Checking the math on 1.65 kwatt off grid solar system

[mitiempo]

Originally Posted by sailor4life7777

Yes this: "As long as there is no shading and the controller can handle the voltages, parallel has no advantage over series"

Shading is a problem with any wiring arrangement, more so with series. In an off grid situation just be sure to place the panels where they will not be shaded.

[StuM]

Originally Posted by sailor4life7777

Do you mean to say "As long as there is no shading and the controller can handle the voltages, parallel has no advantage over series?", not the other way around? Series only downside is from shading and from requiring a charge controller that can handle large voltages, correct??

The advantage of series is higher voltage which means less amps which means thinner wire or less voltage drop.
The disadvantage of series is higher voltage which means it's more dangerous.

[mitiempo]

Originally Posted by StuM

The disadvantage of series is higher voltage which means it's more dangerous.

True, about as dangerous as the 120 AC coming out of the inverter.

Done properly there should not be a problem.

[redneckrob]

Originally Posted by sailor4life7777

This battery: https://www.aliexpress.com/item/4000...65422794%21sea

Do you mean to say "As long as there is no shading and the controller can handle the voltages, parallel has no advantage over series?", not the other way around? Series only downside is from shading and from requiring a charge controller that can handle large voltages, correct??

Thanks again to everyone for all the replies!

It's important to consider the real world vs the ideal calculated world. If every solar panel remained equally clean and degraded at exactly the same rate, then with no external shade there's no difference between parallel and series except what you stated. In the real world, birds's crap on a panel, they get dirty, and they degrade at different rates. At this point, you have to remember that effectively no panel can produce more than the weakest panel. I'll give you a simplified example of the impact of this. Imagine you have ten 100 watt panels of the same voltage/amperage in series. Now an osprey craps on one, or it gets dirty, or some cells die on it, and it can only produce 90 watts. Now no panel can produce more than 90 watts. So your 1 kW system can only produce 900 watts. Now imagine the same system with them all in parallel. Only the single panel is impacted, so you get 990 watts. It's the different between a 10% system degradation and a 1% system degradation.
(Yes armchair EEs, I understand it's the amps and volts, this is simplified for demonstrative purposes).

In reality most systems would have three or four panels in series and put those strings in parallel to get a bit of the best of both worlds. And indeed if for some reason you have to put your inverter/battery a half mile from your panels, the cost savings in smaller wire and less line loss may very well push you to a higher voltage series string, so you'd have to let us know that to provide an informed opinion. But basically the more parallel you are the more robust your system is and the more you can just install and forget it. The more series the more sensitive it is and the more you'll have to monitor and tend to it.

[sailor4life7777]

Originally Posted by redneckrob

It's important to consider the real world vs the ideal calculated world. If every solar panel remained equally clean and degraded at exactly the same rate, then with no external shade there's no difference between parallel and series except what you stated. In the real world, birds's crap on a panel, they get dirty, and they degrade at different rates. At this point, you have to remember that effectively no panel can produce more than the weakest panel. I'll give you a simplified example of the impact of this. Imagine you have ten 100 watt panels of the same voltage/amperage in series. Now an osprey craps on one, or it gets dirty, or some cells die on it, and it can only produce 90 watts. Now no panel can produce more than 90 watts. So your 1 kW system can only produce 900 watts. Now imagine the same system with them all in parallel. Only the single panel is impacted, so you get 990 watts. It's the different between a 10% system degradation and a 1% system degradation.
(Yes armchair EEs, I understand it's the amps and volts, this is simplified for demonstrative purposes).

In reality most systems would have three or four panels in series and put those strings in parallel to get a bit of the best of both worlds. And indeed if for some reason you have to put your inverter/battery a half mile from your panels, the cost savings in smaller wire and less line loss may very well push you to a higher voltage series string, so you'd have to let us know that to provide an informed opinion. But basically the more parallel you are the more robust your system is and the more you can just install and forget it. The more series the more sensitive it is and the more you'll have to monitor and tend to it.

That was a brilliant response, thank you very much! If I wire the 3x 550 watt panels in parallel, do I need a separate charge controller for each panel? Or can I use just 1 charge controller for all 3 panels?

My understanding was also that if I wire them in series, I should be able to charge the batteries more during cloudy days and during dusk/dawn due to the higher voltage potential. How much of that would I lose if I wire them in parallel, is it a negligible amount or a significant amount?

I will be placing the batteries/inverter very close to the panels so I won't need a lot of wire.

Thank you to everyone for all the great replies.

[StuM]

Originally Posted by sailor4life7777

That was a brilliant response, thank you very much! If I wire the 3x 550 watt panels in parallel, do I need a separate charge controller for each panel? Or can I use just 1 charge controller for all 3 panels?

Based on your original post, you can use one controller as long as it can handle Voc=49.90 and an input of 40 Amps (3 x A=13.11) and an output of close to 80 Amps @ 24V.

My understanding was also that if I wire them in series, I should be able to charge the batteries more during cloudy days and during dusk/dawn due to the higher voltage potential. How much of that would I lose if I wire them in parallel, is it a negligible amount or a significant amount?

You'll lose very little with a Voc of 49.9 V going into a 24 V bank. It won't take much light to get up to a voltage that will start charging.

[Moontide]

Main problem with series is that shade on one panel can kill the entire array (some panels have diodes to prevent this, but not most). Also DC voltage is more dangerous than AC, and 150 DC is very dangerous. One of the reasons they stopped doing electric motors on boats using 144 volts.


With only the 100 ah battery you have way more charging vs. storage capacity.

[redneckrob]

Originally Posted by Moontide

Main problem with series is that shade on one panel can kill the entire array (some panels have diodes to prevent this, but not most). Also DC voltage is more dangerous than AC, and 150 DC is very dangerous. One of the reasons they stopped doing electric motors on boats using 144 volts.


With only the 100 ah battery you have way more charging vs. storage capacity.

Hard to say if a given voltage is more dangerous in DC or AC. I had heard that as well as a kid but turns out the answer isn't really clear and in many cases may be the opposite. Worth a google.

[StuM]

I've always believed that AC is more dangerous than DC. Pretty much every link on he first page of Google for "is ac or dc more dangerous at the same voltage" confirms my belief.


Here's Ohio University Physics departments take on it for example:
https://www.asc.ohio-state.edu/physi...e_current.html



A.C. is More Dangerous than D.C. A.C. is said to be four to five times more dangerous than D.C. For one thing, A.C. causes more severe muscular contractions. For another, it stimulates sweating, which lowers the skin resistance. Along those lines, it is important to note that resistance goes down rapidly with continued contact. The sweating and the burning away of the skin oils and even the skin itself account for this. That is why it's extremely important to free the victim from contact with the current as quickly as possible (but without endangering yourself) before the climbing current reaches the fibrillation-inducing level.
The frequency of the AC has a lot to do with the effect on the human body. Unfortunately, 60 cycles is in the most harmful range. At this frequency, as little as 25 volts can kill. On the other hand, people have withstood 40,000 volts at a frequency of a million cycles/sec or so without fatal effects."

[sesmith]

You didn't mention what your electrical needs are but you should double that storage or go with less panels, or both.

Here's a data point, FWIW. On our off grid cabin, I have 960 watts of panels and 460 amp hours of storage at 24 v (lead acid golf cart batteries). I'm also using a 3kw inverter. We run a 10 cu ft refrigerator full time, microwave, led lighting, sureflow water pump, occasional tv and tool use. Works out perfectly for us. We aren't there in the winter, though. Would need more of everything for that.

For your situation, you could lose one of those panels and double your storage, and the #s would make more sense, so long as the supply fits your needs.

[redneckrob]

Originally Posted by sesmith

You didn't mention what your electrical needs are but you should double that storage or go with less panels, or both.

Here's a data point, FWIW. On our off grid cabin, I have 960 watts of panels and 460 amp hours of storage at 24 v (lead acid golf cart batteries). I'm also using a 3kw inverter. We run a 10 cu ft refrigerator full time, microwave, led lighting, sureflow water pump, occasional tv and tool use. Works out perfectly for us. We aren't there in the winter, though. Would need more of everything for that.

For your situation, you could lose one of those panels and double your storage, and the #s would make more sense, so long as the supply fits your needs.

It's apples to oranges comparison of lead acid and lithium ah.

[donradcliffe]

After investigating a solar panel fire on a friend's boat, I found that it was caused by having more than two panels in parallel on the same controller. A panel developed an internal short. The panels are designed to handle this kind of short with two panels in parallel, but not the 5 he had without additional fusing.

A smaller inverter will have lower parasitic losses than a larger one, as they approximately linear with size. OTOH, you will need 15-1800 watt inverter (75 amps) for your morning coffee or running power tools.

[NYSail]

Another for the battery bank is undersized. You will kill it running the freezer/refrigerator over night.

[sesmith]

Originally Posted by redneckrob

It's apples to oranges comparison of lead acid and lithium ah.

No it isn't. The only difference is he can use all of his storage capacity. I can only use half with FLA, charging differences aside. Bottom line is he needs more storage for his plan.

[StuM]

Originally Posted by NYSail

Another for the battery bank is undersized. You will kill it running the freezer/refrigerator over night.

Bear in mind that he's got over 2 KWh (100Ah @ 24 V LiFePo4 (2.4KW - nearly all usable) That's the equivalent of at least 360AH of 12V FLA bank (50% usable).