Designing home DC wiring
Loss at voltage conversion is just a function of how good your converter is, 5% to 20% losses could be expected at each conversion. 

Losses in distribution are the real killer. With 120/240 volt distribution, we don't really think about distribution losses until we are running many 10s of metres of cable down to an outbuilding. If the cable is thick enough for the current, the volt drop is negligible, or at least a negligible fraction of the total supply voltage.

However, with low voltage distribution, you get hit by a double whammy. The currents are higher, to transmit the same power. Any voltage drop is a larger fraction of the voltage you start with, so your power losses are proportionately larger.

There are three practical regimes to consider for DC distribution, 12v, 48v, and 'high' voltage.

12v is worth considering as there is so much stuff around that uses that voltage. However, you need stupidly thick cables to supply an area much more than a single room.

48v is around the highest voltage that's deemed to be 'touch safe'. As it's four times higher voltage than 12v, you only need 1/16th of the cable cross section to supply the same power to the same area with the same losses. It's used extensively in the comms industry, and so there is a significant amount of equipment available for dealing with it, inverters, converters etc.

'High' voltage, so 250 and up, is often used to connect solar panels, and in electric cars. Compared to AC, it's more difficult to handle, arcs don't go out as easily, so you need special fuses and switches. I wouldn't really recommend it from a safety and ease of use point of view for distribution in a home.