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
Notes:
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
Notes:
- 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. https://diysolarforum.com/resources/lcec-household-wattage-worksheet.57/
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
Calculated:
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.
The nameplate wattage will always be the max wattage. The actual wattage will always be less. In the case of a laptop, it gets even more complicated. The load for a laptop is going to vary based on a combination of the state of charge of the battery along with the activity on the computer. For a laptop, the actual usage for most people will almost always be a lot less than the name-plate number.
Almost without exception, the Kill-a-watt measured value will be more accurate (and less) than the name-plate value.