Autarky, or self-sufficiency, is defined as the ratio of energy supplied from PV (either immediately or from a battery) to the amount of energy consumed per year. It differs from energy offset, which is the ratio of energy generated to the energy consumed. For example, if a home consumes 6,000 kWh, produces 5,400 kWh from PV, uses 3,000 kWh of that PV energy on-site, and exports the remaining 2,400 kWh to the grid, the self-sufficiency value would be 50% and the energy offset would be 90%.
Autarky in Aurora can be found as a placeholder variable in Proposals, as well as within the storage page with Sales Mode and Design Mode. The calculation uses selected consumption profile, hourly production pattern based on the designed PV system, and battery operational results to determine total energy self-consumed for the year. Providing measured consumption data or selecting a consumption profile that is similar to the homeowner’s and using a fully strung PV design will provide more accurate results
Application Note: differences with the HTW Berlin Web Calculator
HTW Berlin provides a simple online Autarky calculator with levers for consumption, PV system size, and battery size. Users may see differences with the calculation results due to the following factors
- The calculator assumes a PV system facing south, with a 35 degree slope, and no shade. The yield of the generic system is about 1050 kWh/kWp/year using weather data from BSRN Meteorologisches Observatorium Lindenberg. Aurora’s PV production is based on the selected equipment, panel orientation, shading, stringing, and satellite-based weather data specific to the project location.
- The calculator uses a single measured load profile from a study in Austria. The available load profiles in Aurora represent different lifestyle patterns based on aggregated home models, or users can import their own consumption profile.
- The calculator is based on high-frequency consumption and production data. Aurora has hourly consumption and production profiles. We estimate that the usage of hourly profiles masks grid imports by about 2-4% for typical 100%-energy-offset, solar-only designs, so you may see correspondingly higher Autarky values in Aurora for a solar-only system. The presence of a battery tends to remove these artifacts and the results will be in line with high-frequency models.
HTW calculator: https://solar.htw-berlin.de/rechner/unabhaengigkeitsrechner/