Calculation error: Cash Flows Energy Value inflation

I discovered an error in SAM calculation of Energy Value for future year Cash Flows.

Set up a default residential PV flat plate, then check the "Normalize supplied load profile" in Electric Load Data. Run the sim and look at Cash Flows. Year 18 = $972.06, Year 19 = $966.12. It should always increase.

This happens in all simulations I run when I "Normalize supplied load profile" or even if I upload "User entered hourly data".

A jagged sawtooth ramping of Energy Value appears in Cash Flows, rather than the smooth inflation increase expected.

Thanks,
Kelley Dagley

Dear Kelley,

There is a bug in the electric load calculation that is causing the results you observed. On the Electric Load page, there is an input called "Escalation" which allows you to specify a load that increases (or decreases if its value is negative) from year to year. Unfortunately, SAM escalates the annual load by the sum of this escalation rate and the inflation rate on the Financing page. That means that when the load escalation rate is zero, SAM models an electric load that increases from year to year by the inflation rate. (For some other escalation rates it is appropriate to add inflation, but in this case, we made a mistake by adding it.)

The results you observed were caused by the interaction of the increasing load and decreasing system output (from the degradation rate on the Performance Adjustment page). In the project's later years (Year 19 in your case), the monthly load is more than the the system's monthly output, and that ends up affecting the value of that energy.

We will fix this issue in the next version of SAM. For now, you can work around it by subtracting the inflation rate from the desired load escalation rate. For example, if the inflation rate on the Financing page is 2.5% and you do not want the load to increase annually, use a load escalation rate of 0 - 2.5% = -2.5%.

Thank you for pointing out this issue.

Best regards,
Paul.