Hi Haruno,
Each row in the table represents a year, starting with Year 0. In Year 0 there is no production -- this is the year in the cash flow for the capital investment. In this case, the analysis period (defined on the Financial Parameters input page) is 25 years, so there are 26 rows in the table.
The system starts producing power in Year 1, and the table shows the production in each month by year. So in Year 1, the total production in April was 2.51 million kWh. In Year 2, the production in April was 2.50 million kWh, etc.
The production decreases from year to year because of degradation, which is defined on the Lifetime and Degradation input page.
Best regards,
Paul.