What time of day best to charge battery bank

[SolarHead]

I'm wondering how most people are timing their battery charging. Do you have your system set to start charging the batteries the moment the sun comes up? Or do you hold off and let the first sun of the day power your morning loads, then when the sun is up say 11am to 3pm, have your battery bank charging go during those times since I'm thinking you'd have enough PV to cover both your loads and your charging. Of course I am assuming you can top off your battery bank in 3-4 hours of the middle of the day. Maybe some people charge all day sun up to sun down, just to be able to top off a large battery bank. I have a small battery bank and I'm thinking for the time being have my charging occur towards the middle of the day and let the morning sun power my loads (and not my battery bank). However, I have ordered some more batteries and when they come in I don't know what I will want/need to do yet but , I may have to start charging first light just to be able to top the bank off by 6pm each day. I know our consumption through the night so really I should only be topping off the batteries from what we used during the night. So, should be able to top them off in less than 4 hours. I still am thinking I will power my loads in the mornings, and have my inverter set to charge batteries later in the day when I have quite a bit more PV coming in. I have a Sol-Ark and so far I haven't been able to figure out how to configure it to hold off on starting charging batteries till later in the day. It seems to send charging power to the batteries first thing in the morning which I don't like. I wish it would hold off till later in the day when I have more PV. I'm still working on it so hope to figure something out. Was just wondering if I'm worry about something that I dont need to worry about. Maybe its best to start charging the batteries at first light, I don't know. That's why I was asking what do most of you do, or recommend? and why.

 

[John Frum]

Do you have your system set to start charging the batteries the moment the sun comes up?

How would you manage this?
Do you have a diversion load setup?

This is a very simple but representative topology for almost all systems I see here.
The charge source supplies current to the whole system.
The loads take what they need and the balance goes to the battery.
If the charge source can not cover the load the balance comes from the battery.

positive
|<->fuse<->battery<->shunt<->|
|<-fuse<-charge_source<------|
|->fuse->load--------------->|
                      negative

 

[SolarHead]

I'm with ya, but my Sol-Ark currently covers the battery first, loads second. Theres a setting in PowerView that sends commands/settings to the Sol-Ark and I change change it to "loads first" and it automatically sets it back to "battery first". I have an email in to support to see whats up. I'm thinking if I could send PV power in the mornings to loads and hold off on the battery charging till mid day, I'd pull less from the grid. Currently sun is up a bit, not enough to power but like 2kw watts coming from a 10kw solar panel array, and those 2kw are going to my battery bank. My loads are being covered by the grid. In the mornings 'd rather send the 2kw to my loads, not the batteries. This is a support issue and I didnt intend to cover that in this thread.

I was just wondering what most people tend to do with their PV power in the mornings when their module array just isnt able to produce but so much. Mid day I seem to have an abundance of PV power at which time I can cover my loads AND charge battery at same time. Some of this will change when I get a larger battery bank I imagine.

 

[John Frum]

I'm with ya, but my Sol-Ark currently covers the battery first, loads second. Theres a setting in PowerView that sends commands/settings to the Sol-Ark and I change change it to "loads first" and it automatically sets it back to "battery first". I have an email in to support to see whats up. I'm thinking if I could send PV power in the mornings to loads and hold off on the battery charging till mid day, I'd pull less from the grid. Currently sun is up a bit, not enough to power but like 2kw watts coming from a 10kw solar panel array, and those 2kw are going to my battery bank. My loads are being covered by the grid. In the mornings 'd rather send the 2kw to my loads, not the batteries. This is a support issue and I didnt intend to cover that in this thread.

I was just wondering what most people tend to do with their PV power in the mornings when their module array just isnt able to produce but so much. Mid day I seem to have an abundance of PV power at which time I can cover my loads AND charge battery at same time. Some of this will change when I get a larger battery bank I imagine.

Given the above topology, how does your Sol-Ark distinguish between a load and a battery?
Are you using some other topology?
Are the Sol-Ark and the battery BMS communicating?

 

[John Frum]

Let me be succinct, you are asking "q: should I?" and I am asking "q: can you?".

 

[SolarHead]

I'm not sure the Sol-Ark distinguishes between a load and the battery. There is a setting "battery first" , or "load first" but no matter how many times I change it to load first, and click "save", it instantly changes it back to battery first.

Currently I have AGM batteries, no BMS. In a few weeks from now I hope to have LifePO4 and remove the AGM bank.

I was just asking the basic question does it make sense to send PV power to loads in the 7am to say 9 or 10AM time period, then after 11am when full sun and plenty of PV power, continue to cover the loads but also send power to charge the batteries. I think all of what I'm seeing and doing will change once I get a larger battery bank. What I now have is 183AH and I can use only 50% of that. So I have 91.5 AH in my current battery configuration. It lasts half the night and in the mornings the sun comes up and it starts charging the batteries. I'd rather it hold off , use the PV to cover loads (as much as possible), then around 11am or 1pm continue to cover loads but start charging the batteries.

Just wanting to know what other solar users tend to do. Do you let the little bit of PV in the morning hours to to battery , or do you let it go to loads? from there, I can figure out the technical aspect of figuring out how to get it done. It would a lot easier if the Sol-Ark setting of "loads first" would stick when I click "CONFIRM" button to save. Even the TOU (time of use) settings are set to stay off of charging battery in the morning hours, but the Sol-Ark doesnt listen to my TOU setting for that. If theres PV, it goes to the batteries without my control at this point in time.

 

[John Frum]

I was just asking the basic question does it make sense to send PV power to loads in the 7am to say 9 or 10AM time period, then after 11am when full sun and plenty of PV power, continue to cover the loads but also send power to charge the batteries.

Personally I'm not interested in speculating about this until its a demonstrated possibility.
Since the Sol-Ark, battery and load are all in parralel how would the Sol-Ark somehow route traffic through one of 2 parallel paths?

Just wanting to know what other solar users tend to do.

The only similar thing I've ever seen or heard of is a diversion/dump load.
Typically a diversion/dump load is used to continue utilizing a wind turbine after the batteries are charged.

For solar setups a similar idea is to let the sun terminate the charge.
The batteries get whatever the loads don't take from the moment the panels start making power.
When the batteries are full, the charger is left in absorption mode so that the charger continues to service the load therefore leaving the batteries maximally ready to service the load when the charger can no longer make power.

I'm having trouble assessing your skill level so I will post this here in case its useful

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

If not please disregard.

 

[Nobodybusiness]

I'm not sure the Sol-Ark distinguishes between a load and the battery. There is a setting "battery first" , or "load first" but no matter how many times I change it to load first, and click "save", it instantly changes it back to battery first.

Currently I have AGM batteries, no BMS. In a few weeks from now I hope to have LifePO4 and remove the AGM bank.

I was just asking the basic question does it make sense to send PV power to loads in the 7am to say 9 or 10AM time period, then after 11am when full sun and plenty of PV power, continue to cover the loads but also send power to charge the batteries. I think all of what I'm seeing and doing will change once I get a larger battery bank. What I now have is 183AH and I can use only 50% of that. So I have 91.5 AH in my current battery configuration. It lasts half the night and in the mornings the sun comes up and it starts charging the batteries. I'd rather it hold off , use the PV to cover loads (as much as possible), then around 11am or 1pm continue to cover loads but start charging the batteries.

Just wanting to know what other solar users tend to do. Do you let the little bit of PV in the morning hours to to battery , or do you let it go to loads? from there, I can figure out the technical aspect of figuring out how to get it done. It would a lot easier if the Sol-Ark setting of "loads first" would stick when I click "CONFIRM" button to save. Even the TOU (time of use) settings are set to stay off of charging battery in the morning hours, but the Sol-Ark doesnt listen to my TOU setting for that. If theres PV, it goes to the batteries without my control at this point in time.

Have you tried changing it from the front panel on the inverter?
The app is notoriously buggy that way.

Most changes I do are directly on the inverters.

Me Personally Solar goes to loads until it produces more than needed then charges batteries.

I have a 20 Kw array so never using 20kw of loads.

Have you talked with Sol-ark about this?

 

[SolarHead]

Okay. I'm a BIG dummy. I had been trying changing the energy pattern using PowerView web app and not on the Sol-Ark touch-screen itself. This is strange. I changed the energy pattern on the Sol-Ark itself over to "Loads first" and it saved it.

If you do it in the PowerView web app, it doesn’t save it. It always reverts back to "battery first" if you use PowerView.

So, I put it on loads first in the Sol-Ark screen. It seems to save it, even if you go into PowerView and click "confirm" and go back in, it continues to stay on "loads first".

Must be a bug in PowerView itself (you said it was buggy).

 

[bixelps]

Like Biasjo my batteries start charging once the PV starts to produce more than the house requires. I think it the best approach is it exercises the batteries the least as some days are cloudy and they then never charge. My theory is that less battery cycles is best.

I have spent the day with Sol-Ark tech support and I can confirm that they are courteous and available. Two very good things. However, there is considerable confusion there about how all these features work. To be fair is it a complicated inverter with many possible modes. I often get answers that conflict with the manual or I get the "I'll talk to someone" or "that's proprietary" answer.

For example I was told that "load first" was "experimental". The manual does not even mention this feature it so perhaps this is true. Mine is set on Battery first but I may "experiment" myself this weekend. I have a theory that this relates to the TOU settings. Right now the TOU settings will make sure the batteries are at least up to the SOC%/V threshold before any power is allowed to be discharged from them. This can be very confusing to watch. I speculate that "Load first" would mean something else.

There is also bit of confusion with this inverter as to the meaning of "Load". For the most part I think this tends to mean things connected to the breaker marked "load" in the inverter. However, those of us using the grid breaker to connect to our main panel tend to think as the house as the load. Anyway, keep this in mind when you see this word in the manual.

 

[SolarHead]

I don't know if this helpful or not, but I will mention. I started out weeks ago trying to get my TOU settings very well fine-tuned , and I had battery discharge starting at 9pm (keep in mind I currently have a very small AGM battery bank so I was trying to milk them for what they're worth), and offer 500 watts all night down to 50% SOC. This was working (or so I thought) such that I had things configured so PV would not go to charging batteries until like 10am because I wanted PV power to go to load first.

Side note, I had emailed Sol-Ark a few times asking about the "Batt First" versus "Load First". They eventually just told me to NOT use "load first" since it was really for people in Hawaii and the feature had not been fully developed yet and it would cause problems or behavior that was difficult to troubleshoot. So, I changed it back to "Batt First" and have left it there ever since.

Okay, back to my post. I thought I had "fine tuned" the TOU setting for maximum battery utilization. I contacted Sol-Ark they said most customers (not all) find that having the same settings in each and all of the 6 time slots worked best and they got more out of it. Well, I tried it. I changed all 6 time slots to 500 watts and down to 50% SOC. I thought okay, this is pretty generic, probably wont work for me. Well, after 2 days I noticed that the batteries lasted longer through the night it seemed, I used less grid even though the batteries started discharging / offering power to the home sooner, like at 630pm ,where I had been holding them back saving them for later to start discharging at 9pm. I was surprised to see that having all 6 time slots set to same values actually worked better. I think I may know why, my gut says something but I don't have any hard evidence as to reason why. My gut says the firmware has been coded such that it has more intelligence than I originally thought it had. I think the firmware probably has a lot of if/then statements and it works to take PV power and utilize it to cover loads better, while keeping batteries charged but at steps. I have seen power going to charging the batteries in the morning, then it gets up to like 53% and it will start discharging, but it helps manage loads somehow. The Sol-Ark really wants to charge batteries if PV is available regardless of any settings. At least this is my theory based of what I have seen but I don't have any hard proof. I think they were right when they said try having all 6 time slots the same. Even when I had tweaked the time slots and had it holding off to start charging at 10am, and had it really strict, I saw some behavior where it seems my Sol-Ark had a mind of its own. It seems to want to charge batteries if there's PV power, regardless of your TOU settings. Maybe this is part of their proprietary special sauce where the firmware is slick enough to manage the charging/discharging better than my TOU settings.

There is also bit of confusion with this inverter as to the meaning of "Load". For the most part I think this tends to mean things connected to the breaker marked "load" in the inverter. However, those of us using the grid breaker to connect to our main panel tend to think as the house as the load. Anyway, keep this in mind when you see this word in the manual.

I don't think there is confusion here. I think its pretty clear. "Limited to Load" means Sol-Ark will send power to critical panel ONLY. "Limited to Home" means it will send power to critical panel, and power to the main panel to help assist its needs as much as possible. To understand this, you need to keep in mind that the GRID breaker is a bi-directional breaker.

 

[SolarHead]

To be fair is it a complicated inverter with many possible modes.

You are 100% correct. That's why the Sol-Ark has been called a Swiss Army Knife of inverters. It will fit into and work in many different situations and configurations. I don't wave the Sol-Ark flag and say everything else is junk. There's some really good products on the market and they seem to continue to improve with time.

 

[Substrate]

AGM's need ALL the time they can get, because if you do not charge that last 1%, you hard sulfate and walk them down in capacity.

What you should do is know your solar-insolation hours. These are far different than from sunrise-sunset hours, when the first hour or two in the morning, and the last hour or two in the afternoon are disgarded. You'll need to look this up for your location. You will be presented with seasons/months, so always choose the "winter" solar-insolation hours.

Now based upon that, you calculate how much your panels are capable of supplying during the day, AND if it will sufficiently charge your battery's capacity.

You also have to define whether you are "daily cyclic", or standby / weekend warrior. If you are daily cyclic, you usually don't have the luxury of time on your side, unless you have planned carefully. This means that MOST people UNDERcharge their agm's by using the conservative recommendations that are fit for the standby / weekend warrior crowd. Most manufacturers also use the very conservative settings (usually having their system fall back to float too early).

In the end, if you are daily cyclic, you forget about float, and hold at the CV voltage (usually 14.4 - 14.6v temperature compensate) until current falls to about .005 to .01C. Sometimes you will simply run out of time later in the day to do so. OR, your system may fall back to float too early (like on a timed basis of only 1 hour in cv/absorb). If that is the case, you can fudge it by raising the float voltage to a higher level like 13.8 to 13.9 volts.

This doesn't hurt, because unlike and ac-charger recharged system, the sun drops and turns the switch off for you every day.

The importance of getting that last 1% charged isn't emphasized enough to avoid premature walk-down, and the usual advice from others that are NOT daily-cyclic sure don't help!

If you are not daily-cyclic, then the usual default conservative settings are fine.

 

[SolarHead]

The importance of getting that last 1% charged isn't emphasized enough to avoid premature walk-down

I have seen my inverter show 100% by noon on the battery, but I see power still being sent, and the graph shows the battery still taking charge, this happens on up until about 3pm and by then I consider them full charged when I see about 15 watts being sent to the battery. I figured it was getting the final 1% late in the day. I have a small AGM bank, but plan to go to LifePo4 soon about 4x the amount of AH so things should get more interesting. Not sure if they will need that late day final 1% topping of charge or not.

I'm a "daily cyclic" and have looked at insolation hours. Although I get sun up to sun down like 9 hours right now in the spring, the actual solar hours which I assume is same as insolation hours is below (and its much less). Its the "meat" of the day that you truly get to cover loads and charge the batteries. I can see where a SW facing small additional array would certainly help gather more power late in the day.

solar hours for my location
Jan: 4.2
Feb: 4.93
Mar: 5.36
Apr: 5.44
May: 5.57
Jun: 5.7
Jul: 5.48
Aug: 5.63
Sep: 5.22
Oct: 4.84
Nov: 4.33
Dec: 3.93

 

[SolarHead]

Here's some of what I'm talking about with the Sol-Ark charging the batteries up in the AM when the sun rises, then within about 25 minutes of charging it decides its going to use the 52% battery charge (I take my batteries down to 50% at night, and allow 600 watts from battery through the night), that 2% charge is then used and sent to the home, then 20 minutes later, it's back down to 50% and starts charging again. It must be the firmware is coded to say okay I now have less PV than load, so use battery if battery has anything above bottom charge. Then PV comes alive with more sun and the battery is back down to 50% so it starts charging again. One would assume that once a battery hits the low point, it would then only go up (starting and stopping as PV comes in) until it reaches 100% but that's not the case. I suspect that since I have a small battery bank and I'm depleting it close to sunrise, is why I am seeing this dead, then charge, then discharge, then charge all within say an hour or so. The grid at 550am to about 7am is heat pump which is assisted with 600w of battery.. I see the PV dip today at 7:40AM and I guess that's when the firmware says PV decreasing, battery has charge so it offers it to home. While I'm okay with the battery charging/discharging like that in short period of time in the mornings, I would not want to see it do this in the evenings because I like to go into night with 100% charge. I have seen it where the battery discharges some during the day but its minimal and short-lived, it can bump to 99% and then in minutes its back to 100%. I have all 6 time slots in my TOU settings set the same (600w discharge down to 50% SOC) so maybe clouds, maybe load fluctuations during the day is why the battery discharges and charges. Once PV is strong, say 9am, the battery does not discharge , it charges continuously until it hits 100%. As mentioned, I started out trying to force the Sol-Ark into when I wanted it to charge and discharge with my TOU settings, but then after kind of letting it manage , it seemed to get more out of my system than it was with me trying to force it. Maybe someone sees this same thing occurring , is it just Sol-Ark, other inverters as well? I don't see it as a problem, just trying to get an understanding as to what its thinking and doing. Maybe I will see a different experience once on LifePo4 batteries and off of the AGM.

 

[Substrate]

I'm not familiar with that monitor, but making the switch to LiFeP04 can cover up a lot of sins, so you don't have to worry. Many variables will simply be gone:

No need to charge that last 1 percent nor charge to full.

If you blow your power budget calculations and over-purchase battery capacity, you don't have to worry about under-charging like you would with the agm. If over-capacity due to mistake, other than emptying your wallet faster, you'll have much more in reserve for days of autonomy / bad weather, and in case your power needs actually increase with more toys / loads.

No cyclic or daily-cyclic stuff to worry about.

Now we have something to work with and plan around - 4 hours of solar-insolation using winter hours. Measure your load vs time for a day and you can plan your needed LFP capacity and solar-panel needs much more easily.

I'd make the switch to LFP sooner than later just so you don't have to be concerned with all these nagging details that plague most daily-cyclic AGM setups.

 

[SolarHead]

The monitor I'm using is PowerView.

I'm waiting for the LFP to ship, looking to get them in another 2 to 3 weeks.

183AH now, with 91AH usable (50% SOC), on AGM.

I'm getting 400AH of LFP, planning to go down to 20% SOC, so about 320AH usable if my calculator is right.

 

[SolarHead]

I'm grid connected (safety net), which also covers up some "sins" as you put it. Design sins. Never heard that before but got a chuckle.

I've heard where 100% off-grid and acid batteries require someone that really has a lot of experience in the design process, which makes sense when you look at what acid batteries require, and days of autonomy.

 

[Substrate]

The devil's in the details.

One reason flooded was popular was that you could simple EQ your sins away too. And take care of stationary electrolyte stratification with insufficient recharge current at the same time ...

But with LiFePo4, all that nitty gritty lead-acid maintenance goes away and we can concentrate on other details like top balance.

It may seem like I'm harping on those who don't know these things, but I'm not - none of us start out knowledgeable, that why Will and everyone on the forum are a great resource.

Also, I didn't know about your specific agm brand/model until I saw it in another thread. I might have just said - get the most you can out of them, and then later consider LiFeP04. Perhaps hang on to them for a side project for now.

Also, perhaps trust-but-verify. That means you might feel better if you buy a Fluke voltmeter (something you can trust out of the box) to make sure that things like battery terminal voltage are what they say they are in the various monitor systems you are using. It's a case of "who ya' gonna trust? - an $8 voltmeter from the grocery store? Your bms app? You can trust a Fluke". *Something should be a reputable standard you can rely on to be the ultimate arbiter of all the stuff hanging off your system. Might as well make it a good one."