Inverter Sizing

[newuser1]

Hey everyone.

I am getting quotes for inverters on my system, and I wanted to see if this seemed right to the smart people in this forum.

I won't be doing any upgrades or expansions - just installing the 2250 watt array and charging my 16 Trojan L16P 420 ah, 6v Batteries. It will be 48v and I have a 9kw generator.

They recommended the FLEXware 500 with 1-VFX3648 3.6kW 120V 48VDC Pre-Assembled Off-Grid System

Any thoughts are appreciated!

New User

[Mike90250]

You need to add up your "LIKELY" loads that will be on, (a couple lights, fan , whatever) and then be sure the inverter has enough left over to start the fridge (call it 1500W starting surge) when needed.
Only YOU know if the inverter is large enough. I use a 6KW inverter on a 48V bank. Lights only flicker when starting the chop saw. Well pump is a non-event.

[Sunking]

You have quite a bit of mismatch with your panel wattage and battery capacity. With a battery capacity of 48 volts @ 840 AH really needs a minimum of 70 amps of charge current (C/12) and with 2250 watts of panels into a MPPT controller can only supply at best 45 amps or C/18 do you are pretty short on panel watts. L16's are tall batteries and stratification will be an issue and without at least a C/12 charge current will them to stratify and can cause permanent damage. For that size battery you really need to consider having 3500 watt panel array.

As a rule of thumb the inverter should be no larger, or at least not much large than the panel wattage. With your 48 volt 840 battery they can support up to 5000 watt inverter with a C/8 discharge current, but that is way more than the 1-1 ratio of panel watt to inverter watt ratio.

[newuser1]

Thanks guys!

It sounds like the inverter will work for the job (its fine for my fridge and water pump)

Sunking - should I decrease the battery bank size, or can I just supplement more charging with my genny? (I cant go bigger on the solar array, space limitation)

Thanks for the help so far...

[Sunking]

Cannot answer your question. Battery capacity is determined by your daily watt hours usage. Panel wattage is determined by your daily watt hour usage and location neither of which I know.

[newuser1]

Cannot answer your question. Battery capacity is determined by your daily watt hours usage. Panel wattage is determined by your daily watt hour usage and location neither of which I know.

I'm confused, then how do you know the charge rate is not right, per your previous comment? I have no expectations on usage. I'll be happy with what I get. Insolation is approx 5.

Just trying to see how to reduce the chance of stratification, as I am already going with cheap batteries.

THX

[Sunking]

I'm confused, then how do you know the charge rate is not right, per your previous comment?

Because charge rates will usually fall between C/8 and C/12 on a properly designed system. Exception would be in areas with very low Solar Insolation like Seattle WS.

For example in you case based on batteries being 48 volt @ 640 AH, and solar insolation of 3 Sun Hours, No way you have 5 Sun Hours in winter. More like 3 or 4, maybe less so I will use 3 Sun Hours
Daily watt hours = [48 volt x 640 AH] / 5 days = 6.1 Kwh/day

Panel wattage = [6100 wh x 1.5] / 3 Sun Hours = 3050 watts, round up to 3100 watts
Expected Charge Current = 3100 watts / 48 volts = 65 amps

So 65 amps on a 640 AH battery is a perfect C/10 charge rate.

If by chance you have 4 Sun Hours in winter the panel wattage = 2287, round up to 2300 watts. Charge current = 48 amps or a C/13 which is just barely acceptable.

If by chance you really do have 5 Sun Hours in winter, changes the rules and leaves you two options. Either use AGM batteries because they do not need a minimum charge rate, or over size the panel wattage to give you the minimum C/12 charge rate on Flooded Lead Acid batteries. But 5 Sun Hours is very rare winter insolation and very few places in the world get 5 Sun Hours in winter.

So now maybe you see why I can see problems so quick, your ratios are way outside acceptable limits. It indicates you just bought stuff and had no idea of how it works together and hoped it would work.

[newuser1]

Because charge rates will usually fall between C/8 and C/12 on a properly designed system.


So now maybe you see why I can see problems so quick, your ratios are way outside acceptable limits. It indicates you just bought stuff and had no idea of how it works together and hoped it would work.

Thanks, the math makes sense. I'll need to challenge the local shop to design the system better. I suppose I should have known better than to go with a "Package". Damn marketing got me. Thanks for saving my battery bank.

As for your last comment, luckily I didn't and I checked here first, but I understand your assumption - as I've read plenty of posts in the forum.

Newuser