Considering all costs, the cheapest source of energy for domestic use is

The cheapest source of energy for domestic use considering all costs is sunlight. This is because sunlight is free, abundant and does not require any infrastructure or maintenance costs to capture and utilize. Solar energy can be captured through the use of solar panels and converted into electricity, which can power homes and appliances. Additionally, sunlight can also be used for passive solar heating and lighting, which can further reduce energy costs. In comparison, electricity, biogas and water require infrastructure, maintenance and fuel costs, which can make them more expensive in the long run.