There are many technologies that use energy to make energy, make something that is better for the environment or that is just lower cost and makes money.
Besides solar energy for electricity at LCOE, QD could make Hydrogen for energy, energy storage, and water desalination.
There are costs and land usage for solar farms, but everything has costs, and on rooftops that's efficient use of unused area.
Besides, when we have solar farms in space, efficiency takes a big bump up and costs down, with no land coast. ;-)