Ronski's Solar & battery DIY build with whole house backup

The battery heating system works, as I'm not currently force discharging the batteries don't get their late afternoon warm up, so they are dropping to 8°c and the heaters turn on and warm them up to 12°c

The first big hump is when the charging kicks in at 2am, then it starts dropping at 5am, where the green and orange lines start rising again is the heating system warming the batteries up. Temperature outside at the moment is 0°c, and the garage is 3°c

Temperatures-heating.jpg
 
I tend not to trust the Victron temp unit if it's the one bolted to the battery terminal, as the current going through =heat and false true battery temp.
Nearly got caught out Thu/Fri night Victron showing 4C....VK BMS internal sensors T1/T2 showing -1.6/-1.4C, BMS shut down charging @3C.

My own fault I had removed the fuse from the Google nest thermostat during the summer, no heat came on in the camper @3C.
-6C here Friday first light.
 
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They are not bolted to the terminals, they are fitted to the side of the cells, located between the bar which holds the pack together and the cells, the only source of heat there is the cells themselves.

They both measure a few degrees lower than the BMS temperature sensors, so should be plenty of safety margin.

I also calibrated the sensors - beaker full of water and ice cubes, left it to stabilise then set to zero.
 
Ron-ski said:
They are not bolted to the terminals, they are fitted to the side of the cells, located between the bar which holds the pack together and the cells, the only source of heat there is the cells themselves.

They both measure a few degrees lower than the BMS temperature sensors, so should be plenty of safety margin.

I also calibrated the sensors - beaker full of water and ice cubes, left it to stabilise then set to zero.
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Prob my setup in the Van, battery is well wrapped up, the terminals are covered under a blanket.
When I really notice it is when charging up in the winter at 30+ amps, huge difference between the terminal Victron sensor and the JK BMS one.

I'll move the Victron sensor when the weather warms up a bit!.
 
Ron-ski said:
The battery heating system works, as I'm not currently force discharging the batteries don't get their late afternoon warm up, so they are dropping to 8°c and the heaters turn on and warm them up to 12°c

The first big hump is when the charging kicks in at 2am, then it starts dropping at 5am, where the green and orange lines start rising again is the heating system warming the batteries up. Temperature outside at the moment is 0°c, and the garage is 3°c
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What sort of charge rate are you getting when they're sub 11C at the start? My insulation is working quite well. Despite the battery temp not dropping much below 13-15C throughout this cold spell they still charge much more slowly. I had the first instance of them not charging to full this morning as they started at 1.4kW, climbed to 2.5kW after half an hour and then the full 5kW in the last 45 minutes or so. It still made 88% though, so not too bad considering they're in the loft and its currently 1C up there!
 
@reef I'm in total control, so its whatever I want, hopefully I'm not damaging them! I charge them between 2am and 5am at 130A, as there are two batteries that's split in half, so each battery is receiving about 65A, or 0.23C which is battery speak for the charge current related to the Ah capacity of the battery. The manufacture of the cells states "The maximum charge current of the battery does not exceed 1C under 0℃～45℃", I think under should mean between. So I should be perfectly safe charging the cell's as I am. Below freezing they should not be charged, or only with very low currents.

www.evlithium.com

EVE LF280K 3.2V 280Ah LiFePO4 Prismatic Battery Cell

Factory sale grade A prismatic cells lifepo4 3.2v 280ah battery for energy storage and power lifepo4 battery
www.evlithium.com

Last night the temperature in the garage got down to 2°c.

PS. There's some interesting info at https://community.victronenergy.com...w-charging-lifepo4-when-freezing-weather.html


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Ron-ski said:
@reef I'm in total control, so its whatever I want, hopefully I'm not damaging them! I charge them between 2am and 5am at 130A, as there are two batteries that's split in half, so each battery is receiving about 65A, or 0.23C which is battery speak for the charge current related to the Ah capacity of the battery. The manufacture of the cells states "The maximum charge current of the battery does not exceed 1C under 0℃～45℃", I think under should mean between. So I should be perfectly safe charging the cell's as I am. Below freezing they should not be charged, or only with very low currents.

www.evlithium.com

EVE LF280K 3.2V 280Ah LiFePO4 Prismatic Battery Cell

Factory sale grade A prismatic cells lifepo4 3.2v 280ah battery for energy storage and power lifepo4 battery
www.evlithium.com

Last night the temperature in the garage got down to 2°c.

PS. There's some interesting info at https://community.victronenergy.com...w-charging-lifepo4-when-freezing-weather.html


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I don't think you'll damage them. What I've found is if they are charged quickly when cold they just accept less by the time they get to 100% SOC. This morning at the slower charge rate they took 7.2kWh for a 61% increase in SOC. At that rate 100% would be 11.8kWh, so exactly what the 'usable' amount is out of the 12.25kW capacity. The other day they belted through at 5kW the whole time at about 16C and only took 9.6kWh for a 90% increase in SOC. I've seen the reverse in summer at about 30C battery temp; I can get slightly more than the stated capacity out of them.
 
I'm pretty sure I'm doing things correctly, the BMS is set to stop charging at 4℃ and start again at 6℃, battery heating kicks in at 8℃ and stops at 12℃, so hopefully all will be OK. Only issue might be if we get very cold weather, and the heating can't keep up, just means charging will stop, or more to the point won't start, once charging they warm up pretty quickly.
 
My batteries currently down to 12%, so I thought I'd look at home assistant and see how much I'd discharged today, it shows 23.12kWh. This is a calculated figure.

Now if we divide that by 88, then times it by 100, it gives me 26.27kWh, which is not that far off my maximum battery capacity of 29 kWh. Considering I don't use the full cell voltage range, that's pretty good.

Edit. Actually, that's not quite right, there was some discharged between midnight and 2am, then the battery was only charged to 87% by 5am, so usable capacity is greater than above.
 
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Ron-ski said:
My batteries currently down to 12%, so I thought I'd look at home assistant and see how much I'd discharged today, it shows 23.12kWh. This is a calculated figure.

Now if we divide that by 88, then times it by 100, it gives me 26.27kWh, which is not that far off my maximum battery capacity of 29 kWh. Considering I don't use the full cell voltage range, that's pretty good.

Edit. Actually, that's not quite right, there was some discharged between midnight and 2am, then the battery was only charged to 87% by 5am, so usable capacity is greater than above.
Click to expand...

Great, always nice when you get more than expected. What are the temps like in their location at the moment, any need for the heater to be working?
 
Before 2am the battery discharged 1.48 kWh.
2am to 5am it charged to 87%
The SOC never increased through out the day.
By 22:51 it reached 10% and stopped discharging - I reserve some in case of a power cut.
Between 5am and 22:51 it discharged 21.99 kWh
I used 77%, so if I divide 21.99 by 77 and times by 100 I get 28.55kWh capacity.


Heatings been on four times this winter, its set to come on when a battery reaches 8c and go off at 12c

Last-30-days-Temps.jpg



Heating relays

Heating.jpg
 
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Happy birthday Battery A, its just turned 1 year old :D

Cycle count is 275, so an average of 0.75 a day, not bad considering how hard I push my batteries, although battery B is at 0.83 a day which is probably more representative, as battery A had an easy life to start with. Battery B is 259 days old.

Battery-A-1-Yr-old.jpg
 
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Getting very close on my plan for my third solar install :D

I've just popped round to our local City Plumbing, to see if I can get any discount off the web prices, got a little bit off, but minimal really, but every bit helps.

For my NW roof array of 12 panels I've got these short listed.

LONGi Solar Hi-MO 6 435WP Black Frame PV Module LR5-54HTH-435M

LONGi new generation HPBC cell technology opens a new chapter in the mass production of high-efficiency cells and continues to lead the reform of the industry.The efficiency of LONGi HPBC cells exceeds 25.0%.The efficiency of the PRO version HPBC cells exceeds 25.3%.
www.cityplumbing.co.uk www.cityplumbing.co.uk

LONGi Solar Hi-MO 5m 410WP Full Black PV Module LR5-54HPB-410M

LONGi's high-efficiency PV modules are widely used all over the world, from alpine grasslands to desert wastelands, and from ponds and vegetable beds to household dwellings. LONGi's ultra-high-value PV module products continue to benefit customers and local economy with its advantages of higher...
www.cityplumbing.co.uk www.cityplumbing.co.uk

For the extra £130 I may just go for the 435w panels, they are a newer series, and are a bit better on efficiency and degradation over time.

For the three on the SE wall I'm looking at these, they work out quite expensive per panel including delivery, but I want a physically larger panel (2063mm x 1134mm) as it would look better, would prefer all black, but can't seem to find all black in that size.

JA Solar 525W Mono PERC Half-Cell MBB LB Silver Frame MC4

High stock levels available on all panels, please contact us via live chat for up-to-date stock before purchase, as stock levels are subject to change. Alternatively, you can email or call us. Part No: JAM60D-42-525-LB-SF Panels - Double Glass Bifacial Rating: 525W Efficiency: 22.4% Width...
www.powerland.co.uk www.powerland.co.uk

This would give an additional 6.795 kWp of solar, and make a total of 15.535 kWp, and should give an estimated 62% more generation.

Figures for the existing system below, are actual figures for the last 12 months, at some point I'll have to see what PVGIS thinks my existing panels should be producing.

Additional-Panels-1.jpg
 
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