Is Lithium the best choices, advive needed

[Pete Shield]

Hi Folks,

I have a large system powering my house. 20 panels, 23 HOPPECK 2V batteries with a Studer Compact Charger Inverter with a Morning Star Tri Star solar converter TS M. The batteries are now 13 years old and kaput. Works during the day, nadda at night. So it is time to change. To replace 24 2V batteries is going to cost a fortune. Is there an easier way out, like a Lithium power wall? Where on earth do I start? Tips and advice sought. Thanks in advance Pete.

[Ampster]

I did a 42 kWh pack of LFP cells from China two years ago for about $125 per kWh. Today that price is higher but less than $200 per kWh including BMS. There are solutions as expensive as $1,000 per kWh with all sorts of guarantees.

If you got 13 years out of Lead Acid there and can deal with that chemistry there may not be any reason to change. I would guess Lead Acid is still less expensive, even considering the limitation of 50 percent usable capacity.

[Pete Shield]

Ok that needs a little translation for me, "$200 per kWh including BMS." what is BMS? The problem is that 24 2V batteries are around 12.000 euros, whereas a lithium solution would cost around half of that, but will the inverter and charger work with Lithium of would they need changing as well?

[Ampster]

A BMS is a Battery Management System. Lithium cells are more efficient but also can become unbalanced more easily so they need a BMS to monitor each cell to protect the pack.The high end examples are tyically self contained with an integral BMS and can be paralleled for greater capacity. I do not have much knowledge about the availability of products in Europe. I belong to another forum which has a number of members from Finland to South Africa and apparently options vary by country.

I use the cost per kWh as a metric instead of Ahrs because unless voltage and Ahrs are stated one has no way of comparing cost. . For example twenty four 2 volt batteries for 12,000 Euros does not tell me much about the capacity or the relative cost of that capacity. I do believe on a long term cost of energy that Lithium chemistry can be competitive with Lead Acid

As far as your inverter and other parts of your system being compatible depends on how much you can adjust their settings. Lithium charging is actually much simpler because no equalization cycles are needed and Float or trickle charging is not needed because there is very slow self discharge with Lithium. A simple Constant Current (Bulk) setting is all that is needed. No long Constant Voltage (Absorb) stages are needed which is one reason why Lithium is more efficient from a charging efficiency standpoint.
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[Pete Shield]

Great thanks for the clarification, each of the 2V batteries is 600 Anrs with a 2.23 V if that helps.

[Ampster]

Twenty three cells at 2.23 volts is close to the voltage of fifteen or sixteen LFP cells at 3.2 volts so your inverter and charging system should work. The good news with LFP is it can be charged below maximum cell voltage of 3.65 volts per cell and that extends their life. I charge mine to only 3.45 volts per cell. You just need to disable equalization and disable or set float to resting voltage of 3.33 volts per cell.

It is interesting to hear that prices in Europe for LFP are more competitive than Lead Acid. I see from comments on other forums that LFP is becoming increasingly popular. I presume you have good resources for LFP cells in your country?