PV-Battery question

Hi there!
Please help me to understand the following:
I have a question regarding Energy storage - Detailed PV-Battery - Distributed - Residential Owner - Battery - Battery Cell and System. 

I have a 4 kW SES installed in my company, which is installed for the company's own needs (lighting and sockets for low-power consumers). The system has an lead-acid traction battery (such as those used in electric forklifts) for storing electrical energy. The battery has a total capacity of 400Ah, 24kW of power and a voltage of 48V. The battery consists of 24pcs ‘cans/cells’, voltage 1 = 2.2≈2V, so 24pcs*2V=48V.

I am trying to model my own station with SAM, but I am getting something wrong in Computed Properties or I am doing something wrong.
What is unclear to me is the final numbers in the Total number of cells parameters, which gets a value of 29,400 and Strings in parralel, which is 1,225.

 

I will add a .sam file to make it more clear what I mean. I hope that you will be able to help me. Thanks!

Hi Mykhailo,

The system you describe has a bank capacity of 400 Ah * 48 V = 19,200 Wh, or 19.2 kWh, and a bank power of 24 kW. If the system has 24 batteries, then each battery has a capacity of 400 Ah / 4 batteries = 16.67 Ah/battery.

If you assume a nominal cell voltage of 2 Vdc, you should set the following inputs:

Desired bank power = 24 kW
Desired bank capacity = 19.2 kWh
Desired bank voltage = 48 Vdc
Cell nominal voltage = 2 Vdc
Cell capacity = 16.67 Ah

That results in a battery bank with 24 cells in series (for a 48 Vdc bank voltage), and 24 strings in parallel (for 19.2 kWh bank capacity).

This configuration defines a "cell" as the smallest unit in the battery: Each "string" is a forklift battery consisting of 24 cells. You could also define a "cell" as a 48 V battery by changing the cell nominal voltage to 48 Vdc.

Best regards,
Paul.



 

Hello Paul,
Thank you for your reply.

Indeed, if Cell nominal voltage = 2 Vdc, the simulation works and runs without errors during the download.

I decided that it is still more suitable for me when Cell nominal voltage = 48 Vdc, that is, as you said, the battery can be defined as a ‘cell’. In this case I get exactly the numbers I wanted to see, but in simulation I get an error which I can only clear by changing the parameter from 48 Vdc back to 2 Vdc

Error:

 

Hi Mykhailo,

The voltage table (under "Battery Voltage" on the Battery Cell and System page) for the default lead acid battery type is based on a 2 Vdc cell voltage, so it would probably be best to set the cell nominal voltage to 2 Vdc and recognize that a "string" represent a single battery. Otherwise you would have to modify the voltage table.

I apologize for suggesting that changing the cell nominal voltage to 48 V would work.

Best regards,
Paul.

Hi Paul,
Thank you so much for your reply and help!

Hello Paul,I wanted to make an inquiry regarding an analysis of a commercial "Merchant Plant", in which I set up a photovoltaic system with batteries, loading hourly data for the next 25 years and expecting a generation result, a correct dispatch ("automatic"), and also cash flow. However, I don't understand why it stops detecting the capacity and by year 14 it stops accounting for the revenues as shown in the image.

Thanks in advance!