System Energy Audit and Sizing Spread Sheet

System Energy Audit and Sizing Spread Sheet 2021-01-29

To get the spreadsheet, click on the orange
button at the top of this page.

This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;)

  • There is now a tab for stationary systems (Only AC Loads) and a tab for Mobile (AC & DC loads)
  • Be sure to look at the "Sample" tab in the workbook.
  • One of the best uses of the sheet is to help you identify where to reduce/conserve. (Energy not used is the cheapest)
  • To get the best sizing, use measured values of wattage for the load calculations. If you use the values shown on the back of the device, it will almost always be higher than actual. The higher-than-actual number then gets fed into the system sizing and the difference can get amplified.
    Note: @Brendan Wood posted a resource with 'typical' wattage/power usage for many different appliances.
    If you don't have any other numbers, you can use these to get a 1st approximation of your projected usage.
  • Figuring out hours of use to put in the spreadsheet:
For things like lights that you manually turn on and off, it is usually good enough to just watch what you do for a couple days to make a reasonable estimate.​
For things like refrigerators that turn on and off by themselves, it is handy to put a Kill-a-watt on it and measure the watt-hours consumed over a set period of time. From that it is possible to calculate the daily usage and the time on per day. Here is an example with random numbers:​
Measured with Kill-a-watt
Watts used while on: 6W​
Watt-hours over a 6 hour period: 18Whr​
Average Watt-hours per hour = 18Whr/6hr = 3Whr/hr​
Watt-hours per day = 3Whr/hr * 24 Hr/day = 72Whr/day​
Time on per day = (72Whr/day)/6W = 12 hrs/day​
Edited to clarify run-time math​
Edited to include cross reference with other resources.​
Updated spreadsheet to handle surge wattage​
Updated the resource to a download file rather than google sheets.​
Corrected Error in "Required Total daily Solar output (Sunny)"​
Corrected Error in " Full Surge load Inverter size"​
The forum now supports Xcell files so it is now a direct download from forum archive.​
1/28/2021 - Released Reb B.​
- Added a tab for mobile systems that have both AC and DC loads​
- Cleaned up Format a bit.​
Note: This resource is a duplicate of the resource of the same name in the 'Beginners' resource Section. This resource is linked to the same download file.
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Very nice and useful spreadsheet
This has been so tremendously helpful for planning my system, thank you! Curious about why "# of days to recharge while under load" is a user input. How am I determining the answer to this question? Shouldn't this spreadsheet be able to tell me that?
>Curious about why "# of days to recharge while under load" is a user input.
> How am I determining the answer to this question?
> Shouldn't this spreadsheet be able to tell me that?
It is asking how quickly the user wants the system to recharge from fully drained and then uses it as an input to determine solar panel sizing. Some users will want just one or two days, others might be willing to wait more days to fully charge.
The alternative is to ask the user for Solar Panel size and then calculate the number of days it will take to recharge, but that would kinda defeat one of the purposes of the spreadsheet.
Very thorough, incredibly detailed, and you spent a lot of time. Might be easier to just plug in information from Electric Bill?
very helpful
Firstly, this spreadsheet is gold, thank you so much for this resource.

Secondly, I'm a bit confused. Shouldn't the "Required Total daily Solar output (Sunny)" - cell L19 calculation which looks at the "# sunny days to recharge (from ZERO) while under load" - cell L18 (as you mention in your definitions, it is the number of sunny days required to recharge the battery from ZERO (or in this case assuming from max discharge) while you are still using power) be referencing the "Battery capacity" - L14 x "max. discharge" - L11 as well as the "Daily Storage Requirement" - cell L10)? You are only considering daily requirements and not replenishing the entire battery in your current formula.
You have: L19 = L10+ L10/L18
Should it not be: L19 = L10+ (L14*L11)/L18

If I'm wrong I may need an explanation why you are not referencing the battery's capacity in a. calculation to full recharge, where a recharge is directly dependent on how much of the battery has been depleted on not only on your daily usage.

Good catch!!! I fixed it yesterday. Sorry it took so long
Awesome..Thank you very helpful.
Brilliant, thank you!
Thanks for making this available, great resource.