Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels, therefore, lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon.
Summary of Advantages of Monocrystalline PV Panels:
Monocrystalline solar panels have the highest efficiency rates since they are made from the highest-grade silicon. The efficiency rates of monocrystalline solar panels are typically 15-20% as opposed to 12-13% for Polycrystalline panels.
As a result, Monocrystalline silicon solar panels are space-efficient, i.e. needs less space to produce the same amount of electricity as Polycrystalline panels.
Monocrystalline solar panels live the longest.
Tend to perform better than similarly rated polycrystalline solar panels at low-light conditions.