Optimising off grid system components to each aother?

[SIGP2101]

Here is what I have already:

3 X 235W 36V 8A PV.
Midnite Classic 150 controller, 96A capable.

6V Battery Bank # of batteries to be determined.
Inverter is to be determined.

Now based on two known component how would you go about pairing up battery bank with and inverter with the rest of the system.

What I am hoping is determine # of batteries needed and right inverter as well for the system to be at optimum balance.
I will adjust my needs to what ever comes out of it. I am hoping that 700W will give me enough energy to run small fridge and few lights.

Thanks!

[inetdog]

Best not to try to balance anything until you have at least some idea of what you loads are and therefore what your 24 hour energy consumption will be. It is that that primarily determines your battery bank size, not the panel wattage you have.

[Sunking]

You are heading for disaster. You are making a very common mistake putting the cart in front of the horse. You start by determining how many watt hours you will need in a day, and then determine your Sun Hours for your location. Then you design the system and everything works out.

But to answer your question based on 700 watts of solar panels and a MS Classic 150

At 12 volt battery as small as 450 AH up to 700 AH with up to a 700 watt inverter.
At 24 volt battery, 225 to 350 AH, 700 watt Inverter
At 48 volts 112.5 AH to 175 AH, 700 watt Inverter.

Took 5 seconds to figure out, and 1 minute to type it.

[SIGP2101]

Best not to try to balance anything until you have at least some idea of what you loads are and therefore what your 24 hour energy consumption will be. It is that that primarily determines your battery bank size, not the panel wattage you have.

I know what you are saying BUT my system requirements are determined by accessability of location, size and weight how much one person can carry. So far there is enough space for only 3 panels and that is it. Max amount of Kg one person can carry to that location is 30Kg. So I will be limited to what system can produce and I have no problem adjusting my needs to it. That is why I need to optimize system for longevity.

Thanks!

[SIGP2101]

You are heading for disaster. You are making a very common mistake putting the cart in front of the horse. You start by determining how many watt hours you will need in a day, and then determine your Sun Hours for your location. Then you design the system and everything works out.

But to answer your question based on 700 watts of solar panels and a MS Classic 150

At 12 volt battery as small as 450 AH up to 700 AH with up to a 700 watt inverter.
At 24 volt battery, 225 to 350 AH, 700 watt Inverter
At 48 volts 112.5 AH to 175 AH, 700 watt Inverter.

Took 5 seconds to figure out, and 1 minute to type it.

Thanks!

Since I am limited to up to 30Kg battery I am zeroing on to 6V 220Ah golf car battery. Would this be a right choice since if I go with 8 batteries to get to 48V I will be way over your optimum quoted-suggested. Any reasons not to do it?

P.S.

And it took me a 2 min to type it. Maybe 3.

[Sunking]

At 48 volts @ 225 AH minimum panel wattage is 940 watts. You would need a 4th panel to support it.

[Mike90250]

Minimum PV is determined by the minimum amps required to maintain healthy, de-stratified batteries, Too low of a charge rate allows the electrolyte to stratify and ruin the battery.
Also you need to figure which months have the shortest sun insolation and not consume more power than can be replaced in those months.
I don't see a backup generator. Even if you get a week long storm, and stop your loads when the battery is 50% low, you will damage the battery every hour it sits without getting recharged (sulfation)
Another idea, is LFP battery, but it's an expensive choice for a beginning system, but it does avoid cell damage at only 30% charged.

[SIGP2101]

Minimum PV is determined by the minimum amps required to maintain healthy, de-stratified batteries, Too low of a charge rate allows the electrolyte to stratify and ruin the battery.
Also you need to figure which months have the shortest sun insolation and not consume more power than can be replaced in those months.
I don't see a backup generator. Even if you get a week long storm, and stop your loads when the battery is 50% low, you will damage the battery every hour it sits without getting recharged (sulfation)
Another idea, is LFP battery, but it's an expensive choice for a beginning system, but it does avoid cell damage at only 30% charged.

Thanks for valuable input.

This is all about three season hunting cabin. During winter months there will be no load on batteries itself. Panels will be snow free, they will be placed almost vertical. During this period I just need trickle charge current to maintain batteries. Have to figure out this one yet and how. During those months I am hoping to get up to 2 hours of sun. Panels will be looking directly at south. Most of sunny days are also extremely cold days as well.

System will have its limitation I know. It won't be designed around needs but user will have to adjust to what system can provide. Recovery time will be 5 days and yes, it will be back up generator for longer then 2 days stays.

[SIGP2101]

At 48 volts @ 225 AH minimum panel wattage is 940 watts. You would need a 4th panel to support it.

Thanks Sunking, this is type of info I need. Also I will read all that is in battery section of the forum. Much appreciated.

You guys are great.

[Mike90250]

Super easy to winterize the system, disconnect all loads (inverter, DC lights,,,,) perform an EQ charge on the last day, top off the fluid in the batteries and the charge controllers will keep the unused batteries fully charged, till some crack head comes by, sees the PV panels and steals them,

[Sunking]

. Have to figure out this one yet and how. .

Nothing to figure out. As Mike said top the batteries off with water, give them a full charge and run a EQ charge and walk away. Only thought required is to remember to top off with water, charge, and EQ, Only thing you have to worry about is me or one of my friends finding your campsite when you are gone. .

[SIGP2101]

Super easy to winterize the system, disconnect all loads (inverter, DC lights,,,,) perform an EQ charge on the last day, top off the fluid in the batteries and the charge controllers will keep the unused batteries fully charged, till some crack head comes by, sees the PV panels and steals them,

Nothing to figure out. As Mike said top the batteries off with water, give them a full charge and run a EQ charge and walk away. Only thought required is to remember to top off with water, charge, and EQ, Only thing you have to worry about is me or one of my friends finding your campsite when you are gone. .

It is good to know that procedure is simple as that. THANK you both!.

Now, I have to find commercially available deep cycle batteries that would be configurable in one of the proposed configurations by Sunking. Thanks for that as well.
New challenge ahead of me. 30Kg or 65 pounds weight limit per battery.
While ago I figured out that I will need roughly 600AH 12V battery bank for my modest needs. That is how I acquired those 3 panels in order to have that 10% charging rate required. But I was mistaken thinking that I will be able to get there by hooking up 6 X 6V 200AH deep cycle batteries in parallel. More digging....

But even if I solve this puzzle another challenge will be to find such a small 700W inverter that works on 24/48Volts. Any suggestions there?

[Sunking]

It is good to know that procedure is simple as that. THANK you both!.

Now, I have to find commercially available deep cycle batteries that would be configurable in one of the proposed configurations by Sunking. Thanks for that as well.
New challenge ahead of me. 30Kg or 65 pounds weight limit per battery.
While ago I figured out that I will need roughly 600AH 12V battery bank for my modest needs. That is how I acquired those 3 panels in order to have that 10% charging rate required. But I was mistaken thinking that I will be able to get there by hooking up 6 X 6V 200AH deep cycle batteries in parallel. More digging....

But even if I solve this puzzle another challenge will be to find such a small 700W inverter that works on 24/48Volts. Any suggestions there?

Hold the bus for a minute. Do you know your daily Kwh requirement? Will it be used everyday or randomly?

65 pound limit is perfect for Golf Cart Batteries because a 6-volt 225 AH battery weighs 66 pounds wet. 4 of those in series or parallel discharged 20%/day is 1 Kwh/day, You can go up to 2.5 Kwh/day, but you sacrifice some cycle life and have no way to CYA for a cloudy day without a generator.

What you really need to do is plan this out. Fist steps are daily Kwh usage, or if random infrequent use allows you some options. Determine what you really need, and I will help you. You might not like the answer, but at least you will know.

But to answer your question you can get 24 volt inverters from 300 to 2000 watts. Example Here. 48 volts start at 1000 watts which is close enough if you need to go that route.

Edit Note: I stand corrected, you can find 48 volt inverters starting at 350 watts Example here

[SIGP2101]

Determine what you really need, and I will help you. You might not like the answer, but at least you will know.

You are such sweetheart Sunking, where do we start? I will tell you all you need to know.
Usage is weekends mostly - occasional long weekends.
Power need as described.

1) Small fridge or chest freezer converted to fridge. No more than 365Kw per year rated. (1000W per day I assume)
2) 50-100W of light on average 5 hours per night. (500W)
3) Laptop 150W 2 hours daily. (300W)

Anything more than above will be supported by small generator.

[Sunking]

1) Small fridge or chest freezer converted to fridge. No more than 365Kw per year rated. (1000W per day I assume)
2) 50-100W of light on average 5 hours per night. (500W)
3) Laptop 150W 2 hours daily. (300W).

1. Does it need to be left on while gone? This is the tricky one. Really need to know what startup and running current is. This determines Inverter and minimum battery size.
2. Use LED and get that down to 10 to 20 watts.
3. I do not know of any laptop that uses 150 watts.

If you have a genny I already gotta a recipe for you.

Panel wattage = 400 to 450 watts. Use two inexpensive Grid Tied panel wired in series.

MPPT 15 amp charge controller with 400 watt panels, 20 amp if 450. Don't buy a cheap one or you are screwed. A good Morningstar Sun Saver 15 amp MPPT is going to cost $200 and worth every penny. So run away from anything under $150 and question anything from $150 to $190. True MPPT controllers will cost $9 to $15 per amp.

Battery 4 Trojan T-105 or T-105RE for a few extra bucks and 2 more years life. Wired in series for 24 volts

20 to 30 amp 24 volt battery charger. Nothing fancy as this is for the genny and you only need a simple CCCV charger that you can set the output voltage from 30 to 34 volts. It is only used to charge the batteries with the genny as fast as possible to minimize fuel burn for those cloudy spells or over discharge. At 34 volts allows you to EQ the batteries for maintenance.

Generator will need to be at least 1000 watts and you do not want to go much higher than 2000 watts. Reason being is maximum fuel efficiency One way over sized will work just , but waist fuel at such low power output levels. Think of it like you driving a city bus to get to work. Sure it works, but gulps a lot of gas doing it. But with 50 passengers is very efficient.

What is outlined from a battery POV will easily give you 2 Kwh per day usable energy. Depending on time of year use and shade issues the panels are not likely to recharge 2 Kwh/day except ijn summer months. However if only used on weekends is not really much of a problem as 2 or 3 days absence if you turn the fridge off will mote than bring them back when you return. If not, that is why you gotta a genny. At 50%DOD with a 30 amp charger, 5 hours makes it new again.

Last thing buy a damn Battery Hydrometer of less than $10 and learn how to use the dam thing for Pete Sake. Let idiots use a volt meter to check the battery SOC. Seriously a temp corrected hydrometer is the only way to determine battery health and SOC in real time. Volt meters only tell you when it is too late.