{"id":77793,"date":"2023-08-07T10:44:47","date_gmt":"2023-08-07T01:14:47","guid":{"rendered":"https:\/\/www.solarquotes.com.au\/blog\/?p=77793"},"modified":"2023-08-07T10:44:47","modified_gmt":"2023-08-07T01:14:47","slug":"battery-degradation-spreadsheet","status":"publish","type":"post","link":"https:\/\/www.solarquotes.com.au\/blog\/battery-degradation-spreadsheet\/","title":{"rendered":"Track Your Powerwall’s Health with Our DIY Degradation Calculator"},"content":{"rendered":"

\"Battery<\/p>\n

Most of us know that home batteries inevitably degrade over time, but understanding how to quantify that degradation and take proactive steps remains a mystery.<\/p>\n

In this article, I’m excited to introduce you to a DIY battery health estimator spreadsheet. By the time you finish reading, you’ll have this handy tool at your fingertips and the know-how to assess your battery’s State of Health (SoH) and make informed decisions about its performance.<\/p>\n

What’s This Spreadsheet All About Then?<\/h2>\n

Recently, SolarQuotes blogger\/installer Anthony wrote two interesting articles about why and how a battery degrades<\/a>, and how to measure it using a monitoring app<\/a>. I recommend reading both of them as a starting point for this article.<\/p>\n

Anthony outlines a method to estimate a battery’s health by manually calculating and estimating its round-trip efficiency and SoH using selected data points over 24 hours. You can do the same thing with this spreadsheet by simply adding the data. The spreadsheet will do the rest.<\/p>\n

Note that this method provides a rough estimate only, and may not be as accurate as more sophisticated battery management systems or monitoring tools that use other metrics and specified test conditions.<\/p>\n

\"Anthony

Recommended reading – Anthony Bennett’s battery degradation articles.<\/p><\/div>\n

What Is Round-Trip Efficiency And SoH?<\/h2>\n

These are two of the metrics used to measure the condition and performance of a battery.<\/p>\n

Battery Round-Trip Efficiency:<\/strong> Represents the ratio of the energy output from the battery during discharge to the energy input during charging, accounting for losses in the process. A higher round-trip efficiency indicates that a battery can store and release energy more effectively.<\/p>\n

Battery State of Health (SoH):<\/strong> Indicates the current overall condition and health of a battery relative to its original capacity. It is expressed as a percentage and considers factors such as capacity degradation, internal resistance, and other wear-related effects.<\/p>\n

How To Use The DIY Battery Health Estimator<\/h2>\n

In a nutshell, to measure the SoH over 24 hours, there on only four parameters we need to know.<\/p>\n

    \n
  1. The SoC at the beginning and end of each charging cycle.<\/li>\n
  2. The SoC at the beginning and end of each discharging cycle.<\/li>\n
  3. The daily kWh used to charge the battery.<\/li>\n
  4. The daily kWh discharged from the battery.<\/li>\n<\/ol>\n

    Sounds simple enough, but the bad news is that not all monitoring apps will give you this information.<\/p>\n

    However, the Tesla Powerwall’s app will! The following example uses the Tesla monitoring app to estimate the round-trip efficiency and SoH of a Powerwall 2.<\/p>\n

    \"Tesla

    Tesla app main screen (left) – click on ‘Powerwall’ tab to open the Powerwall screen (right). Discharged and Charged kWh are shown numerically on top, by graph (middle), and by battery Charge Level by graph (bottom). Use the touch screen on the lower graph to obtain numerical percentages.<\/p><\/div>\n

    Steps:<\/h3>\n
      \n
    1. Download the spreadsheet from the link at the bottom of this page and open it up. All the data entry cells are marked with a red border. Enter your battery’s rated capacity into the first cell (C7).<\/li>\n
    2. Open the Tesla app on your phone and click on the ‘Powerwall’ tab.
      \nMake sure the tab on the top-right is set to ‘Day’.<\/li>\n
    3. Swipe the ‘Discharge\/Charge’ graph to the right, until you find a suitable day to measure. The charge level at the end of the day should match the start (%).<\/li>\n
    4. Note the kWh charged and kWh discharged for that day, then go back to the spreadsheet and enter those figures into cells G12 and G26 marked ‘Charged kWh’ and ‘Discharged kWh’.<\/li>\n<\/ol>\n
      \"Battery

      You must toggle between the spreadsheet and the Tesla app as you enter data. Easiest is to view the spreadsheet (left) on desktop, and Tesla app (right) on phone.<\/p><\/div>\n

      Charge Cycle<\/h3>\n
        \n
      1. \u00a0Go back to the Tesla app and look at the ‘Charge Level’ graph on the lower part of the screen.<\/li>\n
      2. Touch the screen at the left-hand side of the graph and note the ‘Charge Level’ at the start of the 24-hour period.<\/li>\n
      3. Go to the spreadsheet and write the number down in cell C16 marked ‘Charge Cycle\/s Over 24 Hours\/ Cycle No.1\/ Battery Level (Start).’<\/li>\n
      4. Go back to the Tesla app and place your finger on the touch screen to the right of your previous %. Locate the highest level the battery was then charged to in the same charging cycle and note the number.<\/li>\n
      5. Go back to the spreadsheet and enter the number into cell E16 marked ‘Charge Cycle\/s Over 24 Hours\/ Cycle No.1\/ Battery Level (End).’<\/li>\n<\/ol>\n

        Discharge Cycle<\/h3>\n
          \n
        1. Also write the same number (step 11) into cell C30 below in the ‘Discharge Cycle\/s Over 24 Hours\/ Cycle No.1\/ Battery Level (Start).’<\/li>\n
        2. Go back to the Tesla app and place your finger on the touch screen to the right of your previous %. Find the lowest percentage the battery was charged to in that discharging cycle and note the number.<\/li>\n
        3. Go back to the spreadsheet and enter the number into the cell E30 marked ‘Discharge Cycle\/s Over 24 Hours\/ Cycle No.1\/ Battery Level (End).’<\/li>\n<\/ol>\n
          \"Tesla

          Tesla app with red arrows showing charging and discharging cycle data points through 24 hours. From left to right – 20%, 43%, 20% 100%, 20%.<\/p><\/div>\n

          Additional Charge\/Discharge Cycles<\/h3>\n

          If there are more charging and discharging cycles during the 24 hours, continue the above method by moving sequentially right on the Tesla app Charge Level graph, then entering data into the spreadsheet ‘Cycle No.2’ cells for charging and discharging, and so on, until the end of the day. Most days will have two charging and two discharging cycles, however, it’s possible to have less or more. The spreadsheet has allowed for up to four of each.<\/p>\n

          After entering the data above, the Round-Trip Efficiency Estimate and Battery SoH Estimate will appear in the output cells (G44 and G54) below. Once you have these figures, cross-reference them with other days to ensure your data has been entered correctly. You should get a similar result. The next step might be to retrieve the data from the start of your battery’s life and compare.<\/p>\n

          Spreadsheet Calculations<\/h3>\n

          For those who like to dig a little deeper and find out how this spreadsheet works, I would suggest first reading Anthony’s article ‘Battery Degradation Part II: How To Measure It<\/a>‘. The following spreadsheet calculations are based on his methodology.<\/p>\n