Just when I think I got it...

[monicaj]

Welcome back monicaj.

So if you want to use all 4 of those 280 watt panels I would suggest getting at least a 60 amp CC and build a 24volt battery system. You would get about 47 charging amps out of the 1120 watts which would be enough for a 470Ah battery system.

Holy cow. So... I woke up this morning thinking I'd go try to work through figuring out how much power my system would produce and compare it to the other calculation of what I'd like to be able to run.

That is not even going to be slightly within my reach. In fact, it's so far out of reach that I need a space ship. So difficult,, yet I have this burning compulsion to master this stuff. Some day...

ok. So, batteries. I guess lead-acid battery is most commonly used, but how about AGM? I read that they take a really long time to charge and so aren't efficient for a solar setup?

If AGM is a good choice for the battery bank, how does this one look...

https://www.apexbattery.com/12v-250ah-8d-deep-cycle-agm-solar-battery-ub.html?gclid=Cj0KEQjw2fLGBRDopP-vg7PLgvsBEiQAUOnIXNo82DlsTXRQDdVvqzfIXmiG0o7G3wkZ8ognCAcJw2gaAtdV8P8HAQ

...12v 255ah... I would need to get 4, hook 2 sets in series, then hook them together in parallel for a 510ah, 24v battery system?

Should I not go up to 510ah, but go a little lower instead?

[monicaj]

You are welcome.

Let us know what your estimated watt hours loads are going to be and we can help you determine the best battery system or at least come up with a battery system that will match up to your solar panel wattage.

I have the sloppy plan of just matching up the battery system to the panel wattage and then seeing what I can and can't do. I haven't the funds to add more panels.

The 3 big things I'd like to run are: washing machine, freezer, and water pump.

I don't have any of those things yet so I don't know the watts, etc.

But just to see if I have a handle on calculating kWh... (not counting surges)

If:

freezer is 200 watts, then 200 x 12 hours usage = 2,400 watt hours
washer is 500 watts, 500 x 1/2 hour usage = 150 watt hours
well pump is 750 watts, 750 x 2 hours = 1,500 watt hours

2,400 + 150 + 1,500 = 4,050 total watt hours. 4,050 / 1,000 = 4.05 kWh

Am I on the right track?

I have to get off here for now, but I was going to try to muddle through calculating how much power my solar system would produce and see if it would meet the needs of all 3 appliances... I think I would have stumbled.

[SunEagle]

Awesome!! I know this is basic stuff to you, and there's a huge mountain of knowledge that I will never know, but I feel some of the path has just been lighted, light bulbs turning on! THANKS!!

You are welcome.

Let us know what your estimated watt hours loads are going to be and we can help you determine the best battery system or at least come up with a battery system that will match up to your solar panel wattage.

[monicaj]

On the first part you are basically correct. Usually you would wire 2 panels in series first so if they had an Imp = 5amp and Vmp = 10v you would have a set of 2 at Vmp = 20v and Imp = 5amp.

Then if you wired 3 sets of those in parallel you would end up with 6 panels with a Vmp = 20v and Imp = 15amps. So you were correct with the Vmp and Imp values.

Now the wire between the charge controller and the batteries is usually sized for the maximum charging amps of the CC. So if the CC is rated for 60amps then the wire should be rated for at least 60amp or larger. The fuse protecting that wire should be rated at 60amp or lower because you want the fuse to open before the wire gets too hot and causes a fire. Going bigger on the wire size will always help as long as you do not make it too big which makes it hard to connect to the terminals of the battery, charger or inverter.

The wire between the battery and inverter would be based on the wattage rating of the inverter divided by the battery voltage. If you had a 600watt inverter and a 12volt battery the wire could see as much as (600watt / 12v = 50 amps). So the wire would need to be rated for more than 50 amps to be safe and the fuse would be rated 50 amps or less.

This is where we warn people that want to use a 3000 watt inverter on a 12volt battery because that inverter could draw as much as (3000w / 12v = 250amps) which is a lot and requires a very big wire.

Awesome!! I know this is basic stuff to you, and there's a huge mountain of knowledge that I will never know, but I feel some of the path has just been lighted, light bulbs turning on! THANKS!!

[SunEagle]

Huge thanks. I feel cleared up there. So for example, 6 panels... Imps = 5 amps each, Vmp = 10v each... If I made 2 sets of 3 panels in parallel, and then hooked the 2 sets together in series, I'd end up with 6 panels with an Imp of 15amps and Vmp of 20v, right? (Hope so cause I'll be excited if I am)


I feel fuzzy these things below... For a 1000 watt ( 4x 250watt) solar panel 24volt system, using an MPPT CC rated 45Amps...

- The wire between the charge controller and batteries (depending on the length) should be rated 50Amps and have a 50amp fuse. In every case, do you use wire that has a rating of 5Amps higher than the Amps of the CC, or is there a formula?

- The wire between the batteries and inverter needs to be rated about 100amps with a 100 amp fuse. Here's where I'm drawing a complete blank. What is the calculation that determines size of the wire?

I'm staying away from voltage drops and wire length until I'm clear on the other stuff.

On the first part you are basically correct. Usually you would wire 2 panels in series first so if they had an Imp = 5amp and Vmp = 10v you would have a set of 2 at Vmp = 20v and Imp = 5amp.

Then if you wired 3 sets of those in parallel you would end up with 6 panels with a Vmp = 20v and Imp = 15amps. So you were correct with the Vmp and Imp values.

Now the wire between the charge controller and the batteries is usually sized for the maximum charging amps of the CC. So if the CC is rated for 60amps then the wire should be rated for at least 60amp or larger. The fuse protecting that wire should be rated at 60amp or lower because you want the fuse to open before the wire gets too hot and causes a fire. Going bigger on the wire size will always help as long as you do not make it too big which makes it hard to connect to the terminals of the battery, charger or inverter.

The wire between the battery and inverter would be based on the wattage rating of the inverter divided by the battery voltage. If you had a 600watt inverter and a 12volt battery the wire could see as much as (600watt / 12v = 50 amps). So the wire would need to be rated for more than 50 amps to be safe and the fuse would be rated 50 amps or less.

This is where we warn people that want to use a 3000 watt inverter on a 12volt battery because that inverter could draw as much as (3000w / 12v = 250amps) which is a lot and requires a very big wire.

[monicaj]

Ah no. The Imp of each panels is 7.95 amps. 2 of those panels wired in series still have an amp rating of 7.95amps but now have a voltage of 2 x the Voc or ~ 89.6v or 2 x the Vmp ~ 70.4v.

Now if you wire 2 of those panels in parallel you will have 2 x the Imp or 15.9amps but the Voc = 44.8volts.

If you wire 2 sets of 2 panels in parallel you will have 4 panels with a Vmp of ~ 70.4volts and and Imp ~ 15.9amps at peak production.

The wire from the 4 panels will need to be sized to handle 15.9amps x 1.25 ~ 20 amps as long as it isn't too long and drops that 70.4v more than 2%. If it does the wire will need to be bigger.

Huge thanks. I feel cleared up there. So for example, 6 panels... Imps = 5 amps each, Vmp = 10v each... If I made 2 sets of 3 panels in parallel, and then hooked the 2 sets together in series, I'd end up with 6 panels with an Imp of 15amps and Vmp of 20v, right? (Hope so cause I'll be excited if I am)


I feel fuzzy these things below... For a 1000 watt ( 4x 250watt) solar panel 24volt system, using an MPPT CC rated 45Amps...

- The wire between the charge controller and batteries (depending on the length) should be rated 50Amps and have a 50amp fuse. In every case, do you use wire that has a rating of 5Amps higher than the Amps of the CC, or is there a formula?

- The wire between the batteries and inverter needs to be rated about 100amps with a 100 amp fuse. Here's where I'm drawing a complete blank. What is the calculation that determines size of the wire?

I'm staying away from voltage drops and wire length until I'm clear on the other stuff.

[monicaj]

Yes, you need a DC/DC converter. They are readily available on the net. Search "24V to 12V converter." I would recommend getting an isolated one.

Thanks!

[SunEagle]

"The wire between the panels and charge controller need to be rated about 1.25% greater than the Imp rating of one of those panels, and sized not to exceed a 3% voltage drop."

Sorry for the way I'm about to mangle terms...

So, let me see if I understand the first part of that (Imp). I have 4 panels, all have 79.5A as the Imp rating, and since they'll be connected in series, that Imp figure doesn't change. If I split them and connect 2 in parallel, and then connect those together in series, am I right that the Imp rating of the system would be 79.5 x 2? And the Voc of the system would be 44.8 x 2?

I'm going to connect them all in series and make it a 24v system as recommended but wanted to ask that only to see if I'm understanding how things work.

Imp "of the system", and Voc "of the system"... is that the right term to use?

Ah no. The Imp of each panels is 7.95 amps. 2 of those panels wired in series still have an amp rating of 7.95amps but now have a voltage of 2 x the Voc or ~ 89.6v or 2 x the Vmp ~ 70.4v.

Now if you wire 2 of those panels in parallel you will have 2 x the Imp or 15.9amps but the Voc = 44.8volts.

If you wire 2 sets of 2 panels in parallel you will have 4 panels with a Vmp of ~ 70.4volts and and Imp ~ 15.9amps at peak production.

The wire from the 4 panels will need to be sized to handle 15.9amps x 1.25 ~ 20 amps as long as it isn't too long and drops that 70.4v more than 2%. If it does the wire will need to be bigger.

[jflorey2]

The last question: Most of the things I'll be using are going to be 12v... so if my battery bank is 24v, do I need something in between the battery and my 12v stuff to make the volts going to my stuff 12v?

Yes, you need a DC/DC converter. They are readily available on the net. Search "24V to 12V converter." I would recommend getting an isolated one.

[monicaj]

"The wire between the panels and charge controller need to be rated about 1.25% greater than the Imp rating of one of those panels, and sized not to exceed a 3% voltage drop."

Sorry for the way I'm about to mangle terms...

So, let me see if I understand the first part of that (Imp). I have 4 panels, all have 79.5A as the Imp rating, and since they'll be connected in series, that Imp figure doesn't change. If I split them and connect 2 in parallel, and then connect those together in series, am I right that the Imp rating of the system would be 79.5 x 2? And the Voc of the system would be 44.8 x 2?

I'm going to connect them all in series and make it a 24v system as recommended but wanted to ask that only to see if I'm understanding how things work.

Imp "of the system", and Voc "of the system"... is that the right term to use?

[monicaj]

Welcome back monicaj.

The problem with using over 1000 watts of panels to charge a 12volt battery system is you need to use a charge controller that is bigger than 80 amps which they usually do not make. So going to a 24volt battery system is a much better choice.

The maximum DC input voltage I referred to is listed on the Charge Controller specification documentation. You are correct it is determine by adding up all of the panel Voc ratings that you wire in series. So if you had 4 of those 280watt panels shown in your first post with a Voc = 44.8v you would get a value of 179.2v which easily exceeds a quality 80Amp CC DC input rating. You could wire those 4 panels as 2 pairs (2 wired in series) wired in parallel which would lower you DC input voltage to about 90volts but you would still probably exceed the maximum wattage for a 12volt battery system.

So if you want to use all 4 of those 280 watt panels I would suggest getting at least a 60 amp CC and build a 24volt battery system. You would get about 47 charging amps out of the 1120 watts which would be enough for a 470Ah battery system.

If you understand that part we can move forward with wire and fuse sizing.

I love the way you break it down in simpler terms, so I really think I do have a grasp on what you said.

At first I wondered why the 470 was still the Ah of the battery bank when I was adding 2 more panels, but then realized if I were using 12v bank, I would end up using a bank with higher Ah.

I'm ready for the wiring and fuse sizing.

[SunEagle]

Welcome back monicaj.

The problem with using over 1000 watts of panels to charge a 12volt battery system is you need to use a charge controller that is bigger than 80 amps which they usually do not make. So going to a 24volt battery system is a much better choice.

The maximum DC input voltage I referred to is listed on the Charge Controller specification documentation. You are correct it is determine by adding up all of the panel Voc ratings that you wire in series. So if you had 4 of those 280watt panels shown in your first post with a Voc = 44.8v you would get a value of 179.2v which easily exceeds a quality 80Amp CC DC input rating. You could wire those 4 panels as 2 pairs (2 wired in series) wired in parallel which would lower you DC input voltage to about 90volts but you would still probably exceed the maximum wattage for a 12volt battery system.

So if you want to use all 4 of those 280 watt panels I would suggest getting at least a 60 amp CC and build a 24volt battery system. You would get about 47 charging amps out of the 1120 watts which would be enough for a 470Ah battery system.

If you understand that part we can move forward with wire and fuse sizing.

[monicaj]

I would say that 2 of those 280w panels will require an MPPT CC rated at or above 45amps (2 x 280w = 560w / 12v = 47amps) similar to the Morningstar TS-MPPT 45A

With 45 charging amps the battery system should be rated between 360Ah to 540Ah. So if he installs a 500Ah 12v system it should safely provide about 1200watt hours daily (~ 20% DOD) and that 560 watts of pv should be able to recharge the battery usage.

Now the question is how many watt hours will his loads (lights, fans, fridge, washer, etc.) use a day. I can tell you that you can forget the washer and any large fridge. Also that wattage of the lights and fans need to be low if you plan on running them for long.

For an inverter you need to go with a pure sine wave type around 600 to 800watt. Going larger will end up draining your batteries faster.

Wow! I forgot that I put a post to this forum almost a year ago. I only found out after landing on a different post and deciding register, and found out I was already registered.

SunEagle, I read through my old post and again, felt much appreciation for your detailed answers. It was actually one of your comments on a different post that prompted me to register and ask a question. Here's the post I was looking at since it relates to my question. https://www.solarpaneltalk.com/forum...ight-direction And further down I'll paste your response so you can see what my new question refers to.

I haven't looked at solar stuff in a while (so now I have to get familiar again), and my situation changed from this old post, but I'm hoping that by commenting here, it'll bump this post to the top of the forum list.

My new situation is that I kept both of those panels instead of giving them to a friend. So now I have a total of 4 panels (all the same specs) that I want build a system with. And instead of using golf cart batteries, I just want to use some bigger deep cycle batteries.


So here's what I gleaned so far, please tell me if I'm on track: It's better to wire the panels in series to get lower voltage drop and use smaller wires. I can figure out what size controller I need by using the formula 4 x 280w = 1120. Then 1120 / 12v = 93.3 amps, so I would choose an MPPT CC that is over 93.3 amps. SunEagle said, "The OP just needs to pay attention and does not exceed the max DC input voltage for that CC."

So first quesrtion: To figure out max DC input voltage, I'm looking at the Voc number? So the Voc # on my panels is 44.8. Then 44.8v x 4 = 179.2, and I need to make sure the CC is rated to handle that much voltage coming in, plus a little more?

Second question: Figuring out size of battery bank and inverter... is it a simple matter of doubling the figures since my solar panels are doubled? Like, for the inverter, go from around 700watt to around 1400watt? and battery bank Ah doubled as well? (I have full doubt that it will be that simple but had to ask.)

So then I finally come to SunEagles response to the other post that is about the same questions I been asking... I'm pasting his response, and then below that, my question is in regards to using a 12v battery bank vs a 24v.

----------------

"... So for a 1000 watt ( 4x 250watt) solar panel 24volt system you should get an MPPT charge controller rated 45amps. 4 x 6volt batteries rated about 800 to 1000AH. A 24volt inverter rated no more than 2000watts max. You will wire the panels in series to the charger controller (make sure that CC is rated for the total Voc of the 4 panels plus a little more). The wire between the panels and charge controller need to be rated about 1.25% greater than the Imp rating of one of those panels, and sized not to exceed a 3% voltage drop. The wire between the charge controller and batteries (depending on the length) should be rated 50Amps and have a 50amp fuse.The wire between the batteries and inverter needs to be rated about 100amps with a 100 amp fuse. This system should get you about 5000 to 6000 watt hours a day if you don't discharge your batteries more than 25%. I do not know if that is enough or too much since you haven't determined your actually daily watt hour needs.

You can go to a 48volt system which requires 4 more 6 volt batteries. This will reduce the size of your wires and fuses due to the higher voltage as well as your Charge controller amp rating. The area you have to watch out for is that you will still need enough amp output for that CC to keep that battery system happy with a C/8 to C/12 charge rate where C = Battery system AH."

------------------

I'm not yet focusing on fuses and wiring between batteries (and when I do, I think the above info will get me through - Thanks again, SunEagle!).

As far as 12v battery bank vs 24v... I need to see if I can get a general understanding of the differences/benefits. Is it that a CC that is 24v will more efficiently get power to the bank? Faster? From the last sentence in the above paragraphs... Higher voltage means reduction in wire and fuse size? Whew. This is some hard stuff to grasp.

The last question: Most of the things I'll be using are going to be 12v... so if my battery bank is 24v, do I need something in between the battery and my 12v stuff to make the volts going to my stuff 12v?

Notes: I know that the normal way a system is created is by first looking at the load, figuring out what you want to run. But I only have these panels and I really don't have funds to add more. So I'll learn to use a killometer and check surges, wattage and amps, etc, before I try to add it to the system. I lived for a year on 80 watts of solar power, and really couldn't do much (still loved it though, lived near a huge forest), so when I get back off grid, 1,000 watts will seem like a luxury.

Thanks in advance to all you people on here for freely giving your time and knowledge to help. It's very much appreciated.

[VTSE]

after you v determined the wattage of the appliances you wanna install then you should now determine the inverter size and controller.

[monicaj]

Thanks Amy.