PV Watts Spreadsheet

Energy Generated

We want to find the overall energy generated throughout the year. However, the PV Watts hourly data has the DC Array Output in watts and the AC System Output in watts.

To use these to calculate the energy we need to use a Reimann sum. That is, we sum up all of the rectangles in the output power graph. Each of these rectangles is one hour wide and some number of watts tall. The area of each rectangle is in units of watt-hours.

Summing all of these rectangles estimates the hourly energy output.

Monthly Sums

We can use a pivot table to sum the montly energy and compare against what PV Watts generates.

Value of Energy

The rate of compensation by the utility for solar power generated and sold to the grid can vary by the time of day and year. Using if-then logic, we can assign a different price based on the time of day, and multiply the energy generated in that hour by the price to get the value of the electricity.

If we have a simple peak and off-peak rate structure, we can check if the energy was produced within the peak time by using the hour of day. We can then multiply this.

Checklist

  • generate time series in PVWatts
  • upload time series to spreadsheet
  • compute total energy using Riemann sum
  • write time of use logic using if
  • implement time of use logic to calculate value of solar

If-Then-Else

This is a common logic structure in computer programming.

If something meets a certain condition, then the computer takes an action.

If it does not meet that condition (else), the computer takes and alternate action.

You may have seen something like this in a programming class.

if a > b
    print a
else
    print b

In spreadsheets, this is written as

=IF({condition}, {then put this in cell}, {else put this in cell})

For example, if the value in cell A1 is greater than B1, put A1 in this cell with the formula, else put B1 in the cell.

=IF(A1>B1, A1, B1)

AND and OR

Our condition can be a combination of things. For example the time of day is after 2pm (14) and before 8pm (20).

If the time is in cell A1, we could write

=IF(AND(A1 > 14, A1 < 20), {then this}, {else this})

Spreadsheet References