Upgrade second guessing

[Offgridiot]

With this much additional power you will certainly need to rethink your battery bank, and system voltage for that matter. I have a friend who bought 3 Midnite Solar controllers for his system because he was unclear how the whole solar array wiring configuration worked. Basically he spent $1400 usd more than h needed.

My current system with 2244 watts of solar power does us just fine (we don’t have to run the generator) through about 7 months of the year. The new panels will add about 5 times that amount of potential but I realize most of that potential will be wasted in the summer months. It’s the winter months where I’m hoping it shines (okay that’s 2 unintended puns now that I guess I should acknowledge ) in comparison. Approximately 6 times the solar gain on all our overcast days should save us the cost of much of the diesel we burn in the generator. I’ve also got plans in place to reduce a significant part of our electrical load (heating water with the wood stove instead of the electric tank). The new batteries should provide more usable capacity than my old FLA ones did when they were new.
There are definitely things I would do differently if I was building a whole new system from scratch, and going to 48 volts would be the first decision but adding another $3K to the price of the upgrade was/is beyond my budget. My system actually started configured at 12 volts, and 7 or 8 years ago, I upgraded to 24 volts, after which we’ve been really happy. No more nuisance trips of the main breaker.

 

[littleharbor2]

My current system with 2244 watts of solar power does us just fine (we don’t have to run the generator) through about 7 months of the year. The new panels will add about 5 times that amount of potential but I realize most of that potential will be wasted in the summer months. It’s the winter months where I’m hoping it shines (okay that’s 2 unintended puns now that I guess I should acknowledge ) in comparison. Approximately 6 times the solar gain on all our overcast days should save us the cost of much of the diesel we burn in the generator. I’ve also got plans in place to reduce a significant part of our electrical load (heating water with the wood stove instead of the electric tank). The new batteries should provide more usable capacity than my old FLA ones did when they were new.
There are definitely things I would do differently if I was building a whole new system from scratch, and going to 48 volts would be the first decision but adding another $3K to the price of the upgrade was/is beyond my budget. My system actually started configured at 12 volts, and 7 or 8 years ago, I upgraded to 24 volts, after which we’ve been really happy. No more nuisance trips of the main breaker.

Keep in mind, your battery, whichever battery it is, will have charging limits. If you increase your PV 5 times over you will need to limit charging output on good sunny days.

 

[Offgridiot]

Keep in mind, your battery, whichever battery it is, will have charging limits. If you increase your PV 5 times over you will need to limit charging output on good sunny days.

Thank you for this. To think it through, I’ll have 4 controllers. 3 capable of throwing 94 amps each at the batteries, and one rated for 80 amps. On a winter morning, overcast skies could suddenly clear up, and the controllers want to process all energy, throwing as much as 362 amps at the batteries.
I assume you’ve seen my battery bank diagram in the first post. Each battery has a 200 amp BMS. Won’t the 362 incoming amps be distributed across the batteries in a safe manner? Or do I need to limit the total incoming amps to 200 (or less) amps match the capacity of the BMSs?

 

[littleharbor2]

Thank you for this. To think it through, I’ll have 4 controllers. 3 capable of throwing 94 amps each at the batteries, and one rated for 80 amps. On a winter morning, overcast skies could suddenly clear up, and the controllers want to process all energy, throwing as much as 362 amps at the batteries.
I assume you’ve seen my battery bank diagram in the first post. Each battery has a 200 amp BMS. Won’t the 362 incoming amps be distributed across the batteries in a safe manner? Or do I need to limit the total incoming amps to 200 (or less) amps match the capacity of the BMSs?

I honestly don't know the answer to that. I couldn't say yes or no without knowing.

 

[Offgridiot]

Ok, it took a while but i am up to speed. Your reference to post #25 was the key to my understanding your diagram.

Solarod says its theoretically a perfect balance so I'm on board with how you propose.


You did everything right. I should apologize and thank you for pointing me to post #25, i was way off.

Nice work. This is your thread so take it where you want or start a new one with a more descriptive title for your next question (that helps drag people in).

….speaking of dragging people in….
Not sure if this approach breaches forum etiquette but you might be able to answer a question that was brought up after we last chatted. When you suggested that I take this thread where I want, well I’m not too sure how to navigate that kind of thing but this is what I’ve come up with so far. I don’t want to make assumptions about having a direct line of communication with any individuals on the forum just because they were kind enough to engage before but,

The following is from post #23, I think.

Keep in mind, your battery, whichever battery it is, will have charging limits. If you increase your PV 5 times over you will need to limit charging output on good sunny days.

Thank you for this. To think it through, I’ll have 4 controllers. 3 capable of throwing 94 amps each at the batteries, and one rated for 80 amps. On a winter morning, overcast skies could suddenly clear up, and the controllers want to process all energy, throwing as much as 362 amps at the batteries.
I assume you’ve seen my battery bank diagram in the first post. Each battery has a 200 amp BMS. Won’t the 362 incoming amps be distributed across the batteries in a safe manner? Or do I need to limit the total incoming amps to 200 (or less) amps to match the capacity of the BMSs?
————

Are you comfortable answering the 2 questions at the end of my reply to littleharbor?

 

[MisterSandals]

Are you comfortable answering the 2 questions at the end of my reply to littleharbor?

Not sure I’d say comfortable but I will tell you what I think.
For a single 4P battery as you have it wired (with @Solarod mention that it’s perfectly balanced), the current would be evenly split between the 4 batteries (.25 total charging amps to each).
With 2 of those 4P batteries in series (4P2S), with only one way to wire in series (as you have drawn in post #1), it’s probably as good as you can do. I would think that each of the 8 12V batteries would get equal current and .125.

I’m counting on my friends here to roast me wickedly if I am wrong!

If you built this as 2S4P I’d feel a little more confident, but I am struggling to know why.

If you build it, you could test the current with a clamp on meter to verify and we could work from there if it’s not even.

Helpful?

 

[Offgridiot]

Not sure I’d say comfortable but I will tell you what I think.
For a single 4P battery as you have it wired (with @Solarod mention that it’s perfectly balanced), the current would be evenly split between the 4 batteries (.25 total charging amps to each).
With 2 of those 4P batteries in series (4P2S), with only one way to wire in series (as you have drawn in post #1), it’s probably as good as you can do. I would think that each of the 8 12V batteries would get equal current and .125.

I’m counting on my friends here to roast me wickedly if I am wrong!

If you built this as 2S4P I’d feel a little more confident, but I am struggling to know why.

If you build it, you could test the current with a clamp on meter to verify and we could work from there if it’s not even.

Helpful?

Very helpful. Thanks again. I sometimes feel like I have just enough knowledge to get me in trouble. If I’m honest, there’s more than merely second guessing going on. Third and fourth guessing happens. My brother even found a couple t-shirts that suit us perfectly. They read, “Hang on. Let me overthink this.” It’s a genetic malady I have to live with.
Now to the question of how I’m going to safely get all those potential solar amps (362?) into my batteries….but that’s probably a subject for a different thread altogether.

 

[MisterSandals]

Now to the question of how I’m going to safely get all those potential solar amps (362?) into my batteries

I’d start with your SCCs throttled way back to get a feel for how slowly you can charge and still have full batteries at the end of the solar day.

Pointing an array east and west still best if you can physically do it.

 

[Offgridiot]

I’d start with your SCCs throttled way back to get a feel for how slowly you can charge and still have full batteries at the end of the solar day.

Pointing an array east and west still best if you can physically do it.

Of course! Thank you! Why wouldn’t a (good quality, high end) controller have a current throttling function? Duh! I anticipate having an easier time getting to sleep tonight. Last night was kinda LOL

I’ve seen where people point arrays east and west but I always assumed that it had to do with shading issues to the south. I pretty much have shading issues to the east and west (I chose my building site because of southern solar exposure) so I’m not sure if that array setup would be helpful, especially in the depths of winter. Again, I’m sure there are factors I’m not considering, and I’m willing to explore the concept for my situation. I mean, I do have the space to adjust my plans if it makes more sense. My panel expansion plan includes 3 arrays. I can see that in some situations, it might be advantageous to orient one array each to the east, south, and west (or southeast, south, and southwest) but unless I set up a tracking system, I’d be concerned (in the winter) about missing out on gain from the east array in the afternoon. Why is it best?

The SCC throttling solution is winning the battle in my (cluttered) mind so far….

 

[MisterSandals]

I’d be concerned (in the winter) about missing out on gain from the east array in the afternoon. Why is it best?

Thats the point, you cannot use all of your array at once so spreading it out over a longer period would let you harvest more overall.

 

[Offgridiot]

Thats the point, you cannot use all of your array at once so spreading it out over a longer period would let you harvest more overall.

If I’m following you correctly, if I had good solar exposure in the morning and evening (I don’t), then I could spread out, in moderation, my solar income over a longer period every day. I think that pointing all the panels at the brightest part of the overcast skies, generally to the south, will probably give me more than pointing a third at the trees to the east, a third to the south, and a third at the trees to the west. The irradiation of every site is unique, and it would definitely be interesting to be able to tweak array angles after installation but budget constraints don’t allow for a tracking setup. Oooh! Maybe a light meter would be a good investment….

 

[MisterSandals]

will probably give me more than pointing a third at the trees to the east, a third to the south, and a third at the trees to the west.

Yes but having more than you could use facing south is worse than "less than optimal" pointing east and west.

Maybe a light meter would be a good investment….

A solar panel makes a good light meter. Measure volts and amps (shorted, measure with clamp meter) to get possible more usable numbers (watts!) than from a light meter.

 

[Offgridiot]

Yes but having more than you could use facing south is worse than "less than optimal" pointing east and west.


A solar panel makes a good light meter. Measure volts and amps (shorted, measure with clamp meter) to get possible more usable numbers (watts!) than from a light meter.

Up the coast here (half a day’s travel north of Vancouver BC), we live in a temperate rain forest. I’m not sure overcast means the same thing for me as it does for someone in Silicon Valley. As an example, my existing (unthrottled) solar array gives me around 2000 watts (never seen it above 1900 or so even though it’s theoretically possible to get 2244 watts from it) in the summer. I’ve logged almost 13KWh on good days. At the other end of the spectrum is a typical day like today where, when I checked a short while ago, I’m pulling 110 watts (and that’s rapidly fading). My solar harvest for the day is almost over, and I’ve accumulated 0.6 KWh. Yesterday was 0.5 KWh total. I’d have to buy a couple more pallets of panels before I was into the territory of having more than I can use today.
We’re expecting a few days of cool, clear weather starting tomorrow, where I might be able to avoid running the generator on one of those days, and if we could count on more of that kind of weather in the winter, I might see the logic in the assorted-array-direction approach but under the circumstances, I’m having a hard time embracing it.
To be clear, I still bow down to your grasp of all things solar. I can be stubborn and a little thick. If you still think I should stay open to the idea, please let me know.

 

[MisterSandals]

As an example, my existing (unthrottled) solar array gives me around 2000 watts (never seen it above 1900 or so even though it’s theoretically possible to get 2244 watts from it)

Okay, sorry, i got your situation confused with someone else i was helping (2 different extreme over-panel setups).

Yea, with those 8 batteries in 4P2S, 2000W (2000W / 28V = 71A) pretty sweet.

Sorry, carry on!