Battery‐Tipps
I know it is boring but, it is invaluable: spcqike's comments about 12V, 24V, 25V, 48V, 51V batteries and battery Lead vs LiFePo4 cells:
A single Lead cell has a nominal voltage of 2V, but can have a real voltage of 1.75V to 2.4V, depending on its charge state. That said,
- a 12V battery can have 10.5V to 14.4V (as it has 6 cells)
- a 24V battery has 12 cells and
- a 48V battery has 24 cells, giving a total of 42V-57.6V, depending on its charging state.
A single LiFePo4 cell has a nominal voltage of 3.2V, a minimal voltage of 3V and a maximum voltage of 3.4-3.45V.
- So you need either 4, 8 or 16 cells to get a 12/24/48V battery.
- In case of 16 cells you get a voltage range from 48V-55.2V with a nominal voltage of your mentioned 51.2V.
- So, a „51.2V“ lifepo has a lower (maximum) voltage than a 48V lead acid battery. And in terms of 12/24/48V, it’s a 48V battery. Not a 51.2V one.
The HOYMILES requires min 22V to start working (Anlaufspannung)
then it works until Voltage drops below 16V (Betriebsspannungsbereich)
The HOYMILES has poor performance at 24V The higher the production (above 500Watt), the worst is the performance of the Hoymiles at 24V. You can only notice this by monitoring the Amperes the 24V battery delivers.
Thus, the above leave the 48V as the only sensible option (for significant power generation e.g. above 300W) A very lengthy (german) discussion about this is here: Nach 6 Monaten Trial & Learnings - Meine 51,2V / 100Ah / HM-1500 onBattery Anlage
The shortest night has approx. 6,5 hours with no light, ca 22:30h - 5:00h.
The longest night has approx. 15,5 hours with no light, ca 17:00h - 8:30h.
You can calculate the "average" hours with no light: 6,5 hrs + 15,5 hrs = 22 hrs / 2 = 11 hours on average day
...which is of limited use. A better average is the monthly one:
Apparently you should not! Opinions differ on how much you should use. You should form your own opinion on this (and read the manual of your battery).
Nevertheless, all say that you should not drain your battery down to zero 0 % percent and that you should avoid charging it to 100% percent.
OpenDTUonBattery can master both situations (under and over charging).
Remember that your battery provides power to a HOYMILES, which also has an efficiency rating, let's say 96% percent.
Below table gives an example of a 4,8kWh (48V, 100Ah) battery that should not be drained below 15% and not charged above 95% It gives you the available battery capacity and shows how many Watt p. hour your Hoymiles would be able to deliver during the night hours:
Easy answer and difficult at the same time.
Let's suppose you have a base consumption (Grundlast) of 160W per hour at night:
Then, even during the long winter nights, you only need a 2,4kWh battery! Right?
Not quite!
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First, the above calculation is based on using 100% of the battery. But as we explained earlier, it is not recommended to use 100% of your battery's capacity. The examples above showed us discharging the battery up to 10% percent and charging it up to 95% percent thus, 85% percent of the total battery capacity is only being used. Below is the battery size needed if you only use 85% of the total battery capacity:
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Second, 160W per hour maybe the case during night time (when you are sleeping). During the long winter nights though, you will probably be at home watching TV or cooking during the some night hours so, the consumption will probably be much higher (at least for some hours).
Keep in mind, during the day you need solar power to cover your daily needs AND charge the battery.
Also, the charging process has some losses. If we take for example a 90% efficiency of the charging system, then the table below shows how much energy we need to send to the battery:
(The number of hours with sufficient light for your PV Panels is lower than the number of daylight hours shown on the table)