The production yield calculations used in the Eturnity platform are conservative by design. They are based on databases provided by the European Commission (PVGIS). The simulation considers the solar production profile (with 15-minute temporal resolution) at the specific location, as well as the inclination and orientation of the PV modules.

If you prefer to use higher or lower production yields in your Solar Expert projects, you have the option to manually override the specific annual yield (kWh/kWp) of the system. PV module degradation (performance decrease over time) is considered using a standard value.

Eturnity provides standard consumption profiles (also with 15-minute temporal resolution) for various combinations of hot water and heating systems. When you set the total annual consumption of the building higher or lower than the standard value in the profiles, the profile is scaled accordingly.

Through the CSV Import function in Eturnity Solar Expert, you can import individual consumption profiles into your project and simulate a system based on them.

There's also the possibility to activate an individual load profile library for you, which contains your own consumption profiles.

The calculations for self-consumption and independence are based on an algorithm that essentially performs the following function: The simulated production profile values are overlaid with the selected consumption profile (e.g., single-family house – oil, gas, wood) in 15-minute resolution.

For each 15-minute interval, the following is evaluated:

By summing the corresponding 15-minute values, the annual totals for grid consumption and direct consumption are calculated.

The percentage independence is calculated as follows:

Independence = (Total electricity consumption – Grid consumption) / Total electricity consumption

The percentage self-consumption is calculated as follows:

Self-consumption = (Direct consumption + optional battery storage) / Total production

The production costs for one kWh of electricity from the roof are calculated according to the widely used formula in the electricity generation sector for calculating the "Levelized Cost of Electricity" (LCOE). The following parameters are considered:

The discount rate serves to discount the revenues and expenses of the project. This ensures that all future cash flows are considered with an estimated current value. This approach is used to reflect that future cash flows cannot be compared 1:1 with today's payments due to interest rates.

On the Eturnity platform, the discount rate is entered in the "Opportunity Costs" field. With this rate, you determine how high the return on investment is against which you want to compare the PV system, such as investing money in a bank account as mentioned above.

The standard values for annual maintenance costs (e.g., for photovoltaic systems and battery storage) can be adjusted by you. When a new project is created, it is initialized with the standard values. You can then individually adjust the annual maintenance costs per project.

Battery Maintenance Note: When setting maintenance costs for batteries, it's important to consider that you should set the amount so that any reinvestment at the end of the service life after X years, divided over the PV service life, should also be included. The simulation only considers any necessary reinvestment in a battery after X years in this form.

The investment amount used for calculating the various values explained here consists of:

Financial returns consist of savings from prevented electricity purchases (self-consumption × electricity consumption tariff) and income from electricity sales (feed-in amount × feed-in tariff).

This applies to:

For manually entered tariffs, there's additionally the possibility to define power tariffs and fees for load profile meters. Any savings through lower billable power tariffs are considered if the installation of a PV system leads to a reduction in load peaks in consumption.

Load profile meter fees are only considered for systems > 30 kWp and are calculated as additional expenses, i.e., reduction of returns.

The following are also considered:

These parameters can be set individually per project.

Important Note: The offers show the average annual return. The returns (according to the above calculation) are cumulated over the lifetime of the PV system (e.g., 25 years). With positive inflation rates, this often leads to slightly increasing annual returns. The cumulated returns are then divided by the lifetime of the PV system and shown as average annual return.

The Internal Rate of Return (IRR) is a measure from investment evaluation and enables the estimation of an average annual return for investment projects. In the Eturnity platform, the IRR is calculated based on the generally valid formula.

For the calculation, all expected cash flows (income and expenses over the project duration) are compared to the initial investment. The cash flows are discounted with the internal rate of return (see explanation under electricity generation costs/production costs).

To evaluate the investment and calculate the internal rate of return, it's assumed that the Net Present Value (= present value/current value), i.e., the initial investment minus the discounted cumulated cash flows, must be 0.

The payback period is the point at which the entire investment from year 0 has been recouped. This is interpolated from the cumulated cash flow.

The cash flow is calculated individually for each year:

The difference in cash flows between these two simulations is calculated individually for each year and represents the cash flow in year x. Then the cash flow is cumulated. The payback period is linearly interpolated between the two decisive years (year x where the cumulated cash flow is negative for the last time and year x where the cash flow is positive for the first time).

If the cash flow remains negative over the entire 25 years of simulation, the last two years are used for interpolation.

Within a project, you can choose between different financing models in the "Financing" tab. The lease model assumes continuous repayment of the loan through payment of constant, regular amounts (lease rate).

The lease rate calculation is based on standard formulas for annuity loans. The initial debt, interest rate, and term are specified directly by you in the project. Using a sum formula, the lease rate is calculated based on this information.

If the variant with consideration of operating costs is selected, the specified annual operating costs are added to the incurred lease rates according to the chosen payment interval (monthly/annually). Otherwise, the corresponding operating costs have a reducing effect on the returns generated by the PV system.

By setting a marginal tax rate, any tax savings can be considered. In certain countries/cantons/federal states, tax deductions for investments in renewable energy are granted for certain projects.

For any tax savings on investment costs and calculations of the above key figures (e.g., Internal Rate of Return) to be considered, the "Advanced Economic Calculation" must be activated in the project.

Tax influences are considered by showing effective costs, i.e., investment minus expected tax savings.

If the marginal tax rate is set to 0 and/or the "Advanced Economic Calculation" is not activated, tax influences are not considered in the project calculations.

CO2 savings are calculated as the difference between CO2 emissions in the current situation (without PV system) and in the future situation with PV system.

To calculate current emissions, the specified annual electricity consumption (kWh) is multiplied by a country-specific factor for CO2 emissions of 1 kWh of electricity from the average electricity mix. The country-specific CO2 emissions factor is regularly updated by Eturnity. The source is visible on the PDF.

To calculate emissions for the future situation (with PV system), the annually produced electricity amount (kWh) is multiplied by a reduced factor for CO2 emissions of 1 kWh of electricity from the average electricity mix. The country-specific factor is reduced by a generic value for the assumed CO2 emissions of PV modules.

CO2 emissions from PV systems are considered over their lifetime. The value of CO2 emissions from PV modules is regularly updated by Eturnity. The source is visible on the PDF.

Further CO2 emissions information is calculated using this difference:

If the corresponding information has been entered in the project (settings), the number of residents is also considered for this calculation. By default, two people are assumed.

For technical support, parameter customization, or questions about these calculation methods, please contact:

Eturnity Customer Support:support@eturnity.com