The CO2 avoided is based on a calculation from a methodology of the United Nations, and it’s adjusted to the energy consumption from the grid. This methodology is explained under option 2 in scenario A of the “Methodological tool - Tool to calculate baseline, project and/or leakage emissions from electricity consumption”
For each MWh, the factor utilized in this conversion is the equivalent of 0.4tCO2. Therefore, based on the capital invested, and the respective energy consumption assigned, for the calculation you would have to multiply the "personal" MWh by this factor.
For example if an investor has invested 1.000 EUR and the equivalent of that investment is 100MWh of the production since the project started producing, the investor would have avoided 4 tCO2.