How do I account for an existing PV system?

An existing solar system can result in negative usage in certain months (typically summer months). Here's how to properly model this in the OnGrid Tool:

  • If both the starting and ending rate schedules don't have TOU energy charges, simply enter in the net usage amounts, positive or negative, for each month.
  • If the starting rate schedule has TOU energy charges, please do the following:
    1. Do not enter in usage data using the Quick Rate Data Entry Tool
    2. Enter in net usage for each month.
    3. Find the net TOU usage for each season (e.g. summer and winter) and the total yearly TOU usage. Use that to find the percentage TOU usage for each season. For example, suppose the net summer peak usage is -200 kWh and the net winter peak usage is 1000 kWh. The the total yearly peak usage is 800 kWh. Then the summer peak percentage is -25% and the winter peak percentage is 125%.
    4. In row 188, set the basis to "Overall Bill"
    5. Enter in the percentages for each TOU period and season. Per the example above, "-25%" would be entered in cell C191 and "125%" would be entered in cell C194.
    6. If the ending rate schedule also has TOU energy charges (and has the same TOU scheme as the starting rate schedule), then enter in the same TOU percentages as the starting rate schedule's in cells D191 through D195.
  • If the starting rate schedule doesn't have TOU energy charges but the ending rate schedule does, enter in the net usage for each month. For cells D191 thorugh D195, you will have to guess the TOU percentages based on:
    1. The customer's current usage and usage pattern
    2. The daily and seasonal solar production curve of the existing PV system
    3. The size of the existing PV system
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