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My solar-powered weblog is now on Lithium Iron Phosphate

My solar-powered weblog is now on Lithium Iron Phosphate

2023-05-19 07:07:25

In my last blog post I mentioned how a small photo voltaic venture – to energy this weblog on a Raspberry Pi – escalated right into a full-blown off-grid photo voltaic setup, giant sufficient to energy the pc I take advantage of in the mean time to put in writing this replace. On this replace, I wish to talk about my battery improve.

For me, the large lead acid battery (as pictured under) was all the time a comparatively low-cost non permanent resolution.

solar contraption
A 12 Volt 230 Ah lead-acid battery

Lead-acid batteries are usually not very best for photo voltaic setups for multiple reasons, however essentially the most problematic challenge is the sluggish charging velocity. I solely have a couple of hours of direct daylight per day on account of my specific scenario and the battery simply couldn’t take in daylight quick sufficient.

For the final 5-7 years, the go-to battery chemistry for photo voltaic is LiFePO4 or lithium iron phosphate as a substitute for lead-acid batteries. This battery chemistry will not be as energy-dense as Lithium-ion, however the upside is value and security. Particularly, LiFePO4 cells aren’t as risky as Lithium-ion cells. They might begin outgassing, however they do not begin a hearth.

Extra importantly for my scenario: LiFePO4 batteries can cost and discharge at a lot higer charges than lead-acid batteries. It is attainable to cost LiFePO4 cells with a C-rate of 1! Which means if a battery is rated for 100Ah (Ampere-hours) you may cost with a present of 100 Ampere! My photo voltaic setup won’t ever come even near that quantity, however not less than it is good to have some headroom.

lithium cell
A single 3.2 volt 230Ah Lithium Iron Phosphate prismatic cell

I did ponder shopping for an off-the-shelf battery however I made a decision towards it. You haven’t any management over the model and high quality of the LiFePO4 cells they use and extra importantly, what is the enjoyable in that anyway?

So I made a decision to order my very own cells and construct my very own 12 Volt LiFePO4 battery consisting of 4 cells in collection (4S) as my current system can be based mostly on 12 Volt. Different widespread configurations are 8S (24 Volt) and 16S (48 Volt).

box with 4 cells

It turned out that I may simply purchase my cells regionally in The Netherlands (as an alternative of China) due to a company that makes a speciality of batteries (no affiliate). As the value was proper, I purchased successfully 3 KWh for simply shy of 500 Euros.

I made a decision to purchase B-grade cells as these are cheaper than A(utomotive)-grade cells. I may need gone for A-grade cells as to not danger something if I’d construct a extra critical battery financial institution for my complete house. But lots of people report no important variations between A-grade and B-grade LiFePO4 cells for photo voltaic battery banks so in the long run, it is all about your specific apetite for danger.

Simply shopping for cells and placing them in collection (in my case 4S) will not be sufficient, a BMS or battery administration system is required, which you place in collection with the battery on the damaging terminal. I ordered a 100A Daly BMS from China which works effective. I am even ready to make use of Python to speak with the Daly BMS over bluetooth to extract knowledge (voltages, present, State of Cost and so forth).

Daly BMS

The BMS is important as a result of it protects the cells towards deep discharge and overcharging. As well as, the BMS tries to maintain the voltage of the cells as equal as attainable, which is known as ‘balancing’. Charging stops completely when simply one of many cells attain their most voltage. If different cells have a a lot decrease voltage, it signifies that they will nonetheless be charged however the one cell with the excessive voltage is obstructing them from doing so. That is why cell balancing is important if you wish to use as a lot of the capability as attainable.

The Daly BMS is sort of dangerous at cell balancing so I’ve ordered a separate cell balancer for $18 to enhance cell balancing (but to be put in).

my battery build

ikea box

Ikea sells a Kuggis 32cmx32cmx32cm storage field that appears to be good for my small battery. Because it has two holes on the perimeters, I simply routed the constructive and damaging cables by them.

Now that I’ve put this battery in place I’ve seen an enormous enchancment concerning photo voltaic cost efficiency.

Grafana Chart

I’ve really probably created a brand new drawback: my photo voltaic cost controller can solely deal with about 400 Watts of solar energy at 12V and my setup is sort of near reaching this output. I’ll have undersized my photo voltaic cost controller and it has come again to chunk me. For now, I’ll simply observe: if that peak of 400 Watts is barely reached for a quick time – as it’s proper now – I do not suppose I’ll improve my photo voltaic cost controller as that might not be value it.

As we’re nonetheless in Might, my greatest yield is 1.2 KWh per day. Though that is paltry as in comparison with common residential photo voltaic setups, that 1.2 KWh is greater than a 3rd of my battery capability and may run my laptop setup for 10 hours, so for me it is ok.

See Also

It is humorous to me that each one of this began out with only a 60 Watt photo voltaic panel, a 20 Euro photo voltaic cost controller (non MPPT) and some 12V 7Ah lead acid gel batteries in parallel.

I believe it is past superb you can now construct a 15KWh battery financial institution full with BMS for lower than €3000. For that amount of cash, you may’t come even near this type of capability.

Perhaps my battery construct might encourage you to discover constructing your personal battery. LiFePO4 cells are available in an entire vary of capacities, I’ve seen small 22Ah cells or big 304Ah cells so you may choose one thing that matches your want and funds.

If you happen to’re in search of extra data: there are fairly a couple of Youtubers that specialize in constructing giant battery banks (48 Volt, 300Ah, ~15KWh) to energy their houses and garages.

Though Will Prowse reviewed LiFePO4 cells up to now, he at the moment focusses totally on off-the-shelf merchandise, like “rack-mount” batteries and inverter/chargers.

I additionally just like the off-grid-garage channel quite a bit, the channel as examined and explored fairly a couple of merchandise.

Harrold Halewijn (Dutch) additionally has fairly a couple of movies about photo voltaic setups on the whole and photo voltaic battery setups. He is actually into automation, together with versatile (next-day) vitality costs.

Additionally in Dutch, a cool article about some individuals constructing their very own large-scale house storage batteries (15KWh+)

One other Dutch individual construct a solar power factory with a battery capability of 128 KWh for skilled vitality manufacturing. Truely superb.

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