I am planning a 24V system with 1000 watts of
solar, a Midnite
Classic 150
MPPT solar controller, and a 24V input Magnum 4000 watt hybrid
inverter.
Those are the main components. I also need 12V to
power various items such as
water heater controls, some
electronics,
led lights, and the furnace fan.
I initially was going to go with just lead acid, but am entertaining the idea of
LiFePO4. I want to have at least 3.5kwh of useable
battery capacity and so was considering four Lifeline 6V 300ah
AGM (so they can mount on their side in the space available).
I am not comfortable right now with the state of
LiFePO4 to sink $3000 into it as the main
battery bank, but I am considering using the LiFePO4 as the 12V house battery so I can
experiment with it. If I have great results, I would eventually switch out the AGMs for 8 big LiFePO4 cells.
The
current plan is complicated, but I think it has some potential. I would utilize the high
current from the solar during the peak sun hours to bulk charge the lead acid, then when they needed to be in absorption charge state, I would switch to
charging the LiFePO4 house battery. In this way I would be able to utilize the remaining peak sun amps instead of letting them go to waste.
I am thinking of programming a microcontroller (just an Atmel 8 bit) to
monitor the four 3.2V 100 ah LiFePO4 cells of the house battery and also control the
charger for them, which would be powered off of the main house batteries/Midnite
MPPT solar
charger. I may need a
sensor to determine the level of insolation available at the
solar panels and I need to
research what the Midnite controller would do if it was
charging the 24V lead acid in absorption and suddenly a 15 amp load on those
batteries kicked on (the 24V to 14V LiFePO4 charger).
Even though this all sounds complicated, it does sound doable, and doesn't really use that many more
parts than other methods since I need 12V and you can't directly tap from two of the cells in the 24V lead acid pack without causing imbalance (unless you use special devices). It may be a fun way to dip one's toe into LiFePO4 without breaking the bank, as a 12V 100AH pack should cost me under $600 from CALB.
Opinions?