Buying a ESS ( Energy Storage System) or Solar Storage Battery is an important part of Eco energy and the whole money saving is bundled into one. But there are a few things that most manufactures and retailers do not tell you.
Picking a battery that “meets your daily use” is not good advice, this is generally because off setting the solar production to the total would result in a smaller battery.
One of the key parts of the battery, and inverter, is its ability to run your home from your solar, or if you do not have solar installed then its energy trading. A battery (LFP) are rated for capacity, which you know as kwh, but they are also rated for the current, this may be more than what the battery should output if you intend to have a longer life from your battery.
It is common to have batteries made of 100ah cells or 200 and 280ah, While there are larger batteries available the low cost options have the same principles A 0.5c rate is 50% of the cell rating, 0.2c is 20%.
If your sold on the “Cycle life” then you really need to pay attention, as a 0.2c rate is the rate of current used in a lot of testing. So if you have a 100 or 200 ah cell, then your 6000 cycles will be based on a 20/40 amp discharge rate.
If we then look at the “power” that means 1024watts of power for a 100ah battery and 2kwh for your 200ah battery. So what is your load and your peak loads and how much current will you pull from the batteries?
Pulling power from the battery.
For the most part taking into consideration the “normal loads” and your “peak loads” you can use 2.5kw of battery power which will have a 0.5c rate (50amps) but you would not want to keep hitting this load often or your battery cycle life will lower.
The DOD ( Depth Of Discharge) also plays a role within the battery life cycles, in the above chart we can see how many cycles you can obtain from your battery based on the DOD at 0.5c. We would like a 6000 cycle battery pack, which equates to a life time of 16 years. 2000 cycles is around 5.4 years.
RenewSolar batteries (premium) have a reserve, this means that you will have around 15% reserve which results in a longer battery cycle life. By limiting the upper and lower discharges and charges it lowers the stress on the battery and this results in a longer life cycles battery and happy customers. The spec and settings are adjusted.
The more budget friendly battery packs are 100% or 90%, but may account for the full cyclic power.
An example of this may be the 280ah cells that have a real capacity of 306ah
Looking at our 280ah battery packs you would assume a 14.33kwh of usable power where as they would have 15.66kwh in either case, both packs (low and high) may be marketed as 15kwh battery packs.
HOW MUCH BATTERY STORAGE.
You should consider your total power used in a day, paying attention to high use days and ensure that your battery is around 50% bigger to reduce that DOD. It is likely that you would be targeting between 80 and 50% as there is not so much difference – 16 years vs 13 years.
The second key, is load sharing, buy adding more smaller batteries, you share the load between the battery packs this lowering the power draw (C rate) and extending the battery life cycles.
Here is a quick chart of inverter load draws.~
3kw 58 amps
5kw 97 amps
8kw 156 amps
12kw 234 amps
Taking the example above, if we have a 5kw inverter. we would want 2 100ah batteries to achieve a 0.5c or one 280ah battery pack.
A 100ah battery pack has 5.12kwh of power storage, you simple multiply the voltage (51.2) by the Ah which will give you the watt hours of power.
Do not forget…
Having a lot of batteries requires a good charger, a 50amp charge is suitable for most systems, this is 2.56kw of power, the more batteries you have the charge is divided between the batteries, this could mean that you will add to the charge time. If you have a higher power charger you can adjust the power to reduce charge times. but it is worth looking at the PV ( solar charger) current, and the AC charge current.
Also inverters can also be misleading. for example a 6000w inverter may provide 6kw ONLY where there is 3kw + from solar and 3kw from the battery, therefore during the night, the inverter may be limited to offer a peak output of just 3kw.
Your solar array should be sized to cover the recharging of the battery and your day time loads.
No responses yet