I have a 5kw solar panale system on my garage roof. 21 245w panels.. 5kw inverter. South faceing. During pring, summer and autumn I produce more during the day then I use. I am at work most of the productive time anyway, but partly compensate for that having
my water heater on timer.
I got hold of the batteries from a citroen zero. It was in an accident, actually minor damage, but was not economical to fix apparently. 2 years old. It is a 14,5 kw lithium battery. 80 cells. In the car all 80 cells are connected in series for around 300v (80 x 3,7v). The picture with meter saying 160v is only half the series. It cam almost fully charged at 4,0v. First I had to disassemble the battery. I consist of 10 packages of 2 modules, each with 4 cells. Then I opened each module and rotated 2 of the cells so everyone has the same polarity on same side. In 6 of the modules 2 are one side and the other 2 the opposite. This is so I can easily connect 6 and 6 together in parallel. Then I connected 13 in series. total 78 cells used (2 as spare). This will give me approx 48 (54,6-40v) and 250ah.
I will only charge it to 53,3v (4,1 per cell),because it is charged this way in the car. This will hopefully prolong battery life. The battery is conntrolled by a 30a BMS (to small for the battery since balancing currint is only 40ma), but hopefully the bank is well balanced.I have connected a 40amp fuse. the charger is 25ah. I can adjust voltage and has set it at 53,3v. I could increase voltage closer to 54,6v for faster charging and higher capacity.
I will charge the batteries by day. I use a timer to control this. It is now set to start charging at 10 am to approximately 4pm. I will adust this as summer approach. The inverter(s) are set to start discharge the battery fro around 5pm to 8am. I have set it this way due to shading on my garage this early in spring. I use timers so i wont need an expensive inverter. Like the synnyboy battery inverters ($$$$). I have 2 small grid tied inverters that are meant to be used with batteries (locked at 75% load). They will produce 500w and 400w. This way I can adjust the charge and discharge rate during summer. I will have to adjust the timers and 1 or 2 inverters during the year, to compensate for more or less sun. max 900w and minimum 400w. Now, when I have the 500W inverter on during night for approximately 14h I will save maximum 7kwh, but probably less since it will not cover higher load then 500w. I use approximately 24kwh per day, or 1kw per hour. And probably a base load of 800w with shorter peaks when water boiler and other high power utilities are on. But hope to be able to use more of my own power.
Of course there are limitations with this setup, but it is easy to build and relatively cheap. What remain is tidying up the cables
(dont know it the pictures work. Usless tread without pictures )
(some of the pictures are rotated, I am not able to correct that. Sorry)