diy solar

diy solar

I am trying to decide if running in SOL is better than SBU for my needs.

Mattb4

Solar Wizard
Joined
Jul 15, 2022
Messages
3,735
Location
NW AR
My system.
6-100w panels in 2S3P
EAsun 3kw hybrid inverter (iSolar MLV 3KW-U)
2 -12vDC 100ah AGM batteries in series for 24vDC

Loads are 12cuft upright freezer at about 70w running (day total is about 1.3kwh)
Computer and LTE router at around 50w max. (I figure about 300wh a day since it gets shut off overnight)
Lighting and miscellaneous phone chargers, digital clock and such (day total 150wh?)
Hybrid inverter, hard to get a accurate figure, but I am guessing it runs about 50 to 100 watts

As of now I am switching between SBU at 8am to UTI at 8pm so that the batteries are not drained too low overnight.

However I am looking at the SOL selection and wondering if it would be a better fit and remove the need to manually adjust the hybrid inverter from SBU to UTI. Yes, I can just give it a whirl, but I would be interested in any personal experiences people have with running in SOL mode.
 
With your batteries in series and SBU, I would suggest setting your low voltage cutoff setting to 24v so UTI takes over charging automatically when the batteries deplete to that voltage. That way your inverter won't shut off if one of the batteries drops below the cutoff voltage. You shouldn't have to manually switch.

You can also set it to SOL so the UTI takes over when the solar drops out. Your freezer probably goes through a defrost cycle every 8-12 hours. It can draw 400-500watts for 15 minutes or more. It can be possible for the defrost cycle to begin when your batteries are close to the low voltage cutoff. If one of the batteries goes below that point, then the inverter will shut off. That happened to me and I had to separately recharge the dead battery and then the other battery till both were full, then hook them up again. With SOL, I don't get the benefit of a longer discharge in my batteries, but I prefer having the security of my batteries being kept at a higher capacity all through the night and not worrying about an inverter shutting down at 3 am.

Edit: I forgot your batteries are AGM. My voltage setting are for my Lifepo4 batteries. Your setting is probably different.
 
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Thanks for your reply.

My freezer does not have a defrost cycle. It is an older model I bought back in '93 from Sears. Still works good.

Unfortunately I can not set the low voltage cutoff on my unit greater than 21.8. It does not stick for some reason. I would happily set it at 24.2v if I could. If I can get the monitor software program that I downloaded to run (Need a cable to hookup) I will attempt to adjust it with it.
 
Had to download software from SRNE versus the software EAsun I had downloaded and installed first. It never would communicate with the hybrid inverter. Certainly not intuitive to how to use it and it is odd that it reports battery values as 12vDC (have to double settings to get 24vDC battery settings) but after several false starts, Success! I finally got the low battery to AC pass through set at 24.2vDC as displaed on the hybrid inverter. (12.1 in the Configuration tab of the software).
 
I tried the SOL setting out and decided it was not suitable. Way too much cycling from solar to grid happens when it does not have the battery there to buffer things.
 
Well with the new LiFePO4 battery I am back to trying out SOL with the addition of solar only charging (OSO). What I hope to accomplish with this is to maximize solar usage. The charging profile for LiFePO4 battery means the hybrid inverter actively turns off solar input once the battery is charged. So to make the most out of the sun I need the battery to be in a state of sufficient discharge to spend most of the day charging from PV. Then spend the rest of the time, before the sun comes back, discharging down before utility is forced to take over AC duties but not recharge the battery. I have set my low voltage transfer to utility at 25.6 (around 20% capacity).

Boy it is hard to figure best practices.
 
My first issue with SOL arrives early this morning when the sun comes up and the unit switches to battery. Because it is early the unit finds sun and loses it again which means the utility transfers to inverter and back out again. It really needs a time of day setting to allow for dawn and dusk sun position. Not good to be constantly transferring. So for now I am back to SBU
 
SBU operation does the same thing for switching back and forth repeatedly early morning. That once again leaves me with having to manually set the preferred mode from UTI to either SBU or SOL depending on time of day and state of battery charge. Bummer.
 
You have to change the voltage settings for when it goes to battery and when it goes to utility.
If it's toggling back and forth, these settings are too close.
During beta i was under paneled. To grid has always been set to 50v (3.125) but when back to battery was set at 53 and utility charging set to disable (I can't actually completely disable utility. Even set to disable, my pair of inverters leak 1.75 amps of charge each while powering loads) the inverters were toggling several times per night. So, knowing I was getting more panels and neede to reconstruct arrays.... I set 54 as back to battery and just Let It Cycle.
Now that the arrays have been reconstructed and there are more panels, back to battery is set to 52 volts and utility only kicks in every other week when we've had three consecutive bad days of solar. But set at 52 volts it only stays on long enough for the sun to get back up.
 
Thanks for the response. My problem with getting the best setting is the conflict of wanting to achieve charging when sun is available and thus maintaining loads at the same time with solar and now this issue of trying to transfer to solar when it is not sufficient to carry anything. I have my back to battery set at the default setting of 28.0v. (24 volt controller) I will try adjusting it to 26v (half your 52v) and see if that helps.
 
The setting change has stopped back and forth transfers at early morning. But it does not seem to want to transfer from utility now even with enough sunlight that charging is occurring. I made it do so by tripping the AC input breaker and it then locked in to inverter. I will have to experiment more with the "Back to Battery" voltage setting.
 
Mine is set to sbu, solar first charging, utility charging disabled.
When the battery falls to 50 volts at 4:00 in the morning, utility picks up the load plus an amp or amp and a half of what I call buffer current. This ends up being a net charge to the batteries. I kind of like that because after hitting my low voltage setting it puts a small charge on the batteries and brings them off the bottom until the sun comes up at 730 and starts charging normally.
By 830 or so the battery voltage has recovered to 52 and we revert to normal ops.Screenshot_20220329-170626.png

And then I added 2 more strings and that cycle, which was way more prevalent before, became less so. 5 or 6 cycles in the last month.
Screenshot_20220901-114528.png
 
And the state of charge is happy here.
I do still need more solar, and more battery, but it's cycling well with the loads that are currently a portioned to this system. I still have three circuits on my reliance manual transfer switch that are powered by grid. One is a GFCI circuit that I need to troubleshoot and the other two are my 240 volt well pump that I am too big of p**** to try.
 
I also do not have charging from AC enabled. The battery seems to drop to the "Transfer to utility" set point (25.6v) at about 2-3am in my case. When checking at 5am in the morning it is resting at 26.0v which is not bad (40% SOC) and prepares the battery to accept solar charging. With a good sun day charging the battery usually reaches full around 2pm to 4pm.

Today unfortunately is overcast and production is not great. May take into another day to reach full charge.
 
I have Transfer to utility: 25.4v this seems to then rest at 25.6v under no load
Utility to battery power: 26.6v
Battery fully charged recovery point: 26.6v

This is running with SBU. SOL would be better for minimizing battery cycles but would lose a lot of solar production.

The last few days have been poor weather so charging has been a bit of a hit or miss. Yesterday the day was foggy and overcast until 2pm but after that clear blue skies and max solar input. Got the battery completely charged by evening and that gave me power back until 5am in the morning before transfer to the utility occurred.

When I add in another battery, my other 3 panels plus the additional chest freezer as loading, I am sure I will need to make adjustments.
 
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