“A source ZEB produces at least as much energy as it uses in year, when accounted for at the source.”
Source or primary energy is the measure of net zero status for source NZEBs. Primary energy is the energy used to generate and deliver secondary energy (predominantly electricity in the case of India) to the site.
Energy supplied to the source NZEB site and exported from it gets multiplied by site-to-source conversion factors which allows energy used for generation in power plants and transmission to be factored. Conversion factor for electricity in India, independent of the location of building, is currently assumed to be approximately three. A grid connected building with annual energy demand of 100 kWh can be qualified as a source NZEB if 300 kWh of renewable energy is supplied on-site or off-site.
Source NZEBs are a more comprehensive model of reducing the impact of building energy consumption on natural resources because primary energy is the metric used. However, they do not discern between pollution due to different fuel types nor for variations in primary energy across peak and non-peak loads. Electricity supplied at peak hours uses more primary energy than when supplied during non-peak hours.
Site-to-source conversion factors for different secondary energies are different. However, electricity is the predominant secondary energy used in India and thus difference in conversion factors can be ignored. Disparities due to primary fuel like nuclear, coal, natural gas and hydro used for producing electricity cannot be ignored if accuracy is to be maintained.
Currently, regional variations in source to site conversion used for generating electricity in India are not available. Variation in fuel types like coal, hydro and nuclear fuels has also not been computed. A single national average conversion factor for all regions and fuel types reduces the accuracy of source energy numbers.