Connecting new 15kw inverter /charger with 80a MPPT to existing solar system

Stan,

There are several ways of slicing this system up... First need to know your daily loads (peak Watts "power" and Watt*Hours "energy") usage per day...

One way is to put the entire home on backup solar (and genset?) power... Or, just to power a "protected" subpanel for your "critical" loads... A fridge, LED lighting, washing machine, solar friendly water/well pump, LED TV, laptop computer, cell/tablet charging, etc... That is (I would suggest) around 3,300 WH (3.3 kWH per day) for a "near normal" small and/or very energy efficient home... Use propane/wood/etc. for heating, hot water, cooking...

If you have a 48 volt @ 640 AH flooded cell battery bank... Then a "optimal" daily energy usage would be (from the battery bank)... 2 days of storage, 50% max planned discharge for a full time off grid home:

• 48 volts * 640 AH * 0.85 AC inverter eff * 1/2 days storage * 0.50 = 6,528 WH per day (i.e., two dark and stormy days, discharge to 50% state of charge for better battery life).

Next need to figure out your solar array. Say San Diego California, fixed array facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

San Diego
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.00	5.49	6.06	6.50	5.91	5.42
Jul	Aug	Sep	Oct	Nov	Dec
5.66	5.96	5.79	5.39	5.32	4.89

Relatively sunny region... Say you want to run 6,528 WH per day on an average December day...

• 6,528 WH per day * 1/0.52 off grid AC system efficiency * 1/4.89 hours of sun (December average) = 2,567 Watt "Dec" break even array...

For full time off grid, break your loads into two types... Your "base loads" (those that mush run 24x7, and your optional loads (washing machine, irrigation pump, TV, induction cooker, etc...)--Or loads that you can turn off during bad weather (or run a genset when needed). You should plan on only using 50-65% of your "predicted" solar harvest for base loads... And use the rest when the sun is shining and you have a couple days to fully recharge during poor weather....

• 6,528 WH per day December average harvest * 0.65 base load fudge factor = 4,243 WH per day base load fudge factor
• 6,528 WH per day December average harvest * 0.50 base load fudge factor = 3,264 WH per day base load fudge factor (more conservative)

Obviously, I don't know much about your system... But this is roughly how the bits and pieces I know at the moment would work out..,

Also, your 15 kWatt hybrid/offgrid AC inverter is way too large for a 640 AH @ 48 volt battery bank... A much better fit would be 3,200 to 6,400 Watt AC inverter. Your present FLA battery bank would be hard pressed to supply 15+ kWatts of power "reliably".

And if you look at your average power... Say most of it is 5 hours per evening (everyone home, cooking, lights, etc.):

• 6,528 WH average battery load / 5 hours per night = 1,307 Watt average load

Much closer to a 3,200 Watt AC inverter than a 15 kWatt inverter. For example at full load:

• 640 AH * 48 volts * 0.85 AC inverter eff = 26,112 WH total bank capacity
• 26,112 WH battery bank / 15,000 Watt fully loaded AC inverter = 1.7 Hours from 100% to 0% bank state of charge

Not very useful--Less than two hours of energy--And the battery bank may not even last a fraction of that (depending on type of batteries, age, health, state of charge, etc.).

With solar--Conservation is your #1 project... Off Grid Solar energy is expensive. The less energy you need, the smaller and less expensive your system will be... Especially if this is for backup power (use GT or Hybrid inverters to feed solar power back to the home/utility via net metering normally--Backup power only when power failures occur).

Probably way too much information (at least for your original question)... But as you an see, the wiring to support your "protected loads" with a 3.2 kWH inverter would be ~30 amp @ 120 VAC circuit... Not 50+ amps at 240 VAC...

-Bill

I still don't quite understand your needs... And where you are located (I guessed San Diego or the area)?

1) Utility connected power? Then GT Solar is the cheapest/easiest method to generate "substantial" amounts of power for your home with a relatively cost effective solution (say around $0.15 per kWH).

2) Why battery+solar power? For emergency usage? Do you get only a few days a year (on average) of lost power? A genset can be a cost effective solution... The price of fuel is crazy right now--But call it around $1.00-$2.00 per kWH fuel costs. If you have natural gas or propane on site. If not, then gasoline or diesel options. Need fuel conditioner and recycling fuel back to car (such as once a year back to car and refill with fuel+stabilizer--That can be a good week or two a year solution.

3) Going full time off grid... That is not a cheap solution... Maybe around $1-$2+ per kWH typical for off grid solar. System has to be larger than GT Solar system as you have to supply power 24x7 (solar+battery power) or using backup genset (winter, storms, overcast, etc.)... And while solar panels are historically "cheap", batteries, copper wiring, racking, etc. are pretty much at a high right now... And depending on what battery type you pick, you will have to replace the batteries every 5-10 years or so.

4) Hybrid Solar system.... Basically an 'off grid' system that also operates with Utility power--Both "Off Grid" and "Grid Tied" capable "hybrid" AC inverter (many OG inverters are really hybrid type right out of the box). The advantage of Utility power, and net metered/GT Solar. But the costs and maintenance issues of OG solar...

Because off grid solar (and generator) power is expensive.... Generally that means you work to reduce your loads as much as possible... Or in a backup/emergency power situation, you only run a subset of your loads (LED lights, the refrigerators, use propane for cooking, etc.).

For longer term--You can look at more energy efficient solutions... For heating, a Mini-Split Heat pump is around 3x more efficient than a standard resistance heater (somewhere down to freezing weather). For lighting, LED is much more efficient than filament bulbs.

For hot water, there is thermal solar, heat pump water heater, or even lots of solar panels heating an electric water heater (some folks prefer over the 'fun' of solar therm panels+tanks+pumps+plumbing).

If you already have Utility Power--GT Solar (with a backup genset) can be a nice solution--And the GT Solar can save you money (depends on your utility rate plans). But even then, looking at conservation first (energy star appliances, lots of insulation, replacing central heat/air with mini split heat pumps, etc.) can save money--Without the expense of solar (especially Off Grid Solar).

Getting a Kill-a-Watt type meter to measure you loads (120 VAC single plug)... You will soon see that loads running 24x7 (or at least many hours per day) like TVs, computers, lighting, heating, refrigerators, etc. can really add up quickly. Just to give you some ideas about the math:

• 120 Watt refrigerator * 24 hours per day * 0.50 duty cycle = 1,440 WH per day = 1.44 kWH per day
• 300 Watt desktop computer * 10 hours per day = 3,000 WH per day = 3 kWH per day
• 15 Watt low power laptop computer * 10 hours per day = 150 WH per day = 0.15 kWH per day
• 1,200 Watt microwave * 1/3rd hour per day (20 minutes per day) = 400 WH = 0.4 kWH per day
• 1,500 Watt heater * 24 hours per day * 0.33 duty cycle = 11,880 WH per day = 11.88 kWH per day

A small/very energy efficient home/cabin (near normal electrical existence) can be around 3,300 WH or 3.3 kWH per day (x30 days = 100 kWH per month).

The typical North American home is around 300-500 kWH per month (using natural gas/propane for heating, cooking, hot water)... A full electric home can be 1,000 kWH per month to 3,000 kWH per month (i.e., central Texas with full A/C and electric home).

A kill-a-watt type meter:

https://www.amazon.com/s?k=kill-a-watt+electricity+monitor&sprefix=kill-a-watt

And a whole house monitor (can measure large loads like Electric Water heater, central heating, and branch circuit loads):

https://www.theenergydetective.com/

The above links are just examples of possible products (starting point for your searches). For many folks, when they measure their electric loads, changing their habits (turning off unused equipment) and picking more efficient devices (energy star fridge, turn off old "beer fridge in garage", replacing desktop with laptop computer, lots of insulation and weather stripping, etc.)--Saving up to 50% on electrical usage is possible.

Without a firm handle on your needed loads, rough location, other loads like well pump, electric home, etc... It is hard to be very specific at this point.

-Bill