# Matching battery's, panels, and charger to my inverter

j4ray Registered Users Posts:

**13**✭✭ Ok so I bought a aims power 6000w 24v inverter for an off the grid small cabin/house. I'm in the middle of the build and don't want to do things twice. I've been researching and researching on what and how to match everything else to that inverter. I have 6 100w renogy panels to start with and just got a 40amp mppt charger. I'm having second thoughts about the charger, maybe I could get another one and run them parallel(if I do that will they have to be synced)? Because I started looking at the amount of battery's I will need to make it work. Also still not sure what size and how many battery's. Or what size charger I need.

Please help me

Thank you

Please help me

Thank you

## Comments

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13✭✭3,741✭✭✭✭The purpose of the system is to provide for your electrical needs... in other words, your loads.

When designing a system we need to know what are we designing it for, in other words, your loads.

It's very similar to buying a pickup truck... if you asked my advice on what truck to buy, I would ask the weight of your load and the weight of your trailer.

After you tell us about your loads, we can choose a battery size that can handle the load. The final step is to buy enough solar panels and controllers to charge the battery.

By the way, we need the peak load in watts, and the daily energy use in kilowatthours.

--vtMaps

33,545adminIf you design a system to power your air compressor+saws+etc. for construction--It may be "too large" for your daily needs when construction is completed.

What is your system design? Type of batteries, Amp*Hour rating of the battery bank (or how many batteries, and voltage/Amp*Hour rating of each battery)?

A 6,000 Watt AC inverter on a 24 volt battery bank is a bit of miss-match... That is a lot of current to pull from a 24 volt battery bank.

-Bill

13✭✭3,741✭✭✭✭Will there be any laundry machines, clothes dryers, hair dryers, microwaves, laser printers, or irons?

--vtMaps

33,545adminFor A/C, if you only use it during hot summer afternoons (lots of sun), you might get away with a smaller system (running system all day and into the night is a real power draw).

But, before I do that, can you let me know (very roughly, nearest major city) your cabin is located. I would use something like this (look at list of cities) to figure out how much sun per day you have, by season.

http://solarelectricityhandbook.com/solar-irradiance.html

-Bill

13✭✭3,741✭✭✭✭By the way, where will your batteries be kept? Hopefully in a cool place.

--vtMaps

13✭✭3,741✭✭✭✭--vtMaps

13✭✭33,545adminBattery bank--Assume 2 days of storage and 50% maximum discharge (typical "optimum" off grid system & for maximum battery life), 48 volts (larger system if you bump up system size for more A/C loading later).

- 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max discharge * 1/48 volt bank = 324 AH @ 48 volt battery bank

Then there is sizing the solar array for charging the battery bank. 5% to 13% is typical for solar charging. 5% for seasonal/weekend usage... 10%+ for full time off grid. 13% plus perhaps for your afternoon solar powered A/C.- 324 Ah * 59 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,241 Watt array minimum

- 324 Ah * 59 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,483 Watt array nominal
- 324 Ah * 59 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,227 Watt "typical cost effective" maximum

Then there is sizing the array based on amount of needed energy... Using this link (fixed array):http://solarelectricityhandbook.com/solar-irradiance.html

## Lafayette

Measured in kWh/m2/day onto a solar panel set at a 60° angle from vertical:Average Solar Insolation figures

(For best year-round performance)

- 3,300 WH per day * 1/0.52 off grid system eff * 1/4.01 hours of sun per day = 1,583 Watt array for "Nov" break even month

So--just for day to day usage--even a "small" array could work pretty well. Now let us look at what a 13% array could do for you.- Jan: 3,227 Watt array * 0.52 AC system eff * 3.40 hours of sun per day = 5,705 Watt*Hours per day (typical January)

- Nov: 3,227 Watt array * 0.52 AC system eff * 4.01 hours of sun per day = 6,880 WH per day (typical November)

- Summer: 3,227 Watt array * 0.52 AC system eff * 5.0 hours of sun per day = 8,390 WH per day (min-typical summer)

So if you use a 13% array and a 3.3 kWH "per night" battery bank (324 AH @ 48 volts), for summer you could have:- 8.4 kWH summer capacity - 3.3 kWH night time loads = 5.1 kWH per day available for "day time" A/C (minimum)

Seems like a possible solution--Run it for a few years with a minimum battery bank and see how it works?-Bill

13✭✭3,741✭✭✭✭Also, consider that you don't really know what your needs are... you will be in much better position to expand the system at 48 volts.

One more thing... you haven't mentioned how far the panels are from the charge controller. Longer distances work better with a 48 volt system.

--vtMaps

13✭✭13✭✭33,545adminNote that Power = Voltage * Current... So if you choose a 24 volt battery bank, the current is 2x higher.

For example, lets say you have 8 batteries: 6 volt @ 225 AH "golf cart" batteries. You can arrange them as:

- 4x 6 volt batteries in series = 24 volt string; 2x parallel strings for 24 volt @ 450 AH battery bank
- 8x 6 volt batteries in series = 48 volt string @ 225 AH battery bank

They both store the same amount of energy:- 24 volts * 450 AH = 10,800 Watt*Hours

- 48 volts * 225 AH = 10,800 Watt*Hours

However, for example, when charging (say 10% rate of charge), the current on the same bank:- 24 volt bank: 450 AH * 0.10 = 45 amps charging
- 48 volt bank: 225 AH * 0.10 = 22.5 amps charging

Both are the same power (same size solar array, same size AC genset, etc.)--But the wiring has to be heavier and instead of using a 30 amp solar charger, you need a 50+ amp solar charger (more expensive solar charger for "same job").This is bit in the "weeds" where you are at in the process right now. We still do not know how much power/energy you need to "be happy". Normally, we would start with your loads and figure out your daily loads, then size the rest of the system.

If, however, you have other limits (most people do not have an unlimited bank account)--Perhaps you only want to spend $xxx money on batteries at this time--We can use that and size the system based on the limited amount of batteries. And if you need more power, you can use your genset (to power saws, fill a cistern once a week with a genset, etc.).

Note refrigerators and well pumps can make a system "much larger". And add A/C, that can make the system even larger.

We just need to figure out what your needs/limits are, and then size the system to mee those needs.

-Bill

13✭✭2200w continuous during the day while I am at work. That's with the a/c on. 600w continuwith the a/c off.

So im guessing 4.9kwh peak, 2.2kwh daily, 0.6kwh daily with out the a/c on.

13✭✭33,545admin- 4x 6 volt @ 225 AH batteries series = 24 volt string @ 225 AH
- 2 strings in parallel = 24 volt @ 450 AH (8 batteries total)
- 8 x 6 volt @ 225 AH batteries in series = 48 volts @ 225 AH

Note that 8 batteries (2s strings @ 24 volts vs 1x string at 48 volt) stores the "same amount of energy". (no difference to above energy usage calculations).Just that 24 volts take 2x current (heavier wiring, heavier charge controllers, etc.)...

- 450 AH battery bank (24 volt) * 0.10 rate of charge = 45 amps
- 225 AH battery bank (48 volts) * 0.10 rate of charge = 22.5 amps

-Bill13✭✭33,545adminIs your inverter TSW our MSW? What is its taste load (power usage just turned on)?

If the inverter is a MSW unit and/or uses >>20 Watts tare, you may want to think about a different inverter.

It all depends on your energy needs, or you adapt your energy usage to what you can afford. And maybe 2-5 years in the future, you revisit your setup.

1kWh power day=led lighting, rv water pump, laptop, radio, cellphone, internet.

3.3 kWH power above + fridge + well pump + washer + a few fans (near normal electrical life with lots of energy conservation).

Power usage is a highly personal set of choices. My suggestions as a starting point are just suggestions. What works for me or others may or may not work for you.

-Bill

13✭✭## AIMS Power (PICOGLF60W24V240VS) 6000W 24V DC to 120/240V AC Pure Sine Inverter Charger

33,545adminSo yours is a PSW/TSW type inverter--Better for running all of your AC loads (MSW--Modified Square Wave can cause issues for some devices/loads).

Just an FYI--Many folks here have had less than ideal function/reliability with AIMs inverters--Others have been pretty happy. (I will offer no opinion other than some of the much more expensive/better brands of inverters do tend to be more reliable).

A 6,000 Watt inverter with 18,000 Watt surge draws a lot of current at 24 volts:

- 6,000 Watts * 1/0.85 inverter eff * 1/21 volts cutoff = 336 Amps (max load, minimum input voltage to inverter)

- 18,000 Watts * 1/0.85 inverter eff * 1/21 volts cutoff =1,008 Amps (max surge load)

Those levels of current are very difficult to get from a 24 volt battery bank--Probably around 200 Amps maximum (perhaps close to 300 Amps for a couple second surge) are more realistic "maximum" currents.I would suggest ~2,400 to perhaps 4,000 Watts as the maximum AC inverter for a 24 volt battery bank with "reasonable size" wiring and lead acid batteries.

Not to say you cannot do more--But I would not suggest it unless you are willing to experiment to confirm you get 6/18kWatts from the inverter.

-Bill