you can get your hands on and keep the project moving.

You want to compare the difference in annual energy to inverter size then compare that to the price upcharge for a larger inverter. It's not going to make any ROI $ense to spend more money on an inverter to get a few more kWh per.

mickri said:

I plan to install a small solar system at my home. The panels add up to 3840 watts. One 1800 string and one 2040 string. I would like to use a SMA SB3.8-1 SP-US=41 3.8 kw inverter. Would this work or do I need to go to a larger inverter

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Two MPPT tracker, should work with your two different length strings.
Need to double-check voltage (and current) but likely are OK for this inverter, which accepts a wide range.

Certainly don't need a larger inverter; these will rarely if ever max it out.
Oversize array is be cause PV is cheap, off-season and other hours of the day have less sun and output drops off, so over-paneling keeps it maxed out for a while.
If you had more panels, then larger inverter could produce more.
If strings are different orientations, peak power would be lower but holds up for more hours of the day.
Reason for 3.8kW model is 16A output, 20A breaker, 100A panel & main breaker, 120% rule.

I assume this is for net metering. California ... sign up with utility prior to April 14th, so NEM 2.0 not 3.0