Optimising off grid system components to each aother?

[SIGP2101]

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.

Thank you sooo much for wasting your time on me!

To answer some of your questions:

Fridge will not be in use while nobody in camp.
Already have 'Solarworld' panels, 3 X 235W 36V 8A PV and Midnite Classic 150 controller.
Do not have batteries and inverter yet, that is why I am seeking expert's advice in order to have balanced system.

I was liberal with my usage estimates just to be on the safe side. Battery Hydrometer is a must, I agree.
So what is your opinion on how to best utilize what I already have? My PV array alone should give me close to 29A under ideal conditions at 24V system.

[Sunking]

OK now we are getting somewhere. Knowing it is not a daily system it will work. Do I understand this correctly? You already have 3 x 235 watt panels and a MS Classic 150? If so perfect.

Wire the 3 panels in series. That give you a peak current of 26 to 29 amps. Obtain 4 6-volt Golf Cart sized batteries. My first pick would be Trojan T-105RE. These are made specifically for Solar and should give you a good solid 3 to 5 year service if you learn how to use the hydrometer. Next in line would be standard T-105 a good medium quality 2-3 year battery. My last choice would be if budget is a concern is a US Battery 6-volt Golf Cart battery as large as you can afford. They range from 200 AH in the GC2 case up to 400 in L16. But limit size to 350 AH. Bottom line on battery capacity with 700 watts of panels into a 24 volt battery is minimum is 220AH up to 350 AH. Trojan make a lot of 6 volt batteries. Use this guide to see all Trojan Options. Be sure to scroll all th eway through. But you are looking for Flooded Lead Acid and for capacity use the 20 Hour Rate. There are a lot of them stick with 6-volt.

As for Inverter we need to know a bit more about the fridge. Both Trojan and USB can handle C/5 discharge rates. That means a 225 AH battery can deliver 45 amps without excessive voltage sag. At 24 volts is 1000 watts, and you can probable get away with 1500 watts for short burst. A little tip here. If you need some large power for short period of time like a saw or something if the batteries are charged, mid day bright sun, and generator on you can run 1500 watts for a while because you get 50 amps from batteries, plus 25 to 30 from solar, plus whatever battery charger amps you buy. That will be your ace for large temporary loads like a saw or microwave oven.

Last do not skimp on cable and terminations. Best bet is buy pre-made terminated cables of large AWG between battery post and battery to Inverter. Will talk about that later when you narrow things down with Inverter.

[SIGP2101]

First of all, THANKS for your unprecedented support. I consider myself lucky SOB bumping into this forum.
Sunking you are fountain of knowledge who is willing to share it. My hat down. Now before you get all excited lets get back to our regular broadcasting.

Do I understand this correctly? You already have 3 x 235 watt panels and a MS Classic 150?

Yes you do, that is correct.

Wire the 3 panels in series. That give you a peak current of 26 to 29 amps. Obtain 4 6-volt Golf Cart sized batteries. My first pick would be Trojan T-105RE. These are made specifically for Solar and should give you a good solid 3 to 5 year service if you learn how to use the hydrometer. Next in line would be standard T-105 a good medium quality 2-3 year battery. My last choice would be if budget is a concern is a US Battery 6-volt Golf Cart battery as large as you can afford. They range from 200 AH in the GC2 case up to 400 in L16. But limit size to 350 AH. Bottom line on battery capacity with 700 watts of panels into a 24 volt battery is minimum is 220AH up to 350 AH. Trojan make a lot of 6 volt batteries. Use this guide to see all Trojan Options. Be sure to scroll all th eway through. But you are looking for Flooded Lead Acid and for capacity use the 20 Hour Rate. There are a lot of them stick with 6-volt.

Thanks for demystifying battery bank for me. Would T145 260Ah be happy medium for me then or should I push it to upper max? 350Ah as per your suggestion. But then I will be running into my weight limit requirements.

As for Inverter we need to know a bit more about the fridge. Both Trojan and USB can handle C/5 discharge rates. That means a 225 AH battery can deliver 45 amps without excessive voltage sag. At 24 volts is 1000 watts, and you can probable get away with 1500 watts for short burst. A little tip here. If you need some large power for short period of time like a saw or something if the batteries are charged, mid day bright sun, and generator on you can run 1500 watts for a while because you get 50 amps from batteries, plus 25 to 30 from solar, plus whatever battery charger amps you buy. That will be your ace for large temporary loads like a saw or microwave oven.

At this moment I do not have much data/knowledge about fridge itself. I will be shopping for something that requires up to 600Wh per day. That is me thinking. I know I kind of working backwards on this but I am willing to accept limitations of the system and use it properly. For example, fridge will be working during days but lights will not and vice versa. Fall, winter and early spring we do not even need fridge. There is a cold storage room for that. Fridge will be required during hot summer sunny days.

Last do not skimp on cable and terminations. Best bet is buy pre-made terminated cables of large AWG between battery post and battery to Inverter. Will talk about that later when you narrow things down with Inverter.

Plan is to connect battery terminals with solid copper bars 1" X 1/4". Connecting points will be tin plated. Now inverter cable itself is open for debate, I have no clue there, thicker the better.

[Sunking]

First of all, THANKS.

You are welcome

Thanks for demystifying battery bank for me. Would T145 260Ah be happy medium for me then or should I push it to upper max? 350Ah as per your suggestion. But then I will be running into my weight limit requirements..

You have to decide. with 29 charging amps your range is 220 to 360 with 300 being a perfect match at C/10. However much pain your wallet and back can handle. Just remember it also effects your AC powered charger for the genny. You want to buy a charger that produces as close to C/8 charge current as you can get. Example if you buy 240 AH battery you want a 240 AH/ 8H = 30 amp charger.

At this moment I do not have much data/knowledge about fridge itself. I will be shopping for something that requires up to 600Wh per day..

At 600 wh per day Inverter is not going to be big concern. The Inverter has to be able to handle the Start Up current of the compressor, plus all loads that may be on at the same time. There are some 24 volt DC models made for Solar, but they are expensive.

Plan is to connect battery terminals with solid copper bars 1" X 1/4". Connecting points will be tin plated. Now inverter cable itself is open for debate, I have no clue there, thicker the better.

Bus bars are excellent. Cable size is going to depend on maximum current and distance. When you know Inverter size I can be more specific. What I can say is the Inverter will probable be 1000 watts or less. But the wire will likely be #6 to #2 AWG copper with appropriate fuses.

[Mike90250]

Even a converted freezer/fridge, for weekend use, would need to have 12 hours or so, to "chill down". You may be better off with dry ice for the weekend

[inetdog]

.... You may be better off with dry ice for the weekend

Fortunately the CO₂ emissions from dry ice do not count.

[SIGP2101]

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

OK, how about 6 X 6V-220Ah = 36V battery bank? Would that be in sync with my (3 X 235W 36V 8A) PV array?

[Sunking]

OK, how about 6 X 6V-220Ah = 36V battery bank? Would that be in sync with my (3 X 235W 36V 8A) PV array?

I would need to know the Make and Model Number of the 36 volt Inverter you will be using before I can answer.

[SIGP2101]

I would need to know the Make and Model Number of the 36 volt Inverter you will be using before I can answer.

How about 2 of these? http://www.bixnet.com/dae400.html

[Sunking]

How about 2 of these? http://www.bixnet.com/dae400.html

I'll be damned, you actually found 36 volt inverters. Do not know the Inverter brand but should work fine.

[SIGP2101]

I'll be damned, you actually found 36 volt inverters. Do not know the Inverter brand but should work fine.

It is probably Chinese made product and that is why I want to get two. To have spare one just in case. Price is right. So my question is still standing. Will 220Ah bank at 36V still be in sync with my solar panels. Your recommendation for 24V was to be between 220AH and 350 Ah. But what is the optimum number for 36V BB?

Thanks!

[Sunking]

It is probably Chinese made product and that is why I want to get two. To have spare one just in case. Price is right. So my question is still standing. Will 220Ah bank at 36V still be in sync with my solar panels. Your recommendation for 24V was to be between 220AH and 350 Ah. But what is the optimum number for 36V BB?

Tell you what, I am not going to feed you, I will teach you to farm and fish so you can feed yourself. Answer your own question.

A FLA battery has both minimum and maximum charge/discharge rate. Max = C8, and Min = C12. Where C is the battery Amp Hour Capacity and 8 and 12 are hours.

Amp Hours = Amps x Hours or AH = A x H
Hours = Amp Hours / Amps or H = AH/A
Amps = Amp Hours / Hours or A = AH/H

So if you have a 100 AH battery what is C/8 and C/12?

100 AH / 8 Hours = 12.5 amps
100 AH / 12 Hours = 8.3 amps.

So if you have a 100 AH battery you can charge or discharge it from 8.3 to 12.5 amps. So now you tell me what can a 225 AH battery handle at C/8 and C/12

So how much power does it take?

Watts = Volts x Amps. So using that 100 AH battery as a example lets say it is a 48 volt battery. How much power to push 8.3 amps? 8.3 x 48 volts = 398 watts. How much at 12.5 amps? 12.5 x 48 = 600 watts.

So now you tell me what is required to charge a 36 volt 225 amp hour battery. I want the minimum and maximum and maximum panel wattage. Give it a try, its easy peasy. I or someone else will tell you if you got it right.

FWIW this only works with MPPT controllers, not PWM. .

[SIGP2101]

Tell you what, I am not going to feed you, I will teach you to farm and fish so you can feed yourself. Answer your own question.

A FLA battery has both minimum and maximum charge/discharge rate. Max = C8, and Min = C12. Where C is the battery Amp Hour Capacity and 8 and 12 are hours.

Amp Hours = Amps x Hours or AH = A x H
Hours = Amp Hours / Amps or H = AH/A
Amps = Amp Hours / Hours or A = AH/H

So if you have a 100 AH battery what is C/8 and C/12?

100 AH / 8 Hours = 12.5 amps
100 AH / 12 Hours = 8.3 amps.

So if you have a 100 AH battery you can charge or discharge it from 8.3 to 12.5 amps. So now you tell me what can a 225 AH battery handle at C/8 and C/12

So how much power does it take?

Watts = Volts x Amps. So using that 100 AH battery as a example lets say it is a 48 volt battery. How much power to push 8.3 amps? 8.3 x 48 volts = 398 watts. How much at 12.5 amps? 12.5 x 48 = 600 watts.

So now you tell me what is required to charge a 36 volt 225 amp hour battery. I want the minimum and maximum and maximum panel wattage. Give it a try, its easy peasy. I or someone else will tell you if you got it right.

FWIW this only works with MPPT controllers, not PWM. .

Fair enough, following your example my
C/12 is 675 Watts
C/8 is 1012 Watts

and my max PV is 705 Watts. So I am not right in the middle but I am in between, closer to the minimum req. for my intended BB. How good or bad this is?

[Sunking]

Fair enough, following your example my
C/12 is 675 Watts
C/8 is 1012 Watts

and my max PV is 705 Watts. So I am not right in the middle but I am in between, closer to the minimum req. for my intended BB. How good or bad this is?

Right on the money. C/10 is the sweet spot so 25 amps x 36 volt = 900 watts. So told you it was easy.

[SIGP2101]

Right on the money. C/10 is the sweet spot so 25 amps x 36 volt = 900 watts. So told you it was easy.

Time to do some shopping Thanks Sunking! More questions coming as I progress with this project this spring.