Maximizing Selling to Grid While not Hurting Batteries

[SDman]

Hello all - newbie to the forum as am in need of some guidance. We've had solar w/battery backup since 2011, but I am realizing to some degree that I am a bit ignorant with regards to some aspects.

System is listed in profile (32 panel array, 8800W, Midnite Classic/Lite 150 VDC Charge controllers, 24 Trojan 2V, 1110 AH batteries = 48V, GS8048 inverter) and has been online since 2011. Overall have been happy with performance, however the batteries are not holding charge anymore and is time to replace them. Not sure if will go with the Trojan again or not (have yet to find local distributor), but this has led me to a new series of questions, showing my ignorance:

1. The system is not being maximized on usage - we are grid tied and system will hang in "float" mode throughout much of the day, yes powering attached loads as needed, but not pushing excess to grid. Only way I can get maximum production is either to hit the equalize or bulk button, thus will maximize the array, but...am I damaging the batteries....which leads to the next question.
2. When selling excess to Grid, either through Bulk or Equalize, does the power from the panels go through the charge controllers into the batteries, then out of the batteries through the inverter to the grid or is the power from the panels bypassing the batteries to the inverter then the grid (topping off batteries as needed)?
3. With my described system, and this is a big question - why can't the panels go direct to the inverter, bypassing the batteries for a sell (yes keeping them topped off, but not cycling through). To me, this would make the most sense for our situation for 95-99% + of the time as we have load control on the hotwater heater, which is really our only "big draw" during the evening. Having a selection/programming such that - PV => Inverter => Sell to Grid (bypassing batteries but keeping them topped off) thus maximizing energy, but if grid drop, then kicks over to batteries for the critical loads. When Grid activated again, system goes back to recharge of batteries and once topped off, then moves back to the Sell cycle.

I've looked at the manuals over the years and just did not see any clarity on what I want to do, let alone is it possible. I know that people all over (CA, CO, TX etc.) have panels on their roofs, selling to grid as the sun shines and then back to the grid sun down and they don't have batteries on their system. Is it possible to do w/the system I have as described.

Or...do I have some of the settings incorrect? Manual states that charge controllers should be set "higher for EQ, Absorb, Float than the Mate 3". Currently they are set the same.

Looking for help/guidance from the Community. Have all the settings listed for inverter, charge controllers and Mate3 as well as main wiring diagram if helps.
Regards,
SDman

 

[robby]

Hello all - newbie to the forum as am in need of some guidance. We've had solar w/battery backup since 2011, but I am realizing to some degree that I am a bit ignorant with regards to some aspects.

System is listed in profile (32 panel array, 8800W, Midnite Classic/Lite 150 VDC Charge controllers, 24 Trojan 2V, 1110 AH batteries = 48V, GS8048 inverter) and has been online since 2011. Overall have been happy with performance, however the batteries are not holding charge anymore and is time to replace them. Not sure if will go with the Trojan again or not (have yet to find local distributor), but this has led me to a new series of questions, showing my ignorance:

Wow that system must have cost a small fortune back in 2013.

1. The system is not being maximized on usage - we are grid tied and system will hang in "float" mode throughout much of the day, yes powering attached loads as needed, but not pushing excess to grid. Only way I can get maximum production is either to hit the equalize or bulk button, thus will maximize the array, but...am I damaging the batteries....which leads to the next question.

2. When selling excess to Grid, either through Bulk or Equalize, does the power from the panels go through the charge controllers into the batteries, then out of the batteries through the inverter to the grid or is the power from the panels bypassing the batteries to the inverter then the grid (topping off batteries as needed)?

Yes power is going into the batteries and the Inverter is drawing power from the Batteries. If the batteries are fully charges and the PV is producing more power than the load is pulling then it is essentially pulling all the power from the PV and the Batteries are just stabilizing the current flowing from the SCC .
Also if the SCC Amperage starts to drop (due to clouds etc) the batteries handles the slack.

3. With my described system, and this is a big question - why can't the panels go direct to the inverter, bypassing the batteries for a sell (yes keeping them topped off, but not cycling through). To me, this would make the most sense for our situation for 95-99% + of the time as we have load control on the hotwater heater, which is really our only "big draw" during the evening. Having a selection/programming such that - PV => Inverter => Sell to Grid (bypassing batteries but keeping them topped off) thus maximizing energy, but if grid drop, then kicks over to batteries for the critical loads. When Grid activated again, system goes back to recharge of batteries and once topped off, then moves back to the Sell cycle.

You cannot directly sell the PV and do all of those things because you have a separate charge controller and Inverter and it's just older system and not an integrated hybrid system.
I use a Sol-Ark 12K Inverter which does all the things you want to do.

I've looked at the manuals over the years and just did not see any clarity on what I want to do, let alone is it possible. I know that people all over (CA, CO, TX etc.) have panels on their roofs, selling to grid as the sun shines and then back to the grid sun down and they don't have batteries on their system. Is it possible to do w/the system I have as described.

Nope.

Or...do I have some of the settings incorrect? Manual states that charge controllers should be set "higher for EQ, Absorb, Float than the Mate 3". Currently they are set the same.

Looking for help/guidance from the Community. Have all the settings listed for inverter, charge controllers and Mate3 as well as main wiring diagram if helps.
Regards,
SDman

 

[SDman]

Robby,

Thanks for the feedback and yes, was a touch expensive for sure and man have prices come down. But, hindsight is 20/20 eh? We needed it at the time due to middle of nowhere and needs on the ranch. Too many time we've had issues w/grid down, more so in winter and cattle need water and mama needs heat! Ya, we've got other generators (diesel, gas/LP, PTO), but sometimes nice to not worry w/all the other hassle/hookup.

But, please bear with me as I want to make sure I understand. You stated:

Yes power is going into the batteries and the Inverter is drawing power from the Batteries. If the batteries are fully charges and the PV is producing more power than the load is pulling then it is essentially pulling all the power from the PV and the Batteries are just stabilizing the current flowing from the SCC .
Also if the SCC Amperage starts to drop (due to clouds etc) the batteries handles the slack.

So PV thru charge controllers to battery, then out of battery through inverter to critical loads w/excess to grid. If batteries fully charged, it is just a pass through and the batteries are just stabilizing the load draw (cloud, well pump, welder etc. kicks on)? Thus batteries are not cycling (life expectancy) and this does not count as cycling the batteries when selling? Would assume no as technically we are not discharging/charging (cycling) the batteries, thus not hitting battery life as you stated? Correct?

If the above is correct and selling through the batteries w/out cutting their life (cycling) is actually happening, then I think I'm good and just need to track down some new batteries.

But do have another question - how to get the system to automatically push the excess PV to grid? Only way I know is to hit "bulk or EQ" and then it is forcing the excess to grid (through the batteries...but their full, thus not being impacted correct?)? Is setting the charge controller slightly higher than the Mate3 or is the manual deal (me?) every time?

Thoughts and comments are appreciated!
SDman

 

[robby]

Robby,

Thanks for the feedback and yes, was a touch expensive for sure and man have prices come down. But, hindsight is 20/20 eh? We needed it at the time due to middle of nowhere and needs on the ranch. Too many time we've had issues w/grid down, more so in winter and cattle need water and mama needs heat! Ya, we've got other generators (diesel, gas/LP, PTO), but sometimes nice to not worry w/all the other hassle/hookup.

But, please bear with me as I want to make sure I understand. You stated:

So PV thru charge controllers to battery, then out of battery through inverter to critical loads w/excess to grid. If batteries fully charged, it is just a pass through and the batteries are just stabilizing the load draw (cloud, well pump, welder etc. kicks on)? Thus batteries are not cycling (life expectancy) and this does not count as cycling the batteries when selling? Would assume no as technically we are not discharging/charging (cycling) the batteries, thus not hitting battery life as you stated? Correct?

Correct assuming the PV is completely supplying the loads and the Battery bank is staying at 100%.

If the above is correct and selling through the batteries w/out cutting their life (cycling) is actually happening, then I think I'm good and just need to track down some new batteries.

At this point in time the only kind of batteries that make sense $$ wise is LFP batteries.
If the Inverter etc is 13 years old you might want to consider upgrading to a Hybrid. That way the system is not just on standby at night but is actually powering your house.

But do have another question - how to get the system to automatically push the excess PV to grid? Only way I know is to hit "bulk or EQ" and then it is forcing the excess to grid (through the batteries...but their full, thus not being impacted correct?)? Is setting the charge controller slightly higher than the Mate3 or is the manual deal (me?) every time?

I don't know enough about that Inverter to advise you.
Maybe someone on the forum has one and will chime in.

Thoughts and comments are appreciated!
SDman

 

[Steve777]

Not sure about the Midnite Classic 150 Lite, but the regular 150 has a rebulk setting, which allows the charger to go back into bulk charging earlier. This will allow the PV power to be directed to the batts (bulk charging) while you are selling back (perhaps not with as fine a control as a more modern AIO would allow, but should get you somewhat there).

 

[SDman]

Robby -

Appreciate the feedback and the confirmation. Understood on the hybrid, but at this time she's still working and we need the batteries and a hybrid is going to be additional cash outlay, but will book mark the info on the Sol-Ark 12K Inverter. Will also check out the forum for battery ideas and alternates. Need to cross compare aH (kWh) vs. $$ on depth of discharge vs. life - newer battery tech vs. the old deep cycle lead acid, thus need to research and learn a bit more on what would be compatible with system. Looks like there is a sub forum for general battery discussion (energy storage) - need to visit/review.

Steve777 -

Thanks for the info. Right now the Classic 150 is the main w/the 150 Lite in "follow-me" mode. I see on the status panel under config/tech the rebulk volts. Current float is set at 52.8V w/rebulk @ 52V. Will review a bit more to see if setting correct or not.

Lastly, need to hit the solar pump forum as we've got 3 solar pasture wells, working well and have 4th drilled, but need to get the proper mounting rack like the other 3. Can't remember where we got those other ones from (vendor). Might take some pictures and see if anyone has idea's else measurements and fab one up (winter project).

Again, appreciate your comments and the assistance!

SDman

 

[upnorthandpersonal]

Not sure if will go with the Trojan again or not

In 2024, I would not go lead-acid for this. LFP is cost effective now (can even cheaper than lead-acid).

 

[shvm]

13 years is very long for Flooded Lead Acid. 5-6 years is the average while 7-8 years is good.

From what I've heard, Lead Acid loves to be kept fully charged (and boiling). Not surprising yours lasted so long. But they're very inefficient compared to LFP.

 

[wpns]

Last time I looked at FLA for backup power, the float charge power requirements were going to eat my lunch. Of course, now that panels are so cheap, you can just account for it in your power budget.

 

[SDman]

All - appreciate the feed back.

Digging into it further as I have 3 realistic option, based on what I've found so far:

1. Replace existing with FLA - getting quote coming
   1. Expensive
   2. Shorter Life
   3. Higher Maint.
   4. Direct replacement
2. Replace existing w/LFP - need to talk w/batter MFG (recommendations?)
   1. Not cheap
   2. Longer life
   3. Lower Maint.
   4. Compatibility with existing Radian 8048/Classics and Mate3
      1. Found thread of a guy who did a change w/a 8048 to LFP, but he had to jump through some hoops to trick it into powering up.
      2. Understanding how BMS works into this.
3. Replace w/new inverter/CC/LFP (Sol-Ark 12K potential) and work the battery equation at same time or later.
   1. Not my favorite as I am a tightwad and hate seeing good equipment tossed to the side for newer technology.

It all comes down to cost and to some degree flexibility. The end goal is not full off grid, but more power outage related and minimizing our electric bill ($0.1010/kW w/out facility charge). We have no Net metering and only get $0.02/kW if push to grid due to Co-ops electrons are more special than ours.

Our loads on critical circuits are low with only the well pump/HW heater being the biggest draws, else fire place fans, freezers, fridge and some LED lighting in critical area's (shop, utility room etc.) 50A is the main circuit out (9600W @ 240V), thus load limited there. In general, want the system to wakeup in the morning, and start pushing. Most won't make it back to the grid due to distribution at the meter interface to other users (house, shop, barns etc.), but want to maximize the usage as much as possible to offset incoming electric. As of now, if cloud cover, grid supplements as typical. Average usage is 50-55kWh/month with solar output of around 29 kWh/month.

Again, really appreciate the feedback
Open to thoughts or idea's and or vendors (unless that is a no-no via forum rules).

Thanks,
SDman

 

[Steve777]

@SDman one other option (or perhaps a sub-option) would be to replace the batts with a sealed version of L-A such as AGM. Probably not less expensive, but industrial AGM batts can last 15+ years, especially in situations where they are largely kept at or near float (as I am guessing your FLAs were).

It still would be more expensive than LFP at this time, so not sure I'd recommend it, but it is an option with some advantages over FLA.

 

[RCinFLA]

If you are selling to grid from power stored in lead-acid batteries, you will always lose.

Replacement battery cost will be greater than what you save on grid power.

 

[sunshine_eggo]

If you are selling to grid from power stored in lead-acid batteries, you will always lose.

Replacement battery cost will be greater than what you save on grid power.

And the inherent 15% more energy needed to restore that which was consumed.

 

[Hedges]

If you are selling to grid from power stored in lead-acid batteries, you will always lose.

Replacement battery cost will be greater than what you save on grid power.

At least if you are charging lead-acid in the day, then discharging at night when selling to the grid.
My estimate of AGM cost is $0.50/kWh of cycle life.

If you have DC coupled PV, PV panels --> SCC --> battery --> inverter --> grid,
you can keep batteries at float while exporting surplus power to grid.
The batteries will carry the 120 Hz ripple current. Capacitors are not able to. I don't know how much that affects battery life.
So maybe AGM or FLA forklift battery is OK in that application.

But with LiFePO4 purchase price maybe half of lead-acid, and cycle life 5x to 10x longer, it is close to a no-brainer.
Except for some very simple or small systems where AGM or Gel may be good.
And you do need to use your brain to make a lithium system work.

I think packaged LiFePO4 batteries like PowerPro and various server rack models should cost around $0.05/kWh. DIY can be $0.015/kWh.
(kWh of cycle life, not capacity.)

 

[RCinFLA]

Even immediate grid push from DC coupled PV with lead-acid batteries is a loser. Even when there is no net power drawn from batteries.

The large 120 Hz ripple current from 60Hz sinewave inverter will stress the lead-acid batteries shortening their lifespan. For DC coupling of PV power, the batteries are acting as a large filter capacitor to smooth the large ripple current from showing up on DC charge controller.

Filter caps on inverter battery input are for high freq PWM switching and have little effect on reducing 2x AC line frequency ripple current. You would need 4-5 Farads of ultra-low ESR supercaps to reduce 2x AC line frequency ripple current from battery lines.

If batteries are too small in AH's or cabling introduces too much series resistance allowing ripple current to show up on PV DC charge controller, the PV power yield will be reduced due to the ripple current. For optimum output, PV panels must have a smooth load current for the given illumination level. Any ripple showing up on PV panels is like wobbling of MPPT point.

 

[SDman]

To all - found a decent link here at DIY Solar forum from Rich V. chasing the same thing I am....

FWIW - https://diysolarforum.com/threads/older-radian-system-setup-with-sok-lifepo-batteries.67501/

SDman

 

[Steve777]

It's not entirely clear to me what you are trying to do here. Is it just replace the batts (and maybe the inverter), but use them in the same fashion you have been (no sell back to the grid, keep the batts for grid down power). Or are you thinking of changing your use mode, that is sell the excess power back during the day, and perhaps even run on batts at night even when the grid is up to minimize your grid usage? Or something else? No right or wrongs here, but it may effect what equipment changes you want to make.

I have an even older system (Trace SW4024, 2600W of PV and ~32KWH of L-C (lead-carbon) AGM batts). I have a resell agreement with my PoCo, and generally have used the batts only as grid-down backup (which we have more often than you'd expect). My first set of batts were industrial L-A AGMs from a cell tower, I got them at ~5 years old. They lasted almost 20 more years with me. So I can't say I saw any problems with ripple current from the inverter while selling back. I went with L-C industrial batts when those were dying for two reasons: First Li batts were still 2x the price of L ones back then. And Lead Carbon seemed like an interesting technology, they are spec'd for almost 3-4000 cycles which was comparable to the Li ones of that day.

However today, in my system upgrade (hopefully happening soon), I am definitely going with LFP batts. They cost 1/2 as much for similar capacity, are WAY smaller and lighter too. But my batts will be in a conditioned space, I might have decided something else if I had severe cold where my batteries were being kept.

Certainly for cycling the batts every day (trying to minimize your grid usage even at night) LFP make sense; not only cheaper and smaller, but better able to take the cycling than FLA or regular AGM. And even if you are just using the batts for grid down situation, LFP are the more economical solution.

What you've only hinted at is possibly replacing the inverter and CC too. And that may make sense depending on your goals. Yes, people with grid-tied inverters sell back to the grid without any need for batteries. They do that because the grid-tied inverter have built in CCs which go directly to a DC buss in the inverter to go on to become AC; no need for a batt. AIO and hybrid inverters tend to have the same electrical topology (plus a battery); they can pull or push DC from/to the batt but can make AC directly from the PV input without involving the batt, if needed (at least most of them). Separate inverters and CCs cannot do that.

Again it all really depends on your goals. Do you want to add more PVs someday, have a bigger backup for grid-down situations, be more independent of the grid and your PoCo, sell back to your PoCo? Knowing the answer to these question will enable you to make the best choices about equipment.

FWIW, on my current system, I have my Midnite Classic 150 programmed for Absorb: 28.0v, Float: 27.1v and ReBulk: 27.2v. This was after speaking to Midnite about how they'd recommend the settings. Typically during sunny days the batt voltage drops as sell back occurs, and then a rebulk cycle begins, feeding max PV power to the batts. Batt votage is stable, it is going out of the batts as fast as it is coming in. AFAIK this was the intent of the rebulk setting. Since I have not yet had to "play" with LFP batts, can't advise how this would work with them and with a BMS in there too. But with L-A type batts, this sort of setup would maximize PV power going to the batts to be resold to the grid (or used elsewhere), which was one of your questions.

If you want to research just doing a LFP batt replacement, then I'd check out some of the threads about using Midnite Classics (and your inverter) with LFP. I know folks are doing it, but might be good to know upfront what they needed to do to make it work.

 

[SDman]

Steve777,

In essence, the system was originally intended as Grid-Tied Backup. Thus power out, batteries kick in and services critical loads only, power on, back to the grid for critical loads. We have rarely run in HBX (battery only) mode as the storage just isn’t there and obviously cycling decreases life.

Over the years, I have been “forcing” into Bulk mode (didn’t know enough about re-bulk) during daylight hours. System is in a conditioned space (utility room of one shop) and thus when we “push to the grid”, we are just pushing to the main Co-op pedestal (we do have an agreement w/them (required if pushing to grid), but in SD no net metering, thus only avoided cost ~ $0.015-$0.02/kW). Other users (house, two other barns, another shop etc.) are tied to that same pedestal on the same bus bar, thus very little actually makes it out to the “true grid”, past the bi-directional meter and is almost entirely used on site by other users (Geothermal, A/C, dryer, welding in shop, etc. etc.) – items that are NOT connected to the critical backup loading.

As for the inverter/CC’s, again, tightwad here, but I cannot get past replacing something that is currently functioning properly. Yup, might need a little more thought or TLC, but It’s just the farmer in me. If push comes to shove, then, yes, we would replace, but I don’t think we are there yet (as far as I know). Even with having a hybrid, we would want to have the batteries for critical load as dragging out the generators can be a chore mid-winter around here.

Understood on the re-bulk and a smart setting and that’s exactly what I want – backup, but when not needed, maximize array to “grid”. Key is as you said – research research research and thus far have only found Rick V. doing what I want to do with an older Radian/Mate 3 system. However, you made a good point w/Classics and LFP and how the BMS plays in there.

Always something to learn!

Appreciate the feedback.

Regards,

SDman

 

[Steve777]

Steve777,

In essence, the system was originally intended as Grid-Tied Backup. Thus power out, batteries kick in and services critical loads only, power on, back to the grid for critical loads. We have rarely run in HBX (battery only) mode as the storage just isn’t there and obviously cycling decreases life.

Over the years, I have been “forcing” into Bulk mode (didn’t know enough about re-bulk) during daylight hours. System is in a conditioned space (utility room of one shop) and thus when we “push to the grid”, we are just pushing to the main Co-op pedestal (we do have an agreement w/them (required if pushing to grid), but in SD no net metering, thus only avoided cost ~ $0.015-$0.02/kW). Other users (house, two other barns, another shop etc.) are tied to that same pedestal on the same bus bar, thus very little actually makes it out to the “true grid”, past the bi-directional meter and is almost entirely used on site by other users (Geothermal, A/C, dryer, welding in shop, etc. etc.) – items that are NOT connected to the critical backup loading.

As for the inverter/CC’s, again, tightwad here, but I cannot get past replacing something that is currently functioning properly. Yup, might need a little more thought or TLC, but It’s just the farmer in me. If push comes to shove, then, yes, we would replace, but I don’t think we are there yet (as far as I know). Even with having a hybrid, we would want to have the batteries for critical load as dragging out the generators can be a chore mid-winter around here.

Understood on the re-bulk and a smart setting and that’s exactly what I want – backup, but when not needed, maximize array to “grid”. Key is as you said – research research research and thus far have only found Rick V. doing what I want to do with an older Radian/Mate 3 system. However, you made a good point w/Classics and LFP and how the BMS plays in there.

Always something to learn!

Appreciate the feedback.

Regards,

SDman

Makes sense, and I understand your desire to not throw away perfectly good working equipment. A couple of added variables in the equations are: Hybrid AIO inverters generally cost less than separate MPPT CCs (a factor if you expect to increase your panel count), and they can accept higher working voltages leading to cheaper wiring for the same wattage. It is good to also look into inverter (and CC) efficiency of the different equipment, as well as "idle current" losses.

Just a few more factors to take into account.

 

[Lawrence_SoCal]

Totally get not throwing out good equipment.
BUT
First, as noted above, is your desired goals/end-state. Then, does any of your equipment cost-effectively support that goal. If selling/replacing the old gear is cheaper/more effective/'better', then fight the urge to be your own impediment.

And the battery tech will probably (hopefully) change significantly in next 5[ish+] years

My recommendation
- plan out goals as Steve suggested, with some information gathering on your specific electrical usage, usage patterns including TOU (if they apply to you now, or soon will... which seems likely).

for example, some of us have the 'fun' of really high electric rates, and a high differential on Time-of-Use (TOU) rates. As such, positive ROI comes from capturing kW during daylight hours and then using that during the much more expensive (typically) afternoon/evening Peak rate time (load time shifting). But you may be in a Power Company (PoCo) situation where this doesn't apply [though don't be surprised if/when it comes... so being aware of local utility commission discussions/plans makes sense​

- do a green-field / fresh slate design, as an informational exercise, intentionally designing system in a way to handle device failures (ex bypass switch around a hybrid-inverter)

for example, it depends on your usage as to whether the 12K, or larger/smaller unit makes sense for you?​

- recognize, that things like Hybrid Inverters and higher lifecycle count batteries like LFP, are designed/driven by market with high(er) electricity costs.​

- In a low-cost electricity market, where load shifting doesn't make much financial sense, and goal is almost entirely grid-down critical load backup, it could easily be true that a simple AC-coupled battery be the most cost-effective solution? with sizing being based on desired runtime with given load. Cost will depend on whether going with pre-packaged, UL listed solutions (depending on AHJ , insurance, and your risk tolerance, etc. considerations)​

And note the above conversation on why certain batteries held at Full/100% will last longer than others, especially those designed for a certain level of regular discharge (ie load time shifting)​

- then see what makes sense to re-use
doing the above makes it mess less emotional, and far more ROI/goal focused, and what makes most sense

It all comes down to cost and to some degree flexibility. The end goal is not full off grid, but more power outage related and minimizing our electric bill ($0.1010/kW w/out facility charge). We have no Net metering and only get $0.02/kW if push to grid due to Co-ops electrons are more special than ours.

Something to be careful with - kW = rate (ie mph), billing based on amount (ie distance covered)

As of now, if cloud cover, grid supplements as typical. Average usage is 50-55kWh/month with solar output of around 29 kWh/month.

Are you sure of those numbers? that seems really low. granted I'm much further south, but my 7.4kW panel system can produce (export) 30kWh in a _day_ in summer.

I ask, as a big consideration as noted earlier is desired runtime. modern LFP batteries are such that running for days with that sort of usage is entirely possible. And at that point, I'd want to consider making sure PV will work while on battery (ie power house and possibly charge battery depending on overall production and load at the same time .. beware cheap solutions that can't do both simultaneously)

 

[Rich V]

Hello all - newbie to the forum as am in need of some guidance. We've had solar w/battery backup since 2011, but I am realizing to some degree that I am a bit ignorant with regards to some aspects.

System is listed in profile (32 panel array, 8800W, Midnite Classic/Lite 150 VDC Charge controllers, 24 Trojan 2V, 1110 AH batteries = 48V, GS8048 inverter) and has been online since 2011. Overall have been happy with performance, however the batteries are not holding charge anymore and is time to replace them. Not sure if will go with the Trojan again or not (have yet to find local distributor), but this has led me to a new series of questions, showing my ignorance:

1. The system is not being maximized on usage - we are grid tied and system will hang in "float" mode throughout much of the day, yes powering attached loads as needed, but not pushing excess to grid. Only way I can get maximum production is either to hit the equalize or bulk button, thus will maximize the array, but...am I damaging the batteries....which leads to the next question.
2. When selling excess to Grid, either through Bulk or Equalize, does the power from the panels go through the charge controllers into the batteries, then out of the batteries through the inverter to the grid or is the power from the panels bypassing the batteries to the inverter then the grid (topping off batteries as needed)?
3. With my described system, and this is a big question - why can't the panels go direct to the inverter, bypassing the batteries for a sell (yes keeping them topped off, but not cycling through). To me, this would make the most sense for our situation for 95-99% + of the time as we have load control on the hotwater heater, which is really our only "big draw" during the evening. Having a selection/programming such that - PV => Inverter => Sell to Grid (bypassing batteries but keeping them topped off) thus maximizing energy, but if grid drop, then kicks over to batteries for the critical loads. When Grid activated again, system goes back to recharge of batteries and once topped off, then moves back to the Sell cycle.

I've looked at the manuals over the years and just did not see any clarity on what I want to do, let alone is it possible. I know that people all over (CA, CO, TX etc.) have panels on their roofs, selling to grid as the sun shines and then back to the grid sun down and they don't have batteries on their system. Is it possible to do w/the system I have as described.

Or...do I have some of the settings incorrect? Manual states that charge controllers should be set "higher for EQ, Absorb, Float than the Mate 3". Currently they are set the same.

Looking for help/guidance from the Community. Have all the settings listed for inverter, charge controllers and Mate3 as well as main wiring diagram if helps.
Regards,
SDman

Please post your inverter & CC settings. You can look at my thread for comparison. I have no problem pushing all of my solar output to the grid.

 

[SDman]

Rich,


Midnite Classic and Midnite Lite 150VDC's (Note that the Lite is just a "follow-me" off the Classic. Attached in PDF "Midnite).

Mate3/Radian in second file.

I have a copy of what you posted on your settings in the file. I've got Border States chasing an IBR and some LFP batteries with questions into Midnite (they are also chasing a solar rack mount/panels for our new (4th) solar pasture well.

Any holes/questions?

 

[Rich V]

Rich,


Midnite Classic and Midnite Lite 150VDC's (Note that the Lite is just a "follow-me" off the Classic. Attached in PDF "Midnite).

Mate3/Radian in second file.

I have a copy of what you posted on your settings in the file. I've got Border States chasing an IBR and some LFP batteries with questions into Midnite (they are also chasing a solar rack mount/panels for our new (4th) solar pasture well.

Any holes/questions?.

The only thing I see that may be causing your poor sell to grid numbers is the settings for battery float & sell volts.
My sell is 54 V vs your 52 V. My float is 55.2 v vs your 52.8 V.
Also I'm not familiar with your charge controller so that is an unknown as I us the Outback CC and it coordinates with the rest of the Outback system.
I'm very happy with the SOK batteries so that is what I would recommend. They are now selling at a great price. https://www.currentconnected.com/product/sk48v100-48v-server-rack-battery/