Same but not the same?

[Whats-n-Watts]

Hello all. I have a question but first to see if I am thinking logically or not I will give you my thoughts. These kits are the same powder but different number of panels. My thoughts are one is geared towards someone that uses power the most or higher loads during day and the other towards more nightly load hence the same amount of batteries. As in fewer panels because they are primarily charging the batteries with very low load during solar production hours. More panels in the same 20.4kw storage to charge batteries plus run a significant load?
Is that the dynamics going on with these opposing kits with same capacity?
90 percent of my use is during darkness is why I want to be clear.
Thanks for any input!

 

[sunshine_eggo]

It doesn't really matter when you use the power in a 24 hour period.

The amount of PV you have and available solar determines how much you can use per day.
The amount of battery you have determines how long you can go between charges.

A common approach is to size the PV to the expected daily need for the worst performing time of the year. Then one determines how much reserve they want... 1, 2, 3 or more days of battery capacity.

Systems designed along those lines tend to have a perceived surplus battery capacity because the PV provides direct power to loads after the battery is fully charged, and the full charge may last until 3-4pm or so before the battery starts supplying the loads, and overnight loads are likely lower than daytime loads.

However, the same approach would work for your 90% dark-time utilization, but you would more regularly use a larger portion of your battery capacity. In your case, the same buffer might require a 50% larger battery.

 

[Whats-n-Watts]

It doesn't really matter when you use the power in a 24 hour period.

The amount of PV you have and available solar determines how much you can use per day.
The amount of battery you have determines how long you can go between charges.

A common approach is to size the PV to the expected daily need for the worst performing time of the year. Then one determines how much reserve they want... 1, 2, 3 or more days of battery capacity.

Systems designed along those lines tend to have a perceived surplus battery capacity because the PV provides direct power to loads after the battery is fully charged, and the full charge may last until 3-4pm or so before the battery starts supplying the loads, and overnight loads are likely lower than daytime loads.

However, the same approach would work for your 90% dark-time utilization, but you would more regularly use a larger portion of your battery capacity. In your case, the same buffer might require a 50% larger battery.

Both having equal battery capacity with different size arrays goes against the understanding I had and that is battery capacity dictates aray size to say in off-grid 5kw to get through the night so you need that much capability of solar plus any day loads based on peak sun hours.
Like I said it looks like on was for a situation where charging is majority of the load during the day and the other compensates a little more for a higher daytime load with more panels. Makes sense if so because otherwise they are pretty much the same from what I can tell.
My daytime load will be charging the bank and running a high efficiency 14,000 btu window unit, one 1.2 amp refrigerator and two clock radios. Night time will only go up from that by maybe 800 watts tops for one 15w led lamp, a 32 inch flat screen TV and a coffee pot.
I don't need days of back up as far as battery power goes. If I do it the way all say to do it I would need quite the battery pack. The kw per 24hr calculations suggests I need that entire amount in 4 hours. Maybe I would if that load was all at night or I wanted days of reserve which I don't need. I have a generator that will power an entire 1200 sqft home as well as grid access. One flick of the switch and problem solved providing the grid is up should my generator have a hiccup.
In my case it seems bank for off peak hours use and provide enough PV to recharge them and run a small load. Knowing what the unit uses during the day thow that many panels at it to cover it. Daylight hits the spot my panels will be facing south at 9am now since the time change and remains in full sun with zero shading (other than a cloud) until 6pm so that's not an issue.
My shed has it's on system as well as my well pump. I'm going with hydronic heating at night as well as solar air heaters during the day. The house is new construction with an open floor plan. Very well insulated and sits in full sun all day.
In short is it possible to do what I am saying without component clashes? Providing power needed to charge the bank and meet actual daytime loads?
Thanks for helping!

 

[sunshine_eggo]

Both having equal battery capacity with different size arrays goes against the understanding I had and that is battery capacity dictates array size to say in off-grid 5kw to get through the night so you need that much capability of solar plus any day loads based on peak sun hours.

Not really.

Array size is dictated by daily energy needs. If you're using lead acid batteries, then you need to consider array size because you don't want to charge at too high of a current.

One may also choose to upsize their array because local weather may be sporadic, and you want more array for when you have good sun, so you can be sure to get the battery charged quickly.

Like I said it looks like on was for a situation where charging is majority of the load during the day and the other compensates a little more for a higher daytime load with more panels. Makes sense if so because otherwise they are pretty much the same from what I can tell.
My daytime load will be charging the bank and running a high efficiency 14,000 btu window unit, one 1.2 amp refrigerator and two clock radios. Night time will only go up from that by maybe 800 watts tops for one 15w led lamp, a 32 inch flat screen TV and a coffee pot.

This sounds like a relatively normal loading situation unless you are nocturnal and you sleep during the day. If on A/C, your A/C load should decrease at night. If it's a heat pump, you will need more at night, so you may be looking at different patterns at different times of year.

I don't need days of back up as far as battery power goes. If I do it the way all say to do it I would need quite the battery pack. The kw per 24hr calculations suggests I need that entire amount in 4 hours.

I literally have no idea what you mean by this.

Maybe I would if that load was all at night or I wanted days of reserve which I don't need. I have a generator that will power an entire 1200 sqft home as well as grid access. One flick of the switch and problem solved providing the grid is up should my generator have a hiccup.

If your goal doesn't include trying to nearly eliminate generator use, then that is a perfectly acceptable option.

In short is it possible to do what I am saying without component clashes? Providing power needed to charge the bank and meet actual daytime loads?

Component clashes? If I understood what you're getting at, I might be able to comment.

It's very simple:

How many kWh will you use per day, E?
How many hours of irradiance do you have in your worst case season, h?

Battery size is E kWh
PV size is E/h = Watts

You then adjust from there based on desired outcomes.

 

[Whats-n-Watts]

Not really.

Array size is dictated by daily energy needs. If you're using lead acid batteries, then you need to consider array size because you don't want to charge at too high of a current.

One may also choose to upsize their array because local weather may be sporadic, and you want more array for when you have good sun, so you can be sure to get the battery charged quickly.



This sounds like a relatively normal loading situation unless you are nocturnal and you sleep during the day. If on A/C, your A/C load should decrease at night. If it's a heat pump, you will need more at night, so you may be looking at different patterns at different times of year.



I literally have no idea what you mean by this.




If your goal doesn't include trying to nearly eliminate generator use, then that is a perfectly acceptable option.



Component clashes? If I understood what you're getting at, I might be able to comment.

It's very simple:

How many kWh will you use per day, E?
How many hours of irradiance do you have in your worst case season, h?

Battery size is E kWh
PV size is E/h = Watts

You then adjust from there based on desired outcomes.

In short I need to run a a/c or heat only during the daylight hours depending on the time of the year. Zero load other than that except for charging the bank.
PV for Climate control daylight hours load + PV for battery bank charging = PV array size
Is that not correct?

 

[sunshine_eggo]

In short I need to run a a/c or heat only during the daylight hours depending on the time of the year. Zero load other than that except for charging the bank.
PV for Climate control daylight hours load + PV for battery bank charging = PV array size
Is that not correct?

It can be, but that will oversize your array.

In the formula above, you have 24 hours of battery power.

The array replaces your daily energy consumption. This will be split between powering the load directly and topping off the batteries.

How many kWh will you use per day worst case?
Will you want to use the unit even in the event of poor PV conditions?

 

[Whats-n-Watts]

In short I need to stuff about 16kwh back into my bank that was used overnight and run a window air-conditioner during the day while that happens.

 

[sunshine_eggo]

This:

In short I need to stuff about 16kwh back into my bank that was used overnight and run a window air-conditioner during the day while that happens.

Is inconsistent with this:

In short I need to run a a/c or heat only during the daylight hours depending on the time of the year. Zero load other than that except for charging the bank.

and neither answer this:

How many kWh will you use per day worst case?

Please answer the above; "per day" is in a 24 hour period. We're trying to get to here:

It's very simple:

How many kWh will you use per day, E?
How many hours of irradiance do you have in your worst case season, h?

Battery size is E kWh
PV size is E/h = Watts

You then adjust from there based on desired outcomes.

So, we'll also need to know your available solar irradiance in hours.

 

[Supervstech]

So...
Are you saying the ac uses 16kWh during the day? And you want to replace that at night with a generator?
Or your overnight use is 16kWh? And you want to know how large the pv needs to be to replace it, AND operate the ac in the day?
To know that, we would need to know your available sun hours from your location.

 

[sunshine_eggo]

So...
Are you saying the ac uses 16kWh during the day? And you want to replace that at night with a generator?
Or your overnight use is 16kWh? And you want to know how large the pv needs to be to replace it, AND operate the ac in the day?
To know that, we would need to know your available sun hours from your location.

From the beginning, this has been very cryptic.

the 16kWh is from "X" - things only powered at night.
the only thing powered during the day is the window unit consuming ? kWh.

We'll get there...

 

[timselectric]

We'll get there...

You have more faith than I.

 

[sunshine_eggo]

You have more faith than I.

I've convinced myself I'm seeing a convergence...

 

[Whats-n-Watts]

I've convinced myself I'm seeing a convergence...

What I am saying is that let's "say" I use 16000 watts from my bank at night. My only day load is air-conditioning in the summer and heating in the winter during daylight hours. Is it not safe to say that my aray has to accommodate daytime load as well as replenish the battery bank?
I am in Southeast Georgia and there are 4.25 winter peek hours and a solid 6 in the summer. Where I plan to put my panels receives full sun from 8:30 am until 3:30 and a couple hours more in the summer.
I have grid utilities on the property but my solar will no be tied to it.
16000 watt over 4 hours peek plus PV to cover daytime load as to not fall short of power to fully charge the array is what I am suggesting. Maybe I am thinking about this wrong but I would think if someone has a 16000 watt load during the day and a 16000 watt load a night then they would need to generate 32,000 at the very least per day. I can't expect to fill batteries if I don't allow for the daytime load I wouldn't think. Having said that 16,000 + HVAC load during sunlight hours.
Example: (4,000 x 4hr charge)+(1,000 x 6hrs load while charging) = 22,000 watt output per day for the array
Which takes me back to OP. It seems some kits are set up for daytime load with small back up for outages only while others seem to be geared towards 24 hrs solar i.e. off-grid or little grid use. The 24hr rule doesn't apply to all situations to me when it comes to array size. Power needs are individual.
If I have no daytime load at all and only need to fill batteries then that's all the array I need. But you throw a daytime load in and it's not enough.
If my only concern was daytime load I wouldn't need much bank.
In my mind it all makes sense ?

 

[sunshine_eggo]

What I am saying is that let's "say" I use 16000 watts from my bank at night. My only day load is air-conditioning in the summer and heating in the winter during daylight hours. Is it not safe to say that my aray has to accommodate daytime load as well as replenish the battery bank?

Yes. Your array must accommodate all the energy needs in a 24 hour period - as I've stated multiple times.

I am in Southeast Georgia and there are 4.25 winter peek hours and a solid 6 in the summer. Where I plan to put my panels receives full sun from 8:30 am until 3:30 and a couple hours more in the summer.

Well, there's one piece of the puzzle. 4.25 hours irradiance.

Since you've given a time window, is there shading outside those hours? 4.25 hours means no shading from sunrise to sunset based on your array orientation input to get that number.

I have grid utilities on the property but my solar will no be tied to it.
16000 watt over 4 hours peek plus PV to cover daytime load as to not fall short of power to fully charge the array is what I am suggesting. Maybe I am thinking about this wrong but I would think if someone has a 16000 watt load during the day and a 16000 watt load a night then they would need to generate 32,000 at the very least per day. I can't expect to fill batteries if I don't allow for the daytime load I wouldn't think. Having said that 16,000 + HVAC load during sunlight hours.
Example: (4,000 x 4hr charge)+(1,000 x 6hrs load while charging) = 22,000 watt output per day for the array

Okay, so you've finally arrived at the requested 24 hour number? 22kWh? Whew. Finally.

Which takes me back to OP. It seems some kits are set up for daytime load with small back up for outages only while others seem to be geared towards 24 hrs solar i.e. off-grid or little grid use.

Kits schmits. YOU need to design your system based on YOUR goals/needs. THEN you decide if you can find a kit that meets your needs.

The 24hr rule doesn't apply to all situations to me when it comes to array size.

Incorrect.

Power consumption used in a 24 hour period determines the minimum array size. Period.

Since you've finally divulged your 24 hour consumption:

22kWh/4.25h = 5.17kW array = minimum array size to meet 22kWh daily demand.

See how it doesn't matter one bit when the power is used?

Power needs are individual.

Absolutely, but the same rules apply.

If I have no daytime load at all and only need to fill batteries then that's all the array I need. But you throw a daytime load in and it's not enough.
If my only concern was daytime load I wouldn't need much bank.
In my mind it all makes sense ?

But your mind is failing to draw the right conclusion. 24 hour consumption determines array size. Period. You've literally calculated it that way. What difference does it make if the numbers were reversed? 16kWh during the day and 6kWh at night.... not one bit.

Now, you've estimated that you need 16kWh of battery due to nightly consumption. This means that you'll have to:

1. Always have clear skies and perfect solar conditions - no clouds, etc.
2. Never over-consume during the daytime.
3. Deliberately NOT consume during the day in hopes of having enough to get through the night.

It's these variables that further encourage one to assume the batteries need to cover a full 24 hours of consumption. If you're willing to whip out the generator any time you fall short, that's fine. Maybe only 16kWh is enough.

Additionally, with a 5.2kW array, you're going to fall short some days. You have two choices:

1. Increase the array size (25-50%) to ensure that you can "catch up" when good days follow bad.
2. Run the generator with each shortfall.

Now you can pick your kit.

 

[Whats-n-Watts]

Yes. Your array must accommodate all the energy needs in a 24 hour period - as I've stated multiple times.



Well, there's one piece of the puzzle. 4.25 hours irradiance.

Since you've given a time window, is there shading outside those hours? 4.25 hours means no shading from sunrise to sunset based on your array orientation input to get that number.



Okay, so you've finally arrived at the requested 24 hour number? 22kWh? Whew. Finally.



Kits schmits. YOU need to design your system based on YOUR goals/needs. THEN you decide if you can find a kit that meets your needs.



Incorrect.

Power consumption used in a 24 hour period determines the minimum array size. Period.

Since you've finally divulged your 24 hour consumption:

22kWh/4.25h = 5.17kW array = minimum array size to meet 22kWh daily demand.

See how it doesn't matter one bit when the power is used?



Absolutely, but the same rules apply.



But your mind is failing to draw the right conclusion. 24 hour consumption determines array size. Period. You've literally calculated it that way. What difference does it make if the numbers were reversed? 16kWh during the day and 6kWh at night.... not one bit.

Now, you've estimated that you need 16kWh of battery due to nightly consumption. This means that you'll have to:

1. Always have clear skies and perfect solar conditions - no clouds, etc.
2. Never over-consume during the daytime.
3. Deliberately NOT consume during the day in hopes of having enough to get through the night.

It's these variables that further encourage one to assume the batteries need to cover a full 24 hours of consumption. If you're willing to whip out the generator any time you fall short, that's fine. Maybe only 16kWh is enough.

Additionally, with a 5.2kW array, you're going to fall short some days. You have two choices:

1. Increase the array size (25-50%) to ensure that you can "catch up" when good days follow bad.
2. Run the generator with each shortfall.

Now you can pick your kit.

Actually I'm not getting a kit. Individual components seems less expensive with a little shopping. As I said the location for the array gets full sun from 9 am until 3ish. No need to crank a generator when I can just throw a lever.
I was just pointing out an observation about these kits. Same power but different set up. As far as the 24hr goes I simply meant that it's not always scattered over a 24hr period. It makes sense to me to know you have enough power for daylight hours load as well as to fill the bank in an off-grid situation.
Was just a passing thought. But I'm looking at the evidence of what I am saying in these kits. Same bank with different arrays. Maybe you have a better explanation maybe you don't. Oh, and I wasn't asking anyone to choose my kit, tell me what to kit to pic or how to design a kit to fit my needs so your obligation was self inflicted. The question/ topic wasn't that at all. But thanks anyways ?

 

[Whats-n-Watts]

You have more faith than I.

Maybe all would have faith if they stuck with the question instead of taking a dirt road ?

 

[Supervstech]

Maybe all would have faith if they stuck with the question instead of taking a dirt road ?

The topic has not once strayed from the original topic.
We are trying to explain to you how solar works.

 

[Whats-n-Watts]

The topic has not once strayed from the original topic.
We are trying to explain to you how solar works.

Look at the kits I posted. Then explain to me why one has a larger array than the other with an equal bank. That was the question. I already know how solar works which wasn't the question.
I am fully capable of comprehension of an answer if someone is capable of comprehnding the question. ?

 

[Supervstech]

The kits have differing inverters and panel count.
Bundles frequently pack stuff in sale quantities.

Its up to the buyer to decide what they need.

 

[Whats-n-Watts]

The kits have differing inverters and panel count.
Bundles frequently pack stuff in sale quantities.

Its up to the buyer to decide what they need.

So my mind wasn't failing me after all. Exactly what I thought and said to start with. Same battery pack but different watts of array. One can logically and realistically draw the conclusion I did. More array covers a heavier daylight load which validates everything I was saying. I need enough array to ensure my batteries are fully charged for the off peak hours as well as handle my climate control loads for daylight hours which is also when my batteries will be charged. So yes it matters when the electricity is used and how much of it to size the array is a practical and logical explanation for the difference of array size between various kits. Seemed like a pretty simple question to me. I quickly realized you didn't fully understand my question. It happens.
Sizing a bank based on 24hr use is not a one size fits all method. I see no reason to have bank to cover any daylight load my a/c has if my array can cover both task (charge bank while running the a/c only. That's kinda what the panels are for. I have a generator as well as grid to fall back on so at the moment inclement weather doesn't effect me at all. I don't need apocalyptic storage. Just enough to get through the night other than heating/cooling I carry enough electricity in my brain to cover the power my minimalist wife and I use.

Thanks for your feedback ?