So, lets spec out and set up a system of LiFePo4 batteries and inverter

[J.P.M.]

That was my point JPM. This is a DIY crowd and we have to dumb it down. Otherwise you just go round in circles trying to explain something they will never grasp. Sun Hours is universally accepted interchangeable with Kwh/m2. That is all they need to know.

Lighten up JPM I was not being critical. You should know me better than that by now. Don't take me so serious. I was just pointing out the crowd you are talking too need KISS, not theory.

No offense taken. I believe you understand some of my background well enough. Besides, and with all possible candor, if I took your behavior on this venue seriously, I'd have been out of here long ago.

As for dumbing it down, I look at this rodeo as primarily an information exchange. I attempt to keep my pie hole shut except where I feel I have something to contribute, and my eyes and mind open to new ideas and ways of looking at stuff where I'm ignorant. Where/when I do feel I might have something substantive/informational/new to contribute or offer, I attempt to do so in a way that I believe is technically correct and as complete as possible/necessary without talking over folk's heads, while at the same time not engaging in enabling or condescendingly simplistic and what I consider somewhat insultingly dumbed down **** and talking down to people.

What folks take away from my mental spoor is something I have no control over, nor do I care to have any. The usual take what you want and scrap the rest suggestion applies. I can only try to be technically correct while simultaneously tailoring my presentation as best as I can SWAG it to be as understandable as I gauge the demeanor of potential readers/receivers might allow.

Respectfully,

[Sunking]

Your right JPM, carry on. Semper Fidelis.

[J.P.M.]

Your right JPM, carry on. Semper Fidelis.

Aye, Aye Cap.

Maybe not right for everyone. Just for me and just for now.

[sensij]

My question relates to my premise earlier that Solar Insolation is the sum total of irradiance in a 24 hour period and that Sun Hours is the window of time for that radiation. The former can inform our view as to the total possible energy storage while the latter will constrain the ability to charge a battery in that time frame because it could exceed its maximum charge rate, even if there is enough insolation in a 24 hour period.


I believe the discussion started because of a dispute over whether or not Solar Insolation was equivalent to Sun Hours. I have seen these two terms used identically, and in other instances have seen Sun hours refer to the actual hours the Sun shines in a particular season.

Sun Hours is universally accepted interchangeable with Kwh/m2. That is all they need to know.

I'm late to this party. Sun Hours and average daily insolation are, by every reference I trust, communicating exactly the same information, with only a factor of 1000 and a difference in units between them.

NREL's Sun-hours do not give any information about how the irradiance is distributed over the course of the day, and as a daily unit, it does not lend itself to being resolved into actual hourly content. Insolation or Irradiance can be easily calculated in smaller units of time, which is the necessary information to guess if a charge will have sufficient time to complete (for those designing with somewhat more rigor than some KISS methods would employ).

As bcroe (and others) have astutely shown, for an off-grid system, east - west oriented panels (or perhaps more optimally southeast - southwest) provide a distribution of power that is better suited to charging FLA. A south facing system will have a high peak but less breadth, typically a better match to AGM. I am unaware of a simple metric that distinguishes a wider and flatter distribution of power vs a narrow one with a higher peak. Both systems might have the same sun hours, but the way in which they charge a battery will be very different.

Edit:
I haven't read the whole thread, so forgive me if I've missed something important that explains how a lithium ion thread ended up on this tangent.

[lkruper]

I'm late to this party. Sun Hours and average daily insolation are, by every reference I trust, communicating exactly the same information, with only a factor of 1000 and a difference in units between them.

NREL's Sun-hours do not give any information about how the irradiance is distributed over the course of the day, and as a daily unit, it does not lend itself to being resolved into actual hourly content. Insolation or Irradiance can be easily calculated in smaller units of time, which is the necessary information to guess if a charge will have sufficient time to complete (for those designing with somewhat more rigor than some KISS methods would employ).

As bcroe (and others) have astutely shown, for an off-grid system, east - west oriented panels (or perhaps more optimally southeast - southwest) provide a distribution of power that is better suited to charging FLA. A south facing system will have a high peak but less breadth, typically a better match to AGM. I am unaware of a simple metric that distinguishes a wider and flatter distribution of power vs a narrow one with a higher peak. Both systems might have the same sun hours, but the way in which they charge a battery will be very different.

Edit:
I haven't read the whole thread, so forgive me if I've missed something important that explains how a lithium ion thread ended up on this tangent.

Thanks, I stand corrected. I misinterpreted something I read earlier in the thread.

[J.P.M.]

I'm late to this party. Sun Hours and average daily insolation are, by every reference I trust, communicating exactly the same information, with only a factor of 1000 and a difference in units between them.

NREL's Sun-hours do not give any information about how the irradiance is distributed over the course of the day, and as a daily unit, it does not lend itself to being resolved into actual hourly content. Insolation or Irradiance can be easily calculated in smaller units of time, which is the necessary information to guess if a charge will have sufficient time to complete (for those designing with somewhat more rigor than some KISS methods would employ).

As bcroe (and others) have astutely shown, for an off-grid system, east - west oriented panels (or perhaps more optimally southeast - southwest) provide a distribution of power that is better suited to charging FLA. A south facing system will have a high peak but less breadth, typically a better match to AGM. I am unaware of a simple metric that distinguishes a wider and flatter distribution of power vs a narrow one with a higher peak. Both systems might have the same sun hours, but the way in which they charge a battery will be very different.

Edit:
I haven't read the whole thread, so forgive me if I've missed something important that explains how a lithium ion thread ended up on this tangent.

I'd add, or stress, that the ways in which arrays can be oriented to match the necessary load and characteristics of an application are better determined by using insolation data (expressed as kWh/m^2 per time period) or estimates of that data using vetted methods rather than some vague, confusing and misleading term. I'm not sure how I'd use "Sun-Hours" in any quantitative way without converting it to Wh or kWh/area per time period at some point, making the use and concept of "Sun-Hours" unnecessary and simply more work with the possible additional "benefit" of adding confusion for the less informed. IMO, The term "Sun-Hours" is simplistic, misleading and unnecessary, and as such might better be avoided for little, if any, effort.

Using "Sun-Hours" seems similar to expressing distance between two points as how many hours it takes to get somewhere assuming all the traveling is done at a velocity of 100 km/hr. regardless of any other factors.

Take what you want of the above. Scrap the rest.

[Sunking]

"Sun-Hours" in any quantitative way without converting it to Wh or kWh/area per time period at some point, making the use and concept of "Sun-Hours" unnecessary and simply more work with the possible additional "benefit" of adding confusion for the less informed.

Well I really do not know cuz I wuz edjacated in the USA, , but WH/H=W is a lot simpler than WH / Wh/m^2 = W to me.

But WTF do I a know, it is all alphabet soup to me. Imajune my shok when I gradeated from enjuner scrool and found no traane to driv. It wuz a under water tube with a prop. no windoes, a bom for powr, and sum dude called Skipper driving it that yales a lot. KISS

[PNjunction]

IMO, The term "Sun-Hours" is simplistic, misleading and unnecessary, and as such might better be avoided for little, if any, effort.

.. erm, flame suit on! ..

It is better than nothing, and I find it really funny trying to micro-manage a variable like solar-insolation. The money spent on a professional analysis to get that last 1% of precision could be better spent on designing in a bit of a sloppy fudge-factor, as bad as that sounds. Go a little overboard - what is wasted when times are perfect, will be paid back when times aren't so, even according to PVwatts or micro-managed power budgets. KISS might actually save money.

Add to that real-world issues like infrastructure degradation (internal resistance of batteries increasing over time, unforeseen voltage drops, and the like, and the 1% precision goes out the window. A sloppy fudge might save one's butt, or batteries.

And getting back to LFP, (or pure-lead agm's for that matter), where you can just hit them nearly as hard as you want to, there is a lot of room for a fudge-factor of just over-panelling a bit - again a waste when looked at from nearly static insolation statistics, but insurance when times don't fit the model.

The only time a micro-managed power-budget would seem useful to me, would be for convincing the board of a commercial entity to invest in it after a long laborious set of engineer's meetings. If I walked in with grass-stalk in mouth, pulled my suspenders and said "yuuuup, looks like you could do with just one more panel", the contract would be over, even if the KISS method actually worked.

I was taught a long time ago not to design a system around what works when initially installed - but design for 4 years down the road from the start! The simplest application of that is when buying batteries is not to plan on replacing batteries when they reach 80% capacity, but to think like they are like that right out of the box to start with and increase your initial capacity by say 20% more than calculated at the outset. That kind of thing.

[inetdog]

For those who wonder why the battery manufacturers tend to specify end of life as being 80% of original capacity, there are severas factors:
1. When you are down to 80% you have usually run out of capacity fudge factor in a commercial design and are coming up short on power.
2. There is a knee to the cycle life curves and once you reach 80% capacity you are falling fast.

Something that is often overlooked is that when you are figuring discharge and charge rates (like the general C/8 maximum charge rate for ordinary FLA) you need to remember that at 80% capacity you have to scale the bulk charging current back using that same 80% factor to avoid overstressing the aging batteries.

[lkruper]

For those who wonder why the battery manufacturers tend to specify end of life as being 80% of original capacity, there are severas factors:
1. When you are down to 80% you have usually run out of capacity fudge factor in a commercial design and are coming up short on power.
2. There is a knee to the cycle life curves and once you reach 80% capacity you are falling fast.

Something that is often overlooked is that when you are figuring discharge and charge rates (like the general C/8 maximum charge rate for ordinary FLA) you need to remember that at 80% capacity you have to scale the bulk charging current back using that same 80% factor to avoid overstressing the aging batteries.

That's horrible! And also a good reason to not initially set up the amount of charging amps to the maximum that new batteries can handle? I did not know this.

[sensij]

That's horrible! And also a good reason to not initially set up the amount of charging amps to the maximum that new batteries can handle? I did not know this.

I'm not sure it should change your thinking in the up front design. First, capacity will degrade more slowly if you are regularly getting to fully charged... undersizing an array won't help. Second, the array will degrade over time too, perhaps not as fast as the battery, but the potential to overcharge will be diminished.

Really, if a few years down the line you find that you need to drop your array output during a couple high insolation weeks, a small piece of cardboard and some tape is an easy fix. From what I understand, the costs of undersizing an array are much more likely to add up than the risks incurred by designing toward the top of the charge rate specification.

[lkruper]

I'm not sure it should change your thinking in the up front design. First, capacity will degrade more slowly if you are regularly getting to fully charged... undersizing an array won't help. Second, the array will degrade over time too, perhaps not as fast as the battery, but the potential to overcharge will be diminished.

Really, if a few years down the line you find that you need to drop your array output during a couple high insolation weeks, a small piece of cardboard and some tape is an easy fix. From what I understand, the costs of undersizing an array are much more likely to add up than the risks incurred by designing toward the top of the charge rate specification.

I was wondering how to lower the charge amount, and your solution of blocking light from solar panels would certainly work. In my particular current need, I will be setting up grid-powered chargers for battery backup. It may be that a good AGM like Lifeline that can take 5C might be the way to go for that. I could set it up to normally take 0.2C - 0.3C and if the battery degraded, it could take the higher amps with no damage to the bank.

[Sunking]

I was wondering how to lower the charge amount, and your solution of blocking light from solar panels would certainly work. In my particular current need, I will be setting up grid-powered chargers for battery backup. It may be that a good AGM like Lifeline that can take 5C might be the way to go for that. I could set it up to normally take 0.2C - 0.3C and if the battery degraded, it could take the higher amps with no damage to the bank.

You are still a brick short of a load. Battery charge current is only controlled by the amount of charge current available by the source and the SOC voltage of the battery. Your job is to size the charge source and set the voltage to the correct. You have no control of the charge current. It is what is. If you have a 100 amp curreent source, and a discharged battery it gets 100 amps period. As the battery charges up, current tapers off to zero as it reaches full charge voltage.

[inMichigan]

When I want to cut back current, I either reduce the max limit in the CC controller, or, turn off some of the breakers in the combiner boxes to preserve the voltage while knocking out sources of current.
InMichigan

[lkruper]

You are still a brick short of a load. Battery charge current is only controlled by the amount of charge current available by the source and the SOC voltage of the battery. Your job is to size the charge source and set the voltage to the correct. You have no control of the charge current. It is what is. If you have a 100 amp curreent source, and a discharged battery it gets 100 amps period. As the battery charges up, current tapers off to zero as it reaches full charge voltage.

I did not explain myself clearly enough. What I was trying to propose is that with AGM batteries like Lifeline that can take a high current, if a grid-tied charger were chosen that puts out 0.3C of the 20 hour AH capacity, when the battery degrades to 80% of that capacity, it can still take the same current (unlike flooded). Perhaps a hybrid golf-cart battery that can also take a higher amperage could also be used in this way.