What does this question mean?
'how efficient can this resource be compared to fossil fuels? '

It means:  Compared to coal, oil, and natural gas, would you need to spend
more or less on this resource to heat a house, or to heat 10,000 houses, or
to generate the electricity for a city ?

The 'efficiency' of a resource boils down to how much energy you can get
from it, use for living, and then clean up after, for a dollar.

Master planned communities outside of chicago. note: population density means people living in an area per square mile. chicago, an urban and highly populated area has a much more higher density than a desert, amish community, settlement, or nomadic region.