Volatile energy prices and the pursuit of energy resilience drive households and housing cooperatives to invest in renewable energy generation (REG) with an aim to reduce grid dependency (GD). The optimal sizing of hybrid renewable energy systems (HRES) calls for minimizing both imported and exported energy plus non-exportable energy dump on site. The Total Energy Transfer Index (TETI) is a novel indicator to quantify energy transfer between buildings and the grid. However, the TETI does not specify the on-site energy dump. The present study introduces another indicator, the Weighted Energy Transfer Index (WETI), which is the weighted average of imported energy fraction, exported energy fraction and energy dump factor. The results of a computational study involving a conceptual Finnish townhouse suggest that using the TETI as a design criterion still allows oversizing the HRES. On the other hand, the results imply that a realistic target level of grid dependency for an HRES from energy prosumers’ perspective is TETI < 1. The economic viability of an HRES presumes that the levelized cost of energy (LCOE) does not exceed the price of imported energy. The computational results suggest that in Finland, the grid parity of an HRES is obtained at the electricity prices between 17…29 €c/kWh, including transfer charges and taxes.