Solar Performance

[NapoleonDynamite]

Day 4 on the boat, just wondered if someone could help me understand this, as my understanding seems a bit tgtbt.

We've not yet hooked up to shore power, was advised not to keep the lithiums at full all the time, but let them drop, use them, before charging again.

But that is proving difficult as the lowest the charge has gone is 93%, then it seems to charge up again off the solar, usually sits at 98-100%.

We moved on day 1 & 2, not moved on 3 & 4. Have seperate 240v fridge and freezer, used hairdryer and 42" tv. 

1.32Kw solid panels of solar.

Is the solar really that good already?

I'm prepared to be laughed at.

 

 

Edited March 10 by NapoleonDynamite

[nicknorman]

We can't see state of charge, but seeing as how the battery voltage got up to 14.2v it must  be pretty well fully charged. You don't specify the battery capacity nor the amount of solar you have, but it does seem that you are quite frugal with electricity having used about 100Ah (at 12v) a day. And it has been fairly sunny in the last few days. So yes I think the figures are pukka and solar "is that good"!

[NapoleonDynamite]

1.32kw solar and 600Ah

Current state of charge

[nicknorman]

Thanks. So you can see that the maximum charge power on one day was 653 watts which at 13.5 volts is 48 amps. Bearing in mind you only used about 120Ah during that 24 hour period, it would only take 2 1/2 hours to fully charge your batteries. Maybe you should use more power! We got an air fryer that is great and we hardly used the gas oven any more. And some people run an immersion heater from their excess solar, to give hot water.

Bear in mind we are approaching the equinox and for December/January the solar output is a lot less, you may not have a surplus of power at that time. But for the rest of the year you should have plenty.

Edited March 10 by nicknorman

[Francis Herne]

The last few days were excellent for solar output. You're not going to get better than that at this time of year.

 

Today is overcast here for me and I'm seeing more typical output for the time of year, about 1kWh from 800W of panels. In the same conditionsyour 1.2kW of panels would have got ~1.5kWh today if the battery weren't full, so only a bit more than what you've used.

 

I'd expect solar to cover your current usage from now until late September, with a significant excess in the summer. Easy to use up any surplus with a 240V system - electric cooking, immersion heater etc.

Edited March 10 by Francis Herne

[NapoleonDynamite]

Thanks, we've got an airfryer, just haven't moved it onboard yet. What do the 3 different colours on the solar graph mean?

[nicknorman]

2 minutes ago, NapoleonDynamite said:

Thanks, we've got an airfryer, just haven't moved it onboard yet. What do the 3 different colours on the solar graph mean?

Pretty sure it is the status of the charger - white is bulk, ligher blue is absorption and darker blue is float.

[Russ T]

The solar this past week has been amazing. Cold days, sun rising in cloudless skies. 

The fridge will be running less than in the summer, and you are not seeking the shade of a tree to hide beneath.

Enjoy it until October. 

[NapoleonDynamite]

2 minutes ago, nicknorman said:

Pretty sure it is the status of the charger - white is bulk, ligher blue is absorption and darker blue is float.

It is, but what does that actually mean 🫣

[Russ T]

7 minutes ago, NapoleonDynamite said:

It is, but what does that actually mean 🫣

Have a read. Actually, if you have lithium batteries its probably best not to read that. Though some terms apply, its mainly for lead acid batteries

 

Edited March 10 by Rod Stewart

[nicknorman]

11 minutes ago, NapoleonDynamite said:

It is, but what does that actually mean 🫣

A typical smart battery charger has these three states. Bulk is when the MPPT can't drag the battery voltage up to the regulated value yet, it is just outputting as much current as it can and the voltage is below the regulated voltage. Once the voltage rises to the regulated value, it switches to Absorption. In this mode the voltage remains constant at the regulated value, and consequently the current starts to decrease. Depending on the MPPT's settings, it will switch from Absorption to Float either after a specified time, or when the charge current has dropped below a specified value. This is notionally when the battery is fully charged.

In Float mode, the regulated voltage is lower such that the battery is not being charged any more, but loads on the battery (ie fridge etc) are supplied from the solar. This is why there is quite a bit of energy showing in the darker blue section - the batteries became full early in the day, and for the rest of the day the solar was effectively directly running the fridge etc.

 

If you want to keep the batteries below 100% then one way to do that is to use the BMV712 battery monitor (that it looks like you may have) which has a relay output that can be set to operate when the SoC reaches a certain value, say 80%. Victron can sell you a cable that plugs into the VE.Direct port of the MPPT and the other end to the relay connections of the BMV712, so the BMV switches off the solar at the specified SoC and turns it back on again a lower specified SoC.

If you have a SmartShunt instead of a BMV then unfortunately you can't do this as the SmartShunt doesn't have a relay.

Edited March 10 by nicknorman

[DShK]

OP, if you have a victron cerbo in your system I can provide you an automatic way to control your charging. If you don't you can do it more cheaply with a raspberry pi... it is a bit more technical this way though.

 

I have set up a system which will turn solar on/off automatically depending on controllable thresholds. It can also turn off a battery to battery charger to terminate alternator charging. I even have it so it controls charge current to try and keep the batteries around 50% when on a shoreline.

 

Happy to advise you if you'd like.

[ditchcrawler]

But if you are not on shore supply you battery is not sitting fully charged all the time it is cycling as you wont be getting hardly any charge between 5pm and 8am in which time you will have the fridge, TV, pumps all working at some point using power. If you have more than one battery you could switch one or more off. I am surprised a fridge, freezer ,Large TV and other things only use 7% of your battery capacity overnight

[Russ T]

2 minutes ago, DShK said:

OP, if you have a victron cerbo in your system I can provide you an automatic way to control your charging. If you don't you can do it more cheaply with a raspberry pi... it is a bit more technical this way though.

 

I have set up a system which will turn solar on/off automatically depending on controllable thresholds. It can also turn off a battery to battery charger to terminate alternator charging. I even have it so it controls charge current to try and keep the batteries around 50% when on a shoreline.

 

Happy to advise you if you'd like.

Ah. If only you were around 6 weeks ago when I was pulling my hair out trying to get that to work on a Pi/ node red.

[DShK]

Just now, ditchcrawler said:

But if you are not on shore supply you battery is not sitting fully charged all the time it is cycling as you wont be getting hardly any charge between 5pm and 8am in which time you will have the fridge, TV, pumps all working at some point using power. If you have more than one battery you could switch one or more off. I am surprised a fridge, freezer ,Large TV and other things only use 7% of your battery capacity overnight

Lithium's don't want to be kept at 100% for any sustained time really...

Just now, Rod Stewart said:

Ah. If only you were around 6 weeks ago when I was pulling my hair out trying to get that to work on a Pi/ node red.

Sounds like you managed it in the end though?

[Russ T]

1 minute ago, DShK said:

Sounds like you managed it in the end though?

Well. Kind of. I got the solar bit working.Not sure how elegant it is though.

 

 

[DShK]

4 minutes ago, Rod Stewart said:

Well. Kind of. I got the solar bit working.Not sure how elegant it is though.

 

 

https://drive.google.com/file/d/1y-QYOOnZk2l3BSYyeyDFPpf60l6zCbw_/view?usp=sharing

 

Here's my flows, maybe it'll be of help to you. Should be able to import it if you download it.

Edited March 10 by DShK

[Russ T]

1 minute ago, DShK said:

https://drive.google.com/file/d/1y-QYOOnZk2l3BSYyeyDFPpf60l6zCbw_/view?usp=sharing

 

Here's my flows, maybe it'll be of help to you. Should be able to import it if you download it.

Oh wow. That's great. Thanks very much.

 

Sorry OP for jumping on your thread.

[IanD]

28 minutes ago, DShK said:

Lithium's don't want to be kept at 100% for any sustained time really...

Sounds like you managed it in the end though?

If by "100% SoC" you mean the high voltage used for cell balancing/resetting SoC counter (typically around 14.4V) then this is true -- for example a couple of hours every couple of weeks in my case, you can see this happening in the plot (all controlled by the BMS). You can also see the reported SoC (at the same voltage) dropping about 1% per week, all current-counting SoC systems do this -- and you can see it being reset to 100% by the cell balancing cycle.

 

If you mean "normal fully charged/float voltage for every day" (typically around 13.5V, 98% SoC in my case) then LFP will happily sit there for as long as you want them to -- mine sit there about 8 hours per day while the sun is shining, then drop back overnight.

 

 

 

Edited March 10 by IanD

[DShK]

4 minutes ago, IanD said:

If by "100% SoC" you mean the high voltage used for cell balancing/resetting SoC counter (typically around 14.4V) then this is true -- for example a couple of hours every couple of weeks in my case, you can see this happening in the plot (all controlled by the BMS).

 

If you mean "normal fully charged/float voltage for every day" (typically around 13.5V, 98% SoC in my case) then LFP will happily sit there for as long as you want them to -- mine sit there about 8 hours per day while the sun is shining, then drop back overnight.

 

 

 

Interesting. My understanding was that it was not good for the chemistry to be held at anywhere near full for any length of time. It would certainly be an easier solution for being on a shoreline than my current setup, I could just knock the charge voltage down.

[Francis Herne]

1 minute ago, DShK said:

 

Interesting. My understanding was that it was not good for the chemistry to be held at anywhere near full for any length of time. It would certainly be an easier solution for being on a shoreline than my current setup, I could just knock the charge voltage down.

That's true for most lithium chemistries, but the LiFePO₄ cells used in boats are quite tolerant of being held near full charge so long as they're not overcharged.

[IanD]

12 minutes ago, DShK said:

 

Interesting. My understanding was that it was not good for the chemistry to be held at anywhere near full for any length of time. It would certainly be an easier solution for being on a shoreline than my current setup, I could just knock the charge voltage down.

 

Correct, if by "anywhere near full" you mean "above 13.5V or so". If you want to guarantee that the cells stay balanced and the SoC counter stays accurate, it's recommended that you occasionally take the cells up to 100% SoC for a brief period as I described, this doesn't have any bad effect on lifetime so long as you then stop charging and allow them to drop back to 13.5V.

 

In my case the BMS and Quattro deal with all this automatically, also prioritising free solar power when possible instead of wasting expensive shoreline power. If you don't have a system like this and the BMS in the batteries doesn't make this happen, it's a good idea to do it manually -- but you certainly don't want to be doing a balancing charge up to high voltages (e.g. 14.4V) every day.

 

If you don't do this (get up to 100% SoC) there's no guarantee that the SoC reading won't get more and more inaccurate -- the 1%/week drift I showed is actually very small, others have reported much bigger errors, especially with batteries (some Fogstar, for example) which don't accurately measure and integrate small currents. IIRC one poster had an accumulated 50% error in the reported SoC... 😉 

Edited March 10 by IanD

[ditchcrawler]

I think the OP must have 1000 Ah battery bank running that load all night for just 7% of capacity drop. he must be using at least 70Ah at 12 volts 

Edited March 10 by ditchcrawler
I like adding bits

[DShK]

16 minutes ago, IanD said:

 

Correct, if by "anywhere near full" you mean "above 13.5V or so". If you want to guarantee that the cells stay balanced and the SoC counter stays accurate, it's recommended that you occasionally take the cells up to 100% SoC for a brief period as I described, this doesn't have any bad effect on lifetime so long as you then stop charging and allow them to drop back to 13.5V.

 

In my case the BMS and Quattro deal with all this automatically, also prioritising free solar power when possible instead of wasting expensive shoreline power. If you don't have a system like this and the BMS in the batteries doesn't make this happen, it's a good idea to do it manually -- but you certainly don't want to be doing a balancing charge up to high voltages (e.g. 14.4V) every day.

 

If you don't do this (get up to 100% SoC) there's no guarantee that the SoC reading won't get more and more inaccurate -- the 1%/week drift I showed is actually very small, others have reported much bigger errors, especially with batteries (some Fogstar, for example) which don't accurately measure and integrate small currents. IIRC one poster had an accumulated 50% error in the reported SoC... 😉 

Haha I currently have sterling batteries (swapping these to the butty, and installing a fogstar), the BMS is terrible. The SoC reading is made up, and the balancing is basically non existent .I have never managed to get the cells to come back into balance, and I've had extended arguments with sterling to get them to replace the battery (and one which just stopped functioning entirely)

 

But yeah, worth doing to calibrate the smartshunt reading. I do this by setting my SoC setpoint to 101, and the smartshunt will declare them to be 100 when the tail current hits a certain value.

Edited March 10 by DShK

[cheesegas]

32 minutes ago, DShK said:

Haha I currently have sterling batteries (swapping these to the butty, and installing a fogstar), the BMS is terrible. 

 

But yeah, worth doing to calibrate the smartshunt reading. I do this by setting my SoC setpoint to 101, and the smartshunt will declare them to be 100 when the tail current hits a certain value.

Sterlings use a Daly BMS board inside, which is a similar price to the JiaBaida (JBD) one in the Fogstars and is equal on paper.

 

However, in practice, the Dalys seem to have a much higher failure rate and are terrible. Balancers seem to just not kick in sometimes, and as you've found out, the SOC is very inaccurate. JBD have massively improved the SOC readout with the firmware revision as of about a year ago, on mine it rarely deviates a few % from the Victron BMV. Older firmware versions however weren't as good, tending to prematurely reset to 100% under high current charging.