Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU

Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU for off grid and hybrid photovoltaic systems. How to calculate solar panel battery has many variables. A storage cell sizing calculation formula is therefore not very easy. As an experienced energy project manager, I  have made a global calculation where I define the variables what is inportant.

Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU

If you search the internet for Solar energy battery, you will find many good hits. To store electricity in cells for later use is an old use. In recent years there have been many developments that have contributed to it being financially attractive. Now remains, to make the right choice.

Let's start with the different type of storage cells that are useful for solar energy saving. There are two kinds of power storage facilities. Namely high and low voltage. High voltage is more than 100 volts. Low voltage is 12, 24, 36 and 48 volts.

Don't forget, this is just an example, one from many! There are no affiliate links on this website, and I'm fully independent

High voltage solar battery:
The RESU batteries from LG Chem are equipped with JH3 Li-Ion cells. This cell technology ensures good/strong performance and a compact design. This makes the battery easy to assemble and suitable for outdoor and indoor applications. The 400V RESU models from LG Chem are compatible with SMA inverters. The price is about €5.357,00 euro. Useful storage capacity is 9,3 kW. More information here.

This high voltage storage comes of course with a Battery management system. Also called "BMS". You still need a solar inverter to charge it, and a DC/AC inverter to connect to the grid. A hybrid inverter is the most recommended.

Wikipedia is explaining what a BMS is:

Battery management system

From Wikipedia, the free encyclopedia

A battery management system(BMS) is any electronic system that manages a rechargeable battery(cellor battery pack), such as by protecting the battery from operating outside its Safe Operating Area, monitoring its state, calculating secondary data, reporting that data, controlling its environment, authenticating it and / or balancingit.[1]
A battery pack built together with a battery management system with an external communication data busis a smart battery pack. A smart battery pack must be charged by a smart battery charger.

The batteries from LG Chem, the RESU10 has only a BMS system. You need a hybrid solar inverter to save the energy from your panels into this storage facility.

Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU

The Tesla Powerwall 2.0 is another example of a high voltage photovoltaic storage:
It is an AC-coupled battery system, including a 13.2kWh NMC lithium-ion pack and inbuilt inverter. A very good example for our solar power battery pack calculation.
The inverter is included with the Powerwall 2.0, which has a price tag of $ 5,500. He can store 13.5 kWh and supply 5 kWh of constant electricity. This is still being boosted to a maximum of 7 kWh. The price range is a little higher the the LG RESU10. But a DC/AC inverter is included! That meens, if you buy the Powerwall 2.0, its just a matther of giving it a place in your home. Connect it with youre electra system, and there you go! You still need a solar inverter to charge this battery! Here are the specs for the Tesla powerwall 2.0.

If you surf the internet with
"Solar energy storage",
you will find many more examples on the market.

Both examples give a lot of information for calculating the cost per kW, to store the electricity that is produced by the solar panels.


LG Chem RESU

Usable Energy Capacity 8.8kWh
Real Power, max continuous 5 kWh
Price is about €5.357,00 euro
long life (60% SOH after >6,000 cycles @ 90% DOD)
Acording https://batterytestcentre.com.au/results/lg-chem-resu/

LG Chem recommends 3.3kW for maximizing battery lifetime.

Tesla Powerwall 2.0

Usable Energy Capacity 13.5 kWh
Real Power, max continuous 5 kWh
Price is about € 6.880 euro

Tesla recommends 3.3kW for maximizing battery lifetime.


Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU

Tesla is a very strong marketing promotor, and nowhere is to find how many cycles a powerwall 2 does. For calculating the kW price, you need to no the battery life in cycles. Of course inside the optimal conditions given for that specific type! There is a workaurond. The garantie from the powerwall 2 gives us 10 years.

The best use of photovoltaic storage has the highest efficiency if it is being charged during the day. When the sun goes down, the cells are discharged. We apply this principle to the Storage cells from Tesla. Warantie for 10 years means 365 days x 10 years = 3650 cycles. For the LG we have to add a DC to AC inverter. LG recomment SMA. For a maximale life time we need a 3.3kW inverter from SMA. The most suitible is then the Sunny Island 4.4M-12 for an averige price off €2.190,00 euro. The LG wil have a price ( €5.357,00 + €2.190,00 ) = €7.547,00

The calculation of cost per kW:

  1. LG Chem RESU
    The totaal storage is 8.8kW multiply with the cycles ( 6000 ) = 52800 kW.
    Divide the price in euros Cents with total of previous
    754700 euro Cent / 52800 = 14,29 cent the kW.
  2. Tesla Powerwall 2
    The totaal storage is 13.5kW multiply with the cycles ( 3650 ) = 49275 kW.
    Divide the price in euros Cents with total of previous.
    688000 euro Cent / 49275 = 13,96 cent the kW.

This Solar power battery pack calculation shows that the price per kW is almost the same. But ultimately that is not the case. The powerwall 2 has a shorter lifetime than the LG. After all, it has les cycles.

If we apply the same principle that we applied to tesla storage to the LG. Charge during the day and discharge during the night. The LG (6000/3650 = 1.64) has a 164% longer life. This means that the cost per kW of the powerwall 2 must be multiplied by a factor of 1.64 (164%). The final cost price will then be 13.96 cents the kW multiplied by 1.64 = 22.98 cents per kW.

Solar power battery pack calculation - Tesla Powerwall 2.0 - LG Chem RESU

Changes in the kW price can be caused by:

  1. Different DC/AC inverter for the LG. For example an SMA hybrid inverter.
  2. The efficiency of the LG Chem RESU10 has dropped to 60% after 6000 cycles.
  3. Tesla now has a Powerwall 2 version without DC / AC inverter. For use with a hybrid solar inverter.
  4. Other discharge cycles than within 24 hours of charging and discharging.
  5. Prices will go down in the future.

The Solar power battery pack calculation is not a final calculation. But it gives a good indication of price efficiency for value.

More accurate calculation for your private energy production?

All prices and data are found on the internet. They are not directly from the manufacturers of these brands.