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. You do this in the 3D Panel layout, separately for each panel field: select the panel field and, in its sidebar under Specific yield (in the new interface within Overwrite properties), turn on the Enter manually toggle and type in the value. In a 2D variant, the same field is on the Panel layout page, per roof. Eturnity still deducts the losses from the Shading / snow losses page from this value. In the UK, the value only applies to projects outside MCS scope. 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.

With Create new profile on the Consumption profile page, you import your own consumption data as a CSV file into your project and simulate the system with it. If the yearly consumption from the file should apply too, switch on Substitute the currently used yearly consumption value with the value from the imported CSV file during the import; otherwise Eturnity only takes the pattern over the year from the file.

There's also the possibility to activate an individual consumption 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 discounts the costs and the electricity production for calculating the production costs, because future payments are worth less than payments made today. The payback time and the internal rate of return do not change with it.

You enter the discount rate per variant in the Opportunity costs field: under Financials › Profitability in the PV System tab, Equity capital section. Use the return that the money would earn elsewhere, for example in a bank account.

You set the annual Operating Costs (maintenance) of the PV system and the battery storage per variant. New projects start with standard values that Eturnity sets for your company. You find the operating costs under Financials › Profitability in the PV System tab, and the operating costs of the battery in the Battery storage tab.

Battery Maintenance Note: If the battery has to be replaced during the service life of the PV system, include the replacement in the battery's operating costs: in the Battery storage tab, under Battery operating costs based on, select the Annual fixed costs option and enter the battery's ongoing operating costs plus the cost of the replacement battery spread over the years of the service life. The simulation only takes a battery replacement into account in this way.

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:

You set these parameters per variant: under Financials › Profitability in the PV System tab (Operating Costs, Electricity Price Development, Operating lifetime), and the operating costs of the battery in the Battery storage tab.

Important Note: The returns (according to the above calculation) are cumulated over the operating lifetime of the PV system (e.g., 25 years). With positive inflation rates, this often leads to slightly increasing annual returns. In the offer PDF, the “02 PV system” pages show the amount over the whole operating lifetime (“Total net savings”) and the first year's savings per month (“Monthly Savings - Year 1”). Some pages in the previous design additionally show an average return per year, i.e., this amount divided by the operating lifetime. “Annual yield” in the PDF, by contrast, means the electricity production in kWh.

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. The opportunity costs play no part in this.

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 Operating lifetime of the variant, the last two years are used for interpolation.

On the Financing page, select the Financing calculator under Financing provider / method and then the model under Financing type, depending on the method Debt financing, Leasing with operating costs or Leasing without operating costs. 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.

With Leasing with operating costs, the annual operating costs are added to the lease rates, spread according to the selected Leasing period (monthly, quarterly or yearly). With Leasing without operating costs, the operating costs reduce the returns of the PV system.

Eturnity only includes tax savings if you do both in the Project settings: enter your marginal tax rate as a percentage under Tax savings and switch on the Extended economic calculation toggle. In certain countries/cantons/federal states, tax deductions for investments in renewable energy are granted for certain projects.

For any tax savings and additional subsidies on investment costs and calculations of the above key figures (e.g., Internal Rate of Return) to be considered, the Extended economic calculation must be switched on in the Project settings.

The offer overview in the offer PDF then shows “Expected tax savings” and “Effective costs”, i.e., investment minus expected tax savings. On the “02 PV system: profitability” page, the tax savings do not appear as an amount; the “Total net savings” do not include them.

If the Tax savings value is 0% and/or the Extended economic calculation is not switched on, 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, as an annual value in kg CO2. If both the variant and the page template of the PDF page include the heating technology, the change of heating counts as well: currently the CO2 emissions of the existing heating including hot water, in future those of the new heat generator (if the Add new heat generator toggle on the Heating system page under New heating system is switched off: the existing heating type with the new heat demand). Eturnity calculates the emissions of a heating system as the consumption of the energy source times the CO2 factor. You set these factors per variant: Profitability page, Heating system tab, Resource settings table, CO2 emissions row; the heat pump uses the electricity factor that you enter for Electric heating.

To calculate current emissions, the specified annual electricity consumption (kWh), including the consumption of EV charging, is multiplied by a country-specific factor for CO2 emissions of 1 kWh of electricity from the average electricity mix. The factors are fixed in Eturnity and cannot be changed, for example 0.128 kg CO2/kWh for Switzerland, 0.422 for Germany, 0.264 for Austria, 0.356 for Italy and 0.304 for the United Kingdom. If no specific factor is stored for a country, Eturnity uses the Swiss factor. Only the previous design of the offer PDF prints the sources, under “Basis of calculation”; the new design shows no source.

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. This means the total production in the first simulation year, including the electricity fed into the grid. The country-specific factor is reduced by 0.052 kg CO2/kWh for the assumed CO2 emissions of PV modules. The result is the CO2 saving from the solar power: the future emissions are the current emissions minus this saving. The saving therefore depends on the annual yield and the country (in Solar Expert, the country of the customer's main address), not on the electricity consumption.

CO2 emissions from PV systems are considered over their lifetime: the 0.052 kg CO2/kWh stands for the manufacture of the modules, spread over the electricity they generate during their lifetime. This value is also fixed; as above, its source appears on the PDF only in the previous design. Part of the saving can become negative: the PV part if a country's electricity mix causes less CO2 than the PV modules (in Eturnity only for Norway), the heating part if the new heat generator, with the factors entered, causes more CO2 than the existing heating, for example when switching from wood or pellets to a heat pump. A negative part reduces the total saving; if the total is negative, the comparison values below become negative too.

Further CO2 emissions information is calculated using this difference:

The footprint reduction compares the saving with the CO2 emissions of one person, not of a whole household, so it can exceed 100%. The community solar calculator counts one person per unit. In Solar Expert, the one person also applies when a heating part is included. Solar Expert uses the Number of people on the Building page only for the footprint on the heating pages of the PDF; if nothing is entered, it assumes two people there.

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

Eturnity Customer Support:support@eturnity.com or via chat in the Help Center in Eturnity Expert