Expand a 12v solar system

[Solarson]

Haha Sunking, I like it, but a bar towel would be more appropriate - I opened a cold beer when I saw your response. Now we're getting somewhere! Wish you'd spotted my first post when I was looking for help on the initial 12v box setup.

Add more panels - easy
Replace batteries - done deal
Run 24 or 48 volts - makes sense

So how many more 235 volt panels?
How many & what size batteries to hit target?

[Sunking]

Not sure how to answer your question because I am confused. You said you consumed 12 Kwh in 20 days or ,6 Kwh/day and you want to add another 1 Kwh per usage correct? So a total of 1.6 Kwh/day?

Without a doubt 1 more panel and a 24 volt 340 AH battery.

Take a look at Trojan J305P-AC battery. It is a 330 AH 6-volt battery. You would need 4 of them in series.

Last note beware of Prime Number of Panels like 1, 3, 5, 7, 11..... There is only two configurations of all in parallel or all in series. Don't let yourself get in that trap. You want as many panels in series are possible. The number of panels is limited by your Charge Controller Voc Input limit. A 150 Voc controller can take as many as 3 and no more than 4 panels. So you can get away with 3 panels if the controller allows it. To put 3 of your panels in series will require a Voc of 150 volts so not sure what yours is. Otherwise two in series will be max. Get a handle on it and report back.

I need to know your controller and panels Voc rating. Do not pass GO until you and I know that.

[Mike90250]

So that's eight 6v t-105's in a sealed externally vented box. Stepped up to 24v (series and parallel) , then into a charge controller. What's the spec for that?

I know an inverter can convert as required to ac but how do I get 12v dc for the legacy wired setup?

When you expand, you have to give up the 12V toys. Seriously, the 12V is a loosing deal. If you are going for 8, T105's, just go to a 48V system, it will work better and have less losses than a 24V system

[littleharbor]

When you expand, you have to give up the 12V toys. Seriously, the 12V is a loosing deal. If you are going for 8, T105's, just go to a 48V system, it will work better and have less losses than a 24V system

Not to mention, at 48 volts your CC will accept 4X the solar input that it will @12 volts.

[Solarson]

When you expand, you have to give up the 12V toys..... just go to a 48V system, it will work better and have less losses than a 24V system.

All the toys? I've got a ton of choice for 12v lighting - have that installed already. I've heard of 24v lighting - but theres not much here in Europe.

Just looking now at suppliers for 24v vs 48v systems - the 24v seem to run happily to about 1,500w and the 48v start just above at 2kw - but twice the price (for one third more). It looks like 48v is suited more to 2kw/3kw+ installations?

[ButchDeal]

All the toys? I've got a ton of choice for 12v lighting - have that installed already. I've heard of 24v lighting - but theres not much here in Europe.

yo can use a buck converter like :

https://www.amazon.com/DROK-Waterproof-Converter-Regulator-Transformer/dp/B017SQ2PUG/ref=sr_1_4?ie=UTF8&qid=1476994951&sr=8-4&keywords=48V%2Bto%2B12V%2Bbuck&th=1

but a small inverter is likely cheaper, more efficient and cheaper LED lights.

[Sunking]

Just looking now at suppliers for 24v vs 48v systems - the 24v seem to run happily to about 1,500w and the 48v start just above at 2kw - but twice the price (for one third more). It looks like 48v is suited more to 2kw/3kw+ installations?

There is some correlation between battery voltage and and Inverter size, absolutely. From Industry practices you will notice

12 volts up to 1000 watts and less. Myself personally unless you are in a RV/Camper forget 12 volts just to limited
24 volts up to 2000 watts
48 volts up to 4000 watts

You can see this in Charge Controller Ratings. Largest you can buy is 80 Amp MPPT. A 80 Amp MPPT controller has the following maximum power input limitations vs battery voltage.

1000 watts @ 12 Volt Battery
2000 watts @ 24
4000 watts @ 48

But here is what I think the OP and so many are really missing. In a residence you really do not want to use DC to run your whatchamacallit. You really want to run everything like everyone else does at 240/120 VAC. There are numerous reasons and they all lead right back to your wallet. DC gizmos are much more expensive and limited. Low Voltage distribution is extremely expensive. Example lets say you had a 24 volt gizmo requiring 10 amps of current or 240 watts over a one-way distance of 25 feet (50 cable feet). You are going to need a very expensive roll of #8 AWG cable to run just that one device. With 120 VAC 10 amps (1200 watts or 5 times more power) you can run the circuit 50 feet one-way with dirt cheap #14 AWG. That is 5 times more power at 1/4th the cost. You do not need to be a rocket scientist to understand that. The only DC circuits you want in an Off-Grid home system is the wiring between the Panels to controller, and two short runs between Controller to Battery and Battery to Inverter. .

Run everything with AC power from an Inverter in your home. Not any old Inverter will do, a real one made for the purpose with a Built-In Battery Charger, Generator Support, and hard wired. There will not be any receptacles to plug into the Inverter, it will have one Hard Wire Output you run 3/4 wires to your AC Distribution Breaker Panel like any home has with code compliant wiring and circuit protection via GFCI.

You must have GFCI because an Inverter cannot produce enough fault current to operate a 15 or 20 amp breaker fast enough. And unless you Inverter is at least 2500 watts, cannot even deliver 20 amps, let alone operate a 20 amp breaker. A GFCI breaker built into the Inverter or main panel breaker will trip instantly if there is as little as 0.1 amps of fault current and does not need a Ground to function properly.

[Solarson]

Well you've sold me on the way forwards with the specifications spelt out - thanks, appreciated. I agree AC is the best way for upgraded off-grid as appliances are considerably cheaper and plentiful power is relatively cheap to produce these days. However I'm still going to step down 10amps of 12v for the low voltage system in the bathroom - I don't want to rip out all the tiles and fixtures just to put in some AC.

[Sunking]

Why cant you use the same wire? 20 times more power available.

[Solarson]

In the bathroom the 12v is running the LED lighting and the 'compost loo' has a 12v integrated extractor fan.

I'll look into using the same wiring for lighting the rest of the house - didn't think of that!

I like the idea of keeping some basic 12v lighting + back up water pump as a fall-back so the place is still functional if the inverter fails

[Solarson]

.... So a total of 1.6 Kwh/day?....Without a doubt 1 more panel and a 24 volt 340 AH battery....... Take a look at Trojan J305P-AC battery. It is a 330 AH 6-volt battery. You would need 4 of them in series.

Correct 1.6 Kwh/day.
Over here the Trojan J305P and the well established Trojan L16G (390 AH) are the same price - would you still go for the J305P?

[Sunking]

Correct 1.6 Kwh/day.
Over here the Trojan J305P and the well established Trojan L16G (390 AH) are the same price - would you still go for the J305P?

L16 any day of the week.

[Solarson]

next thing I would do is upgrade to 24v you are wasting a nice set of batteries, parallel wiring batteries to keep using an old junk 12v inverter.

Is it worth upgrading if I'm not using the capacity from the current set-up? 4 x 12v x 105AH batteries have 2,520WH - that's allowing for 50% discharge. PV's are generating 1KW a day and the discharge rate is 600W a day.

I don't want to mix my measurements but doesn't that mean I've got a lot more power being stored than I'm using?

[Logan5]

With your current set up, you can upgrade to 24v until your batteries are done. it does not mater if you run 24 or 48v you can still use common 12v appliances and led lights, with step down converters, with the exception of inverters. I find off grid cabins seldom even need an inverter, If you take the time to learn what is available as DC native appliances. If you decide to go with a 48v battery bank you can easily run a 24v refrigeration unit with a high amp step down converter. Laptops and LED TV are available in 19v, so a 48 to 19v step down takes care of them. Make sure you install a switch so you can easily cut the power to step downs when not in use. Do not replace your batteries until you learn from the mistakes you made. You need to pass your "brick wall" before you destroy another expensive set of batteries. Finally Solar is a poor source of charge power for batteries. Make sure you have a stiff power source for initiating your new batteries and for periodic maintenance and balancing.

[SunEagle]

Is it worth upgrading if I'm not using the capacity from the current set-up? 4 x 12v x 105AH batteries have 2,520WH - that's allowing for 50% discharge. PV's are generating 1KW a day and the discharge rate is 600W a day.

I don't want to mix my measurements but doesn't that mean I've got a lot more power being stored than I'm using?

You are making an assumption that your batteries will allow you to discharge 50% a day and still have a long life. Most FLA batteries will last longer and have more cycles if you do not discharge more than 25% a day.

You also have to remember that you might end up going for more than a couple of days without any sunshine. That will kill your batteries a lot faster.

[Sunking]

I don't want to mix my measurements but doesn't that mean I've got a lot more power being stored than I'm using?

No Sir, lets say you have 4 batteries. They are 12 volts @ 100 AH. Battery capacity is easy to determine Watt Hours = Battery Voltage x Amp Hours. So 12 volts x 100 AH = 1200 watt hours in any country or language except planet Nobama where it can be anything you want. For the rest of the world 1200 wh. So if you have 4 batteries totals 4800 watt hours.. So no wlets arrange them in 12, 24, and 48 volts

4 batteries in parallel is 12 volts @ 400 AH = 4800 wh
2 batteries in series in parallel with 2 batteries aka 2 x 2 is 24 volts @ 200 AH is 4800 wh
All 4 batteries in series is 48 volts @ 100 AH or 4800 wh.

Take away here is POWER ADDS in both series or parallel circuits. Does not matter how you arrange the four batteries, power does not change. But here is the kicker. In the real world the 48 volt system will deliver more power and cost less.

[Solarson]

How is 100 AH (48v) more power than 400 AH (@12v)?

[inetdog]

It is not more *energy* stored in the batteries. But because of the lower current to get any specific amount of power from the battery bank a 48V system can use smaller wires and have lower power losses in the wires. Hence is can *deliver* more power in a practical situation.

[Solarson]

You are making an assumption that your batteries will allow you to discharge 50% a day and still have a long life. Most FLA batteries will last longer and have more cycles if you do not discharge more than 25% a day.

You also have to remember that you might end up going for more than a couple of days without any sunshine. That will kill your batteries a lot faster.

Ok, got it, but if Im using 600 wh a day thats only 12% of the batteries 4800 wh. I'd have to go 4 days with no sun for them to get to 50% discharge, and that's not happened in the past year.