OK. It looks like you really wanted to use the "Names" function to describe what is IN the cell for clarity, not use the contents of the cell for a calculation.

Yes, that would make it easier to see what the results of the calculation would be. You've "named" the contents of cell A4 as "power_consumption" and A5 as "time"; then defined a calculation as =power_consumption*time. The result is the same as =A4*A5; but it's in words instead of cell references.

However, be aware of the scope of the Name function. You still need to track the sheet the info is on, since you're working on separate sheets. From the Excel help file on Names:

The scope of a name
All names have a scope, either to a specific worksheet (also called the local worksheet level) or to the entire workbook (also called the global workbook level). The scope of a name is the location within which the name is recognized without qualification. For example:

If you have defined a name, such as Budget_FY08, and its scope is Sheet1, that name, if not qualified, is recognized only in Sheet1, but not in other sheets without qualification.
To use a local worksheet name in another worksheet, you can qualify it by preceding it with the worksheet name, as the following example shows:

Sheet1!Budget_FY08